hot spot

[megalith6]

hi,

i am having big trouble with the 'hot spot' effect whilst experimenting with DIY cin?-to-disc transfers

hot spot appears at centre-top-right of some frames

was advised to place small disc of neutral density filter onto the projector lens to compensate for the bright spot, but up or down on the lens, please - due to the 'camera obscura' effect?

thanks,

[BolexPlusx]

That's interesting. I always thought the hot spot appears in the center of the screen.

I actually use the same screen I use to project shows for what limited DIY telecine work I do, and I've never had problems with hot spotting. It's just a regular matte projection screen.

Many people say that a sheet of regular non-glossy white paper is the best, and I believe that hot spotting is what they are avoiding by using this material (not sure though, since I've never needed to try it.)

[megalith6]

Hi Bolex Plus,

good to hear from you

>That's interesting. I always thought the hot spot appears in the center of the screen.
I actually use the same screen I use to project shows for what limited DIY telecine work I do, and I've never had problems with hot spotting. It's just a regular matte projection screen.

i get it all the time - video transfer box or matte, hard white formica melamine board (actually a cupboard door!)

>Many people say that a sheet of regular non-glossy white paper is the best, and I believe that hot spotting is what they are avoiding by using this material (not sure though, since I've never needed to try it.)

hm. guess i'll just have to experiment moving the neutral density filter around?

thanks,

ric

[BolexPlusx]

Question:

How close is the projector to the screen?

[megalith6]

Question:

How close is the projector to the screen?

Answer: 2 feet

ric

[BolexPlusx]

Hmmm!

Try 3 or 4 feet.

<font color="#a62a2a" size="1">[ January 20, 2006 10:43 PM: Message edited by: BolexPlusx ]</font>

[megalith6]

ah,

video transfer screen 3"x4"

[img]graemlins/gulp.gif[/img]

[BolexPlusx]

Oh!,

I use a full sized screen (52" by 92"), and move in when doing telecine for an image maybe a foot high.

I'm surprised you aren't having problems with keystoning coming in that close.

[megalith6]

Hi Bolex Plus,

I use a full sized screen (52" by 92"), and move in when doing telecine for an image maybe a foot high.

i repositioned everything when it became clear the video transfer box was not going to give me the smoothest of transfers - i set the projector lens back 4' from a matt white formica board, which dulled down the 'hot spot' no end; i got a better transfer this way, but i am still not satisfied with the result ... although it is an improvement (re 'flicker')

I'm surprised you aren't having problems with keystoning coming in that close.

keystoning? i did notice some tiny stationary white flecks in the playback, i am hoping this is just something to do with the extempore screen i was using?

thanks,

ric

[BolexPlusx]

Keystoning works like this:

A projected motion picture beam is rectangular and increasing in size as you move further from the projector. When you shove a screen in the way, you basically "slice" the beam at that point. If the screen is at right angles to the beam, the image will be a nice rectangle, but if it is not, whichever side of the screen is further away will receive an image grown larger than the closer side. This will give you an image with an angle on top and bottom edges. The same thing happens in the vertical plane if the projector is much higher or lower than the centerline of the screen.

I figured that to put an image on a screen from only two feet away, the video camera and projector would have to be at quite an angle in order to "see" the same point, so you would wind up with a keystoned image.

I unknowingly bought a cinemascope print once, and figured if I put the screen at enough of an angle I could spread the image out to full width. It sort of worked, but due to keystoning it looked awful. I gave up and bought a 'scope lens, then I discovered that on a small screen I could only get in image about a foot and a half high and also get it to fit horizontally. Then I bought a big screen and finally saw the film as meant to be seen. I liked it so I bought a bunch more. I'd have saved a lot of money if I'd just not bought that first film!

<font color="#a62a2a" size="1">[ January 23, 2006 05:44 PM: Message edited by: BolexPlusx ]</font>