Reciprocity Failure

Some of my old folding cameras have depth of field charts inscribed on

the back of the camera. For those which don't, I taped on a chart to

help me estimate DOF as it is not particularly intuitive with long

lenses. While DOF is not an issue with the pinhole camera,

reciprocity failure is, and it is just as unintuitive, especially for

me as I have no previous experience with it.<br>     I just

ordered some Ilford Delta 100, so I went to the company's web site and

downloaded <a

href="http://www.ilford.com/html/us_english/pdf/100_Delta.pdf">a fact

sheet</a> containing a handy reciprocity failure exposure adjustment

chart. I clipped out the chart, printed it about 2 inches square and

taped it to the back of the Zed 2000. It might be nice to have one

that showed a bit larger range of values, but I think this one is

going to cover most situations for me.<div></div>

Nice chart Mike, and I think I'll follow your example and do the same (I've been wanting to experiment with some night photography - should be just the ticket).

 

And, I think the depth of field charts are a good idea too - somehow much quicker than squinting at all those tiny lines on the lens.

 

M.V.

What I've found (through decidedly non-scientific testing processes) is that the manufacturer's reciprocity compensation may be as exaggerated as the given EI. At least, following it to the letter has usually resulted in some degree of overexposure. It could be my sloppy technique, but I keep telling myself to do a proper test ... one day.

I think some skepticism in regard to such things is a good idea. The DOF chart on my Dolly Supersport is pretty useful, but the dial-type scale on my Kodak Monitor is not even in the ballpark. The on-line calculators seem pretty accurate, so it is easy to roll your own.<br>     I'll try to keep some notes on my next roll through the ZED 2000 regarding exposure.

Mike, you might also want to try Fuji Acros 100. It has no reciprocity correction necessary up to 2 minutes. From 2 minutes until about 15 minutes, you jsut give an extra 1/2 a stop or so. Pretty remarkable.

Thanks, Joseph. I can see I need to do further research on this issue. I have read that Tmax is also resistant to reciprocity failure.

Pat Gainer did quite a bit of reciprocity testing with several films, including Delta 100. He generated a new chart using a formula that he and someone else came up with. Much easier to work with, as Delta 100 requires no compensation all the way out to 15s or so. Even at 30s you only need 1/2 stop extra.

 

I'll send along that chart later today - it's on my other computer.

 

allan

Allan, thanks for the tip. I found <a href="http://www.apug.org/forums/showthread.php?t=11566&highlight=reciprocity+misbehavior"><b>Gainer's thread on APUG</b></a> which referred to the issue. I'm not sure my calculator will handle the suggested equation, but maybe I'll find some more info further along as I have only read the first few postings. If someone out there has a better calculator, I'd be interested in knowing how the Ilford chart holds up for Delta 100 using the Gainer equation.

Well, the equation turns out to be simpler than I thought as there was a typo in the posting showing a "," where there should have been a ".". Still that is a lot of calculating to do on the fly. Would be nice to get this graphed out for some popular films and compare to the manufacturer specs. I'm still reading the APUG thread...

<p>Mike,

 

<p>I placed the spreadsheet I generated up <a href="www.kaiyen.com/photo/reciprocity_failure.xls">on my website</a>. I included a few other films in there. However, only Delta 100, TXT, and HP5 are from Pat's numbers. I just put the others in there so I had a single sheet, and they're based on extrapolations from published charts.

 

The Delta 100 data is pretty different.

 

allan

Hey, thanks! There was a little error in the link, which is actually <a href="http://www.kaiyen.com/photo/">http://www.kaiyen.com/photo/</a>. I downloaded the file, but I don't have anything handy that will read the .xls format. Is that Microsoft's spreadsheet file format? I'll try to track down some freeware. Should be very helpful to have that all graphed out.

I see there is also a link in the APUG thread to <a href="http://home.pacbell.net/mkirwan/Reciprocity.htm">this chart</a>. Haven't tried printing it yet.

I think I've picked up the data sheet for every film I use, but much of the time I've referred to Steve Simmons' <i>Using the View Camera</i> for reciprocity figures. OK, that's sheet film, but he gives examples from a variety of makers in all three types of emulsion with a range of metered times from 2secs to 120secs. It's been very useful.

Allan, I downloaded your file, and it opens OK, though for some reason Excel reports that the file is corrupt.

<p>

Mike, that graph looks good - I was surprised that the curves are so straight.

Well, reading on, people are talking about changing development time, applying the Fibonacci series, etc. - a rather complicated business. I guess I'll just try to develop some useful rules of thumb in the 1 sec. to 100 sec. range and plow ahead. My impression is that working in resonably good light with medium to fast film, the film latitude should take care of a lot of the problem.

Weird. I don't know how all that extra stuff got into that URL. sorry. I also don't know why it's listed as corrupt, but perhaps I uploaded it using the wrong setting. I'll go fix things up, and make a pdf version of the chart. Should be up in about 10 minutes...

 

My main point is that Delta 100 reciprocity failure is _much_ better than the Ilford chart indicates. You can get away with much less compensation.

 

allan

Oh - that graph from APUG that Mike posted is an logarithmic graph. The lines will come out straigt. A linear graph (which is what the pdf I just posted on my site is) will give you the curves we are all used to.

 

allan

"<i>My main point is that Delta 100 reciprocity failure is _much_ better than the Ilford chart indicates. You can get away with much less compensation.</i>"<br><br>Thanks again for the help. I'm replacing the Ilford graph on my camera back with a table based on the Gainer data.

Here's a table with reciprocity failure correction for various films. I put the 100Delta over on the left as that is what I'll be using most. Also whacked off the HP5+ column on mine to make more room. The values are derived from the Gainer work discussed in the APUG thread mentioned above.<div></div>

That's handy - I can easily tape that to my pinbox. Thanks.

Actually, if I hadn't already order the Delta 100 I'd probably just forget all this and go with the Fuji Acros which Joseph suggested. At least this way I'll have something for comparison when I do get around to the Fuji.

Mike, I've never actually tried any Acros shots in the 5 to 10 minute range with only +1/2 stop of exposure, but I know it definitely holds up fine up to a couple minutes with hardly any correction necessary. When in doubt a little extra exposure never hurt anything I guess.

 

I'm gonna do some night shots pretty soon w/ my Yashica TLR which will probably end up posted in the classics forum, so you can keep a lookout for those, and I'll give some firsthand info about the longer 5 or 10 minute times. In the meantime, that chart you guys have generated looks really helpful. I usually prefer time corrections over aperture corrections.

I didn't do any real generating of the numbers; I just checked the math against the equation to make sure it all looked ok. Some fellow in the APUG list went to the trouble of calculating the thing. Those log log charts were not very useful for actual picture taking. My only contribution was putting the thing into a jpg which I thought would be easy for people to print out who needed something like this as a starting point. Alan's chart is pretty easy to read, and it could also be pasted on a camera back.