Can't focus fixed lens clearly

[LUV2TINKER 0]

Been toying with an old Ultrak KC4300bk, standard res., b/w box camera (analog).

It currently has what I'm told is the original lens - fixed, manual focus, F1.2. 4mm wide angle - not an auto iris lens.

 

Can't get the focus to zero in on an object. I turn the focus back and forth in microscopically small increments in "near" and "far" directions, and it never gets completely into focus.

It does this in all lighting conditions from low light to daytime image conditions.

I'll zero it in as well as I can get it on an object at like 15 feet away, and that object never gets very well focused. And nothing else in the image before or after that object is in focus either.

I tried unscrewing the lens a little from the camera to slightly increase the focal distance from the back of the lens to the CCD. But that didn't help.

 

The "near" and "far" focusing collar seems to just move the entire lens assembly closer to the CCD. So I'm wondering:

Are there 2 lenses in this lens assembly? And if so could the distance between them be off a hair?

[SEANHAWG 1]

Perhaps your lens is not getting close enough to the CCD. Probably just needs a back focus ring adjustment. Loosen up the back focus ring screw on the camera and then turn the back focus ring all the way clock wise, then put on the lens. It may be the case that you need to turn the back focus ring all the way counter clockwise

[Numb-nuts 1]

I am amazed how few installers understand what back focusing is and how to perform it. You need to have the iris fully open so will need some ND (neutral density) filters to reduce the light entering the lens before making adjustments. It should be possible to get the camera to focus continuously through it's range and then fine focus with the front ring on the lens. Any good CCTV book will advise how to achieve this it's NOT difficult but can make so much difference to the resulting image. A set of ND filters will cost from about £45.00.

 

Pursue this and you will be very pleased with the results you can achieve. I do this on all cameras unless the picture is outstandingly crisp, then I don't mess with them.

[camera-newbie 0]

Do these ND filters attach to the lens or just sit in front of the lens? I took a camera class or watched something online a few years back and they had some filters that could attach to the lens body as I recall.. Anyway, just wondering if you do this even for dome cameras,etc.. Does it matter what kinda of ND filter -- meaning can I visit my local camera store, pick one up and temporarily attach it to the lens in question and go to town and remove it afterward? Sorry for rambling..

[Soundy 1]

With an older camera, it's also possible that the CCD is, for lack of a better term, worn out... and it's possible the lens itself has become defective over time (excessive heat causing plastic parts to soften, moisture or contaminants getting inside the lens, etc.).

 

One thing you can do is take the lens off and ensure both front and rear elements are clean (because the rear element is so near the focal point, the smallest imperfection there can cause a significant image problem). Look at the sensor as well, and make sure it's clean (I've seen them muddled by fingerprints, dust, even some kind of substance that seemed to be vegetable oil).

 

If that doesn't help, try a different lens, to narrow down whether the problem is the camera, or the lens itself.

[Soundy 1]

The idea of an ND filter is to force an auto-iris camera to open the iris all the way; otherwise, a partially-closed iris (due to bright daytime light) will cause a greater depth-of-field, and if your focus point isn't set right, your image will go out of focus when it gets dark and the iris opens up again. With your setup, it shouldn't be necessary: just set the manual iris to full-open when doing your initial focusing, then if you want, try closing it down a bit to increase the DOF and sharpness.

 

If you do use one, you'll normally just hold it in front of the lens while focusing. Some guys use actual photographic ND filters; some use a piece of welder's glass (#4 or #5 shade). Ultimately, you could do it with a pair of sunglasses, in a pinch - the purpose is to reduce the light and force the iris to open fully.

[camera-newbie 0]

Thanks Matt! I'll keep that in mind when I get that far this weekend..!

[SEANHAWG 1]

I have had thousands of these cameras move through our warehouse, I wouldnt spend money on getting any kind of filters or to do to several knit picking techiniques to get a razor sharp image. Its an old B/W camera that was used back in "Saved by the Bell" days and you arent going to get a huge amount of performance from it. Just adjust the back focus ring until you see it come into focus a little and then focus it with the lens.

[LUV2TINKER 0]

Thanks for the reply.

 

The back focus adjustment on this one is controlled only by the distance you screw a black piece (which the lens screws into) into the camera. In other words, the CCD doesn't move forward and backward on this camera by turning the knurled knob labeled C/CS like it does on, i.e. a Ultrak KC552BCN model I also have.

There's a locking screw at the top on the camera for locking it in position once you've threaded it in the proper amount to back focus it.

This back focus adjustment was originally screwed in as far as it would go into the camera (clockwise), which moves the lens as close as possible to the CCD. I backed it out (turned it counter clockwise, which moves it farther away from the CCD), to various positions, and it didn't solve the problem. The farther out I turned it, the farther I had to move the lens focus past the center point it started out at when the adjustment was screwed all the way into the camera.

So I ended up with it set all the way to "far" (ran out of room to fine focus it)

So the back focus was probably about set in the proper position to start with - screwed all the way in.

BTW, I did have it in a very low light area while adjusting the back focus.

So that's why I was asking if the distance between the 2 lenses might be off a bit, and if that could cause this problem. Can't seem to wrap my head around what problems there would be if those 2 lenses weren't the proper distance from each other.

This camera and lens setup is exactly what I need for my application, - b/w with plenty of light at night (the only time it's recording), because it has the F1.2 and the 4mm wide angle lens.

 

 

Perhaps your lens is not getting close enough to the CCD. Probably just needs a back focus ring adjustment. Loosen up the back focus ring screw on the camera and then turn the back focus ring all the way clock wise, then put on the lens. It may be the case that you need to turn the back focus ring all the way counter clockwise

[SEANHAWG 1]

I wonder if its the lens then and not the appropriate one for the camera. If you can take a picture of the lens, I can probably tell you if it is or not. Do you have a vari-focal lens that you can try, probably have one that is attached to your KC552BCN.

[LUV2TINKER 0]

Sean, I've looked at pictures of these 4300's on the web, and the lenses appear to be identical to this one, and so does that black piece they go into. This lens says: Ultrak CCTV lens 4mm F1.2 Japan.

It has a rectangular gold sticker on the the rear end of the collar that says "8 J".

But I have to admit to being confused about this "back focus setup". The little bit of info I have for the KC4300 (mostly just specs) states that it accepts either C or CS lenses. But this lens doesn't state whether it's C or CS, and I've never seen a picture of what the lens that's on there actually includes. Like maybe part of it that I think is the lens is an adapter. And the same thing applies to the KC552BCN I bought that came with a 3rd party lens on it.

In short, I have no idea what the adapters look like. But neither lens will fit on the other camera, even though both cameras supposedly support both C & CS lenses.

[LUV2TINKER 0]

Just figured out the adapter. The lens on the KC4300 does have that 5mm spacer adapter on it. So that knurled part that you screw in and out of the camera is in fact for adjusting the back focus, like I was doing unsuccessfully.

And the reason I couldn't interchange the lenses between the 2 cameras, was because I was using the adapter.

Just put the 3.5 - 8mm F1.4 lens from the 552 on the 4300 and the 4300 focuses just fine, but probably won't have enough light at night for my application.

But at least I know that the 4300 is okay. I'll try to put the lens I couldn't focus on the 4300 on the 552, but I'll have to reset all the dip switches first.

[Numb-nuts 1]

Do these ND filters attach to the lens or just sit in front of the lens? I took a camera class or watched something online a few years back and they had some filters that could attach to the lens body as I recall.. Anyway, just wondering if you do this even for dome cameras,etc.. Does it matter what kinda of ND filter -- meaning can I visit my local camera store, pick one up and temporarily attach it to the lens in question and go to town and remove it afterward? Sorry for rambling..

Firstly, you do not tinker with the lenses of speed domes, static domes use 12mm lenses and if using a varifocal lens you would well advised to use the manufacturer's setting as these are somewhat awkward to set up.

 

In general the only lenses you will need to back focus are those fitted to body cameras. Tavcom sell a suitable set priced competitively. You will need at least ND1 and ND3 but a IRP (infrared Pass filter) is also useful. CCTV lenses are to the best of my knowledge not made to accept filters so I fix mine with bluTak during setting up.

[LUV2TINKER 0]

Just want to make sure I understand how this part works, and I definitely want to be corrected if I have this wrong.

I always think of the iris as being that "hole" inside the lens.

In this non-auto iris lens (no power going to it), wouldn't the iris always be fully open? If so, then why would you need to attenuate the light entering the lens while back focusing it? I mean I did attenuate the light on it anyway, while I was adjusting the back focus, but did I really need to?

 

I am amazed how few installers understand what back focusing is and how to perform it. You need to have the iris fully open so will need some ND (neutral density) filters to reduce the light entering the lens before making adjustments.

[Soundy 1]

Just want to make sure I understand how this part works, and I definitely want to be corrected if I have this wrong.

I always think of the iris as being that "hole" inside the lens.

The iris, specifically, is the set of blades that forms an adjustable opening. That opening, the "hole" inside the lens formed by the iris, is the aperture.

 

In this non-auto iris lens (no power going to it), wouldn't the iris always be fully open?

If it's a fixed-aperture lens (like most M12 board lenses), then yes. If it's a manual-iris lens, you'll need to make sure it's wide-open, but that's done with a ring on the lens (usually marked "open" and "closed").

 

If so, then why would you need to attenuate the light entering the lens while back focusing it? I mean I did attenuate the light on it anyway, while I was adjusting the back focus, but did I really need to?

Generally, no, you won't need to. The exception might be if the camera's ESC (electronic shutter) or gain control can't compensate for a very bright scene - for example, if the image is washed out with the iris wide open. HOWEVER... if you need to close down the iris to compensate for that in a normal view, then you'll probably need to LEAVE the iris at that partially-closed position for regular operation, and being a manual iris, you don't have to worry about it opening up again on its own and thus affecting the DOF.

 

Summarizing: this problem is specific to auto-iris lenses being partially closed when focusing, and then losing DOF when they open again in low light. The ND filter is intended to reduce the light and force the auto iris to open fully thus giving you the least DOF while focusing, knowing that the iris closing down later will only increase the DOF. Manual-iris and fixed-aperture lenses should not require ND filters to set up.

[LUV2TINKER 0]

Soundy, thanks for that info, including the part about the manual iris lenses. I don't have any of those, and wondered about them. Mine are just fixed iris.