# Thread: Reciprocity calculation for Tmax 400

1. ## Reciprocity calculation for Tmax 400

Regarding adjustment for reciprocity, is there a quick calculation you can do to determine the adjusted time for Tmax 400 (for example, I read once that for FP4+ and HP5+ you can take the metered time and raise it to the exponent of 1.48 to get the new time)?

Tim

2. ## Re: Reciprocity calculation for Tmax 400

http://www.kodak.com/global/en/profe...shortexposures

with tmax 400 it is only one and one half stops at 100 sec, so for all but very long exposures your quick estimation for the adjusted time would be :

adjusted time = metered time

3. ## Re: Reciprocity calculation for Tmax 400

Thanks Dan- The reason I'm asking though is because I've been reading alot of threads on people trying really long exposures/ dusk/night exposures, and have trying to figure it out as well. So I would be looking at times in the realm of minutes. I'd love to find a "this is how you do it" article, but it's so variable from person to person- different films with different personal EI's, different developers and techniques, even different metering techniques, etc. I'm trying to find a base to start from, then go by trial and error.

Tim

4. ## Re: Reciprocity calculation for Tmax 400

I have my own data that I used when this was my main film that compensates for exposures up to 512 seconds (8:30). If you'd like, I can post it here.

5. ## Re: Reciprocity calculation for Tmax 400

Andrew- that would be great, if it's not too much trouble....
Tim

6. ## Re: Reciprocity calculation for Tmax 400

i thought i posted this the other day but.....

i use the pinhole designer. it give you the ability to calculate reciprocity for several different films. it is set up for f22 (that is the largest aperture. it is used for pinhole stuff so it will calculate smaller stuff) so you may have to calculate on your own if you shoot larger than f22. i use it with great success.

eddie

7. ## Re: Reciprocity calculation for Tmax 400

I'll post the data when I get home today...stay tuned.

8. ## Re: Reciprocity calculation for Tmax 400

Originally Posted by eddie
i thought i posted this the other day but.....

i use the pinhole designer. it give you the ability to calculate reciprocity for several different films. it is set up for f22 (that is the largest aperture. it is used for pinhole stuff so it will calculate smaller stuff) so you may have to calculate on your own if you shoot larger than f22. i use it with great success.

eddie
Thanks Eddie- you posted this on APUG. Will look into it further.

Tim

9. ## Re: Reciprocity calculation for Tmax 400

Originally Posted by timbo10ca
Thanks Eddie- you posted this on APUG. Will look into it further.

Tim
cool. i thought i was loosing my mind.....

10. ## Re: Reciprocity calculation for Tmax 400

Here is my exposure compensation curve for TMY. My curves (not shown) also indicate that development compensation is not necessary. The contrast is the same for each curve. My test goes up to 100 seconds. After that, you can extrapolate the curve, but you should test it first.

How it works is metred time is on the bottom. Look up from indicated time 'til you hit the curve, look to right and that is your compensation. So, if your metres says 4 seconds, you should give a third stop more exposure or 5 seconds.

I used this data for years with exellent results. Hope it helps.

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