Dark edges on CCTV image at Wide Angle - Normal?

[KillingTime]

Hi,

 

Just purchased a CCTV camera with a Sony IMX317 sensor and a 2.8-12 C mount lens. Brand is 'ELP'.

 

At nearly all focal lengths there are dark patches at the edges of the image. See attached. These edges disappear when you zoom in (10-12mm).

 

Has anyone seen this issue before and know what causes it?

 

The lens has 1/2.5" printed on it, and the IMX317 sensor is listed as 1/25" also, so it's either;

 

1) A badly made lens, or

2) The lens it mounted incorrectly (it is screwed all the way in), or

3) All 2.8 varifocal wide angle lenses look like this.

 

This normally happens if the sensor size is larger than the lens is designed for, so the focused image is smaller than it needs to be. I have no reason to suspect the sensor as it outputs QHD at 30fps. It probably is an IMX317, which leaves the lens, or the mounting distance.

I know that these types of lens also come in 'HD' and '3MP' variations (mine isn't either), which presumably means the optics are better, but that shouldn't cause the dark edges AFAIK.

 

Thanks.

[MrHappy]

A body camera with a varifocal lens... how vintage

 

I'd assume the frame is the inside of the lens

 

Lens is in the wrong place or the wrong format

 

unscrew it, fit a space, change the lens ?

[PeterJames]

23 minutes ago, MrHappy said:

 

 

unscrew it, fit a space, change the lens ?

QFA probably needs a spacer ring

[KillingTime]

5 hours ago, PeterJames said:

QFA probably needs a spacer ring

 

Tried a spacer ring and the lens wont focus at all.

 

I assume all 2.8-12 varifocal lenses don't look this way then... If not I'll buy something else.

 

Thanks.

[sixwheeledbeast]

I'd agree with above, it looks like it says CS mount not C on the side of the lens?

If it's suppose to have a C mount but you have a CS then the Flange Focus length will be out.

You can only use a spacer ring going C>CS not CS>C.

[james.wilson]

If its only when fully zoomed out it's probably seeing the edge of the lens. Buy I larger format lens is another option

[KillingTime]

Had another play around with the camera this evening and found the problem.

 

The CS lens screws into a silver threaded adapter that in turn screws into the camera body. The silver adapter is held in place by a grub screw. See below. By undoing the grub screw you can rotate the silver adapter and that alters the lens to sensor length.

 

It only needed a few turns inwards in my case. The lens controls are now facing the bottom and not the top though. Not a huge issue.

 

Thanks for the replies.

[PeterJames]

4 minutes ago, KillingTime said:

Had another play around with the camera this evening and found the problem.

 

The CS lens screws into a silver threaded adapter that in turn screws into the camera body. The silver adapter is held in place by a grub screw. See below. By undoing the grub screw you can rotate the silver adapter and that alters the lens to sensor length.

 

It only needed a few turns inwards in my case. The lens controls are now facing the bottom and not the top though. Not a huge issue.

 

Thanks for the replies.

Yes thats called back focusing

[MrHappy]

Manual Iris too

 

I think I've loads of 1/3 format lens in s box somewhere,

 

I hoard stuff,

 

Lobbied a redcare stu, some webways & some emizons out the other week...