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  1. #1

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    how far can you take a slide projector?

    Hi there,

    So i am considering possibilities for an arts project involving outdoor projection. The projection surfaces are the sides of a large concrete building. I will project from distances varying from 10 to 30m. Budgetary concerns and a preference for film grain over pixels, has led me to considering slide projectors.

    These are my concerns:

    1. From what i understand, at 30 metres, 500w 35mm slide projectors won't cut it. Will larger format slide projectors such as the Beseler Slide King give me a rich image from such a distance (minimal ambient light)?

    2. I want the projection to be as big as possible but many of the projectors I come across come with 70mm or longer lenses. Are wide angle lenses a rare commodity?

    I live in Australia so there seems to be less of this stuff on ebay compared to the states. Any local tips would be much, much appreciated.

    Cheers,
    Sherwin

  2. #2

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    Not sure how helpful this is but I seem to recall that the light from a projector falls off at a rate equal to the inverse of the square of the distance. In other words it's not a linear reduction.
    So a projector optimised for use in a room at (say) 5m distance is going to look pretty dim even at 10m and probably hardly viewable at 30m. Maybe check that out first.
    Second is that boosting the light output is problematic because the heat will likely destroy the transparency, if not the projector. Standard cooling fans might not cut it.
    The longer lenses you're noting were made so that conventional 35mm slide projectors could fill a standard screen in a larger hall or venue. There were also zoom lenses made.
    I think you'd suffer less frustration by hiring a powerful digital projector from a specialist audio visual supplier. Kayell might be a useful point of enquiry.
    I don't think the subtlety of film grain is going to be apparent when projected on the side of a large concrete building!
    Last edited by Leigh Youdale; 08-16-2010 at 01:43 AM. Click to view previous post history. Reason: addition

  3. #3

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    Thanks Leigh. Digital projection is probably the way to go and if it weren't for the significant cost difference I probably wouldn't be considering analog. This project is set to screen every night for 22 nights so the costs add up!

    I may be able to rig the slide projectors so that they are 10-15m from the screen. This makes a wide angle lens imperative. I was wondering if anyone could name a few lenses (that I might be able to find on ebay) or any 35mm or medium format projectors which come with a wide-ish standard lens.

    Cheers

  4. #4
    Greg Davis's Avatar
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    When I was in college, some of the classrooms used a slide projector that was 30 meters away, roughly. I don't know what kind they used, but they do exist.
    www.gregorytdavis.com

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  5. #5
    Steve Smith's Avatar
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    Quote Originally Posted by sherwin View Post
    Digital projection is probably the way to go
    For the size you want to magnify the images to, I don't think a digital projector will be bright enough. They are only just bright enough at 'normal' projection sizes.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  6. #6
    Lee L's Avatar
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    It's really more a matter of how large your projected image is rather than distance. You're concentrating the illuminating passing through the slide over a given area. With a wide lens at a short distance covering the same screen area as a long lens at a large distance, the image will be approximately the same brightness. Both digital and slide projectors have a wide enough range of brightness that you'd have to be specific about models to get any relative brightness information, and you'd also need to be specific about the ambient light levels you're trying to overcome.

    Projector lenses vary widely in quality, from plastic zooms (and zooms are typically slower than fixed focal lengths) to great fixed length fast lenses with excellent glass. If image quality is a concern, you'd need to factor that in. Schneider, Zeiss, Leitz, Buhl (in the US), among others make excellent slide projector lenses. Wide angle slide projector lenses are rare. Usually a 90mm or longer lens works for the majority of common slide projection setups. Also, with a short lens, you'll need to have the projector closer and tilt it more to cover the same area, leading to 'keystoning' in the projected image, i.e. the bottom of the image will be narrower than the top, and the sides will fan out going from bottom to top.

    Lee

  7. #7
    David Brown's Avatar
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    Lots of variables here, but what you are talking about is a "long throw" projector with appropriate lens. Such things do (did) exist. 35mm projectors were routinely used in auditoriums for distances over 30 meters. Sorry, I do not have any suggestions for sources; but if it were me, I'd start with the AV guys at a local university.

  8. #8

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    Thanks everyone.

    Based on your feedback, I'm going to dig around for some long throw projectors (did i mention that I need more than just one!). I don't hold out much hope but to maximise my chances, what kind of variables am i looking for to indicate that a projector is 'long throw'? So far i've only been looking for a high watt lamp and a fast lens. Anything else?

    Thanks again

  9. #9
    holmburgers's Avatar
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    When has a digital projector ever looked brighter or better than an analog projection? IMHO, never. Not to mention, once you find the suitable analog projector, you could probably buy two and do a stereo slide show before you could afford one digital projector. But I digress....

    There are always some long throw lenses on eBay, specifically I remember seeing some Buhl ones. I'm sure they're now selling for a fraction of what they cost new. I'm sure resources abound with regards to high-power projectors, etc. Make sure you have backup slides and an excellent cooling system.

    Long throw simply equals long focal length I believe.
    If you are the big tree, we are the small axe

  10. #10
    David Brown's Avatar
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    Quote Originally Posted by holmburgers View Post
    There are always some long throw lenses on eBay, specifically I remember seeing some Buhl ones. I'm sure they're now selling for a fraction of what they cost new. I'm sure resources abound with regards to high-power projectors, etc. Make sure you have backup slides and an excellent cooling system.

    Long throw simply equals long focal length I believe.
    Well, yes and no. As for the lens, think of telephotos. But the light source matters for true distance projection, also (as mentioned). You might even have to mount the slides in glass.

    Something like an Elmo or this:

    http://cgi.ebay.com/Kodak-Ektapro-90...efaultDomain_0
    Note the 300W lamp!!

    Here's one in Oz - http://cgi.ebay.com/KODAK-EKTAPRO-50...tion_Equipment

    In the Kodaks, at least an Ektagraphic, not a Carousel made for home use.
    Last edited by David Brown; 08-16-2010 at 06:48 PM. Click to view previous post history.

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