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04-14-2013, 11:53 PM   #1
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Sigma 85mm sharpness test / aperture series on Pentax K-30

I got my Sigma 85mm a few days ago, and today I took it out a little bit to start to get acquainted with it. I wanted to compare the performance at the various apertures, so I made the following series of shots of the same subject, all shot within a few minutes of each other. The pictures were taken handheld sitting in my vehicle with my elbows braced against the steering wheel and door frame.

I think that all the focus was pretty accurate on all of the shots, except for the one at f/2.8. It should be sharper than it is, so I think that focus was off just a hair for some reason. I went back later in the day and took the shot again at f/2.8, but lighting was different since the sun was near setting at that point. You can see the second f/2.8 shot at the very bottom of this post.

The pictures were all captured in RAW, with very minor adjustments made during developing using Adobe Camera Raw 7.3. A minor Smart Sharpening was also applied in Photoshop CS6. Click on each of the pictures to view the full size image.

























I am very pleased with what I am seeing from this lens so far. I'm happy with the sharpness and contrast at f1.4, and it only gets better as you stop down. I think that this subject with bright afternoon sunlight was a little bit of a torture test for a large aperture lens since there were a lot of high-contrast areas with the white paint job and with the tree branches in the background against the sky. Unsurprisingly, there is some CA in high-contrast areas at the largest apertures, but that is not unexpected and is easily dealt with in Adobe Camera Raw with just a few clicks.

Here is the shot at f1.4 again, and then below that the same shot with CA and vignetting corrected in ACR:





And finally, as mentioned above, here is the revised f/2.8 shot since the focus was slightly off on the first one taken during the series. The lighting is different, but you should be able to see that the lens is very sharp at f/2.8. There was a some magenta in the highlights on the headlight, but most of it was easily removed using the purple "Defringe" slider in ACR.




Last edited by Edgar_in_Indy; 04-14-2013 at 11:58 PM.
04-15-2013, 12:54 AM   #2
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Impressed with the sharpness wide open. There is quite a bit of purple fringing wide open in high contrast areas but pretty much gone by f2.8 and as you say can be handled PP.

Nice lens.
04-15-2013, 01:24 AM   #3
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You've gotta just love these brick wall tests, oh... no wall.

The big question is after all this, is she a keeper and are you happy with her?
04-15-2013, 02:09 AM   #4
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That is a great series for showing a newbie like me what purple fringing is as I've never really spotted it before. Compare the 1.4 to the 8 though and the difference is amazing.

04-15-2013, 03:46 AM   #5
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I want one

Amazing at f/1.4! I will be following this lens a little more closely
04-15-2013, 05:50 AM   #6
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Awesome - even I am eying on this lens. Let's see. I am happy with Samyang which also is pretty sharp wideopen but Sigma remains in the wishlist - next lens to acquire dependinig on what Pentax has for us.

This one is from Samyang @ f1.4 (note this is Facebook's highly compressed image)

04-15-2013, 06:50 AM   #7
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QuoteOriginally posted by kerrowdown Quote
You've gotta just love these brick wall tests, oh... no wall.
Yeah, didn't you hear? Brick walls are out and cement mixers are in when it comes to lens tests.

QuoteOriginally posted by kerrowdown Quote
The big question is after all this, is she a keeper and are you happy with her?
Yes, I'm very happy. I was actually grinning when I first put the lens on my camera and checked the first f1.4 images on my camera screen, since the sharpness looked good when I zoomed all the way in on the preview image. As I said, the high contrast and the harsh lighting here is kind of a tough test for a lens at large apertures. I bought the lens primarily for shooting people in conditions where there is not a lot of light. I've already used the lens at my daughter's gymnastics and at an indoor birthday party, and some of the images at f1.4 were amazing.
04-20-2013, 01:43 PM   #8
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I revisited the scene of the first set of pictures, and I wanted to see how the same subject would photograph with less-harsh lighting. Last time when I shot the truck, it was in full midday sunlight. Not an ideal situation for a large aperture, with the sun reflecting off all the shiny bits and all the high-contrast areas, and probably not the intended use for such a large aperture.

This time, it had just finished raining. The sun was starting to peak out, but there was still a lot of cloud cover in the sky. As I suspected, these conditions were better suited for wide-open shooting. The purple and green fringing that was present on the reflective areas were now mostly gone. I'm still impressed with how sharp the lens is, even at f/1.4.

As before, click on the image for the full-size 16MP image. (And please ignore the suspicious-looking substance on the differential "pumpkin" on the front axle.)

















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