Shooting a TV with a Bolex

Stephanie Zimmer · May 1, 2006

Hey,

Does anyone know if you can shoot a television screen without getting bars using a Bolex? Shutter? Any optional accessory to find/rent? Thanks,

Stephanie

Clive Tobin · May 1, 2006

...Does anyone know if you can shoot a television screen without getting bars using a Bolex? Shutter? Any optional accessory to find/rent? Thanks, ...

This is covered in the instruction manuals for our crystal motors, such as the one for the TXM-20Ba which can be seen at http://www.tobincinemasystems.com/page107.html . Unfortunately the Milliframe Controller required for doing it semi-properly is discontinued and we don't have any left.

Another solution is to film off an LCD (liquid crystal display) screen TV set. These don't have an inherent heavy flicker like a CRT (cathode ray tube) regular TV set so should be less prone to giving a shutter bar. I don't know if this is also true for the new plasma type TV sets.

Stephanie Zimmer · May 2, 2006

This is covered in the instruction manuals for our crystal motors, such as the one for the TXM-20Ba which can be seen at http://www.tobincinemasystems.com/page107.html . Unfortunately the Milliframe Controller required for doing it semi-properly is discontinued and we don't have any left.

Clive,

Thank you for your response. I went to your website and it gave a very thorough explanation. I was acutally planning on buying the one of your motors from a rental house this week for another reason.

If you don't mind, however, I'd like to ask a couple more questions. What if the tv set in frame was shot using stop motion? Will this change the formula? (I was planning on purchasing the TTL motor for this as well as other time lapse) If not, what if the footage was transfered to tape at 29.97 fps?

Thanks again for your time,

Stephanie

Nick Mulder · May 2, 2006

What if the tv set in frame was shot using stop motion?
Stephanie

Bolex cams with the 130deg shutters (most of the windup variable shutter reflexes ?) expose at an equivalent of 1/40 of a sec at 12fps - but that is taking into account the light lost through the prism, not a very helpful number when it comes to questions such as yours...

(130/360 * 1/12) = 1/33 of a second 'real' shutter speed, which is faster than a TV screen so you will have problems. stink bums batman :ph34r:

...but :lol: your bolex will have the T setting which will allow you to manually acheive much greater shutter-angles by simply holding the shutter open for as long as you want ...

However, there is the the problem of being human you will not expose your frames to equal amounts and you will end up with a flicker of another sort - soooo... you need to reduce the error by increasing the exposure time - this way your range of (human) error is proportionally much less than the exposure time (cool) - you'll need to be fully stopped down and maybe some ND filtering, lower screen intensity etc...

Stephanie Zimmer · May 2, 2006

...manually acheive much greater shutter-angles by simply holding the shutter open for as long as you want ...

However, there is the the problem of being human you will not expose your frames to equal amounts and you will end up with a flicker of another sort - soooo... you need to reduce the error by increasing the exposure time - this way your range of (human) error is proportionally much less than the exposure time (cool) - you'll need to be fully stopped down and maybe some ND filtering, lower screen intensity etc...

Nick,

Thanks so much for responding. One question - sorry if it seems basic. You're saying that you with the T function you can keep the shutter open as long as you hold the run button down however you will get a flicker with the inconsistency. So instead you need to increase exposure time. Is this not controlled the same way with holding the run button? Just trying to figure out logistics. Thanks.

Nick Mulder · May 2, 2006

Nick,
Thanks so much for responding. One question - sorry if it seems basic. You're saying that you with the T function you can keep the shutter open as long as you hold the run button down however you will get a flicker with the inconsistency. So instead you need to increase exposure time. Is this not controlled the same way with holding the run button? Just trying to figure out logistics. Thanks.

As long asyou hold the run button forward... rather than using the button on the front, use the switch on the side with M - STOP - P on it - when you push the run button on the front it is mechanically linked to this switch and will put it into the M position for normal running, pushing it forward will on the I setting will expose only one frame at 1/33 of a second, if you set it to T it will be open for all the time you keep it in the P position - 1 sec, 10 secs, 46 days whatever...

what will cause the error is you in this case... say you needed to expose for 1 second - as you are a human you will not be able to expose for 1 second everytime (ever as a matter of fact), there will be a regular error in which %95 of your times will be out by a maximum amount of error say 200 mS (1/5 of a second) either way - which means at least %5 of your exposure times will be either faster than 800 mS or slower than 1200ms - this will cause flicker as you will be out between two adjacent frames by up to %34 of exposure - %5*%5 = %0.25 of the time - like potentially every 400 frames or so - bad!

(not screen flicker from the CRT, just general flicker...)

If you were to ND your lens or similarly decrease the amount of light reaching the film you could use a 10 sec exposure - in this case your 'switching off at the right time error' is still ~ 200 mS - this time tho the numbers come up as %5 of the time either faster than 9800 mS or slower than 10200 mS ... this will still cause flicker as you will be out between two adjacent frames by only %4 of exposure every 400 frames or so - not so bad

I pulled the base figures outta my ass here, but the ratios and hopefully that mathematical logic hold up - its late here and I've probably made a hash of it!

I have made a servo drive for my bolex for time lapse using the P switch and long exposures (I've had virtual 350deg shutter angles this way)...

check this site out for ideas: http://www.sciencephotography.com/faq_chap2.shtml

I'm working on a stepper type system at the moment with xtal sync - well, it will use xtal's and will let me know when its in sync but its not a true closed loop system (yet)

Clive Tobin · May 3, 2006

If you don't mind, however, I'd like to ask a couple more questions. What if the tv set in frame was shot using stop motion? Will this change the formula? (I was planning on purchasing the TTL motor for this as well as other time lapse) If not, what if the footage was transfered to tape at 29.97 fps?

The TTL motor is about 3/8 second "adapted" (for prism) exposure or physically about 1/2 of a second in the normal timelapse or manual mode. This should give an exposure of about 15 complete video frames or 30 fields, which should tend to wash out any residual flicker though there still may be a little.

Transferring to tape at various speeds will vary the rate of any remaining flicker.

There are still rare people doing 16mm kinescopes. Noise and Light in Seattle 206 528-5577 is one, they are using a Palmer SW3 in a setup that I put together. The SW3 has a 288 degree shutter opening, with an out of focus shutter, for almost no trace of shutter bar, better than you will ever get with a Bolex.