An easy way to figure bellows factor

[Brian Ellis]

I thought reciprocity failure varied with the film and that extended exposure due to bellows extension brought reciprocity failure into play. I'll leave that discussion to the know it alls.

Reciprocity failure does vary with films, though for b&w film the tables I use only separate TMax films from all others (TMax films can be exposed for a longer time than others before reciprocity starts to fail - see http://www.largeformatphotography.in...xton-tmax.html - written before Kodak changed the TMax films to their current state but the principles presumably remain the same). However I would think, without really knowing, that bellows factor may or may not also be important. If you're making a 20 or 30 minute exposure it might be insignificant. If you're making a 4 or 5 second exposure, maybe not. Since there seem to be formulas for everything these days there's perhaps a formula for this somewhere.

As reciprocity failure sets in and you increase exposure time with b&w film you'll also increase contrast if you use the same development time as you use without that increase. So if you want a normal negative ("N" in zone system terms) it's necessary to reduce development time to take the contrast increase into account. Some reciprocity tables provide the amount of decrease for varying amounts of exposure increase.

[StoneNYC]

Reciprocity failure does vary with films, though for b&w film the tables I use only separate TMax films from all others (TMax films can be exposed for a longer time than others before reciprocity starts to fail - see http://www.largeformatphotography.in...xton-tmax.html - written before Kodak changed the TMax films to their current state but the principles presumably remain the same). However I would think, without really knowing, that bellows factor may or may not also be important. If you're making a 20 or 30 minute exposure it might be insignificant. If you're making a 4 or 5 second exposure, maybe not. Since there seem to be formulas for everything these days there's perhaps a formula for this somewhere.

As reciprocity failure sets in and you increase exposure time with b&w film you'll also increase contrast if you use the same development time as you use without that increase. So if you want a normal negative ("N" in zone system terms) it's necessary to reduce development time to take the contrast increase into account. Some reciprocity tables provide the amount of decrease for varying amounts of exposure increase.

I have to disagree with you here, the Kodak chart

http://www.kodak.com/global/en/profe...4016/f4016.pdf

States that reciprocity correction starts at 1 second which is no different than many other films, whereas Acros100 starts at 2 minutes...

http://www.digitaltruth.com/products...anAcros100.pdf

So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction.

Tmax's rate of failure after failure begins, over the long term, compared to many other films does seem better, but you need to be clear about the difference.

[Drew Bedo]

I mostly use either a 150mm or a 210mm lens.

The 150mm = 6 inches. For each inch of extension beyond infinity the bellows correction in 1/3 stop.

The 210mm = ~8 inches. For each inch of extension beyond infinity the correction is 1/4 stop extra exposure.

I can do this in my head all day long. When another lens is on the camera, a run through the arithmatic gets me where I need to go.

[redshift]

"So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction."

Why do people have to be so friggin judgmental?

Both of you cited documentation.

Brian added a caveat, "written before Kodak changed the TMax films to their current state".

Why can't a person try to add to a discussion without someone crawling up their butt with accusations of being false and misleading?

So many fora seem to be about little dick disease instead of a place to share experience.

[StoneNYC]

"So to say that Tmax has a much better reciprocity failure rate than most other films is false and misleading, especially to those who are less experience at long exposure and reciprocity correction."

Why do people have to be so friggin judgmental?

Both of you cited documentation.

Brian added a caveat, "written before Kodak changed the TMax films to their current state".

Why can't a person try to add to a discussion without someone crawling up their butt with accusations of being false and misleading?

So many fora seem to be about little dick disease instead of a place to share experience.

Because when you say something, people with less information and understanding often read it and then aren't properly informed.

I'm guilty of doing this a lot on here, and people correct me. And that's ok. If I say something misleading I want someone to point it out so that others who don't know as much, don't go down the wrong path, who then spreads his "knowledge" to his friends who know even less, it's just better to try and keep info good from the start.

[Terry Christian]

There's absolutely no judgement of the person intended necessarily when someone calls something false or misleading. There's no need to take it as a personal affront.
If, hypothetically speaking, Stone were to day that Rodinal is a solvent developer, it would be false and definitely misleading to someone who might be looking for a fine-grain developer, but my telling him he's incorrect doesn't mean I've assaulted his character.
So keep calm... (and praise Rodinal). ;-)

[BrianShaw]

I can do this in my head all day long.

I wish I could, but I just can't. I think it is a lack of experience (and perhaps insecurity) on my part since I do close-up work very seldom. For extension factor I use a tool similar to these rulers:

http://www.cookseytalbottgallery.com...ecordNumber=24

http://www.southbristolviews.com/pic...ic/SBVCALC.pdf

[StoneNYC]

There's absolutely no judgement of the person intended necessarily when someone calls something false or misleading. There's no need to take it as a personal affront.
If, hypothetically speaking, Stone were to day that Rodinal is a solvent developer, it would be false and definitely misleading to someone who might be looking for a fine-grain developer, but my telling him he's incorrect doesn't mean I've assaulted his character.
So keep calm... (and praise Rodinal). ;-)

Rodinal!!!!!

I recently saw someone post that "Rodinal is a great fine grained developer" .... I let that one slide... Hehe

[BrianShaw]

Because when you say something, people with less information and understanding often read it and then aren't properly informed.

I'm guilty of doing this a lot on here, and people correct me. And that's ok. If I say something misleading I want someone to point it out so that others who don't know as much, don't go down the wrong path, who then spreads his "knowledge" to his friends who know even less, it's just better to try and keep info good from the start.

No, Stone... you are completely wrong on this one. Absolutely and utterly incorrect. You don't do it a lot; you only occasionally do that.

[Bob Salomon]

You are making this very simple thing very complicated.

It does not matter wht focal length lens you are using. All you need to know is the size of the object you are shooting and how big it is on the ground glass.

If it is the same size on both open up 2 stops. If it is half as large on the gg open up 1 stop. If it is a quarter the size open up 1/2 stop. If it is 1/8 the size don't worry about it.
If it is twice the size open up 4 stops.

Or put a ruler in the scene where the subject will be and compare the size of an inch on the gg. Same rules apply as above. Works with or without movements.