Why a mottled image on gg?

[tonyowen]

With a 135mm Xenar f4.7 lens the image on the gg is clear.
With a 180mm Symmar f5.6 lens the image on the gg is mottled
With the Symmasr in its 315mm mode [f12] the gg image is mottled.
Closing the Xenar lens down does not produce the mottled effect
The gg is mounted 'rough side' inwards.
All help and comments welcome

regards

Tony

[Bob Salomon]

With a 135mm Xenar f4.7 lens the image on the gg is clear.
With a 180mm Symmar f5.6 lens the image on the gg is mottled
With the Symmasr in its 315mm mode [f12] the gg image is mottled.
Closing the Xenar lens down does not produce the mottled effect
The gg is mounted 'rough side' inwards.
All help and comments welcome

regards

Tony

Try another 180, best one not convertible.

[tonyowen]

Try another 180, best one not convertible.

Yes, but why, and what, causes the mottled effect?

regards

[Bob Salomon]

Yes, but why, and what, causes the mottled effect?

regards

If it happens with the 180 and not your other lens the suspect is that specific 180! Do you see any haze? Mold? Separation? Especially on the reargroup.

[John Layton]

Maybe give us a bit more info, such as - have you processed the films to corroborate with what you are seeing on the gg? What were the lighting conditions? What kind of camera/ground glass? Does the ground glass incorporate a fresnel lens? (look at the gg with a magnifier and you might see a field of concentric circles - indicating the presence of a fresnel). Fresnel fields (technically a "collapsed" lens) have focal lengths...and if badly mismatched with the focal length of the camera lens you are using, could cause the appearance of unevenness, which can change drastically with your (eyes to screen) viewing angle. Typically, though, the affect would not appear as "mottled."

...and yes - do look carefully at the lens - from each side (front and back) with shutter closed under slightly oblique light, and also through the lens with shutter open, again under very slightly oblique light - preferably with something middle to dark toned in the background. Then, with this light/background...move the lens around as you look through it. (does sound like an older vintage lens with some issues).

....and let us know what you see!

[tonyowen]

! Do you see any haze? Mold? Separation? Especially on the rear group.

Nothing obvious, lens and individual cells kooks visually clear.
regards

[tonyowen]

have you processed the films to corroborate with what you are seeing on the gg? What were the lighting conditions? What kind of camera/ground glass? Does the ground glass incorporate a fresnel lens? (look at the gg with a magnifier and you might see a field of concentric circles - indicating the presence of a fresnel). .and yes - do look carefully at the lens - from each side (front and back) with shutter closed under slightly oblique light, and also through the lens with shutter open, again under very slightly oblique light - preferably with something middle to dark toned in the background. Then, with this light/background...move the lens around as you look through it. (does sound like an older vintage lens with some issues).....and let us know what you see!

Have processed paper negs - nothing matches 'mottling' ; lighting conditions dull, Camera Calumet CC400, don't know type of ground glass; don't know about frensel,

It's night here but I'll try and get some digital images of effect tomorrow - maybe my loose term of mottled is confusing the issue.
I use an 8x Agfa lupe to focus directly on the gg.

Yes it does seem peculiar to the 180/315 lens - but what and what can be done?

regards

Tony

[Bob Salomon]

Have processed paper negs - nothing matches 'mottling' ; lighting conditions dull, Camera Calumet CC400, don't know type of ground glass; don't know about frensel,

It's night here but I'll try and get some digital images of effect tomorrow - maybe my loose term of mottled is confusing the issue.
I use an 8x Agfa lupe to focus directly on the gg.

Yes it does seem peculiar to the 180/315 lens - but what and what can be done?

regards

Tony

First of all you don’t test on paper. Use film!
Second your terminology is confusing. Clear and muddled are not correct terminology! Sharp or fuzzy, or out of focus would be more descriptive!
Third when you are focusing with a loupe you first need a focusing loupe, not a cheap magnifier.
Your Agfa loupe is focusing on the top of your gg.
You are automatically out of focus by the distance that your loupe is focused on to the ground side of your gg.

[Pfsor]

Trying to compare both lenses on a different camera would tell you where the problem is. My 2 cents.

[Gary Beasley]

This is most likely an artifact of the fresnels focal length not being matched up well with the lenses focal length. As long as you can see well enough to focus and compose I wouldn't fret too much over it.