When to apply corrections

Bill Martindale

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Yesterday after watching Martin's video on the film and development cycle I decide to have a try myself using a couple of old folders I have. I used Fomapan 100 rated at 80 ISO and measured with a Profisix Light Meter in incident mode. That gave me 2 seconds exposure at f22. Looking at the reciprocity chart for the film that translated to 6 seconds. As there was a degree of Bellows extension I used Keith Haithwaite's formula to determinate that correction. My lens was a 150mm and the extended bellows measured 220mm. I calculated the factor to be 2.15. Multiplying the 6 seconds by 2.15 I gave 13 seconds exposure. I have just developed the first negatives and they are THIN. So the question is should I have applied the bellows factor first then calculated the reciprocity or did I do it in the right order? For the last frame I took a "check shot" out of the window and that is fine. If I had done the bellows before reciprocity the exposure would have been 23 seconds. According to the reciprocity chart 4 seconds would increase to 19 and 5 seconds to 27 so 2x2.15 is near enough to 4.5. I would have based my time on an average between 19 and 27, 23 seconds.

Any thoughts?

I should say I am a film/darkroom only person and have plenty of experience developing film but not a lot with long exposures like this.

Thanks

Bill
 

mpirie

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I was taught to add reciprocity departure after everything else was compensated for.

The reason behind that thought is that bellows extensions and filters reduced the amount of light reaching the film, so reciprocity departure as last in line as it compensates for reduced sensitivity at long exposure times.

Mike
 

Keith Haithwaite

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I can't remember what formula I posted Bill but for a few years now I have used an app on my Android phone call Reciprocity. It allows you to: select the film you are using; set the filter factor if you are using one; set the focal length of the lens; the bellows extension and finally the indicated exposure on your lightmenter. The calculated exposure is then shown.
According to the details you give: Fomapan 100, no filter factor, 150mm lens, 220mm bellows extension and a 2 seconds lightmeter reading the app gives a calculated exposure of 24 second. :)
I wouldn't be without it but I do keep aa set of tables in my bag for emergency use.;)
 

Keith Haithwaite

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If memory serves I seem to recollect a couple of guys using recycled old Android phones to be able to use this app Bill so perhaps it's not available on the iPhone. This is a screen grab of the android app page.
1614264811975.png
 

thronobulax

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According to Kachel, reciprocity correction (increasing exposure) solves for getting good exposure in the shadows. However, it also moves the highlights up an one has to correct for that during development.

How are you all calculating corrected development times in this scenario?
 

Keith Haithwaite

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There are a few on the App Store but nothing by this chap. This looks much simpler to use.
It is very simple and very accurate in my experience Bill. I've just been looking through my collection of old phones to see if there was one I could give you but once again my battered old brain cells sparked into life and I seem to recollect passing on my last suitable phone c/w app to our own Ian Barber to try about 3 or 4 years ago - I'm hope if I've got that wrong he will correct me. :eek: It's certainly worth a small investment if you intend to pursue longer exposures in the future.
 
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Bill Martindale

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Thanks for looking Keith. I rarely do long exposures or need bellows extension so I think I will manage fine with your formula. It was only that it was a really wet day here, I was fed up and having seenMartin's video thought I would give it a try.

Martin - That app certainly looks like it does all I want. I will buy that one.
 

Bill Martindale

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I have bought and downloaded the App as suggested by MartIn. I bought the basic version and if I input the figures I have it tells me 13 seconds which is what I used.
Martin - Do you use the basic or the Pro version?
 

Keith Haithwaite

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................... I bought the basic version and if I input the figures I have it tells me 13 seconds which is what I used.
.............
Hmm, with respect I think you need to re-check your app input Bill as I believe the 13 seconds is wrong. Using your figures:

Bellows correction factor from the standard formula: = (Bellows Ext x Bellows Ext) / (Focal Length x Focal Length)

= (220 x 220) / (150 x 150)
= 484 / 225
= 2.15
Bellows Correction Factor =2.15

Exposure Correction BEFORE Reciprocity calculation = Indicated Exposure x Bellows Correction Factor
= 2 x 2.15
= 4.3 seconds

Exposure After Reciprocity Correction:
From Android App = 24 seconds
From Foma Chart = 27 seconds

The difference in times above are probably caused by rounding up fractions somewhere.
 

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martin henson

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The bellows extension, if I am correct is near enough 1 stop, so if the metered time was 2 seconds, the exposure is doubled to 4 seconds, the reciprocity according to the reciprocity app for Fomopan 100 is 13 seconds, however, there is Fomopan classic in the app, using that its 19 seconds, which one to use, I am not sure having never used it,
 

Bill Martindale

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Been thinking about that myself and I think the answer lies in the rating of the film. The App I think assumes you are using 100 ISO but I usually rate it at 64 or 80 ISO. So adding some compensation to adjust for the lower speed does bring it more into line with the 19 seconds answer. The film is a conundrum in itself. As Martin said there is Fomapan 100 and Fomapan 100 Classic but I have never seen an explanation of the difference. Anyway they were my last sheets of the film, from now on I will use FP4 Plus or HP5 Plus.

Keith - Having had a look at the attachment it is totally different to the one I have. Mine seems to be for the Classic and as Martin said 4 seconds becomes 19. Seems that there is a lot of dispute over the reciprocity characteristics of that film.
 

martin henson

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I think information on reciprocity times vary from the manufactures times, are they right, I think Ilfords times are spot on, however, you really need to try times and do a little experimentation, I have found that usually more time needs to be added, a few seconds in the films state of reciprocity will not make that much difference to the exposure, the danger is not giving enough time as happened to you, and I would also say most of us have been there at some point.
 

Keith Haithwaite

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Bill, in the six years I've been using Fomapan 100 5x4 (always shot at box speed) I can tell you that there is no 'Creative' tag on any of my film boxes, nor do I know of anyone that has seen one, so I too am mystified as to where it originated from. Retailers I've bought it from in both this country and in Europe advertise it as 'Classic' but I always receive an untagged box so yes, it is a conundrum.

The Android app I use, and the PDF chart, are both based on the Fomapan 100 Classic formula for calculating reciprocity adjusted times whereas the iPhone app is clearly very different judging from your times. However, you mentioned that your negs were very THIN (your caps) so something is clearly awry.

Anyway, I've no doubt the' Creative or Not' question will carry on puzzling the 'net as it has for a while now and photographers will, as they should, make adjustments to suit there own techniques and workflow.
 
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