8mm Forum: "Why should we have to manually adjust the focus during a screening?"

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Posted by Jan Bister (Member # 332) on June 19, 2005, 05:26 PM:

... And that's exactly what I happened to be asking myself recently... and then I got to thinking: What if one were to attach some kind of motorized unit with a wired remote control (more of an on/off/reverse switch, really) to the projector's focus knob, therefore enabling one to remotely adjust the focus without having to get out of one's favorite cine chair and running back to the projector everytime?

So I'm wondering - do such projectors with "auto-focus" already exist? Is it feasible to make your own? Perhaps from some kind of battery-operated toy motor combined with a gear assembly and some sort of rotating clamp to attach to the focus knob?

How many of you guys actually find you have to adjust the focus at least once or twice throughout a feature presentation?

Posted by Kevin Faulkner (Member # 6) on June 19, 2005, 05:44 PM:

Regularly [Frown]

The larger the aperture of the lens the less depth of focus you have. Heat can warm up the gate and film runners which can contribute towards this but I think a major player is the stripe on the film. My theory is that the thickness of the stripe, particularly the paste variety, can vary and do all sorts of things to the focusing.
One of the reasons I say this is because I have noticed that if I play optical prints or silent prints the focusing is far more stable.
Another time I noticed this was when I was round Keith Wiltons house one evening and we viewed the first reel of Master and Commander. This was a test print and had no stripe applied to the film. Keith didnt have to adjust his focus once after he initially set it up and also the print was rock steady. I would certainly have had to adjust during a 400ft reel at some point.
Any other theories?
Yes some electronic gismo attached to the lens and say measuring any movement from optimum in the film path and moving the lens to compensate would have been great but then think of how precision this would have had to be.
As for remote control of the focus on the machine...I always stay by my machine during projection in case something untoward should happen so dont find it a problem to give the focus knob a twist if need be.

Kev.

Posted by Jan Bister (Member # 332) on June 19, 2005, 06:10 PM:

I pretty much do the same thing, alas the distance between my ST-1200HD and the screen is fairly large, and for the best big-screen effect I find that the spot right in the middle between projector and screen - um - hits the spot. Not only that, but if I walk back to the projector I'm further away from the screen and find it even harder to judge whether or not the image is in focus as I adjust it! [Eek!]

I guess I'll see if I can dig up some motor + gear assembly at a toy or DIY store and let the mad-scientist side of me do the rest [Big Grin]

On a side note... while it certainly isn't a bad idea to stay near the projector just in case, I've gained enough trust in my unit to just let it do its thing in the background. Heck, I won't even feed it any film that I haven't carefully inspected for sprocket damage and bad splices and things like that. Which I do with every newly-acquired print. [Smile]

Come to think of it... They don't seem to have to readjust the focus at the local multiplex when showing those 35mm features... not that they do a very good job at that to begin with. (sigh) [Roll Eyes]

Posted by Paul Adsett (Member # 25) on June 19, 2005, 07:05 PM:

Of course all this would be a non-issue if projector manufacturers had used a rear-sprung gate design instead of the gate being sprung on the lens side. The rear sprung design eliminates all problems associated with stripe thickness variation, so I really wonder why they all opted for front springing. The only S8 sound projector I have heard of that was designed this way was the Braun Visacoustic. My Bolex 18-5 silent R8 projector has a rear sprung pressure pad, and once focussed it stays that way.

Posted by Jan Bister (Member # 332) on June 19, 2005, 07:43 PM:

Wasn't the Bolex 18-5 a super-8 machine, or am I thinking of a similar but different model? And if so, would that model have the lamp-side pressure pad, too?
Other projectors with this feature that I'm aware of, besides the Braun Visacustic, are the Beaulieu 708-EL and (I think) the Fumeo range of machines.
I find it rather curious that Elmo never used that design. If they'd done that on the GS-1200, plus give it 2400ft. reel capacity, I'd have taken out a home equity loan to buy about a dozen of them. [Big Grin]

Posted by John Whittle (Member # 22) on June 19, 2005, 07:52 PM:

quote:
Yes some electronic gismo attached to the lens and say measuring any movement from optimum in the film path and moving the lens to compensate would have been great but then think of how precision this would have had to be.

That's what's built into the autofocus of the Kodak slide projector. You can remote focus the lens and then once focused, a system is used to adjust the lens as the slide warms in the gate and changes position and moves the lens to compensate. Of course to apply this to super 8 would take greater precision, but the technology existed back in the 1970s.

This is just one of the things projectors would have today if the industry "still existed". BTW studio screening rooms and laboratory screening rooms for 35mm have remote focusing which is often necessary when running "green" film.

John

Posted by Jan Bister (Member # 332) on June 19, 2005, 09:26 PM:

Radio Shack, here I come! [Wink]

Posted by Douglas Meltzer (Member # 28) on June 20, 2005, 12:21 AM:

Jan,

The Bolex 18-5 was a standard 8mm projector that came out in 1961. In 1965 the "Bolex 18-5 Super" arrived on the scene. The 18-5 is possibly the coolest looking projector ever.

Doug

Posted by Jan Bister (Member # 332) on June 20, 2005, 12:38 AM:

Aha. [Smile]

Perhaps I was thinking of the 18-3, too. Otherwise I'm only aware of the SM8, which was about the last super-8 (sound) projector made by Bolex themselves, before they started slapping their name on other manufacturer's machines.

I do love the 18-5's look, though. It's so Metropolis. [Big Grin]

Posted by Kevin Clark (Member # 211) on June 20, 2005, 04:45 AM:

Hello Jan
Two suggestions to cure your focus issues:
1. Train the missus / kids to use the focus knob while you sit and enjoy the movie!
2. Grab a pair of Opera glasses / mini binoculars so you can see the screen focus better from your projector position (how long is your screening room though?)
From my experience with the Elmo F1.0 lens it needs such a fine adjustment to correct film focus / stock thickness or film warp issues that you would find it difficult to get such a small and acurate movement from any home made electronics / stepper motor invention. Could vibration be contributing to the focus shift if the lens barrel is a bit loose in the focus assembly?

Posted by Rob Young. (Member # 131) on June 20, 2005, 05:44 AM:

The Beaulieu 708-EL does have a rear sprung pressure plate in an attempt to illiminate focus shift. Whilst it certainly seems more stable than on my Elmo, it still needs "tweaking" now and again.

On a minor point and something you hopefully rarely have to do with a print, but just try loading a half-run print in the Beaulieu gate and lining the sprocket holes up with the claw! Tricky! So opening the gate for whatever reason after the film is threaded is a nightmare!

I personally find that it depends how the film has bowed on the spool that affects focus stabilty. Films that have been spooled up for a long time can show more focus drift towards the end, ie. towards the spool core. I once read that if this particularly bad, the effect can be reduced by re-spooling the film the other way round for a few days, ie. if the film is emulsion out, re-spool in emulsion in and vice versa to reverse the bow.

Also, I think gate tension can be a factor. My Elmo had the gate springs replaced a while back and this increase in gate tension does seem to hold the film flatter and mean less fiddling with the focus.

Final bit; someone on another thread was talking about Spondon Films which were based here in the UK. Sadly David Adams who ran Spondon and was a thoroughly nice man to deal with passed away but I remember at one time he did consider manufacturing a remote control focus device that could be fitted to the projector. I think he asked for feed-back but didn't really get enough interest to persue this venture.

Posted by John Whittle (Member # 22) on June 20, 2005, 11:40 PM:

quote:
I once read that if this particularly bad, the effect can be reduced by re-spooling the film the other way round for a few days, ie. if the film is emulsion out, re-spool in emulsion in and vice versa to reverse the bow.

An interesting observation. There was a SMPTE study back in the 1970s about 35mm which at the time was still shipped and run on 2000 foot reels and on acetate base. 35mm film is reverse wound on take up from the feed and rewinding is over/under. Film stored foot out was found to exhibit a focus shift thru the reel.

No such shift was detected with 16mm film (which is normally not reverse wound) or other small gauge films.

I wonder if part of the problem can also be traced to slitting operations at the laboratories. Since Super8 prints are either made on 16mm film or 35mm film and then slit out. The 35mm width yields four prints and no factory edge remains. Stress introduced at this point may lead to base distortions (especially in Estar materials) years later. We are now in the midst of real long term testing. All previous testing was done on an accelerated basis (heat/temperature) which so far has not proved to be very indicative of real world conditions.

Be wary of increasing gate tension since it can lead to increased print wear and in the case of Estar prints, increased mechanism wear on the claw and pull down parts.

John

Posted by Rob Young. (Member # 131) on June 21, 2005, 08:10 AM:

John, you are absolutley right about too much gate tension.

What I meant to suggest was that when the springs were replaced, the gate tension returned to the proper recommended level as I suspect the tension had reduced over the years with the old springs.

Sorry; didn't make myself very clear!

Posted by Tom Photiou (Member # 130) on June 22, 2005, 11:00 AM:

Get on boys, i was wondering how we can get hold of that bloke in Gremlins, you know, the inventer bloke [Big Grin]

Posted by Rob Young. (Member # 131) on June 22, 2005, 11:50 AM:

Yeh, lets find him!

As well as the "bathroom buddy" and the "kitchen companion" he could make us the remote control "feet-up focus finder" or even the "lazy lens" which would auto focus itself.

Actually, thinking about it, I find that the biggest problems I have with prints not staying in focus oddly occurs after I've had a few beers. I can't understand this; it must be some weird affect the alcohol fumes have on the emulsion...or something.

Posted by Tom Photiou (Member # 130) on June 22, 2005, 12:31 PM:

I know, i my Dr askd me about my day, i told him "iget up in the morning and have a small whiskey, dinner time i have a beer and sandwhich, a tot of whiskey in the afternoon, T time i go home have my lunch and wash it down with a coupleo f cold beers" He said whats your proble? i replied,
" i keep falling over" [Big Grin]

Posted by Mike Peckham (Member # 16) on June 22, 2005, 01:15 PM:

Jan

It looks as though somebody else thought the same thing as you, I found this picture in the January 1985 edition of 'Movie Maker'.

It was on display at the 1984 Photokina in Cologne. The designer said "...the Telefocus attachment that allows the user to adjust the focus of his projectors from his armchair, say. No alterations are needed to the projector - a motorised eccentric weight is simply clamped to the focusing knob".

As we don't see many of them around, I guess the idea didn't get off the ground?

Mike [Cool]

Posted by Tom Photiou (Member # 130) on June 22, 2005, 01:53 PM:

Blimy Mike your a walking catalouge, Does anyone have one, if so how good did it work? Very unusual.

Posted by Michael Clark (Member # 369) on June 22, 2005, 02:31 PM:

I seem to have a strange problem where I can't get the entire picture in focus. Sometimes, I'll focus the folks heads, (upper 2/3rd of the screen) and then the bottom third of the screen is out of focus. Or vice versa. Sometimes only one side of the screen is in focus, while the opposite side is out of focus. I try to make sure the projector and screen are in perfect allignment, but I still have this problem occasionally.

Michael.

Posted by Tom Photiou (Member # 130) on June 22, 2005, 03:05 PM:

As i found out this could be one of two things, either the lens is shot or more likely an adjustment on the projector is required, which projector do you have?

Posted by Tony Milman (Member # 7) on June 22, 2005, 03:34 PM:

My technique is quite simple.

Either I reach for another beer or I slide my spectacles up or down the nose......

works for me..... [Wink]

Posted by Jan Bister (Member # 332) on June 22, 2005, 09:27 PM:

Mike: what a find! No kidding about the 'walking catalogue' part - that gadget is EXACTLY what I was envisioning (although not as miniaturized, probably bigger and more clunky) [Smile]

Michael: Hmm, focus problems... is that with your Sankyo 460? My question is, does it have a plastic or metal pressure plate, is it properly adjusted for the right pressure, and is the film nicely lubricated and pliable or does it tend to be dried out (which may contribute to focus problems)? It probably is a good idea to check that the lens is not loose inside the lens holder and sits firm and tight. Interestingly enough, most focus issues are with the left or right side of the image being in-focus and the other side being out-of-focus, rather than the top and bottom. That can be cause by a worn-out (plastic) pressure plate or a film that has a main stripe but no balance stripe...

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