Infrared testing with Kodaks and D50

Discuss older Nikon-based Kodak digital SLRs, including DCS 100, DCS 200, NC2000, DCS 400/600/700-series, etc. Ask questions, post general comments, anecdotes, reviews and user tips.
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Anssi Krooks
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Infrared testing with Kodaks and D50

Post by Anssi Krooks » Sun May 14, 2006 8:28 am

Summer is finally getting to Finland and yesterday I made quick comparison between DCS 420, DCS 760 (with IR-cut-filter removed) and my newly acquired D50. There's no doubt that DCS 760 is the best of three cameras what comes to tonality, D50 seems to have quite strong IR-cutter and with DCS 420 it was very challenging to get decent exposure. The filter I used was cheap 730 nm and lens was Nikkor 17-35/2.8.

http://turbaani.1g.fi/kuvat/Infrared/
D1X, DCS PRO SLR/n, DCS 760, DCS 420c & Canon Pro70

Ross_Alford
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Post by Ross_Alford » Fri Jun 09, 2006 11:16 pm

I bought the DCS420 thinking it would be good for IR since it has notoriously high infrared response, but I get the same effect as you can see in Anssi's photos--it doesn't seem possible to get consistent exposure across the frame; if the middle is correctly exposed the top and bottom are washed out. I suspect there must be severe problems with internal reflectiions of some sort. I think I've even noticed this in non-IR photos; the magenta cast you often get in parts of the image seems worse along the long edges of the frame, probably from infrared.

nik0web
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Post by nik0web » Sat Jun 10, 2006 5:07 am

Ross, you've got me thinking about the internal reflections. The camera was designed for film and the sensor uses only a small area out of the center. The lens is however still projecting an image even larger than the film size. What happens to all that stray unnecessary light. Do you think it'd be a good idea to paint the area around the sensor? A small piece of black cloth, with a hole in the center, might be used as a test.

<i> A modest man never talks to himself.</i>
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Ross_Alford
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Post by Ross_Alford » Sun Jun 11, 2006 12:30 am

I was thinking about that, too. maybe either or both of painting the area around the sensor and perhaps elsewhere in the mirror chamber with flat black paint or surrounding it with black felt or velvet cloth (lint would be a problem I suppose, and you'd have to be careful that anything you did didn't interfere with the shutter blades. I have looked at my IR attempts and other photos affected by the extra magenta issue again and I really do think that's the problem.

You'd have to check any paint or cloth for IR reflectance, which could be done by photographing it with another camera with IR filter attached--many "black" paints and other materials have very high IR reflectance, possibly deliberately to cut down on heat loading. Maybe the mirror chamber of the N90s happens to have fairly high IR reflectance, too, which would be why the problem is mostly with IR and not so much with visible light.

nik0web
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Post by nik0web » Sun Jun 11, 2006 5:38 am

After I posted my suggestion of trying a piece of paper or cloth arround the sensor it occurred to me that when the mirror goes up and the shutter opens there may be a lot of turbulence. Maybe the cloth/paper needs to be restrained???
Keep your mirror up!

Camnut
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Post by Camnut » Sat Jun 24, 2006 11:59 am

In the 420 you only need to mask the two horizontal bare metal strips, only they are exposed to the 36mm shutter area.
If you make a 2 sec exposure w/out lens and look at the CCD you understand at the moment exactly from were came the purple strips (the folded metal framing the ccd peeps from up and down of the shutter area efectively reflecting all the light to the upper an low corners of the ccd)

If you try to glue anything BE VERY AWARE with glue fumes, they can stick to CCD ruining it.

I will try to use two pierces of black isolating tape to try to solve it.

P.S I found that if you unplug the kodak back cable you can power the Nikon w/out powering the back. This way you can 'play' with the camera w/out eating precious battery or disk space.

Anssi Krooks
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Post by Anssi Krooks » Sat Jun 24, 2006 3:04 pm

Thanks for the tips - I'll try to cover the metal strips areas with black electric tape later on and try again to shoot some IR. I also ordered better filter so the only promblem that remains is to expose right and it means lots of bracketing with this camera. ;)
D1X, DCS PRO SLR/n, DCS 760, DCS 420c & Canon Pro70

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