Would be grateful if anyone is able to share their experience with regard to exposure adjustment for reciprocity failure, with Ilford FP4. Is the table provided by Ilford accurate? Are any adjustments to development needed?

The exposure reading is, for example, 30 secs @ f/32. The adjustment needed according to Ilford would be 150 secs @ f/32.

Many thanks!

PS - I'm shooting on 10x8/processing in Pyro PMK (if that makes any differen

-- Stephen Vaughan (stephen@vaughanphotos.freeserve.co.uk), September 18, 2001

Answers

I shoot FP4 and HP5 and find that the reciprocity info from Ilford is pretty good. The problem comes when you are making an exposure which is longer than the Ilford chart covers (not sure but I think it goes to 30 sec. max?). Then you have to extrapolate from the chart and use your gut. When in doubt I error on the side of more exposure - it seems hard to over expose when you get into really long times. This weekend we were making an exposure on a foggy morning deep in the forest and the meter said 1 min. so we gave 10 min, and the negs look fine. You're "supposed" to reduce development when reciprocity comes into play but I almost never do. Maybe this is because the types of scenes where long exposures are necessary are by nature fairly low in contrast to begin with, but I find that normal development gives me the results I want. (I'm using D-76 1:1, by the way. No experience w/ pyro.)

Good luck!

-- Mark Parsons (Polar@thegrid.net), September 18, 2001.

You can actually extrapolate the rest of the times for the graph using a number of statistical software. Plug in the numbers from the Ilford chart and let the program graph it. The program can then extend the graph indefinitely. It will also give a formula for the graph. I extrapolated the new times for FP4 up to 1 hour (I don't have the corrected times in front of me) using a program called Cricket. I then tested the corrected times for 1, 2, 4, 8, 15, 30, and 60 minutes. All the exposures came out correct. I heard MS Excel can also extrapolate data but I've never tried it.

I also don't change the development times when I use ID11 1:1.

-- floren (flcpge@yahoo.com), September 18, 2001.

If you wish to calculate a corrected exposure time based on the ILFORD chart, use the formula

Ec=Em^1.48

Where Ec is the corrected exposure, and Em is the measured exposure, in seconds. Measured exposures of one second or less do not require any compensation.

Note that this formula is based on the chart. The chart was determined from experimentation. Times calculated past the chart should be good estimates, but are not based on ILFORD experiments.

David Carper ILFORD Technical Service

-- David Carper (david.carper@ilford.com), September 18, 2001.

doing HABS/HAER work, i have often found myself in some pretty ridiculous exposure situations, in the middle of abandoned tunnels, dark buildings, bridge abutment housings, unlighted machinery rooms, etc. as mark mentioned above, it is pretty hard to overexpose in those kinds of situations. if my meter reads 30 secs or 2 minutes, or some such, i just wave my finger in the air to see which way the exposure is blowing, and open the shutter. i wander around a little while and come back and close it. i have never once had a bad neg using that technique, and oddly, there doesnt ever seem to be any noticeable difference between negatives exposed for wildly differing amounts of time. i used to obsess about this kind of thing, but long experience has taught me i dont need to worry about it.

-- jnorman (jnorman@teleport.com), September 18, 2001.

Stephen, as the previuos answer said, it is difficult to overexpose the film with long exposures. I also use PMK with FP4 on 810. Normally I guess a longer time when my meter indicates more than 1 min, and my negs always turn out fine. Somethng to keep in mind is to make sure the film is settled in the holder before exposing the film.

-- Dave Anton (daveanton@home.com), September 18, 2001.

Ilford's recommendation has seemed reasonably accurate to me, but then I rarely expose beyond a few seconds.
BTW, reciprocity failure increases contrast, because it affects the shadows much more than the highlights. This increase in contrast is the opposite to what most people expect, and the instinctive response is to give a fuller development. In fact, you should downrate the film, and pull the development slightly to get the shadow detail back and keep the highlights in check.

-- Pete Andrews (p.l.andrews@bham.ac.uk), September 19, 2001.

I have made an exposure calculator for reciprocity failure that also indicates development compensation factors. I intended it for use with pinholes, but it will work for any long exposure. The times are for T-Max 100 and Tri-X, but there is a blank field so you can add your own favorite film. Anyone can print it out and either paste it onto some matte board or laminate it in plastic.

http://unblinkingeye.com/Articles/Pinhole/Calculate/calculate.html

-- Ed Buffaloe (edb@unblinkingeye.com), September 19, 2001.

This is what I use for HP5+ in PMK

Meter Adj -Dev % 1" 1.2" — 2" 3" — 3" 5" — 4" 7" — 6" 12" — 8" 19" 5 15" 50" 10 22.5" 1'30 12 30" 2'25" 14 45" 4'10" 16 1' 6'20" 18 1.5' 14' 20 2' 28' 24 3' 1°30' 27 4' 2°10' 30

The beauty of reciprocity "failure" is that often with such long exposures, you also face low contrast. Thus, if you think that +3 is all you can coax out your developer but this table calls for -20% development, just ignore the -20% and you'll get maybe a +4 development.

-- John Hennessy (northbay@directcon.net), September 19, 2001.

I typed in a nice table from the one on my light meter but it was rendered as a string of unintelligible numbers here.

If anyone wants my numbers, e-mail me and I'll send a text file.

-- John Hennessy (northbay@directcon.net), September 19, 2001.

I wonder if it's possible to submit a table in HTML to this forum?

Row 1, column 1	Row1, column 2	Row 1, column 3
Row 2, column 1	Row2, column 2	Row 2, column 3

If this came out OK, you can see how it was done with the 'view page source' option, but formatting a table by hand is a real pain.

-- Pete Andrews (p.l.andrews@bham.ac.uk), September 20, 2001.

Hmmph! Nearly right, but the text formatting needs to be done for each box individually. Very labourious.

-- Pete Andrews (p.l.andrews@bham.ac.uk), September 20, 2001.