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Fringe obsession & looking 4 signs of uncorrected aberra
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PostPosted: Mon Dec 18, 2017 5:39 pm    Post subject: Fringe obsession & looking 4 signs of uncorrected aberra Reply with quote

In another thread Ian (quite correctly) wrote that i'm suffering from "fringe obsession, ... looking 4 signs of uncorrected aberration" in 100% crops. I have a interesting example from this mornings work which i'd like to share. It is a large window (about 14 meters high) made of small pieces of coloured glass. The glass is unusually thick, and it consist of massive broken pieces - not the usual thin flat glass panes.

For time being i won't add much technical information.

To make sure that i'm not pixel-peeping this time, i have re-sized the original Sony A7 JPGs from 4000x6000 to about 250x400px.
To say it again: These are not 100% crops, but re-sized images!



Both images were shot within a few seconds. The light was exactly the same, and all camera settings were exactly the same. And even the lens was the same nFD 2/135mm, always at full aperture.

Nevertheless these two images are really different. My client would never accept the colors of the left one, since only the right image looks right! And it would be very difficult if not impossible to "correct" the left image with post-processing...

What happened ...??

Stephan

Hint: the thread title, of course Wink


PostPosted: Mon Dec 18, 2017 7:05 pm    Post subject: Reply with quote

Should have used 1x1 pixel, then there would be no difference.


PostPosted: Mon Dec 18, 2017 10:50 pm    Post subject: Reply with quote

Have you got wb and tint settings from exif or from eg lightroom for those images? When I get inconsistent results like that I normally find the difference is due to the camera, and reflected typically in those values.
Were you just doing jpg's, or RAW?


PostPosted: Tue Dec 19, 2017 12:09 am    Post subject: Reply with quote

Different portions of the image? ie you had it set in the middle of the right and edge of the left? The difference is a result of poorly corrected aberrations?


PostPosted: Tue Dec 19, 2017 12:11 am    Post subject: Reply with quote

Very slight focus difference. Had similar when using some projection lenses... LCA


PostPosted: Tue Dec 19, 2017 12:56 am    Post subject: Reply with quote

Assuming the focus or position didn't change between photos, some camera setting responds to a subtle change in the light. Some camera setting is not static. Look at frames of video; not all are identical because ambient light is not steady!


PostPosted: Tue Dec 19, 2017 6:11 am    Post subject: Reply with quote

My only guess is that if you had white balance set to "auto" maybe the camera decided to interpret the scene differently via white balance settings.


PostPosted: Tue Dec 19, 2017 9:37 am    Post subject: Reply with quote

kds315* wrote:
Very slight focus difference. Had similar when using some projection lenses... LCA

Yes, it's a bad case of "purple fringing" (the lens was a little back focused). The stained glass would also turn green if the lens were front focused.

Cheers!

Abbazz


PostPosted: Tue Dec 19, 2017 10:16 am    Post subject: Reply with quote

There is an old English idiom worth remembering:

https://en.oxforddictionaries.com/definition/a_bad_workman_always_blames_his_tools

a bad workman always blames his tools

PHRASE

proverb

A person who has done something badly will seek to lay the blame on their equipment rather than admit their own lack of skill.


PostPosted: Tue Dec 19, 2017 3:40 pm    Post subject: Re: Fringe obsession & looking 4 signs of uncorrected ab Reply with quote

stevemark wrote:
In another thread Ian (quite correctly) wrote that i'm suffering from "fringe obsession, ... looking 4 signs of uncorrected aberration" in 100% crops. I have a interesting example from this mornings work which i'd like to share. It is a large window (about 14 meters high) made of small pieces of coloured glass. The glass is unusually thick, and it consist of massive broken pieces - not the usual thin flat glass panes.

For time being i won't add much technical information.

To make sure that i'm not pixel-peeping this time, i have re-sized the original Sony A7 JPGs from 4000x6000 to about 250x400px.
To say it again: These are not 100% crops, but re-sized images!



Both images were shot within a few seconds. The light was exactly the same, and all camera settings were exactly the same. And even the lens was the same nFD 2/135mm, always at full aperture.

Nevertheless these two images are really different. My client would never accept the colors of the left one, since only the right image looks right! And it would be very difficult if not impossible to "correct" the left image with post-processing...

What happened ...??

Stephan

Hint: the thread title, of course Wink


So, camera, light and lens settings are identical...

Hand held or tripod? what did you specifically focus on within all that back lit colour and contrasting black framework? was the focus pinpoint accurate?
I only ask because I am not that knowledgeable outside of product photography and just dabble really. But, to me as a novice, I wonder if there would be a subtle shift in what the camera would read were the focus point to shift slightly within all those different areas of back lit thick glass and dark. How far from the window would you have to be with a 135mm lens? I don't know how to work that out but I assume quite a distance. That would magnify any movement...

I don't know what I'm talking about but if I wanted to bullshit some fellow idiots, that would be my angle on what caused the difference.

Very interesting post Steve.


PostPosted: Wed Dec 20, 2017 9:58 am    Post subject: Reply with quote

Abbazz wrote:
kds315* wrote:
Very slight focus difference. Had similar when using some projection lenses... LCA

Yes, it's a bad case of "purple fringing" (the lens was a little back focused). The stained glass would also turn green if the lens were front focused.

Cheers!

Abbazz


Exactly my experience too Sebastien!!


PostPosted: Wed Dec 20, 2017 4:58 pm    Post subject: Reply with quote

Projection lenses often have severe green/red fringing in front and behind the plane of focus. I guess this will be because they were designed to produce the optimum performance on the plane of focus i.e. the projection screen.

Even the 2-3000USD Schneiders and ISCOs are like that.


PostPosted: Wed Dec 27, 2017 4:51 pm    Post subject: Reply with quote

Sorry i didn't follow my own thread - there were a few "urgent" additional jobs to do before christmas ... as usual Wink
Detailed answer and additional images will follow.

Stephan