Hi,

recently, I was notified that Symmar designed lens can have their front or back elements use separately. For example, my APO-Symmar 210 f/5.6 can become a 370mm f/12,

my question is how to calcualte this resulting focal length and aperture?

and where can I find more information regarding this?

Any hints is greatly appreciated. Chin.

-- chin fan so (zcfs@home.com), November 09, 2001

Answers

Who told you the Apo Symmer converts.

The Symmar was a convertible design.

-- Bob Salomon (bob@hpmaretingcorp.com), November 10, 2001.

Sorry, Chin. The plain SYMMAR converts, the APO-SYMMAR doesn't.

-- Wilhelm (bmitch@home.com), November 10, 2001.

Hi all,

Thank you for the responses, I tried my Apo-Symmar, looks like it works, under the ground glass, the image is OK, let me process the film, may be it will be not acceptable.

Chin.

-- chin fan so (zcfs@home.com), November 10, 2001.

I have inadvertantly used an Apo symmra 240 without the rear element attached and it worked fine .. crisp and sharp at abotu 20 ft.

-- Ted Harris (slberfuchs@aol.com), November 10, 2001.

"I have inadvertantly used an Apo symmra 240 without the rear element attached "

Considering the size of the rear element how does one "inadvertantly" do this?

-- Bob Salomon (bob@hpmaretingcorp.com), November 10, 2001.

The real question here is not whether the APO Symmar (or another lens, for that matter) can or cannot be used as a convertible since it MOST DEFINITELY CAN BE. As Chin has found out, all you have to do is remove the front or rear grouping and you have a lens of a different focal length. That means it can be used as a convertible. The real question is if doing so will produce an acceptable image. Apparently, Schneider doesn't feel that the resulting image is acceptable, but that doesn't mean that someone else will disapprove. Chin, let us know the results or you test shots so the rest of us can decide if we want to try using our "non-convertible" lense as convertibles.

-- Ken Burns (kenburns@twave.net), November 10, 2001.

To answer Bob's question (I think you hvae heard this before in another forum) and shed further light ont he general discussion...last sunmmer I was at my sister-in-laws' wedding to her long term partner. We were staying in Port Jefferson, Long Island and I had some gear along to do some lighthouse shooting, etc. At the last minue she asked me if I would shoot the wedding. Unreliabel photographer, was afraid he wouldn't show till after the ceremony, etc.

I had nmy 90 mm Grandagon and 150 Apo Symmar and, mirable dictu, my 240 Apo Symmar. I hadn't paid much attention to mounting the 240 on a Technika/linhof board befroe we left NH when i switched it over from the Sinar board it usually lives on, frankly not even sure why I took it. Anyway I forgot the spacer ring so I couldn't get it mounted on my Phillips 4x5 without removign the rear element and mounting it that way. I was in the process of remounting it when the bride-to-be came charging up and told me I had a grand total of 10 minutes to shoot the formal shots. I took some real quick with my 690 Fuji then went back and finished setting up the 4x5 for the formal shots udner the rose arbor ..... you can figure the rest ... was totallypressured, forgot I had not put the rear element back on when I grabbed the 6x9. Set up, thought brieflyto myself how odd it was that I needed so much bellows extension but racked of 4-5 shots and got ready to do candids during the acutal ceremony (I HATE wedding photography). A half hour later when I went to breakd the stuff down and pack it up I realized what I had done as I saw the rear element neatly lying in my case on the lens wrap. thankfully I had bracked all the shots so exposue wasn't a problem.

When I got home Sunday I processed all the chromes and was quite surprised that I had more than decent shots with the front element only. I looked at three different chromes on my light table with a 4x luope and they all looked just fine. I would never do it on purpose and suspect that I would see a difference if they were blown up larger than 16x20 but these wee wedding shots and the biggest prints I had made were 8x10.

That's the story. yes it works. OTOH I remember when I used to shoot with a Symmar convertible and there is no way that it was as sharp as the lenses I am using now.

OK Bob you can stop laughing ....

Cheers,

Ted

-- Ted Harris (slberfuchs@aol.com), November 10, 2001.

Hi guys,

unfortunately, the pro-lab I usually go to close today, I'll have to wait til monday to let you guys know the result.

I stop down to f/22 which means the effective light is as dim as f/48, may I ask Ted what aperture u stopped down to?

Thank you. Chin.

-- chin fan so (zcfs@home.com), November 10, 2001.

Hi Chin .. I was bracketing 16-22-32

-- Ted Harris (slberfuchs@aol.com), November 10, 2001.

Any "positive" (Magnifying) lens can be used to make an image. The Symmar and Apo Symmar lenses are comprised of two positive lenses set up to be used at the same time. The nature of the way they work together has to do with the original design and intention of the engineers who developed it. The older designs were also represented as "convertibble" which recognizes that each separate lens group can also be used to make an image. Although that's still true with the modern version the manufacturer no longer represents it that way; perhaps because of the difficulty of explaining the feature and/or perhaps because the quality of image of the single element is not compatible with the intentions of the engineers.

This will work with any lens: Unscrew and look at and thru the lens group. If it works like a magnifier it will form an image. If it works like a "minifier" (makes the image of what you are looking at thru it smaller) then it cannot make a projected image or be used as a camera lens.

This is of the nature of experimentation by the individual photographer and good bad or indifferent results can be had. Like any modification or alternate use of any product the manufacturer leaves such uses entirely up to the owner and is smart to not have any advice about it.

-- Steve Grimes (skgrimes@skgrimes.com), November 11, 2001.

It is also possible to develop problems with the assembled lens if one is,'t careful. First there may be one or more shims that control spacing of the front and rear groups. These are easily lost if one isn't careful and misplacing or mis-installin these may effect lens performance. The threads in a shutter can be easily damaged by cross threading. Resulting in a major shutter repair - or replacement.

-- Bob Salomon (bob@hpmaretingcorp.com), November 11, 2001.

And jsut a quick addition to Bob's comments. The shims, spacers, etc. thta are required for use in one circumstance with longer lenses may not in another and cause further problems. When purchasing longer lenses (240 mm and up) mounted in large shutters you should always make sure the necessary spacers are present or readily available.

-- Ted Harris (slberfuchs@aol.com), November 11, 2001.

It looks pretty sharp to me under a 8X loupe, it's more than expected, it's acceptable to me, i think i will still use it that way.

Thank you all. Chin.

-- chin-fan so (zfcs@home.com), November 12, 2001.

one more, I don't observe any noticeable difference in sharpness campare to phots taken with or without the back element as long as it's stop down to f/16 or more

-- chin-fan so (zcfs@home.com), November 12, 2001.