Schneider Symmar convertible 150mm lens questions

[wfraser]

Hello! Long time lurker, first time poster!

I just got myself a Schneider Symmar (not Symmar-S or APO Symmar, just plain Symmar) 150mm f/5.6 lens, which the serial number ages as 1967 or 1968, and I have a few questions about its convertible nature.

As a 150mm lens, it's great, and using it is pretty straightforward. But part of the reason I got it is because it's also supposedly usable as a 265mm f/12 if you remove elements of it.

In its normal 150mm configuration, yep, I rack the bellows out about 150mm from the film plane and yep it's in focus.

If I remove the front element, I get a good deal of magnification, but it now needs to be racked out somewhere in the neighborhood of 300mm for it to focus, which is beyond what my camera can do without rear movements.

If I remove the *rear* element of the lens, I can set the it about 190mm away from the film for some modest magnification.

I'm a bit confused. I was led to believe that in fairly simple lenses, the focal length is approximately equal to the distance of the lens from the film. And in the normal config of this lens, it matches that perfectly. But neither of its "converted" configurations is close to its 265mm rating. Why is that? Also, which one is the "correct" conversion for this lens?

[Corran]

The rear element is the one to use by itself for the longer focal length. Since the rear element is behind the shutter, you have to use more bellows because the lens is physically closer to the ground glass. In other words, if you measure it again from where the rear element actually is, then it should be around 265mm as you expect.

On some shutters, both the front and rear threads are the same size/pitch. Therefore, you can unscrew the rear element and put it on the front, reducing the bellows draw needed. I don't know about your shutter in particular. I have a 150mm Symmar here in a Linhof shutter and that doesn't work, so YMMV.

[Mark Sampson]

The correct conversion is to remove the front group. The optical experts here will be able to explain why the bellows extension is longer that way. If you use the front group alone you'll get some pretty soft and disappointing images. I tried that once with a convertible 180 when I had no one to ask. Later I tried the rear element alone, at f/22, and it was good- better than I'd been led to believe. BITD people told me that Schneider intended the longer f.l. to be used for portraiture, where corner sharpness is less important. I don't know if that's true. Best of luck!

[Pere Casals]

This is effect is well known...
The nodal point of the full lens is aprox in the lensboard plane

A cell used alone has the nodal inside the cell,

You may use a tube extension to extentnyour draw

The green aperture scale is for the rear cell alone, the front cell alone has no aperture scale

Stop to f/22 for sharp corners with the conversion

It's an excellent glass...

[wfraser]

Ahh, that makes sense! I was measuring to the lens board, and sure enough, the rear element protrudes about 30mm behind that.

> Schneider intended the longer f.l. to be used for portraiture, where corner sharpness is less important.

Great, that's exactly what I intend to use the longer focal length for!

Thanks for the answers!

[Pere Casals]

Something else, the conversion may have some focus shift, so after stopping the lens you should check focus gain, focus may change a bit, the full lens doesn't have that issue.

[B.S.Kumar]

On some shutters, both the front and rear threads are the same size/pitch. Therefore, you can unscrew the rear element and put it on the front, reducing the bellows draw needed. I don't know about your shutter in particular. I have a 150mm Symmar here in a Linhof shutter and that doesn't work, so YMMV.

Unless the lens cell is symmetrical, wouldn't that "reverse" the lens? The element that is supposed to face the film would now face the subject...

Kumar

[Dan Fromm]

On some shutters, both the front and rear threads are the same size/pitch. Therefore, you can unscrew the rear element and put it on the front, reducing the bellows draw needed.

In the Compur/Prontor/Copal standard, the #1 shutter is asymmetric. The other sizes have the same threading front and rear.

Schneider recommends removing a jes' plain Symmar's front cell to get the "half-lens'" focal length.

[Daniel Unkefer]

If I remember correctly , using an orange filter will help as well, when using only the rear cell.

[pepeguitarra]

I have the lens and I have used both the 150mm and the 265mm (rear element only). In both cases, I found them to be very sharp and easy to focus on the Intrepid 4x5. The filter is not a bad idea. I was advised not to used the dual system because it exposes the inners of the lens and the shutter to dust. Since I now know that, I take precautions.

20190224_161024 by Palenquero Photography, on Flickr