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Pawlowski6132
28-May-2010, 11:36
I have a convertible lens, 210/300. I use it on my 4x5. To "convert" it to 300, I just need to remove the front element correct?

I know, try it and find out right? The problem is, I can't seem to extend bellows far enough to get focus. Either that's the issue (I'm a little surprised. I think bellows are about 21") or I have to move the rear element to the front which, I haven't tried yet.

thanx in advance for your insight.

Joe

MIke Sherck
28-May-2010, 11:51
We need to know which convertible you have. Schneider, or some other?

Mike

IanG
28-May-2010, 12:41
Sounds like an early Sironar. Tell us more.

Ian

Vick Vickery
28-May-2010, 13:45
Since 300mm is about 12", that makes no sense; with most convertibles you remove the front lens group, but go ahead and try taking off the rear group and see what happens...you should still have plenty of bellows to focus at infinity with the remaining lens group on either the front or rear of the shutter.

Vick Vickery
28-May-2010, 13:47
Another thought...are you sure you have a convertible lens and not just a lens thats been installed on a shutter with a convertible f-stop scale?

Bob Salomon
28-May-2010, 13:57
Rodenstock's instructions were to remove the rear group, not the front. That way those delicate shutter and aperture blades are protected and the shutter is less likely to be bothered by dust, dirt, smoke or other pollutants

However, a Rodenstock Sironar 210mm lens converted to a 420mm f11 not a 300mm when the front group only was used.

And you don't switch groups around to convert.

IanG
28-May-2010, 13:58
Since 300mm is about 12", that makes no sense; with most convertibles you remove the front lens group, but go ahead and try taking off the rear group and see what happens...you should still have plenty of bellows to focus at infinity with the remaining lens group on either the front or rear of the shutter.

Not with early Sironar's unlike Symmar's they weren't simple symmetrical convertibles.

Ian

Peter K
28-May-2010, 14:41
And you don't switch groups around to convert.
Are you shure? A rear diaphragm increases spherical abberation and pincushion distortion.

With the Symmar convertible the focal lenght increases 1.75x without the front group. So a Symmar 210mm without front group has a focal length of 370mm.

Pawlowski6132
28-May-2010, 15:06
Ok, here's what I have:

Schneider-Kreuznach
Symmar
1:5,6 / 210
1:12/370

That's what it reads on the lens.

Omn the Synchro Compur shutter thre are two sets of apertures; one silver and one green. The green set corresponds to the 370.

Also, just measured and my bellows fully extended are around 18" or so. I'm not really sure where to start and end the measurements on the camera itself. Shouldn't I be able to use the lens at 370?

Also, can anyone comment on the reputation of this lens? It came with the camera and I've known no other lens. I don't want to get on the "glass is always greener" merry-go-round but, would like to know if I can do much better with regards to resolving power. I like a lot of deatil in my portraits.

thanx,

Joe

Peter K
28-May-2010, 15:21
With the rear element on the front the needed bellows extention decreases only a little bit but as mentioned before the performance decreases too. So you will need either a longer bellows or an extension tube.

Mark Sampson
28-May-2010, 15:22
You remove the front cell to make it a 370/12. Due to some optical property I don't quite understand your bellows draw will be more than 370mm @ infinity. As a 210, it's a very fine lens. More modern multi-coated lenses will have more contrast, but your resolution should be more than sufficient. Converted to 370, I would think that the corners of your images will not be as sharp; this usually doesn't matter in portraiture, and Schneider's recommendation at the time suggested that the converted f.l. was meant for that. The only real answer to your questions about resolution, etc., is simple: "Try it".

Jan Pedersen
28-May-2010, 15:35
Mark is spot on. Converted lenses (Rear group only) Requires more bellows extension than a lens with the combined focal lenght. A rough guess is about 450mm for your 370.

Peter K
28-May-2010, 15:54
A rough guess is about 450mm for your 370.
A realy good guess, it's 445mm.

The Symmar 210 is mounted in a shutter size #1 so rear and front cell have different threads. :o

Chauncey Walden
28-May-2010, 16:06
So, with 18 inches of bellows (454mm) you should be able to focus at infinity but not much closer.

Bob Salomon
28-May-2010, 16:11
Are you shure? A rear diaphragm increases spherical abberation and pincushion distortion.

With the Symmar convertible the focal lenght increases 1.75x without the front group. So a Symmar 210mm without front group has a focal length of 370mm.

Yes I quoted from a Rodenstock data sheet on the Sironar lenses from when they were current.

Jan Pedersen
28-May-2010, 20:17
A realy good guess, it's 445mm.

Once in a long while we get lucky. :)

Scotty230358
7-Jun-2010, 14:01
I have exactly the same problem with a Schneider 180/305 covertable. Apprently I need about 370mm of bellows draw to use it as in its coverted state. As my camera only has 340 bellows draw max I'm stuffed. Symmons suggests in his book "Using the View Camera" that convertables work quite well in their shorter configuration but performance drops off quite markedly when coverted to the longer focal length.