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Old January 6th, 2008, 03:00 PM   #1
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letus extreme 35

When attached to ex1, what field of view is set for the zoom on the sony and how close of focus is used. What is the best iris setting on the sony. Next, a 50mm lens would project what type of magnification onto the ground glass. How about a 100mm or 30mm lens. I hope this question isn't stupid, but I have not found this subject addressed.

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Old January 6th, 2008, 04:09 PM   #2
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Jack

Don't have an EX1 yet so can't tell you the exact settings with the LEX mounted. I do know that the lens readings will be off, though, because you have extra glass inserted into the optical path, so the readings will be the same every time you put the LEX on, but they won't resemble reality.

The idea of a shallow depth of focus (DOF) is to direct attention to various parts of the screen by keeping those parts sharp and throwing the rest of the screen out of focus. The way to do that is to open up the aperture on the taking lens, and to have a fast (wide aperture) lens to begin with. So if you have a fast lens and you stop it way down, you're actually defeating the purpose of a DOF box. So most people who have a DOF box on will be wide open, or nearly wide open, on the taking lens.

After that taking lens (the stills lens, in this instance) has cast its image onto the ground glass, then you want your camcorder lens to adjust iris as much as possible to get the right exposure for your final recorded image. If you stop down on your camcorder lens, the added depth of field doesn't usually do much else except make your ground glass image sharper, possibly more grainy.

I tend to leave both lenses at full open or maybe a stop or two from full open. That's because up 'til now, most of the opticals in the DOF boxes have tended to eat a stop or two of light themselves, applying a kind of ND effect just by putting them on. That's changing as I write, of course, as the opticals are developed more and become more transparent.

Anyway, this leaves me up to a four stop latitude between both lenses to correct for my exposure. Additionally I have the built in ND filters of my camcorder, and also a set of separate 4x4 ND filters in a matte box setup to control things further if I really need to.

As far as the focal lengths of the lenses themselves (i.e. what mm's) go, in a nutshell you have regular lenses, wide lenses and tele lenses.
The definition of a standard lens is one which approximates the distortion and magnification of the human eye. It doesn't magnify things, nor move them away.

Most people go with 50mm as a standard lens for a 35mm stills camera. Actually the theoretical standard is 43mm, so 50mm is actually a touch tele, but most of the world uses 50mm as the standard.

A medium tele would be good for portraits, at around 85mm or 105mm.

135mm and more (180,200,300,500,1000mm) would be your long telephoto lenses. Good for bringing far things close, like sports, airplanes. They have the quality of "stacking" elements in a shot so that near and far elements look
stacked together. These lenses all have less inherent depth of field as well, and thus require more careful focusing to get things sharp and keep them that way.

35mm and wider tends to get more things in the shot (wider angle of acceptance), the things are smaller, less stacked (more widely spaced in the depth plane), more distorted, and generally sharper overall (more depth of field). Focal lengths typically go from your standard-medium wides of 45, 40 and 35mm to your regular wides of 28,, and 24mm, and out to your superwides of 22mm, 20mm, 18mm, 17mm, 16mm. Much wider than 16mm and the lenses tend to give in to barrel distortion and the sides of buildings, for instance, start to belly out/curve inwards. Go out to 12mm and 8mm, and you're in fisheye territory - the distortion is so much that everything's circular, apparently as a fish would see things.

That's lens theory, in a nutshell. Since the modern DOF boxes are based on stills lenses and a 24x36mm sized GG, those stills lens angles and measurements apply directly to our DOF boxes too.

As a stills photographer I collected a bunch of lenses over the years. I'd say mostly I use the following lenses on my DOF box to greatest effect:

18mm f2 superwide (rarely but always carry it)
24mm f/2 wide (mostly for establishing and beauty (scenery) shots)
35mm f/1.4 medium wide (a lot, for action shots)
50mm f/1.2 standard (mostly use this lens)
85mm f/1.4 portrait tele (a lot, for headshots)
105mm f/2 macro mid tele (a lot, for closeups)
135mm f/2.5 tele (sometimes, mostly use it when the 180 is too long)
180mm f/2.8 tele (a lot, for stacked shots)

HTH
JM2c, YMMV, etc.
Chris
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Old January 6th, 2008, 04:55 PM   #3
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Chris, thanks for the reply. If you would be so kind to answer one more question. The Fujinon lens is rated at 31.4 to 439 in 35mm terms. When a 50mm lens is attached would the field of view become 39.6 degrees. Also, if a 20mm lens was attached would the field of view become 84 degrees and 100mm would be a field of view of 20.4. If so, then the Letus becomes not only a means of creating limited depth of field, but also a sort of multiplier.

thanks again. I'm just trying to get my head around this concept.
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Old January 6th, 2008, 05:27 PM   #4
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I'm not Chris but I have the EX1 and the Letus Extreme.

A fifty should be 39 degrees. Right now due to some unknown problem, i have to zoom farther into the imaging screen to lose a vertical vignette on the right side of frame. so i did a little test with a 20 and 24mm lens and a nikon fm body. (really crude by the way) it appears that currently i'm getting the angle of view of the 24mm with the 20mm on the letus. if i widen to get the full 20mm the edge gets dark.

i'm waiting to get to support at letus and figure this out. in the meantime one thing is certain. it looks really, really nice. and the control of the depth is great.

check out philip blooms blog and see what the combo can do.

vince
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Old January 6th, 2008, 05:33 PM   #5
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Vince, when you put the 20mm on the letus you are getting a field of view of around 78 degrees. Is the image distorted in any way? I guess what I am asking, would this make a good wide angle adaptor?
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Old January 6th, 2008, 05:41 PM   #6
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The angle of view appears to be exactly as it is on a still film camera body. The obvious difference is that when you pan the ex1, any oddity associated with the lens pans with you.

What the Letus does is give you a multitude of lens options with control of the depth of field.

And the images look pretty cool to me. I just want to get rid of the vignette associated with the adapter so I can fully capitalize on all of the primes I have.

vince
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Old January 6th, 2008, 07:39 PM   #7
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What Vince said.

Basically all you're doing is making a "live optical" or "live telecine", if you prefer, videotaping a 35mm stills frame image off a ground glass.

As if you had a 35mm stills camera like a Nikon, popped the prism off the top so you could see the ground glass, and were taking a macro picture of that image with your camcorder.

Now the Letus GG is actually up to 20% bigger than a 24x36 frame, so you'll be cropping off the edges to get to the original 135 lens viewing angles. That's why the actual numbers are not precise (or precise + or - 5%).

So when you put a Letus or other DOF box on, you've actually consigned the Fuji lens of the EX1 to be an internal lens, just focusing on the GG. The Fuji lens is no longer the principal taking lens. Your Nikon lens becomes the one that looks out into the world. The Fuji lens is only seeing what the Nikkor lens sees.

So yes, if your Fujinon is 32-440mm 135 equivalent, and you use a 24mm stills lens on your DOF box, then your viewing angle becomes that of the 24mm lens. Or if you put a 500mm Nikkor on the front, then the viewing angle of a 500mm (what, about half a degree?) is what you get.

In other words, once you have a DOF box on, then it's only the lens on the DOF box that counts. The Fujinon lens becomes part of the camera body, as it were, and disappears from the lens tables and equations.

Vince
This is still all pretty much of a dark science here. If you look at the DIY section in Alternative Imaging, you'll see loads of threads as to why your frame is vignetting. Usually this will happen with the wider lenses, as they have to carry more glass to get rid of distortion, focus on a plane, etc., and then also cover the full 135 frame adequately.

Typically I'd only expect full (no fall off) coverage with a 24mm lens. Wider and that kind of thing starts to crop in and has to be accounted for.

When I was building my own, and at the suggestion of others on another part of this site, I added a $15 condenser between the GG and the achromat. This spread the light out a little more to the edges, got rid of the fall-off for my machine.

Also, if I'm not mistaken, the imagers inside the EX1 and HVX aren't centered to their camera bodies, so you may have to do some adjusting to get the falloff centered. There's other threads about this issude on this site, and I think that even Philip Bloom has encountered this problem when setting up his rig.

Even today, when these DOF boxes are becoming ever more sophisticated, there's still room for tweaking and further improvement.

So definitely on this one, YMMV.

Cheers
Chris
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Old January 6th, 2008, 07:59 PM   #8
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Quote:
Originally Posted by Vince Gaffney View Post
Right now due to some unknown problem, i have to zoom farther into the imaging screen to lose a vertical vignette on the right side of frame.
Vince. I have the same issue! I have a letus Extreme and I use an 85mm (see attached original CanonXTiCamera85mm.jpg) Canon EF, and I have a 28mm and a 50mm and a 300mm. I think you are right. I have to zoom in further than I did with a V1U. I even tested it with the Letus35 Flip. I get a fair picture at 80% zoom (see attached Letus35Extreme85mm80zoom.jpg) and a better picture at 90% zoom (see attached Letus35Extreme85mm90zoom.jpg). But that changes my 85mm to a 90mm or even a 100mm. I attached my comparisons.

Let us know what you find out.

Winston
Attached Thumbnails
letus extreme 35-canonxticamera85mm.jpg   letus extreme 35-letus35extreme85mm80zoom.jpg  

letus extreme 35-letus35extreme85mm90zoom.jpg  
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Old January 6th, 2008, 08:03 PM   #9
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Chris,

I agree with everything you wrote. The only problem is my Letus does it with any focal length Nikon lens I mount to it at any stop combination. There's a weird thing happening on the right side of the frame that looks like I'm seeing a reflection off the inside of the adapter. It moves into frame as you zoom.

My M2 doesn't do this with any lens, but i hate that's it's upside down.

I'll talk to Letus tomorrow and see what they suggest.

I also talked with Phil and he's having edge to edge sharpness issues, but said that Letus is on it.

Winston, I'll let you know. I hate losing the width on these lenses.

Vince
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Old January 6th, 2008, 10:31 PM   #10
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Thanks for your efforts, and please post them here when you've found something. I expect an EX1 in the near future and will probably be looking for the same answers.
Cheers!
Chris
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Old January 6th, 2008, 11:07 PM   #11
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Follow focus

Hi. Have an EX1 and buying a Letus. Use Nikon lenses.
Follow focus? Best one to use with this combo?
Thanks all!
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Old January 6th, 2008, 11:14 PM   #12
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Sorry for having gone slightly off topic. Found my answer. Getting the redrock.
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Old January 6th, 2008, 11:16 PM   #13
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Good choice.
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Old January 7th, 2008, 09:45 AM   #14
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Red Micro has some pretty attractive packages. What are the main pros and cons between Red Micro and Letus Extreme?
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Old January 7th, 2008, 11:39 AM   #15
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Best to check out the Alternative Imaging part of this forum. There's plenty of information about all of the various DOF boxes available.
I'd even go so far as to suggest that you make use of that information and then go to the DIY section as well, and try making your own. It doesn't cost a lot, and then you'll really know how to buy (or make) the right box for you. Actually Redrock also has a DIY project package, I believe.
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