8mm Forum: How to set up scope focus

This is topic How to set up scope focus in forum 16mm Forum at 8mm Forum.

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Posted by Mark L Barton (Member # 1512) on May 31, 2017, 07:12 AM:

Hi all. I am projecting onto a large 15ft screen with an Elf 16MM with a scope lens in dedicated elf bracket, yet I cannot get a sharp picture. On much smaller screens and using a freestanding scope holder I can get a razor sharp image, but not on this long throw.
Your advice please.

Posted by Maurice Leakey (Member # 916) on May 31, 2017, 02:02 PM:

Mark
1) Set the anamorphic to the approximate throw on its scale
2) Without the anamorphic in position run a film and focus the normal backing lens
3) Swing anamorphic into position
4) Continue running the film and then fine trim picture with the anamorphic
5) Finish with a final "tweak" with the backing lens

Posted by Mitchell Dvoskin (Member # 1183) on May 31, 2017, 02:10 PM:

This is what I do:

On the scope lens, there are marking indicating either meters or feet, depending upon the scope lenses vintage and origin.

1. Loosen the tiny lock screws so that you can turn the outer ring of the scope lens, lining it up about where the markings indicate the distance between the projector and the screen.

2. Run a film with high contract end titles (white letters against a dark background) with just the prime lens without the scope attachment.

3. Focus the prime lens, tape down the focus knob so it does not move.

4. Place the scope lens in front of the prime lens. There should be no vertical ghosting above or below the letters. If there is, you can fine tune by re-focusing the prime lens with the scope lens in place.

5. Turn the scope lens's focusing ring until there is no horizontal ghosting to the left or right of the letters.

6. Done. Tighten the tiny lock down screws so the scope lens focus does not shift.

NOTE: I have seen very few razor sharp 16mm scope films. Many are slightly off from the lab. However, any softness should be very minor.

NOTE: There are a lot of second hand scope lenses out there that have had some of the internal elements knocked out of alignment, and will never focus correctly. Since at short distances you can focus correctly, I don't think that this is your problem.

Posted by Clyde Miles (Member # 4032) on May 31, 2017, 04:59 PM:

ok, what about a scope lens that screws into a primary lens, how does that work?

Posted by Steven J Kirk (Member # 1135) on May 31, 2017, 08:47 PM:

Best to break out the tape measure and actually measure the distance. Then set that on the scope lens. Then you know one is good and it is just the normal focussing on the back lens.

Posted by Mitchell Dvoskin (Member # 1183) on June 05, 2017, 03:29 PM:

> ok, what about a scope lens that screws into a primary lens, how does that work?

Same concept. Vertical ghosting is adjusted by focusing the prime lens, horizontal ghosting is adjusted by focusing the scope attachment. Does not matter if it is screwed or a separate bracket. The distance marking on the scope attachment get you close.

Posted by Maurice Leakey (Member # 916) on June 06, 2017, 02:41 AM:

I should point out that ghosting is caused by the intermittent and the shutter being out of phase with one another. It has nothing to do with focus.

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