Reciprocity Timer App

Well... when you have a scientist tapping his foot on the floor waiting for his latest 'series' of images of stained polyacrylamide gels... or the batch of petri-dish cultures to be made... (as 'singletons' and 'groups with the control') and your official 'quitting-time' time was 37 minutes ago (when they should have been brought in three hours ago when they were first removed from the incubator and 'inspected')

Dammit!!! THAT must be why most of the hair disappeared from my head... (and my beard became somewhat 'patchy')... while both the 'finger-print' and the 'nail' on my right forefinger had all but 'disappeared' due to my having left the Palm Pilot at home with 'dead' batteries. :cool:

I have just installed new batteries in my old out-of-date... but experienced Palm Pilot and about to boot up the old Mac to 're-load' the memory in the 'one-hand hold-able' AAA battery powered abacus.... and I can add my latest 'screw-up' into its memory.

Ken
 
If you follow the method I posted above, which I've used for nearly 40 years of LF photography, it's all very simple and no technology is required. All you need is some sort of tape measure; I've always used those soft, flexible tape measures used by folks who sew. Measure from the film plane to the nodal point of the lens. Since I don't use retro-focus type lenses, that's from the film plane to the center of the lens. Simple. Quick. Accurate enough.
 
There have been many ways of doing this promulgated over the years Alan, I was merely pointing out that if you knew the basics you would never be stuck. :)
 
Or work out the exposure for a moon rise over Hernandez by recalling the luminence of the moon's surface in c/ft2....
 
KenS said:
Ian,

My 'reading' of the bellows extension... lens FL = 150mm. Distance from film plane to the rear nodal point of your lens = 270 mm. Therefore your extension is 'only' 120mm.... not 270mm. At least.... that is 'my reading' of the information you have provided.... The 120mm extension means that you are not even at the 1:1 magnification ratio on your film.

If my 'reasoning' is correct you are obviously well over the 'correct' exposure time on which you must/maybe have to 'add additional time' to allow for 'failure of the law of reciprocity'.

But again... I now have a somewhat 'weary/fuddled' brain having spent too many hours trying to learn to scan my negatives 'properly'... and I may not be 'reading' your information correctly.

Ken
Click to expand...

The App uses total extension as the basis of the calculation. If you have a 150mm lens and total bellows extension of 300mm, you get a 2 stop compensation. If you were to input that as 150mm of extension, the App would apply zero compensation.
There is some info in the App itself regarding the methods by which compensation is calculated, and it gives an explanation of the two entries for Fomapan 100, one being described as 'Classic'. I'm not sure that it takes you much beyond trying both and deciding which gives you the most useful result.
Alex


Sent from my iPhone using Tapatalk
 
Stephen Batey said:
Or work out the exposure for a moon rise over Hernandez by recalling the luminence of the moon's surface in c/ft2....
Click to expand...

Haha! Sorry, I never could wrap my head around all that c/ft2 stuff. ;) Good thing I never tried to use an SEI photometer. :)
 
Stephen...

I still have an SEI meter (from many many moons ago .. ) played around with it for a while... was aware of their accuracy but could NOT REALLY GET INTO IT for every day use... so... I took the battery out and put it away. It now rests 'peacefully'(with minimal experience) in its leather 'holster', in a drawer.

Ken
 
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