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  #1  
Old 23rd May 2022, 10:15 PM
Nat Polton Nat Polton is offline
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Default Enlarger Lens Aperture

I always close down the enlarger aperture one or two stops when printing.

I was wondering if if an enlarging lens can be stopped down too much?

i.e. can it be detrimental to the image if the lens is stopped right down ?

Cheers.
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Old 23rd May 2022, 11:33 PM
Mike O'Pray Mike O'Pray is offline
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Nat, isn't there a diffraction problem that arises above f11 that adversely affects the print?

What this diffraction(assuming I have used the correct word) means I have no idea nor how much difference it makes to a print. I think the bigger the print the more it affects its quality but of course the bigger the print the less likely you are to want to use f16 as the print exposure times become very long

Mike
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Old 24th May 2022, 04:24 AM
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Uwe Pilz Uwe Pilz is offline
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I use the 50 mm and 80 mm Rodagons in my enlarger. These are said of being good lenses. I checked how much the need stopped down.
You may work stopped down one and a half stop, and I do so for larger prints and slow papers. But the highest sharpness in the corners I get only if I stop down two stops.
I checked diffraction effects not during printing, but during shooting. The optical laws are the same. Degradation starts at f/11 (50mm) or f/16 (80 mm), but this is just remarkable. One or two stops more closed it can be seen easily.
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  #4  
Old 24th May 2022, 08:35 AM
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Reginald S Reginald S is offline
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Quote:
Originally Posted by Nat Polton View Post
I always close down the enlarger aperture one or two stops when printing.
Looking at the specs of enlarging lenses this seems to be the comfort zone of these type of lenses, but let's regard the physical optic a bit.

Enlarging lenses are designed to project a flat image with even Illumination and sharpness over a wide field (size of the print) without being too dark in projection.

It's a physical characteristic even of simple meniscus lenses to project nearly perfect in the middle of the lens (stopped down) but loosing quality in sharpness wide open, which will need some stopping down.

I do believe in diffraction, but diffraction depends on the diameter of the diaphragm, which appears, in my memory, at diameters less than 2mm.

Apertures/aperture values are not simple numbers - they are "formulars" depending on the diameter of the entrance pupil and the focal lenght of each lens, themselves expressed in the writing onto the front of old lenses.
Let's say the writing " f:4,5 , f= 250mm" on my old Tessar lying on my table means "aperture 4,5 devided through the focal length 250mm" will show us the entrance pupil .

Like usual with formulars we can use them viceversa which will help to find the wide opening value of let's say a meniscus lens of 50mm diameter and a focus point / focal length of 300mm..

Once given the wide opening value as a number one could do some logarhytmics for finding the necessary diameters for f/ 8 or f/5,6 and so on..

Anyway, my Tessar shows an opening of 5mm at f/32 which will not bring any sweat to my neck.
Checking the stopped down diameter of a 50mm lens otherwise could be a good idea concerning diffraction.

Sorry for boring you, but I have to state that Iam totally fascinated from the math and phsics behind my lenses :-)

So, this all theory will say something but not all about the performance of your lens at different apertures.

That's the reason to me for testing my enlarging lenses with test negatives and at typical print size, with different apertures.
This will give great impressions of sharpness from center to the edges but it will show the performance of the enlarger, too (given or not given right angle of the axis enlarging base and enlarging head).

Don't be surprised with the results of your setup :-)
And it could happen that you will use only one specific aperture in the future, if you are after quality of your prints.

Last edited by Reginald S; 24th May 2022 at 08:41 AM.
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Old 24th May 2022, 10:11 AM
Nat Polton Nat Polton is offline
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DIFFRACTION That's the answer!

It's coming back to my cloudy memory.
I read about diffraction in this situation many years ago. Unfortunately it went in one ear and out the other at the time.

You have all brought it back to me.

I shall print out the very detailed contribution by Reginald.
His explanation is a lot simpler to understand than the textbook that I read years ago. Thank you Reginald. Also Mike and Uwe.

Cheers All.
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Old 24th May 2022, 10:50 AM
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Reginald S Reginald S is offline
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Quote:
Originally Posted by Nat Polton View Post
DIFFRACTION That's the answer!
I'm thinking of diffraction being a part of the answer - don't forget the lens design itself.

The engineers of these days had to find compromises.
Concerning illumination, distortion freedom or sharpness while naturally working widely open, reaching best quality doesn't work over the full aperture spectrum.

On the other hand stopping down 1 or 2 stops could mean that stopping down 3 stops would fit your lens better.
Who knows before testing a bit.

These days I'm fiddling around with a selfmade LED design because I am substituting the old bulbs of my enlarger.
It may happen that I have to bring in either another dimmer or neutral dense filter glasses while printing smaller sizes; I never would stop down and leaving the optimum zone of my lenses to minimize the light power which I need for larger prints.
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Old 24th May 2022, 11:35 AM
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Quote:
Originally Posted by Reginald S View Post
I never would stop down and leaving the optimum zone of my lenses to minimize the light power which I need for larger prints.
Sorry, I meant "smaller" prints.
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  #8  
Old 24th May 2022, 11:47 AM
Richard Gould Richard Gould is offline
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I once attended a darkroom printing weekend held by Robin Bell in London, back when I was a lot younger than I am today, and his advice about stopping down the enlarger was I kind of stop it down all the way, gives me plenty of time for dodgeing and burning, a second or 2 out at 30 or 40 doens't matter either way, but at 10 seconds it shows up a lot, Somthing I have for many years lived by and it has never let me down, If it is good enough for a printer of Robin Bell's dtatus, he has printed for everyone who was anything, all the big names in photograsphy, then it's good enough for me
Richard
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Old 24th May 2022, 02:14 PM
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Reginald S Reginald S is offline
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If it's good enough then it is good enough.

I bought my darkroom equipment from a retired and professionell photographer.
Everything has approximatively been from the sixties, the Durst enlarger, the Unitub development machine..
It comes with Rodenstock Rodagon lenses which obvisiouly once have been good enough.
It has been an old lens design from one or two generations before.

Later I bought new Componon S lenses and I have to say wow, what a difference in brilliance/contrast, and there is of course a little bit more of sharpness.
Thanks to make my own experience.

If the LED light is sattled perfectly in my enlarger I have to test my lenses concerning light falloff and overall sharpness depending on the aperture.
I will do this with 4 test negatives, one for each corner, and another one for the center of the projection.
The negatives are there so this will cost me nothing, and I could share the results to the forum.

If anybody is interested in 35mm or 6x9cm negatives for making his own tests, please let me know, because I could give away a handful of them.
Reginald
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  #10  
Old 24th May 2022, 03:51 PM
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Tell you what team, I have to print tonight for the negative exchange.

I'll make two prints from same neg, one being 2 stops down from wide open, and one with the lens screwed right down to something tiny.
RC paper, dry tonight, and we can look tomorrow.

Place your bets!
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