135 in 4x5 back for tests

[jim steines]

Would there be any sort of issue taping a square of 135 film to a darkslide to do developing tests so I dont have to waste 4x5 film, apart from taping each one in the same place? Also have to find a tape that doesnt leave residue but apart from that cant really think of another reason this wouldnt work.

[Vaughn]

No guarantee that the emulsions of the roll film and the sheet film are exactly the same, nor that developing technique would be exactly the same...but it all may be close enough.

How about exposing one sheet of 4x5 film, and then cutting it into strips (ie five 1"x4" strips) to try different development times, etc? One could be sure that all strips received the same exposure that way, too.

[jim steines]

an excellent idea, will do that instead. Thats what Im going for, consistency in my developing process as I'm just starting out using tubes.

also, with metering with a digital camera how vital is it to account for the light-loss induced by the bellows length when using a normal lens? how much does changing focus affect this?

[Vaughn]

...also, with metering with a digital camera how vital is it to account for the light-loss induced by the bellows length when using a normal lens? how much does changing focus affect this?

If focusing at or anywhere near infinity, no correction needed.

The formula for correcting for bellows extension is:

bellows factor = (bellows extension)squared divided by (focal length)squared.

Just keep the units the same for the extension and focal length.

So if a 150mm lens (6 inches) is used at infinity the bellows are usually extended 150mm or 6 inches...which gives you a bellows factor of 1. Usually in landscape work, no correction is ever needed.

Same lens used for a close-up and the bellows measure 12 inches, you would have 144/36 = 4 So you have to increase the exposure be a factor of 4 (or two stops) over what your meter gives you. Extended 8" would be 64/36 -- close enough to call it 2, or one stop.

[jim steines]

Good info, thank you.

[wentbackward]

Apparently digital cameras are configured for a 12% grey point so they protect the highlights, whereas you want to do the opposite for film.

[jim steines]

I ignore the meter and eyeball the actual photo, as I shoot manual flash a lot.