This is topic Projector problem? in forum 8mm Forum at 8mm Forum.
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Posted by Tim Halloran (Member # 586) on May 14, 2006, 06:28 PM:
Hello, I'm new to posting on this forum and was wondering if I could get some feedback from some of you experienced folks.
I've been using this Elmo ST600D projector for about a year now with no problems--or so I assumed. I project both old commercial films and my own stuff with this machine and as most of you probably know, it is bright and quiet and I was very happy with it. The lens on the projector is an "Elmo Super Zoom Lens, F:1.3, f=15-25mm." I always assumed that the image was really nice as I would just focus the projected image to what looked good to me and that was that.
But this past weekend an astute (and perhaps more "critical") viewer asked why the edges of the projected image "seemed to be slightly out of focus." So I adjusted the focus on the image so that the outer images indeed became very sharp. But to my great surprise, the center of the projected image went slightly out-of-focus. I then became obsessed with this repeatedly adjusting the focus back and forth. I could get the center of the image sharp (what I presume I have been doing up to this point), but the outer edges would go soft. If I sharpened the outer edges, the center would go slightly soft.
So my question is, is this just the nature of how this projector projects an image? Or is there something out of whack with the lens in there? The discrepancy in focus is ever so slight but I would think that it should be uniform across the projected picture plane, correct? Just for reference, I project at approximately 13 feet onto an old beaded DaLite screen. The screen is in excellent shape, however, with a perfectly even surface. Don't know if this matters but I thought I'd let you know.
Any thoughts or ideas about this? Is this something that can be remedied or is it something that is just a part of projecting 8mm film? Thanks in advance for your time.
Tim
Posted by Jan Bister (Member # 332) on May 14, 2006, 07:47 PM:
Hi Tim, welcome ![[Smile]](smile.gif)
Let's see... there are several possible reasons. For starters, I'm assuming that your projector is more or less centered toward the screen so as to avoid any noticeable keystoning effect (the rectangular shape of the projected image going trapezoid). But that's a very unlikely reason for the focus issue anyway.
Does this happen with all of your films or only certain ones? If only certain ones, this suggests that the films in question are on the dry/brittle side and should benefit from a treatment with FilmRenew to allow them to run more smoothly through the machine. If it happens all the time:
1. The film gate pressure plate may have insufficient pressure because the springs have weakened over time. Remedy, remove them, stretch and re-install, but careful not to have too much pressure or the film might chatter, lose its loop and/or be damaged by the claw.
2. The gate itself has gone slightly out of alignment, so film either bows or warps very gently to the side as it runs through the film path, causing it to no longer run flat through the gate.
3. The projection lens (or its holder) is loose and needs tightening.
Hope this is of some help, for starters. Good luck
Posted by Winbert Hutahaean (Member # 58) on May 14, 2006, 10:25 PM:
Tim, Jan has given right directions and those are likely to happen in the projectors and films.
I also got the same problem, and mine is due to the presure problem. The easiest/quickest thing I did was inserting a small paper that I have made it round into space between the lense ring and projector wall. After that I chekced to the screen if the focus is right or no. If still not, then I will insert the paper deeper.
But of course that is only for temporary (emergency).
Have a try,
Posted by John Clancy (Member # 49) on May 15, 2006, 03:43 AM:
I don't know the Elmo ST600 but if it's anything like a lot of Elmo's with the swing out gate then there is an adjustment screw for the angle the lens sits in front of the gate. If this has been screwed right in then the lens will not sit straight in front of the film and you'll only be able to focus parts of the projected image.
Hope you find the forum useful Tim.
Posted by Kevin Faulkner (Member # 6) on May 15, 2006, 05:40 AM:
John is spot on. There is very small screw which acts as the stop position the lens holder/gate closes at. If you look at the lens from the front of the projector, the screw is on the right side of the lens holder at the bottom. Its a very critical adjustment and you will probably find that only a very slight tweak is needed.
All the Elmo super8 machines have this adjustment so as I say, it applies to all the machines.
If for instance you were to replace the Elmo lens with say a sleeved Schneider this will allow you to get the optimum out of the lens and the slightly different fit of the barrel. Also if you use the f1.0 you will probably need to adjust this to get the best out of it due to its lower depth fo focus.
Over years of use I think the end of the screw flattens and you will notice that the screw has bitten into the metal which it stops against. These will all contribute to the very slight shift you have noticed.
Before making any adjustments it's wise to check a number of films especially if they are magnetic sound as thickness variations between the 2 stripes will also give the same effect. In theory the adjustment should be made on fresh processed silent film which should be dead flat but in practice I have found it better to do over an average number of sound films.
Kev.
Posted by David Kilderry (Member # 549) on May 15, 2006, 06:30 AM:
Hi Tim,
You have already received good advice here from the guys with regard to the adjustment screw. The name of the problem you have is vignetting. It is a problem in all film guages and relates primarily to the lens in relation to the film plane.
It is generally only a problem if the lens has been altered from original or the film plane has altered in relation to the lens. A warped or buckled film will display this problem of vignetting as the film gate is unable to flatten the frame across the centre of the image. These problems are more common in 35mm projection as lenses are frequently changed (especially with very shory focal length lenses and reverse anamorphics), and excessive xenon lamp heat in the gate can cuse the film to warp or buckle.
Hope you fix it.
Regards,
David
Posted by Paul Adsett (Member # 25) on May 15, 2006, 07:34 AM:
It's suprising that Elmo did'nt use a hardened steel insert or tab for the lens adjusting screw to push against. As Kev says, the screw definately bites into the aluminum tab so periodic adjustment is required.
While we're on the subject, does anybody have a solution for eliminating the slop between the elmo lens barell and the cylindrical lens mount on the projector?
Posted by John Clancy (Member # 49) on May 15, 2006, 10:12 AM:
Paul, I don't have the lens 'slop' on all my Elmo's but with the one that does I've just put a small piece of electrical tape at the top of the barrel. This does the trick on the machine in question.
Posted by Andrew Wilson (Member # 538) on May 15, 2006, 11:18 AM:
does the GS1200 STEREO have the same set up then?.andy.p.s does it matter which version it is i.e 1,2 or3.
Posted by Tim Halloran (Member # 586) on May 15, 2006, 12:00 PM:
Thanks everyone for all the great feedback and advice--some good suggestions to consider. I'll get to work and report back with the results.
Tim
Posted by John Clancy (Member # 49) on May 16, 2006, 03:55 AM:
Andrew, all the GS versions have the same setup. It doesn't take much to set the focus precisely. On films where there is only a main stripe present (i.e. no balance stripe) I have been known to stick a screwdriver in while the film is running to adjust the focus. It's a nice facility to have.
Posted by Kevin Faulkner (Member # 6) on May 16, 2006, 06:35 AM:
Andy, yes the GS ver 1,2 & 3 are the same for this adjustment.
The lens slop that some have mentioned is caused (I think) by wear in the wormgear that engaes with the small lup on the lens for focusing. Normally this lug sits in the worm with no side to side movement which keeps the lens tight. Eventually this wears and you end up with this sloppy feel to the focusing.
This worm is no longer available so putting a sliver if paper etc down one side of the holder does help or I have managed to slip a thin piece of tubeing over the lug which can help but the problem is that this tubing will get worn through fairly quick. For tubing I have used a small piece of electrical wire covering.
Kev.
Posted by Paul Adsett (Member # 25) on May 16, 2006, 08:02 AM:
The lens 'slop' on my GS is between the outside diameter of the lens and the inside diameter of the lens housing on the projector. This is why I much prefer the Eumig projector designs where the lens is spring loaded into a v-groove, so the lens is uniquely located and cannot move around. True, the Eumig's do not have the hinged lens housing (so gate cleaning is a bit more of a fuss), but it does'nt need it as the v-groove is precision machined to be exactly perpendicular to the plane of the gate. The Elmo design is essentially a cylinder(the lens) located within another cylinder(the lens housing) so it cannot be precisely located and can slop around. Those little machined 'flat strips' on the inside of the lens housing are an attempt at a 'v-groove' location feature, but it is very poor compared with that big machined 'V' on the Eumig's.
[ May 16, 2006, 07:38 PM: Message edited by: Paul Adsett ]
Posted by Kevin Faulkner (Member # 6) on May 16, 2006, 05:30 PM:
Paul, I agree but would say that the ultimate is the good old standard screw thread and manual turning of the lens.
Kev.
Posted by Paul Adsett (Member # 25) on May 16, 2006, 05:53 PM:
Right on Kev! My Bolex 18-5 has the threaded lens barrel and a hefty ball spring plunger pushing in from the side. ZERO SLOP! Come to think of it that machine also has a great gate design all round, with rear sprung gate and also the hinged design like the Elmo which opens up wide for cleaning.
Posted by Graham Ritchie (Member # 559) on May 17, 2006, 12:29 AM:
Hi Tim
An easy and quick way to check you lens alinement is to run you projector without film,lamp on,zoom down to a acceptable size, check on screen that as you move your focus in and out that both your left and right edges which is your apature plate you are seeing on the screen,both go in and out of focus evenly,as an example say your left side is in focus but you have to adjust it to achive the same on the right then your lens is out of alinement,what you are trying to achive is an eveness of focus on the left and right edges,to obtain this there should be a small screw that acts as a stop situated at the bottom of the lens holder, adjusting this in or out should correct it,if after running film through the projector you find that both left and right are in focus but the centre isn't,then the film is bowing in the gate, this can be due to the film itself,to much spring pressure on the edge of the film,the film might not be running true from the top sprocket or even the claw might be protruding to much, hopefully you won't have to go down this path and a simple lens alinement fixes it, hope some of this might help best of luck.
Graham
Posted by Tim Halloran (Member # 586) on May 17, 2006, 01:31 AM:
Thanks Graham but it's not a left-to-right focus problem--its a center "spot" and the radial edges which alternate focus. This is what leads me to the conclusion that its simply an inherent quality of the projector's lens and how it projects light onto a flat surface.
Jan, should we send people over to the discussion on filmshooting.com? (Jan has been over there contributing to the dialog). For those of you who are interested, here is the parallel thread in a different community responding to the same question:
http://www.filmshooting.com/scripts/forum/viewtopic.php?t=14031&sid=f932a47cf74a220f1c06bdf39efc0e4d
In one of my later posts I wrote this:
"[The] answers [at 8mmforum.com] were uniformly different than the responses I got here...I just find it so curious that the two different communities almost universally came to such different conclusions about the problem. Really very interesting."
Tim
Posted by Kevin Faulkner (Member # 6) on May 17, 2006, 03:58 AM:
Tim,
OK I have reread your original thread again after see what was written on the other forum. I do agree with some of the answers but not all. It is possible to get a very good sharp overall image on the Elmo but yes there can be differances between lenses. Seeing the image at the BFCC on a 24ft wide screen demonstrates that this is indeed possible and without a curved screen.
One of the best lenses is the Elmo long throw zoom. This can give a pin sharp edege to edge image. I am useing a Schneider 1.1 xenovaron in my xenon and with some tweaking I can also achieve a pin sharp image over the entire screen width. A lot of this is dependent on the film and the condition etc. You will see that a lot of mag sound film is in fact curved instead of flat. This seems to be something to do with the application of the stripe and/or the way the film is subsequently stored on the spool.
If you do some checks with a decent lens and some smpte silent (unstriped) test film you will see that the machines and lenses are capable of some superb results.
The adjustment screw we were talking of does allow you to get rid of some of the effect of curvature in the film and a lens with a good large rear element is a must. Most lens manufacturers take all these factors such as curvature into account when designing lenses so that the end result is very acceptable.
Another superb lens is the Sankyo f1.0. This got rave reviews many moons ago and I suspect it comes from the same stable as the Elmo 1.0. Never sure if Elmo made thier own lenses but I bet there are some good and some bad examples and maybe yours is not one of the better examples.
Interesting that Hertieur of France, I think, used a small jewel in the gate above and below the frame which pressed in at the centre to help keep the film as flat as possible.
Kev.
Posted by Paul Adsett (Member # 25) on May 17, 2006, 06:39 AM:
Kev, I have to say that the best lens in my inventory is an Eastman Kodak f1.0 fixed focus 20mm lens. I got it off an old Kodak M100 projector which was Kodak's Rolls Royce super 8 professional quality sound machine with 2000ft reels- the best S8 projector they ever made. Anyway I use this on my Eumig 938 and the picture is stunningly sharp and as flat as a pancake. I am trying to adapt one of my GS1200'S so I can use it on that projector as well. The Kodak projector in this picture looks just like the M100, but the M100 had the take up reel at the back, and of course the 2000ft arms were much longer than those shown here:
Posted by Kevin Faulkner (Member # 6) on May 17, 2006, 06:47 AM:
Paul, That sounds like a good lens. I have to say that I hadnt heard of this Kodak machine before. And with 2000ft capacity! Do you have one of these machines?
Kev.
Posted by Paul Adsett (Member # 25) on May 17, 2006, 06:57 AM:
Hi Kev,
No, but I used to! I first came across one about 30 years ago, just when I was getting into S8 film collecting. I rented it from a local A/V store, and the picture quality amazed me so I bought it off them. However, the sound quality was pretty bad compared to my Eumig 820 and it scratched film, so I got rid of it, but was foresighted enough to keep that fabulous lens . Kind of wish I had kept the whole machine right now, maybe I could have fixed it up. I have eited my post above to show a picture of a projector very similar to the M100. I will see if I can find an actual M100 pic to post.
Posted by John Clancy (Member # 49) on May 18, 2006, 02:19 AM:
Isn't that the machine shown running on Men Behind The Movies part 1? That machine certainly has the Kodak F1.0 lens so I think it must be the one.
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