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Old April 8th, 2007, 12:34 PM   #1
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modified Letus

better , bigger , thinner GG, bigger condenser.
need to solve some problems with lense, but overall result encouraging.
(on these picture vibrator was off, so it is a static render of the GG).
http://www.giroud2.com/divers/fx1f.jpg
http://www.giroud2.com/divers/fx1d.jpg
http://www.giroud2.com/divers/fx1e.jpg
http://www.giroud2.com/divers/fx1g.jpg
http://www.giroud2.com/divers/fx1h.jpg
http://www.giroud2.com/divers/fx1i.jpg
http://www.giroud2.com/divers/fx1j.jpg
http://www.giroud2.com/divers/fx1k.jpg

Last edited by Giroud Francois; April 9th, 2007 at 02:43 AM.
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Old April 9th, 2007, 04:58 AM   #2
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It looks nice, but I have a question?
does all Letus adapters suffer from the chromatic aberration seen
on your pictures?

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Old April 9th, 2007, 06:32 AM   #3
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Hello

Probably the original Letus is a little better with chromatic, but i dismantle it before i made any test in the original configuration.
For having tested 3 of them, i can say they could fit your needs as long as you are not afraid to dismantle it for cleaning or adjusting.
I am currently experimenting different GG and lense so the result is far from perfect, but chromatic abberation is a problem easy to solve.
So far i am happy with the vignetting and the GG, so i will now try better lenses.
My opinion is the Letus is good for DV, but not for HDV.
The relative cheap price (375$ for the cheapest option) make it affordable for those who want to build a good adapter without the hassle of chasing for hard to find parts.
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Old April 9th, 2007, 08:31 AM   #4
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Giroud.
The background in your pictures suggests the "new thinner GG" is a plastic bag of some sort, or a thin-film diffuser as discussed earlier on this forum, thus a hazy, greasy bokeh that many find undesirable. Too much aerial image is being let through, and while this results in a sharp image, there is less depth of field, negating the purpose of the adapter. Simply, the "new GG" you have installed just does not diffuse enough.

This is a screengrab taken with the Beattie focusing screen which suffers, but not as badly, from the same problem:
http://www.thelifeguardmovie.com/mis...fx1test3sm.bmp

As you can see, the background is hazy, greasy and not completely diffuse.

Thin-film focusing planes have less grain and less light loss, which initially make them attractive for this kind of work. However, the image quality suffers as it is usually only diffuse in one direction due to the manufacturing methods of the thin film and striation patterns in the bag.

You might (probably will) find that your image will be much more film-like and of general higher quality if you install an actual ground glass as your focusing plane. As light-loss has been a continual battle with these adapters I wouldn't expect to settle with perfect light performance at the loss of a decent image.

Others may phrase this differently, but my point comes to a summation when you look at sharp lines in the background of your images that should be out of focus. Instead, details can be seen clearly.

I modified my Letus a long while ago, before selling it, so perhaps I can offer some advice.

Replace the achromat with a Century Optics +7 58mm. This all but eliminates chroma aberration. ~$220 MSRP, but ebay sometimes has it cheaper.

Find a focusing screen such as the Canon EE-S Super Precision Focusing Screen that has a fresnel condenser built in to the side of it. Combined with the use of the Century Optics achromat, the use of the plano-convex lens you found inside the Letus between your achromat and ground glass plane will no longer be needed, reducing weight and chroma aberration, as well as barrel distortion which is also evident in your screengrabs.

If you come across a situation where you have too much grain, you can increase the number of batteries by replacing the battery back instead with one that is wired for 3 AAs, providing 4.5v. I did this and it helped immensely in heavy grain situations with the lens stopped down.

Finally, I added an LED to the battery pack to indicate when power was switched on, so I did not drain the batteries. You may want to consider this modification if you are already cracking things open and have some simple soldering skills.

http://www.thelifeguardmovie.com/mis...us/ledind2.jpg

If you find your results already desirable then by all means stop here. But there are ways to improve the image you have by great lengths and I do not think you are taking full advantage of the adapter's capabilities.

Finally, to leave you with an example of what your footage *should* look like, I once experimented with my own spinning disk design, where the disk was covered with a sample of lighting gel diffuser that diffused the image perfectly, at the great expense of light loss and grain, even while spinning. Here that is:

http://www.thelifeguardmovie.com/mis...ffusertest.mov

Notice the nicely rendered bokeh discs where there is strong light, and how out-of-focus the background is.
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Old April 9th, 2007, 09:12 AM   #5
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Ben,
does this means, that this (yours) modification of letus uses STATIC GG? -> canon's focusing screen together with century optics glass - or i am making mistake here?
please, be so kind and explain it in more detail.

thank you,

filip
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Old April 9th, 2007, 10:02 AM   #6
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Quote:
Originally Posted by Filip Kovcin View Post
Ben,
does this means, that this (yours) modification of letus uses STATIC GG? -> canon's focusing screen together with century optics glass - or i am making mistake here?
please, be so kind and explain it in more detail.

thank you,

filip
Filip,
The replacement of the GG just means a different focusing screen, not a different functionality of the adapter. The vibrating ability of the Letus is not compromised, the screen still vibrates.

However provided there is acceptable lack of grain, there is no reason the motor cannot remain switched off for static use, although benefits are questionable.
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Old April 9th, 2007, 11:16 AM   #7
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thankx for fast answer.

filip
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Old April 9th, 2007, 12:00 PM   #8
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quote :"The background in your pictures suggests the "new thinner GG" is a plastic bag of some sort, or a thin-film diffuser...."

you bet, but you loose.
my GG is thin glass (0.2mm).
I must admit it can be worked a bit more (grain is too fine), since even on static you cannot see it.
I think the chroma aberration is due to the condenser (not the original) and i will try another one.
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Old April 9th, 2007, 01:25 PM   #9
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Quote:
Originally Posted by Giroud Francois View Post
quote :"The background in your pictures suggests the "new thinner GG" is a plastic bag of some sort, or a thin-film diffuser...."

you bet, but you loose.
my GG is thin glass (0.2mm).
I must admit it can be worked a bit more (grain is too fine), since even on static you cannot see it.
I think the chroma aberration is due to the condenser (not the original) and i will try another one.
Many people habe had sucess aluminum oxide at 320 grit, in European standards. The screenshots are definite evidence that the thin diffuser would benefit from a thicker grain.

Keep in mind that .2mm may be too thin for any effective diffusion to take place.
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Old April 9th, 2007, 01:48 PM   #10
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i was stuck on my last effort for the static adapter requiring GG at 1000 grit.
so i was trying my best for this one at 1000, but it is definitely too fine.
i will rework it a 600 to see if it helps.
for the glass, i found a company (SCHOTT glass http://www.us.schott.com/special_app...SID=ab26a662b9) that make thin glass, optical quality (mainly for LCD screen) at many different thickness.
I ordered some sheets (10x10 cm) at 0.2 and .4 mm.
it is tricky to work (easy to break) and expensive but for a vibrating system, the lighter you go , the best it is.
I use a diamond cutter, and it is really easy to cut.
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Old April 9th, 2007, 06:49 PM   #11
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Within limits, thickness of a diffuser should only affect diffusion if the material itself is opaque through its entire thickness on ot simply on one surface.
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Old April 10th, 2007, 02:37 AM   #12
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my experiment with thin glass was driven by several factor.
first i consider light travelling thru glass is a bad thing, so i will try to minimize the thickness of GG and condenser and macro lens.
The second benefit is you loose weight and that is good also.
I will try some test with 2 thin GG mounted together (grounded side insinde).
this would give the best protection against dust while maxing out diffusion and grain (and you still get a GG that is only 0.4mm thick)
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