From contact sheet to enlargement

So, a two-part question based on some experiments this weekend. I've only been back to printing for a month and honestly can't remember how I used to print based off contact sheets before.

1) Let's say I have the exact same paper for contact sheets and 5x7s. If I can see that a frame looks perfectly exposed on the contact sheet, is there some formula to figure out the same exposure for 5x7 without having to do test strips?

2) OK, so I DON'T actually use the same paper for contacts. It should be possible to get an exposure that looks exactly the same as my contacts on different paper though, right? Most of my negatives on the contact sheets--of course unfiltered--had a pleasing medium contrast. I had difficulty replicating this in 5x7...looked muddy. Needed to add filters. Some of the contrastier enlargements look fine, but when I go back to the contact sheet I realize I still prefer the lower contrast of the contacts. I'm going to try to reprint a few this weekend, but since it was bugging me...is there any reason that the same level of contrast/exposure cannot be easily replicated from contacts to enlargements?? Or is my eye fooling me, and what looks like medium contrast is actually much lower, and simply works at 35mm size but not at 5x7 or larger?

The concept of the "Proper Proof" is the answer to your question. (ala Fred Picker).

If you do a "proper Proof"

Click to expand...

Set the enlarger head to the height it would be for your target full-frame print size, in your case 5x7. Mark that position so you can easily go back there.
Put an empty 35 carrier in the enlarger
Focus using the edge of the carrier
Put in your desired proof filtration, some folks like soft, some like "normal"
Set the lens to the f/stop you'd use for enlarging
Expose for your minimum time to maximum black time

Now you can make a useful proof sheet.
For example, if if the negative looks good on the contact, you can put it in the carrier and make a 5x7 enlargement that looks just like it, without changing anything, except where the negative is.
One note, The proofer glass and the sleeve (if you print in the sleeve) will add a little density, so for the enlargement you may need to back off on the time slightly. After some testing you'll always know what that factor is.

If you want to use a different paper, test and figure out what the required exposure difference is, then use that correction factor.

Doing proofs with the enlarger at some random height, without filtration, at some guessed f/stop and time is a waste of time, paper and money.

Test strips, test strips, test strips.

You can't expect to guess time of an enlargement and get a perfect print by looking at a contact sheet.

You can't expect to guess time of an enlargement and get a perfect print by looking at a contact sheet.

Click to expand...

Not perfect perhaps, but you should be very close, no guessing required.

Try to stick to the same paper for the same set of contacts generally. I.e. if you're printing frames on a given roll, try to keep it to one paper unless you have a very good reason not to. Once you test one frame, one should be able to generally use the same time/grade on the others, adjusting by feel for variance in exposure and contrast. Obviously an initial test sheet and a few others will have to be made for problem frames.

The distance of the bulb, the aperture, and the enlargement factor will determine the exposure time. It is possible to compute a new exposure time based on these factors and it will look like the formula for bellows factor, but... it's usually not worth it, in my opinion. Bear in mind that your test strips need only cover a very small portion of the enlarged frame. So waste a little bit of paper and take it easy You'd likely waste more time making measurements and running numbers than you would simply doing a quick test strip or two.

I've gotten to know my typical exposures times well enough to do decent guesstimates without test strips, but when enlarging I might want to dodge and burn or use a different enlarging lens or different developer concentration etc... not to mention that I do all my contacts on RC glossy (quick! flat!) but almost never do enlargements on that, so... although I can get in the ballpark, usually it's just not worth it to try to skip steps.

2) Not sure what caused your difference in tonality, but... I don't use small or med. format contacts to judge tonality. Did you do your contacts with the same bulb? Same paper, developer etc.? Same aperture? Anyway, at the end of the day you want to optimize your parameters specifically for the enlargement, the contact is just for quick comparisons and cataloguing.

Test Strips. But if you want to try cheating, my best guess would be . . .

24mm<1"

<1
<1.4
<2
<2.8
<4
<5.6

5"<5.6"

Multiply your exposure duration by a factor of five. Maybe.

OK, well, I guess the gist is there are no shortcuts and my contacts possibly have nothing to do with my final print. But I'll try bdial's method next time I make contacts .