Tessar. What affect would a lateral shift of the front group have upon image formed?

[Roger Hesketh]

I have been having a play.

I decided to have a go at mounting some orphaned Eastman Ektar cells that I have utilizing the Jim Fitzgerald timber barrel technique.

http://www.largeformatphotography.in...ght=ektar+wood

He used Walnut I thought I might use teak.Then I remembered that I have a largish roller blind shutter to which the two lens groups could be mounted to either size. I started looking through some piles of photographic detritus that I have here for some bits and pieces to help me with getting the spacing of the lenses right and one of the things that fell to hand was the lens panel from an old field camera. (Sanderson I suspect). It has a rotating middle section and a panel across the middle of that which shifts from size to size.

The thought was that if the front group where mounted to that panel on the front of the roller blind shutter it would be possible if one so desired to affect a lateral shift of the front lens group in relation to the rear lens group. Obviously there would be a correct neutral position but it would be possible to adjust the lens position either side of neutral.

Now I know with some lens designs it is possible to get varying degrees of soft focus by changing the separation of lens elements and introducing differing levels of spherical aberration. I have no idea what affect a lateral shift of the lens elements might have though.

Your thoughts would be appreciated please. Is this lateral shift modification worth doing and what effects might it have?

Thanks in advance.

Roger

[Jody_S]

Interesting. I've made barrels out of steel (ran out of brass...) for a Schulze & Billerbeck Euryplan, threaded for the lens elements of course, but I never thought of making one out of wood! It's easy enough to experiment for spacing with steel, I just made the barrel 1/4" longer than I anticipated, threaded right to where the Waterhouse slot was to go, then ground the barrel down progressively until the image 'looked right' on the GG. In practice, I couldn't tell the difference between 'correct' spacing and 1/8" or so longer.

[E. von Hoegh]

I have been having a play.

I decided to have a go at mounting some orphaned Eastman Ektar cells that I have utilizing the Jim Fitzgerald timber barrel technique.

http://www.largeformatphotography.in...ght=ektar+wood

He used Walnut I thought I might use teak.Then I remembered that I have a largish roller blind shutter to which the two lens groups could be mounted to either size. I started looking through some piles of photographic detritus that I have here for some bits and pieces to help me with getting the spacing of the lenses right and one of the things that fell to hand was the lens panel from an old field camera. (Sanderson I suspect). It has a rotating middle section and a panel across the middle of that which shifts from size to size.

The thought was that if the front group where mounted to that panel on the front of the roller blind shutter it would be possible if one so desired to affect a lateral shift of the front lens group in relation to the rear lens group. Obviously there would be a correct neutral position but it would be possible to adjust the lens position either side of neutral.

Now I know with some lens designs it is possible to get varying degrees of soft focus by changing the separation of lens elements and introducing differing levels of spherical aberration. I have no idea what affect a lateral shift of the lens elements might have though.

Your thoughts would be appreciated please. Is this lateral shift modification worth doing and what effects might it have?

Thanks in advance.

Roger

Asymmetric aberrations, the type and extent of which I cannot even guess.

[Mark Sawyer]

If the elements are significantly off-axis from eaach other, the most obvious effect would be extreme coma, along with distortion, chromatic aberration, unflat focal field (probably not even a nice even curve), and God knows what other aberrations. Resolution will be reduced, and at the edges may just fall apart.

[IanG]

Interesting thoughts Roger, I have quite a few Roller blind shutters spare

You've given me an idea to make a new casing which will take Waterhouse stops and allow lens cells to be fitted either side of the shutter cirtain, thanks.

Ian

[Jim Fitzgerald]

Roger, this is an interesting idea. When I did my Walnut barreled 14" Commercial Ektar it never occurred to me that I might have a problem with lateral alignment. I guess I was having one of those days when everything was working in my favor. I'd try it again if I ever came across something like this again. The hardest part was getting some threads started in the walnut. let us know how it goes.