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Old April 8th, 2008, 09:05 AM   #46
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Philip just confirmed in the other thread my Letus has backfocus problem :(

So, it seems I wasn't as lucky with my Letus, as I was with my EX1 - with:

- the achromat chipped off
- the gg rectangle not level (twisted some 10deg in the viewfinder when on rails)
- the noise and vibration higher than on most other units (it seems)
- now, with backfocus problem

If I were not located in Europe, I'd be sending it back today - but with all the hassle, customs etc. I really don't know what to do... It can produce nice images, in spite of the flaws! Below's my setup (on the right; taken with my mobile), and the nice bokeh I got in my very first trial shots after some lenses arrived from eBay... At last, no need to shoot from miles away, in order to pull the subject off the background:)
Attached Thumbnails
Letus Extreme and...-image82.jpg   Letus Extreme and...-dsc00045a.jpg  

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Old April 8th, 2008, 09:06 AM   #47
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my achromat is chipped, my backfocus was out. The achromat is fine, the backfocus is easily sorted. Don't worry, it's worth it in the end!
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Old April 8th, 2008, 10:33 AM   #48
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Does your letus motor shaft have a dap of hot glue on it? My did and it came off and I believe I am getting less artifact and sky issues when shooting a plain background like the sky. See my blog with pics showing the hot glue.

Never got a proper response about why the hot glue is on the motor shaft for balancing, and how that is calibrated.

The extra noise may be because of the extra weight on the end of the motor shaft, also check to see if any thing is loose, make sure those allens screws are locked down! With the absence of the glue on the motor shaft the unit is more quiet but still it make a buz- vibration sound which is normal.

Instructions from Letus site for adjusting back focus:

1) Remove the front tube
2) You will see the plastic ground glass holder. Using a ruler or calipers, carefully measure from the back of this black plastic to the surface of the adapter behind it. It should be 7.5 mm all around.
3) If you find this distance is off, very gently push / pull the 3 metal stand offs holding the ground glass holder in or out to achieve a distance of 7.5mm all the way around.
4) If you are already at 7.5mm and your focus is still off, then adjust each of these to be slight less or slightly more all the way around.
5) If you cannot achieve focus at infinity at all, then you will want to pull the stand off posts out very, very slightly more than 7.5mm
6) If infinity focus is hitting before you reach the infinity mark on your lens, then you will want to push the stand off posts in very, very slightly to be less than 7.5mm.
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Last edited by Steve Cahill; April 8th, 2008 at 11:13 AM.
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Old April 8th, 2008, 11:20 AM   #49
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Frankly, I don't know if having paid that much money, I'm supposed to even dismantle the adapter - usually, my warranty would be void if I did! I expected a high precision, high quality device; what we're getting is more like a home-made toy.... I read the thread on the GG plane adjustment for back focus in the forum on LetusDirect site; how can adjustment like this be left to a trial&error, pushing/pulling method!!! This device is supposed to work with HD cameras like the EX1, and should be equally precise.

Here is a sample showing both:

- the softness of tele (couldn't get the fence and trees in the background any sharper with either of my 3 lenses)

- the motor rattle (yes - apart from the low freq hum from vibration, I'm getting now intermittent high freq rattle which comes and goes).

Doh!
Attached Files
File Type: wmv LEX_rattle_and_soft_tele.wmv (497.7 KB, 128 views)
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Old April 8th, 2008, 01:10 PM   #50
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I used calipters to make the adjustments at each of the post and in-between, as well. Set the Calipters at the correct distance 7.5mm and lock them and just gently put the calipters under the GG metal plate and make sure it is square when you get the calipters into position, repeat this at each mounting post and in between 2x. This is also a good opp to clean the adpater, I now use compress air to do so, more robust than the rocket blower.

You thought you paid a lot did you? Well welcome to the wonderful world of video production.

These companies that make these adapter are home grown, with a very few exceptions. Did you not do your home work and read the user groups with the challanges we have been faced with? Phil Bloom has great footage but also great info about his experience with adapters, that details his experience. Check out my blog where I took the Letus apart and made some discoveries. Unless you are buying a name brand Sony, Panasonic, Red then yes these adapters are home grown, with clever people bringing to market from their garage, products that fit a price and performance that may or may not be suitable for your use.

I to have been disappointed with the quality of the build of these adapters, but they have been affordable and useable, but they come with their own challenges and hopefully you can study the users groups and learn what others have learned and get up to speed right away. The adapter does not come with a detailed instruction manual and how to adjust FAQ. One thing I find fault with all the companies.

Hopefully the companies that make this first generation of adapters will listen to the users and improve the products for the next generation that they make.

This has been a interesting experience into the world of DOF which has opened many doors and which has been pretty unreachable with video cameras . Call it a curse or a blessing, but you have the power to turn it on or off now.
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Old April 8th, 2008, 03:43 PM   #51
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Steve, when will you be getting something on your blog about aligning the GG? think that will be excellent. I'm really hoping you shoot video of it for us :)

I've had a ton of issues over the past few days getting my focus adjusted properly but I'm getting much closer. A few videos would be awesome. Thanks for all the info you guys have been putting on here!
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Old April 8th, 2008, 06:25 PM   #52
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I need to do that, thanks for the reminder. Heading out to NAB so it would have to be after that.

Do you have hot glue on your motor shaft? I have gotten a world of difference with it not being there.

Here is how I adjust back focus... see pic.

Also here is some more back focus techniques using a Red Camera and a Nikon lens http://www.youtube.com/watch?v=pRicc1HU44c

We do not have easy way to adjust the Letus, except to pull it apart.
Attached Thumbnails
Letus Extreme and...-cal.jpg  
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Old April 8th, 2008, 11:53 PM   #53
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Hey Steve,

Thanks for the pic. I just got a set of calipers tonight and got everythng measured up right now.

What do you mean by hot glue on the motor though? I'm curious bc when I got my Letus the other day, the first thing I found when I had to crack it open was that there was a large amount of it that actually sealed it to the wires on the base. I cut that away a bit and my vibration got better.

Do you mean though that you actually removed as much glue as possible? I'm really interested in that bc it seems it would give a much cleaner vibration than that unmeasured amount of glue that is still on there.

Thanks for the help!

EDIT:
I also just noticed in your pic you have a bit of hot glue on the tip of the motor as well. Was that there for you when you received it?
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Old April 9th, 2008, 01:48 AM   #54
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Steve,

Not backing off from what I said my opinion on the LEX quality is, I must admit your pictures and hints are invaluable; thanks for that. I didn't decide to put mine apart yet (waiting for what Aaron answers me), but it doesn't look that complicated.

Looking at those photos, and reading about pulling the three stands to get the gg plane in the right distance from the base, I wonder:

- assuming I manaage to adjust it for back focus at infinity, how long will it stay in the new position? I mean, the 3 stands should be threaded or something, so that - by turning them - one could easily and precisely adjust the distance, and it would be permanent. From what I understand, by pushing/pulling we're just using the rubber elasticity, or what? How is it supposed to hold after adjustment? Thanks in advance for your clarification.
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Old April 9th, 2008, 01:57 AM   #55
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I can answer that a little :)

The stands all have rubber feet that wedge into bored holes in the case. They are tight too. If you pull them out or end needing to for some reason, they suck trying to get back in. I went with the one recommendation of a toothpick - which works to help guide them back in - but dont do that. It flakes and then you end up having the pull the face off the letus to get the chip that went under the condenser and wont budge no matter what :(

Anyway, they do move, just very inaccurately. Maybe in the future, Quyen will come up with a pin that has a rubber elbow on it and a threaded base for adjusting. That would be cool.

But to finish the answer, it seems like it will hold fairly well. I imagine after a while it'll need readjusted. So make sure you have a set of calipers and I also bought today a pair of needle point tweezers for model making to help should i have to bother with those rubber feet again. Hope that helps some.
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Old April 9th, 2008, 06:39 AM   #56
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The Letus EX came with the hot glue on the motor shaft, as seen in the pics @ http://web.mac.com/stevecahill/Steve...Autopsy_1.html

Some users have it some do not, mine is no longer there, it came off. I was told it is put on to set the vibration correct, but do not know what the specs are to determine this. With hot glue it is guessing game with a dap of glue here?

Note that the calipers with their sharp edges will take some paint off of the GG holder when setting the back focus. This will get on the glass, use compressed air to remove it, and or take the edge off of the calipers with some emery cloth to minimize the flaking of the paint finish with the calipers when setting the distance. I just wedge the calipers underneath the posts and square them up with the GG, this sets the distance. I cannot feel it move, but it sets it equal distance all around. I can image these rubber seats will wear, become stiff with age and will fail at some point. do we have a part number for their replacement?


I agree, a screw type back focus adjustment is in order, that will raise the price another $200.00 See http://www.youtube.com/watch?v=pRicc1HU44c
How RED Camera deals with back focus.
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Old April 9th, 2008, 06:49 AM   #57
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Quote:
Originally Posted by Steve Cahill View Post
I just wedge the calipers underneath the posts and square them up with the GG, this sets the distance. I cannot feel it move, but it sets it equal distance all around.
Excellent idea, Steve - if I decide to do it myself, I'll use it, as my adjustment most probably requires increasing the distance from base (i.e. moving the GG towards the lense, to achieve infinity focus). Thanks!

PS. But still, this is pathetic! Would you dismantle and "adjust" like this a $2,000 lense, for instance? I bet you wouldn't... Well, the Letus is also part of the duct the picture enters your camera through!
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Old April 9th, 2008, 07:52 AM   #58
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Quote:
Originally Posted by Steve Cahill View Post
I agree, a screw type back focus adjustment is in order, that will raise the price another $200.00

Well, Letus could make a precise adjustment much cheaper for us, by providing the lense mounts with a bit thinner flange, and a set of spacers to be put between the mount and the adapter - this way, by adding or removing spacers, easy and permanent adjustment would be possible...

But pulling / pushing within the range that some rubber will allow? Or balancing vibrating parts with some glue drop?

C'mon, Letus!
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Old April 9th, 2008, 08:56 AM   #59
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OK, I know what you are talking about now. Mine does not have the glue on the tip but it does have a ton of glue around the base front side of the motor - as well as the back. I see yours has the glue on the backside and is clean on the front. I mean I have a large amount here, I wonder if its necessary... I'm wondering if I would get a performance boost. In my tests in bright lit sun or in shadow, I cant stop down past 2.8 on most of my lenses and get away with a pan or tilt. Any thoughts from anyone?
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Old April 9th, 2008, 09:24 AM   #60
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Originally Posted by Jeremy Hughes View Post
Any thoughts from anyone?
Just one: even more disappointment.
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