Problems focusing with 14" lens

[ericantonio]

Dary Abby

Hola more smarter people than me! I have a question about a lens. Specifically, maybe it's not mounted correctly on my shutter

Lens:
14" Red Dot Arter f/9
Acme #4 shutter

I have a super hard time focusing on this lens. I put my Velostigmat 19" F/10 lens on camera, and I can focus just fine.

With the 14", it's like ......almost is focus........but it's so hazy. Like its never really quite there, either front of focus or just behind the focus, it's just "not there". Even if I stop down it's not quite in focus.

I thought maybe my GG is messed up or what. Then I put my 12" 6.3 lens on it and bam! Clear as day.

Is it possible that the lens is not on the right shutter? Meaning...the distance from the front lens element is not correct distance to the rear element? I don't really know much about lens science and I don't know if this is the original shutter. It's just that whatever I do, it just doesn't seem like it's in focus.

[domaz]

Did you try just taking the lens, pointing it out a bright window in a dim room so that it projects onto a white wall. If the lens is really that bad you might notice during this simple test if the cell spacing is off, especially comparing it with a known good lens. It's possible someone did "funny stuff" to your lens like took it apart to clean it and then put the lens back together the wrong way. Or polishing it with Cerium Oxide to make it look clean. Wouldn't be the first time this happened...

[ericantonio]

Did you try just taking the lens, pointing it out a bright window in a dim room so that it projects onto a white wall. If the lens is really that bad you might notice during this simple test if the cell spacing is off,


Curious, how would I know, if I did this, if the spacing is off? What would I see on the wall?



especially comparing it with a known good lens. It's possible someone did "funny stuff" to your lens like took it apart to clean it and then put the lens back together the wrong way. Or polishing it with Cerium Oxide to make it look clean. Wouldn't be the first time this happened...

Lens looks nice, not like it's been cleaned or anything, and yes, I'm thinking of that funny stuff. We all do it. Take things apart, put it back together, and then "honey, the car won't start again!".

There is a stop down screw flange on both ends because the #4 Acme opening is wide. So that stop down will make a more narrow lens screw into the front and back. I have a 12" on same shutter and it screws in on the widest opening of both ends.

[domaz]

Curious, how would I know, if I did this, if the spacing is off? What would I see on the wall?



Any lens will throw an image on the wall this way. You can typically gauge how sharp it is that way, that at least might rule out ground glass / camera issues.



There is a stop down screw flange on both ends because the #4 Acme opening is wide. So that stop down will make a more narrow lens screw into the front and back. I have a 12" on same shutter and it screws in on the widest opening of both ends.


I'm not totally visualizing this description, but is it possible one of the lens element is not totally screwed into the shutter because of an obstruction?

[ericantonio]

Any lens will throw an image on the wall this way. You can typically gauge how sharp it is that way, that at least might rule out ground glass / camera issues.


I see I yah, totally get it.



I'm not totally visualizing this description, but is it possible one of the lens element is not totally screwed into the shutter because of an obstruction?

I hear ya, I'll try to get a photo. In the meantime, I have another problem, I haven't used this lens in like forever, so now the shutter is stuck in the closed position. But I'll try to add a pic.

[ericantonio]

https://i.imgur.com/L6z8kCL.jpg

https://i.imgur.com/AbhiIp5.jpg

The inner black rings are step down rings to add a smaller diameter lens on it.

I checked the elements. They seem fine, 2 in front and 2 in rear. Looks like the rear element screws off and it is same thread and size and front rear element. Wonder if they are interchangeable. But now, dang it, the lens is stuck closed. Arggghhh. Another day another challenge. Will keep playing with it until I either break the shutter or free it loose.

[Jim Noel]

The elements may be reversed, OR they may have been dismantled in order to clean the interior surface and then remounted out of order, or without internal bushings to establish correct separation of the elements.
Also, check to insure each element will focus an image on the wall.

[ericantonio]

The elements may be reversed, OR they may have been dismantled in order to clean the interior surface and then remounted out of order, or without internal bushings to establish correct separation of the elements.
Also, check to insure each element will focus an image on the wall.

Yikes, sounds highly technical for me. Ugh. I wanted to remove that step down filter so I can put it on my other Ilex #4 but it seems to be in there pretty good. It doesn't have a notch for a spanner.

Internal bushing....I didn't see one. On either the front or the back pieces. Hmmm. Is this something a tech can check if I get a CLA on the shutter? Will it be cost effective?

[Vaughan]

Also, check to insure each element will focus an image on the wall.

That won't work with groups that have negative strength.

[Dan Fromm]

That won't work with groups that have negative strength.

Vaughan, Apo-Artars are dialytes. Symmetrical double more-or-less anastigmats. Dialytes. e.g. Goerz' Celor, have been sold as convertibles.