Symmar 360mm/620mm convertibile bellows extension

[Ales']

Hi, Im buying my first 7x17. It shoud arrive in soon. Now im buying lenses. I have 305 g claron and 508mm f7 ilex.
To fill and you extend the range of focals available, i was considering symmar 360mm/620mm. Ad for coverage Forums says that both 360mm and 620mm cover 12x20. So coverage is no problem for 7x17.
My doubt is Max extension on 620mm on infinity. My camera will have 620-640mm of extension. Plus I can order top hat lens board to further extend focusing range.
But before I buy this expensive lens
Did anynone tried it using only real cell? What is the distance between shutter and film plane at infinity?

 

[Daniel Stuefer]

I've only used shorter symmars, and never measured the actual distance, but I do know from experience that you need noticeably less bellows extension when using the front cell rather than the rear cell - simply because the optical centre will be a few cm further forward. So if you use the front cell, it should be fine (optical centre will probably be 2-3cm in front of the lens board in that case, which means you should need about 590-600mm of bellows).

 

[Ales']

I've only used shorter symmars, and never measured the actual distance, but I do know from experience that you need noticeably less bellows extension when using the front cell rather than the rear cell - simply because the optical centre will be a few cm further forward. So if you use the front cell, it should be fine (optical centre will probably be 2-3cm in front of the lens board in that case, which means you should need about 590-600mm of bellows).

Sadly, in order to achive 620mm on this lens i have to unscrew the front element

 

[Daniel Stuefer]

Symmars are symmetric. It does not matter which element you unscrew.*

It also works with every other lens of the same design, even if the convertible nature of it is not advertised.

*edit: sharpness and rendering may differ a little between the two configurations, as the lenses would be flipped in the two different configurations (like when reversing/not reversing any other lenses). Focal length, however, is the same no matter which way around your lens is - for any lens.
Therefore, 620mm will be achieved with either lens group, but exact characteristics might be slightly different due to orientation. It will (most likely) be noticeably softer than the lens at 360mm either way, as is the nature of these "converted" optics.

 

[Daniel Stuefer]

To satisfy my curiosity, I measured bellows extensions my 180/315 symmar:

Normal: 15cm
Front cell only: 25.5cm (+10.5cm)
Rear cell only: 41.7cm (+26.7cm - way more than I had remembered/expected!)

Field of view is exactly the same between front/rear cell (as it should be). As a saving grace for the rear cell - it was noticeably sharper wide open (judged from the corners). At f/45 I couldn't tell much of a difference by eye (I didn't do film testing as I don't feel like wasting sheets on this right now - nor do I have the time to do this with a proper setup).

As a conclusion: I don't think you'll be able to focus the 360mm symmar with only the rear cell with 620-640mm of bellows extension. At the cost of some sharpness, the front cell will most likely work fine.

 

[PetrL]

According to the attached catalog, a 760mm bellows extension is required for the Symmar 360 and using only the rear lens element.

 

[Ian Grant]

The older Symmar lenses are not very sharp when split, Schneider suggests for Portraits particularly wide open - a soft focus lens.

I'd look at better lens options.

Ian