Convertible lenses

[joe_freeman]

Ok, I'm confused. I have a Schneider 300/500, which just does not

give acceptable sharpness results when converted. Filter or not,

closed to f/90 or not. I'd really love to have a convertible lens

that performs sharply at ALL focal lengths. I'm assuming that there

has to be a brand out there somewhere. I know Weston had a Turner

Reich and Adams had one for Moonrise. These are two guys who are

known for definition in their images. So did they just get lucky

with the lenses bought, I hear that some Turner Reichs are sharp and

some not depending on the quality control that particular day.

I'm going on a trip soon, so something I want is to be carrying 1

lens, like Weston on his Guggenhiem. All my images are 8x10 contacts

too.

Does anyone have experiance with a turner reich, a bausch and lomb

protar triple convertible, and so on... what are your results?

Please be very critical of them, the lens you guys recommend to me

has got to be sharp at all focal lengths. Please, advise me to which

ones I need to stay away from also. I know that the schneiders are

useless when converted.(when definition is required at least)

thankyou for all comments.

[brian_ellis3]

I'm surprised that your lens doesn't provide sharp contact prints. If you were enlarging I might understand better but any even semi-respectable lens should provide very sharp contact prints. I wonder if perhaps there is something wrong with your lens. Anyhow, FWIW, I use a Wollensak 13"/20"/25 1/2" F 6.8 triple convertible lens for 8x10. I can't use the 25 1/2" length on my camera but both the 13" and 20" lengths provide very sharp contact prints, particularly when I use a yellow filter at the 20" length.

[Troll]

Goerz Dagors can be used nicely with the front element removed, at about 1.7x combined focal length. Are you quite sure that your Symmar isn't sharp? You probably need to check the focus shift more carefully, especially if you're going all the way down to f:90.

[john_hicks___]

I vaguely recall reading something about a bit of focus shift when using convertibles.

[donald_miller1]

Joe, I will echo what others have said and that is that I find it difficult to believe that a Schneider lens is unsharp especially in the making of contact prints. It is sometimes that focus shift can occur when one is converting from one focal length to another, but this should be apparent when focusing on the ground glass. The thing that I am wondering is that if you are stopping down to F90 as a matter of practice in the belief that it will give a sharper image you will find that this is counterproductive due to the matter of refraction of the light rays as they pass by the constricted aperature. Most lenses function to their optimal design when the are shot at 2 - 3 stops down from wide open. I never shoot my 8X10 below F64 and preferably at F45. In my 4X5 I never shoot below F32 for the reason that I have mentioned.

 

When I started shooting some years ago, I had the mistaken belief that stopped down was sharper...I found that, after much frustration, my unsharpness was due to refraction from stopping down too much. When I began to use my camera movements to aid in the focusing process as the primary focusing control and making aperature as my secondary means my images improved.

 

I shoot Schneider glass almost exclusively and have no regrets in the sharpness arena. I hope that this is helpful. Good luck.

 

Regards,

 

Donald Miller

[david_clark4]

Hi Brian, I've a Wollensak triple also. I'm curious to know why you can't use the 25 inch element? Best, David

[s.k. grimes inc]

When using the lens with only one element group be sure that the single element is behind the shutter and not in front of it. That means that the lens/shutter as mounted on the camera will have no glass showing in front of the shutter. Sharpest results are with the lens set up this way and any other way for any other reason will not give the sharpest result.

[roger hein]

Hi Joe,

 

As others have stated there is usually severe focus shift - especially in old/

classic lenses - and in convertibles. I too am surprised you can't get a sharp

neg for contact printing from a 'modern' Schneider lens. Out of curiosity is

there any sign the lens has been disassembled?

 

I've used several old convertible lenses and none were as critically sharp as a

'fixed' non-convertible lens. For contact printing though, among the

convertibles I've had (T-R, B&L Protar, Cooke), my Cooke Triple gives the

sharpest results. I was disappointed with the Protars and had expected them

to be better, the T-R was 'ok' but like all old lenses there's quite a bit of

variability from lens to lens so I may just have had a bad one.

 

Good luck!

 

Cheers,

Roger...

[bob_salomon]

" due to refraction from stopping down too much"

 

Diffration not refraction.

[tracy_storer1]

A couple of above posters have mentioned "focus shift" but none

have explained for Joe what that means. Joe, you need to check

focus at the shooting aperture, (the focal length changes a bit

when you stop down).

I hope a combination of everyones info helps. Tracy

[joe_freeman]

First, thanks for all the replys.<p>

I just checked Schneider's website, and even they claim that when converted, their lenses will not be sharp, around the edges at least. Everything I'm experiancing is in accord with what they say. No matter how much I play with focusing once closed down, it will not come into focus.

I don't think diffraction is so much of an issue at 90, b/c when using it at 300 at f/90, I have no problems. I'm not hoping to get this lens to perform in a way it's not able to, but, what I would like to know is what convertible lenses do you guys find to be sharp at all their focal lengths? thanks again.

[Troll]

Joe, I think you're beating a dead horse. What's sharp enough for me is probably not going to satisfy you. My 16x20 print of "Moonrise" isn't really critically sharp if you look at it through a magnifying glass, but there are a few 40x50 prints of it which are plenty good at normal viewing distances. (It was made with a single component of AA's Turner Reich lens.) To get the kind of performance that you expect, I think you're going to have to buy individual lenses of those focal lengths. I'm not trying to put you down, I just think that your standards are higher than mine.

[david_goldfarb]

I think this is just the downside of using a converted lens. I've occasionally used the rear cell of a Dagor, which doesn't look too bad, but it never looks as good as a lens designed to be that focal length, and never as good as the two cells combined. I only do it when I don't have a lens of the appropriate focal length.

 

You also have longer focal length and smaller effective aperture working against you, so camera stability becomes a bigger issue. Are you sure this is not the problem?

[armin_seeholzer]

Hi Joe

 

f 90 then you can`t get really sharp pictures because, then you are really in the diffraction limiting part.

For example my Symmar 210/370mm works sharpest at f 32-45 as only with the back element. In 210mm it is sharpest at f22, of course a convertible will always be a compromise!

Good luck!

[gary_meader]

Joe-

My convertible is the Schneider 240/420. The 240 configuration

barely covers 8x10, but is OK w/o movements. The 420 does

shift focus, but when I use an orange filter, the contacts are fine.

One thing I find interesting: when going to the longer length, the

image circle doesn't change. You'd think as you pull the bellows

out to accomodate the length, the image circle would grow huge.

Not so. Go figure.