A reciprocity cry for help.

[77seriesiii]

so I am new to LF and am using 4x5 Foma 100 (live in Germany so it is inexpensive). We took the camera out yesterday and it was a bumbling affair, no light meter, no watch, only a slight understanding of recip, and then the battery died in our Rollei...All in all an eventful day. with the DSLR we metered a shot for ISO 100, f22 at 15 secs and then my brain started to fry.

I am technical in nature...doing IT for a living and used to fly for the US Army but when I look at Foma's chart:

Schwarzschild effect
Exposure (seconds) 1/1000–1/2 1 10 100
Lengthening of exposure 1x 2x 8x 16x
Correction of aperture number 0 -1 -3 -4

I get that the exposure is a factor of ten but I have no idea how to fill in the blank spaces between 1, 10 and 100 seconds. I have scrounged the forum here and have read quite a bit on outside forums/websites that talk one through reciprocity so I grasp what is going on and why this is an issue but for the life of me I am not having the light bulb moment that will enable me to figure this out on my own.

So I am approaching the forum, with me hat in hand, and am begging someone out there to enlighten me, provide a spark of some sort, so I can get through this and make some reciprocity charts.

Many thanks

Erick

[Vaughn]

How about putting the numbers on a graph and using it to get the in between times?

Vaughn

[77seriesiii]

that would work? for some stupid reason I was hung up that it was a logarithmic curve line...time to make some graph paper or buy it in the morning.

Is it that easy?

Thanks

./e

[Alan Davenport]

Is it that easy?

Probably. See how the numbers fit on a graph. If it gives a reasonable-looking curve between the known values, you'll be safe enough interpolating.

[Vaughn]

Is it that easy?./e

NO... I just tried to graph it several ways with no real luck -- found out I forgotten much of my math and graphing!

I have a list of corrected times for Tri-X that Michale Kenna worked out -- if anyone knows long exposures, he does!

Skipping some of his numbers...(first is metered exposure/second in corrected exposure)

2sec/4sec.....10sec/50sec....40sec/240sec(4.5min)...80sec/630sec(10.5min)...3min/25min
6min/60min...10min/120min...20min/4hours...40min/8hours


Many of my exposures under the redwoods tend to be in the 5 to 30 minute range -- no wonder my shadows tend to drop out sometimes...LOL!

Vaughn

[cjbroadbent]

Wallace is probably right in the real world of recipricity before TMax. (I am repeating myself, sorry) Once you are over a minute, anything goes; so a sixy second exposure and a sixty minute exposure both look good - but just a little different. I do it with T film and go and have lunch while the film does it's work. Stopping down and shooting long exposures keeps you out of trouble.

[Doremus Scudder]

Erick,

Here is a graph I made in Microsoft Word for Fomapan 100 reciprocity corrections. The values are extrapolated from the (scant) data that is found in the Foma data sheet. The file was too large to upload as a simple Word document, so I've put it in a .zip file

I've changed the values to full stops as they read on the meter to make things easier to apply. Intermediate values can be estimated. These are not exact, but within a fraction of a stop (i.e., close enough).

Hope this helps

Doremus Scudder

[venchka]

I can't help your aching head or fill in any blanks except to say that apparently Foma film has terrible recirocity compared to other films. I'm heading out this weekend with my first batch of Foma 200.

Good luck!

[Wallace_Billingham]

also keep in mind with photography everything is usally measured in stops and a stop is simply double or half the light of the stop below or above it.

So in looking at your Foma numbers the difference between 10 seconds and 100 seconds is only 1 stop. In the real world (with B&W film anyway) you will not notice much if any difference if you are a stop off.

I use a lot of film from Eastern Europe and for what it is worth I always err on the side of more exposure not less.

[photographs42]

also keep in mind with photography everything is usally measured in stops and a stop is simply double or half the light of the stop below or above it.

So in looking at your Foma numbers the difference between 10 seconds and 100 seconds is only 1 stop.................. ????

I didn’t study NEW MATH but using old math, 10 seconds to 100 seconds is 3 ¼ stops.
Jerome