How to calculate Lens size required

[masterarcher 0]

Hi

 

I have a home shooting range and wanted to setup a simple Camera and TV for veiwing targets closeup from 10M away at my shooting station.

50cm above my target I have a shelf coming out 80cm with a small spotlight to shine on the target, next to this I wanted to put a small camera to veiw a closup of the target, the target face is 17cm square and will be 80cm from the camera lens, I have seen a lot of CCTV cameras for £25-£35 but only have a 3.6mm - 6.00mm lens, I need the camera to fill a tv screen with the target image so I thought I would need a narrower field lens like a 9mm, 16mm or even 25mm lens, I do not know how to work out what size lens I need on a CCTV Camera, can anyone help with my calculation on the size lens I need for this job otherwise I shall have to go for the 16mm as a lucky dip.

 

Thanks for any advice tips or tricks that may help me.

 

Thanks

[Blake CCTV 3]

Hi have a look here I find this useful.

http://www.theiatech.com/calculator.php

[masterarcher 0]

Hi

 

Cheers for the link, I checked it out I shall try the app when I get chance, the online calculator could not realy show a result for what I wanted.

 

If someone has a camera that is moveable would you be able to help me by placing a piece of card roughly 17cm square about 80cm from the lens and let me know if it fills the screen of the monitor and what size lens you have?

 

Thanks for any help

[masterarcher 0]

Bought the app for the iphone but has not really given me any better idea on the size lens I need.

 

Is there a calculation they use in the trade like -

Distance times view area divided by 3 ?

[GrouchoBoucho 0]

try this calc: http://www.pelco.com/sites/global/en/sales-and-support/downloads-and-tools/tools/lens-calc.page

 

17cm = 0.558'

80cm = 2.625''

 

select 1/4" camera, put 0.558 for the height (since the camera view is wider than it is high), and you get about a 12mm lens (view will be about 23cm wide).

 

(and actually, you can just plug in 17 and 80 for the image height and distance, and get the same results - the units aren't really relevant as the two measurements are the same relative to each other)

 

given the height above the target, the actual distance will be a little more, and the target won't appear square in the frame anyway because of perspective distortion... not much you can do about that without getting into a tilt-shift lens.

 

a better idea would be simply to get a better camera with a varifocal lens, so you can adjust the focal length until the view fits the way you want. 3-33mm lenses are relatively common and should cover any size sensor at any distance or angle in your range.

[masterarcher 0]

Hi

 

Thanks for your info, very handy, I could get away with a 16mm fixed lens.

I may just look at some zoom lens to give me more leeway.