Reciprocity - Horror of long exposure times?

Reciprocity Table

When it comes to pinhole images and thus when it comes to such long exposure times, there is another parameter added to photography which you do not have to care about when you use lens based cameras and usual exposure times less than one second and maybe faster than 1/1000 of a second. That parameter is the reciprocity failure. People only using digital cameras may never have heard of it and maybe never have to care about it.

Put it simple: The longer the exposure time the less sensitive the film gets. That means that you have to correct the measured exposure time by a factor depending on the measured exposure time --- and the film. For most films on the market that can be several f-stops when times get longer than say 100 seconds. And the problem of reciprocity gets even harder when you count in vignetting where with wide angle pinhole cameras the image gets maybe 2 f-stops more light in the center compared to the corners.

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One word about the title of this post: You can control reciprocity and long exposure time pretty well. There is enough good data about the reciprocity failure of films and if you do not forget to correct the measured exposure time you can have as reproducible results as with normal exposure times. So forget about the horror.

To deal with long exposure times and wide angle pinhole images (that means with vignetting) you can use a film with only small reciprocity failure or a film which is so fast that reciprocity does not play that much of a role.

Low reciprocity failure, there are some films which match this criteria. One is - and probably it is the best film when it comes to reciprocity failure - Fuji Neopan Acros. It has nearly no reciprocity failure up to 100 seconds (that means, even when rating it ISO100, with very long exposure times it is faster than all the ISO400 films.) One problem with Acros: It is not that easy to get it in Germany, I could not find a shop selling it for a long time, but now that I have settled with another solution there is one online shop which has it in 4x5. But you do not get it in 8x10". And compared to other films it is damn expensive. So I only use this film in the little Zero2000 but there I love the results I get.

The other film out there with pretty good reciprocity failure is the Adox CHS 100 (well all of the Adox CHS line, but I only use the CHS 100). It is not as good as the Acros, but still much better than the rest. And compared to other films it is real cheap as sheet film and available in many sizes.

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OK, these two films are pretty good when it comes to reciprocity failure, but one has to say, that you need really long exposure times so that you get shorter times with them compared to e.g. Ilford HP5. Well compared to HP5 and not using the reciprocity corrections Ilford suggests in the films data sheet.

There are some really interesting articles about reciprocity corrections out there in the web. One very interesting article is written by Patrick Gainer: Low Intensity Reciprocity Failure I think this is a must read for every pinholer.

The essence of this article - use this formula to calculate long exposurte times:Tc = Tm + a * Tm^1.62 where Tc specifies the corrected time, Tm the measured time and a a factor dependent of the used film. I use this equation with the following values for a: 0.23 for Fomapan 100, 0.11 for Ilford HP5, 0.022 for Adox CHS 100 and 0.0072 for Fuji Neopan Acros. And I created a small cheat sheet for the films I use which I always carry with me when I am using my pinhole cameras. That is what you can see in the image above. The table contains the corrected values for each f-stop of one of my pinhole cameras which are f138 for the Zero2000 and the Zero45, f176 for the Zero45 with one extension frame, f216 for the Zero45 with two extension frames and f256 for my 8x10 camera.

And then there is another interesting article about reciprocity corrections which you can find on in this thread: Click! There, René posts interesting reciprocity data for some films. His formula for calculating the reciprocity failure looks like: Tc = exp(a * ln(Tm) + b) where b is defined by the starting point of the reciprocity correction and a is defined by the steepness of the reciprocity curve. And here is what he found out for several films:

Filmabstart time (s)
Ilford RC paper1.010116
Efke 25/50/1001.080.120.5
Kodak BW400CN1.16-0.78120
Fuji Neopan Acros1.16-0.78120
Fuji Superia 100/200/4001.2-0.142
Fuji Superia Reala 1001.2501
Polypan F1.25-0.172
Fuji Pro 160/NPH4001.2501
Kodak Portra 160/4001.3-0.6910
Ilford Delta 1001.34-0.616
Fomapan 1001.370.260.5
Fuji Superia 800/16001.4-0.282
Lucky SDH 1001.4601
Shanghai GP3 1001.4601
Ilford FP4, HP5+1.37-0.531

Looking at the data, the formula of René and Patrick do not produce too different times up to 400 seconds, above that time Patricks curve gets steeper. But for normal times at daylight outside it does not matter which formula you use. And another note, Renés data does not fit very well my experience with HP5+, so the data for HP5+ is from me.

Posted: Monday, November 1, 2010

Week 44: Pond, Palatinate Forest ...

Pond, Palatinate Forest, rsph810, lith print

Last weekend I spent a day together with some folks I know from a German Nikon internet community. We went to palatinate forest to photograph some great rock formations. The parking was at a small pond. I went there together with a friend and we were the first ones to arrive. So I used the wait to do a photograph of the pond with my 8×10" pinhole camera. This was a 45 second exposure and it turned out very well. A nice negative to print. I lith printed it on Fomatone and the developer was already a little bit aged. It gave me the nice color separation of green and reddish which gives the image a lot of mood.

Posted: Wednesday, November 3, 2010

Week 45: Birches ...

Birches, Zero2000, kallitype

This is an older image from our trip through southern Germany in the summer. It is three birches at lake Titisee in the black forest.

At the moment I play around a bit with enlarged negatives. This image comes from a 6×6 image which I printed on Ilford RC paper and then copied it on Arista APHS II litho film which I developed in very diluted paper developer. So with this method once the paper positive is done, everything else is pretty straight forward and standardized. The litho film is exposed the same for every negative and it is developed the same time for every negative and even the kallitype is exposed the same time for every print.

Posted: Thursday, November 11, 2010

Where is week 46?

Actually, I am behind schedule a bit. I had a cold last week and guests over the weekend. So there was no time to go to the darkroom. That will happen tonight. And there are several negatives which might show up on the blog soon.

Stay tuned!

Posted: Monday, November 22, 2010

Week 46: Einfahrt freihalten ...

Einfahrt freihalten, Zero2000, lith print

We had guests last weekend and we had a trip with our guests to Baden-Baden. I had my little Zero2000 with me, loaded as ever with Fuji Neopan Acros.

We went to the palace in Baden-Baden, called Neues Schloss. In 2003 it was sold to some investors from Kuweit who are going to transfer it into a hotel. I will show just a few detail images of this place. The image above shows the entrance to the area with an old sign which asks to keep the entrace free.

Posted: Tuesday, November 23, 2010

Week 47: Festspielhaus Baden-Baden ...

Festspielhaus Baden-Baden - Entrance, Zero2000
Festspielhaus Baden-Baden

Here is another one from our trip to Baden-Baden. It is the entrance to the Festspielhaus which was a train station before but is now made into a theatre or concert hall. The side-print shows a broader view of the building. If you are interested, here are the coordinates to their english web-site: Festspielhaus Baden-Baden

Interesting enough, after all the lith and kallitype printing, I am still able to make straight prints. Well with a light sulfur toning as you can see.

Posted: Sunday, November 28, 2010

Week 48: Bus Stop ...

Bus Stop, rsph810, lith print

This is an image I made specifically for a kind of challenge in an internet forum I participate. Although it is a Nikon related forum I am allowed to show pinhole images. And there are others who also show their pinhole images there. Now the image above is not the version I show there. I did two different prints. A pretty straight print which I toned and a lith print. When I uploaded my image to the challenge I decided for the toned version. Well, about ten minutes later I regretted because I like the lith version more. So the side print is the print I show in the challenge and you can form your own opinion about it.

Posted: Sunday, December 5, 2010
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