Perhaps give us some specifics regarding what film(s) you used and how long the exposures were (as indicated by the meter). Reciprocity characteristics of different films vary wildly. For example with many current films the amount of reciprocity compensation required for a 2s exposure would be minimal. So don't give up yet. You can also compensate slightly for underexposure in processing (depending on the film/developer).
At two seconds measured exposure you could still be within acceptable exposure latitude of most films - for a technically perfect negative. If you shoot HP5+ for example, it may be that you needed 2.5 seconds, and that's not going to make an enormous difference in your negatives. If you were measuring for 30 seconds and needed 70 seconds according to the chart, then you're more in trouble.
Originally Posted by mporter012
But keep in mind that just because a negative isn't technically perfect doesn't necessarily mean it will not yield a good print!
So process your film and learn from your experience, just like everybody else has had to do. If you don't use a multitude of films it's only a matter of time until you know how to compensate for reciprocity failure. We all learn some of our lessons the hard way.
If it's Fuji Acros you'll be fine; some others, not so much. In my (limited) experience, the lighting conditions that lead to super long exposures often have a wide range of scene brightness, and the exposure is essentially selecting what part of the range to display. As such, I almost always "get something," it just may not be quite the way I visualized it.
Originally Posted by mporter012
Having just come off Worldwide Pinhole Photography Day and having accidentally exposed a sheet of ISO 100 film as though it were paper at ISO 6, I've had recent experience! :blink: (In that case, reciprocity failure worked in my favor.)
Ok, so the roll that had several long exposures was t-max 100 - ranged from 2-4 seconds.
Don't worry about it. TMX 100 needs very little reciprocity compensation for those exposure times. Depending on who you talk to, you don't need to compensate at all for 2 seconds, and even at 4 seconds you're not going to lose much. If I recall correctly, in Howard Bond's tests he found for his purposes he needed only an extra half second for a metered time of 4 seconds with TMax 100.
i'm doing some long exposure photos with ektar 100 4"5", like 1h exposure....i didnt understand very well the procedure to find the reciprocity failure. anyone can help me?
Look up the datasheet for the film and they will usually provide a reciprocity chart such as this one (I'm pretty sure this is for Tri-X 400)
Now meter your scene. Lets say your meter says you need to expose your film for 5 seconds. Well take your finger and place it on the number 5 (on the "Calculated Exposure Time" axis. Now move your finger up until you hit the curve. See where your finger is in reference to the vertical axis now (Adjusted Exposure Time).
So for example:
10 second exposure on your meter = you really need to expose for ~50 seconds
20 second exposure on your meter = you really need to expose for ~2 minutes
The problem is that with Ektar 100 there is no chart on the datasheet. Usually when I shoot Ektar at long exposures, this is what I used (found somewhere on the internet). You can curve fit these points to interpolate reciprocity for an hour long exposure.
Calculated Exposure Time = Adjusted Exposure Time
1 sec = 1 sec
2 sec = 2 sec
4 sec = 4 sec
8 sec = 8 sec
16 sec = 20 sec
32 sec = 40 sec
64 sec = 115 sec
2m 18s = 4m 16 s
4m 16s = 9m 23s