Reciprocity Timer 1.0

[Allen in Montreal]

You could probably make a killing on a basic darkroom timer,

Just a basic timer, autorun is a must, 10 stages would be best, programmable and be able to name the steps and save.

Simple but no one has made the ideal simple timer yet.




http://www.largeformatphotography.in...ad.php?t=86345


http://www.largeformatphotography.in...t=86345&page=4

[Roger Thoms]

I just started using the reciprocity timer and I works well, at least it did for the three exposures I used it on. It would be nice if the beeps were a little louder, I could barely hear them and yes the volume was up all the way. Also didn't see Tri-X 320 on there.

Roger

[thrice]

Any plans for an android version?

[Underaglassbell]

Hi All. I have just had Apple accept my first iPhone App into the store! It is a simple little app I originally made for my own use that I thought others might also get some value from.

It allows you to select from a list of available films and a metered exposure duration - from there it will calculate an actual exposure including reciprocity. The maths is based on as many formaulas I could find for some common films. You can currently select from Ilford B+W, Velvia (color filtered and unfiltered), Provia, Tri-X and Ektar. I will be more than happy to add new films if anyone has the mathematics and can send it to me.

The app also includes a slider to let you add or remove stops of initial exposure (for example if you add an ND) and gives you a count-down timer to time-out your shutter.

It's pretty simple - but I have found it really useful.These shots were made using it.

I have it listed at $1.99 - but will obviously review that depending on feedback and workload.

You can get it here.

Hi, I purchased this app recently and used it for the first time today, in conjunction with the 'ND timer' app.

I was shooting with a roll of efke IR820 Aura (100) film, and I used your 'efke' setting; I take it that is right - meaning the Reciprocity is the same for most efke films, or have I got this wrong?


It seems a great app though. I would really love it if you could include Portra 160/400 in the next update, as I do tend to shoot with them quite frequently, and it would be nice to have them in the app for reference.


Regards,
DaN

[Geraldine Powell]

I don't understand how to use the reciprocity timer. I tried it for the first time yesterday and got a weird result that had to be wrong. Here is what I input:

HP5+ film.
the meter reading was f32 at 20sec, so I put in 20"
Focal length 120mm
bellows extension 300mm (That gave bellows: 2 and 2/3 srops)
no filters, so that was 0

That gave just over 25 MINUTES as the exposure time. What am I doing wrong?

Also, how do I prevent the iphone5 turning itself off during the countdown?

I read through all 12 pages of this thread but no-one seems to have had this problem.
Geraldine

[Ken Lee]

I entered the same parameters and got the same result, which may be perfectly correct.

An increase of 2 2/3 stops for bellows extension equates to a factor of 6.5x, so 20 seconds becomes 130 seconds.

If we look at the reciprocity table given by Ilford for HP5+, see see that 130 seconds is "off the chart", but perhaps the author of the software has determined the formula according to an exponential function.

By 30 seconds, the curve is basically linear, but rather steep: to go from 30 to 35 seconds of measured time (X axis) requires an additional 50 seconds of exposure (Y axis). At that rate (10 seconds compensation for each additional second), compensation might add up pretty quickly.

Am I overlooking something ? Perhaps some brighter lighting would help get things down to a more reasonable exposure.

[Geraldine Powell]

Thank you for the reply. I opened up 2 and 2/3 stops. Was that correct? Anyway, what I did to the lens aperture would not affect the app on the iphone. 25 minutes just seems too long compared to an other image I took under the same lighting. I am off now to process the negatives and I will report what I find.
Geraldine

[Ken Lee]

Opening up by 2 2/3 stops allows you to shorten the exposure by a factor of 6.5 X, so the 20 second indicated exposure goes down to 3 seconds.

Next, we consider reciprocity failure: the app tells us that a 3-second exposure with HP5+, should actually be given 6 seconds. That matches the Ilford chart too.

So if you compensated for bellows extension but not for reciprocity, you will have under-exposed by 1 stop.

Depending on the subject, that may or may not matter. If the subject is very contrasty, then some detail in the shadows will have been lost. If the subject is of low contrast and not particularly dark, then you can still get an optimal print.

[Geraldine Powell]

I don't understand why I need to shorten the exposure time if I have already opened up 2 and 2/3 stops. I thought you either open up the stops or you lengthen the exposure time, not both.
Anyway, I had the shutter open for 25 minutes at the settings I described. I expected total over exposure but actually the image looks good in the negative. I wil scan it tomorrow and then I will really be sure. Maybe the app was right on. The first negative I shot where I forgot reciprocity failure was grossly underexposed.
I think it would be very helpful if we or someone could make a tutorial of how to use this app so it is really clear to inexperienced people like myself.

[Ken Lee]

I don't understand why I need to shorten the exposure time if I have already opened up 2 and 2/3 stops. I thought you either open up the stops or you lengthen the exposure time, not both.
Anyway, I had the shutter open for 25 minutes at the settings I described. I expected total over exposure but actually the image looks good in the negative. I wil scan it tomorrow and then I will really be sure. Maybe the app was right on. The first negative I shot where I forgot reciprocity failure was grossly underexposed.
I think it would be very helpful if we or someone could make a tutorial of how to use this app so it is really clear to inexperienced people like myself.

You don't need to shorten exposure time. You needed to lengthen it because of bellows draw, and then some more for reciprocity. If you shot at infinity, there would be no need for bellows compensation. However, you shot at greater magnification than 1:1, so 2 2/3 stops more exposure were needed as compensation.

Next comes reciprocity failure. Some films handle long exposures better than others. This is a separate consideration from bellows extension, and needs to be calculated after bellows compensation - which is what the app does.

This page gives the formula for bellows compensation (see the section entitled "How Many More f/stops are Required ?"). That the app is a lot more convenient.

Reciprocity varies with brands of film, and with length of exposure. Fuji Acros requires very little compensation, even for rather long exposures. More traditional films like Tri-X or HP5+ lie at the other end of the spectrum, and require a lot of compensation. So that app is actually pretty straightforward: you enter the parameters, and it tells you the results, quite reliably, and for a great range of variables.

I recently shot some close-up images near a window in an otherwise dark room. The metered exposures were several seconds, but with bellows draw and reciprocity, the required exposures were 40 seconds. I followed the app's recommendations and things worked out satisfactorily. Here's one of those photos.

Antique Rulers, 2012
Sinar P, 210mm Macro Sironar
4x5 TMY, Diafine