Film-Tech Forum ARCHIVE: Most Reflective Screen for 16mm?

This is topic Most Reflective Screen for 16mm? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Gareth North (Member # 3542) on 08-28-2018, 08:42 AM:

Hi,

I have a Bell & Howell Super 16mm projector. The gate on it has been enlarged and I show material I've shot in Super 16mm on it.

I have never been truly pleased with the image brightness and wish I could squeeze a bit more light onto the screen (the bulb is new) and I don't want to switch projector.

So was wondering if getting a new screen could be beneficial? I notice there is some talk about screen reflectivity with some screens better than others:-

https://www.projectorcentral.com/projector_screens_brightness.htm

Just wonbdered if this is something beneficial to investigate and if realistically I would notice any gains? Or if anyone has any other suggestions?

Best Regards

Gareth North

bolexh16user.net

Posted by Marcel Birgelen (Member # 6801) on 08-28-2018, 03:23 PM:

There are screens with higher "gains", which are essentially more reflective than those with lower gains. Whether you're using 16mm, 35mm, 70mm or digital really doesn't matter, the gain factor works essentially the same, regardless the medium.

A screen with a higher gain will give you more brightness, but nothing comes for free. The higher the gain, the bigger the artifacts. Screens with high gain factors suffer from hotspotting, where the brightness falloff between the center and the edges is far more noticeable than on a lower gain screen, often resulting in a visible hotspot in the center or increased "vignetting".

Posted by Gary A. Hoselton (Member # 3447) on 09-03-2018, 08:09 PM:

Gareth, ways for more brightness out of your projector are faster lens (lower f number), a two blade shutter rather than three blades, and brighter bulb (the Osram ELC-HL is a bit brighter than regular ELC for same wattage dissipated, and our site host Larry Urbanski sells them). Might be able to trim a two blade shutter back slightly for more brightness till on the edge of travel ghost, but this would be ticklish to do.

My observation of screen reflective brightness is that a reflectivity of 1 will reflect same amount of light in all angles from screen, from straight back to the sides and up and down, most of which is wasted. This is a matte screen in factory-clean condition.

Screen gain is increased by slight deformations of the screen surface designed to reflect some of the wasted light back towards the projector. My mini-perf Hurley screen has gain of 1.2, which reflects fairly uniform gain out to 50 degrees horizontal from centerline, barely including center of my two outside front seats where picture looks fine with no color distortion.

With higher gain screen surfaces, get noticeable brightness dropoff to sides, especially irritating when using two projectors because bright side swaps each changeover. Beaded screens especially bad for this effect. Fix is to curve screen about a radius half way back in seating area, which should reflect uniform gain to all of seating area.

Posted by Gary A. Hoselton (Member # 3447) on 09-04-2018, 02:25 PM:

If you want to try reducing shutter blocking of light and are working with a B&H 5xx-25xx projector, it is surprisingly easy to remove the mechanism, especially in later designs with less stuff in the way. Hold mechanism in your hand with shutter up, turn the shaft, and mark what you could remove just before shuttle begins pulling down and just after shuttle stops pulling down. Remove material, and remove same amount from other blade or split between blades if a 3-blade shutter for balance. Seems like this should work.

I revere my Bolex H-16, good memories, but it now it spends its time on the shelf as a display. Have the anamorphic adapter mounted, looks neat.

(Note: in previous post I forgot which site I was on; Brad Miller is host of this fine site and I am grateful to him for keeping this campfire going. The edit function wouldn't let me change my foof.)

Posted by Gareth North (Member # 3542) on 09-10-2018, 02:51 AM:

Hi,

Thanks to you both for your replies. I already have a 2 blade shutter and don't want to tweak it anymore from none spec so looks like i will replace and get a screen with better gain.

You should still shoot with your bolex! Its still a lot of fun.

Best Regards

Gareth North