How to use Symmar-S as a convertible...

[Ed345]

I've just got a Symmar-S 150mm 5.6 lens. It seems from searching around that although it wasn't marketed as being convertible like the earlier Symmar and there is no 2nd aperture scale it can be used as a convertible.

Removing the front element gives a longer focal length than the 150mm, and removing the back element gives a longer focal length again.

Measuring the distance from the lens board to the ground glass when focused at infinity gives distances of about 210mm and 300mm.

1) Are these the distances the correct focal lengths or does removing an element change the calculations?

2) Is there an easy way of working out the aperture scales for the new focal lengths, or is it case of physically measuring the aperture and knowing the focal length...?

Ed

[Bob Salomon]

It isn't convertible.

[Ole Tjugen]

Removing the front cell gives a rear cell which needs quite a bit more bellows extension than the focal length of the cell. The old 150/256 f:5.6/12 needs about 300mm extension with the rear cell alone focused at infinity - my guess is that the Symmar-S is rather similar.

[Bob Salomon]

Removing the front cell gives a rear cell which needs quite a bit more bellows extension than the focal length of the cell. The old 150/256 f:5.6/12 needs about 300mm extension with the rear cell alone focused at infinity - my guess is that the Symmar-S is rather similar.

Accept it is a different design and not convertible.

[Mark Sampson]

The long-lost Symmar-S brochure I once had explained that they had given up the convertible feature, in order to improve the performance of the whole (both cells) lens.
You could try using the rear cell alone, and figure that you're losing two stops (e.g. f/5.6 marked = f/11). It might be sharp enough for you at small stops, and your exposure should be reasonably close.
I took the rear cell out of a 180/5.6 convertible Symmar once, not knowing then that the front cell was the one to remove, and got some pretty blurry negatives. I'd say that's not worth messing with. When properly converted that 180 lens looked pretty good @f/32.

[Ole Tjugen]

Accept it is a different design and not convertible.

I think it is pretty clear that the Symmar-S is not a convertible. But in a forum full of people who use magnifying glasses, bits of old unidentified lenses or in best case old Petzvals far beyond their design limits, who can say what someone will find gives an interesting rendition of the subject matter?

The old convertible Symmar isn't very good as converted either. Expect some colour fringing near the edge, and sharp(ish) image circle might well be smaller than fo rthe complete lens.

There are some who want ultimate sharpness at all times, and others who like to have a possibility of "field modifying" a lens to get the focal length they need at the moment - or the optical defects they want at the moment. I have seen some rather interesting macro photos done with a "converted" Heliar on a Voigtländer Bergheil camera - published in Voigtländer's own photo magazine "der Satrap" in 1934. Just about any lens is "more convertible" than a Heliar...

[Ed345]

I was aware that using the lens without one of the elements would mean it wasn't at it's sharpest, and may be only suitable for soft focus portraiture. But it sounds like this may have been optimistic. I guess when the lens focused on a plane I assumed that it would be all fine if I stopped down a bit....

I may try it and see how just how bad it is on something non-critical and report back.