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Old September 25th, 2004, 02:05 PM   #1
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DIY EF adapter: alternatives?

Forgive me if I am being wildly hypothetical as I don't have any video gear YET - waiting for the XL2 - but am excited about using my EF slr lenses with it.

The Canon EF adapter has 7x mag. which is fine with me, I want that. But I also want to be able to use the lenses at lower magnification, which xl1solutions claims is possible using their adapter. However, Charles P. more or less challenged that claim successfully, as we've not seen or heard of xl1solutions since.

NEVERTHELESS, I have visualized my EF's hovering over the opening of the XL2 and I think it is possible to reduce the magnification. My assumption is based on a very simple diagram:

http://www.fluffbucket.com/grapix/camera.gif

Replace the film plane with ccd, and imagine the cone of light falling on it. The light cone expands or shrinks depending the distance between lens and ccd.

Using the Canon EF adapter, the EF light cone dwarfs the ccd. To get more of the light cone onto the ccd, the ccd and the lense would need to be closer. Follow my logic, am I doing good so far? Okay, the next step is: how to move the lens closer to the ccd.

http://www.xl1solutions.com/EFD%201%20(3).jpg

http://www.bhphotovideo.com/images/l...ges/146134.jpg

When comparing the pics of these two adapters it seems to me that the Canon puts more distance between the lens and ccd, it is thicker than the xl1solutions adapter, which would result in a larger light cone falling on the film plane. The xl1solutions adapter gets slightly closer to the body

http://www.xl1solutions.com/EFD%201.jpg

I don't know the measurements of the adapter, but the adapter ring seems to be around 1.5-2cm, not much, but it means that it is possible to move the ef lense even closer.

What if you could push the lens right up against the body? How much more of the light cone would fit on the ccd then? How would an adapter with 0.0 cm thickness look like? Let's forget about the EF lenses for a sec. How about a non-EF lense small enough to pass through the opening of the XL2, could not such a lens press right up to the ccd itself? In that case ALL of the light cone would fall onto the ccd. But I want to use EF lenses so I can't think about that right now.

My initial picture for an EF lense adapter with 0cm thickness would not be an adapter at all. It would have to be an off-mount lens cradle/bracket/platform of some considerable size that would hold both body and lens in alignment, securing the lens in front of the lens mount without an adapter. Seal the space between lens and body with tape as light would spill into the hairline space.

Not very portable and def not pretty - if I were to make one; but someone good with aluminum...

I've seen some pretty neat DIY contraptions out there.
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Old September 25th, 2004, 06:54 PM   #2
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In order for a lens to focus from infinity (just for argument, the moon) and it's minimum focus distance (MFD), like the lens designer intended, the exact distance from lens flange to film plane must be maintained. If you move the lens away from the film plane you gain near focus (you can focus closer) and if you move the lens closer, you lose MFD. In plain english give up on the EOS lenses and adapting them to the XL series cameras. Unless, of course, you are doing wildlife or surveillance videos.
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Old September 26th, 2004, 01:16 PM   #3
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Jeff is right. IF you want to do what to reduce the film plane image size down to a 1/3 inch CCD then you have to do it in a different way. You need to use a series of optical lenses between the 35mm and the CCD to reduce the image size (NOT the flange focal length). This will give you the FOV of your 35mm lens but you loose the 35mm DOF quality of the image. There is one product out there already that does the conversion between cine lens and 2/3inch CCD's but its incrediblely expensive and TOOOOO complicated to make yourself.

BTW one GREAT plus of reducing the film plane size of a lens is you increase the brightness quite of bit.

Good Luck.

-Brett
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Old October 3rd, 2004, 11:38 PM   #4
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Brett is right. There are the 35mm adaptors being worked on here, do search for 35mm adaptor AND xl1 with results by post option activated (the standard option is useless for these large threads).

The issue has been discussed before, to get 35mm FOV without DOF, all you really need is a triplet relay lense, for proper chromatic correction accross three colours (pluss the tubing to mount it. The problem (I have read elswhere) is that companies don't tell you which three colours (could be red blue and infrared, or alteraviolet. So you have to make enquiries that it is actually the correct wavelength in red green and blue. This is going to cost you (doublets maybe cheaper and good but lack abreviation correction in one colour, but low dispersion doublets are better in that). What I don't understand is why don't just correct in two to match to the third. The relay lense has to be bigger than the cone passing through it, to get away from barrell distortion (I forget how much bigger but likely to be as much as 20%). So suddenly you find a price jump to big triplets. Triplet Quality is another thing, there is a 35mm adaptor test chart listed in those threads and that should be able to be used on a relay. It has colors to test for colour misalingment and grid of lines to test for lense distortion and can be used to test for graininess.

I have read on the forum, of somebody saying that their off the shelf FOV adaptor has a lense in it, but don't know what brand.

Have a good day.
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Old October 4th, 2004, 12:58 AM   #5
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I have a 35mm EF TILT_SHIFT lens that creates a blurring effect that is very striking, not dissimilar to a shallow dof...

I wonnder if this effect can be preserved when mounted on the ef adapter after the 7.x magnification.
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Old October 5th, 2004, 01:00 AM   #6
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I am not familiar with the tilt lense, but if you use the lense uncondensed (no relay lense) (giving you magnification) you will have the DOF, but not FOV.
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Old October 5th, 2004, 06:48 AM   #7
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Yes, the TS lens will still have the ability to change and control the DOF. However, the DOF will be much larger than on 35mm and the amount of tilt and shift on the lens may not be enough to achieve your desired effect.
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