Schneider symmar triple convertible (180/285/355) f/stop scale question?

[wdavidprice]

I'm looking at one of these that has been re-mounted in a Compur

shutter that does not have the three way f/stop scale, just the scale

for the 180mm. Does anyone have one of these with the three way scale

that I can get a picture of? I checked with Grimes on having one made

but they want too much for my budget. One more question...the plate

on the shutter I have shows f6.8 to f32...seems to me it should go

higher that that...any thoughts?

[mskovacs]

I haven't ever tried, but you can calculate the diaphragm diameter for a given f/stop and focal length and make your own. Without even placing a micrometer on the delicate diaphragm, you could calculate the positions for both focal lengths relative to the marked ones very easily with a quick spreadsheet.

 

f/stop = focal length / diaphragm diameter

[jim_rhoades]

If that's the one being sold on e-bay by camera$ it was remounted with the wrong scale. I asked them over a month ago to price it knowing that it would need S-K's work. They said, what you see is what you get. I would love to have that lens for my 5x7. But I crossed them off my list of who I would buy from.

[User_503771]

Does your lens have any original Schneider markings that would indicate that it's a *triple* convertible? I ask this because I've only rarely heard of such a beast, and have never seen one or seen a live example of one. There are many Symmar convertibles (two focal lengths) out and about; I have a couple of them myself.

 

In any event, what you need to be able to measure is the exit pupil, which is the image of the diaphragm at the rear of the lens.

 

Another way you can measure the apertures, which will work if you have a known focal length with known accurate f-stop markings:

 

Take the "known" lens, open it at "T" (or "B" held open with a cable release) and focus to infinity, trying to fill the field with good consistent light. Adjust the aperture to a couple of stops down from wide open (say, f/8 or f/11). Take off the back and take a meter reading. Keeping the meter at the same position, stop the open lens down until the meter reading is exactly one stop lower than the last one. Mark the spot.

 

Continue doing this until the aperture is stopped all the way down. Then check your reading at your initial aperture, and continue opening the aperture and marking 1-stop intervals.

 

This works surprisingly well!

[User_503771]

One more thing:

 

Once you have a light reading for f/8 (or whatever other stop you've decided to use), it will apply to a lens of any focal length, focused to infinity and pointed at a light of the same intensity.

 

So, you could conceivably focus your camera to infinity, then swing it around to a light source that you trust is consistent, and measure the light that way.

 

But the point is: At the film plane, the meter reading will be the same for "x" amount of light coming through at f/8, whether it's a 180 mm lens or an 1800 mm lens -- f/8 is always f/8. The light intensity will always be the same, at the film plane, from one lens to the next.

 

Hope this helps.

[ken_schroeder]

Check wisner.com. The site lists a millimeter scale for the convertible lens sets he sells. You should be able to adapt it for your lens and shutter.

[michael_briggs2]

<p><i>"Does your lens have any original Schneider markings that would indicate that it's a *triple* convertible? I ask this because I've only rarely heard of such a beast, and have never seen one or seen a live example of one."</i><p>

 

<p>It's likely that the lens being asked about is the one that was listed repeatedly over the past months on ebay, and which just sold. The factory writing on the front cell show three focal lengths: 180 mm f6.8, 355 mm f13 and 285 mm f12. The serial number 2,271,xxx dates the lens to late 1949 or early 1950 (<a href="http://www.schneideroptics.com/info/age_of_lenses/"http://www.schneideroptics.com/info/age_of_lenses/>http://www.schneideroptics.com/info/age_of_lenses/</a>).

It has the red triangle symbol that Schneider used on their first single coated lenses. This is a different Symmar from the more recent and much more common "convertible" Symmars which give a single extra focal length by removing the front cell.</p>

[steve_hamley]

You might find this post interesting. Look for Jim Galli's response about these lenses actually being triple convertible (asymmetric) Dagors.

 

http://largeformatphotography.info/lfforum/topic/499722.html

 

Steve