How do single focus anamophic lenses work

[Nikkor]

I'm just wondering how the iscoramas,etc... differ from the double focus ones. Any lens diagrams?

[dhessel]

They have a variable power diopter in front of normal anamorphic elements that are fixed set at infinity focus. The variable diopter consists of a Plano-concave lens all the way towards the front then a Plano-convex lens then the anamorphics. The focus ring moves the the two Plano lenses closer and further apart varying there power. When the two Plano lenses are touching they have a 0 power when at their max they have a .5 power in the case of the iscos. The design and concept is simple but finding lenses large enough to work on anamorphic adapters is not easy. I have tested and seen this first hand on an isco and with some cheap demostration lenses and was able to make it work with a Kowa. It worked in concept but the quality was not so good. Also in theory the lenses I used should have had a 0 power when together but they didn't so it lost infinity focus. 

[tonydtv]

Is that what Isco has patented? Seems like a very simple optic setup...

[dhessel]

I took my 54 apart and that is exactly what is inside, no more no less. I was able to repeat the design on a Kowa and it worked as expected in that I could focus just by moving the plano-concave lens. Getting a high quality result that works flawlessly is the tricky part that may or may not require some customization. The elements look like regular plano-concave and plano-convex lenses but that doesn't mean that they aren't in some way a custom design by Isco. 

[JohnBarlow]

Referring to ISCO patents, the trick is in the balance between lens curvature and glass index, and, unfortunately, that's where things start to get expensive. Custom glass with custom index is very pricey.

 

Some time ago a poster asked about replacing the front glass on a 54. After some enquiries, out of curiosity,  I discovered for this size optic the mould fee would be about $1500. Made from cast iron the quality would be bad at 60-40 scratch dig, so would need further tooling costs to polish it down to an acceptable 20-10. 

 

Basic conclusion was that it would be cheaper to purchase another 54 after all the messing about.

[tonydtv]

Interesting. I bought a junked Bell and Howell anamorphic adapter a while back, took it apart and it seemed to be the same setup if I remember correctly. I'll have to dig that one up again.