And, might I ask, where does focusing the image enter into the equation? At that difficult, less accurate stopped down level? - David Lyga
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 LygaI'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.
Bingo!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.
@Jens Hallfeldt do you happen to know what apertures they were fixed at?
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?@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 already tried both ways.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.
All of which applies well to your preferences and your equipment.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
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.
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'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.
This is a question that a Lyft to a professional lens designer.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?
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.Sorry, darkroom printer, yes, but halftone? Don't even really understand that genre. - 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?
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