my LEX woes continued...
 

Not having any support from Letus, and with a very important project coming soon - I managed to make my Letus usable (far from perfect - the GG' stands pushed back in order to stop the whining, but at the cost of infinity softness; the GG not level but at least being able to fix the front tube on the rails, etc).

Now I am facing another problem: when setting the critical focus of my EX1, with GG stationary (and of course without lens), I cannot get the peaking to be even close to uniform over the whole frame. When it's on in the middle (only possible near the upper edge), it disappears at both sides; slightly turn the focus ring and it appears on the right side, but vanishes from the middle; it never appears on the left side!

Now, is this how the new, "improved" EX1 achromat is supposed to behave? I don't think so; in fact I have serious doubts whether mine is indeed the improved version (it came fixed to the main adapter body, not as a separate screw-on part). What do you think?

Another reason for non-uniform focus might be the GG is not planar; given the nature of push/pull actions involved in back-focus adjustment, and how crude and unstable that is - it almost seems impossible to ensure it's 100% planar!

And indeed - after I set it to peaking near the GG's middle area and put a lens on, my test shots exhibit considerable softness near the edges (particularly the right one - funny, because the left edge area has been impossible to achieve peaking at all, and yet it's much sharper with the lens on)...

Any comment welcome!

I'd be willing to bet that the GG position is the source of your focus problems. If rolling through the focus causes the peaking to move left/right, I'd say it is very likely the GG is shifted. These are very minute changes, and I'm honestly a little surprised about the crudeness of the adjustment. For some reason I remember Steve Cahill saying the improved Nikon mount has a depth adjustment?

-Sean

It does, kinda. You can push and pull it out slightly before you lock it down with the alen wrench