Lenses needed please?

[some bloke 0]

Hi, first post but not into cctv business so not much point in doing an intro really.

 

I am setting up an in car agricultural night vision pest control system. The planned set-up is two low light camera's connected to a monitor with 2x av in and 2x 940nm IR floodlights mounted on the roof of the 4x4.

 

Camera 1 would be to view the general area and spot rat, fox or rabbit movement on crops, golf course, chicken pen areas etc.

Camera 2 will be mounted behind a rifle scope to view the quarry through the crosshairs and fire the bullet at the brain for a humane despatch.

 

I have so far equipped myself with:

Two roof mounted Bosch ufled 940nm IR floodlights (1x10 degree + 1x30 degree)

A dash mounted 1/2" ccd Watec B/W low light camera - without lens.

A 1/3" super had ccd day/night bullet camera with 6mm lense as the scopecam

1x dash mounted monitor.

12V power supplies and phono leads.

 

I'm confused about lenses. I will occasionally be using the kit late afternoons or early mornings but over 90% during the hours of darkness: I have read that since the lighting will be variable day/night, the cameras will lose focus from one light wavelength to the other.

 

So my question(s) finally, are:

Do I need IR lenses?

Auto or manual iris for the observation area camera please?

If a short/wide lens on the scopecam sees unneccessary imaging either side of the rifle scope am I effectively "wasting" pixels or other capacity which is reducing the potential image quality of what is seen through the riflescope?

 

Thanks in advance for any help and please forgive me for not knowing all the lingo.

[Soundy 1]

I have so far equipped myself with:

Two roof mounted Bosch ufled 940nm IR floodlights (1x10 degree + 1x30 degree)

A dash mounted 1/2" ccd Watec B/W low light camera - without lens.

A 1/3" super had ccd day/night bullet camera with 6mm lense as the scopecam

1x dash mounted monitor.

12V power supplies and phono leads.

 

I'm confused about lenses. I will occasionally be using the kit late afternoons or early mornings but over 90% during the hours of darkness: I have read that since the lighting will be variable day/night, the cameras will lose focus from one light wavelength to the other.

This is not SPECIFICALLY true - there are other variables involved.

 

Loss of focus at night is usually due to one of two phenomena. Most commonly, an auto-iris lens is focused in bright light, which causes the iris to close down, thus increasing the depth of field. In low light, when the lens opens up, the DOF becomes a lot shallower, and quite often most of the scene will be out of focus. The fix/workaround for this is to either use a manual-iris lens, or force the iris open for focusing, either by focusing in low light, or by using some sort of neutral-density filter over the lens, or perhaps by adjusting the iris/drive level control, if the camera is so equipped.

 

The other possibility for this is when you're using a "true day/night" camera; that is, one with a movable IR cut filter. Because IR wavelengths focus differently than visible light, when the camera goes to night mode and removes the filter, the IR portion of the image can be out of focus relative to the visible light. The fix for this is an IR-corrected lens, often simply designated as an "IR lens".

 

 

So my question(s) finally, are:

Do I need IR lenses?

Most likely, only if the camera is a "true day/night" type... but it doesn't hurt to use one anyway.

 

Auto or manual iris for the observation area camera please?

Since you'll be working 90% of the time in very low light, an auto iris will be wide open 90% of the time anyway... so really, it probably doesn't matter. I'd go AI just so the camera can close the iris down a bit for that other 10% of the time.

 

If a short/wide lens on the scopecam sees unneccessary imaging either side of the rifle scope am I effectively "wasting" pixels or other capacity which is reducing the potential image quality of what is seen through the riflescope?

Yup.

[some bloke 0]

Thank you so much Soundy. Another couple of questions if I may please:

The 1/2" ccd dash mounted camera has a cs mount.

 

Would there be any more light input if I used a fixed length lense rather than variable?

And would a 2/3" lense allow more light through?

 

I should add that I am after the best possible image to help correctly identify the quarry and place an accurate shot at the longest possible range. I'm anticipating the 10 degree IR floodlight should enable me to easily achieve 100 yards.

[Soundy 1]

Thank you so much Soundy. Another couple of questions if I may please:

The 1/2" ccd dash mounted camera has a cs mount.

 

Would there be any more light input if I used a fixed length lense rather than variable?

And would a 2/3" lense allow more light through?

The answer to both is, "not necessarily". The spec you're looking for is colloquially known as "the f-stop" and is normally listed something like "f/1.4" or "1:1.4". For any given lens, at any given focal length, the same f-stop will allow the same amount of light. It's a inverse ratio of the aperture diameter to the focal length, and quite simply represents a fraction: focal length divided by aperture diameter.

 

For example, for a 10mm lens at f/1.4, the aperture's diameter will be 10/1.4, or 7.14mm. For a 25mm lens at f/1.4, the aperture would be 25/1.4, or 17.86mm in diameter. Either way, the same amount of light is passed. Likewise, if you put a 7.14mm aperture in a 25mm lens, the f-stop would be f/3.5 and would allow about 1/8 as much light. Designated sensor size has no direct relevance; neither does fixed vs. variable focal length, although large-aperture lenses tend to be easier to find in fixed variants.

 

I find most lenses tend to fall within f/1.4 to f/1.8 maximum aperture... I've seen f/1.2, f/1, and even f/0.85, but these tend to be harder to come by, as well as more expensive. Keep in mind that there's always a trade-off, too, and the wider the aperture (lower f-stop number), the shallower the depth of field and the more critical focusing becomes.

[some bloke 0]

You are a gent sir - thank you so much. " title="Applause" />