Saturday, May 8, 2010

Xenotar Byron

Target for this month-- finish first batch of Xenotar Byron conversion, one for NY Jeff, one for myself..

To breaking the limits of original 110A/B front standard, to mount bigger size lens/shutter, I did try many ways to expand its ability, from beginning the target was to accept #0 shutter only, then by add additional spacer ring, now Byron accepts #1 shutter too, but due to the 'bottle neck' that spacer ring brings, some lens with big  rear element is limited.
Lens board study
150 Lens mount study

For even bigger lens like Xenotar 2.8/150, that mount on a #2 shutter (Yes! #2 shutter, not #3!!), I had to re-design whole front standard to take it. But at least initial test showed it is possible! see here:
Project I'm possible
The nearest distance Xenotar can get

Now, for a easier way to mount/un-mount this big eye, I need to develop another front standard/ lens board system, differ from the previous version.

They will be similar to normal view camera, with a somewhat rectangular lens board, and front standard will have a spring clip to lock the board.

The board, with maximun size of open hole to 60mm, Byron surely expands its lenses option, and since front standard extrudes a little bit, avoiding struts conflicting with shutter, so #2 shutter is possible too.

But the best thing this new system brings, is the opportunity to embrace 75mm wide angle lens without any difficulty. Previous version lens board takes 75mm too, but camera bed will block a little bit at one side, shading the image.
75mm lens on Byron

With new design, it may be no problem any more, but I need test first.

New system is specifically designed for big size lenses, it may not allow lens to stay in camera body when folded. I will try to keep the lens in, if lens board reverse the direction.

Oh, another minor thing, bellows needs new size too, for those big rear...

I got a Grandagon 4.5/75mm lens in #0 shutter, the one shown in image above,  a beauty.

New front standard/ lens board system plans to take this lens as wide angle end limit, not because front standard extruding or backward some distance, to avoid the blocking of camera bed, but by rising the lens a little bit.

It is about 7mm blocking on one side of frame, caused by lens backward too much thus camera bed shades the frame. It is no use to change lens board or front standard, because the distance requirement between lens and focal plane is fixed when focusing at infinity.

The only chance to avoid the blocking, is to rise the lens. 

I checked Grandagon data, it has 195mm image circle in f22, so there is plenty area to move.
Image above shows the reason one side of frame is blocked, 75mm lens is way too much backward, thus makes camera bed extruding and blocking the frame. On other LF camera like Technika, camera bed can be dropped a bit, to avoid the blocking, but Byron can not drop the bed.

Another way to solve the problem is by rising the lens a bit, makes less blocking area, thus eliminates the shading in negative area.

This way works in two conditions, 1. lens image circle is big enough for rising. 2. lens rises enough distance.

195mm image circle is big enough for rising, the only problem is how high can we  rise the lens?
In new front standard/ lens board system, front standard opening size is big, 61mm in diameter! Even bigger than previous version's lens board (60mm). images above shows that a #0 shutter should be able to rise no less than10mm, I believe it should solve the blocking problem.

But again, I need the test to approve it.

And why 61mm in dia. opening? Well, I want to directly mount the lens, and Grandagon 75 has a 60mm dia. rear, that is why.

(16/05 add)
Just back from factory, lens board spring clip parts are so small, and complicated, very difficult to assembly, and I don't like the effect, need to find a simpler way to hold the board......

(18/05 add....)
Had reduced spring clip into one part only, with spring(s), and bolts.
(To be continued..)
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