Color Paper as Paper Negative?

[mkillmer]

It may be critical - the portrait was taken with a studio flash and the following filters:85B-85C-25Y- 20M - could this blue to red shift be exaggerated because I did not use a UV filter?

 

[Photo Engineer]

UV is important with papers just as IR is. You should use both.

PE

 

[mkillmer]

UV is important with papers just as IR is. You should use both.

PE

Thanks, PE!
I never heard of IR blocking filters before, just did a search and they are easy to find. I wonder if this would help remove the hotspot I have in the centre of the images?

 

[Photo Engineer]

Color papers are tungsten balanced. As such, they have a lot of IR sensitivity to get them "out there" into the short IR range for matching the films. If you do not filter things properly, colors can be off. This can even happen with films.

PE

 

[Daire Quinlan]

Yeah I've encountered this before, ably answered by PE as well :-D I looked into IR blocking filters but they don't come cheap.

This one was the one that made me notice it first, this is the corrected scan,


This is just the red channel, looks very IR
Dead Link Removed

 

[Photo Engineer]

The red sensitivity of color papers is quite far into the red compared to camera films. It is made so due to the Tungsten balance of the paper and the need to match the dye set in C41 films. This imparts some IR sensitivity.

Some automobile glasses are IR blockers. I bought a 5x5 square of it for cheap.

It worked.

PE

 

[Dr Croubie]

The red sensitivity of color papers is quite far into the red compared to camera films. It is made so due to the Tungsten balance of the paper and the need to match the dye set in C41 films. This imparts some IR sensitivity.

Some automobile glasses are IR blockers. I bought a 5x5 square of it for cheap.

It worked.

PE

Wouldn't any blue or bluish filter also block IR? Or does paper go that far into IR that normal filters can't touch it?
Ask anyone who ever bought a Leica M8 if they've got a few spare IR/UV filters lying around...

Also, depends what you call cheap, I'd say $75 for a 52mm is a bit pricey, but not outrageous.

Meanwhile, if RA4 paper does go into far-IR, has anyone tried it with a 720nm filter to take IR photos?

 

[Photo Engineer]

Only the red layer is slightly NEAR IR sensitive. Not FAR IR sensitive! Automobile window glass scraps are cheap and filter IR. Also,, many modern window glass is IR blocking.

Not all Blue glass is IR blocking though. It depends on bandpass.

PE

 

[Dr Croubie]

Only the red layer is slightly NEAR IR sensitive. Not FAR IR sensitive! Automobile window glass scraps are cheap and filter IR. Also,, many modern window glass is IR blocking.

Not all Blue glass is IR blocking though. It depends on bandpass.

PE

Damn, I thought I'd found a cheap way to make LF IR shots, it's always too good to be true though...
And yeah, for some reason I keep thinking colour filters are just high-pass and low-pass, whereas you're right, they're probably more like bandpass.
(I blame the audio engineer in me, where HP/LP filters are cheaper and easier to make, but that doens't really translate to light...)

 

[73764]

What about exposing the paper 3 times, using red, green and blue tricolor filters? Giving the longest exposure through red (with IR-filter?), less through green filter and the least through blue filter (with UV-filter?) you could maybe balance the colors taking into account the sensitivities of the different layers and the temperature of the light. Not practical with portraits but maybe with still lifes.

 

[mkillmer]

Any suggestions as to what is wrong with the weird red colours here?

If someone can tell me how to fix the colours in photoshop, I can apply the appropriate filtration...
any thoughts?

 

[Photo Engineer]

A Wratten 70 filter has a good level of IR blocking so R/G/B is a good and bad idea. Good for IR blocking but bad for difficulty level. If you are up to it!

As for the reds in the apples, I have no idea as I have no comparison. Single stimulus experiments are hard to comment on!

PE

 

[Truzi]

Mmm... Pomegranates... one of my weaknesses.

 

[mkillmer]

What about exposing the paper 3 times...

Interesting idea. I have a pretty good tripod and head, but I suspect registration might get messed up.
I'm sure I'll try it this weekend! - Thanks!

 

[mkillmer]

How do I determine the CMY components of wratten filters? For instance what is an 85c or an 85b?

 

[Photo Engineer]

How do I determine the CMY components of wratten filters? For instance what is an 85c or an 85b?

Have fun! This is part of the problem of CMY exposures.

PE

 

[Dr Croubie]

Interesting idea. I have a pretty good tripod and head, but I suspect registration might get messed up.
I'm sure I'll try it this weekend! - Thanks!

Well, I've read that Heinz Kilfitt had a tripod set in concrete in his basement for taking lens testing measurements. How ridiculous do you want to get?

Or there's the other alternative: leave the camera alone with no filter and play with the lights. A few strobes with CMY filters in an otherwise completely darkened room. Shoot one colour at one strength, change the filter (it won't matter if you bump the light a teensy bit), and shoot again at a different strength. (again, definitely only for still life)
I can see that there's a lot of paper to be wasted in experimenting...

 

[mkillmer]

I can see that there's a lot of paper to be wasted in experimenting...

Hopefully not wasted...

 

[Colin DeWolfe]

Any suggestions as to what is wrong with the weird red colours here?

If someone can tell me how to fix the colours in photoshop, I can apply the appropriate filtration...
any thoughts?

I actually quite like it.

 

[Photo Engineer]

Well, with C/M/Y filters you can do it in one exposure, but with R/G/B filters you need 3 exposures and can only do still life. Both require a lot of experimentation.

Although C/M/Y is easier. You generally need to expose, as I've mentioned, using the paper as if it were a slow tungsten film with a red bias.

PE

 

[mkillmer]

Here I've used a "Coffee" and a Yellow filter. There was too much yellow and green, but I was able to balance it out pretty easily in Lightroom.
You can see how much I need an IR cut-off filter - the background is a Matt Black ultrasuede - no red at all!

 

[Daire Quinlan]

This was taken over the weekend, Filtration isn't perfect by a long shot, my daughter maintained that she didn't like it because her dress is actually "bright red and black, not orange and brown" She was, of course, correct. I elected not to try and explain the complexities of trying to colour match an RA4 paper negative shot under daylight conditions and developed using out of date kodak chemicals at room temperature



It's supra endura, ektacolor rt/lu chemicals, filtered with an 85B and 65M/55Y. Metered for about 1asa or thereabouts, which seems to be pretty much spot on by the look of the negative. Inverted it's a little blue so the above is corrected a small amount, but not by too much.

 

[mkillmer]

It's supra endura, ektacolor rt/lu chemicals, filtered with an 85B and 65M/55Y. Metered for about 1asa or thereabouts, which seems to be pretty much spot on by the look of the negative. Inverted it's a little blue so the above is corrected a small amount, but not by too much.

Looks great to me - I can't filter all the way up to 65M and 55Y - each colour in my filters only go to "35" combined, that's why I use 85C+85B +20M +25Y (under flash). This suggests to me that 85C must be similar to 40M+30Y.

 

[mkillmer]

A bit of a disaster...
I've added the brand new UV/IR cut-off filter, but have ended up with a very flawed colour image - reds and greens have disappeared.
The image had a blue/green bias that I corrected in photoshop.
The Angel is wearing a pink dress and the eggs are white, pink, green and gold. The dragon is the correct colour.
I hope this is because the developer is exhausted.

 

[mkillmer]

The previous picture reminds me of one I took in January last year - it was old developer and I lost all red as well...