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Old November 8th, 2007, 12:39 PM   #1
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Can you make your own LetusHD100 "Extreme" Version?

So I have a DVX100A that I will use with my newly purchased Letus35 Extreme (hopefully being shipped as we speak?) But now I also purchased the JVC GY-HD100U and I want to use this puppy on both cameras.

The issue with the JVC camera is that if I attach the Letus35 Extreme to the front end of the Fujinon lens, the camera is going to look ridiculous. I took a closer look at some pictures of the LetusHD100 and it looks like it has a 35mm lens that attaches to the JVC body and then the adapter looks exactly the same as all the other models.

This got me thinking...hmmm...can I be clever enough to just purchase a Nikon to JVC Adaptor lens adapter from MTF Services and the connect the Letus35 Extreme to the front end of the lens? Does this make sense?

I went ahead and purchased a Nikon to JVC Adaptor lens adapter from MTF Services ($350...ouch!) and attached it to the JVC GY-HD100U...wow...extreme telephoto! So I figure that is how the HD100 works. By adding a nikon lens to the front end in lieu of the stock Fujinon...you get this extreme telephoto and probably makes it real easy to focus on the LetUs Extreme screen...does this make sense?

Anyone with a HD100 care to explain how their current model works?
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Old November 8th, 2007, 02:03 PM   #2
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it won't work. Save your money

What you need is a jvc specific relay, which is basically a small fixed lens that will focus exactly on the screen of the letus extreme. The Letus guys should have an add on the extreme to do this with the jvc in the next 3 months.
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Old November 8th, 2007, 07:57 PM   #3
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is this a relay that can be bought anywhere? B&H Ebay?
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Old November 8th, 2007, 10:11 PM   #4
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Coco,

It's not easily possible to focus on a 24mm screen directly to a 1/3" CCD block within a short distance. Some people have tried using a 50mm backwards, I'm not sure of the success with this.
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Old November 9th, 2007, 01:16 AM   #5
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Quote:
Originally Posted by Coco Bermudez View Post
is this a relay that can be bought anywhere? B&H Ebay?
You wait until the Letus boys have made it.
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Old November 9th, 2007, 04:00 AM   #6
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I would imagine Quyen is working on something a bit better, sharper and wider than the current Minolta 50mm relay setup for HD100 and XL families of cameras, otherwise the existing setup would have been already grafted on back of the Extreme.

I would suggest not messing with improvisations.

They are unlikely to be any better optically than attaching to the front of your camera's standard Fujinon, which is going to be a risky fix in any event for a number of reasons I won't go into unless you want the boring pedantic details I am prone to wax into.
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Old November 9th, 2007, 06:42 AM   #7
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The way PS Technik accomplishes focusing a 24mm screen onto a 1/3" CCD block using a relay lens is actually because the optical path from the screen to the CCD block is optically much long than it appers from the "outside footprint" of the mini35. Over 10 inches if I remember correctly.. it's somewhere in one of my threads posted here when I was discussing building my own relay lens to go directly onto the CCD block of the HVX (hacking off the stock lens - I think was the thread title)

The other good thing with their relay lens was the fact there was 0 light loss.

I'll definitely be curious to see what the Letus boys come up with.

(Man I wish I had more time to delve into design and stuff, but you know how it goes :-)
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Old November 9th, 2007, 07:37 AM   #8
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Phil, as owner of both Brevis and LetusEx which would you say has produced the most consistent "sharpest" image results for a well lit shot or scene with 35mm lens at between f2.8 - f4?

Thanks
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Old November 9th, 2007, 09:54 AM   #9
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Dennis.

P+S may have something else a little clever in there between the groundglass and relay lens as well as the lengthened path due to prism/mirror foldback.

Whilst doing a recent visual check of the groundglass outdoors by letting bright light come in through the relay lens onto the groundglass from behind, a bit of dust on the outside of the rear element of the relay was projected perfectly sharp onto the groundglass.

Last edited by Bob Hart; November 9th, 2007 at 09:56 AM. Reason: thought there was error but there was not
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Old November 9th, 2007, 11:15 AM   #10
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I think PS did something funny to shrink the image down before sending it through prisms and then that way could design a workable relay lens that does not have the trouble of taking a 24mm wide image down to 1/3" CCD.

Anyway for the Letus brothers, consider something like this into your next relay lens design, it has always come in REALLY handy for keeping the taking 35mm lens at the optimal f-stop and reducing light going to the CCD:

http://www.edmundoptics.com/onlineca...productid=1677

In an old thread in the Brevis, SGPro and M2 shootout by Phil Bloom, Ing Poh Hii (see http://www.dvinfo.net/conf/showthrea...=81526&page=12) suggested the ability to reduce light by using or swapping various GG screens but so far no one has caught onto that. Effectively it would allow you to chose the effective ASA you would like to work and as a DOP or cinematographer this should matter! ie. one might pick 60 to 100 for outdoor and 200 for indoor.

In the end the BEST dynamic range obtainable is what anyone using a 35mm adapter should be most concerned with. I still would like to see that brought into a shoot-out! Phil Bloom so far is the only one I know who owns all three adapters! hint - hint
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Old November 9th, 2007, 06:19 PM   #11
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The choice of "CF" groundglass screens offered for swapping in and out of the Brevis does that. The principle was discussed more distant in history back and Dennis implemented it with his CF screens.

What some motion picture cameras do and the current crop of adaptors might benefit from is having a slide which carries a piece of filter gel to be inserted between the groundlgass and the SLR lens. This would enable control of light independent of SLR lens aperture settings,

In slides, pieces of ND filter gel can be stacked or a piece of colour corrector can be stacked with the ND.

This might be a lower cost alternative to the bulk and awkwardness of matte boxes for those who want to go agile.

With motion picture cameras, Bolex and CP16, the gel slide goes in very close to the film plane.

There might be a problem with internal light reflection off the GG back onto the filter gel then back onto the GG again in designs where the groundglass texture is on the rear face and the GG front face and gel rear face becomes a parallel mirror pair.

In this arrangement, the gel slide might have to be positioned closer to the rear of the SLR camera lens which then might introduce some sharpness issues.

On one of my home made glass disks, I had imperfect front surface polishing with lots of microscopic dimples. I have not been able to get the same contrast since I learned a better polishing technique and reworked the disk. Flare and lowered contrast due to excess light may be happening within the disk over several passes of reflection between the groundglass faces if the light is strong enough. A thicker groundglass will be more vulnerable to spill as light can spread wider with each generation of internal reflection.

The next challenge for Dennis - an anti-reflective coating on the shiny face of the CF screen.

Last edited by Bob Hart; November 9th, 2007 at 06:27 PM. Reason: spell error
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