Enlarging lens won't close beyond f16

Mike Chalmers

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Hey folks,

I have the Rodenstock Rodagon 105mm F5.6

I've been using at around f9 but was considering doing some dodging and burning and to give myself time I thought I could close down to f32.

Maybe I'm doing something wrong, but the lens doesn't want to go past f16, despite the other apertures being easy to move between.

Any thoughts?
 

pentaxuser

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Just a couple of thoughts; I take it you have used it in the past beyond f16 and if so how long ago? If you are using it in the enlarger then to see more clearly what is happening it might be worth taking it off the enlarger and see what happens to the aperture up to f16 and then how the blades look when you try and go beyond

pentaxuser
 

Vaughn

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It might have an aperature pre-set. One can 'lock' in an f stop then open to lens wide open to focus and when you close the lens it stops at the pre-set f stop.

From the product info:

"Additionally, for ease of use, the lens is fitted with an illuminated f/stop scale, a convenient preset aperture setting, and a click-stop diaphragm that can be de-clicked depending on preference."

The 50mm lenses were set by pulling out the front of the lens a little.
 
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BSP

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Hmmmm.....just gotta ask....."Going beyond f/16" ? How about diffraction-softness? Or is this no issue when enlarging?
 

Vaughn

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BSP said:
Hmmmm.....just gotta ask....."Going beyond f/16" ? How about diffraction-softness? Or is this no issue when enlarging?
Click to expand...
IDK -- a $1200 enlarging lens might be able to handle it fairly well.
 

MattKing

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Many enlarging lenses have a function that allows you to set the aperture to a particular f/stop - the one you wish to use for the exposure - and then restrict the aperture from closing further. That permits you to turn the aperture setting scale back and forth - turn it one way to open up the lens wide for focusing and cropping, and then turn the aperture all the way to other end to set the aperture at the exposure setting.
Your lens probably has that feature, and it is probably set to f/16.
Try pulling down in the aperture setting ring - that often engages or dis-engages the function.
That function is sometimes also combined with a function that turns the click stopss on and off.
 
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Mike Chalmers

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Ah yes this sounds like exactly what it could be. I'll try this out when I go back to the darkroom.

Thanks for all your quick help. I'm always a bit embarassed at my lack of knowledge and constant questions, but this forum is the best.
 

AgX

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I don't think so.

I myself got an older version from 70s or 80s, with silver ridges at the aperturte ring. And that got an aperture ring with click-stops at full values, and closing down to 32.
The next model, with black ridges, already had switch-off click-stops and preset min. aperture.
 

mrosenlof

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I have that lens, and I don't have it in hand right now, but I'm pretty certain there is a pre-set feature. Pull downward away from the lensboard (gently!) on the aperture ring and turn.

I would still be concerned with diffraction at f/32. Diffraction from small apertures negates well corrected lenses regardless of their quality.
 

Pieter12

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Once you have your issue solved, you might want to try a couple of things. Using a grain focuser, look to see if the focus softens from diffraction as you stop down the lens. If you do see diffraction at f/32, try a 2-stop ND filter gel (ND .6, pretty inexpensive) in the filter drawer if your enlarger has one. You'll get the additional time without losing sharpness.
 

MattKing

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The diffraction at f/22 and f/32 with a 105mm lens will reduce the quality of the image, but the question is: how much?
If the reasons for choosing the smaller f/stop relate to unreasonably short printing times - a common problem when the print is relatively small and therefore the magnification is low - then any such change in quality will be also be relatively small, due to the low magnification.
The smaller aperture could also help if you are having trouble keeping negatives flat. The resulting improvement in depth of field (or possibly, depth of focus) may very well far exceed the harm caused by increased diffraction.
 

wiltw

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Vaughn said:
IDK -- a $1200 enlarging lens might be able to handle it fairly well.
Click to expand...

Diffraction affects ALL lenses, not just $120 ones vs. $1200 ones...physics is what is behind diffraction, light rays bending thru small holes (the aperture)...the smaller the hole the more the diffraction. Period. An expensive lens might have less chromatic abberations (color separations) than a cheap lens, but diffraction happens no matter what.

Both diffraction and chromatic abberation shows up to a greater degree at higher magnification, and when we enlarge a medium format neg with 105mm lens we are not using as high of magnification as someone who shot with 135 format film and enlarged with 50mm lens. That is why medium format can use a smaller aperture than 135 format, both for the picture taking lens and for enlargement in the darkroom. Going to f/22 is 'marginal' for medium format, in that regard, depending upon the pickiness of the photographer.
 
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wiltw

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"All Rodagon lenses are equipped with an illuminated f-stop display, a practical pre-set aperture und a click-stop diaphragm which can be switched to stepless control for focal lengths up to 135 mm."

--Rodenstock englarging lens PDF
​
...but then the 150mm Rodagon does NOT have the preset!
 

Vaughn

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wiltw said:
Diffraction affects ALL lenses, not just $120 ones vs. $1200 ones...
Click to expand...
Wish I had placed bets on how fast we'd get this reply from someone...
 

Vaughn

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As the original quote states..."All Rodagon lenses...up to 135mm".
 

Toyo

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I can't help you with the diaphragm problem not going past f16.
For what it is worth, most enlarging lenses seem to perform at their sharpest at one or two stops down from their maximum aperture.
In this case f8 or f11
Happy printing
T
 
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Mike Chalmers

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Thanks folks, that was indeed the issue i.e. me being daft

mrosenlof said:
I have that lens, and I don't have it in hand right now, but I'm pretty certain there is a pre-set feature. Pull downward away from the lensboard (gently!) on the aperture ring and turn.
Click to expand...

This is what I did and it worked perfectly, thanks. There is also a switch that allows click stops or smooth aperture changes for more precision I suppose.


I hadn't actually put this together in my head, but you're correct - I've been making small ~6"x5" prints to test things out before I waste larger sheets. I did have a concern as I believe my timer (Durst DES100AT) can do a minimum exposure of 2", which is not ideal (though I wouldn't be surprised if I'm doing something wrong here also).

Thanks everyone for your help - I'm beginning to see this as a community darkroom which makes up for the fact I don't have seasoned pros working around me that I can ask for help!
 

pentaxuser

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Reading all of this made me try my Rodenstock Rodagon 80mm f5.6 lens. In my case pulling it down allows a step-less movement of the aperture throughout its range and pushing it up gives a click stop aperture feature. However in my case the click stop can be clicked through the full range and there is no switch to prevent any movement as appears to have been the case in Mike Chalmers case when he first reported the problem.

In Mike's final reply #24 he makes no mention of a switch which so I wonder what was stopping his getting beyond f16

Perhaps Mike can clarify this point as to whether there is or isn't a switch on his lens that does effectively halt movement beyond a pre-set aperture.

I can say just to repeat myself that on my Rodenstock Rodagon f5.6 80mm lens I can see no switch

Thanks

pentaxuser
 
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