Blurred images during night

[wauwau 0]

Dear all,

 

well, I am quite a greenhorn... anyway.

On our farm, I am running a Bosch Dinion XF (nite surveillance is important) and replaced

the standard vario lens (2 - 8 mm) by a tele vario lens (6-15mm)

with auto-iris. During daytime, the image quality is perfect, however while the old lens obviously adjusted to the changing illumination during dust and dawn, the new lens seems to have problems. The images get quite blurry in the nite.

 

The new lens has only a focus and zoom ring - and the connector to the camera. Did I do something wrong?

 

Thanks for your help

BR

[atropine 0]

I had that problem with my day/night camera too. It sounds like the 2-8mm lens is an IR lens, while the 6-15mm lens isn't. Normal (good quality) lenses have special lens coatings which make all the colours of the rainbow focus at one point, even though they are at different wave lengths and normally wouldnt. This makes the picture much sharper. This process can be done for Infra Red lighting also, so that all the visible light colours plus infra red light all focus on the same plane (the CCD).

 

You can try manually focussing the lens when it moves into night mode, but that also means refocusing for colour mode. Your pictures will never be as sharp in night mode however, due to there always being a mixture of visible and infra red lighting. The lens can not simultaneously focus both.

 

I think it would be best to just buy an IR lens.

[rory 0]

Even with IR lenses you can still get blur. Glare from certain lighting like spot lights will cause such a problem, and ofcourse if its really dark then it can seem blurry.

 

Anyway, regardless of whether they claim there should be no focus shift, focus the camera under low light. If it has a backfocus, adjust that (wont go into details but search for backfocus on the forum). Make sure it stays in focus in low light, full light, and IR if it uses any. You will need to do this in a controlled environment for best results. (eg. Large Garage).

[atropine 0]

Oh yeah, good point, maybe his camera just isn't focused properly to begin with. Better not go buying that new lens just yet!~

[securitymonster 0]

focus the camera under low light

 

Exactly! Try focusing the camera after the sun has gone down.

[jisaac 0]

security monster is a nut dont listen to him!

Just kidding. Ya just focus it after dark. If you can get it clear. Then you had a back focus issue.

[survtech 0]

Or focus during the day using a piece of #5 welding glass in front of the lens to allow the iris to fully open.

[C7 in CA 0]

Or focus during the day using a piece of #5 welding glass in front of the lens to allow the iris to fully open.

 

Thanks for that tip!

[rory 0]

Thanks for that tip!

 

with a black sheet over yourself and the monitor .. or yah wont be able to see anything good enough on the monitor to be able to focus properly

[C7 in CA 0]

Thanks for that tip!

 

with a black sheet over yourself and the monitor .. or yah wont be able to see anything good enough on the monitor to be able to focus properly

 

Thanks for the tip!

[CameraGimp 0]

There could be two issues effecting you.

 

1. IR can focus at a different point. If you remember light going through a prism from your school days you should know that white light gets split into a rainbow red to blue. This is exactly what happens in a camera lens and it is called chromatic abberation. Fortunately a camera lens is made up of a number of pieces of glass and the smart lens designers make these bits so all the colours end up back together or at least the good ones do. The principal is exactly the same for IR. The light going through the prism goes blue to red and the IR is just beyond the red. Only thing is we can't see it.

 

The problem is because we can't see it many lenses are designed to bring it back to focus. Why bother if you can't see it. That is why you should use IR corrected lenses (not IR coated!)

 

2. This is probably the more important one. If your lens is auto iris your depth of field will reduce as the light goes down and the iris opens. As a result something that was in focus can go out of focus. To avoid this you have to as recommended adjust your back focus with the iris fully open. This is worse case.

 

Open the iris by focusing at night, using a strong filter (welding glass) or if you now what you are doing setting the camera to a fast shutter speed.

[survtech 0]

Thanks for that tip!

 

with a black sheet over yourself and the monitor .. or yah wont be able to see anything good enough on the monitor to be able to focus properly

Just don't use a white sheet (and a pointy white hat) .

[C7 in CA 0]

I'll be sure and leave my dunce cap at home

 

[wauwau 0]

Adjusting the focus during nite was the solution. As it is a tele objective, it was obviously not really in focus during daylight (but I couldn't see that).

 

Thanks a lot for your really helpful work!

 

BR

[cctv_down_under 0]

Just a point, a lot of mechanical filters when removed change the view, becasue the distance from filter, lens to ccd is now different.

 

I do not want o look like a Bosch rep again, but you dont need any ND filters for the Bosch cams which is pretty cool, you dont need to adjust the iris or anything for back focus, simply adjust into back focus mode and the picture stays the same

[rory 0]

Just a point, a lot of mechanical filters when removed change the view, becasue the distance from filter, lens to ccd is now different.

 

I do not want o look like a Bosch rep again, but you dont need any ND filters for the Bosch cams which is pretty cool, you dont need to adjust the iris or anything for back focus, simply adjust into back focus mode and the picture stays the same

 

are they moving the CCD mechanically?

 

Ps. the Sanyo Pan focus doesnt even need to be focused