Enlarging from 5x7 to 8x10 to 11x14

[robc]

OK I thought about it.

formula is:

for calculating time for bigger print size from original

T2 = T1 * 2^Fdiff

where:
T1 is original print time.
T2 is new print time
Fdiff is fstop difference in stops.

for calculating time for smaller print size from original
Fdiff should be made negative. i.e.

T2 = T1 * 2^(Fdiff * -1)

that should do it if you use your fstop meter to meter fstop difference at different enlargements/magnifications.

[Jfnphotography]

I made a test print.
I used Kodak Projection Print scale, put it on the paper set the enlarger lens to f11 then exposed for 1 minute. My paper was black, so I cut the time down until I was happy with the results. My end time was f11 at 3 sec. for a nice print. Do I have something set wrong on the enlarge? My exposure time is real short. Should I be at a higher f-stop to use the projection print scale?
Thanks, Jacob

[robc]

if you are printing to only 5x7 from a 4x5 neg size then enlargement factor is very small, so head will be close to paper and very bright. You may need to use some neutral density, at that scale, to increase the print time.

[Brian Ellis]

robc's mention of an exposure meter reminded me that Ilford makes (or used to make) a very inexpensive ($30 or so) enlarging exposure meter. I had one and it worked very well but I found the wheel in the Kodak book quicker to use so the Ilford meter sat in a drawer. However, I had a table of magnification factors for my Beseler MXT enlarger at any given height that was created by Daryll Nicholas and that table really made the Kodak wheel easy to use. Without such a table (or more math ability than I possess) the Ilford meter probably would have been the easier of the two.

[robc]

using the formula I gave, you can calculate a factor to be used for magnification from any size to any size. This only needs to be done once. But there is a problem with all of these formula and look up tables. Say you have worked out a time factor for magnification from 5x7 to 10x8. The factor will only be accurate if your neg crop area is exactly the same as used to calculate the factor and when you upsize to 10x8 you also use the exact same crop area as when calculating the factor. In practice from one neg to another, this won't be the case, so the factor won't be 100% accurate.

Only if you meter(or measure height difference) for each usage will the formulas be accurate. That also includes focus being set at both heights before metering or measuring height difference. For that reason, its often easier to just take an approximation and make a test strip. Therefore the original formula I gave is accurate enough as a starting point for a test strip. But since the question was asked an answer was given although it may not be the most practical option. It will however be accurate if done on a neg by neg basis.

[Jfnphotography]

Made an 5x7 then a 8x10 last night, I found that from F22 if I went up to F16 and added 2 sec the print came out just like the 5x7, I didn’t get a chance to try the spot meter. I will have to try that next time.
Thanks for everyone help.
Jacob

[Andrew Wittner]

Another way to do it which, unlike all these other methods, is super fast and easy to do, and is 100% accurate, is to use the enLARGE enlarging app available for iPhone/iPad. Costs about the same as a single sheet of 20x24” paper. Lets you make eg. a perfectly matching 20x24” enlargement from a tiny (eg. postcard) pilot enlargement!

[Rick A]

Purchase an Ilford EM-10 exposure monitor and learn to use it. Keep notes when printing and soon you will find you don't need it very often, but still a valuable tool.

[Drew Wiley]

A basic enlarging meter with an easel sensor makes life easy. I have three of those - good ones, each waaaay more expensive than that EM-10, but don't even bother when printing black and white. A simple test strip does what I need. (I had/have other uses for those meters, so didn't waste any money; and one of them was bought used anyway, at a comparative bargain).