Sironar 240mm turns into a 700mm "lens" ???

[Daniel Grenier]

Hi guys.

A seller on ebay has a lens for sale and he states: "YOU ARE BIDDING ON A REALLY GREAT 240MM F5.6 RODENSTOCK SIRONAR......WHICH CONVERTS TO A 700MM LENS WHEN YOU USE THE REAR LENS GROUP ALONE...."

I've had one such 240mm Sironar for years and I've never heard this claim (till now) that it can morf into a 700mm by removing the front element !

If any of you have first-hand experience with this, care to share your thoughts? Namely what kind of quality do you get out of this 700mm "lens" ?

(I know, I know.... I should just try this myself but why waste the film if there's a ready made answer here).

[IanG]

I have an early 70's 150mm Sironar the shutters marked with a dual aperture scale so I decided to try just the rear elements. I was very surprised to find the focal length was very much longer than I expected somewhere around 400mm. (It's in Italy on loan or I could post the marked FL)

My other 150mm Sironar's are later versions and symmetrical like Symmars. Try yours and see, but the chances are unless the aperture scale is marked for both yours won't give 700mm.

Back in the 70's I tried shooting with a Symmar split but it's not as sharp, and you need to stop right down. You could get away with it on occasions but I decided it wasn't worth it.

Ian

[Steve Hamley]

No first hand experience, but reportedly some earlier Sironars were intended to do just that.

Steve

[IanG]

No first hand experience, but reportedly some earlier Sironars were intended to do just that.

Steve

These are also the early Sironars that de-laminate. So there won't be many around now.

Ian

[Bob Salomon]

Actually Rodenstock's literature for that series states that you remove the rear elemnet to convert it. Not the front element. This helps to protect the shutter as well as convert the lens.

Using the front element only the 240mm 5.6 becomes a 720mm f16.

When any of these types of lenses are converted the resulting lens is not something to rave about.

To quote the Rodenstock brochure for the Sironar from 8/75:
"....allows the front component alone to be used as a "telephoto lens". In this case, it is only necessary to unscrew the rear component. At maximum aperture the Sironar front component may be used as a portrait lens (if a Rodenstock Imagon should not be available). This "incorrectly corrected" system will add an artistic touch to the pictures. ...... optimum sharpness will be obtained between f45 and f64 (with the rear element only). At smaller apertures resolution will be degraded by diffraction.


For those who must know the following is the conversions when using the rear element only with the Sironar (pre N series).

105mm - 315mm f16
135mm - 405mm f16
150mm - 450mm f16
180mm - 540mm f16
210mm - 420mm f11 (may be a typo)
240mm - 720mm f16
300mm - 900mm f16
360mm - 1080mm f22

You will need lots of bellows for these lenses to focus to infinity when converted and don't buy the lens for its' longer focal length.

[Daniel Grenier]

..... will add an artistic touch to the pictures. ...... .....

Thanks kindly for the detailed info, Bob.

I'll try that when I want to ""add an artistic touch" to my pictures (so much nicer than saying 'will make your pictures fuzzy', don't you think ?)

[Bob Salomon]

Thanks kindly for the detailed info, Bob.

I'll try that when I want to ""add an artistic touch" to my pictures (so much nicer than syaing 'will make your pictures fuzzy', don't you think ?)

I think it is past fuzzy.

I used to try to use these things converted in my studio in the 60s using both Rodenstock and Schneiders. Not only are they less then crisply sharp they also require massive extensions which create other problems like adequate support to avoid vibrations. In many cases two tripods were required and then the whole thing became very cumbersome to use in the field and the infinity point was too far away to use in the studio and when used in the studio even more extension was required.

Best to buy and use them as unconverted lenses.

[Geert]

For those who must know the following is the conversions when using the rear element only with the Sironar (pre N series).

105mm - 315mm f16
135mm - 405mm f16
150mm - 450mm f16
180mm - 540mm f16
210mm - 420mm f11 (may be a typo)
240mm - 720mm f16
300mm - 900mm f16
360mm - 1080mm f22

You will need lots of bellows for these lenses to focus to infinity when converted and don't buy the lens for its' longer focal length.

Thanks Bob,

now I know why there's an extra aperture scale on my 210 Sironar!
Having experience with vonverting old Symmar lenses, I'm not tempted to use it that way. Too soft.

G

[IanG]

Thanks Bob.

My shutter actually has markings for 6 focal lenghts, but if you don't have the full information it's not clear. It's a Copal O and I guess the scale is common for 135mm,150mm &180 or 105.

But you quote- Front elements "....allows the front component alone to be used as a "telephoto lens". In this case, it is only necessary to unscrew the rear component. At maximum aperture the Sironar front component may be used as a portrait lens (if a Rodenstock Imagon should not be available). This "incorrectly corrected" system will add an artistic touch to the pictures."

But then this is rear elements ".... optimum sharpness will be obtained between f45 and f64 (with the rear element only). At smaller apertures resolution will be degraded by diffraction.


Thtat seems rather ambiguous. So they are saying you can use either ?

Ian

[Bob Salomon]

Ian,

Sorry. It should be with rear element removed. Front element only when converted.

People do use the rear element only but it does expose the shutter to possible damage.