first test of my Sigma 105mm F2.8 DG DN Macro Art

[Lou Jost]

In another thread I linked to an interesting video by the president of Sigma talking in detail about this lens. I found it very interesting. I'll put the link here too:
https://www.youtube.com/watch?v=zoMLAvZ ... e=emb_logo

[ray_parkhurst]

I don't bother about distortion but I like the excellent CA control and the superb sharpness over the whole frame, a good piece better than my old Sony FE90.

Distortion is fairly irrelevant for single frames of many subjects. Only reason it was apparent was that you shot a semiconductor wafer. Distortion becomes more troublesome when doing stitching, ironically even more so for the kind of natural subjects that are more tolerant of distortion for single images.

[lothman]

the renowned German computer magazine ct (with special photography edition issue 2/2023 page 61) tested the Sigma 105mm macro. They state it achieved in the centre 90% of the theoretic possible resolution tested on a Sony A7riv. I gave it a try and compared single shots and a 16x-pixelshift shot. Magnification was slightly below 1 and shot at f2,8, LED panels used for illumination.

a) So that's the overview:

Sigma 105 overview

b) this is a 100% crop

crop from a single frame

c) this is the 100% bilinear resized to the pixelshift image

crop from a single frame scaled to pixelshift size

d) and finally the result of the pixelshift image

crop from 16 frame pixelshift

It can be clearly seen that there is significantly more image information in d) than in b) or c). In other words, the Sigma 105 has a much better resolution even with an open aperture than the 60 megapixel sensor of the Sony A7Rv can record. The test evaluation of "90% of the theoretical resolution" describes the data handling of the camera rather than the resolution of the lens. I think they should question their testing methodology. I emailed them, but got no reply

[rjlittlefield]

lothman, thanks for the vivid demonstration.

Others: images in lothman's thread may be broken in some browsers, due to a conflict between http and https. To work around this problem, just revisit lothman's post using this http link:
http://www.photomacrography.net/forum/viewtopic.php?p=288434#p288434 .

--Rik

[Beatsy]

When cropping in 1 to 1 looking for detail, the limitations of the debayering process become very apparent. Pixel shift effectively removes debayering from the equation.

Did you use 4-shot or 16-shot pixel shift?

On the microscope, I find simple 4-shot makes a huge difference to resolution on its own. 16-shot doesn't make that much of a "huger" difference though. It does improve things further, if there is more detail to be had, but not by as much as when going from single shot to 4-shot.

Convincing test shots though. Well spotted!

[Lou Jost]

When cropping in 1 to 1 looking for detail, the limitations of the debayering process become very apparent. Pixel shift effectively removes debayering from the equation.

Did you use 4-shot or 16-shot pixel shift?

On the microscope, I find simple 4-shot makes a huge difference to resolution on its own. 16-shot doesn't make that much of a "huger" difference though. It does improve things further, if there is more detail to be had, but not by as much as when going from single shot to 4-shot.

Convincing test shots though. Well spotted!

I prefer to use 8-shot shifting, which for most lenses seems adequate. Lothman, do you see much difference between 8-shot and 16 shot shifting?

[lothman]

Did you use 4-shot or 16-shot pixel shift?

I gave it a try and compared single shots and a 16x-pixelshift shot. Magnification was slightly below 1 and shot at f2,8, LED panels used for illumination.

Lothman, do you see much difference between 8-shot and 16 shot shifting?

Sony allows 4x or 16x pixel shift and no I did not compare all modes.

[Lou Jost]

Hi Lothman, I didn't know Sony left out the 8-shot option. Good test!

[lothman]

Did you use 4-shot or 16-shot pixel shift?

@Beatsy
the idea behind your question whether a 4x pixelsshift would be almost as good as 16x is intriguing. Can I take 4 pictures out of the 16x ensemble in order to let the Sony Imaging edge software calculate a new 4x pixelshift? Then I would have the identical setup/object/lightning. And if yes which of those 16 files, 1-4 or 1/5/9/13....?
regards
Lothar

[Beatsy]

Yeah, sorry I didn't notice you'd mentioned 16-shot. My eye was attracted to the purty pictures before I got to that part

If you're using Sony Imaging edge (Viewer) for conversion, you can choose the option to produce 4 files out of 16. Each of those will be a 4-shot pixel-shift image - albeit with the pixels shifted "half a pixel off" the usual position in normal 4-shot shooting. Offsets are only up, down, left and right. Shouldn't make much difference.

Otherwise, if using PixelShift2DNG, then I think the files are done as 4 groups of 4-shot pixel shift. So the first 4 files of 16 would comprise a single 4-shot set.

I'm not sure if Imaging edge will let you process just 4 from a set of 16. It should, but Sony apps are weird. My PC is busy doing a big batch of files, so I don't want to try and run two instances to check right now...

Edit: I had to know so I risked it. Yes, you can just use the first 4 files to get a 4-shot image with Imaging edge, even if part of a set of 16 shots.

[lothman]

Edit: I had to know so I risked it. Yes, you can just use the first 4 files to get a 4-shot image with Imaging edge, even if part of a set of 16 shots.

Thanks, I will try this and post this result also in this thread.

[Lou Jost]

I think a more secure test is to just choose the 4-shot option, do that, then the 16 shot option, and do that. It surely matters which four images you choose out of the 16. Better to let Sony make the right choice.

[lothman]

I could not manage to do a 4x pixelshift image from 4 shots out of the 16x files, so I did another 4x shot.

100% crop from a single frame:

100% crop from the 4x pixelshift

same as above (4x pixelshift) scaled up to the same size as the 16x pixelshift

and finally the crop from the 16x pixelshift (done some days ago):

I think quite a huge improvement from the 16x pixelshift compared to the 4x pixelshift.

regards
Lothar

[Lou Jost]

Wow, you just sold me on the Sony camera!

[chris_ma]

impressive indeed!

so far I always was sceptical of sonys implementation of pixelshift because on most sample images I've seen there were zipper artefacts, but your example looks really clean. maybe people simply didn't use a sturdy tripod?
I wonder how it compares in resolution to my Panasonic S1R...

if you feel comfortable to send me your wafer to berlin I could do a comparison frame with a 8 pixelshift image on a S1R and a printing-nikkor. I would cover shipping costs of course.