8mm Forum: 12.5mm Eiki Lens

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Topic: 12.5mm Eiki Lens

Mike Felling
Film Handler

Posts: 34
From: Riley, IN, USA
Registered: Aug 2011

posted February 19, 2015 12:18 PM

Hello All,

I recently acquired an 12.5mm 1.4f lens for my Eiki NT. I installed it last night and the picture is massive. I did however run into an issue. It seems like I cannot hit the sweet spot for the focus. It shows some blurring even when I have it set at the best possible setting. Are there any other things I can do to achieve a better focus with a short throw lens? I will include that my projector height needs to be a little higher.. I did have to angle it up a bit.

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Paul Mason
Jedi Master Film Handler

Posts: 540
From: Aldershot, Hampshire, UK
Registered: Nov 2013

posted February 19, 2015 01:59 PM

Mike,
The screen needs to be at 90 degrees to the projector beam both vertically and horizontally. Try tilting the top of the screen forward to offset the projector upward angle.

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Paul.

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Maurice Leakey
Film God

Posts: 5895
From: Bristol. United Kingdom
Registered: Oct 2007

posted February 19, 2015 02:50 PM

Short focus lenses are notoriously difficult to focus. It's most important, as Paul says, to ensure that the light beam is fully square on to the screen.
If the projector has an upright tilt, or is tilted down, move the screen accordingly to the same tilt position and also ensure it's 90 degrees sideways on.

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Maurice

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Mike Felling
Film Handler

Posts: 34
From: Riley, IN, USA
Registered: Aug 2011

posted February 19, 2015 06:34 PM

Ok great! I had originally thought perhaps it was a faulty lens or the lens had been taken apart and not been fixed correctly, but it does look very very new and virtually untouched. I didn't know that short throw lens's were harder to focus. Always learning [Wink]

My screen cannot be moved so I will have to get the projector elevated and square with the screen. Hopefully that will help the focus.

One other thing I noticed is that the film does fluctuate a bit with the focus on its own. Anything I could do to help this?

Also. about this Eiki lens. I have a Singer Graflex Zoom adapter, and it will not fit the 12.5mm lens, but does fit my 50mm. Any reason for this?

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Clinton Hunt
Jedi Master Film Handler

Posts: 845
From: Waharoa,North Island,New Zealand
Registered: May 2010

posted February 20, 2015 12:45 AM

Hi,
"One other thing I noticed is that the film does fluctuate a bit with the focus on its own"

I have a couple of films that also do this and that is because the films are warped/bent - this maybe the problem and if it is then not much can be done apart from always re-focusing as it screens !
Or the focus knob is loose and the running of the projector causes it to un-focus...I'm no expert so I maybe wrong?

Cheers :-)

--------------------
Cheers from me in New Zealand :-)

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Dominique De Bast
Film God

Posts: 4486
From: Brussels, Belgium
Registered: Jun 2013

posted February 20, 2015 04:36 AM

Mike, I have converter that can be used only until 38mm lens, when used on a 25 mm one, a part of the picture is missing on the screen. Maybe it's the same problem with your accessory : a limitation on some lens sizes.

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Dominique

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Maurice Leakey
Film God

Posts: 5895
From: Bristol. United Kingdom
Registered: Oct 2007

posted February 20, 2015 04:39 AM

Clinton observes that the focus knob may be lose. This may be caused by the rubber piece on the shaft of the focus knob which could have gone soft.
Details of replacing this sleeving have been posted on the Forum recently.
http://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=8;t=003345#000000

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Maurice

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Mike Felling
Film Handler

Posts: 34
From: Riley, IN, USA
Registered: Aug 2011

posted February 20, 2015 12:14 PM

Maurice, and Clinton, To be honest, It is probably time to replace my focus tube. I did take it out and inspect it, and its not coming apart, and actually looks like its already been replaced at some point. But this could still be the reason for my focus issues.

Dominique, Hmm.. I see what you saying. With my 12.5mm the Zoom adapter will gently sit in, but will not thread (I hope that makes sense) It will say sitting in the lens.. but gives a total circle picture. So I'm wondering if its even possible to use at all in that combination.

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Paul Mason
Jedi Master Film Handler

Posts: 540
From: Aldershot, Hampshire, UK
Registered: Nov 2013

posted February 21, 2015 07:51 AM

Mike,
Zoom adapters are computed to work certain lenses only for spacing and coupling threads - usually with the same maker's lenses. They are designed for standard focal length and mild wide angles as they would have to be huge to cover the beam of 12.5mm, 20mm, 25mm and 32mm lenses. For example the Bell & Howell zoom adapter works with the 40mm and 51mm lenses. On the whole proper zoom lenses and fixed lenses give better results.

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Paul.

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Mike Felling
Film Handler

Posts: 34
From: Riley, IN, USA
Registered: Aug 2011

posted February 21, 2015 12:24 PM

Great, thank you for that info Paul. I did manage to elevate my projector last night, and it gave a pretty stunning picture. Much better focus than when it was not angled correctly. You definitely gain a new love and respect for film when you can actually see it in the proper proportion.

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David Ollerearnshaw
Phenomenal Film Handler

Posts: 1373
From: Penistone Sheffield UK
Registered: Oct 2012

posted February 21, 2015 03:36 PM

Sounds like the keystone effect. Some screens the more expensive ones had a top bar where the screen would tilt forward to counteract the effect. My setup uses a projector stand which puts the projector roughly with the lens pointing at the centre of the screen.

Thinking now both the stand and screen must be getting on for 40 plus years old. The screen came from DRH who are still about.

--------------------
I love the smell of film in the morning.

http://www.thereelimage.co.uk/

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