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# Thread: Comparative reciprocity failure of available sheet films

1. Originally Posted by silveror0
Tom,
About 5 yrs ago, I queried Ilford regarding the same reciprocity curves for their films. FWIW, here is an edited excerpt from their response:
We do use the same curve for ALL our films and it is essentially an average curve designed to be a reasonable guide for all our films. We are conscious that this is a weakness in our current Technical Information and we intend to provide curves for individual films when time and resources permit. However, there will be some batch to batch variability in this characteristic and so careful workers will need to run their own tests.
I asked basically the same question on the Ilford website some months ago, and the eventual answer coming back from their technical people was simply that they "stood by their curves". After reading all of this I'm getting a little annoyed at their simplistic and misleading answer to me.

2. Thanks for all your hard work on this guys, I will be using the chart for my long exposures moving forward- I'll let you know how it works out.

3. Originally Posted by gainer
If you have a pocket calculator such as the T1-30XIIS, you need only know 1 number for each film you use and one constant, 1.62, that is good for all films. The sequence of entries is as follows, where Af is the film constant, tm is the metered time, and tc is the corrected time.

tm^1.62*Af+tm = tc

Let's say that your film requires 0.5 seconds correction at tm=1 second. For that film, Af = 0.5. Now you're out shooting lumps of coal at in the deep woods (a common, though not often photographed, sight in West Virginia) and your meter tells you it will take 100 seconds. (Wish I had such a meter.). You whip out your TI30 and do:

100^1.62*.5+100 and the answer is 20424.9 seconds. But suppose you have another film with Af = 0.1. then:

100^1.62*.1+100 = 273.8
Patrick,

Is there any advantage to the TI30X compared to any other scientific calculator one might own? I see from the specifications that the TI30X has an equation recall function but as this is a short equation I assume a adhesive label on the back of the calculator would sufficient.

Tom.

Tom.

4. Originally Posted by Tom Kershaw
Patrick,

Is there any advantage to the TI30X compared to any other scientific calculator one might own? I see from the specifications that the TI30X has an equation recall function but as this is a short equation I assume a adhesive label on the back of the calculator would sufficient.

Tom.

Tom.
It just happened to be the one I found at my local drugstore that would do those functions. There is now a TI-30XIIS which I bought when I mislaid the other. More streamlined looking but otherwise about the same. Handy to have around in any case.

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