Letus extreme edge to edge Sharpness

balster

balster

Active member
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I am using the Letus Extreme with the custom EX1 achromat and just did some sharpness testing. I used one of my Carl Zeiss lenses, a 85mm with Nikon fitting. Great lenses by the way. Edge to edge looks good but I am not quite satisfied. Namely the right side of the screen makes me think because it won't focus with the rest of the screen. I would guess it's a ground glass issue. Any thoughts?

You can check the fullscreen image on my blog http://blog.s106.com
 
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I have the exact problem. The right side is a little soft. In addition, the GG shifted towards the right side more. Anyone else has any other suggestion?
 
hi myCharlie,

in response to your side note... wich effects do you mean?

back to subject;

anybody tried anything with the ground glass?
 
i think you can safely rule out the zeiss lens. the ex-1 has exhibited some weird CA in certain situations...dunno about the letus.
 
Balster,

I have the same problem with my Extreme. (Actually, it's more of a EX1 problem.) I've tried adjusting the gg screen, which didn't really help and I wouldn't recommend it. I've also mounted the Extreme slightly offset from the EX1. What I did was turn the adapter to the left (looking from the front) and tightened the three screws on the 77mm thread. There is a slight gap between the adapter and the thread ring on the right side (looking from the front again) and no gap on the left side. (Make sense?)
Well, I found this somewhat corrects the blurry right side and leaves the left side in focus.
 
is this common stuff for Letus Extreme users??
I thought the extreme has the sharpest image amoung all adapters???
 
Just ran across this thread - I was just doing some testing now with the new Nikon mount I also see softness on the right side of frame of my Letus.
I was trying to adjust to get rid of it, and couldn't do it.

The right side just won't get anywhere near as sharp as the center and left of frame, which look tack sharp.
And it's not a matter of it being off axis really (I think) because even at its sharpest point is wasn't as sharp as the center - it's not like I could pull focus to make the right side sharp is what I'm saying.

I was checking this while looking live at a res chart via the component outputs of the HVX sending 1080i out to a 1080 47" LCD TV to check for focus.
 
Luis, I have the same exact problem. Not sure if Letus can do anything about it at this time...since they're busy working on the Ultimate model which will bring them more revenue.
 
Sumfun said:
Here's a thread that discusses the right side of the screen being out of focus - without using the Letus adapter. Maybe it's related to the problem you're seeing.

http://www.dvxuser.com/V6/showthread.php?t=131333
Click to expand...

Hmmm, that thread is all about the EX1.
I'm shooting with an HVX - and my focus is fine without the adapter.
This is definitely an issue with the alignment of the Letus.
Can't help but think the GG isn't perfectly square - but I'm just guessing.

Didn't really want to do it - but I guess I'll have to find the time to open it up and check it myself.
 
This thread on the adapter not focusing on the right side seemed to peter out with no solution. I just shot 11 hour of interviews and noticed the right side out of focus. What is the CAUSE and what is the SOLUTION.
 
Hi

I have found the same issue, I was able to minimize it by first adjusting the ground glass so it was 7.2mm from the letus body, then looking at the focus through the ex1 touching up as needed to get the best focus. The adjustment is very small.

Then checking backfocus for infinity using a wide lens. I had used the nikon mount
with the small adjustment screws. It takes some patience.

the new backfocus ring looks promising but comes at a price.

Chuck
 
I have not seen this problem myself, but I have opened my Letus to change the backfocus of the screen. The method of assuring that the back focus is correct and especially that it is flat to the film plane seemed extremely wanky to me and far below the general standard of everything else in the units build. When I was adjusting the backfocus I just pushed the screen back or forward on the pins and it was up to me to make sure I did it equally on all sides. Perhaps yours are out of alignment.

I would suggest either sending the units back to Letus or opening it up yourself and trying to measure or eyeball whether it is flat to the film plane.

Complaints about Letus backfocus have become very common here and it would not surprise me at all if this was just a varient. Just a wild guess though.

Lenny Levy
 
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