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Adjust focus on Iscorama fixed taking lens


M Joel W

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Hi, I'm working with an Iscorama pre-36 with a Nikon taking lens that came with the Iscorama. I assume (correct me if I' wrong) that the taking lens is meant to be focused at infinity? 

It's not. It's focused well past infinity. But there's no focus ring that I see to adjust it. I tried opening things up with a spanner wrench but quickly realized I was going to break something as soon as I removed one retaining ring and the rest didn't turn easily.

I can provide photos, but maybe someone knows something?

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I removed some bits to try to access the optical assembly... here it is with them put back on. You can see a scratch mark on the retaining ring where I tried to open it up with a spanner wrench. It didn't work so I left it. The scratch is just on the surface of the ring.

I think I'm very ignorant but I assumed I could just rotate the optical assembly within the threads in the lens and it would adjust the infinity focus. How does the aperture fit into this? I don't know how the lens is held together...

I don't like fiddling with infinity focus and I liked the idea of matched coatings and a pseudo-monoblock so I was hoping I could get this set and stick with it. I tried using it like this and it's focused way past infinity still. It's not just a tolerance error with the Nikon adapter, it's WAY off.

I also bought a 50mm 1.8 FL as a back up, though. This might be a fool's errand.

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Edited by M Joel W
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The taking lens for the Iscorama is meant to be at infnity always so it is set to Infinity focus with no focus ring. There is no point in having a focus ring on this lens since the the focusing is all handled via the anamorphic front. If it is not focusing at infinity then either your camera/mount adapter is out of spec or the lens needs to be collimated. The thing is anamorphic lenses like these require proper collimation, the anamorphic front and taking lens must be focusing in synch to get a sharp image. The front anamorphic block is set to infinity and is focused using a variable strength diopter infront of the anamorphic block, the taking lens must also be set to infinity to get a sharp image. I have don't know how to go about adjusting the focus on that lens but it will be difficult without a collimator.

This is probably a job for a lens tech but if you want to try yourself you can make a DIY collimator using an old film camera. I did this a while back to fine tune the adjustmens for a anamorphic lens that I have. First I attached a lens to an old film camera and focused to infinity using the VF. Next I locked the focus at infinity so I could no longer change it by accident. Then I  removed the shutter leaving the hole where the film would be exposted. I then made a focus chart using a printer and mounted that behind the hole where the film would be. I mount this camera and lens on rails infront of the lens I want to adjust that is attached to another camera so I can view its output. The cameras are setup so that the lenses are face each other. Last I placed a light behind the film camera with the film door open. You just look at the output from the camera with the lens you are adjusting and adjust the focus until you have a sharp image of the chart at infinity. 

This is definately not the most accurate way of doing it but was the best DIY solution I could readily come up with.

Edited by David Hessel
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That’s a clever DIY solution, David!

If it’s a simple enough adjustment you could just have the lens mounted to a compatible mount camera pointed at a distant object and kept checking through the viewfinder until the image is sharp. The problem is working out how to adjust the lens back-focus.

Normally a lens is focussed using double threads so that the inner optical block moves forwards or back without twisting, and the iris will have a long lever that connects the outer ring with the inner mechanism and slides through a slot as the inner part moves. This lens seems to be missing all that. I’m not really familiar enough with stills lenses to know what  it might originally have been.

Without examining it, I can’t tell how this lens has been locked at infinity, but I wouldn’t just start unscrewing lock rings. Some will hold in elements, others might control spacing between groups, etc. 

It might be best to take it to a lens tech and at least get an idea whether it’s easily adjustable. It might be fairly simple.

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