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Old March 11th, 2008, 08:01 PM   #1
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EX1 and Letus Extreme with PL Mount Focus Issues.

I haven't been able to achieve consistent focus with the EX1/Letus and PL mount. Infinity focus was never achieved.

Wider lenses were especially difficult. 18, 25, 35 - It's was strange you could get focus at about six to eight feet, but beyond that nothing.

Longer focal lengths seemed to work ok.

I know many people have had success with this set up. Any suggestions?

The ground glass was sharp, and we had all the latest EX1 pieces from Letus and Zacuto.
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Old March 11th, 2008, 08:33 PM   #2
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just a question...

It has been my experience that wide angle prime lenses generally have a very long dof.

If this is true than is there any point to use the Letus with such short lenses???
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Old March 11th, 2008, 10:53 PM   #3
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Incorrect backfocus adjustment is notorious on all the adapters and will be worst on wide angle lenses. Contact Hien Le at Letus and he will hopefully run you through a method of back focus adjustment. This is a major flaw in the design. It should be easy to set backfocus yourself on.


Steve - DOF is deeper on a wide but there are many reasons to want to use them with a 35mm adapter
1- It is still much more shallow than the stock lens.
2- If you need a wide shot in a sequence where you are already using a 35mm adapter you need to maintain a consistent look.
3- You can get wider lenses than the stock lens.

Lenny Levy
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Old March 12th, 2008, 02:17 PM   #4
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Thanks. Will call Letus. Hopefully there is a dependable way to adjust backfocus so that it doesn't have to keep being re-adjusted. It's such a time killer... we ended up having to remove the adapter and shoot with the fixed lens for the wider shots, which as you can imagine doesn't really match.

Also, I noticed that the whole adapter has a tendency to spin on it's own mount even when the alan screws are fairly tight. The screws are just tightening against a flat surface instead of into a thread... so by the time you get the 35mm lens, mattebox, filter and follow focus (weight)... the screws don't hold.
anyone?
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Old March 12th, 2008, 07:15 PM   #5
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I contacted Letus about backfocus and got the following instructions:

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

This procedure, while a little bit of a pain as it involves a lot of trial and error, worked perfectly in achieving spot-on backfocus with the Nikon mount - I haven’t had an opportunity yet to test it with any PL mounted glass. I will note that precision is key in that you want to make sure that the three posts are pulled out equally so that the ground glass is flat to the focal plane.

Adjusting backfocus is similar to the M2, but, in my experience, I was never able to get as good an image with the M2. My only complaint about Letus is with the company in regards to their customer service and more directly their customer communication. That said… I have been very pleased with the quality of the Extreme.
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Old March 12th, 2008, 07:42 PM   #6
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Well this doesn't sound good. It sounds harder than with the M2 because you have the extra work to get the individual posts on the same level or your edge to edge focus will suffer. I wonder why this isn't done properly in the factory? If you buy it with a PL mount and pay for the mount to come installed, one would expect perfect back focus at the right FFD.

And then people say the Mini35 is over priced. It is not. It's just well made and plug and play. You never need to mess with it. You just put your camera on and shoot. What you pay for is precision, which the more affordable adapters all seem to lack. They all seem to need a lot of messing around. I was hoping the Letus Extreme would be different. I hope this is just one case and not the normal.
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Old March 12th, 2008, 08:40 PM   #7
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I'm not happy with this process. It sounds far to wishy washy to depend on when you're on set and really need things to WORK and work well.
I'm going to give it a try and see how the process feels and what kind of results I get. If I'm still not comfortable with it, then I'm going to send it back a get a refund. I would much rather pay the extra money and have something that works or just not own at all (and rent) - bummer.
thanks everyone.
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Old March 12th, 2008, 11:15 PM   #8
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For my 2 cents, I can say that so far I have been very happy with the EX1/Extreme combo - I say so far as I have only had both for a pretty short period.

I had an M2 with an HVX and could never get anything close to edge to edge sharpness. Even after having the optical bock replaced to have it ‘more’ centered down the barrel, I still had soft edges. Additionally, the spindle running through the M2’s ground glass wasn’t set perfectly perpendicular to the focal plane, So even though I had the backfocus spot on, when the adapter was running, the ground glass would spin slightly closer and then farther in relation to the camera’s own lens with each revolution… Creating vibrating focus. This was an issue that wasn’t perceivable at normal speed, but at offspeed at 60fps… Very noticeable.

I’ve also used the both the pro and mini35s, and I will certainly agree that they are very well built - in fact, due to their robustness, they are the only adapter that I will rent from a camera house, although I would like to try the Movietube. However, the mini35 and Movietube cost a lot more than the M2 or Extreme. The mini eats more light than the cheaper adapters, and while it is better engineered, a short at the battery mount plagued my last shoot with one, and cost me a number of great takes when the ground glass stopped spinning mid-take. This, along with the fact that I find the mini’s oscillating ground glass noisy, is the reason that I purchased the extreme.

The thing about all of these lens adapters is that they are all work arounds… And ad hoc solutions…. Again my experience with some change…
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Old March 12th, 2008, 11:18 PM   #9
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I forgot to add that with the Extreme, I didn’t find adjusting the posts equally to be that difficult at all.
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Old March 13th, 2008, 12:17 AM   #10
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Quote:
Originally Posted by Tom Burt View Post
I forgot to add that with the Extreme, I didn’t find adjusting the posts equally to be that difficult at all.
that's good to hear. I'm going to give it a try and see how it sticks. I basically want to know (and experience first hand) that I can get the adapter to be IN FOCUS consistently through out a shoot. I don't mind checking back focus once in a while... but if I have to completely take the adapter apart every time I change a lens, or bump the camera, or move the camera or what ever than that's going to be a total deal breaker. I don't mind working out a few kinks though. we shall see.
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Old March 13th, 2008, 04:38 AM   #11
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Tom you are working with Nikon right? Cine lenses are much more of a problem when it comes to back focus at wider focal lengths.
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Old March 13th, 2008, 05:55 PM   #12
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It seems I will be playing with a Letus PL soon. I'm looking forward to check if it will also have the back focus issues.
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Old March 14th, 2008, 02:32 AM   #13
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Yeah… So far, only Nikon. But I’ve never had an issue particular to wide cine lenses and backfocus. Perhaps, I’ve just been very lucky, but it seams to me if the actual lens is correctly collimated, then it shouldn’t be any different from a longer lens and the correct FFD. But if I’m wrong, please correct me…

The only potential backfocus issue that I’m watching with the Extreme at the moment is can the vibrating ground glass vibrate out of backfocus? My concern stems from not knowing what is actually holding the posts and thus the ground glass in place. I will say that when I adjusted the FFD, I did find it fairly easy to manipulate the posts. Again, this is not a problem I have had so far in my limited use of the Extreme or even heard of, but something I have an eye on.

Please let me know how your shoot with the Letus and PL goes. I had a job coming up that I actually purchased the Extreme for (Ex1/Letus/S4s), but it’s now gone back to the original plan which is film… Which is cool, but I am very curious so see how the system plays in production.
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Old March 17th, 2008, 07:28 PM   #14
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Originally Posted by Tom Burt View Post
Please let me know how your shoot with the Letus and PL goes.
Well, not very well. I got to test it during the weekend. It makes very sharp pictures but I was quite disappointed with the engineering and design part at times and also somewhat the build, although this is just referring to the PL mount itself. The PL mount although it "worked" I found it quite flimsy and temperamental. I like the M2 PL mount much better(although the Letus Extreme adapter runs miles around the M2). I think it is better designed and made. The Letus PL mount felt like one of them cheap knock off accessories from India that you can buy on ebay. It doesn't even feel like aluminum. More like die-cast or something.
What I didn't like about the design was the way the mount attaches. Just three screws that you tight against the mount. No threads or even holes. Quite flimsy and inaccurate. By the way, you MUST have rods. I have read people saying you don't necessarily need them but that is just not true. Without rods, every time you tight (and otherwise) the mount the whole adapter will spin and get out of alignment. The whole connection through the filter threads is already a big design flaw in my opinion. Not stable enough, flimsy and risk damaging the filter threads and lens. But that is also how the other adapters connect.
Now the thing that really is annoying and quite unacceptable if you want to claim to be a professional tool is that infinity focus was not right. Even though the instructions that come with the adapter said the focal flange distance is adjusted at the factory this is just not true. The owner of the adapter shoots mostly with Nikons so he doesn't seem to care much and his widest PL is just a 50mm. But I took a 35mm and a 18mm PL and they wouldn't focus to infinity. I know they focus to infinity just fine on an Arricam so the problem is clearly the Letus. But then when I re-read the Letus instructions I found out the problem. They state they adjust the FFD at the factory using a 50mm lens. What a "unwise" move if you ask me. :( You should always adjust that with a wide angle lens since it's more critical with them, then the longer lenses will be all in focus too. A 50mm is hardly a wide angle. This is surely the reason and it shows the inexperience and somehow amateurism of the company. They are clearly not well rounded when it comes to real cinema lenses. Not surprisingly as all these cheaper adapters are more of a prosumer/cool toy thing than a real pro tool made to be dependable and to work without flaws, and the fact they are all mostly specialized in using still lenses for motion photography shows that. Also because all the compromises they have. At least now they are starting to overcome some of these compromises, like including a flip function etc. Things that the Mini35 always had. All together, the Mini35 is just much more professional, well thought out and works out of the box as it should. I have shot hundreds of times with a mini35 and I have never needed to adjust the FFD or have it failing on me in any way. Besides that, the Mini35 feels much more professional and is plug and play. Feels as well built as an Arricam. But it cost a lot. I would never buy it. But for rental it's the best option. I don't even think any of the cheaper adapters would survive rentals.
The saying is still true when it comes to 35mm adapters. You get what you pay for. Get a Mini35 and it will work. People who shoot professionally and can't afford to have things not working as they should on a shot will pay the premium. That's why P+S is still in business. Hobbyists and lower end professionals will put up with the compromises, lack of quality and design flaws to save some money. I was thinking of buying a Letus Extreme but I guess I will continue to rent a Mini35 when I need a 35mm adapter.

Come to think of it, this is not much of a fair comparison. P+S makes parts and accessories for high end film cameras. I doubt the Letus company even has a collimation bench. But for what is worth it, here are my impressions since you asked. Having said all that, if you can manage to focus your lens or have some time to waste messing to fix something that should have come right from the factory, the Letus Extreme makes one of the sharpest images I ever seen from a 35mm adapter.
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Old March 19th, 2008, 02:42 PM   #15
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Quote:
Originally Posted by Tom Burt View Post
I contacted Letus about backfocus and got the following instructions:

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

This procedure, while a little bit of a pain as it involves a lot of trial and error, worked perfectly in achieving spot-on backfocus with the Nikon mount - I haven’t had an opportunity yet to test it with any PL mounted glass. I will note that precision is key in that you want to make sure that the three posts are pulled out equally so that the ground glass is flat to the focal plane.
I attempted this process and DISASTER I am now dealing with. First of all, when pushing the post into the adapter 2 of the 3 posts just bounced right back. They were completely unadjustable. Then as I feel like I'm finally making some progress the top suction POPS OUT! Now my gg screen is just dangling by the bottom posts. Is there any secret to getting that suction foot back in the little hole? I'm 3 hours in and no dice.

Quite an unintuitive process and especially annoying as an hour later I find out that Letus has released a new Nikon mount with a much easier back focus adjustment (why did they not let me know this product was an option and now available!!!). I really love this adapter but its starting to get on my nerves for sure. First I get sent an adapter with a cracked front tube, then the EX1 optimization kit that I pay $350(!) for doesn't give me edge to edge sharpness and then I'm told I need to adjust my gg screen which was supposed to come factory pre-set. The more I deal with them the more I feel like I have a returned/refurbished adapter and that doesn't make me so happy!
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