Have I got the wrong lens?

[michaelmorris]

I’ve recently bought a lens, but I’m not convinced I have got the right lens. I want a 160 degree FOV lens suitable for a ½” chipped video camera. The lens I’ve got is C mount and needs a C to CS mount adaptor to bring it to focus on my Watec 902H2 camera.

I’m not at all happy with the extreme vignetting I’m getting (see attached picture)

Is this vignetting

A – due to the lens being actually one designed for a 1/3” chip?

B – due to the need to add the C to CS adaptor?

C – what I would expect from a ½” lens with this field of view, regardless of whether or not it needs the C to CS mount?

Attachments:

[arp]

Hi Michael,

I'm not sure if factors A or B have resulted in the images you get, but the inscribed circle maximises the FOV that is recorded by the camera chip.

I suggest you try it on the night sky, to see if the stars are in good focus and then you can estimate the FOV. IF the image circle was larger you would lose the wide FOV and not achieve 160 degrees.

Such a fisheye type of lens can be operated as an allsky camera, although real-time video with the Watec 902H2 camera will most likely be limited to mag +1 stars, and will only record the brighter meteors. The small image scale will give low quality astrometry when measuring meteor trails.

Very wide angle lenses often incur substantial light loss at the end of the FOV.

Best regards,

Alex.

[michaelmorris]

Now got an alternative lens and can confirm that the Ragecam 2.4mm lens on EBay advertised as being for the Watec 902 is definitiely NOT 1/2" format.