I haven't had time to test the difference between open and closed iris on the camera. Thinking about it, I believe it wouldn't make much of a difference changing the iris on the camera lens, as opening and closing the iris on the photographic lens itself. Because changing the camera iris doesn't change how the scene is perceived by the photo lens, which is what matters when using the Letus.
But that has yet to be proven by test.
(tomorrow maybe)

Great, look forwards to your test,
and appreciate your effort, we all as a community learn here!

Ok, here goes.
I shot some flowers with varying ND, F stop and shutter trying to get the same exposure. I didn't use a monitor or waveform to judge accurately, but I think the results are obvious.
So, if you step down the camera using ONLY the shutter speed, with iris wide open and Shutter at 1/25, then the ground glass can be clearly seen on brightly lit areas.
If you step down using ND and/or F stop, the image looks clearer.
I believe that using the highest possible F stop on camera, then the image will be clearer, and this makes sense if you consider that you increase the depth of field this way, so the ground glass is sharply focused, as opposed to having an open iris and a more shallow depth of field.
Of course this is not a scientific test, as no scientific instruments were used, nor was a scientist present. And we all know that these are though times for scientists with 2012 approaching and all.

Thank you for your test, pictures look very sharp.
Good to know you can still shoot wide open on camera, so that light loss is minimal, I mostly concerned about low light shooting, and possible light loss.
The lowest f stop on camera is 1.7 did you have to zoom in more, so that it become 2.4?

Thanks again.

Oleg.

Yes, the zoom reading was 1.4m and F2.4 was the most open at this length.

What were the settings for the last picture you posted? I'm seeing an artifact on the out of focus light in the background there not seen in the other photos -- like you can kind of see the pin of light through the bokeh. There's documentation of this artifact elsewhere, but you seem to be avoiding it in all the other photos.

Do you remember what settings you had for each photo?

Brandon, if you roll over with your mouse you can see the settings for each photo.

no ND
F 9.5
S 1/50

I haven't noticed it until now.
What is it? Is it random?

Well, I can't find the other thread, now, but YAY! I actually don't have the Letus Extreme yet (should be here soon), and this artifact was a concern for me till now. It looks like the camera iris needs to be kept fairly open, or else somehow the bokeh is slightly see through. Makes no sense to me, but it is a great relief to know how to work around it.

Bummer about having to keep the camera open, though, because that means it'll be harder to focus on the ground glass (I'd think).

EDIT: Keep in mind my sole form of education in all matters is trial and error -- I'm sure there is someone more "head-learned" than I who can make sense of this in a technical way.

Me, I's just happy 'bout the purty pictures. :)

I second that !

Found the thread:

http://www.dvinfo.net/conf/showthread.php?t=106882

Thanks.
From what I see from the pictures I posted, using ND and having the iris wide open, produces a sharply focused ground glass that doesn't show through.
To my eyes the sharpest picture is the one with ND1/32 f2.4 S1/25