Guys, I have re-read the posts and tried this again
On every enlarging lense I own (4 off Rodenstock Rodagons of various focal lengths) except the Schneider when I stop down the grain in the Peak stay in focus
With the Schneider the grain goes a little mushy when closed down 2 stops & comes back sharp when opened up again
The view on the baseboard stays looking sharp in both cases - to my eyes
I have not yet tried printing the image at both apatures - but I guess this is the next step and then examining the image with a lupe.
I don't know what has happened to the lens but I doubt it was designed to do this.
It is also easy to work around - I just focus when stopped down
However, if I need to produce top quality prints I will be using a different lens to the Schneider
Thanks for the help/sugestions & input
Martin, it does appear that it could become a paper weight, as per Dave's suggestion.
With the cost, generally, of these lenses still quite cheap and reasonably plentiful, get another one, or something better.
Once on a photographic hike, were quite cold and wished to make a hot drink, the person with the stove was kilometres away, so we made a fire using winter sunlight and a 50mm lens focusing sunlight on some loose cotton fibres to get a flame, works a treat, perhaps you could use it for something similar?
Please print with the lens and see if it works.
When using a 25X grain focuser, I can see the grain getting mushy around 2-2.5 stops down with all my enlarging lenses and I have a few.
I believe what you are seeing and what Ctein pointed out in Post Exposure is that the lens is becoming diffraction limited at that point and is an indication that perhaps the Schneider is indeed a better lens than the others you are testing. Ctein's chart shows that most lenses of 2.8 peak at about 2 stops down and lenses of 5.6 aperture are quite often peaking wide open to about 1 stop down.
I would think DF's advice of making a print is well taken and I would think there is nothing wrong with your lenses other than I would be wondering why the other lenses are sharp beyond their peak apertures.
I doubt it's diffraction limitation so much as your eyes not being able to see the grain as clearly. I'm not convinced the human eye is equipped to clearly see that. And it may SEEM as though you're getting a focus shift... but I'd be willing to bet that as you stop down and your DOF increases, the point of optimal focus becomes less and less clear. Especially considering the loss of sensitivity to the eye.
But if you DO decide to dump the lens... well... I could really USE a paperweight...!!! I'd be happy to cover your shipping...!!
Sparky - I will continue to use it - I want to try checking the focus in print sharpness
Originally Posted by Sparky
Also I will try focusing with it stopped down
But if I do dump the lens I will think of you first
PM me with your details if you want
Be warned - the lens is firmly attached to a DeVere Mounting Flange
I was just kidding martin - trying to suggest that it's actually (probably) a really good lens and you shouldn't even think about getting rid of it unless your prints are definitely lacking relative to other lenses you've used. The other thing we never looked at is the enlarger... if you're using something like a beseler - I could easily see the focus shifting just from turning the diaphragm...
oh - but i guess it's a devere - so NO chance of lens board movement... I have a 504 too...!
The shift is most likely caused by a change in distance between the front and the rear element of the lens. Might be caused by opening the lens to clean the inside and reassembling it a little different as it was before. As long as you are aware of this it is no big issue. You will get sharp prints as long as you focus a second time after stopping down.
Maybe the shift can be corrected by rearranging the elements. But if you are not experienced in this it might be better to leave it as it is.
Perhaps the issue is caused by the change in depth of field and the thickness of the image layer. At f5.6, you might be focusing on the (for example) surface of the image layer, whereas at f11, you might be focusing on the whole image layer. The following article emphazises that instead of focusing on 'grain', you should focus to maximize image contrast - to quote from page 3 of the article:
"Good focus is achieved by finding the highest degree of contrast difference between light and dark, in a bit of blurry detail, while avoiding the use of film grain."
I've run into focus shift with a few older as well as second-string enlarging lenses, not with any of my
apo ones. If this only transpires wide open, you can still get close wise open, then stop down one stop for the final critical focus. No big deal. There some superb camera lenses out there which also have
focus shift with the first stop. They could have easily corrected such designs, but then the max aperture would be smaller. The lens is likely to still be perfectly usable. But if the focus shift is progressive the further you go, you've got a lemon.