DA* 50-135 comparison

OK, so maybe it don't say much for real life, but I know some people like to "see" examples for new items.

I took the same photo with the following lenses:
Pentax 18-55mm kit lens
Pentax SMC-FA 50mm f/1.4 prime
Pentax DA* 50-135mm
Sigma DC 18-200mm

All lenses set at 50mm or closest value to fit the object in the frame as close to identical as possible. Also set to the least common denominator of f/5.6 so all images would be as consistent as possible for each lens.
The camera (K10D) was of course on tripod, no SR.
Lighting was consistent via Wireless AF-540-FGZ bounced off ceiling.
RAW images were processed using SilkyPix with all default settings. (both JPEG and TIFs are available)

The images are 100% crops to show a smaller section of the image. The images are the same size in pixels, but due to slight differences in lenses they may show slightly different amounts of the subject. (I tried to keep things as close as possible on the camera end, but some human error still prevails)

Hopefully the test was consistent enough to be worthwhile to some.

You can view the four images here:
http://moringello-east.no-ip.com:8080/public/images/lens_test/

The tifs folder contains the same images in TIFF format (duh). They might show a bit more detail, but I really don't see it. I think the jpeg images show enough detail to show the differences.

2007-08-16_IGP6620.jpg : <lens ???>
2007-08-16_IGP6621.jpg : <lens ???>
2007-08-16_IGP6624.jpg : <lens ???>
2007-08-16_IGP6625.jpg : <lens ???>

Can anyone match up the correct lens with the corresponding image?
At least try to guess the DA* 50-135.

Well the 4th one is the sharpest, so it should be between the 50 and the 50-135. I'll guess that it's the 50-135, but only because I want it to be - I don't have any idea whether it would be better than a prime with such a reputation as the 50.

I'd guess that the 3rd one is the Sigma, since it appears so much darker than the others. Interestingly when I tweaked the levels so that I could see it, it didn't seem too bad at all.

So on sharpness alone, assuming there are no experimental errors in the focusing, that should make #2 the 50 and #1 the 18-55.

I don't know, I have no idea really.

In order of sharpness: 4 2 1 3

It will be interesting to know which lens is which, but it only gives part of the picture. At f8 the results could be entirely different, so if you shot lots of landcscapes at f8 it would make this test of limited value.

However, it's an interesting exercise.

So which lens is which?

I reckon it goes

18-55
FA 50
Sigma
DA*

how close am I?

Interesting...

Everyone correctly guessed on the 50-135mm and the 50mm.
But everyone got the 18-55 and 18-200 mixed.

I normally shoot with wider apertures , but I think John has a good point. I may try again with f/8.0 and see how they compare.

Anyway, the order is:
2007-08-16_IGP6620.jpg : Sigma 18-200
2007-08-16_IGP6621.jpg : Pentax 50mm f/1.4
2007-08-16_IGP6624.jpg : Pentax 18-55 kit
2007-08-16_IGP6625.jpg : Pentax DA* 50-135

Honestly, not sure why the 50mm prime isn't the top dog. I may want to re-run. Or I may just leave the Six-Sigma testing to the scientists. (I am a quality assurance software engineer by day, no need to continue when I get home... I just can't help it. )
I think the test is good enough for comparison sake, but I wouldn't make bets on consistency or relevance in all possible cases.

Well it's not at all surprising, given how much darker #3 is than the others.

As I said, tweak the levels and it's not at all bad. I've tweaked the levels on the Sigma shot, too, and it's not at all obvious to me that either is sharper - once you get them looking about the same in terms of saturation and contrast, there's not much between them.

Looking closely, it appears to me that the Sigma is sharper at the very top, but the 18-55 is sharper at the top of the paw just below the bow, so they can't be both focused on exactly the same spot.

If you're going to re-run the test, I'd suggest you look at why one of them was so much darker than the others, and also be exceptionally careful to focus on the same point each time.

If you do re-do the test it'd be worth including crops from the centre and from a corner as well. Consumer zooms are often reasonably ok for central sharpness but quite soft in the corners, especially wide open. For example I've had very decent results with studio portraits using the 18-55, especially at apertures of F8 or smaller, but found problems with sharpness with foreground detail in the corners when taking landscape shots. When I later did some trials using a lens test chart the difference in corner sharpness between various lenses was quite surprising.

OK, round two...

Auto focusing on a tight target is very hit or miss. My first attempt to redo the test was to focus on the head of a large nail on a plain background. High contrast, nail was perpendicular to ground (basically a single narrow plane of focus to contend with). After twenty minutes I found it was impossible to auto focus correctly... manual focus even with my bad eyesight allowed a much sharper image! That is just wrong. (Who knows what was happening with the irregular surface of my last test subject!!)


Anyway, this time I used a flat plane for focusing to help eliminate the chance that the camera roamed to the wrong spot. Autofocus was now quite easy with a larger area to connect upon.


Taking some suggestions, all images are at 50mm f/8.0. (I threw a couple of f/2.8 for the 50-135 and the 50mm prime for comparison).
I also added an image from the far edge of the DA* 50-135 at f/8.0. The sharpness is pretty consistent with the center.

For consistent focusing, I centered on the text "Extra Virgin Olive Oil" for all images. Again not all 50mm lenses have the same field of view, so the images aren't exactly the same. But they are all 100% crops with the same pixel width/height.

http://moringello-east.no-ip.com:8080/public/images/lens_test_2/

Notes:
1. The DA* looks abysmal at f/2.8. Could this be my fault? I made several attempts with the same results. I guess this softness is normal on lenses when open wide, but I was surprised by the extent of suckage, er, um "softness".
2. The 18-55 lens is still a bit darker than the rest (I made no attempt to make corrections or other falsifying changes to the images)
3. The 50mm f/1.4 prime lens is petty good at both f/2.8 and f/8.0


** Hopefully I covered everything and have decent test.
I tried to let the camera and lens do the work they were meant to do, and I did not try to fudge the results with extra processing of the images.
If something is inconsistently focused or metered, I do not believe it is my fault... but I am open to suggestions on how to determine that or make corrections.

It does sound weird. Other than in poor light, I find the AF on the '10 pretty good. For instance, from my office I can point the camera through a window with leaded lights, at a tree, behind which is a telephone wire, behind which is an aerial on a roof.

With camera set to spot focusing (I rarely change it from that setting), slight movements of the camera and a half press result in the focus shifting quickly and precisely from the leaded light, to a leaf, to the wire, to the aerial - all through the glass of the window.

This is with the FA 28-200. The 75-300 FAJ is a bit slower, and a bit whirrier, but it's still pretty good.

It's not until the light gets rubbish that I find I can focus quicker and more accurately myself.

Can't really comment on your results. The softness at F2.8 does seem disappointing.

But I never believe my own tests until I've done them several times and thought carefully about what I might be buggering up myself. So I'll take some convincing that it's as bad as the impression you give. No disrespect, it's just hard to judge someone else's experimental technique.

Done. Just for the DA* at f/2.8 and f/8.0.

Anyway, yeah, I usually get pretty good focusing results with the K10D.
I guess I'll have to play for a while and see if it is the DA* lens or just me, somehow.

I agree with your last assessment. I don't expect these to be concrete laws dictating the lens' ability. I am not working in a lab but I did take several shots and they seemed to be consistent.
So in a "real world" sense, these should give a good feel of behavior.
In general this is the closest thing to a lab environment my photography ever gets. I am usually hand held and in all sorts of conditions.
In the end, I guess these images really don't mean a lot.

Anyway, I also have some interesting shots I'll have to post of the vignetting and reflections in the 50-135 lens. Unfortunately I don't have comparisons against other lenses, so I may hold off until I can try to duplicate the environment.

It could be my screen but the images of the Balsamic Vinegar bottle appear to have vertical stripes, but only in the DA* 50-135mm shots.

I can see them in the F8 ones.

Strangely, I'm also seeing some very similar but not quite vertical stripes in the 18-200 shot.

I have no explanation for these.

Yeah, that is just the way the screen printing (or emulated look) was done on the label. I think lines are just sort of a moire pattern effect.

Perhaps. To me, it look as if the lens is focused slightly forward of the subject.

G

At f8 all the lenses are much harder to tell apart, at screen resolution anyway.

The test tells me that the 18-55mm performs very well when stopped down. Also that the 50mm, as expected, works well at two stops down and even better when stopped down to f8.

The new DA* is not exceptional in this test but the worst of the lenses is probably the 18-200mm.