6mm or 12mm which displays more of a picture?

[Tim 0]

Which lens 6mm or 12mm displays more to make a wider picture. Thank God for this forum

[cctv_down_under 0]

the higher the number the narrower the angle and the further away the focal point, most people use varifcal lenses for this reason, if you have troubles with this I suggest using a viewfinder, this is a small device that you can look through and adjust to get the right scene size then you know what to use...you could always use a mathmatical conversion to work it out and here is a chart for you, keep in mind it differs by sensor size.

 

I have a small lens calculator .exe file if you want it, just PM me and I can give it to you

[Tim 0]

I have a look at this here, its a lens estimator, I do believe your talking about this, http://shop.store.yahoo.com/securitysupplyhouse/whccledoine.html

I'm wanting to buy a aspherical lens, they do not have a aspherical varifcal lens THANKS AGAIN & AGAIN

[cctv_down_under 0]

Hell I am no expert with cameras and lenses but I am pretty sure you can geta n aspherical varifocal???

[cctv_down_under 0]

OOps maybe your right... showing my lack of knowledge...LOL...We sell a 3.5 to 10.5 Computar, they are specially made for low light cameras and day night in particular, I just assumed the reason was because they were aspherical, but maybe your right... makes sense...poop...still have a lot to learn about cameras

[cctv_down_under 0]

I just had a closer look at the PDF for those lenses that were low light and yes they are varifocal and aspherical, I would really like someone to shed some light on this topic for me (pardon the pun) as I think there might be more I need to know, my understanding was this:

 

Because the lens does the task of focussing luminesence and chrominance onto the CCD, The difference between spherical and aspherical is that one is more perfectly ground than the other as the spherical is more likely to have abhorations at the edge making for a lens shape that is not tottaly optically correct..

 

This would mean that less of the aperture of the lens can be used therefore less light would fall onto the sensor, of course some CCD's have differnt shaped parts of the CCD like the X View for instance it has a rounded pixel shape to illiminate the gaps represented by square pixels so that more of an area can recieve light, I think this sensor also has a second glass coating that magnifies the light onto the pixels.. but once again I could be wrong and back to the lens....

 

I think Asherical lenses are ground on both sides so that it can achieve a more accurate defraction of the light therefore having a more accurate focal point.

 

With the faults that may be on the edge of a sphercal lens you an use less of the lens to get the accurate axis from light that passes from not only the barriers of the lens but the edges as well and this would I assume lead to more light being on a sensor, hence the low light ability increase.

 

I think it comes down to the ability for the lens to provide enough lighting to the sensor at low light levels to make the camera represent a signal that is close to 1V Pk to Pk, I think you would find using a daynight camera with a spherical lens would make this representation more like .8V under low light

 

In all honesty the lens makes a big difference and I think the asphericals from Computar have a tint on them from memory (bloody better learn ..I have sold enough of them).. In reality the darker it gets the further you will get from 1V PK to PK so the camera may still have a resonable signal but may drop off the colour representation when dropping, so a good camera choice would be good as well, I find it hard to go past the Ganz wide Dynamic for this type of application.

 

Anyhow, like I said I may be worng so anyone who knows more about this I would be very intersted to find out the right truth.

[Cooperman 0]

Just thought I'd confuse the issue

 

12mm on 1/2" and 6mm on 1/4" (who uses them?) are both standard lenses, and would provide roughly the same picture (coverage).

12mm on 1/2" = standard and 6mm on 1/2" = wide angle, easy peasy;

 

Now the question of aspherical lenses, you're pretty much spot on DVR Expert Australia. The front lens element in an aspherical is shaped to an extremely accurate profile so that the rays of light entering at the edge of the lens, are as near as possible brought into sharp focus at a point where the centre axis rays are focussed (which hopefully will be on the front surface of the imager).

 

Standard 'spherical' lenses will always have (more) aberrations which degrade the picture quality, and which increase as you near the edge of the elements (specifically the front element), although in practice, if you try and use a larger format lens, for example a 2/3" on a 1/2" camera, all the rubbishy bits will be out of view of the imager (is this making sense, if not I need some sleep!).

 

The fact that a lens is 'aspherical' in design doesn't necessarily mean that it is optically fantastic, particularly at maximum aperture. All lenses tend to produce their highest optical resolutions, at or around the mid point of their iris range (i.e. around f5.6 ish).

 

I believe their are a few different methods for producing aspherical elements, and quality can vary with the different processes, but the one overall factor is they must be shaped to an extremely high accuracy in order to work well.

 

From experience, I would say that the one topic which causes the most confusion in CCTV circles is....lenses.

 

Not that long ago, I posted a link to an information site which was about as popular here as Christmas for turkeys (come to think of it, that analogy didn't really sound quite right). I have seen a couple of lens charts there but without looking it up, I don't have the address to hand.

 

Let me know if you want it, and I'll see if I can find them.

[Tim 0]

Both of you have said alot, I'm all ears, the 6mm on 1/2" = wide angle, easy peasy; this would give me a wider angle then.

[Cooperman 0]

Tim,

 

Just to clarify, the focal length of a lens will not automatically imply a degree of coverage, unless you take account of the imager (CCD) size.

 

So with the two lenses you mentioned, 12mm and 6mm, I'll use a pair of almost exact equivalents, to give you a couple of examples.

 

If you used a 12.5mm lens (which is designed for the now defunct 1" format), it would be a normal wide angle on 1", slightly wide on 2/3", standard on 1/2", and a 1.5x Telephoto on 1/3".

 

The 6.5mm (again originally a 1" format lens) would be ultra wide on 1", slightly wider than a normal wide angle on 2/3", wide angle on 1/2", and slightly wider than standard on 1/3".

 

Any work that I do, I always try and use at least one lens series above the imager size I'm working with, so that all the poorer quality (increasing spherical abberations) present towards the edge of the image, are not focussed on the imager.

 

So on 1/3" CCD, I'd go for 1/2" format (or better still 2/3"), 1/2" CCD use 2/3" lenses (or 1").

 

You get the picture?

Sorry, it's too early for puns!

[Cooperman 0]

One other quick point,

 

A 'Standard' lens:-

 

6mm on 1/4", 8mm on 1/3", 12mm on 1/2", 16mm on 2/3", 25mm on 1"

(and for comparison 50mm on a 35mm photographic camera) are all designed to give the same degree of coverage, which is approximately that of the human eye.

 

So anything with a shorter focal length (on a given format) will be classed as 'Wide Angle', and any lens with a longer focal length is a 'Telephoto'.

 

Hope that answers your question Tim.

[Tim 0]

That answered it , THANK YOU

[rikky 0]

If I understood well, that whenever you've got a bigger CCD, like say 1/2", it captures better light and it's less prone to get abberations ??

 

From my own experience in fact I can support the statement that best pictures are being kept with 1/2" over 1/3".

Why in fact are so little manufacturors interested in 1/2" cameras.

 

Apart from pricing issues for camera and lens, are there other issues that make these cameras not so interesting?

[Cooperman 0]

Hi rikky,

 

The imager size issue is not so much about the technical merits of one size over another, but much to do with the cost of production. In general terms, when 'chips' are manufactured, a small percentage are rejected as faulty, so what tends to happen is that in the case of CCD imagers, the larger the imager, the higher the incidence of rejects arising from faulty pixels.

 

In plain english, if you had 100 1/4" CCD chips, the vast majority would be o.k., but if you had 100 1/2" chips, a significant percentage may have manufacturing flaws and would therefore be junked, so overall they cost that much more to produce.

 

Ideally, if manufacturers could produce very high resolution 1/2" or 2/3" chips, the light gathering and signal / noise benefits would be brilliant, but we couldn't afford to use them! You have to remember that when it comes to supporting larger higher resolution imagers, the supporting processing circuitry is going to occupy more PCB space, and require more power, so the whole camera package gets larger again.

 

The abberations issue is purely related to optical performance in the lens. This is easily tested by setting up two identical cameras side by side and then comparing the picture quality with two equivalent lenses. If you ever try a basic 1/3" 8mm lens against an 8 or 8.5mm 2/3" lens (both fitted onto the same high res. 1/3" cameras, just compare the performance at maximum aperture, and it can be quite a revelation. The 2/3" lens will win hands down every time. Even cheaper poor quality lenses can look acceptable if you use the larger format lens, on a smaller CCD.

 

Many clients spend a small fortune on electronics, stick any old bit of glass on the front of a really good camera, and then end up with rubbish pictures.

 

Then they moan that the cameras not much good!

 

Whenever I can, I try and standardise on really good performance 1/3" cameras, then I've got a brilliant range of lenses available to suit practically any situation. Also there's one other benefit worth thinking about.

 

If for example, you use a standard lens on a 1/3" camera (8mm) and a standard on a 1/2" camera (12mm), the coverage may be exactly the same, but the depth of field (at matching apertures) will always be greater on the shorter 8mm focal length, so a target will remain in focus for more of the area under observation.

 

I'd be interested to know what lenses you guys use, both in terms of manufacturers (I think I can guess the answer), but also how you decide what type to buy.

[rikky 0]

Cooperman,

 

As far as I'm concerned, I've been using Computar and Fujinon, which tend to result in quality pictures.

But if better is on the market (as you mentioned your brilliant range) I'm willing to try other brands.

 

Best regards,

[cctv_down_under 0]

We sell a Korean OEM, glass is bought from CBC (Computar) and it is good but still also sell the Computar brand, they are pretty darn good.

[Cooperman 0]

Rikky,

If you are using Fujinon lenses, then you haven't got a lot to worry about.

I think DVR Expert Australia, you've probably got a better feel for the Computar range than I have. I did use some years ago, but I wasn't happy with overall quality across the entire range.

Some were very good, others were decidedly average.

 

Pentax and Canon also produce some extremely good optics ( I haven't used them all, but I've rarely had any complaints with those I have used) , albeit that they are slightly more expensive.

Personally. I'd rather pay a little bit more for a 'fantastic' response from a client, instead of simply 'yeah, that's ok'.

 

One other point, I think I forgot to mention in previous postings. If you use 'C' mount lenses, they are generally much better corrected than 'CS', but again you have to pay that little bit extra.

[rikky 0]

Cooperman,

 

What's in fact the best optics - lens manufacturer at the moment.

 

You mentioned Fujinon is doing pretty well; although on the front of Day/Night lenses they seem to be way behind the others.

Perhaps there doing slower but better ...

[Cooperman 0]

Personally, I wouldn't want to say that any particular manufacturer is the one to go for every time.

 

On balance, I've probably used more Pentax (Cosmicar) lenses than any other, but I wouldn't go so far as to say every lens they make is perfect, because quite obviously they're not. Very solid range, good glass, good coatings, well engineered, but not the cheapest.

 

The general rule is, if you use a good lens on a rubbish camera you'll probably get acceptable pictures. If you use a rubbish lens on a very good camera, you may save a little bit of money, but the results will be dreadful.

Years ago, their used to be noticeable variations in performance from some lenses manufactured in the same batch. Nowadays, production methods are much tighter, so consistency is rarely a problem.

 

If you stick to using a few 'tricks', like 1/2" lenses on 1/3" cameras (already mentioned in previous posting), or using Manual Iris optics on Electronic Iris cameras (indoors), you will generally get much better quality pictures.

[rory 0]

i sell the kalatel lenses

actually they are fujinon, boxed in kalatel GE boxes.

i also use computar and tamron, but prefer the fujinon generally