Perhaps an 'illegal' question from someone who has been in the darkroom since 1964:

[Lachlan Young]

And, might I ask, where does focusing the image enter into the equation? At that difficult, less accurate stopped down level? - David Lyga

I've never had an issue focusing at working aperture in the darkroom - even with 100w lamps. It also ensures that any possible focus shift is eliminated & the image often pops into focus more visibly down the focus magnifier because it is that bit sharper.

 

[David Lyga]

I've never had an issue focusing at working aperture in the darkroom - even with 100w lamps. It also ensures that any possible focus shift is eliminated & the image often pops into focus more visibly down the focus magnifier because it is that bit sharper.

OK, theoretically, you are on sound ground. However, in my over half century of working in the darkroom I have YET to experience any focus shift when stopping down. Also, I find focusing both easier with the extra light and more accurate because of the truncated depth of focus for the negative image at large aperture. My experiences dictate my procedures, both in the darkroom and, in general, in life. - David Lyga

 

[Lachlan Young]

@David Lyga I can't say I've ever encountered focus shift from an enlarging lens either, but I've found that the optimum aperture (not really going to be deeper than f8 with modern lenses) does make focusing more precise.

 

[DonW]

The only lens I used in the darkroom that had a square aperture was a dog. I also found that generally it was the cheaper lenses that used this format which could explain its subpar performance. But then again I have been wrong before.

On the subject of focus shift I have experienced this even with most expensive enlarging lenses.

 

[MattKing]

Aperture shape can play a big role in screen printing. The aperture shape affects the shape of the dots in the screen. If you want round dots, you need a round aperture.

I think the above is the reason some older enlarging lenses wound up in barrels with round apertures. That would make the lens suitable for creating screens for screen printing.

Bingo!
But even if the enlarging lens wasn't going to be used for screen printing, it makes sense that they would make one high quality aperture mechanism and put it to use in multiple applications.

 

[JensH]

@Jens Hallfeldt do you happen to know what apertures they were fixed at?

Hi,

no, sorry.
I hope I still have that old Monochrome catalogs somewhere in my mother's house...
In two weeks I can look for, but can't promise to find them.

Best
Jens

 

[David Lyga]

@David Lyga I can't say I've ever encountered focus shift from an enlarging lens either, but I've found that the optimum aperture (not really going to be deeper than f8 with modern lenses) does make focusing more precise.

I have to admit that I find this quote to be amiss, even a bit sloppy in theory. Why? First, what you are saying serves to denigrate the whole concept of automatic apertures on SLR lenses (which automation has been around since the late 1950s). If focusing is "better, more accurate, when stopped down", then why would automatic apertures EVER be better? Why wouldn't ALL SLR lenses continue to be made with only manual aperture settings? Why would SLR lenses be any different from enlarging lenses in order to benefit from this position that you take, which states that best focus is best achieved only at the actual stopped down position?

When you focus at the actual taking aperture, you are introducing a greater depth of focus (with SLR lenses, enhanced depth of field) into the equation. This augments the range of focus whereby the image still looks sharp. However, when you greatly restrict that "in focus" range by opening up the lens to maximum speed, it is far easier to "zero into" the correct point of focus. Then, the stopping down for the actual exposure "locks in" the precise point of focus by adding leeway on either side of the focus point. Thus, due to the smaller aperture, the best focus point is now assured.

I have a feeling that Nikon would agree with what I have just said. - David Lyga

 

[MattKing]

One of the reasons why you might wish to focus at the exposing aperture is that it removes the possibility that you will inadvertently change the focus when you adjust the aperture.
Also, the optimum aperture will often yield the highest contrast - including edge contrast (acutance). It may be that if you are at the optimum aperture it will be easier to see that the film grain is at its maximum sharpness.
Finally, with some enlargers and lenses and focus aids and magnifications, when the lens is wide open, the image can be very bright. It may be more comfortable to work with less brightness.
So don't discount it, until you try it.

 

[cowanw]

Verito lenses were once used as enlarging lenses and came with a number of preset aperture plates with non round star shaped apertures.
Pre 1970 ish enlarger lenses had eventually round apertures with many more blades than modern lenses. The ones I use (Componons) do have a look but is likely the glass as much as the aperture.

 

[David Lyga]

One of the reasons why you might wish to focus at the exposing aperture is that it removes the possibility that you will inadvertently change the focus when you adjust the aperture.
Also, the optimum aperture will often yield the highest contrast - including edge contrast (acutance). It may be that if you are at the optimum aperture it will be easier to see that the film grain is at its maximum sharpness.
Finally, with some enlargers and lenses and focus aids and magnifications, when the lens is wide open, the image can be very bright. It may be more comfortable to work with less brightness.
So don't discount it, until you try it.

I have already tried both ways.
The pro for focusing at the actual taking aperture is a potentially better contrast, but this (only possible) advantage is mitigated by the less bright projection. I find that it is far easier to zero onto the precise focus by allowing depth of focus to be minimal, and that necessitates using the lens wide open for focusing. Then, upon stopping down, one has 'centered and targeted' the best overall focus for exposure. Since the negative and paper are two dimensional, there is no worry that I have concerning edge detail. The ONLY time I am concerned with focusing upon edge detail is when the enlarger is out of alignment. If it is in alignment, whatever is in focus in the center is also the best focus for the edges.

Over the years (decades) I have found that the BEST way to focus is to hold a magnifying glass within about 2 inches from my eye and close into the projected image.That way, it becomes very easy to target the focus. I depend upon the slight depth of focus to make amends for the very slight negative curvature that becomes apparent with glassless negative carriers. I find that that slight theoretical disadvantage more than makes up for the greater disadvantage of having to keep four extra surfaces immaculate with glass. Of course, when you use 35mm exclusively this is a lot easier to say than if you used sheet film, which just might bend a bit more. - David Lyga

 

[MattKing]

I have already tried both ways.
The pro for focusing at the actual taking aperture is a potentially better contrast, but this (only possible) advantage is mitigated by the less bright projection. I find that it is far easier to zero onto the precise focus by allowing depth of focus to be minimal, and that necessitates using the lens wide open for focusing. Then, upon stopping down, one has 'centered and targeted' the best overall focus for exposure. Since the negative and paper are two dimensional, there is no worry that I have concerning edge detail. The ONLY time I am concerned with focusing upon edge detail is when the enlarger is out of alignment. If it is in alignment, whatever is in focus in the center is also the best focus for the edges. - David Lyga

All of which applies well to your preferences and your equipment.
I am a member of a Darkroom Group. Under normal circumstances we meet together at a location that offers up to seven different enlargers - all 4x5 or 5x7. We have the choice of several different types of light sources - some being much more intense than others. I find that I do different things depending on which enlarger I am using. The relatively dim Ilford 500 Multigrade source on a Beseler frame requires different approaches than the cold light head on the Beseler frame or the Halogen dichroic head on the Durst 5x7 or ......
With my own enlargers I have, in the past, mostly done what you do. Sometimes though I double check the focus at the exposing aperture.
After my recent move, I have had to switch to a new enlarger. I'll see what works best with it (once I finish setting up my new temporary setup).

 

[KenS]

Lachlan, I don't get your point.
At first you had it about the optimum aperture for a lens. That is ONE aperture. Here my clickstop marking of this one apeture is more versatile than substituting an iris for a one-stop aperture.

Concerning optimum apertures for different image scales is something different. But whether exchangable stops are more practical than an iris, I doubt.
There were repro cameras that had a lever attached to their Rodenstock lenses. These lever offered at a scale much more precise readings and thus settings. This would be an alternative to using several one-stop apertures.

I have (and use) a 'levered' 480mm Apo Ronar (f9) that was 'rescued from the Gaphics/Printing Dept. of the nearby university when 'all digital) became the 'in thing'. I had been using a 'plenum' with a black velvet 'sock' as a shutter.,, got an old 'roller blind' shutter that 'died' after about 6 uses.. I am now 'back' to using the hand held plenum as a shutter... not quite as 'reliable' as a mechanical one.. but... as may mentor used to quote those many years ago..."Use what you have.... ..and you'll never want"

Ken.

 

[ic-racer]

I'll throw in my two cents on focusing aperture in the darkroom. I have trained myself to really analyze the projected image for lightness and darkness as if I'm analyzing the first test print. To do that I need the bright, wide-open, image, especially if my eyes are not fully adapted to the dark (in my printing sessions I'm always turning on the white light to analyze test prints).

I have got to the point where I can see the light and dark areas of most negatives projected on white paper and can see where dodging and burning needs to take place without making a full frame test print. The reason this is not so straight forward is that negatives will have about 70% the contrast of a print or the original scene, so one has to imagine what the light and dark areas would be like with the 30% more contrast obtained with a test print.

The way to learn this is to make the full-frame test prints, then go back and analyze the projected image against the processed and dried print.

 

[David Lyga]

I'll throw in my two cents on focusing aperture in the darkroom. I have trained myself to really analyze the projected image for lightness and darkness as if I'm analyzing the first test print. To do that I need the bright, wide-open, image, especially if my eyes are not fully adapted to the dark (in my printing sessions I'm always turning on the white light to analyze test prints).

I have got to the point where I can see the light and dark areas of most negatives projected on white paper and can see where dodging and burning needs to take place without making a full frame test print. The reason this is not so straight forward is that negatives will have about 70% the contrast of a print or the original scene, so one has to imagine what the light and dark areas would be like with the 30% more contrast obtained with a test print.

The way to learn this is to make the full-frame test prints, then go back and analyze the projected image against the processed and dried print.

To be frank and direct here, your statement is a manifestation of intelligence. You have trained your eye to translate the tonal output of the negative (averaged with taking into consideration the quality of projection light) into the limited ability of the print to render tone within its full reflectance capacity. This is more than a handy tool; it is valuable for a final, or "pre-" visualization; Ansel would have been proud of you.

I had to say all of that because all of that is the truth. - David Lyga

 

[RalphLambrecht]

I will ask this because, at least in the past, manufacturers have spent good money in getting this done:

Is there ANY advantage (aesthetic or otherwise) with making an enlarging lens with a stopped down aperture which is nearly circular? Bokeh is of no concern here for obvious reasons. More blades = more manufacturing expense. - David Lyga

EDIT: My question is NOT asking how far one should stop down, but, rather, it is this: Is the SHAPE of the stopped down aperture (circular or otherwise) a factor in print quality?

This is a question that a Lyft to a professional lens designer.

 

[John Wiegerink]

I'm not at home to verify this for sure, but I am positive I have several cheaper enlarging lenses with square apertures. I also have owned a few Olympus cameras with the same type aperture. If I remember right the XA and Oly Pen half-frame cameras used them. My Minox 35 has a square aperture. To be honest I never complained about any of the photos those cameras took. In fact I still have and us the Minox 35mm Golf camera. Now, I can't speak to the square blade iris in the cheap enlarging lens since I have never used it, but I might just be surprised. JW

 

[Bill Burk]

David Lyga, You're a printer, right? Halftone screens (the old glass etched ruled screens) projected a halo of light for each dot. The perfectly round aperture was required for those, because the aperture directly impacted the dot shape.

So enlarger lenses of that vintage (before early 1950's) may have been designed to support halftone photography.

 

[David Lyga]

Sorry, darkroom printer, yes, but halftone? Don't even really understand that genre. - David Lyga

 

[Vaughn]

Sorry, darkroom printer, yes, but halftone? Don't even really understand that genre. - David Lyga

Images in newspapers and magazines, on posters, and all that genre...made using halftone screens. Thus the many bladed process lenses of the past, perhaps.

 

[Orftoden]

I have a chrome Schneider with 9+ aperture blades and a more more modern componon s with if I had to guess 7 aperture blades. The modern lens is a better performer. I’ve never compared the same image made from the two different lenses, but I may have to try now to see if there are any other pleasing attributes from the older lens and it’s rounder aperture.

 

[JimEA]

(this may be a newbie question

I understand how you'd see the effects of a wide open aperture - i.e. less sharpness and (presumably) a greater reliance on the paper being flat and everything well aligned owing to the smaller depth of field at the easel....

My Q is... What would I see that would indicate diffraction from a more closed aperture? What features in the print would be more susceptible to that?

Thx All
Jim

 

[Sirius Glass]

I use the mid range f/8 to f/16.

 

[138S]

EDIT: My question is NOT asking how far one should stop down, but, rather, it is this: Is the SHAPE of the stopped down aperture (circular or otherwise) a factor in print quality?

A bit late...

A circular iris has an slightly better performance than an aperture showing a polygon. (noticeable ? I don't think, in practice)

For the same aperture surface (say in mm2) the circle has a minimal periphery (say in mm), as diffraction is generated in the edges of the aperture hole the shorter the periphery the lower the diffraction generated.

One may mistakenly think that following that reasoning, a very small aperture should have "less diffraction", and in fact there would be less rays diffracted... but what counts is the proportion of rays diffracted related to those that passed straight, and an smaller aperture has less surface...

At the end what counts is the length of the periphery of the aperture compared to the hole surface. And smaller aperture has a worse ratio, and a non circular shape also has a worse ratio than a circular one.

This effect is well known in Pinhole photography, a non well polished hole has more periphery, so way more diffraction !!! As diffraction is quite high in Pinhole it's seen better, try to make an star shaped aperture hole for pinhole...

_____

Also a non circular iris may decrease slightly less spheric aberration than a circular iris when stopping, as for the same aperture the maximum radius of the periphery is larger than in the circular case, probably this can be demonstrated from compex optical calculations, but it would be quite difficult to see it in practice.

 

[Rick A]

David, I have an Eastman projection anastigmat that I use for enlarging, it has a circular aperture and more blades than I can count. It's a wonderful lens.

 

[DREW WILEY]

There was one model of the Apo Nikkor 369/9 which had both an adjustable square aperture, plus a multi-bladed circular aperture, while also having a slot potentially accepting Waterhouse apertures. These are really really well corrected process lenses designed for precise apo round or square dot reproduction. But they also are better than any ordinary official enlarging lens of equivalent focal length, provided you can work with optimal apertures around f/11 to f/22 rather than the f/8 to f/11 of typical max aperture f/5.6 enlarging lenses. Some of my enlarger heads can be just too powerful, so smaller apertures are sometimes realistic. Even relatively wide at f/11, they're sharper than even my excellent Apo Rodagon N's at the same f-stop.
But the Apo Nikkors aren't available in any focal length shorter than 180.
Now if you take that same multi-bladed 360 Apo Nikkor (I have only adjustable round aperture ones), and put it on an 8x10 camera lensboard, does the multi-bladed aperture provide nice bokeh in that particular application. Nope. Although extremely sharp all the way from macro to inifinity, the out of focus rendering is busy and double-lined, much like some very sharp Nikon 35mm lenses with just 6-blade apertures. So the optical formulation is important too, and there was no logical reason to enhance bokeh in a process or enlarging application. I do have an old Zeiss single-coated tessar design 360/9 process lens which does OK for enlarging, but has wonderful bokeh when used for 8x10 shooting. So it all depends when shooting. But for enlarging, these old multi-bladed apertures seem to make no difference.