Teleprompters - how many stops of light do you lose shooting through the glass?

A

analogs

Well-known member
Anyone here use teleprompters that you shoot through and how many stops do you lose shooting through the glass?

Can you tell me what properties the glass are when you loose x amount of light?

I read that most teleprompters use 30R/70T type glass - 30% reflection / 70% transmission.

What is the best R/T ratio without affecting the image too much when shooting through but still reflective enough so that the text is visible to the talent?

Thank you!
 
Most telepromptors/autocues I've used over the years have used a front surface silvered mirror coating with 60% transparency and 40% reflectance which means just over half the light reaches your lens. I would hazard a guess that much less than 40% reflectance would start to make it harder to read in a well lit studio. If as a rule of thumb you said it was 50% the amount of light transmission on those 60/40 units well then half the light would be one stop light loss. If you have a reasonable amount of lighting on your subject it's not a problem. The main thing is to make sure you have the material shroud on the back of the prompter head well closed off around the lens to stop light coming in from behind the camera. Also to help minimize rear reflections keep the front of the lens as close as possible to the back of the prompter glass otherwise sometimes you can get some odd reflections happening on the camera side of the prompter glass/mirror. I always used to let the prompter operator adjust the camera lens position as I once saw a camera op break a glass when trying to push the camera forward on the prompter camera plate. If your prompter is indeed a 70%/30% split then it would be less than a stop of light loss. In practice I've never worried about it as you just adjust light and aperture to suit your requirements.

Chris Young
 
Agreed. Good one! Looks like a neat compact unit. Normally we hire operators with kit from an outfit that supplies the broadcast industry but this looks tempting for owner operators.

Chris Young
 
I cant say as to all the r/t stuff but I am an operator, usually use a Telescript AV system, and several acs have measured the light loss and told me its about 2/3 of a stop. You could just call it a stop to be on the safe side.
 
I am thinking of using two way mirror that is made of plastic and not glass for a DIY teleprompter. Anyone ever used those instead of glass or is it a bad idea?
 
I smashed the glass on one of my two autocues - They don't get much use, so I got the local glass company to cut me a new one from thin optical glass they used to use for overhead projectors, and nowadays their stock is rarely useful. Not slivered at all, and it works really well. Not as clearly defined for the reader, and the screen is greyer than the other, but no artefacts I can see from the camera, and no double vision on the captions.
 
I would think you’d want to very wary of shooting through anything that reduces image quality (softening, distortion).
 
We see somewhere between 2/3 to 1 stop with our prompters which isn't a big deal... The big deal is the amount of flare they induce, even with the special anti-reflective coated (one side) half silver glass that we have. Part of the flare is from the prompter monitor itself, get a little light spill on it and you will have a major jump in the black level. Yes even with "special" prompter monitors that also have AR coatings on the monitor glass.

You can defeat that flare a little with a good privacy filter laid over the glass. Works well but one of the people here says it makes the letters too fuzzy. I do see a slight edge blur on the letters, but it wasn't enough for me to have a problem reading it. Just took them back off and let them deal with the extra flare that shifts from angle to angle.
 
Those systems should come with a hood that goes over the top of the glass, w backing that goes around the lens to make it opaque for the reader, and possibly side flaps, forming an open cube around the lens. further flagging can help with flare if needed. I have heard the fuzzy letters complaint several times (looks almost like a doubling effect or drop shadow), but here’s the thing...always from producers, NEVER, in 13 years, from the reader/talent, who is the only person it should matter to. It’s weird, sometimes you get the doubling, sometimes not, even when prompter set up the same way. Never quite figured it out. I assume its something about where the video lights or room lighting are placed in relation to the glass.
 
Yes, we have lots of spill. With mot prompters and wide angle lenses, you can't completely enclose the sides. I've put black flagging material on some cameras, but it universally gets removed or folded back, even though it never appears in a shot. I just let them keep the flare now, tired of fighting with them.
 
Judging by how much flack (or lack of it, rather) I get from other crew it really shouldnt be much of a problem most of the time, and if the flaps/enclosure are vignetting your shot you can set up proper flags further out.

Now, I AM using telescript AV gear most of the time which is like the Rolla Royce of prompters or something, so maybe that glass behaves differently, or there’s some other secret sauce, dont know for sure.
 
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