TriX vs HP5+

[ChristopherCoy]

Read up on f/stop printing; it does not require an f/stop timer and it will make your life so much easier.

So if I understand this correctly... Instead of 2-4-6-8-10 second intervals, I would do 2.8-4-5.6-8-11-16 second exposures?

And this refers only to time, correct? My lens setting on the enlarger would stay on f11 or f16 the entire time?

I think I get the gist, but with linear intervals, I set my timer on the time, then slide a sheet from one side of the print to the other. How do you do that with fstop printing? If I added 5.6 seconds on top of the 8 second, that would give me 13.6 seconds. I would have to cover that 8 second portion right?

[ME Super]

ChristopherCoy,
You're very close. The f/stop number is the focal length of the lens divided by the diameter of the aperture. The amount of light that passes through an aperture per unit time is proportional to the square of the radius. Thus stepping from 2.8 to 4 halves the amount of light (because 2.8 * (square root of 2) = 4), stepping from 4 to 5.6 halves the light again.

If you want to go by full stops, you should do 2.8-5.6-11-22 second exposures. If you want to go by half stops, then the 2.8-4-5.6-8-11-16 seconds will give you half stops instead.

[MattKing]

Here is a table I use to guide me as I progressively cover more of the print. Each strip ends up being exposed for a total time equal to the interval indicated, plus the sum of the times for all previous (now covered) strips.

It gives me individual test strips that are exposed for the following series of total times: 4, 6, 8, 11, 16, 22, 32, 45 and 64 seconds.

It has the advantage of requiring that the enlarger go on and off just once (at the beginning and end).

[john_s]

You can't compare two films until you have them developed to equal or at least similar contrast levels. This can take some trial and error.

[PhotoJim]

HP5 is a great film. I like it better than Tri-X at 400. Tri-X is more pushable, though.

I get better staining with PMK with HP5 also. I get more dramatic staining on Tri-X, but much worse general stain which is basically like fog. HP5 stains much more cleanly.

Still, if HP5 disappeared I could more than live with Tri-X - and vice versa.

[BradS]

If it's too contrasty, you need to develop it less! Simple as that.
.....

This is, apparently, not the answer the OP is looking for.

[polyglot]

So if I understand this correctly... Instead of 2-4-6-8-10 second intervals, I would do 2.8-4-5.6-8-11-16 second exposures?

And this refers only to time, correct? My lens setting on the enlarger would stay on f11 or f16 the entire time?

Exactly right. "f/stop printing" is a really bad misnomer, it should be called "logarithmic printing" and it has absolutely nothing (sorry ME Super) to do with lens apertures at all*. Paper is a negative just like film, though the curve is funkier and S-shaped. To get a specific change in tone, you want to multiply the exposure by some factor, not add on some constant. Leave your enlarger lens at its optimum setting (generally 2 stops from open) unless that causes problems with stupidly long (>60s) or short (<4s) print exposures and control your density with printing time.

So the 2.8-4-5.6-8-11-16 second sequence gives you a factor of 1.4=sqrt(2), which is half-stop spacing when used as times. When you're printing at lower grades you need bigger steps and when printing at higher grades, you need smaller steps to achieve the same shift in tone; the reason is the changed slope of the paper's response.

I think I get the gist, but with linear intervals, I set my timer on the time, then slide a sheet from one side of the print to the other. How do you do that with fstop printing? If I added 5.6 seconds on top of the 8 second, that would give me 13.6 seconds. I would have to cover that 8 second portion right?

You want the total exposure for each bit of paper to be the number from the sequence, so (assuming you're doing the covering-up thing) each exposure is the difference between respective steps: 2.8, 4-2.8=1.2, 5.6-4=1.6, 8-5.6=2.4, 11-8=3, 16-11=5, 23-16=7, 32-23=9.


* the numerical sequence looks familiar only because it is a geometric sequence with factor sqrt(2). The numbers for full stops on aperture match the numbers for half stops on time because aperture area and therefore exposure varies quadratically with respect to f-number.

[Lionel1972]

There's something I don't get with this Fstop printing theory. I thought that to get 1 stop more exposure you should double the amount of light per time units that expose your emultion. I thought you can do that either by open up the lens by 1 stop (F numbers does go by those non-linear steps) or by just doubling the exposure time (no need to go non-linear on time). Is paper emultion so different than negative emultion to the point that this rule don't apply anymore? I didn't know it needed a logithimic scale like perceived sound volume, it looks quite extreem to me.

[Steve Smith]

I thought you can do that either by open up the lens by 1 stop (F numbers does go by those non-linear steps) or by just doubling the exposure time (no need to go non-linear on time).

Exactly correct. The process known as f stop printing just borrows the logarithmic scale from the aperture and applies it to the time.

1, 2, 4, 8, 16 seconds is the same doubling each time as 2.8, 5.6, 11, 22 seconds. The advantage is in using it for test strips. If you use the traditional method of 10 second steps then at the start going from 10 to 20 is quite a difference. At the other end of the strip e.g. 50 to 60 is not much of a change.

Using the 'f stop' sequence gives an equal percentage change per step. You don't have to use the actual numbers used in f stops. 10, 20, 40, 80, etc. is equally valid.


Steve.

[Lionel1972]

Thanks for the clarification Steve. Once I wanted to see my test strips with one full stop steps I calculated this series of exposure times for 5 sliding positions of the sliding darkslide cover: 40, 20, 10, 5 and 5 seconds. That gives me stripes exposed as this: 5, 10, 20, 40 and 80 seconds which covers the entire range of most of the negative I should encounter. Then I do a second test strip to fine tune my selected time. Maybe 2.8, 5.6, 11, 22 get closer to the actual curve of the paper, but in this case shouldn't we also apply these time steps with our cameras?