Showing posts with label chromatic aberration. Show all posts
Showing posts with label chromatic aberration. Show all posts

Wednesday, 9 November 2016

How to get the best out of the Sony 16-50 OSS Pancake - A Contrarian View




So this folks is a test image taken with the Sony 16-50mm Pancake 36mm @ f6.3 at my standard tests location this represents the longest focal length before image quality starts to decline, it is still more than useable. Check out the 100% bottom left corner crop below, not too bad I would say.


Next time you are on a photographic forum and you feel like throwing the cat in amongst the pigeons just casually drop into the conversation that you think the Sony 16 to 50mm pancake is "not actually too bad". I can almost guarantee that you will become an instant pariah, targeted for unmitigated abuse and your credibility, well you won't have any amongst the photography cognoscenti from that point on.

But is the diminutive 16 to 50 mm OSS pancake really such a horror or does it in fact have some redeeming attributes?  let's discuss that.

Even the most ardent critique would have to concede that the lens is nicely compact, quite well made and a perfect physical match for some of the smaller A series “E mount” cameras (yes I know it is all very confusing now).   Of course they then couldn't helping adding the lens is completely fuzzy and little better than the bottom of a dirty beer glass. 


Well I’m here to tell you it is much better than most forum lurking critics believe, I can say that because I have actually tested the little blighter on a real world subjects using a structured approach. So here's the good bit, what I have ascertained from this testing may actually of be some help to those who also use this little package for real world pics, rather than shooting the obligatory test charts and brick walls, hence this article.

Yes, of course it is far from perfect, but an “almost free” kit lens can never be expected to perform anywhere near as well as an expensive fixed focal length lens, some perspective is needed, and let’s not forget most shots only end up as web images or maybe small prints anyway. In any case there are zillions of these little lenses out there attached to Sonys' and it would be a pity for people not to at least get their moneys worth out of them.





100% Corner Crop @36mm f6.3, Note and this is very important, all the pics in this article are RAW files processed in Iridient Developer, no jpegs allowed if you really want to test the mettle of a lens.


Special Note: Please accept that the actual images probably look quite a bit better than what you see here, fact is, the web compression and the device viewing conditions will always negatively effect what you see in the blog, if a lens produces rubbish I will say so quite happily, but likewise if I say it looks good on my 27 inch 5K Mac Retina screen at 100% view you can be quite sure it is.


The Need for Compact Option

My own initial interest was triggered by my desire to have a compact walk around camera that I could slip into my man bag as I wandered around the streets and byways of foreign cities. I've looked at all sorts of options, Sony RX 100 series, (lovely too but limited in application for me), Olympus and Panasonic mirrorless bodies with pancake lenses ( great but I’d then end up then investing in a whole new system, (which is ultimately what I did, but that is another story), Nikon new DL 1 series compacts, (not yet a known quantity, does they even really exist?) and so on.

Funnily enough I had early on discarded the idea of buying Sony A6000 or 6300 to replace my now well worn NEX 5n travel camera because I had believed that the kit pancake must have been some sort of “evil” and no other Sony lens option/combo would be compact enough for the task I had in mind.  Yes I know about the pancake 16 and 20mm options but they don't suit my needs. It’s not like I don’t know the Sony system well, I have used the Sony Nex 5n for nearly 5 years and have a wide array of legacy lenses and DIY’d bits for it and many A mount lenses and a couple of bodies.

After initially almost biting the bullet and buying an Olympus om-d-em10 mk2 with kit pancake I though why not take a pause and test one of those 16-50s and see if it really is a complete stinker!   If it was Ok then a nice shiny new A 6000 or 6300 could be on the potential menu, I'm glad I did the test and maybe you will be glad also.

One criticism of lens tests that often make is that "testers usually only test JPEG output images", now consider this, there is a radical difference between the quality of JPEG "cooked in camera" images and those that can be liberated by using a state-of-the-art raw converter, and this is especially so with Sony cameras.


In Camera Processing


Lenses with low levels of micro contrast often have their overall quality compromised by the native noise reduction processes which take place within typical "in camera JPG processing" methods, often turning fine details into, well let's say..... watercolour mush. 

It just happens that most kit lenses and many of the cheaper zooms don't have high levels of micro contrast and often once files have been run through the standard camera processing and noise reduction protocols they end up looking far less crisp than equivalent images from much more expensive high micro contrast lenses, I guess you could say high end lenses have more “sharpness wiggle room”.

In the case of the Sony 16 to 50 the problem is somewhat exacerbated by the fact that Sony's implementation of noise reduction has tendencies to smooth over fine textual details anyway, this is intended to keep apparent noise levels low, something which it actually excels at. But..... a side effect of this NR is that for many lenses the JPEG renders a far inferior result to that which could be achieved through appropriate RAW processing. Softening affects are further exacerbated when the ISO is placed above 800 mark, which is a common occurrence for the average shooter, especially when shooting in full auto modes with slow kit lenses.

Sonys’ JPEG processing has certainly improved over the last few years but to my eyes it still has a significant tendency to confuse fine detail with noise, additionally Sony's sharpening algorithms are adaptive but they tend to sharpen medium and high contrast details rather than very low contrast details, again I imagine because Sony wish to keep the apparent noise level low, this makes sense of course as noise reduction and image sharpening are actually flipsides of exactly the same coin.

Bottom line is this, the 16 to 50mm pancake performs considerably better when shot in the raw format, in fact I would go so far as to say it's almost like a chalk and cheese difference. 

If you did nothing other than switch your camera over to RAW and learnt how to use a good quality RAW conversion program you will radically improved the capability of the 16 to 50 mm pancake, but there’s more, a lot more that we can do.




28mm @f6.3, no problems here, check out the edge crop below, taken off the right hand side.





28mm Edge Crop


Not for Brick Walls


The 15 to 50mm pancake will not thrill the thriving “Masonry Wall Photo Collective Group” out there, it’s certainly not optimal for is capturing “flat field” objects in other words being used as a macro or "close to macro" lens, in this realm it is really quite useless.  I seriously doubt that Sony had any expectations of the average user buying the 16-50 pancake to shoot high quality macros and flat art. Mind you macro work of the 3D kind will probably be fine, just don’t expect good results on stamps and coins etc, or of course that lovely brick wall up around the corner.

The 1650 pancake in fact it exhibits considerable field curvature at almost every focal length, which means testing it on a flat chart, as most lens testers are want to do, would and does make it look pretty bad, though in fact for normal 3 dimensional medium to distant photography applications it's fine. (I have a blog post on Field Curvature and how to use it creatively if you are interested, you can find it here: 

https://braddlesphotoblurb.blogspot.com.au/2016/10/decoder-field-curvature.html

Briefly, field having curvature means that when the centre is in focus the plane of focus is not flat, it may curve away from you or back towards you as you move out towards the edge and corners of the frame. In practice a lens with field curvature generally gives a sharper overall focus if the focus point is placed around half way out from the centre of the image towards one of the corners, which corner will depend on the scene and type of curvature present. Many lenses with soft corners actually come reasonably good when focused thus.

Most cameras are factory set to focus using some version of “wide area” focus where the camera chooses where it thinks it should focus and despite the sometimes complex algorithms involved, this method can be somewhat random and I feel may account for why many folk claim the shots from the 16-50 are random in terms of overall focus. Basically this is the deal, quite often the auto focus point selection works against the field curvature and sometimes with it and occasionally it takes a middle ground, net result...... variable focus quality, which of course is a complaint many folk make about this little lens.

In all of the initial tests shots I made I used manual focus, setting the focus point around 30% in towards the centre from the bottom right hand corner. 

Note: This may not be the ideal point but it served as a pretty solid starting point, and generally I found the focus across the whole frame was quite good, regardless of how close the subject I was shooting was. I also tried some shots with the focus point in the middle of the frame and in almost all cases the overall cross-frame clarity was worse. I must point out that this is not an issue specific to the 16-50mm pancake, almost all kit lenses and a great many fixed focal length lenses I have tested show similar characteristics.

Wide area focus may be a wise choice for close to medium distance photos or where you are aiming to isolate a specific subject from the background, after all in these cases who cares about soft corners etc but it is not a wise choice for landscapes and photos where you have objects that range from the medium to infinity distances. For the record it looks to me that the 16-50 pancake set at 16mm has field curvature that moves the focus point further away from the camera as you move towards the corners, meaning if you focus in the centre of the frame the nearest details in the bottom left/right corners will be quite soft, bringing the focus back closer towards the camera leads to a better overall average clarity. This is worth checking out on your copy as most folk complain the 16mm setting is rubbish, something I now know for sure is not strictly true.


Flares Are Not In

You want more, there is much more…..the micro flare control of the lens, especially at the widest apertures and in the 16 to 21 mm range is not ideal, overexposure will lead the highlights bleeding into the surrounding dark pixels. The simple expedient of paying careful attention to your highlight rendering and controlling the exposure often by just 1/3-1/2 stop can lead to better overall images, once they have been edited to taste of course. 

By f5.6 the flare problem has disappeared at all focal lengths, (except 50mm, but even then it's pretty minimal) so if you are going to shoot at the wider apertures certainly pay a little extra attention to exposure.




This is the much derided 16mm setting, without distortion correction applied, not too bad eh, what if I was to say it was shot at f3.5 wide open, would that be a bit more impressive, well yes it was shot wide open! Yes, yes I know there is vignetting but we are talking about resolution at the moment, we I'll get to that soon.





16mm f3.5 Centre Crop 100%


Best Focal Lengths

One enormous shortcoming of most zoom lens tests is that testers usually only check the lens at the widest and most telephoto settings with a further test set somewhere in the mid range. In the case of the 16-50 pancake I could only uncover tests taken at 16, 35 and 50mm despite some exhaustive searching.  

Now listen here, fact is, very few lenses ever work best at the extremes and who is to say that 35mm is the sweet spot anyway? 

Most kit zooms have a sweet spot somewhere in the focal length range, a point where chromatic aberration and distortion are minimal and most likely cross frame clarity best. Some have a fairly wide sweet spot, which is great and some have a pretty tight envelope of reasonableness.

So what about the 16-50? Well there is plenty of good news! The 18mm setting is better than the old 18-55 OSS kit lens, quite a bit better in fact. 19mm proved to be actually about as good as the Sigma 19mm f2.8 so long as you were shooting at say f5 or smaller!

The 21mm setting seemed to be particularly good and I would rate 24-26mm as ideal, with 28mm was almost as good. In fact I compared the 28mm setting to the 30mm f2.8 Sigma and once the files were adjusted for optimal colour/tone/detail rendering the differences were very small, indeed I would rate the pancake as a tad better in the very centre of the frame. By 35mm the quality is starting to quickly decline but at f6.3 it’s perfectly OK for most needs.

The 50mm setting was easily the worst and I would use that only if I had to. The 50mm setting on the 18-55mm OSS was much better overall, though neither are a match for a good fixed 50, of course Sony offers a very nice 50mm f1.8 which could pair nicely with the pancake or you could opt for the Sigma 60mm f2.8, a real standout budget lens, though it lacks OSS of course. 

For the record, just in case you were wondering, the old 18-55mm OSS falls off the cliff at 55mm and I never use that setting, rather I shoot it at 50mm and crop later to get the 55mm view.

In summary used between 18-30mm the 16-50 pancake is really quite a good lens, providing of course you are not shooting wide open. I must add however that in the 21-28mm range you could in fact shoot wide open and the results are still really quite fine. Lets put it this way, for any normal usage I would be happy to go wide open at these settings, the main trade off will be bleeding of highlights, keep the exposure in check and all will be hunky dory.

And now some bad news, well not really bad, but worth knowing. All cheap lenses seem to exhibit some degree of de-centering, which in practice means one side or corner may be softer than the other/s. The 16-50 mm is no exception, the one I tested displayed this characteristic, mainly at 16mm and 50mm. Was it extreme, no, not at all but at a 100% on screen view you could clearly see it, stopping down to f5.6-8 eliminated it. You could be lucky and get a perfect example of the breed but I doubt it, if it is minor and this one was, shifting the focus point around may kill the issue, I tried that on a subsequent set of images at 16mm (once I had ascertained what I was dealing with), and got excellent results. 

Note, you could get a copy that is really out of whack so decentering is something to check for in any cheap kit lens.


OSS Oddity?

Now for something completely different! When looking very closely at the files at a 100% I came across an anomaly that seemed to effect every focal length, shots taken at 1/640 sec appeared to have unsharp areas in them which were somewhat random. What was weird was that these frames were less sharp than the preceding frames which was shot at say f5.6 @ 1/800 or the following frames shot at say f7.1@ 1/500! 

In other words my friends there was an unexpected resolution hole. Odd eh, then I had an epiphany, was this caused by an interaction between the OSS and the shutter speed, was this a shutter speed where the response time of the OSS and the shutter speed just clashed in some strange way?

Easy to test, go back take some shots at 1/640 sec with and without OSS, and guess what, yep I was right the ones without OSS did not exhibit the issue! My curiosity got the better of me and I re-checked the shots and found a similar issue but at a much lower level at the 1/1600 sec mark. 

Please note, this test was done on a Sony Nex 5n, I didn’t get to check later on the A6000 I had handy, so it might be camera model specific, nonetheless it is worth knowing and checking for on your camera. 

This OSS interaction may also account for some of the patchy results many critics claim to see from the lens, after all 1/640 sec is not an uncommon shutter speed to find your camera shooting at during everyday outdoor usage. Of course the problem is easily resolved, turn off the OSS if shooting in bright daylight, on most Sony models you can assign that option to a custom key should you wish.




18mm at f6.3, this is a critically sharp focal length and is better by a fair margin than 18mm on the older 15-55mm OSS lens.




18mm f6.3 Centre Crop @100%, bet you cannot even see that person in the middle in the full frame above!


The Best Apertures

If you’re looking for the very best results sharpness wise, having some idea of the optimum aperture for any given focal length can be helpful, most reviews never look at this in detail usually picking to test at wide open f5.6 and f8 and maybe 11. But what if the truth of the matter lay somewhere in between these? Having checked it all I reckon I can give a pretty good summation for you. Here goes:


16mm f7.1 (stop there, going smaller definitely causes diffraction issues)

18mm f5.6

21mm f5.6

24mm f5.6

30mm f7.1

37mm f8

50mm f10


Now all of the above settings assume you are nailing the focus and not trying to mask poor focus by stopping down more than ideal.


Focus Accuracy

To a degree the accuracy of the auto focus is largely camera dependent and certainly in testing this lens on both an NEX 5N and the much newer Sony A6000 it was obvious the later model camera is far more adept at nailing a moderately precise focus. Most lens reviewers only review using auto focus but let me share a secret with you, even though auto focus is generally pretty good you can often get a more fine tuned focus by using manual, especially with cheap kit lenses. In the case of this lens for the second set of tests I had the focus in DMF and then fine tuned the focus once the focus confirmation beep went off.

Almost without exception I could get a slightly better focus using this method than the cameras auto focus alone would obtain, and remember that this is in good daylight, so the difference would certainly be more exaggerated as the light level dropped, I put the need to do this down to the lenses lowish micro contrast making it hard for the system to see the maximal point of clarity.

Is the 16-50 particularly bad in respect to this? I don’t think so but I am sure it would not be anywhere near as good as a prime or high end zoom, of course there has to be some reason for spending the extra money. The take away being this, if you have the time and want to get the most out of the lens, use the DMF function as it will likely give you a sharper pic under a greater array of situations.


Chromatic Aberration

These days reviewers and photographers will commonly repeat the now accepted refrain that Chromatic Aberration doesn’t matter as you can easily fix it in software, true to a degree, you can fix it and of course the camera does so internally for the jpegs.  


CA is more serious than just being an annoyance, having quite a negative effect on edge and corner clarity. Most of the clarity losses can be reduced, provided the software is able to do a really good job, fact is however there are some significant differences between the results from different RAW applications, but all of them seem to do a better job than Sonys’ “in camera” processing. My tests seem to indicate Sony cameras are not particularly good at correcting CA without trading off some corner and edge detail so again RAW is best.

With the 16-50mm pancake the uncorrected CA is not actually that terrible, I have examined many uncorrected RAW files and overall I think it is actually quite a bit better than many of the kit lenses I have analysed, including the Sony 18-55mm (at least over most of the focal length range).

As expected it's worst at the widest settings and seems to be most minimal at 30mm and longer, in fact you could probably not even bother fixing it at the 30mm setting unless you were printing big. The 50mm has the lowest level of CA prior to fixing, in fact even at a 100% view it is very hard to see it in the uncorrected file.




24mmf6.3 Edge crop @100%





24mm @f6.3, sharp from edge to edge and corner to corner.


Distortion

Freedom from distortion is in not the 16-50s strong suite, with many lenses it's something that often can be just left alone unless you are shooting architecture and occasionally it's a good idea to do just that as correcting distortion will often degrade edge and corner clarity.

Unfortunately this lens really needs the distortion attended to when shot in the 16-21mm range, the 16mm length in particular being occasionally quite unsettling. There is however one giant fly in the ointment, the standard corrections method used in camera and by default in RAW conversion programs significantly crops the image, in fact I would say the lens is actually more like a 14.5 mm one if left un-corrected.

Cropping itself is no major drama but in this case at the 16 to 18mm settings the “de-distorting process” radically messes up the edge and corner clarity. When you turn off the corrections in Raw you quickly realise that not only is the 16mm much wider than stated but the outer resolution is potentially quite good, especially if you do a custom CA correction.

If there are no straight lines near the edges of the frame you could easily leave the 21mm images uncorrected, 24mm I would not bother except for architecture, 30mm could generally be left alone, same for 37mm. The 50mm has a slight amount of pin cushion distortion but you would almost never detect it. My guess is that there’s probably zero distortion somewhere around the 40mm mark, which could make this a good focal length to choose when creating stitched images.

For images shot at 16mm you will get significantly better results by fixing the distortion in Photoshop or a similar app by using the advanced transform tools, as said, it is quite surprising how much extra image area you will liberate via this method.


Vignetting

Once aspect that will show up if you stick with the “full wide” 16mm rendition is that the very outermost corners are very heavily vignetted, that might be occasionally problematic but in many instances such wide angle shots end up in 16:9 ratio crops which cut off the outermost corners thus you would never see it, if you really want the corner vignetting corrected you could make a custom edit in Photoshop using levels and layers or perhaps apply a very selective version of the vignette correction tool, often you can easily clone the corners if they have sky or cloud in them.

Ultimately when shooting at 16mm manual distortion correction will give you much sharper images overall, trust me the "in camera correction" really does seriously mess up the edge and corner clarity in the16mm-18mm range, you might even like to try shooting your jpegs with the correction option turned off when not really needed, you may just be a pleasantly surprised.


The Wrap Up

So to conclude, would I use this as a walk around general purpose lens, hell yeah, no hesitation at all, now that I know my way around its characteristics. Further more I reckon lots of Sony users will be able to get really nice results from it, it’s no silk purse of course but it is much better than a sours ear.

The only real reason for reaching for another lens for regular snaps and holiday stuff would be if you need a more shallow depth of field rendition or a longer focal length, or perhaps if you often shoot pics at the 50mm setting.

It is actually a fun little lens, I quite like the way to zoom works and love that it’s so compact and adds almost no weight to the camera, it also works a treat in combination with the DMF (Direct manual Focus) option. Add into the equation that the 16-50 is crazy cheap to buy with your Sony camera at purchase time, it would make little sense to not grab the camera/lens combo.

If you are prepared to work around its foibles the results are potentially very good, what more could you ask for when so little money is involved?


The Good

Very light and compact

DMF works well

Electronic zoom is good for video and it’s silent.

Has a reasonably wide sweet spot of clarity

Cheap

Nicely wide when you need it.

Even wider is you turn the lens correction off.

Suits a lot of general photography needs

Generally sharp enough.


The Bad

Distortion at the wide end is fairly extreme

Serious vignetting at the wide end of the range in RAW

The longest 10mm of the focal length range are pretty average with 50mm not much good at all, however it's fine for portraits when you are after clarity in the central image portion only.

Slow of aperture, but then no different to other kit lenses

Suffers from significant field curvature, especially so in the sub 21mm range.

Not really suited to macro duties but passable with a plus 2 diopter close up filter and no worse most other kit lenses

No lens hood supplied, it is not significantly flare prone but the addition of a hood does help a bit.

Low micro contrast.



What You Need to Know.

You will get vastly better results with this lens if you shoot in RAW and edit with a state of the art RAW editor, the results from Iridient Developer and Raw Therapee are vastly better than what's on offer via the in camera processing.

You can get significantly sharper edges and corners at the wide end if you are able to elect not to correct the distortion.

Field curvature can play havoc with getting cross frame clarity unless you know where to focus in the frame.

Images greatly benefit from very low radius/high percentage sharpening which brings out the micro contrast.

If you have the accompanying 55 to 210 E mount zoom and you wish to shoot around the 50mm mark go with the 55 to 210 everytime, it is vastly better than the 16-50 at this setting.

Generally you could simply set the aperture to f6.3 right across the entire focal length range and get close to optimal results.





















Monday, 8 August 2016

Review Sigma 18 35mm f1.8 on Olympus EM5 mk 2, A sweet combination.





In my previous post. where I provided some insight into my current explorations of legacy lenses and the M4/3 system (specifically the Olympus EM5 mk2) I mentioned almost in passing that I would be also testing the Sigma 18-35mm f1.8, but at the end of lens testing proceedings.  Well as they say, "something funny happened on the way to the forum" and plans in this case got reversed.  

I have already ran all the preliminary tests on every lens mentioned in that post and know quite precisely how they all perform, but I have yet to take each one out on an extended variable subject shoot so as I can make some final conclusions and piece together a meaningful review for each lens.

So what upset the apple cart?

Tis like this, when I first tested the Big Sig on my Pansonic GH2 I was actually quite disappointed, it really only seemed to resolve well in the centre of the frame and was quite variable in performance at different focal lengths.  In short, I kinda felt well, short changed and I am short enough to start with.  So when I got my shiny new EM5 mk 2 I was never super eager to get down and dirty with Big Sig.




But I had a thought, what if the adapter I was using was no good, I really didn't suspect this initially as all was fine with my other Nikon lenses (my Sigma is a Nikon G mount version) but it seemed a waste to have a reasonably expensive lens sitting there unused.  Whats more, everyone else was saying it was a marvel of modern optics, could be used as a scalpel, make coffee, elevate you to a higher astral plane and all that, I felt it was worth at least further investigation, anyhow I ordered a nice new adapter.

With some trepidation last week I took Big Sig down to my regular testing ground and shot off a few frames at different focal lengths and then promptly went off for a morning coffee with a mate at my favourite haunt.  Once home I popped the files onto my 5K iMac and opened them in Iridient Developer to take a gander, ready for yet more disappointment at the result.  God damn, wow, holy cow batman, sh....,  those are some sharp files dude!  Ah so the adapter was rubbish after all, phew, well that's a relief.

So the thought then struck, these files are so good that really they should be used as the standard against which all my other lenses are measured, which means friends that I had to go back out that afternoon and shoot some more general type shots to prove the point and whilst I was at it, I may as well write the review of Big Sig first and follow up with reviews of the other lenses later.

I also felt a little encouraged to explore this marriage a bit deeper because there are lots of reviews on the net of the Big Sig being used for video work on M4/3 format but very little on its usage for high grade stills and most of those I found really only dealt with JPEGs not RAW files.





On the marriage aspect, the pairing of the Sigma and the EM5 mk 2 is at first a little odd, kinda of like attaching a 4 wheel caravan to a Suzuki Mighty Boy ute, they are just not meant to go together.  What we have here is not so much a lens attached to a camera but more like a camera attached to a lens.  In the end it actually works fine once you realise the lens not the camera is the primary grip, and it will work far better if you were to purchase one of those add-on alloy base plate grips on eBay that you can get for the EM5 mk2 and Mk 1. 

(like this one,  http://www.ebay.com.au/itm/New-Quick-Release-L-Plate-Bracket-Vertical-Grip-Holder-for-Olympus-E-M5-II-EM5-2-/361495453330? hash=item542acede92:g:bIIAAOSwx-9WyrUe )  

So the ergonomics are not perfect but is it worth the hassle, absolutely it is a superb option for serious shooting, but just so we are all clear this is a manual lens when used on M4/3, there is no auto focus option at all and no recording of the lens parameters either.

For most people the prime question would be "does it work well wide open" after all why go this route if you were only planning to shoot at f5.6,  in short, yes it is very good wide open, I don't have the Olympus 17mm f1.8 or 25mm f1.8 for comparison but I feel pretty confident it would be at least as good as they are wide open, albeit with a very considerable weight penalty, it does weight over 800 grams!  

There is as you would expect a slight lowering of contrast and little bit of veiling flare wide open but appropriate adjustments to the RAW files easily deals with that, chromatic aberration is a little more pronounced wide open but I have seen raw files from the Olympus 17mm f1.8 and I reckon the Big Sig is way better in this respect.









The over-riding characteristic of this lens is consistency, it is virtually as sharp in the corners as it is in the centre at every focal length, and that is a rare thing indeed. As a point of comparison the well regarded Panasonic 14 to 42mm mark 2 kit lens is not even within shouting distance at any focal length for cross-frame consistency and you can take it from me that is the best kit lens on offer for M4/3 and generally way better than the equivalents from other formats as well.

Distortion characteristics when used on M4/3 are pretty minimal ranging from very mild barrel distortion at 18mm then turning completely distortion free at 26mm and finally going slightly pin cushion from 28 to 35mm.  Unless you were shooting architecture at 21mm or less I doubt you would ever really notice any issue at all.  

The distortion aspect is a big deal as lenses with low distortion lend themselves very nicely to image stitching tasks, it's not that you can't stitch with most lenses but rather it just works way better if the lens is distortion free.  

Basically correcting distortions before stitching is essential if you want the stitch to appear natural, despite the fact that that in theory it should be fine even if you don't correct first, I have never found it worked out that way in practice.  The problem is exacerbated because correcting distortion alway causes some small loss of image clarity in the corners and along the edges thus when you stitch the final image together you get resolution holes across the full image frame where the edges/corners where brought together.  Long and short of it, the 18 to 35mm Sigma is a very good lens to use to capture the frames for your panorama or matrix stitches.





The excellent cross frame resolution consistency has a rather nice benefit on the EM5 mk2. The EM5s' High Res mode certainly works as advertised but the results can be patchy with many lenses, if a lens has high central sharpness but low or poor edge and corner sharpness you will find the high res images show much better central clarity but gain nothing along the edges or corners from the process. In other words the centre to corner disparity looks worse!  Great results can only be obtained if the lens offers pretty even overall resolution to start with, which again makes the 18-35mm Sigma one of the best candidates I can think of for such demanding applications.

I would judge the Big Sig to be a pretty contrasty lens and probably most people would be very happy with that aspect, me, not so much.  I actually prefer to shoot with lower contrast lenses as I find the files can be more satisfactorily edited for great highlight and shadow rendering, the lower contrast kinda acts like a handbrake on the contrast extremes and goes some way towards giving me a more analogue/film-like rendering.  Anyhow I have some workarounds for this so it's no big deal and as I said most shooters prefer high contrast glass.








The high contrast however has its benefits in terms of colour punch, which the Big Sig seems to have in spades so that's a win, I would describe the colour rendering as quite neutral to perhaps just a little cool but there is no doubt that strong colours show plenty of pop, however it certainly does not display the warmth that say Minolta legacy glass does on the Olympus bodies.

All focal lengths are sharp but if pushed I would say the 28 to 35mm range looks a tad more detailed. The important aspect of the great sharpness performance being that files need very little sharpness boosting, which is always preferable as punching up the sharpness can destroy micro tonality and create otherwise undesirable artefacts, I would describe the lens as displaying an effortless sharpness, it just looks natural and nicely 3D even at quite small degrees of magnification.

The bokeh is good and gives me no cause for concern but it is not as nice as can often be seen from some of the classic legacy glass, especially some of the golden oldies from mother Russia.  It suffers from a little bit of green fringing on out of focus highlights (this is fundamentally longitudinal chromatic aberration) and the characteristic high contrast does mean the edges of the out of focus circles are rendered with a little more clarity than a low contrast lens would, on the other hand the out of focus circles are pretty much just that, circles rather than ugly hexagons or misshapen blobs.  There is one little characteristic I noticed that I feel is quite unique, at middle distances from the camera the out of focus areas when shot wide open can take on a rather 3D characteristic, it's hard to describe and can only be seen at significant magnifications but nonetheless it is a rather different rendering style.






Mercifully the lens doesn't display any double imaging of lines and details in the out of focus areas, which is rather nice and this helps it avoid looking busy and nervous.  Overall I reckon the bokeh is nice enough but if I were after a "short portrait" lens it may not be my first choice, actually it wouldn't be, the lens is just to unforgiving in resolution for most portraits needs, mind you if you threw a classic "softar" style filter on the front of it I imagine it would be rather lovely, I must try that at some time.

I'm generally very sensitive to chromatic aberration, it's one of those things that just disturbs me and I tend to notice its awful presence long before most people do, any lens with a problem in this area will usually not rate with me.  The Big Sig is actually pretty special in this respect, yes there is a bit of CA, but it mainly effects the wider settings, 18mm to around 24mm, beyond that you could largely disregard it and there is really no discernible CA at all at the 35mm setting even when viewed at a 200% view.  This dear friends is a very good thing as fixing CA when it is significant can cause quite a few artefacts around the edges of your image especially if you try to sharpen the files up and even when well corrected it still decreases the resolution potential of the lens. 

Lenses with really bad CA are only useful for monochrome work as far as I am concerned and only if you use only the green channel with a little red channel mixed in.  Anyhow the
18-35 Sigma is about as devoid of CA as you could reasonably expect from any lens costing less than $2000, three cheers for that!





On the mechanical side of things I find the focus ring quite lovely, I have a love/hate relationship with focus rings, mostly hate, especially on modern digital age lenses.  How hard can it be guys?  Most focus rings are either too sloppy, too thin, too tight, too hard to the touch, have too little rotation or too much rotation, or are just plain bloody horrible, the Big Sigs is for my tastes the Goldilocks option, just right!

It is of course a heavy beasty and that is the way things have to be if you want to use the words "fast, zoom and high sharpness" in the one sentence, but frankly this is not lens for walkies in the city shooting street photography or lightweight hiking but as a serious tool for on-tripod use or steadily held in your hand for a limited period of time.  For studio work I expect it would be amazing but as of yet I haven't got to that.





Technically the Olympus EM5 mk 2 and other Olympus bodies are a great match in that a lens like this needs to be either held very steady or used with "in body image stabilisation" otherwise much of that high resolution goodness will go begging, additionally the lens shows the benefits of electronic shutter options more so than most of the other lenses I have tested on the Oly.  All of which means in a odd and perverse way that maybe the Oly OM series is the right camera for this lens (focal length magnification issues aside), you see mounted on the native Nikon DSLR body it has no image stabilisation to assist when the going gets tough and on APSC Sonys' the situation is the same.  Panasonic's do offer IBIS but only on a couple of models and you could use it on say a Sony A7R mk 2 in crop mode, but then that seem kind of a waste of the cameras capability.

So here is my conclusion, this is now my very most favourite M4/3 lens, I will use it regularly when needed a serious tool for paid jobs or landscape and fine art duties and will definitely further explore its very wide envelope of capability, it will certainly be used for Hi Res shots and stitches....but it is definitely nor coming on holidays with me.














Thursday, 9 June 2016

Mastering Your Kit Lens - Part 2

Some kit lens deficiencies are easily resolved in post and some are just ugly to the core, or is that the iris.  For today we consider the factors that can be sorted post shot.  


Here is an uncorrected image taken with an old 28-85 kit lens on a full frame sensor, whilst the lens is not that bad, the edges of the frame show Chromatic Aberration, there is some vignetting, obvious barrel distortion and some loss of corner detail.  At this small size it no doubt looks OK but a good size print would be a different matter.


Chromatic Aberration

Chromatic Aberration can be generally sorted and visually to my eyes makes one of the biggest differences, it effects colour and clarity and I personally find high levels of CA visually disturbing, I almost need to have a stiff drink when I see a bad example. CA can be aperture dependent and is always focal length dependent.

With most cameras these days CA  can be corrected "in camera" if you are shooting in JPEG format,  only the worst cases from the worst offenders will be seen in the final file, however Raw files will normally show the CA in all its awful glory.

It is worth noting that there are two types of CA, longitudinal and lateral.  Longitudinal CA is usually magenta - green and is normally only obvious at wide apertures using fast lenses.  Basically you get differing coloured fringes around the details dependent upon whether you are looking at the area in front or behind the point of focus.  This is hard to fix but far less common and actually rare with slow aperture kit lenses, the good news is if your lens is prone to it, you can prevented with stopping the aperture down to something more sensible.

The other CA, lateral is where we get coloured fringes around high contrast details, the strength of which increases as you move away from the center of the image, hence the term lateral. There is no fringing in the middle of the frame.  No, its not the purple fringing that many people refer to, it can be red, green, blue, magenta, yellow or of course occasionally purple.  

Many people think the pure purple fringing seen in a lot of high contrast photos is CA but in fact its often something else altogether, “sensor blooming” and is normally controllable by avoiding over-exposure.  Note however as said, real CA can also be purple too but is most likely in my experience to be magenta or green.

My experience is that some applications are much better at dealing with CA than others, I won’t make any recommendations as apps are always in a state of flux but don’t give up, if your current application can’t “kill the fringe” try something else.

Ideally you will always get the best sharpness from a lens which exhibits no CA, well chances are you will strike out on that one with a kitty, however it is highly likely that one focal length will display very low levels of CA compared to the others. You will need to dig around a bit.  For example, my Sony 18-55 changes its CA characteristics significantly between  25- 30mm with 27mm being close to perfect.  No other focal length comes close and as you move away from the 27mm setting things get progressively worse but in different colour directions.




         Here we can see a section from the right hand upper corner of the above image at the top of the page,
 the disturbing CA is obvious here and we can also see it has messed with the corner sharpness.  
This is a very old film era kit lens lens and no doubt, was fine for its time, 
but of course digital is far less forgiving.


Vignetting

Unless truly woeful, vignetting is easily sorted, but very high levels can leave your edges a bit noisy once it has been eliminated.   I often add vignetting in post production so it could be a benefit to you anyway. 

The worst cases of VD ( vignetting disease) seem to occur at the wider end of things, with most kit lenses displaying considerable vignetting between 18-24mm.  You may not actually see any vignetting if you're only shooting in JPEG mode,  almost all cameras now correct this in processing, but again for Raw files you will need to roll your sleeves up. 

Generally a little vignetting is actually quite tolerable for most image styles and unless you are shooting landscapes with lots of sky in them you probably won’t be overly bothered by it.


Distortion

Geometric distortions are generally easy to sort and again unless really bad you won't notice the issue.  The only thing to bear in mind is the more you have to correct the distortion the less final image area you end up with, and you may get an accompanying loss of corner/edge clarity once the problem is corrected. These days most cameras correct the worst of the distortion internally when shooting in JPEG format, so again you may never notice it anyway.

I suspect that many kit lenses actually shoot a bit wider than their stated focal length to allow for the needed cropping that occurs via the in-camera editing to get things squared away. The Sony 16-50 is a case in point, I think prior to processing it is probably more like 14 mm at the wide end. That leads me to a killer tip, by default the distortion correction is turned on on almost all cameras when you receive them, if you need a little extra angle of view, temporarily turning it off might just be enough, so long as you can accept the distortion. Even better if you shoot RAW you can disable the default distortion correction in your Raw Convertor application to get that little but extra in the pic.

Another tip to take to the bank on is that if you are shooting at focal lengths that will need distortion correction, just step back a bit and give yourself some extra wiggle room in the editing phase.

Normally the distortion is only really obvious if you are shooting objects with straight lines in them, for example architecture.  I must point out that even many fixed wide angle lenses have considerable distortion so buying an alternative lens may not solve the problem altogether.  From an optical point of view distortion is very to eradicate via lens design and usually involves adding more elements to the lens, making it both heavier and far more expensive, since it is relatively easy to fix in post, the justification for buying well corrected but expensive alternative lenses is somewhat diminished.

There are two primary types of distortion, Barrel and Pincushion.  Almost without exception wide angle lenses tend towards barrel distortion (which bloats the image outwards and telephotos tend towards pincushion distortion (which pinches the image inwards.   Normally for zooms there will be a point where there is no distortion and with most kit lenses this will be somewhere in the 26-35mm range. As a tip, the ideal focal length for easier panorama stitching will be the one that has neither type of distortion.

There is one complex type of distortion known as moustache distortion, in this case the middle part of the frame edge barrels outwards whilst the area about half way between the middle and far outer corners pinches in.  Normally such a distortion only occurs with focal lengths at the very wide end of the focal length range. This complex distortion characteristic unless dealt with in-camera generally defies the best efforts of Raw converters and editing programs, though there are some specialised panorama applications that can correct it.  Again in my experience unless you are doing a lot of architectural work this distortion is not likely to cause you any grief.




And now we have our finished specimen, the CA is gone, the corners sharper, vignetting removed and the distortion but a memory.  Of course it is a little cropped due to the distortion corrections, hence my tip to shoot a little wide if possible.



The final optical Aberration of concern is field curvature, I am not even going to start to deal with that in this blog entry, it deserves its own post so we will save that.