Gelling the light source for B&W scanning

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JimKasson
MOD JimKasson Forum Pro • Posts: 39,833
Gelling the light source for B&W scanning

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Jim

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JimKasson
OP MOD JimKasson Forum Pro • Posts: 39,833
Re: Gelling the light source for B&W scanning

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Here's what a raw histo looks like with no gel.

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just Tony
just Tony Veteran Member • Posts: 4,023
Same idea, different application
1

My homebuilt spectrophotometer that I had configured for printer/paper profiling had poor S/N at the extreme red and blue ends of the spectrum with my 4700K halogen source. A magenta filter was a worthwhile game changer.

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MOD Hamiltionian Senior Member • Posts: 1,153
Re: Gelling the light source for B&W scanning
1

JimKasson wrote:

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Here's what a raw histo looks like with no gel.

Looks like you are 65% down in the red and 25% down in the blue.  So you are losing 22% of potential signal, and could get a theoretical 12% bump in SNR from an ideal illumination.

I've briefly tried to tune the color temp of my source when shooting black and white test targets but couldn't get all channels even with this method.

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spilla Senior Member • Posts: 1,104
Re: Gelling the light source for B&W scanning

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Jim

I find this interesting, but I’m ignorant of some basics. Is SNR limiting for this application? It seems like it should already be quite high with little room for additional improvement. If so, wouldn’t another solution be exposure bracketing? Perhaps the limitation there is all the processing along with focus stacking which I know you already do,

JimKasson
OP MOD JimKasson Forum Pro • Posts: 39,833
Re: Gelling the light source for B&W scanning

spilla wrote:

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Jim

I find this interesting, but I’m ignorant of some basics. Is SNR limiting for this application? It seems like it should already be quite high with little room for additional improvement.

There's always room for improvement. Whether any improvement would material is another thing. I don't really know about that last.

If so, wouldn’t another solution be exposure bracketing?Perhaps the limitation there is all the processing along with focus stacking which I know you already do,

Yes. The workflow is complex enough without adding exposure bracketing. Gelling the light source would not impact the workflow at all.

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spilla Senior Member • Posts: 1,104
Re: Gelling the light source for B&W scanning

JimKasson wrote:

spilla wrote:

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Jim

I find this interesting, but I’m ignorant of some basics. Is SNR limiting for this application? It seems like it should already be quite high with little room for additional improvement.

There's always room for improvement. Whether any improvement would material is another thing. I don't really know about that last.

If so, wouldn’t another solution be exposure bracketing?Perhaps the limitation there is all the processing along with focus stacking which I know you already do,

Yes. The workflow is complex enough without adding exposure bracketing. Gelling the light source would not impact the workflow at all.

Well I’m interested to see the results. Even though I don’t scan film, I enjoy following along with your process and scans.

2ndviolinman Regular Member • Posts: 306
Re: Gelling the light source for B&W scanning

One of the things I kept when I ditched my darkroom stuff years ago was a 4x5 Beseler dichroic color head and film carriers. My thinking was that, someday, I could use the color head as a light source for camera scanning of flims, with the ability to color correct in the analog domain when scanning.

Never thought of this aspect of light source color, but interested.

JimKasson
OP MOD JimKasson Forum Pro • Posts: 39,833
Re: Gelling the light source for B&W scanning

2ndviolinman wrote:

One of the things I kept when I ditched my darkroom stuff years ago was a 4x5 Beseler dichroic color head and film carriers. My thinking was that, someday, I could use the color head as a light source for camera scanning of flims, with the ability to color correct in the analog domain when scanning.

Never thought of this aspect of light source color, but interested.

A dichroic head might make a fine light source. Availability of bulbs might be an issue, as well as heat and vibration from the fan. I’d be most worried about that last one.

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JimKasson
OP MOD JimKasson Forum Pro • Posts: 39,833
With Rosco #247 minus green

JimKasson wrote:

JimKasson wrote:

With light sources anywhere near D50, when scanning B&W negatives or positives, the green raw channels saturates well before the red and blue ones. It occurred to me that gelling the light source might even this out, and give me a higher SNR in the scans. I've ordered a couple of Rosco Minus Green filters to experiment with.

Has anyone else tried this? If do, did it help?

Here's what a raw histo looks like with no gel.

Here's the histo with a Roscoe minus green filter.

The green and blue channels are well matched, and the red is improved.

Jim

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MOD Hamiltionian Senior Member • Posts: 1,153
Re: With Rosco #247 minus green

Nice!  That is a significant improvement.  Did you calculate how much filter you would need beforehand, or from trial and error.  Result looks pretty close to optimal.

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JimKasson
OP MOD JimKasson Forum Pro • Posts: 39,833
Re: With Rosco #247 minus green

Hamiltionian wrote:

Nice! That is a significant improvement. Did you calculate how much filter you would need beforehand,

No . I just took a stab. That was the first gel I tried.

or from trial and error. Result looks pretty close to optimal.

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