Schneider Symmar convertible 150mm lens questions

**Pere Casals** · 19-Mar-2019, 07:04

Originally Posted by Dan Fromm

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

The early symmars had 3 aperture scales for each of the two cells alone and for the full assembly, those those were of (related) Dagor design, IIRC. I tested the front cells alone of the plasmat type at it looks as good as the rear cell alone, but then the aperture scale has a shift ...

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This is the dagor type, showing that the scale for the front lens alone is shifted some 1/3 stop, so we should expose 1/3 stop longer to compensate. I gues that the plasmat type needs similar compensation if using the front cell alone, at least this would be the starting point.

Originally Posted by Daniel Unkefer

If I remember correctly

, using an orange filter will help as well, when using only the rear cell.

This has been said, but C.Perez tests include the Symmar 150 conversion with and without a yellow filter, showing no benefit from the filter usage. This was not a lab test, but it's good enough to deliver interesting information.

For the converted configuration, results in that test suggest that chromatic aberration is not the problem, but spheric aberration in the corners when wide open that lowers performance to 20 lp/mm in the corners, reaching 30lp/mm in the corners by f/22. ...while the center and mid of the conversion is always very good at around 50 lp/mm, not bad.

So IMHO the conversion it's pretty operative, with corners a bit softer, which it's irrelevant in many images. For portraits sure it's irrelevant. For landscape we may have the sky in the two top corners, and we may have water in motion in the botton corners...

Then, if we use for example the symmar 210 converted to 370mm (because of the larger circle) for 4x5 we don't take the outer boundary, so the image it's really good even in the 4x5 corners, being a very lightweight choice.

Those old symmars are a piece of gear.

**Corran** · 19-Mar-2019, 08:24

Originally Posted by B.S.Kumar

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

I wondered about that too, and I'm really not sure the effect. It's been years since I played around with doing such a thing, and I just can't remember.

Originally Posted by Dan Fromm

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.

Interesting that the older Symmar is in #1, I never noticed. My newer APO Symmar is in #0. Anyway, I don't remember what lens I tried that on, so never mind about that idea.

**Daniel Unkefer** · 19-Mar-2019, 19:43

Really old Symmars were Dagors, before they were Plasmats. F6.8 aperture should offer a clue: also the cell configuration.

**wfraser** · 22-Mar-2019, 15:58

So I did a bit more research myself, and according to Schneider, when using just the rear element, the distance from the film to the lens board is indeed quite a bit longer than the focal length. Even when accounting for the length of the rear element itself, so the nodal point must be behind the lens when in this configuration.

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For the 150mm Symmar, the focal length being 265mm, the lens has to be racked out to 325mm for infinity focus. The rear element is only about 30mm long.

**Pere Casals** · 22-Mar-2019, 19:08

Yes, it should be behind...

**Mark Sampson** · 22-Mar-2019, 22:41

I used to have a Schneider brochure from 1972 or so, announcing the new Symmar-S lens line. In it they explained that they had given up the convertible feature in order to achieve better performance with the lens groups combined. Seems believable. At Kodak we had a 300mm Symmar-S that had amazing resolution, but I never tried using the rear group only, a la the earlier convertible lenses. Would have been interesting to see.

**Pere Casals** · 23-Mar-2019, 00:59

Originally Posted by Mark Sampson

Symmar-S that had amazing resolution, but I never tried using the rear group only, a la the earlier convertible lenses. Would have been interesting to see.

Mark, it delivers a very soft image, because cells are not individually corrected. The rear cell is uncorrected que in the inverse sense than the front cell, the compensation ends in a corrected system.