Reciprocity Disaster with Delta 100?

images39 · May 26, 2018

I think I might have made a huge error while using Ilford's reciprocity compensation factor for Delta 100. I was on the California coast last weekend shooting long exposures (in some cases with a 10-stop ND filter). Ilford recently (Aug. 2017) published a data sheet with a reciprocity table for all their films. The table lists a factor of 1.26 for Delta 100. The sheet instructs you to take your metered exposure and increase it by using the factor as an exponent. The example they give is HP5 and a meter reading of 10 seconds. The factor for HP5 is 1.31, so they take the 10 second metered time and raise it to the power of 1.31, giving a 20 second exposure.

My problem is that I thought the factors could be applied to minutes as well as seconds. But after returning home, I realized that you get very different results if you use minutes. Yikes! Delta 100 has a factor of 1.26. Some of my metered readings were 4 minutes; applying the factor gives you 5.7 minutes. BUT, using seconds instead (4min = 240 seconds) you get 998 seconds, or 16.6 minutes. Very different from 5.7 minutes! I think Ilford should have made clear in their data sheet that you must use seconds when applying the factors. I'm probably going to have some seriously underexposed negatives after investing a weekend and 10 hours of driving to photograph the coast.

I also noticed that there are other reciprocity tables out there that give different results for Delta 100. What method have other APUGers used with success? I'm confused on this...

Dale

Tom Taylor · May 26, 2018

I have had good success using the reciprocity curve published in the data sheet. Awhile back I wanted to take a night shot of the Ferry Building in downtown San Francisco and arrived at 5pm to snag a free parking spot that comes available for a short time about a block away from the Ferry Building. I rolled the 8x10 Toyo G with the big series 5 Gitzo tripod into location, set it up, and was already and waiting for it to get dark when I discovered that I left the table at home. No use wasting a sheet by guessing so I packed up and came back the next day with the table. However just as I was getting ready to pull the dark slide the lights on the building went out and stayed out. (It turned out that the power line supplying electricity to that whole block on the Embarcadero was accidently severed by a construction crew.). So I packed up and returned the following day, again snagging a free parking spot about a block away, and finally got the shot. As a result of all this I keep a copy the curve in all my backpacks.

Thomas

images39 · May 26, 2018

Do you know if the curve gives the same results as Ilford's factor table? For example, for a 60 second metered exposure, do the factor table and the curve both give approx. 3 minutes?

Thanks,
Dale

pentaxuser · May 26, 2018

My sympathies. The sheet does say that the table uses seconds but doesn't bother with a NB, then adding in bold type that the factors only work when exposures remain in seconds. It is a pity that the example is as short as 10 secs. If it was, say, 1 mins 10 secs then it could show the conversion to seconds from minutes and seconds and then how to arrive at the correct exposure with the correct calculator button.

I have no experience of long exposure photography but I could see myself making the exact same mistake.

pentaxuser

images39 · May 26, 2018

I'm fairly new to long exposure photography, so am still learning the ropes. It's frustrating that there are conflicting charts and factors out there for Delta 100 reciprocity compensation...

mshchem · May 26, 2018

images39 said:
I'm fairly new to long exposure photography, so am still learning the ropes. It's frustrating that there are conflicting charts and factors out there for Delta 100 reciprocity compensation...

I would drop a note to Ilford. Here's another reason for Acros. I bet someone at Ilford or on this forum can help. I once shot a roll of Ektachrome with a medium format rangefinder only to discover I had forgotten to remove the yellow K-2 filter from previous roll of black and white.

gijsbert · May 27, 2018

16.6/5.7 is about 2.9 so 3x so 1.5 stops so you could process the film as if you are pushing 1.5 stops
Although it sounds like like a huge difference in seconds, in stops it's not that big.
Hope the shots turn out usable!

mshchem · May 27, 2018

https://en.m.wikipedia.org/wiki/Reciprocity_(photography)

mshchem · May 27, 2018

I got out my collection of Kodak databooks. For all the old traditional films. If you had an indicated exposure of 100 seconds, you could either open the lens by 3 stops or increase exposure time to 1200 seconds. So if you had metered 1 min and 40 seconds as proper exposure , you would actually need a 20 minute exposure. Also with an indicated exposure of 100 seconds in addition to dramatically increasing your actual exposure, EK also specify a 30% reduction in development times .

I think your conclusion of underexposure is correct. I would ask Ilford. You may only be off by 1 stop? Using normal development you may just have slightly thin negatives, if you over develop its going to get pretty hard.

My feeling is you may not be in that bad of shape?

images39 · May 27, 2018

Thanks for the comments and information. I'll find out soon how the negs turn out. Rolls had exposure times ranging from 1/8 sec to 8 minutes (a pretty big spread). I instructed the lab to reduce development time by 15% on half of the rolls and 20% on the other half. Anxious to find out how they look and if the long exposure negs are printable.

Dale

Doremus Scudder · May 27, 2018

images39 said:
I'm fairly new to long exposure photography, so am still learning the ropes. It's frustrating that there are conflicting charts and factors out there for Delta 100 reciprocity compensation...

Ilford augmented their general recommendations for reciprocity failure, which were an average for many different films, with the publication of the reciprocity factors for particular films more recently. Therefore, the best and most accurate information is that with the factors (which you seem to have used). Yes, you've likely get some underexposed negatives from your trip, but develop and proof them anyway; there may be some that are better than you expect.

And, I'd recommend that you take some time and, using the factor for the particular film you shoot, make yourself a table that extends well out past the longest exposure you anticipate making. Mark the table with seconds, minutes and hours to correspond to your meter, etc. and keep the table with you in your kit. It's a whole lot faster and easier to consult a table than to drag out the phone, get the calculator app up and going, enter all the data, etc., etc. Plus, if you want to change exposure (e.g., f-stop change or changing light), you won't have to recalculate, just look at the next column on the chart.

And, when in doubt, err on the side of overexposure. If your meter says 10 minutes and you expose 20, you're not even adding a stop (reciprocity failure negates the doubling rule).

Best,

Doremus

bernard_L · May 27, 2018

images39 said:
It's frustrating that there are conflicting charts and factors out there for Delta 100 reciprocity compensation...

Some of these charts out there on the vast Web provide as sole service a tabulation of t raised to some one-size-fits-all power. Ilford's data has different values of the exponent for the various films; presumably they took the time to perform tests. Why not trust the manufacturer?

Ian Grant · May 27, 2018

Ilford publish a generic Recirocity table for all their films, I added the new factors and drew the comparisons here:

I have the figures for longer exposures in a spreadsheet. Personally I've always done my own tests as there are other factors as well.

One problem is films have two ISO speeds one for Daylight and another for Tungsten, these days not all manufacturers list the Tungsten ISO, Ilford dropped it for their films except Ortho Plus. At one time a lot of studio work was done with Tungsten lighting so the Tungsten speed was important.

So FP4 has a daylight speed of 125 ISO but that drops to 80 ISO for Tungsten light, but being Orthochromatic Ortho Plus drops further - it's 80 ISO in Daylight and only 40 ISO with Tunsten light. ADox films which were later made under Licence from DuPont by EFKE were all named using their Tunsten speed initially the DIN speed but later changed to the ASA/BS speed. EFKE Kb/R/Pl 25 had a daylight ISO close to 50 and a Tungsten ISO of 25 because of it's being an Orthopanchromatic film (less red sensitivity).

Ian

images39 · May 27, 2018

Thank you for posting the chart and information. I think some of the confusion stems from the older Delta 100 Tech Data Sheet, which showed the generic curve. That curve gave very different compensation factors, as shown in your chart. For a 30 second metered exposure, it called for 155 seconds. Quite different from the 73 seconds you get with the new factor.

Dale

klownshed · May 29, 2018

images39 said:
I instructed the lab to reduce development time

If they're underexposed you'd need to increase development time, wouldn't you?

As the exposure due to reciprocity failure is obviously non-linear, if you work backwards from your exposure time of 5.7 minutes (344 seconds) you get an uncorrected time of 103 seconds (103^1.26=344) so you've effectively exposed the film as if the correct meter reading was 103 seconds instead of 240.

images39 · May 29, 2018

klownshed said:
If they're underexposed you'd need to increase development time, wouldn't you?

As the exposure due to reciprocity failure is obviously non-linear, if you work backwards from your exposure time of 5.7 minutes (344 seconds) you get an uncorrected time of 103 seconds (103^1.26=344) so you've effectively exposed the film as if the correct meter reading was 103 seconds instead of 240.

Yes, so the longer exposure frames might be woefully underexposed. I don't believe that increasing development would make up for that.

klownshed · May 30, 2018

images39 said:
woefully underexposed

Taking the reciprocity failure adjustment away, you exposed for an unadjusted exposure time of 103 seconds instead of 240. That's just over a stop, so not woefully underexposed at all and one which Delta film should cope with just fine,

Reciprocity Disaster with Delta 100?

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