Letus Extreme - Half a Stop of Loss but...

P

pernell91

Active member
the area of ground glass I have to focus on is so small that I had to zoom in to the point where the most open aperture I could have is 2.8 stops - so an additional 1 stop of light lost there from zoomed out and wide open...

I am new to the Letus Extreme so I am hoping that I am not doing things quite right and that I can regain a bit of light.

anyway i am hoping that maybe some experienced letus / adapter users might be able to help a bit, or am I experiencing the Letus at its optimal setting already? I was expecting .5 stops of loss but not 1.5 which completely changes the game for interior shooting.
 
no, this is correct.

the adapter itself loses .5 stops, then you add a lens, which will lose probably .5 stops again, and then your camera loses a 1.3 stops zooming into academy frame. all in all you are looking generally at 2 stops in total. Hence the recommendation of 35mm owners to get ready to learn how to light prpoerly if you adopt an adapter.
 
Yeah, it's like Papa said, the light loss rating is based on how much light the adapter looses, not your camera or lens. If that was the case then no one would be able to give a rating because of all the variables.
 
also, the image seems to move around when i turn on the vibrating GG. i was locked down on a tripod doing a still shot and the image in the frame just seems to move around a little bit. and also, if i move the camera, the edges of the window i zoom in on can shift into the image and back out, like they are swinging around inside there, i don't know if that is going to work well with any kind of moving shot. i'm feeling a little confused with this item so far. i'm really hoping i just have to get the hang of it and i'm doing something wrong
 
i mean with the image moving around the frame like that i won't be able to do compositing in post, forget motion tracking, this is way worse than rolling shutter problems...
 
Sounds like the GG or one of the vibrating post is loose. I used to have a similar problem with my unit. Sent it back for repair and Letus got it back to me within a week good as new.
 
zergtherobot said:
unless your using a brevis. Which apperently loses half a stop of light with the adapter and a lens attached.
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Seems like an inaccurate rule of thumb, since any given lens's maximum aperture can be different. Is there any clarification on which lens that may be true with?
 
trudd said:
Seems like an inaccurate rule of thumb, since any given lens's maximum aperture can be different. Is there any clarification on which lens that may be true with?
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Brevis quoted that figure with a 50mm f1.4 lens attached. If I recall the Brevis behaves differently in that its light response isn't linear. Closing down a stop doesn't necessarily means losing twice as much light.
 
The .5 light loss figure has always been dubious. that's what redrock said when I bought one 2 years ago and the real loss was over 2 stops.

Realistic figures usually assume a 1.4 lens with a video camera wide open though.

You should get less than 2 stops loss with a Letus Extreme however , closer to 1 stop depending on your camera and lens. It seems pretty extreme that you have to zoom in so far that you are at 2.8 to get a decent image.
What camera are you using?

Lenny Levy
 
trudd said:
Seems like an inaccurate rule of thumb, since any given lens's maximum aperture can be different. Is there any clarification on which lens that may be true with?
Click to expand...

*edit* nvm. didnt realize this was answered already.

But to add to Huy's answer, I believe that figure is also based on a brevis in non-flip configuration.
 
There were so many calls of snake oil and deception on the light loss thing we gave up trying and put together several technical tests for public viewing. There's a thread (I published the clip in post 50) with something like 20 pages of posts drifting around here as a result of the first clip. In our light loss video as well as the recent cf1/2/3 comparison we demonstrate what one stop on the bare video camera looks like on a waveform monitor as it's moved from f2.8 to f4 . We've tested this now on the HV20, XH-A1, EX1 and HPX500 and in every case, that one f-stop results in about 20 IRE drop on the scope. Sliding in a flipped configuration Brevis with a 50mm lens at f1.4 affixed, you'll see about 10 IRE drop. That's ~ 1/2 stop total loss relative on four different cameras tested with a flipped MP.1 including the 50mm f1.4 The tests are 100% repeatable by anyone just recording an evenly lit white wall and analyzing the clips in an NLE's waveform.

The clips demonstrating our live tests are here: http://www.cinevate.com/website/index.php/videouniversity/ in the Light loss clip as well as part 1 of the CF1/2/3 clip comparision.

Btw, the difference in various f1.4 lens is too small to make a measurable difference with the adapter. You won't see 1 stop total loss with CF1Le until the 35mm taking lens is at f5.6 which gives an idea of how hard it is to measure differences between f1.4 lenses. Light loss differences amongst adapters vary even more dramatically as the taking lens is stopped down...which is why we always test at wide open and f5.6
 
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Does sound exactly like an OIS on issue with the frame movement.

As to the need to stop dowm to f2.8, this I don't quite understand...

I set camera and taking lens (my fastest is a Zeiss 50mm 1.4) to wide open, and zoom into where the vignetting stops (about Z78 on my HVX200A), and I'm good to go. That's about one stop loss as far as I know...a half each for LEX (with HVX optimizer) and lens. No need to stop down further at all.

Maybe there's something I'm not following in the discussion...or maybe not...
 
OIS can be in issue, however the problem description suggests that the element oscillation is too high, which results in image wobble. That's why we use a microchip to control it.
 
Lenilenapi said:
The .5 light loss figure has always been dubious. that's what redrock said when I bought one 2 years ago and the real loss was over 2 stops.

Realistic figures usually assume a 1.4 lens with a video camera wide open though.

You should get less than 2 stops loss with a Letus Extreme however , closer to 1 stop depending on your camera and lens. It seems pretty extreme that you have to zoom in so far that you are at 2.8 to get a decent image.
What camera are you using?

Lenny Levy
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the canon xh a1

i can get the edges of the rectangular hole to disappear at 2.6 but anything less and i'm getting one edge or another in there it seems

i will check to see if OIS fixes the weird image bobble
 
That's vignetting you're seeing. The aperture thing is normal per my experience (also A1 on Letus). On an FD 50mm f1.4 I have to zoom in at 75mm or more to get rid of vigetting, with a stock lens f-stop of 2.6. On a 24mm f2.8 I have to go to Z80 or more.

I experienced a similar issue with the image wobble; something was loose inside the adapter and Letus fixed it for me.
 
Huy Vu said:
That's vignetting you're seeing. The aperture thing is normal per my experience (also A1 on Letus). On an FD 50mm f1.4 I have to zoom in at 75mm or more to get rid of vigetting, with a stock lens f-stop of 2.6. On a 24mm f2.8 I have to go to Z80 or more.

I experienced a similar issue with the image wobble; something was loose inside the adapter and Letus fixed it for me.
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no its not vignetting, i'm zooming into the rectangular area (black all around it) that the letus is presumably projecting its image onto. anyway, its not ovular or gradual, its like looking through a rectangular window
 
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