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ruilourosa
27-Apr-2014, 06:52
hello

Could someone confirm me that any longer symmars or plasmat tipe lenses convert into longer lenses by removing the front element out of the shutter?


Thanks

Rui Lourosa

ruilourosa
27-Apr-2014, 08:09
well, they do of course, but are there any data in what focal distances will they convert, im specially interested in lenses over 400mm,

thanks again

rui

Bob Salomon
27-Apr-2014, 11:17
Rodenstock's instructions for the Sironar was to remove the rear element to convert it. This also, of course, help protect the shutter and aperture blades from damage.

ruilourosa
27-Apr-2014, 11:36
Well there are lenses that work both ways, but what i was looking for is some kind of data sheet that shows what are the focal distances for each cell... im looking for a long decent lens

thnks

Rui

Bob Salomon
27-Apr-2014, 13:01
Well there are lenses that work both ways, but what i was looking for is some kind of data sheet that shows what are the focal distances for each cell... im looking for a long decent lens

thnks

Rui

A converted Symmar or Sironar is not a decent lens when converted. They also need a lot of bellows extension.

djdister
27-Apr-2014, 13:43
Well there are lenses that work both ways, but what i was looking for is some kind of data sheet that shows what are the focal distances for each cell... im looking for a long decent lens

thnks

Rui

I don't know if anyone has gathered all manufacturer data together in one place. For convertible lenses (that were meant to be convertible), you could check on the specific lens brand, i.e. Schneider or Rodenstock, or etc. The Schneider website has data for "Vintage" Schneider lenses for example. If you look at convertible lenses for sale on ebay, a front shot of the lens shows the different focal lengths.

ruilourosa
27-Apr-2014, 14:46
bob... my standards are quite low... im doing direct positives and i would apreciate a fair amount of aberrations... :)

thanks for the answers

cheers

rui

RichSBV
28-Apr-2014, 11:00
It's been years since I researched convertible lenses, but I have many and love them more than any other.

My first suggestion would be an old Turner Reich. Triple convertible with the 12/19/25" being very common. If you get a decent one, they perform very-very well, even with a bit of balsam separation around the edges.

The old Daggors are also convertible but for some odd reason they go for much more than they're really worth...

Next would be a Symmar. The old convertible ones used to be common and work extremely well standard and pretty good converted. You'll find all Symmar convertibles as f/5.6. Back when I found that the Symmar-s (f/5.6) lenses are the same AND convertible. They just stopped advertising them as such which saved them (and made them) a lot of money.

There is a simple formula for combining the two cells focal length to find the combined focal length. I don't remember it but have it laying around somewhere.

I have never seen a compiled list of convertibles and their cells. Goof luck with that. If you find one, let me know!

For me, I would grab an old Turner-Reich and be happy with it. Oh, wait... I did ;)

RichSBV
28-Apr-2014, 11:06
I wanted to add:

If you buy a lens that is not marked on the shutter with the converted lengths and f stops, you can figure it all out yourself. You can actually measure the effective llens stop through the lens with a controlled light source (nighttime lighted white wall for instance) and measuring off the GG. You can also directly measure the size of the stop and use the formula against the length of the lens.

Finding the length of the lens is as simple as focusing at infinity and measure the distance from the lens to the film...

I did an f-stop ring for one of my lenses years ago by measuring off the GG and it worked just fine. Paper label and pencil was all that was needed for the shutter.

Remember though that if you use the rear cell (removing the front), you can add a good 3 inches to the bellows draw for the focal length!

Randy Moe
28-Apr-2014, 11:40
Mmm, I guess I need to try this on some lenses. I do have the bellows for almost anything...

Anybody try a Cooke or Artar, converted?

Seems aberrations are hip.

ruilourosa
28-Apr-2014, 12:07
Well, thanks for the answers, i find i have a plasmat tipe 300mm nikkor w and it is convertible, the front cell as a focal distance of around 800 or 900mm that probably will do, if i need it shorter i will add a close up in the other end.



i think almost all lenses are convertible (even if its just with one cell) probably with different grades of quality...

thank you very much

rui

IanG
28-Apr-2014, 13:20
i think almost all lenses are convertible (even if its just with one cell) probably with different grades of quality...


Most of us would expect high quality results from a lens when converted to single cells, I think Bob Salomon hit the nail on the head with his comment "A converted Symmar or Sironar is not a decent lens when converted."


However using single cells from a lens may well work if as you say aberrations are not an issue, but that doesn't mean that lens is convertible.




Mmm, I guess I need to try this on some lenses. I do have the bellows for almost anything...

Anybody try a Cooke or Artar, converted?

Seems aberrations are hip.

The Cooke convertible is similar to the Turner Reich (except higher quality) and fairly good converted, the American chappy shot in Yosemite with a Cooke XV convertible and wrote about it in his Bibles :D

I don't have an Artar but I do have the front cell (only) for a 300mm Apo Ronar and if one of my cameras has enough bellow extension might try it. It does form a sharp image on a wall..

Lomography and their poor quality cameras has made aberrations hip :D

Ian

ruilourosa
28-Apr-2014, 13:46
Im not interested in lomography and im not planning to be hip in the near future, im constructing a trailor camera to produce wet plates and daguerreotipes and trying not to spend a lot of money (or at least be reasonable with it). Since the images are not to be enlarged a minor amount of aberrations or lack of quality wont mind, at least in ths beta stage im in, i am trying to build some lenses that could do the trick or adapt, i aleready built some chevaliers achromats, steinheil periskops and rapid rectilinear type lenses, but a convertible would have an edge since im working in a quite empirical way (and having some success). I think in the future i will have to spend a bit of money in a proper long lens... but in the meantime i will try with some other not so good materials... quem no tem co caa com gato...


cumprimentos e obrigados

thanks

rui

Delfi_r
28-Apr-2014, 14:08
I have a 5,6/210 mm Symmar, the rear element it's 12/360 mm, but the bellows draw is around 430 mm at infinity.

I haven't tested it yet, but as soon as I can share something...

ruilourosa
28-Apr-2014, 23:40
thanks!

Merci!