Challenging Camera / Lens Application?

[james2 0]

This may be a bit out-of-place here, but this seems to be the place with the most knowledge on applied use of cctv, so here goes.

 

We need to mount a b&w camera about 2 - 5 feet away from the top of boxes. The height of the boxes varies by about 15 inches. We are trying to read text (characters 3/4 inches high, 7/16 inches wide) that can be anywhere on the box tops.

 

This gives requirements of having a camera / lens system that has enough resolution to cleanly show 3/4 by 5/16 letters which can be anywhere in a 28 by 28 inch region - and the depth of field needs to be 15 inches.

 

Is this going to be a big challenge or is this a piece-of-cake camera / lens application? Do we need to be looking for a high resolution camera (if so, how many lines vertical lines)? Are we going to have problems getting the combination of close-focus and depth of field - and what sort of lenses should we be considering?

 

Thanks for any and all help on this!

 

James Cox

[rory 0]

Hi

 

#1 - do you need vandal proof, or can you just mount a traditional camera with a mount? If you need vandal proof, or resistant, you can optionally use a Vandal Resistant Mini Fixed Dome camera, with a varifocal AUTO IRIS, 4-8mm lens. This should cover you, and you can adjust it at time of installation to zoom in on the box if you need to. If the boxes are just 2 feet away, a 4mm lens probably is not wide enough, so youd need something like a 2.5 -10 mm varifocal lens, so you can adjust it.

 

Take into consideration the glare from lights onto the top of the boxes, but you should be able to make out the letters somewhat ok. Either way you would need a high resolution, color, 480TVL, or even the sanyo 520TVL camera. Also which camer depends on what type of lighting you have there, if it is too dim, you would need a low lux Color camera, and if it is even darker, a BW, though not sure BW will pick up the letters. depends on the colors and their back grounds. Main problem is that a box 2 feet way may cause alot of glare on the camera as it self adjusts. Lighting is the main factor in whether or not you see the images, or if you get glare, etc.

 

Interesting to see if anyone else here has done this type of App before, if so post some feedback, id like to know for future use.

 

Rory

[james2 0]

Thanks for the reply, Roy!

 

Vandalism isn't an issue - although temperature resistance is - these boxes (really fiber drums of varying heights) are being fed to an incinerator and we need to read a label on the one closest to the feed door. We may put the camera in an open-bottom enclosure and have a flow of compressed air through the enclosure to protect it from the occasional gust of hot air from the feed door.

 

Your comments on glare were intereresting - I hadn't really considered that as an issue. We can add lights without too much trouble - would glare be less of a problem if we added two - one to the left and one to the right and aimed them at an angle? That would seem to reduce the amount of light that bounces directly back toward the camera. Also, we can move the camera a bit farther back than 2 feet from the top of the highest box - which also might get us back to the 4 - 10 mm lens.

 

From some experience with an old Pentax K1000 35 mm SLR, I remember that depth of field drops off pretty dramatically as the f-stop decreases - what are the typical f-stops for these lenses? Also, you mentioned Auto Iris - is that a self-contained feature of the lens or does the camera send a signal to the lens to close the iris? The old K1000 was manual everything, so some of this is new to me!

 

The labels are black letters on white glossy paper, so a B&W camera will be best, I guess. I had found a reference to the Sony SPTM320, a B&W camera that claims 570 horizontal lines. (Anyone have any experience with that camera?)

 

I tried a bit of math: the area where the label could be is 28 x 28 inches. Dividing 570 lines by 28 gave about 20 lines per inch which means that in a 3/4 inch high letter there would be about 15 lines. Since I can't control the orientation of the labels, if the letter was sideways (and is 7/16 inches) that would mean that about 9 lines would span a character. That seems sort of on the low side, but might be OK. Of course, this sort of analysis may be totally out in left field - any comments would be welcome!

 

Again, thanks for the feedback - hoping to get more.

 

James Cox

[cctv_down_under 0]

I have done this sort of before, the best is to use a camera like this one...

 

http://www.koreacctv.com/

 

SK-2172X

 

This a low light fully digital camera, it can be controlled by RS485 over a long distance, with the zoom and auto focus you can do it remotely and control your zoom to the right size, the best bit is that it has programable BLC by zones so you can mask most areas that reflect so much and it is also low light, there aare two versions one without low light, they dont cost the earth either, so it is a really good option for this solution, the problem will be heat though because they get a little hot at the best of times so you would need a good enclosure to keep it stable...

 

 

I hope this helps,

 

GC