F-stop printing

redbandit · Mar 22, 2023

ALL of the examples i can find on here, and the internet in genaral all use a base time of 8 seconds for creating a test strip as a means of explaining the "stops" of time to people trying to figure it out...

ie

8, 11.5, 13, 16, etc...

problem is, if the base time of 8 seconds exposure is TOO MUCH FOR THE NEGATIVE... say for example my inkpress multitone paper can only take a grade 2 at 3-5 seconds before it goes to pure unadulterated shit...

how

is using a base time of 8 seconds going to be some magical cure all for my enlarging woes that may or may not exist..

Mick Fagan · Mar 23, 2023

You can start your base exposure at 2 seconds, or 2.8 seconds or at anything you desire. Then work your way through the required steps as needed.

If you can, if you have a colour head enlarger, add all three colours at once to make a neutral density filter. By adding 30 units of each filter, CYM, you will add one stop of density, 60 units of each colour filter adds two stops of density.

So if your standard negative is giving you a base exposure of 2.8 seconds, one stop of density will be 5.6 seconds, add a second stop of density filtration and you are starting at 11.2 seconds.

With the same negative, having either a very small enlargement, or a very large enlargement, you may have a base starting point from 2.8 seconds for the very small print, or 22.4 seconds for the very large print.

In short, make the base rules for your darkroom system, then incorporate as much or as little of the f stop printing method as you need/desire.

redbandit · Mar 23, 2023

Mick Fagan said:
You can start your base exposure at 2 seconds, or 2.8 seconds or at anything you desire. Then work your way through the required steps as needed.

If you can, if you have a colour head enlarger, add all three colours at once to make a neutral density filter. By adding 30 units of each filter, CYM, you will add one stop of density, 60 units of each colour filter adds two stops of density.

So if your standard negative is giving you a base exposure of 2.8 seconds, one stop of density will be 5.6 seconds, add a second stop of density filtration and you are starting at 11.2 seconds.

With the same negative, having either a very small enlargement, or a very large enlargement, you may have a base starting point from 2.8 seconds for the very small print, or 22.4 seconds for the very large print.

In short, make the base rules for your darkroom system, then incorporate as much or as little of the f stop printing method as you need/desire.

if i understand correctly....

if my starting point is 2 seconds with the enlarger set to 0-0-0 CMY...

I add 30-30-30 CMY and increase the timer to 5-6 seconds

koraks · Mar 23, 2023

redbandit said:
if i understand correctly....

if my starting point is 2 seconds with the enlarger set to 0-0-0 CMY...

I add 30-30-30 CMY and increase the timer to 5-6 seconds

No. 2 seconds would become 4. One stop change.

Mick Fagan · Mar 23, 2023

And if you add two stops of neutral density, then your starting or base exposure would/should be approximately 8 seconds.

After you have arrived at your base exposure using 60 units of each filter, you use that as your starting point for changing the contrast by adding and/or subtracting M and Y filtration.

So if your contrast requirement suggests 70Y, your filtration dials will be C60 Y130 M60.

Adding all three filters at once, is the same as adding a neutral grey filter. Once you have this neutral grey filtration in place, you then need to add your contrast filtration, hence the added 70 units of Y to make the Y filter 130 units on the dial. But you have only added 70 units of Y which is what the enlarging paper sees.

Hope this helps.

snusmumriken · Mar 23, 2023

You seem to have two problems.

1) Your base exposure time is unmanageably short. There are several possible solutions to this. As already suggested, you can dial in more of all three colours, or add a separate neutral density filter. You can stop the lens down further. Your negatives may be too thin: you might try to generate denser negatives. Failing all these, you could possibly invest in a longer focal length lens to get your enlarger head further from the baseboard for the same degree of enlargement.

2) The f-stop series from a base exposure of 8 seconds is of course just an example. If you are using an enlarger timer calibrated in seconds rather than f-stops, you can calculate an equivalent f-stop series for any other base exposure. The maths isn't terribly complicated, but if you DM me your email address I can send you an Excel spreadsheet that will do the maths for you in 1/3 stop intervals. (For some reason I can't attach a spreadsheet to a forum post.) HOWEVER, if your base exposure time is short, it may be difficult to time those intervals exactly. For that reason, and for clarity, my spreadsheet rounds the results to the nearest whole second. That can be changed, but personally, I find it more practical - and no less informative - to vary the base exposure in steps of whole seconds. For example, if I reckon my base exposure is going to be around 20 seconds, I'll do a test strip in 2 second intervals. For a base of 10 seconds, I'd do 1 second intervals. f-stop printing is a Marmite thing - you don't have to like it.

L Gebhardt · Mar 23, 2023

The base time is arbitrary. In the f stop timer I use the base time is 1 second, denoted as 0 stops. But a good starting point for me is around +3 stops, which works out to 8s. But you can also go negative and enter in -2 stops, which is 0.25s. The key is each doubling or halving gives the same visible change in exposure as the previous one.

The biggest advantage to me is thinking in stops becomes mor intuitive if you work with multiple print sizes. This allows me to work out the dodging and burning on a small print and use the same recipe for a larger print by just rediscovering the new base exposure. For example if a corner needs to be 1/2 stop darker than the base I can look that up in the chart relative to the base and figure out the amount for any size I’m printing.

Another big advantage to me is the evenly spaced test strip gradations no matter what the print size is. That was harder for me when I was using a chart, but having it built into the timer is a huge time saver.

L Gebhardt · Mar 23, 2023

The f stop timer I built first was from the plans at https://www.brodie-tyrrell.org/fstoptimer/. He had some over view videos that may give you a sense of the way it works. the timer is just doing the math for you, and you can do it yourself in many ways such as charts or just a calculator.

RalphLambrecht · Mar 23, 2023

redbandit said:
ALL of the examples i can find on here, and the internet in genaral all use a base time of 8 seconds for creating a test strip as a means of explaining the "stops" of time to people trying to figure it out...

ie

8, 11.5, 13, 16, etc...

problem is, if the base time of 8 seconds exposure is TOO MUCH FOR THE NEGATIVE... say for example my inkpress multitone paper can only take a grade 2 at 3-5 seconds before it goes to pure unadulterated shit...

how

is using a base time of 8 seconds going to be some magical cure all for my enlarging woes that may or may not exist..

No, my base time is 16s for example. The base time is usually a multiple of two that allows for comfortable dodging and burning. The process is identical regardless of base time.

snusmumriken · Mar 23, 2023

L Gebhardt said:
The biggest advantage to me is thinking in stops becomes mor intuitive if you work with multiple print sizes. This allows me to work out the dodging and burning on a small print and use the same recipe for a larger print by just rediscovering the new base exposure.

I do understand and accept that. My reply above reflects the fact that I only do one print size.

MattKing · Mar 23, 2023

snusmumriken said:
Failing all these, you could possibly invest in a longer focal length lens to get your enlarger head further from the baseboard for the same degree of enlargement.

This is contentious, because theoretically it shouldn't result in a change of light intensity at the easel - if the magnification doesn't change, the light intensity doesn't change.
It will, however, often give you some smaller apertures to work with though - at the cost of having to deal with diffraction.

snusmumriken · Mar 23, 2023

MattKing said:
This is contentious, because theoretically it shouldn't result in a change of light intensity at the easel - if the magnification doesn't change, the light intensity doesn't change.
It will, however, often give you some smaller apertures to work with though - at the cost of having to deal with diffraction.

Really? Surely light intensity falls off with the square of the distance from the source?

grain elevator · Mar 23, 2023

MattKing said:
This is contentious, because theoretically it shouldn't result in a change of light intensity at the easel - if the magnification doesn't change, the light intensity doesn't change.
It will, however, often give you some smaller apertures to work with though - at the cost of having to deal with diffraction.

Your two statements seem contradictory to me. Anyhow don't forget bellows extension.

To the OP, here's a, to me, intuitive and simplified (in some ways, also limited in others) way to do f-stops with a simple timer.
I can do the maths in my head and I dont need a digital timer this way. It's less precise and doesn't always scale to different print sizes very easily though. I must have read about it somewhere on these here interwebs.
Set the timer to, for instance, 1 sec. Now don't touch the setting any more. Do a test strip as follows: 1 push of the button for whole strip, cover first segment. Rest of strip receives another push, you've just added a whole stop. Cover another segment. For more whole stops, you'll add 2 (for a total of 4), 4 (for a total of 8), 8 (for a total of 16)... pushes. I'd lengthen the base time if I need more than 8 pushes of the button.
For close-enough-to-half stops, you just halve the steps described above. That's not accurate half stops, but it is reproduceable. After 2 pushes, you'll add 1 (total of 3 pushes, ~1.5 stops more than one push of button), another 1 (total 2 stops over first segment), another 2 and so on.
I do the actual print with the so established number of button pushes. Adding them up to one lengthy time doesn't work with my timer which is very imprecise with short times, and warm-up of the lamp might spoil such endeavours anyway.
Seems tedious but is an advantage for dodging, I already have the exposure split into shorter segments.

faberryman · Mar 23, 2023

t

grain elevator said:
Your two statements seem contradictory to me. Anyhow don't forget bellows extension.

To the OP, here's a, to me, intuitive and simplified (in some ways, also limited in others) way to do f-stops with a simple timer.
I can do the maths in my head and I dont need a digital timer this way. It's less precise and doesn't always scale to different print sizes very easily though. I must have read about it somewhere on these here interwebs.
Set the timer to, for instance, 1 sec. Now don't touch the setting any more. Do a test strip as follows: 1 push of the button for whole strip, cover first segment. Next segment receives another push, you've just added a whole stop. For more whole stops, you'll add 2 (for a total of 4), 4 (for a total of 8), 8 (for a total of 16)... pushes. I'd lengthen the base time if I need more than 8 pushes of the button.
For close-enough-to-half stops, you just halve the steps described above. That's not accurate half stops, but it is reproduceable. After 2 pushes, you'll add 1 (total of 3 pushes, ~1.5 stops more than one push of button), another 1 (total 2 stops over first segment), another 2 and so on.
I do the actual print with the so established number of button pushes. Adding them up to one lengthy time doesn't work with my timer which is very imprecise with short times, and warm-up of the lamp might spoil such endeavours anyway.
Seems tedious but is an advantage for dodging, I already have the exposure split into shorter segments.

Seems unnecessarily complicated to me.

MattKing · Mar 23, 2023

snusmumriken said:
Really? Surely light intensity falls off with the square of the distance from the source?

No, it is a function of magnification in a projection system. In a non-projection system, like a light bulb on its own, what you say is correct.

grain elevator said:
Your two statements seem contradictory to me.

Not really, longer lenses often add f/22 and f/32 when the shorter lenses can be limited to f/16. It is merely a mechanical difference between the aperture mechanisms installed - not an optical one.

L Gebhardt · Mar 23, 2023

snusmumriken said:
I do understand and accept that. My reply above reflects the fact that I only do one print size.

I would probably not bother with f stop printing by chart if my negatives were consistent and the print size was always the same. I print multiple sizes from 35mm to 5x7 film. With my custom built timer/LED head it's essentially free (as in not calculations) and makes my printing much easier. In other words I use it because it saves me time and money.

snusmumriken · Mar 23, 2023

MattKing said:
No, it is a function of magnification in a projection system. In a non-projection system, like a light bulb on its own, what you say is correct.

Always happy to learn, so I will read into this. For one thing, I need to understand what is the difference between a projection system and a non-projection system. The fact that the light is collimated?

Pieter12 · Mar 23, 2023

MattKing said:
No, it is a function of magnification in a projection system.

So, a longer lens to give the same magnification but at a greater distance is the same intensity of light? Does not seem intuitive, I'll have to check that out with a meter. If I recall correctly, I have used a shorter lens to get a greater magnification (80mm to make an 11x14 vs 135mm to make an 8x10) and used the same exposure time and aperture for both.

snusmumriken · Mar 23, 2023

Pieter12 said:
So, a longer lens to give the same magnification but at a greater distance is the same intensity of light? Does not seem intuitive, I'll have to check that out with a meter. If I recall correctly, I have used a shorter lens to get a greater magnification (80mm to make an 11x14 vs 135mm to make an 8x10) and used the same exposure time and aperture for both.

I think @MattKing is dead right, though. The explanation for the inverse square law that we were given at school was that at, say, twice the distance, the same number of photons (per unit time) were spread over four times the area. In the enlarger case, the light coming through the negative is unchanged (just higher) and the print size is the same, so the same photons are spread over exactly the same area. (I guess the number lost en passage is trivial.) Thanks, Matt, it’s a pleasure to be made to think!

koraks · Mar 23, 2023

snusmumriken said:
so the same photons are spread over exactly the same area

You got it. That's exactly what's happening.

MattKing · Mar 23, 2023

snusmumriken said:
Thanks, Matt, it’s a pleasure to be made to think!

We aim to please .
I expect that there may be some additional losses due to the fact that there is a greater chance of flare outside of that portion of the lens' imaging circle that is in the frame, but that is probably trivial in amount.

aparat · Mar 23, 2023

Some of the most sensible and thorough applications of f-stop printing methodology (including theory) are by Darkroom Automation. You will find a number of informative documents on their website describing all kinds of interesting aspects of f-stop printing, including conversion charts, printable aids, testing procedures, practical tips, etc. I highly recommend it.

Xylo · Mar 23, 2023

It's funny because I once read that light was like peanut butter on a slice of bread. A thick spread on one slice of bread will barely cover four slices, which is the equivalent of a 2x enlargement.

As for the "too much light" problem, you can either put a less powerful bulb in the enlarger or fit it with a dimmer. The later solution was very popular in the darkrooms of big newspapers.

Now, for the stop printing, here's the full story.
Photographic papers don't function in a linear fashion like we think, but they work on a logarithmic scale. That's why on our cameras we double the shutter speed to reduce exposure by 1 stop. To explain the how and why it works like that, I'd have to dig back into my books.

To do the test strip in a log manner:
1- Give the entire sheet a 1 second exposure.
2- Cover the first square of the sheet with some opaque cardboard.
3- Expose the rest of the sheet for 1 second.
4- Cover a bit more of the paper and expose for double the last exposure, 2 seconds in this case.
5- Move cardboard and now expose for 4 seconds.
6- Continue moving the card and doubling the exposures until the entire strip is covered.

You now have a test strip with exposures of 1-2-4-8-16-32-64 seconds.
You like an exposure that is between two cells? just expose for in the middle. It all becomes super easy and all you need to be able to do is multiply by 2.

mshchem · Mar 23, 2023

snusmumriken said:
Always happy to learn, so I will read into this. For one thing, I need to understand what is the difference between a projection system and a non-projection system. The fact that the light is So, d

mshchem · Mar 23, 2023

I am having issues

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