sironar-n - 5,6 - 150mm out of focus

claudius · Oct 31, 2018

i bought this lens some time ago from a proff photographer, looks like new,
but i have always had troubble with the focus,
under the front element there is one small distance ring towards the copal 0 shutter.
could it be that it is NOT supposed to be mounted ?
can this ring be mounted under either front / back element ?

i have checked the groundglass for the correct filmplane distance.
any solutions anyone,

thank you
klaus
denmark

E. von Hoegh · Oct 31, 2018

How do you focus? Using a loupe focussed on the texture of the groundglass, can you get a sharp image?

shutterfinger · Oct 31, 2018

There is a diagram for the lens at http://www.prograf.ru/rodenstock/largeformat_en.html
The vertical dash line is the aperture. Note that the Macro version has the aperture shifted toward the rear.

claudius · Nov 1, 2018

thank for reply.
i am using a linhof angel wiever and 4x loupe. and doing my very best to get sharp image on groundglass.
i belive i should worry about the mounting distance in the shutter.

anyone with knowledge on the proper shutter / lens dist.??

shutterfinger
i looked at the lens layout, but unfortunately not very helpfull.

klaus

M. Axel Wikstrom · Nov 1, 2018

The Copal shutter should space the front and rear elements 20mm apart (+-0.025mm). The spacer (the "distance ring" you describe?) may have been put there to correct for discrepancies in the shutter or lens. Try it with and without the spacer installed. It that doesn't help, then maybe the rear element is not the correct one for that lens. The Sironar should be a sharp lens.

Just a thought; maybe the spacer was put there to make the lens soft for portraits. Try without.

Ian Grant · Nov 1, 2018

I've seen issue with cameras where a frsenel has been removed, or one added incorrectly causing focus issues as registrationis incorrect..

There's no shims used with my 150 Sironar N, they are more common on WA LF lenses where spacing is far more critical.

Ian

KenS · Nov 3, 2018

claudius said:
thank for reply.
i am using a linhof angel wiever and 4x loupe. and doing my very best to get sharp image on groundglass.
i belive i should worry about the mounting distance in the shutter.

anyone with knowledge on the proper shutter / lens dist.??

shutterfinger
i looked at the lens layout, but unfortunately not very helpfull.

klaus

Klaus,
Might I suggest that you take a 'close look' at the ground glass just to MAKE SURE that the 'rough 'face' is towards the lens... otherwise you'll AWAYS be out of focus with the film plane. I have seen an old Crown Graphic with this very same problem

Ken

bernard_L · Nov 3, 2018

claudius said:
but i have always had troubble with the focus,
under the front element there is one small distance ring towards the copal 0 shutter.
could it be that it is NOT supposed to be mounted ?
can this ring be mounted under either front / back element ?

Wrong spacing might turn this into a soft focus lens. And that remains unproven. But, if what looks in-focus on the ground-glass is out-of-focus on film, then you have a problem not with the lens, but with the ground glass, as suggested by Ian Grant and KenS.

Make a test with a focus target; You can buy them, but just as well DIY. Use a tape measure or ruler, seen by camera a a 45° angle (approx.). Arrange to have a known point of the ruler (50cm, e.g.) at, e.g., 1m from the lens. Focus on that point. Develop film. Is that chosen point (e.g; the 50cm mark) the sharpest part of the tape measure? If not, you have a discrepancy between your ground glass and your film plane, and you should not blame the lens.

Ian Grant · Nov 4, 2018

Klaus, do you use other lenses with the camera, if so I assume they are sharp.

If not is a fresnel screen fitted, if one's been removed and the ground glass screen not shimmed, focus will be compromised, or maybe screen and fresnel fitted the wrong way around. This differs between makes. some are fitted permanently below the GG (lens side) others are the viewing side. I've seen and sorted out 3 cameras with issues like this, Also Chamonix made a mistake when they first started using Fresnel screens and didn't alter the ground glass screen frame to allow for the fresnels.

Ian

AgX · Nov 4, 2018

I only found the "Apo-Sironar N 5.6 150mm" in my listings. It got an overall length of 51.0 mmm. A additional shim would have changed that distance.

claudius · Nov 7, 2018

sorry guys, i have been off the net a while.

thank you for all input.

to resume on these:
i have no/few problems with other lenses ( Rodenstock 90mm and 210mm)
i checked the dist to groundglass ,with a depth michrometer, on the ground side, it is the same as film plane.
I took this filmback out of a contraption made for the graphical industry, no need to change/alter groundglass there.
checked the shutter with michrometer, space is 20,02 mm
the fitted distance ring ( shim) is 0,02 mm.

i dont think the spacer itself is the reason for out of focus problem. Agx has same lens, but in APO, with 21 mm distance.
maybe someone has put a wrong element in the shutter instead of the original ?
i will make the test photo with a large ruler soon. .
swap the elements with a 150 mm xenon. if the shutter is the same dist.?

klaus

claudius · Nov 7, 2018

sorry,
AGX is 51mm overall, i misread it as 21mm dist.
klaus

shutterfinger · Nov 7, 2018

If you disassemble either the front group or rear group the elements shapes should match the diagram linked to in post 3 and be in the same orientation, spacing should be similar. Out of position elements or reversed elements tend to stick out like a sore thumb. Now what I do not know is if the front and rear elements are interchangeable with one another, if not its possible someone had both groups disassembled and inadvertently/intentionally transposed front to rear element(s).
F1, f2, F3 - front group. R1, R2, R3 - rear group. A - aperture.

P.S.
the fitted distance ring ( shim) is 0,02 mm
.02mm=.005 thousands.
Its a shim for proper spacing and probably should be there. It should not be the problem unless its on the wrong side of the shutter.
What is the distance from the rear most part of the front group to the shutter blades?
What is the distance from the rear most (internal) part of the rear group to the aperture blades?

lobitar · Nov 7, 2018

I feel it's always a good idea to post a picture of the problem area - that is the front and rear elements unmounted. For instance many of us old hands would be able to tell if something suspicious with the elements. If the back element's not original, or the like.

AgX · Nov 7, 2018

shutterfinger said:
It's a shim for proper spacing and probably should be there. It should not be the problem unless its on the wrong side of the shutter.

If such shim would fit flush at both sides, then it would not matter on which side it is, as the distance between front and rear group would remain the same.

claudius · Nov 16, 2018

sorry for my absence, i took a common cold.

i found the calamity, and i am a little embarrised.
i were only metering all possible ways and failed to take a look at the camera as a whole.
it appears that the groundglassback is not a original part of the back on the camera,
resulting the springloaded back not to fall flat when removing the film holder and start focusing.
problem only shows with full open aperture .
a failure hardly visible unless you know what to look for.

now using another cameraback, no problems.

thank you all for all your concerns
klaus

AgX · Nov 16, 2018

Missing the forest for the trees...

sironar-n - 5,6 - 150mm out of focus

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