1/3 camera and a 2/3 lense?

[troytempest64 0]

Hello All

 

Before I ask my question, let me please first apologise for not being a CCTV professional, so my question may have been asked already. I'm not a complete numpty (hopefully) and have a background in networks, so hopefully I'll understand your answers.

 

I'm not sure whether I've committed a bit of a faux-pas, in the interest of trying to improve a camera installation my sister has on her farm. Basically she has a discreet camera (inside a dovecot) covering the entrance to the farm, keeping an eye on vehicles visiting and loitering.

 

The old camera died, but was never really great, as the position faces west so was prone to being blinded by the setting sun. The old camera (not sure what make) was day/night, fitted with a 16mm lens, but didn't work very well in low light (compared to newer domes there). The gate is located about approximately 7 metres from the camera position, and my feeling was we needed a bit more zoom than the 16mm lens gave.

 

So, to my dilemma...

 

I thought I'd purchase a zoom lens on eBay, so I could manually set the zoom to get the best coverage. I ended up winning a Pentax/Cosmicar C31010 (C14ZME-P) lens, which says it has a C fitting, but (this is the bit that concerns me) a 2/3 inch format. I'd also found a low light camera on eBay at what seemed a good price, but this has a 1/3 CCD sensor, so my question is, can I use them together??

 

Also, as I haven't purchased the camera, what is your professional opinions on the Starlight 540TVL listed on eBay, which I'd intended to buy? http://www.ebay.co.uk/itm/220888194206?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

All answer greatly received (keep it clean though!!)

 

 

Many Thanks

 

 

Rob

[Numb-nuts 1]

Hi Rob.

 

Although your lens will fit the camera, in theory you would lose some of the area around the image you capture (I think).

It may be that your image is cropped ( i.e. you don't see it all). Needless to say you won't be able to rely on conventional calculations and the lens will alter your light sensitivity.

 

The ⅓" CCD sensor is normal for most cameras and you are more likely to find a suitable lens for that than you are to find a suitable ⅔" camera, although they are readily available. Better to re-sell your current lens as there will be people looking for ⅔" lenses. (you might even make a profit). If the lens were a smaller format, then you'd experience a port-hole-effect.

 

So you know the distance to the FOV (Field of view) what is the width or the scene you wish to capture, and at what height is the camera to be mounted? When you know the height of the camera, the distance to the FOV and the scene width, visit this site and use the online lens calculator. If the exact lens you require is not standard, you need to order one that has your requirement within it's range.

 

For example 7m horizontal to the FOV, a camera height of 4m will give an approx distance to the FOV of √(7²m + 4²m) = approx 8m i.e. distance from camera to FOV. Assuming a scene width of a farm type gate, say 4m wide and a ⅓" sensor hit the calculate button and you find you need a ⅓" lens with a focal length of 9.6mm.

You can either buy a 10mm lens if you don't mind narrowing the scene slightly or you can buy a ⅓" varifocal lens something like 3.5-12mm.

 

If any of this is wrong, then I have no doubt someone will jump at the chance to correct me, meantime hope this has helped some.

 

If doves or pigeons use the dovecote, don't forget to house the camera in a protective housing because you know what a nasty mess the birds make.

[Soundy 1]

You'll typically see this "pigeonhole" effect if using a lens designed for a smaller sensor, with a larger sensor (eg. a 1/4" lens on a 1/3" camera). Using a larger lens SHOULD, in theory, have no detrimental effects on a smaller sensor.

[troytempest64 0]

Thanks NumbNuts

 

The dead camera I am replacing had a 16mm lense on it, which was almost OK, perhaps could have done with zooming in a little more. It was not very good in low light/dusk.

 

The new camera (1/3" CCD) I've already purchased, because it's low light. It's on the eBay link in my initial post. This camera is a 540TVL and says it works down to 0.01 lux.

 

The new (actually used) 2/3" lense that I've also bought is a 10-140mm zoom, which I intend to just manually zoom until it's just covering everything we need to see. It's a Pentax/Cosmicar C31010 or C14ZME.

 

My main concern was the 2/3" lens working with the 1/3" CCD in the new camera, and whether it would work OK, as it was something I stupidly overlooked. Interestingly, I've found a spec sheet for the lens which shows some "horizontal angle of view in degrees" for the 2/3" lens in columns for 1/4, 1/3 and 1/2 inch formats, but I don't know if this means if I use that lense with a CCD of that type?? With a 1/3" it shows an angle of view as 26.41 - 2.02.

 

The table is here if anyone could try and make sense of it for me: http://www.cs.unc.edu/Research/stc/FAQs/Cameras_Lenses/Cosmicar-Pentax.pdf

and the lense is the second up from the bottom on sheet 4.

 

Annoyingly neither the camera or lens haven't arrived yet, so I can't try them, so I was just wondering if anyone can confirm if they'll work together???

 

 

Thanks

 

 

Rob

[Soundy 1]

A lens of a given focal length (ie. 16mm) will ALWAYS cover the same angle of view - so a 16mm lens will always transmit the same size image regardless of whether it's designed for a 1/4" sensor, or a 35mm sensor in a DSLR.

 

When you put a smaller sensor behind it, the image is "cropped" to just the area covered by the sensor - this is a common discussion in DSLR circles, a phenomenon known as "crop factor".

 

Because of this, lenses designed for smaller sensors are made smaller and lighter (and thus, cheaper) and designed to only transmit that smaller area of the image that will actually be covered by the sensor. So what happens is, a 1/4" lens will project an image with a diameter that will cover a 1/4" sensor, but if you put a 1/3" or 1/2" sensor there, the image will only cover part of it and the corners will fall outside its light pattern, thus giving the "pigeonhole" or "tunnel" effect.

 

Using the larger lens, again, should have no problems with the smaller sensor. If anything, you might get a clearer picture, as the edges of the image where distortion starts to appear, will fall outside the area of the sensor.

[Numb-nuts 1]

There you go, give it a go you have nothing to lose and a lot to gain. If you do get strange effects, you can always resell and begin with a corresponding varifocal lens. By the way that lens has a huge range if you can't make it fit the width of scene you want, I'd be very surprised. How wide is the scene you want to cover?

 

540 TVL is okay, it's considered high resolution, then there is 600 -700 TVL which is considered ultra high resolution.

(I'm not so sure though these days with the widely available IP megapixel cameras)

 

Let us all know how you get on... I haven't seen the result of a mismatched lens and sensor. Perhaps you can take a frame from a recording and post it here for us to see.