Which do you calculate first? Bellows factor or filter factor? Does it matter? Recipr

[Kleiny41]

I’m photographing my orchids today indoors. I’m using a 210mm lens. My film is 46cm away from the film plane. I came up with about a 2.5 stop bellows extension factor. I’m also shooting with filters (for a trichromie). So with the first exposure a Red 25A- 3 stops of light. For some reason this is blowing my mind. And I’m using HP5, I shoot at box speed.




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[Pfsor]

I’m photographing my orchids today indoors. I’m using a 210mm lens. My film is 46cm away from the film plane.

Your film is 46cm away from the film plane? You won't get any significant image on it.

[Ken Lee]

It doesn't matter which you consider first: bellows factor or filter factor. However, reciprocity compensation should be figured last.

You might find the Reciprocity Timer App helpful if your phone will run it. It accommodates multiple factors and knows about HP5+ and other popular film stocks. See https://itunes.apple.com/us/app/reciprocity-timer/id459691262?mt=8.

I've used it for many long exposures at close range with lenses 210mm and longer, just as you're describing: see here and here for examples.

[Kleiny41]

Your film is 46cm away from the film plane? You won't get any significant image on it.

Really? Why? Even if I use artificial lighting?


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[cowanw]

Do you mean that your lens is 46 cm away from the film plane.

[Kleiny41]

Do you mean that your lens is 46 cm away from the film plane.

Yes, I meant my lens is 46 cm from the film plane.


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[Dan Fromm]

I’m photographing my orchids today indoors. I’m using a 210mm lens. My film is 46cm away from the film plane. I came up with about a 2.5 stop bellows extension factor.

I take it that you measured from the lens board or diaphragm, the two are nearly enough in the same place.

Extension = 46/21 = ~ 2.2 focal lengths. Magnification = 1.2:1 Effective aperture = aperture set * (magnification + 1) = 2.1 * aperture set. You got it nearly right, 2 stops is closer.

For best results your lens should be reversed. If it is in a #1, like many 210s, good luck and have fun.

[William Whitaker]

They're independent quantities. Does not matter.

[Pfsor]

...
I came up with about a 2.5 stop bellows extension factor. I’m also shooting with filters (for a trichromie). So with the first exposure a Red 25A- 3 stops of light. For some reason this is blowing my mind.

Of course you first calculate the bellows factor. You cannot and don't need to calculate the filter factor - its value is already written on your filter, isn't it?

[Bob Salomon]

Of course you first calculate the bellows factor. You cannot and don't need to calculate the filter factor - its value is already written on your filter, isn't it?

I believe he meant the exposure correction for the filter, not what the factor is.