8mm Forum: How to use a scope lens correctly?

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Topic: How to use a scope lens correctly?

Christian Bjorgen
Jedi Master Film Handler

Posts: 996
From: Kvinnherad, Norway
Registered: Oct 2009

posted February 07, 2010 11:34 AM

OK!

So I have my trusty Elmo ST180 with the 1.3 lens, and last night I recieved my "new" Proskar Anomorphic 16, courtesy of mr. Martin Jones of the forum.

I've experimented a little today with my scope trailers, but I seem to have one problem, and that is that I cant get the lens to focus correctly. I cant get it sharp enough.

Any ideas?

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Douglas Meltzer
Moderator

Posts: 4554
From: New York, NY, USA
Registered: Jun 2003

posted February 07, 2010 12:15 PM

Christian,

First get the correct focus without the scope lens, and don't change that focus setting. After mounting the scope lens, adjust the focus on the scope lens as opposed to your standard lens.

2 questions: How is the scope lens mounted onto the projector (bracket, screwed on the threads)?
What is the screen distance from the lens? Certain anamorphic lenses perform poorly at the minimum focusing distance.

There's also the light output to condsider. The ST-180 takes a 100w bulb. Using a scope lens over that 1.3 cuts down the amount of light significantly. If the distance available allows, use the telephoto (25mm) end of your 1.3 lens. That should sharpen things up a bit.

Doug

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I think there's room for just one more film.....

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Christian Bjorgen
Jedi Master Film Handler

Posts: 996
From: Kvinnherad, Norway
Registered: Oct 2009

posted February 07, 2010 12:59 PM

I haven't mounted it yet, still working on a patent for that, so when testing I've just held the lens close to the other one. The distance from the projector to the screen is roughly 10 feet I think.

Light isn't the issue I think. Colours and everything are pretty fine, it's just focusing that's the problem.

Odd thing is, when I tried with my "High Plains Drifter" reel, it worked so-and-so, but not perfect. But when I tried with my Hercules scope trailer I can't manage to focus at all.

Telephoto, what's that?

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Well who’s on first? Yeah. Go ahead and tell me. Who. The guy on first. Who. The guy playin’ first base. Who. The guy on first. Who is on first! What are you askin’ me for? I’m askin’ you!

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Brad Miller
Administrator

Posts: 525
From: Dallas, TX, USA
Registered: Jun 2003

posted February 07, 2010 03:32 PM

The ideal way to set the astigmatism on that anamorphic lens is to intentionally set it to infinity. Then run a print and skew it out of frame so you can see the frameline visible on the screen.

You will notice the entire picture is blurry, but you WILL be able to achieve a solid focus on that horizontal frameline. Adjust the projector's focus control to achieve this. Don't touch the anamorphic after that until you have finished the below steps, and don't re-thread. The projector's focus cannot be even bumped during this once set for that sharp horizontal frameline.

Now adjust the astigmatism control on your anamorphic. You will probably find it to be very close to the minimum distance. Adjusting this down from infinity will bring all of the vertical lines of the picture in focus. Hopefully you don't hit the low end before you achieve this. If you do, then that anamorphic lens won't work for your particular throw (distance between projector and screen).

Once you have achieved ideal focus, lock the anamorphic's astigmatism adjustment so it can't get knocked out of alignment in the future.

From this point on, simply use your projector's focus control.

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Dan Lail
Film God

Posts: 2110
From: Loganville, Georgia, USA
Registered: Jun 2003

posted February 07, 2010 03:44 PM

Brad, I have always adjusted via Doug's method with good results. I'll have to try you method mow. Thanks.

Christian, great forum pic. Was someone running along side the car with a digital camera? [Big Grin]

I also have a home made scope rig. Work's great!

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Christian Bjorgen
Jedi Master Film Handler

Posts: 996
From: Kvinnherad, Norway
Registered: Oct 2009

posted February 07, 2010 03:51 PM

Ok, thanks for the tips guys!

One more thing: What is the ideal distance between the lenses? Should they be touching each other? And what is the best way to mount it?

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Well who’s on first? Yeah. Go ahead and tell me. Who. The guy on first. Who. The guy playin’ first base. Who. The guy on first. Who is on first! What are you askin’ me for? I’m askin’ you!

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Brad Miller
Administrator

Posts: 525
From: Dallas, TX, USA
Registered: Jun 2003

posted February 07, 2010 04:20 PM

The closer the lenses are, the less chance of vignetting (dark corners) you will have.

Ideally you want to use as much of the anamorphic glass as you can, so to get an idea, before you follow the steps I wrote above, set the lens TOO far forward so you get dark corners and slowly bring it back toward the projector's lens (not worrying about focus...do this with no film in the projector) until you get rid of the dark corners, then move it just a bit more. That's your ideal position.

Mounting is projector specific. (Whatever works [Wink]

)

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Christian Bjorgen
Jedi Master Film Handler

Posts: 996
From: Kvinnherad, Norway
Registered: Oct 2009

posted February 07, 2010 04:50 PM

Thanks, Brad, I'll try it out once I build some sort of mount for the lens [Smile]

Dan: It was taking during the Norwegian celebration "Russetiden", which is pretty much 17 days of drinking on a bus. The picture is from one of our trips [Wink]

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Well who’s on first? Yeah. Go ahead and tell me. Who. The guy on first. Who. The guy playin’ first base. Who. The guy on first. Who is on first! What are you askin’ me for? I’m askin’ you!

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