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Author Topic: Color "problems" in the sky IQ250 schneider 55mm  (Read 1510 times)

MonsterBaby

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Color "problems" in the sky IQ250 schneider 55mm
« on: July 10, 2014, 01:51:56 pm »

hi forum.. as i dont know the real term for that.. i have to post and cant google first.

i am supposed to print some pictures from a phase one IQ250.. schneider 55mm  and at the sides i get colorshifts in the sky.. magenta patches.. mostly

i heard that this is "common" to mid format sensors.. ? and u can take a white picture and then build some kind of profile to calculate that..

i dont have access to that camera any more.. does anybody have an idea? how is that effect called? are there "standard" profiles for PS CC for example?

thnx
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Ken R

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #1 on: July 10, 2014, 04:02:29 pm »

hi forum.. as i dont know the real term for that.. i have to post and cant google first.

i am supposed to print some pictures from a phase one IQ250.. schneider 55mm  and at the sides i get colorshifts in the sky.. magenta patches.. mostly

i heard that this is "common" to mid format sensors.. ? and u can take a white picture and then build some kind of profile to calculate that..

i dont have access to that camera any more.. does anybody have an idea? how is that effect called? are there "standard" profiles for PS CC for example?

thnx

You need to make a capture (lcc reference image) with the neutral semi-transparent filter (better known as the white matte plastic) in front of the lens under the same conditions (ideally) as the actual exposure you want to correct then use the LCC tool in Capture One to correct the image.

http://www.youtube.com/watch?v=KBoSHz4kBKA

If you did not do that then you are basically SOL unless you can source the camera/back/lens again and make the reference capture with the camera setup as close as it was setup in the image you want to correct.  

I am assuming you are talking about a large format type (tech) lens since lens cast is not an issue when using SLR lenses.
« Last Edit: July 10, 2014, 04:07:10 pm by Ken R »
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Doug Peterson

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #2 on: July 10, 2014, 04:02:39 pm »

Can you post a photo illustrating the issue you are referring to?

You're talking about the Schneider 55mm LS (as compared to a technical/large-format camera with shift/rise/fall)?

LCC should not be required for a 55LS on a DF/DF+, but hard to know what you're seeing without a photo/screen-grab illustrating it.

MonsterBaby

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #3 on: July 11, 2014, 03:10:15 am »

its hard to see here i guess. it poped up on the 44" print.. it was exaggurated cuz i raised the orange in the raw converter..


thnx ken, too.. thats what i was lookin for.. the question is.. why isnt there a ref. image online somewhere.. of that combo..

and the question is.. do i actually need it ..doug.. ?
« Last Edit: July 11, 2014, 03:16:09 am by MonsterBaby »
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Paul2660

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #4 on: July 11, 2014, 07:27:15 am »

As you shot with the Schneider 55, a traditional LCC would not be needed.  LCC's are for Tech lenses center or shifted to correct for color cast towards the edges of the frames and at times center since the rearmost lens element is so close to the sensor.  LCC's can also help correct tiling, (centerfolding) but I am not sure the 250 has this issue, if the sensor has readout lines breaking it into sections, it might.  LCC's can also help correct the light fall off when a back is shifted or when a TS-E type lens is used (Canon 17mm TS-E for example)  With the 55 Schneider, you would not get light fall issues. 

The Mirror box of the DF, DF+ or other camera body, keeps the rearmost lens element far enough away from the sensor so that won't need an LCC for color cast issues.  NOTE, if you had color cast issues, you would see them in the file before you processed the raw, i.e. before you apply the LCC.  When they are loaded into C1 or LR.  It's very clear on most files especially in the sky.

Can you post a smaller shot, of the entire file?  This might be a profile issue being applied to the raw file.  Did you use C1 or or another raw converter? 

Paul
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Paul Caldwell
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www.photosofarkansas.com

Bart_van_der_Wolf

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #5 on: July 11, 2014, 07:39:32 am »

its hard to see here i guess. it poped up on the 44" print.. it was exaggurated cuz i raised the orange in the raw converter..

Hi,

It does look a bit like Color Cast (brought out by post-processing) that should be fixable with an LCC. I assume we are looking at an extreme corner?

Since you do not have an LCC for the lens settings, and no access to the equipment to do so after the fact, a radial color adjustment masked layer must be made in Photoshop or similar to correct in post.

Cheers,
Bart
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ondebanks

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Re: Color "problems" in the sky IQ250 schneider 55mm
« Reply #6 on: July 11, 2014, 10:07:57 am »

Did you use a greyish filter (polarizer, grad, ND) over the lens? Otherwise it's hard to understand why this cropped sensor would show colour variations in clouds with an unshifted, SLR type lens. I have seen such colour variations in that type of setup when a filter is used.

Also the shot looks to have been taken at high ISO? - it seems pretty noisy when I examine it at full res. Colour can be blotchy in most sensors at high ISO, but still I wouldn't expect it on that wide spatial scale.

Ray
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