Camera from back of theatre for DSM

[james3mc]

For the next show that I'm SMing, the DSM won't have a clear view of the stage, which comes out beyond the pros. arch and has two thrusts as well. I know that there is a camera position on the front edge of the theatre balcony, dead in line with centre stage, with a BNC point and coax running to monitors backstage. I just need to provide a camera.

 

The performance area is 28' wide and the distance from the camera position to the front of the performance area is approx. 35'. If I go onto eBay or similar and get a colour CCTV camera, what sort of lens should I look for so that the whole of the performance area (or most of it) is visible on the monitors? ;)

 

Thanks

james

[JimWebber]

For the next show that I'm SMing, the DSM won't have a clear view of the stage, which comes out beyond the pros. arch and has two thrusts as well. I know that there is a camera position on the front edge of the theatre balcony, dead in line with centre stage, with a BNC point and coax running to monitors backstage. I just need to provide a camera.

 

The performance area is 28' wide and the distance from the camera position to the front of the performance area is approx. 35'. If I go onto eBay or similar and get a colour CCTV camera, what sort of lens should I look for so that the whole of the performance area (or most of it) is visible on the monitors? ;)

 

Thanks

james

 

Hiya James,

 

A simple (?) bit of trigonometry will give you an idea of the lens angle required

 

You will have a triangle with a base of 28', and an apex of 35'

Split this in two to give a right-angled triangle of 14'B x35'H

Using 14 and 35, you can now calculate the hypotenuse = Approx 38'

We can now calculate the angle at the camera end 35/38 = cos (o) = Approx 23 degrees

This is for half the triangle, therefore to see the entire stage it's approximately 46 degrees.

 

Standing by for the pedants to pick holes in my arithmetic...

 

Jim

[james3mc]

Oh I like that - I even understood it.

 

Now how do I turn that into camera-speak. I'm looking on eBay at colour CCD cameras and they don't say anything about angles. The one I'm looking at talks about 1/4 inch and 420 lines

 

It has the following spec :

 

Model JSP DF-2018

Image Sensor 1/4" Sharp Color CCD Optical Sensor

Horizontal Resolution 420 TV Lines

Signal System NTSC / PAL Standard

Picture Elements NTSC: 510(H) x 492(V) PAL: 500(H) x 582(V)

Scanning System NTSC:525 Lines PAL:625 Lines

White Balance Automatic

Minimum Illumination 1.0 Lux at f 2.0

Backlight Compensation On/Off Selectable

S/N ratio Greater than 48dB

Auto Exposure System NTSC:1/60~1/100,000 Sec

PAL:1/50~1/100,000 Sec

Iris Control Support both Video/DC-Drive

Sync System Internal Synchronization

Gamma Characteristic 0.45

Video Output Signal 1.0Vp-p/ 75 Ohm

Operation Temperature -10 C ~+50 C RH95% Max

Storage Temperature -20 C ~+60 C RH95% Max

Lens Mount C/CS Mount

Power Source DC12

Weight 265 Gram

Dimensions (W x H x L) 2.5 x 2.2 x 4.5 inches

 

but I have no idea if it'll do the job. If this works here is it's link :

 

http://cgi.ebay.co.uk/Color-Security-CCTV-...1QQcmdZViewItem

[JimWebber]

Hi James,

 

Unfortunately those specs don't say a lot, and my works firewall blocks e-bay, so I cannot even see it.

 

The fact that it appears to have an industry standard lens mount, indicates that you may be able to get hold of a lens to suit.

 

By the way, please double check my maths above! I would hate it if you went and bought something according to my very dubious mathematical ability.

[T*ny]

Just to chuck a spanner in the works - will the DSM need to be able to see during a blackout? * Is infra red required?

 

*any more than usual of course

[james3mc]

will the DSM need to be able to see during a blackout? * Is infra red required?

Well if it could be achieved easily and of course cheaply. I don't know whether I'd have to buy an IR gun or look for a camera with IR. I also don't know how far the IR throws and how IR is measured - i.e. how 'bright' should it be.

[robertor]

I am in a similar situation. Do you have any well known suppliers for IR sources? How powerful does the IR source, if built into the camera, have to be? Are cameras that switch between colour and IR any good? I found they tend to flicker when switching between modes. Any recommendation's? I believe I can find a CS mount lens appropriate for my stage dimensions, so just need to find a suitable camera.

Many thanks

[sam.henderson]

They had a camera that switched between IR and Colour for relay at the Soho I think rob and it did tend to flicker, it almost looked as if everything was in slow-mo when it changed! I have normally had a Colour monitor and a 'blck out' (IR) monitor seperate.

 

Sam

[Jivemaster]

You borrow a zoom lens with C or CS mount and then read the focal length at the picture you want and look for that lens. Or you go into your local security/cctv shop and get one out of their jjunk box or you ask nicely and I may find a zoom lens on a camera for you either B/w low light or colour 1 lux.

[robloxley]

Lee do an IR-pass filter (in their camera filter section, not with the theatre gels) which is useful in a spare 0.5k fresnel as long as the IR lantern is only turned on when needed (else the gel will burn out); or use IR-pass glass; or hire an IR flood (try White Light).

 

http://www.webcamsoft.com/en/faq/lens_calc.html for lens calculator

[james3mc]

Well I'm almost certainly going to go for the Colour CCD camera with 12 or 20 IR LEDs. On most of them, when the lux drops off to about 2, (i.e. blackout) the IR LEDs come on. I'm sure there'll be a small delay, but the DSM usually needs to see the stage towards the end of he blackout - i.e. are crew & props clear, can s/he give lighting a 'go'.

 

Still not sure which lens to look for, but Maplic catalogue has a helpful table on the subject. And there's always eBay for cheap CCTV cameras with IR.

[TeeJay]

Can't remember all the sums involved but I'm reasonably certain that you are looking for a 8mm-48mm lens for that throw on a CS mount camera.

 

As regards getting infra-red emitters, it's entirely possible that the spill from any 'maintained' (always on) lights in the auditorium will be enough to light the stage enough for an IR camera to operate.

 

If you are combining the cameras, I would check to see the delay in switching from one mode to another.

 

Good luck.

 

(PS I'm loving the new spell checker - so much easier to use than the previous flavour! :o Pity it uses American spelling. )

[back_ache]

I don't think you nessecaryily need a seperate infrared source. I've read before that as the lights chuck out loads of infrared even before they start chucking out stuff in the visual range, some people just tweak the pre-heat setting on the dimmers and let the existing lighting do the work.

[alan v]

We used to have a camera with built in IR capability - it didn't work very well. The problem was that the IR was on all the time - the only way to switch it off was to point a bright light directly at the sensor. Which obviously, is not the most practical solution in a blackout.

 

I think the problem was caused by the sensor being in the camera (just under the lens). The camera was at the back of the auditorium, in the dark, looking at the brightly lit (and well focussed) stage.

 

Now I come to type this, it seems a very odd state of affairs. But that was what was happening.

 

Alan.

 

PS - not spell checked due to Blue Room spell checker craziness.

[GridGirl]

You don't really need an infrared source - we have a permanently installed IR camera and it doesn't have any trouble "seeing" the stage in a blackout. You may have to tweak the contrast/brightness on your monitor, but I've never had any problems.