my convertible lens/filter size solution

[epatsellis]

I'm the first to admit that if I don't carry around little notes, I forget things. I came up with these labels that I put on nearly every lensboard (on the side, with the filtersize upward) now, and it saves me tons of time. I no longer have to either rmember which adapter to use with which lens, or what the converted aperture is on my Sironar, Componon or other lenses that just scream "try me converted, go ahead"

Does anybody else need something like these? I can make them cheap enough that it wouldn't be much more than a buck for a few of them?



erie

 

[jstraw]

Are lenses that aren't designed as "convertible" by way of swapping front or rear elements convertible by removing front or rear elements? Or are these lenses that are designed for conversion via removal?

 

[epatsellis]

Depends on the design, my Sironar is in fact triple convertible, though the 450mm is the only "official" conversion. Tessar designs are convertible by removing the front element, IIRC.

I find that remembering the focal length and f stops for each lens gets troublesome, so the other night I finally printed some of these labels up, and thought I'd share the idea. So far, it's saved me at least 5 mins looking for an adapter ring today alone.

Interestingly, for a short time I had a 360 5.6 Symmar and I still have my 360 5.6 Componon, any way I could measure, they are the same lens, I've shot the same suject with both and you cannot tell the negs apart. If there's a difference between a Symmar (supposedly corrected for infinity) and a Componon (corrected for 20:1) I can't see it, maybe it only manifests itself on a magical optical bench. I just bought a 180mm Componon-S on ebay, I plane to replace the elements on my 180 Symmar, I'm reserving judgement til I have negs in hand, but for $55.00, I either have another enlarging lens or a nice multicoated 180mm lens for the 4x5.


erie

 

[jstraw]

How can I find out if my lenses are convertible? Is there any kind of guide anywhere?

 

[epatsellis]

Google, or alternately, the remove an element, see if ti's a postiive element (i.e. acts as a magnifying glass) and see if it focuses the sun or distant object, that approach will get you an approx. focal length as a starting point. (if you have the bellows length, focus at infinity, measure gg to lensboard distance, then focus on an object 1:1 ( I use 2 rulers, one to measure, one to shoot) and measure the extension, the difference is your focal length)

erie

 

[jstraw]

thanks for the insight

 

[Ole]

Tessar designs are convertible by removing the front element, IIRC. ...

YRW... Tessars are wholly unsymmetrical, and not convertible. Only the more symmetrical lenses can be said to be convertible - Plasmats, Dagors, some Protars, Double-Gauss, Dialytes, etc.

 

[epatsellis]

Quite true Ole,
I should quantify that, removing the front element of some of the tessars I have turns them into wonderful soft, uncorrected lenses. YMMV


erie

 

[Ole]

That's right - Tessars have all the corrections in the front, and all the focussing power in the rear cell. That doesn't make them convertible, though - they just go "bad" without the front cell.

Q.v. what I said about some Protars: Most of them will still focus light if one cell is removed, but only the Serie IV (Zeiss Jena only, not B&L) and Serie VII were made as convertibles.

 

[epatsellis]

yes, but as a long ago ex girlfriend once told me, "sometimes bad is good"

erie

 

[jacobus]

That's right - Tessars have all the corrections in the front, and all the focussing power in the rear cell.

Ole, this statement sounds rather strange to me.

Even if a Tessar had nothing but a flat piece of glass for its rear cell - which is definitely not the case - not "all the corrections were in the front" as any glass within a lens will diminish or enhance aberrations. And no front focussing would be possible with a Tessar if "all focussing power [were] in the rear cell".

Uli