Have a look here: CCTV Lens Calculator

I very rarely use anything other than a 3.5 - 8mm varifocal lens on whatever type of camera is required, it usually covers most scenarios.

Audio on a DVR, cant say ive had to think about that before now, i am quite confident you can get audio on a DVR though.

Just checked and LJD claim to have one, never used them so dont know what they're like to deal with.

I wouldnt rule out a working PIR with audio onto a VCR either as you can use the pir to trigger alarm recordings and therefore use minimum tape.

If on the other hand you just wanted to concentrate on the area specified at 12 meters away with a 5 meter field of view an 8 or 12mm lens might be better.

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Hmm, think I might go for an 8mm lens then. I think the main objective is recording the conversations in the office, the camera is just to see roughly what's going on at the same time IYSWIM.

If no-one was there, would it need to record?

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Although there's no-one in the office upstairs for days at a time there are still staff in the office downstairs where the camera is recording them, who don't have access to the office upstairs. The problem isn't the recording when the powers off so much, it's the starting up again when the power comes back on, and there's still the inadvertant shut down scenario.

Your asking a bit much to record audio at 12mtrs!

Your asking a bit much to record audio at 12mtrs!

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Sorry, didn't explain that bit. I'm looking to put a seperate mic near to the desks so it'll only be 2-3m at the most. Still can't find a suitable mic though. I can find miniature kit type ones that I could build into a box but I can't find a ready to fit option.

Just checked and LJD claim to have one, never used them so dont know what they're like to deal with.

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So they do, never seen them before but they seem to have the most useful site I've seen so far for CCTV products. No mic's though!

Could you hide this anywhere, wires in the ceiling..?

Could you hide this anywhere, wires in the ceiling..?

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I'm sure it could be fitted into something, if I can't find anything that comes in a box I can just screw to the wall then that'd do the job.

What about an AV mic. CSL & Aritech both do a good looking mic. Bearing in mind most DVRs only have a single channel audio input so if its just the one camera then its fine but no good if multiple cameras.