LA-7200 Anamorph Lens Diopter

jaecjaec

I've got a couple of LA-7200 adapters to play with. Despite search the internet, I'm a bit confused over what diopters do exactly. Specifically where to place the diopters. So, I did this quick experiment. It's clearly quick and crude for reasons that I only had one hand free to hold the lens in place, and one to take a snap shot. This is done on a camcorder Canon HF-g10
1. Zoom out, native lens
2. Zoom out, native lens, +1D in front
3. Zoom out, LA7200
4. Zoom out, LA7200, +1in front of the LA7200
5. Zoom out, +1D between the camera and LA7200
6. Zoom in with LA7200 only
7. Zoom in with LA7200, +1D in front
8. Zoom in with LA7200, +1D between the lens and LA7200

I know these pictures are crappy, but am I correct to say that using a diopter between the lens and the la7200 work? It seems to not work as powerfully as putting it in front of the LA7200, but it works? Photo 6 is out of focus, photo 8 is in focus?

This is important to me, and perhaps others, since large, good quality 0.5 diopters are so rare and expensive. 68mm, higher power diopters, such as +1 or +2 may work just as well....

CRFilms

It seems to me this isn't a good test because you're using a camcorder. The problem with LA7200 and DSLRs or mirrorless cams is shooting close with wide open apatures. If you haven't already seen it the eyepatch entertainment guy on youtube has done a lot of vids with the GH1/2 and the LA7200. He uses a "cheap" $20-30 cokin +1 diopter and he gets close focus within a certain range with wide open lenses, but then he loses infinity focus and can only focus up close, but it works for typical talking close ups.

I also bought a cheap close up filter from Adorama and got good close focus with +1. Click my user name and search my "threads started" I've got some pics of focus with diopter and without.

jaecjaec

@CRFilms thanks for the info. I like eyepatch's videos, but had some questions as to what happen if the diopter is placed between the camera and the la7200. Some say it works, some say it wont. On my camcorder, I have full exposure control (really neat little camera) and found that both position works. Though putting the diopter in front clearly works better. I'll have to ask a few friends about the optical theory behind this set up. I had a very difficult time finding good quality low power diopters, and when I found them, I'm having great difficulties attaching them to the la7200, and maintaining a 'professional' look to the rig. Redstan has some low power achromats that is the same 72mm thread as the la7200. I wonder if it'd work.

ishvar

jaecjaec

As it turns out, I can make use of the la7200 and my Cinematics mattebox. Just unscrew the filter holder bracket, and the la7200 buts right up against the back plane. It actually fits perfectly between the two plastic retainers. I get some vignetting at max wide angle on my camcorder (around 30mm) but at about 50mm, there's no problems. Filter, a 105mm filter fits snuggly inside the la7200 housing.

Basically I can use any filter in 105mm size instead of 4x4.

P4INKiller

With some clever rigging you don't need a diopter.
You can focus however you'd like, and use whatever lens you need.

This guy was supposed to make a guide, it's a shame he didn't.

jaecjaec

@P4INKiller I saw that, but I'm not comfortable with exposing the optics to the elements. Plus there's some issues with magnification when the elements are moved like that. I'm actually happy with the la7200 and the diopter since I can screw on ND filters, polarizers, etc...But with the lens element sticking out, glare is a big issue. That's why I'm so happy that it fits the mattebox so well.

tvpglabs

JaecJaec

Where did you find the 105mm macro/close up filter? I've looked everywhere.

Roberto

@tvpglabs
+1
!!!
This diopter seems like some rare exotic bird.

LPowell

The reason you need a diopter for close-up work with an anamorphic lens is to center the convergence between the two anamorphic lens elements inside the adapter. You can regard an anamorphic as a wide-angle adapter that has different magnification factors in its horizontal and vertical directions. When the lens elements are precisely aligned, the anamorphic astigmatism at the plane of focus will coincide in an ellipse of minimum size. When the alignment is off, you'll see the astigmatism stretch out in either horizontal or vertical directions.

To correct the anamorphic astigmatism at close focus, you need to place the diopter in front of the adapter. Placing it behind the adapter will alter the plane of focus of the standard lens you're using behind the adapter, which is probably not the effect you're looking for.

Roberto

Can anyone please tell us where we can buy this 105mm diopter?

itimjim

It's called a Lomo Foton A, and they're as rare as rocking horse shit. I'd then expect to pay a pretty sum for it. There's an 153mm diopter on eBay at the moment (http://www.ebay.com/itm/D-2-5-1-0m-Large-Round-Diopter-LOMO-Zoom-Lenses-153mm-diameter-/250936936509?pt=Camera_Filters&hash=item3a6d01c83d#ht_2298wt_1134) for $750!

Roberto

@itimjim

Thanks. But like the ebay filter for sale, jaecjaec's pic shows an circular ordinary circular filter. The Lomos are rectangular.

itimjim

I know, I'm just saying it will work if you rig it up.

Diopters are really difficult at this size. I have a century focusable, which has a 95mm barrel size, with the interior glass 82mm. I can rig my Tokina +0.4 (72mm) into it, but it vignettes below 35mm. I also have the Cokin P101 +1 which is actually a circular 72mm piece of glass inserted into a 84mm plastics drop in filter holder.

I've got a LA7200 coming in a week or two from the US and will let you know how I get on too. My plan is to use the LA7200 in combination with a few other anamorphics depending on the scene.

Roberto

@itimjim
Let us know how you get on. I find that ETC mode is a good work-around; most lenses work with my Zenit +1 diopter (only 77mm) stuck in the LA7200 with double-sided foam tape.

leoj

Hello does anybody have a good solution for less dust to enter in the Inside of the 7200 ?

I heard some tape is good but where to seal it up not to sure

plasmasmp

Just wanted to bump this topic - I've been testing with a Schneider .25 diopter 67mm in diameter that is great for 2-5 meters. If only I could get one larger.

itimjim

@leoj I've had mine apart, and it's a very open unit, from back to front. Best place to seal is inside the little protruding hood. But it will be tricky to do so.

I've actually hack sawed the front of mine off now, so it's really simple to tape and seal. Advantages of hacking the front off, are being able to push it up to a circular aperture matte box easier and use wider lenses. My 14-140 now works at about 15mm without vignette now, where previously it was around 17-18mm. I'm also looking at adhesive Velcro for the front, to mount a hi-tech mark 4, 2 slot 100mm filter holder with rotating 105mm ring (for pol).

@plasmasmp I don't think you will struggle in the 2-5m range with many lenses that will require a larger diopter before vignette. The 20/1.7 works with a 72mm diopter taped right up to the front element. The 14/2.5 works well wide open without any diopter.

plasmasmp

Here's the results of the .25 diopter behind the lens. This does not effect minimum focus distance, but it does improve the image significantly as you can see in the attached pic.

EDIT: Attached a jpg of a Scarlet X still @ f4 with the .25 Diopter behind the lens

itimjim

Are you getting a vignette with your 67mm .25 diopter? If not, then I don't see any problems.

What aperture were you shooting the above images at?

itimjim

Sorry, i didn't read right.....behind the anamorphic...interesting.

plasmasmp

When you go up to 4k, you need to be at f5.6 to full resolve that much detail, but even at f4 it has a nice soft FD/Pre Ai look to it

itimjim

@plasmasmp have you tried the 14/2.5 pancake combination, as I find this lens works well wide open. It's "crazy" wide though :-)

I'm going to have ago mounting my Tokina 0.4 Achromat in front of the LA7200 to see what results it yields.

plasmasmp

I'm sure it works with the 14mm 2.5 but you're going to have more CA and barrel distortion. The other problem is that with electronic lenses, the sharpening seems to be more noticeable when the picture is unsqueezed resulting in more noticeable aliasing on the GH2. If Vitaliy finds a way to disable the sharpening completely with 4/3 and m4/3 lenses, I would try and get the Leica 14-50 or the Oly 14-35 working with this method. The Tokina .4 also helps at longer focal lengths to sharpen the lens by mounting it in front and sandwiching the la7200 with the .25 in the rear and the .4 in the front. Downside being you've greatly limited focus distance unless stopped down.

itimjim

@plasmasmp Thanks for the advice. I've just tried the Tokina .4 in between the 14/2.5 and the LA7200 and there's an improvement in the edges. I was quite happy with it anyway, but that's quite nice. Ironically it had trouble focussing close-up. I wonder if this might work for the 20/1.7 too?

Based on your video, I've just purchased a Heliopan +0.25 Close-Up 52mm, so I'll give that a whirl sandwiched between the LA7200 also.

If you ever get the chance to try out a Bolex 16/32/1.5x, do it. I love the convenience of single focus (and auto when necessary) of the LA7200, but the difference in wide open quality is astounding in comparison. Just a shame the widest lens I can use is 28mm. I'll post a comparison video when I get chance.

I've not noticed the difference in sharpness handling on the GH2. I always presumed the Panny glass was super sharp due to the coatings. I'm currently looking at diffusion to try to soften them up a bit, possibly a Tiffen ULC. Filters aren't the easiest thing in the world to use with the LA7200 either!

plasmasmp

I want to buy a Bolex 16/32/1.5x or an Isco 42 but they have dried up it seems. We have an Isco 36 and that's fantastic down to 35mm

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