B/W image sensor focusing with IR lighting environments

Tested with a P26 with a b/w sensor and Raytec Vario i8 940nm light.

Using a b/w image sensor during the day (focused during day) will not give the same image clarity at night using IR lighting. I have found that adjusting the focus of the lens at night will sharpen the image greatly. This problem, imo, means that I should only be using dual image camera setups in my situation where one is focused for day (color or b/w) and one b/w focused for the IR lighting. This, unfortunately means, in my setup, that I would need to use 2 dual cam setups instead of 1 to cover the same area.

I’ve been using Mobotix for 15 years. And I always thought the problem was the “strength” of the IR light itself. But it appears that when using IR lighting, the lens will need to be focused for the type lighting involved. It’s unfortunate I took so long to see this as a sensor issue. The hardware side has been “rock solid” for me. I have yet to have a failure. I am still using a d12 from when I bought it new (13 or 14 years ago). And I am the beneficiary of reliability of the “no moving parts” mantra that mobotix stood by for so many years. But, I’m wondering if I should consider moving to a camera that will (auto) adjust focus for the lighting used.

Is there anyone else that can confirm/refute what I am talking about? And is there anyone that has further insight? I also have s16’s that are in an 850nm environment. I have not tried focusing these at night.
As some will know, it can be a PITA to do this on site.

Would be great to see some sample images to better understand the phenomen. Also, have you fiddled around with the sensor gain setting to see if it has any effect?

I have changed settings on gain and it did not help. Manually focusing the lens for the IR environment did miracles. I think what I am going to do is to set this P26 next to an s16 b/w sensor. I’ll have an s16 sensor that I already have focused during the day (this sensor will also have the same 850nm ir lighting at night). And I’ll focus the P26 during the night (under 850nm Raytec vario2 i8 lighting). Then I will take snapshot pictures of both in the day and night. This should prove to be very interesting.

Do you have experience using IR lighting with the x6 b/w sensors?

Incidentally, in case you may ask, I usually use svga for night recording. I do this because resolutions higher than this do not produce any clearer view. Again, I just thought this was the lack of light from the IR emitters. Now, I guess I’m going to see if this is really the case or not with my next test. Also, in my first post, I talked about the P26 focusing. I was able to use higher resolutions once I refocused for IR Lighting. And the picture actually improved.
I’ll report back when I do this 2nd test. It may lead to a 3rd test where I actually take the time to refocus the S16 sensor module lens during IR lighting scenes.

Thank you for taking the time to post a response. Much appreciated.

It is interesting indeed. We have delivered multiple systems with IR illuminators. Mostly for LPR-applications and I haven’t ran across this problem. The application is different, since were using mostly quite narrow lens angles. What are the lens angles and illumination angles you’re using?

This is normal for fixed lenses (no autofocus/IR compensation - the no moving parts side of things).

You should see smaller efect with 850nm IR’s since they are closer to visible light spectrum.
This happens because different wave lengths are affected differently by different materials. Best example is pink floyd: dark side of the moon album cover that shows that the red is affected the least by lens. That’s called dispersion.
This efect usualy goes unnoticed in ANPR scenarios, as camera has filter that allows only IR to pass through, hence it gets focused for specific light waves.

Also similar efect can be seen on colour sensors, where edges of objects seem to glow or have unusual colours. That efect is called chromatic aberration, but in principle is same thing - different wave lengths have different focus point with same lens.

Thank you so much for taking the time to post a response. While I called it a problem with the sensor, I didn’t mean to say that mobotix sensors are defective. My thought all these years was that the IR lighting was not strong enough, lumen wise. I have focused my lenses during the day, all these years, so the night was always substandard under IR lighting. But now I understand how this dynamic works.

I did a test with this P26N yesterday. I left it forcused for 940NM when I had it bench tested in my basement. I took it outside during the day and the image was awful. As expected. Last night, I had to refocus for the 850nm lighting. And the refocusing did the trick. Now, this morning, I see the the image with daylight is subpar.
All of this confirms that I originally came to the wrong assumption many years ago. If I really want clear night images with IR (I have a lot of wildlife recordings at nigh. Bears, cougars, moose, etc), AND, I want clear images during the day. I will day, I will need to use 2 dual sensor cameras to cover that same area I do now. I hope that all made sense.
The other alternative is to start experimenting with mechanical focus cameras.

Thank you again for taking the time to post an explanation. It was very helpful to this old mobotix user.