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Old August 2nd, 2007, 12:45 PM   #16
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I'm sorry but i don't understand what you mean by:

"Diffusing screens create fake bokeh, lavaged and unsharp image, with fixed thus visible grain."

By diffusing screen I mean what you are calling the GG which is usually not actually ground glass, its a screen of some kind of diffusion material (could be ground glass, plastic wax or whatever) on which the 35mm image is focused for the adapter.

I don't know how the Letus works. I read that it has a motor, so I assume it probably has a vibrating or rotating diffusion screen ( call it just a screen if you like). Perhaps I'm wrong.

Though it may seem contrary to our ordinary understanding, on these adapters, the nature of the screen material affects how much light is needed, how much of a diffusion or softening of the image occurs, how sharp the image is and how sharp it is corner to corner, and most surprisingly and most noticably how much apparent depth of field is in the image.

This is clear when you look at the different screens Dennis provides.
The Brevis with the #1 screen is definately sharper than the M2 but that is partly because it is the least diffusing of his screens. They are more similar with the Brevis's heavier screen (#3) though I haven't tested his latest one yet.
I find the heavier screens on the M2 and #3 Brevis to be a much prettier look, but for some jobs they are not appropriate - either too slow, too soft, or too little depth of field.

You still didn't mention whether you actually compared the Letus to the Brevis. I'm not contradicting you here I'm just trying to separate hearsay from genuine observations. There is a lot we can teach each other about these adapters.

I would love to know more about the Letus as it sounds less expensive and apparently works well enough for Barry.

Does it also have a vibrating screen?
How good is corner to corner sharpness?
Do you start to see grain at f stops from 5.6 and higher?
How much freedom do you have to you different shutter speeds or camera speeds ( the new Brevis is pretty good at this).
How fast are the lenses you use?
I've noticed with the Brevis and M2 on my HVX200 that I get no almost no change opening my f1.4 Nikkor lenses beyond f2.5 or so. This is frustrating. Is that also true on the Letus?
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Old August 2nd, 2007, 01:21 PM   #17
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Quote:
Originally Posted by Leonard Levy View Post
You still didn't mention whether you actually compared the Letus to the Brevis.
No, i didn't compare them, i just compared the Letus35FE and the M2. There was a huge difference in sharpness, vignetting and overall image definition, in favor of the Letus35FE. The M2 seemed to not be able to focus at infinity. I and another D.P tried to get that infinity sharpness, but nope.

And about the Brevis, i'm just wondering in my ignorance how can a 35mm adapter work with a fixed GG without showing soon or later some fixed grain. Maybe i'm missing something.

(about Letus35FE)
Quote:
Does it also have a vibrating screen?
Yes

Quote:
How good is corner to corner sharpness?
It's even and this was one of the main selling factors to me.

Quote:
Do you start to see grain at f stops from 5.6 and higher?
No, there is no graing visible at any iris aperture, provided that the shutter is at 50

Quote:
How much freedom do you have to you different shutter speeds or camera speeds ( the new Brevis is pretty good at this).
As mentioned above, over 50 the grain becomes more and more visible.

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How fast are the lenses you use?
Actually i have a 50mm f/1.4 lens, a 24mm f/2.8 lens and a zoom lens. I found that faster lenses than f/1.4 don't add so much because to get a good image you still have to close them to f/1.4, unless you spend $$$$

Quote:
I've noticed with the Brevis and M2 on my HVX200 that I get no almost no change opening my f1.4 Nikkor lenses beyond f2.5 or so. This is frustrating. Is that also true on the Letus?
With the Letus the difference is huge. When i started with my f/3.5 zoom lens i noticed few bokeh, but once i got my 50mm f/1.4 Nikkor lens, the bokeh is extraordinary. This is due to the fact that the Letus35FE has a full sized 35mm GG. What about the Brevis?
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Old August 2nd, 2007, 01:28 PM   #18
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Quote:
Originally Posted by Leonard Levy View Post
I don't know how the Letus works. I read that it has a motor, so I assume it probably has a vibrating or rotating diffusion screen ( call it just a screen if you like). Perhaps I'm wrong.
Letus35 Flip Enhanced uses a vibrating ground glass.

Quote:
Though it may seem contrary to our ordinary understanding, on these adapters, the nature of the screen material affects how much light is needed, how much of a diffusion or softening of the image occurs, how sharp the image is and how sharp it is corner to corner, and most surprisingly and most noticably how much apparent depth of field is in the image.
Mostly accurate, yes. As a base corollary, the coarser the ground glass, the sharper the image and the more evenly-diffused the light will be (i.e., no hotspot in the center and no darkening vignetting in the corners), but also the more light loss. The more transparent the screen is the more light it'll transmit, but the less evenly the light will be distributed across the GG's surface (meaning you're more inclined to have a hotspot in the center and darker corners).

But the texture of the screen changing the depth of field? Not possible. The DOF is decided by the optics of the lens; it'll exhibit identical DOF regardless of what you project that image onto.

Quote:
I would love to know more about the Letus as it sounds less expensive and apparently works well enough for Barry.
I've posted a review for DVXUser; I don't know when it'll go "live".

Quote:
Does it also have a vibrating screen?
Yes.

Quote:
How good is corner to corner sharpness?
Pretty good, but there is definitely softening in the corners.

Quote:
Do you start to see grain at f stops from 5.6 and higher?
Yep.

Quote:
How much freedom do you have to you different shutter speeds or camera speeds ( the new Brevis is pretty good at this).
Shorter shutter speeds start making the grain more visible. 1/60th or slower is best.

Quote:
How fast are the lenses you use?
I was using 1.8.

Quote:
I've noticed with the Brevis and M2 on my HVX200 that I get no almost no change opening my f1.4 Nikkor lenses beyond f2.5 or so. This is frustrating. Is that also true on the Letus?
Not sure what you mean? No change in brightness? Or no change in DOF? There certainly should be changes; 2.5 to 1.4 is almost two full stops.
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Old August 2nd, 2007, 01:46 PM   #19
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OK, so we don't know which is the sharpest adapter.

Brevis is not a fixed screen but vibrating like the Letus sounds.

Your problems with the M2 were greatly exagerated because it was not set up right. That tends to be a problem with all these adapters. it took me 3 days to set up the M2 properly just so that my camera was focused on a centered screen.

These adapters require that the HVX is centered on a screen that is flat to the HVX itself, at an optimum distance from the HVX so that focusing is optimized for the achromat ( tiny differences can alter this radically), and that the 35mm mount is at the proper back focus distance from the screen so that it focuses properly.

Your M2 was not even focusing the 35mm lens properly on the rotating screen. That's why you didn't achieve focus at infinity. I can only imagine what the other misadjustments were, so your comparison with the M2 was not fair to a properly functioning M2. However one thing I don't like about the M2 was there was too much slop in the system altogether.

There's alot of pot luck in this. My M2 was focused perfectly for the Nikon but not for my HVX. When I first got my Brevis it worked fine for the HVX but the Nikon was way off and my complaints to Dennis help lead to his new collimation system.

To answer your questions.

Brevis is a full sized 35mm screen, actually a bit larger. What makes you say the M2 is not? I assume it has to be to get the 35mm lens to back focus correctly.

The Brevis tends to show grain at apertures over f4 on the 35mm lens. This is a problem but easy to expose for inside the HVX so I don't complain. It may vary with the screens.

Corner to corner is pretty good but I always see a slight difference between where center and corners focus best on the HVX. You might not notice this unless you are looking at images with a large resolution chart (3 or 4') which I highly recommend. in fact I think if you use these adapters without a large resoultion chart you're really guessing and can't see if you've optimized set-up.

Brevis seems to have a lot of freedom for more closed shutters so i can shoot high speed. This is a function of the oscillation speed which is variable but a pain to switch.

Re: f1.4 lens, If you put that on your Letus, do you see 2 stops of exposure increase as you open from f2.8 to f1.4?

I don't on the other adapters. i hardly see any change at all. I'm very interested in this. It's odd, and I think may stem from the distance the HVX is from the diffusion screen.
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Old August 2nd, 2007, 01:55 PM   #20
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Barry,

"But the texture of the screen changing the depth of field? Not possible. The DOF is decided by the optics of the lens; it'll exhibit identical DOF regardless of what you project that image onto."

I'm sorry, but although it seems impossible, you are dead wrong here, and the proof is in the viewing. With the Brevis the diffusers radically alter what I'm calling apparent depth of field, but it is 100% real. Its very dramatic difference nothing like putting a promist in front of a lens.

It really bent my brain for a while but evetually i settled on the idea that out of focus circles of confusion are exagerrated by some diffusers. It is an observable fact and I do understand DOF.

Also Dennis claims that he is building screens that compensate for off axis light so that less diffusing screens don't vignette. The #1 screen is very even on an HVX.

This adapter screen business is really a bit of a no man's land where ordinary rules seem to be able to change.

Last edited by Leonard Levy; August 2nd, 2007 at 03:20 PM.
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Old August 2nd, 2007, 02:08 PM   #21
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Having built my own M2 type adapter, from the Redrock plans as a guide, the infinity focus issue is clearly caused by an improper distance of the 35mm lens from the spinning screen. Corresponding to that, you will like see that that close focusing using the 35mm lens will actually be closer than the lens is supposed to get. Essentially, in terms of what we learned from 35mm still photography, if you add an extension tube to your lens, you will be able to focus closer, but lose infiniity focus. So the lens needs to be moved back closer to the spinning screen, or the screen has to be adjusted closer.
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Old August 2nd, 2007, 02:28 PM   #22
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So here are my personal conclusions:
1) M2 is to me too complicated to set up, the result is not better than the others, the image is reversed, many stops are eated.

2) Brevis tends to show grain at apertures over f4 !!!!???? So just use your on camera lens! The bokeh at f/4 is so little that it's not worth using an adapter.

3) Any diffuser just adds BLUR, not BOKEH. Please read some explanation out there in the web to understand how bokeh is achieved and the difference between bokeh and lack of detail.

But at the end what matters is the result, maybe the Brevis gives wonderful results, no matter how, we want great photography, nothing else.
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Old August 2nd, 2007, 02:58 PM   #23
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Giovanni,

I've been in this business for 30 years. I'm an excellant tech. I know what I am talking about.

You have not seen the effect I am describing, didn't realize you hadn't set up the M2 properly, and assumed the Brevis worked differently than it did, so show a touch of humility and don't make claims you can't back up, it only confuses everyone else. We are all in this to learn from one another.

I'm using "Bokeh " to refer to low depth of field in general. Your statement " Any diffuser just adds BLUR, not BOKEH " as I explained to Barry below happens to be dead wrong. You have to see it to believe though. Its very dramatic difference nothing like putting a promist in front of a lens.

(Still photographers tend to be more specific and compare the bokeh of different iris mechisms but we're not being that detailed here.)

I should have been clearer in explaining that it shows grain at apertures more closed than f4 (5.6 and above) though in fact even at quite small apertures the DOF can be much lower than with a clean HVX lens.

If you are happy with the Letus that's great.

However a few things you said about the Letus are contradicted by Barry in his post below:

Quote:
How good is corner to corner sharpness?
Pretty good, but there is definitely softening in the corners.

Quote:
Do you start to see grain at f stops from 5.6 and higher?
Yep.

I would appreciate if you or someone else tests the question of opening f1.4 lenses from 2.8 to 1.4 and posts detail explaining what lenses and video camera they are using.
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Old August 2nd, 2007, 04:34 PM   #24
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I will post some footage in some weeks
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Old August 2nd, 2007, 06:40 PM   #25
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Again, I have used them all, professionally set up and working to their max capabilities.

The Letus loses the most light (expected with the flip) and is the least flexible. It is very easy to set up and hard to screw up. It starts to show grain the more you stop down, the motor is locked to one speed, so this cannot be overcome.

The M2 loses the next most light but is by far the hardest to set up (similar to the SGpro), when set up properly it can be tack sharp and with the spinning GG can be used at high shutters and more closed apertures(though with the light loss you will likely never need them). There is a robust community and it is more mature than many adapters in support and the company behind it.

The Brevis is by far the most versatile, it can be set up much quicker than the M2 but with the number of adjustments that can be made, takes more time than the Letus. Elements are swappable, there are currently 5 different elements for different situations. The CF1 and CF1L can be used with shutters up to 120 (I have got it to 250 before) with the motor vibrating faster and can be used up to F8 (easily). You can slap on CF1L and go without rods and use the adapter handheld in natural light, even indoors, no other adapter offers this. The CF3L element (provides THE most shallow DOF of all the adapters) really needs lenses F2.8 or faster and the shutter needs to stay in the 1/48th area.

They all have pluses and minuses and maybe the Letus is best for some, considering the price especially, but in general, it is inferior to both the Brevis and the M2 (as well as the SGpro).




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Old August 2nd, 2007, 07:27 PM   #26
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Ash,

Thanks, that's very usefull. There's no substitute for real hands on experience.
I agree with you about the difference between the M2 and the Brevis though the Brevis is only more time consuming if you start changing things around.

Were you using the old Letus or the new Letus Flip enhanced though?

- Lenny
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Old August 2nd, 2007, 08:17 PM   #27
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I have used the latest letus as well as the LetuxXL v2 (which I quite liked other than the 1.9X zoom factor). No matter what, the Brevis is easier to set up than the M2. Most M2 shooters leave it on the camera.



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Old August 2nd, 2007, 08:25 PM   #28
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Ash -

Do you remember which version of the SGPro you were using?
I ask, because Wayne is now on Version 3, with a new rod support system as well (hard mount lines up more accurately and easier, i have read). I've got one on order - and will report in accordingly...

Thanks,
Lonnie
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Old August 3rd, 2007, 01:56 AM   #29
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It was not the latest. It it a great product but the least mature so the community behind it is fairly small and lead times are still VERY long. I found it easier to get tack sharp than the M2. It also does not seem to have some of the set up issues that can plague the M2 (wobbling ground glass) and the spinning GG seems more fine tuned. The only real negative for me was the fact that it has to be used on rods. It produces a VERY clean image at almost every aperture and shutter speed. My only real issue with the image was that while all 35mm adapters have a somewhat unnatural bokeh, the SGpro's seemed more exaggerated somehow. This was really only in situations with EXTREMELY shallow DOF though.


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Old August 7th, 2007, 07:12 AM   #30
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As always Ash, I appreciate your real world experience and details. I am solely interested in picture quality, and the issue of the rods is not a an issue for me at all. My uses are usually cinematic in approach, so I'm usually on some sort of support anyways. And Wayne's new achromat appears to be pretty sweet.

However, the bokah is a big deal - thus...
I'm backordered until the 25th of September, but when I receive it, I'd be happy to report in about it.

Thanks,
Lonnie
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