Spectral sensitivity of collodion and orthochromatic film

I'm aware that collodion has a sensitivity to UVA and blue wavelengths, and that it drops off well before the red end of the spectrum. Orthochromatic film _seems_ to be of a similiar sensitivity in that it is not sensitive to red, and goes well into the UVA frequencies and deeper; a range of around 200nm through to ~500nm (?). I have built a 4x5 wetplate camera constructed from red perspex which has proved to work quite well with wet plate, as long as I keep it out of the sun as that dries the collodion out too quickly.

The question is would it work as well for ortho film? or x-ray film for that matter? It should do, but I would appreciate thoughts from others.

Thanks, Peter.

ortho usually peaks at around 450nm and 550nm, with sensitivity usually bottoming out before 600nm.

It all depends on the silver halides. AgI, AgBr, and AgCl are the 3 to pick from each with a different peak frequency, then different spectral sensitizers extend the visible range into the visible range. Some are ortho, some are pan.


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So Ortho film tends to be slightly more sensitive to red?

Why not test and report

Only you have that ruby camera

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Originally Posted by pmviewcam

I'm aware that collodion has a sensitivity to UVA and blue wavelengths, and that it drops off well before the red end of the spectrum. Orthochromatic film _seems_ to be of a similiar sensitivity in that it is not sensitive to red, and goes well into the UVA frequencies and deeper; a range of around 200nm through to ~500nm (?). I have built a 4x5 wetplate camera constructed from red perspex which has proved to work quite well with wet plate, as long as I keep it out of the sun as that dries the collodion out too quickly.

The question is would it work as well for ortho film? or x-ray film for that matter? It should do, but I would appreciate thoughts from others.

Thanks, Peter.

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Originally Posted by arca andy

So Ortho film tends to be slightly more sensitive to red?

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No, quite the opposite: ortho films are blind to red light.

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Originally Posted by arca andy

So Ortho film tends to be slightly more sensitive to red?

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Adding to the already excellent replies here: Short answer=yes/no. Ortho film is more sensitive than collodion, but does not see red. Depending on the exact formulation, ortho film is more or less sensitive up into the yellow-orange range.

Collodion is inherently "colorblind." It only sees some blue and violet down near the UV end of the spectrum. There are also colorblind silver gelatin emulsions. The super-slow gelatin dry plates are colorblind, although they see a tiny bit further into the spectrum because their bromide/iodide emulsion is inherently a bit more sensitive. It takes at least one orthochromatic sensitizer to change that. With handmade emulsions, erythrosin is the most common sensitizer.

To get a panchromatic emulsion, at least one panchromatic sensitizer is added to an already orthochromatic emulsion. There isn't a single panchromatic sensitizer. To get the full benefit of the sensitizers, colored filters are usually used. For example, orthochromatic film requires a yellow filter to see/record dark skies with fluffy white clouds, as opposed to the white skies characteristic of collodion and colorblind dry plates.

As Denise explains, orthochromatic sensitivity goes through green, yellow, into orange. It has a measurable response at least to 610nm, depending on the specific sensitizing dye.

Unsensitized halides including silver iodide don’t see past green.

Not much to add to her post, except to recommend a fog test so you know what works for your setup.