8mm Forum: My projected picture is too small

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Posted by Winbert Hutahaean (Member # 58) on August 09, 2007, 04:48 AM:

Hi all,

Perhaps you remember this post, where I was telling you about my future projection room.

It is now almost finished and yesterday, I turn on the projector at the maximum distance between the projector and the screen at 0 degree. It is about 4.5 m in distance. I was using Elmo ST-800 (a very standard one with the lens did come from the factory, was it 1.2?).

The result was so unsatisfying me, because the biggest picture can be projected was only half of the screen size. The screen size is about 3 m x 4m.

My aim is to get at least 3/4th of the screen size.

I knew for the opposite issue there is a lens that allow us to project the film far from the screen with a result of small picture size. (Do we call it "throw lens"?)

So can we get a lens, where with my projecting area I can get a bigger picture ?.

I knew there will be an issue of less bright light output, but I will be installing ST1200 (150w, 15v bulb) for my permanent projectors.

thanks,

Posted by David Pannell (Member # 300) on August 09, 2007, 06:59 AM:

Hi Winbert,

I don't know what would be the best lens for you, but please don't fall into the same trap as some enthusiasts. You have to remember 'The Inverse Square Law', which means that the light varies inversely as the square of the area. Therefore, for a picture twice as wide, the image will be a quarter of the brightness - YES! A QUARTER!

Also, definition will be subject to the same law of physics, so the image again will be four times as grainy. As your projection distance is only 4.5 metres, or roughly 13 feet, I would be inclined to stay with the smaller image and use a screen to suit. But that's only my own humble opinion.

I have a fairly long lounge where I project, and from lens to screen is about 20 feet. I still only use a 1.5 metre screen, and sometimes even a 1 metre screen. I have tried larger, and I find visitors complaining that it's like sitting too near at a commercial cinema, and they either get headaches or feel dizzy.

Just one person's experience.

Best regards,

Posted by Jean-Marc Toussaint (Member # 270) on August 09, 2007, 07:37 AM:

Winbert, in addition to what David just said:

The standard lens usually delivered with Elmos is the 1.3 / 15-25 mm. The biggest projected picture you will get at 5 meters, in 15mmm setting, will be roughly 1.3 x 1.8 m.

The 1.2 which is the fast longthrow lens (as opposed to the 1.4) is a 25-50 mm optic which will give you a 0.8 x 1.05 m picture at the same distance.

The shortest Elmo lens is the excellent 1.0 (scarce and pricey), which is a 12.5-30 mm, it will give you a 1.6 x 2.1 m pict (approx.).

If you want to go slightly larger, you need to find the Shneider Kreuznach Xenovaron lens, (also scarce but more affordable), it's an f:1.1 / 11-30 mm. You will need an adapter sleeve from CHC. But you wont fill your entire screen. 1.8 x 2.4 m should be your approx. image size then.

But you will soon notice that the larger the image, the darker it will feel, especially with a 150w lamps (even with an Osram Xenophot).

Adapting a two-blade shutter is an option but switching to an Elmo GS1200 or even a Xenon machine is right around the corner, my friend.

Welcome to your new nightmare... [Big Grin]

Posted by Winbert Hutahaean (Member # 58) on August 09, 2007, 11:21 PM:

Hi pals,

Thanks for your wise words. I do follow that projection rules for my own show. But here, in my country, there is still a believe that to have a cinema feelings than we have to get a bigger screen which it is associated with 3/4th of the room.

For a bigger picture, the problem of resolution (grainy) is something that we cannot do much (anyway this is 8mm) but the light output's issue can be solved by changing the bulb (I have a friend here who is able to install the ST-800 with 250w, 24v, using a separate transformer).

So is the only way to have the 1.0 lens installed? (though is expensive). There is nothing such a simple magnifier?

cheers,

Posted by David Pannell (Member # 300) on August 10, 2007, 12:40 AM:

Hi Winbert,

If you switch to that 250-watt lamp, you will also have to increase the cooling quite substantially! [Eek!]

This project then becomes quite a major one. I suggest you check with Kevin Faulkner regarding this type of modification. I wish you luck.

Best regards,

Posted by John Clancy (Member # 49) on August 10, 2007, 04:26 AM:

If you project 'Scope films you may fill the entire width of the screen. That will make 'Scope films all the more special particularly if showing a 'flat' film first.

Now have you put any tabs and masking in place?

Posted by Winbert Hutahaean (Member # 58) on August 13, 2007, 01:47 AM:

John,

I knew Masking (that the black bar on the top/bottom and left/right screen, right)

But what are tabs?

thanks,

Posted by John Clancy (Member # 49) on August 13, 2007, 03:26 AM:

Curtains. Sorry, don't know why I wrote 'tabs'.

Masking also includes the side masks. If you're projecting 'Scope as well as flat all this has to move. It's a simple procedure really requiring a couple of sets of corded curtain tracks. Then once you have it sussed motors and automatic control is an option. 'Tabs' are the final touch.

Posted by Dan Lail (Member # 18) on August 15, 2007, 11:54 PM:

Winbert, I project at a 20 foot throw. The image is eight feet wide and six feet tall with black masking. The projector is a GS-1200 with a 200 watt bulb. The quality of prints like Poltergeist(scope), Die Hard(scope), Wizard Of Oz, etc are spectacular. But, most Niles prints are not so defined and have soft focus, so I adjust the zoom for a smaller picture. have had showing at least once a month with an audience of eight or nine people and have had no complaints of a too large screen. The front row is about ten feet from the screen.

Posted by Winbert Hutahaean (Member # 58) on August 23, 2007, 10:25 PM:

Hi al,

Sorry for being so stuborn [Razz]

...but will this kind of lens give me a bigger picture?

And can we put it on the bracket as what we do with the cope lens? (since this is only for Bell & Howell).

thanks,

Posted by Dan Lail (Member # 18) on August 23, 2007, 10:58 PM:

Wnbert, is your ST-800 lens a zoom lens?

Posted by Winbert Hutahaean (Member # 58) on August 23, 2007, 11:12 PM:

Dan,

quote:
is your ST-800 lens a zoom lens?

I do not really know the technical things, could clarify what did you mean?.

I can tell you that my projectors (both ST-800 and ST 1200) can have a big and small picture by turning the lens ring to the left or right.

thanks,

Posted by Dan Lail (Member # 18) on August 24, 2007, 12:08 AM:

Winbert, you have zoom lens on both your projector. Zoom is a word used that means you can turn the lens to make the picture big or small. I think the lens you might need is the 16mm Bell & Howell "filmovara" lens. It has a large lens on the projector side(back). You would have to mount it in front of your elmo lens. This would make the picture a little less brighter because you are projecting throught two sets of lens.

Is the distance from the front of your projector to the screen 4.5 meters?

Posted by Winbert Hutahaean (Member # 58) on August 24, 2007, 03:05 AM:

Dan,

Yes the distance between the projector and the screen will be about 4.5 meters, anything you wan to say?

quote:
You would have to mount it in front of your elmo lens.

Can we use a bracket system like we have with the scope lens?

thanks,

Posted by Jean-Marc Toussaint (Member # 270) on August 24, 2007, 03:37 AM:

Winbert, I just made a quick test with the Elmo zoom converter for the 16CL 16mm machine. It works. It will convert the 15mm end of your zoom lens into a 12mm. So with the Sankor, it will go to 11,25, giving you an image almost similar in size to the Schneider lens.

You will need a lens holder of some sort as the converter will work when it is stuck to the end of the lens (it's meant to be screwed at the end of the primer).

The Elmo zoom converter, the Filmovara and the Sankor are the same kind of optical devices. Designed for B&H, the Filmovara and the Sankor have a bigger rear barrel, which is better.
But you will have a certain amount of light loss.

Converting your St800 to 250w could be an option (don't forget extra cooling though)

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