Does number of aperture blades even matter on repro lenses?

[Niels - NHSN]

I just purchased a Durst M600 enlarger which came with a Schneider Componar 75mm/4.5 lens. 
As you can see below, it only has 4 aperture blades (left).

I happend to also own an older Componar 75mm/4.5 whith 15(!!) aperture blades.

Both are 3 element lenses, nothing fancy.

Does a circular aperture even matter on an enlarger lens?
And why on earth would Schneider make a "cheap" entry level enlarger lens with 15 aperture blades if it doesn't matter?

[John Seaman]

Niels, I asked a similar question some years ago, with reference to camera lenses, the discussion petering out without arriving at a clear answer (as this one likely will...). Your question is specifically about enlarging lenses, who's image should all be in focus, so the question of Bokeh, being the rendering of out of focus areas, should not arise. Or should it?

Here's the earlier thread:

LINK ------

 

[Niels - NHSN]

As you note, bokeh should have no relevance when reproducing a completely flat field.

So, does it matter if the aperture is square or round? I just find it very hard to understand why Schneider would bother with 15 blades, if  they could achieve the same with 4.

[glen_h]

As none of use are perfect at focus, there might be some bokeh effect.

Reminds me, though.

In case anyone has seen the JWST pictures, with a mirror made from hexagonal segments,

there is an edge diffraction effect that causes bright points to become six pointed stars.

(And which we used to buy filters for, to get the effect on regular lenses.)

 

There is still diffraction even with a flat field in perfect focus.

If there are bright (enough) point sources in the image, they will get a four

point star effect.  Much less with the 15 and more rounded aperture.

 

I asked someone at least related to JWST, and suggested it would

be a simple digital filter to remove them.  It seems, though, that the general

public expects stars to be star shaped, and likes them that way.  And also

mentioned the filters we used to buy for cameras.  (I presume now, we

can use a digital filter to add them.)

 

If you do a 2D Fourier transform in the image, they are easy to find.

(Try that on images from the four blade aperture.)

 

[rodeo_joe1]

I'd be much more troubled by the lack of lens elements than the number of iris blades. Because in my experience no enlarging lens with only 3 elements is really worth buying these days; not when the likes of Rodagons, Componons, etc. can be had for not much more. 

WRT the square 'hole': Yes, it will make a difference at the level of very small detail, especially if slightly out-of-focus, which may well happen at the corners of the print. Proper repro lenses, used for making half-tone screened internegatives in the printing industry, used to have a Waterhouse-stop slot as well as an iris. This was so that square or diamond shaped apertures could be fitted and rotated to align with the screen angle. This supposedly gave sharper edges to the square half-tone dots.

I suspect that half-tone screening was the reason for that square shaped aperture, and that the lens was never really intended for use on an enlarger. Most enlarging Componars have a conventional round(ish) aperture iris.

Oh, P. S. where 'bokeh' enters the picture (sic) is that a half-tone screen requires slight separation from the image. Therefore the dots projected are slightly off-focus and take on the iris shape.

Edited November 8, 2022 by rodeo_joe1
Addendum

[Niels - NHSN]

1 hour ago, rodeo_joe1 said:

I'd be much more troubled by the lack of lens elements than the number of iris blades. Because in my experience no enlarging lens with only 3 elements is really worth buying these days; not when the likes of Rodagons, Componons, etc. can be had for not much more. 

Agree. I found a Componon with M25 thread of similar vintage as the 15 blade Componar depicted above. €20!

[JDMvW]

My Kodak Jiffy 620 may have had square waterhouse stops, if I recall correctly. Some old camera of mine from the early 20th c. did anyhow.

In any case, I have a sort of semiconscious negative reaction to a square aperture or or square hamburgers (Wendy's take note). Nature abhors a square, is it?

High quality enlarger lenses are widely available and mostly pretty cheap these days. Many of them make excellent copy or macro lenses.

[rodeo_joe1]

On 11/8/2022 at 2:17 PM, NHSN said:

Agree. I found a Componon with M25 thread of similar vintage as the 15 blade Componar depicted above. €20!

I used an old 80mm f/5.6 Componon for years with no complaints - until I got my hands on a newer Componon - S version. There's a definite improvement in contrast and coverage (or field curvature?) that sharpens up the corners noticeably and gives a bit more 'snap' overall.