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Old August 15th, 2009, 03:35 PM   #1
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Methods of setting initial focus

I'm trying to determine if there's a "best method" or even consensus on how to set initial foucs using an adapter. I'm aware of two methods:

1) Point adapter without lens at bright light source and focus the camera's lens on the ground glass, with ground glass static/off. Once in focus, attach 35 mm lens and go to work.

2) Attach 35mm lens to adapter, turn it on and focus both the camera and 35mm lens back and forth until image is sharp.

I've tried both; method 2 seems a bit fiddly to me because going back and forth seems to invite me to touch the camera's lens during regular operation.

Has anyone tested the methods? Is one more precise than the other?

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Old August 17th, 2009, 09:59 PM   #2
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My personal preference is 2. with addition of resolution chart like the Lemac chart you may see in a few of my posted images here. I also use the red "peaking" function on Sony cameras. Sometimes, the most subtle movements you will not see just by looking at the image will become evident with peaking selected as you hit the sharpest point.

If you can't get hold of a resolution chart, a newspaper sheet will do at a pinch with he camera set back far enough to frame the broadsheet opened out to two pages.

A black plastic nit comb taped onto a backlit window glass, should resolve with most HDV cameras when a good 50mm prime lens is on front of the 35mm adaptor, at a distance of about 1 metre and the camcorder zoom is at about 70mm.

That puts you in the ballpark of about 800 horizontal lines of resolution. An ordinary hair comb at the same settings indicates about 280 horizontal lines of resolution.

The area of the window glass framed in the camera viewfinder should be about 290mm or about 11.5" wide.
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Old August 18th, 2009, 12:45 PM   #3
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I use the Redrock suggested method of setting backfocus.

1. Attach lens to adapter
2. Stop down lens till image is somewhat dark
3. Adjust lens focus until image is out of focus
4. focus camera lens till grain on disc is sharpest edge to edge

In addition I increase camera gain by 12db during the process.
Works pretty well for me.
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Old August 19th, 2009, 10:19 AM   #4
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John's Redrock method is perfectly valid and is also the original method published by P+S Technik for their Mini35/Pro35 adaptors.

The stopped down stills lens provokes the groundglass texture to become apparent and it is this you focus on. You need to also make sure the iris on the camcorder lens is set wide so that the critical focus is accurately set otherwise you may encounter an unexpected soft image when you operate in low light.

I find and maybe it is my imagination, that there seems to be another approx 50 lines of detail to be had by focusing the relay interactively with the stills lens against a resolution chart. There is a bit of a pet theory that a plane of sharpest image exists within the thickness of the groundglass texture, not at the surface.

The Sony HVR-Z1/FX1 camera family is really good at maintaining relay focus with short bursts of autofocus, the PMW-EX1 not all that good at the same trick.
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Old August 25th, 2009, 10:08 PM   #5
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To some extent which method you choose will depend on your circumstances - are you in the field, outdoors, in a studio, etc? Likewise on the type of adapter and camera - sometimes it is hard to focus on the screen.

I agree with Bob that whenever possible #2 is best as it is really allowing you to focus on the image itself and that is bottom line what you care about, not the ground glass pattern. Tape off the camera lens after setting so you don't get too fiddley.
I also bring a chart with me and check it as often as possible. The red peaking on my Ex-1 is a godsend in the field as I can just point over at a a grove of trees or a wall and quickly check my focus.

Be aware always that the best center focus may not be the best overall focus for your particular adapter. If that leaves corners soft you may want to overshoot the center just a touch.

Lenny Levy
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Old August 30th, 2009, 10:45 AM   #6
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I've always focused the stills lens and let the autofocus do the initial work, then set to manual. Never gave me a soft image.
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