Quote Originally Posted by Photo Engineer View Post
This is all very true if your paper has low or no reciprocity failure.

If there is reciprocity failure than speed and/or contrast may change if you change the time.

In my professional work, I was taught to change the aperture while keeping the exposure time constant! Of course, you pick the center point with time so that lens sharpness is optimal but you have a stop or so on each side of "perfection" to work with between 8x10 and 16x20.

PE
Thanks for the reminder. I learned this from datasheets for reversal color print papers, I think the aim was 10 seconds... Bought a 2.8 lens for the purpose... Threw it out because it wasn't sharp enough...

Really, I don't practice color processes because the chems don't keep 6 months. When it's a hobby, color doesn't give much "time" in the darkroom for the price.

But I can see how this might pertain to B&W paper if "contrast" or "speed" changes due to reciprocity failure. It makes sense to keep the time consistent as possible. If you have to pick another time for a different print size, then re-evaluate exposure and contrast for that print.

In practice, I change my aperture from around f/11 to f/22 to keep my 11x14 print times around 32 seconds. But I also keep other relevant variables constant too for example I stick to print size 11x14 and print full-frame. I'll throw in a 2 stop ND filter when making smaller prints.