Bellows Extension Factor and Reciprocity Failure for ULF???

[FrancisF]

I have cobbled together a 20 x 24 with parts from Filip Harbart. I am using Ilford FP4 with an Apo Nikkor 1210 mm but I have not been getting consistent results because I have not worked out all the issues of BEF and RF. Things are looking underexposed.

If I am getting an incident meter reading of 20, the meter says I need a half second at f128.

If I have 6 feet of bellow (1829 mm) then my bellows extension factor should be:

(1892 squared) / (1210 squared) = factor of 2.28. This is just a little more than one stop adjustment to the exposure. This would increase the exposure from half a second to just a little over 1 second.

The FP4 film comes with a graph to adjust for long exposures. The graph seems to say that a “measured exposure” of 1 second should be adjusted to about 5 to 7 seconds. The graph is a little hard to ready – I am interpreting it.

Any corrections to my calculations or advice about how I should be thinking about this? Thanks!! Francis Fullam, Chicago, Illinois

[Tracy Storer]

Your bellows extension adjustment looks correct, and although I have not used FP4 much, that looks like a good adjustment for reciprocity failure.
If your negatives look thin, I suggest doing some testing at wider apertures, with near infinity subjects.....
Your exposure and development may not be giving you "box" speed. I have always rated sheet film at lower than manufacturers ratings.

[vinny]

a 1 sec exposure for fp4 calls for about 3 seconds
google fp4 reciprocity and have a look
use a sheet of 4x5 film taped in your holder if you aren't happy with blowing $$$$ per test.

[StoneNYC]

I highly recommend the "reciprocity timer" app for apple iOS devices (iPhone/iPad/iTouch/etc) it's highly accurate and helps you take into account your bellows, reciprocity, filter correction, etc.

I would recommend it to anyone having trouble with their calculations (even just as a "double check".

Soon there will be a 3.0 version with "tweaks" to make the app more smooth to operate, but that's all aesthetic, functionally the current version works just fine.

134299

[Andrew O'Neill]

I have found manufacturer's data to be a bit over the top. For an indicated exposure of one second with FP4-Plus, I only give a third stop more exposure. This is from data I generated myself and have used in the field for many years.

[Michael Kadillak]

I agree your bellows correction looks good. I also feel that using an incident meter is a good choice. Remembering this chapter from the Beyond the Zone System (Phil Davis) manual you need to open up two stops.

[bobherbst]

One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

Bob


I have cobbled together a 20 x 24 with parts from Filip Harbart. I am using Ilford FP4 with an Apo Nikkor 1210 mm but I have not been getting consistent results because I have not worked out all the issues of BEF and RF. Things are looking underexposed.

If I am getting an incident meter reading of 20, the meter says I need a half second at f128.

If I have 6 feet of bellow (1829 mm) then my bellows extension factor should be:

(1892 squared) / (1210 squared) = factor of 2.28. This is just a little more than one stop adjustment to the exposure. This would increase the exposure from half a second to just a little over 1 second.

The FP4 film comes with a graph to adjust for long exposures. The graph seems to say that a “measured exposure” of 1 second should be adjusted to about 5 to 7 seconds. The graph is a little hard to ready – I am interpreting it.

Any corrections to my calculations or advice about how I should be thinking about this? Thanks!! Francis Fullam, Chicago, Illinois

[StoneNYC]

One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

Bob

Bob,

That's why some people (mostly cinematographers but also photographers) use T/stops instead of f/stops.

T/stop is the actual transition stop of the light per lens, the lens needs to be tested and marked.

I don't know who would be able to do this but perhaps some research and you'll find someone.

I've specialized by sticking to a particular lens design did 90% of my lens lineup so that I don't have this issue as badly.

The other problem is that shutters aren't very exacting and so one lens might also not match another in shutter speeds.

For ULF being B&W it's not really AS much an issue, but it is an issue.

Once you learn your lenses, you can adjust knowing how they perform, but knowing the actual T/stops will save you a lot of testing.

[Dan Fromm]

One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

Bob

Bob, I came late to this discussion, sorry.

Apo-Nikkors are single-coated. So are RD Apo Artars. Y'r estimate of the light they lose per air-glass interface is high.

Single-coated surfaces lose ~ 1% per surface. See S F. Ray, Applied Photographic Optics, p. 74. 0.99^8 = 0.92, a negligible loss. 0.96^8 = 0.72, approximately in your ball park and a loss of only ~ half a stop. The gain from single-coating for lenses that aren't too complex (dagor, triplet, tessar, dialyte and plasmat types) is so small that for them going from single- to multi-coating doesn't improve transmission very much.

The plasmats that you used on 4x5 and 8x10 have 4 four groups, i.e., have exactly as many air-glass interfaces as the process lenses you find low in transmission and contrast.

I don't know why your dialytes don't perform as expected for you, but your explanation doesn't seem correct. Could they be hazy? Could internal reflections inside your camera be lowering contrast?