Backfocus

[jisaac 0]

if you can buy that in your country .. .

were you talking about if you can buy the #5 welders glass?

[rory 0]

yes it doesnt exist here ..

[rapid 0]

The neutral density filters work great, although find that if you are using IR the focus can shift a bit.

 

Prefer doing it at night as you are looking for reflecting light.

 

Course, I do like the overtime as well $$$

[rory 0]

overtime??

[jisaac 0]

overtime??

exactly..

Man if I was paid overtime pay man that would be a ridiculous amount of overtime pay.

rory pm me your shipping address and I will send you a few. Man those things are a huge time and headache saver

[kandcorp 0]

Just use your sunglasses Rory >>

[rory 0]

tried that already ofcourse ///

[Cooperman 0]

If you want to produce the effect of a variable ND filter, you have to use two polarising filters, one on top of the other. As one is rotated, the light transmission will graduate from clear to virtually opaque.

 

During daylight hours, to set up a camera that is going to be used with Infra Red at night, just use an IR filter of the same frequency (e.g. 830nM pass filter) over the lens, to allow fine adjustments to be made.

 

k_jensen, with regards to the size of the Depth of Field, I never said that large with a small aperture, and small with a large aperture was wrong. I said that the diagrams you linked to were fundamentally wrong.

The size of the Depth of Field, is only part of the story.

[vitHoward 0]

I think Cooperman had it right.

 

A true pinhole (film) camera has an almost infinite depth of field. Everything it "sees" will be in focus. As the iris gets bigger the space in front of and behind the point of exact focus will shorten. By opening the iris, the depth of field shortens allowing us to focus on the target. We create the worst situation and then improve it by closing the iris.

 

A portrait photographer intentially shortens the depth of field to soften the forground and background by opening the iris.

 

Rory, the #5 welders lens are actually #5 cutting torch glass. Check with a welding shop instead of a photo shop. They come in pairs to fit googles. If you can't find then, send me your address and I'll send you some. (or I might try to deliver them in person)

 

Howard

www.videoguardit.com

[kandcorp 0]

Use one of these or similar Neutral Density Filters:

http://www.sonystyle.com/is-bin/INTERSHOP.enfinity/eCS/Store/en/-/USD/SY_DisplayProductInformation-Start?ProductSKU=VF67ND&CategoryName=acc_DIAccessories_DIFilters&DCMP=OVERTUREPI_DF&HQS=DCA_VF67ND

 

This is decent explanation about how to backfocus:

http://www.eagle.co.za/display_cat.php?subcategory_id=991

[Cooperman 0]

Decent ... but unfortunately not totally correct

[kandcorp 0]

Can you please try to explain the errors or the incorrect info given...I would like to get your input as well.

[cctv_down_under 0]

Coops is correct,(I am sure i am wrong and coops will correct me but) the depth of field will change under low light, another thing to consider is that if you are using a camera with a removable IR filter then the distance to the CCD will change because the filter is not there, also the different wavelengths of IR light need corrected IR lenses to concentrate better on the sensor.

 

 

I know there are a lot of cameras that remove the IR filter and then the imgage is better but out of focus because the distance between sensor and ccd has now changed, some cameras actually replace the removed filter with a dummy filter to allow for this correction and others can moved the CCD chip to set the back focus...even remotely.

 

I really do not know why you all bother with it...I stopped using welding glasses and annoying ND filters when I started using the bosch camera's, they have a feature that simulates the ND filter and you do not need to use any equipment at all, for example you can remotely down the coax set the camera to Back Focus mode and the image will not change (well it does but it does not look all that different) so even in bright sunlight you can focus the camera in back focus mode and you do not need the extra set of hands, it is hard enough to focus a camera with two hands as it is, let alone trying to hold a stupid filter at the same time, it is a very handy feature and it works well.

 

I have been to many sites where these cameras are instaled and not back focussed and all you need to do is swithc it into back focus mode and you can instantly show the customer how badly set up their cameras are for night vision.

[k_jensen 0]

I really do not know why you all bother with it...I stopped using welding glasses and annoying ND filters when I started using the bosch camera's,

 

Great feature, Panasonic has the same. BUT not all customers want to pay "over price" for Bosch. Many other cheaper cameras deliver same picture quality at a much lower price. Then you need to Backfocus.

[rory 0]

yep that is a nice feature, but they cant give me an Exview camera like GE can ... and you only have to backfocus if you want to ..

[cctv_down_under 0]

I had heard that the Bosch cameras are expensive on that side of the world, they are cheap here, very cheap in fact, they are cheaper than Samsung, Pelco, Ganz, Ikegami, GE and Sanyo it seems you guys get ripped off over there.

 

I have to partly disagree with you Rory, i think a back focus should always be done when there is a need for a camera to look at a dark scene, however you can get lucky not doing it.

 

All I can tell you is, of the many i tested in this mode, more than half of them were out of back focus and therefore not focussing correctly at night.

 

I have tried the Exview cameras before and had found that although they are sensitive t low light, they did not compare to the Pana or Bosch under low light conditions, I have done quite extensive testing on a lot of cameras, because we always test everything before we sell it, and i have not found a camera that outperforms the Pana for low light ability, mind you the Bosch is pretty good.

 

I think a lot of people think you need to buy the XF camera to get this back focus feature and you do not need to, therefore it really is not that expensive.

 

We took into consideration the time that Back focus takes and set up at the camera end and realised that if we were charging our installers $50 per hour and it took 15 Mins to back focus and 15 Mins more to set up the features due to no remote settings and if it saved 15 mins less per camera to update the settings for the camera up the coax (once you have set one up you can save it and upload it to another camera), plus because of occupational heath and safety standards, we have to have two people at a ladder at any one time we realised that even if we saved roughly 30 mins per camera:

 

Therefore 2 installers = 1hr or $50 per camera and when you multiply that by 16 cameras that is $800 per site...quite a savings, but I have to say the main reason is because when you sit down in front of your DVR and set up the cameras in your chair, the customer is very very impressed.

[rory 0]

Once you focus the camera in low lighting, then it will be in focus at night.

I never backfocus unless I really have to, typically they come backfocused from the manufacturer if they are new. But then with that Bosch you still have to physically focus the camera, so I dont see any real difference.

[Jasper 0]

Is auto back focus a rare feature on most CCTV cameras?

[rory 0]

I would suggest testing the GE Exview with their F:0.95 lens though as they are the lowest you will find for a 1/3" color camera.

 

Either way, if the camera is not Exivew I really dont call it a low light camera.

[AVCONSULTING 0]

Are we getting terms confused? Back focus is rarely needed in my experience (the actual moving of the chip or lens mount). I think people are talking about focusing a lens at night vs being focused during the day and this is in reference to auto iris lenses.

[cctv_down_under 0]

AV is right, the problem is that in low light the lens aperture changes causing a change in depth of field, this can throw a camera out of focus, i agree with rory that if you stick to focussing your camera at night time you have achieved pretty much the same effect, I just find it a pain to open the iris manually then have to place my hand in front of the camera and then hold a ND filter and i hate sticking around on job sites at night....mind you i do not live in the lovely bahamas, where I come from if you are out at night your breath gets frozen in the wind.

 

It is also much easier to focus the camera with the virtual back focus mode, because you can actually see better what you are trying to focus on.

 

It really is a bit of a "who cares" thing, but we back focus all our cameras and we show the customer the "before and after" affect, this really impresses them, then we go back to the DVr and adjust things like compensation or gain settings and they are usually very impressed.

 

i even had one of my techs deliberately set the camera to traffic mode and reduce the gain so that the image was dark, he then took the camera to site and installed it, the customer said "it is pretty good", then with the bilink he defualtted it into low light mode which changed the shutter spped and the gain plus the sens up feature and HEY PRESTO!

 

I actually repromanded him for wasting time, but i wish I had thought of it.

 

Basicaly a back focus does take time, it is indeed fiddly and it is easier with cameas that can do it automatically, there is a big difference between focussing a camera at night and making sure the ccd chip is the correct distance from the lens.

 

Rory i have never seen a lens with that F stop that was inexpensive enough, i wuld be interested to try it, what IRE was that lens rated at.

 

Keep in mind the F Stop is only really a measurement, it does not reflect the light gathering ability of the lens, a plastic lens can have the same f stop but light will not travel very well through it, it really comes down to the quality of the glass that is used and the ability the lense has to ACCURATELY (without floors in the glass causing light bounce) distribute the light to the CCD.

 

I admit the pixel technology in the ex view is good, but being more sensitive does not always mean that it is better under low light and there are always several ways to read the specs

[rory 0]

cool, actually i wont need an exview for this car park as they have a ton of light which they didnt have originally when the first exview was installed, so i can probably try out one of the 1/3" Bosch color cameras, any suggestions which one .. not day night, though WD would be nice .. and a little bit sensitive though .. as its still for night time.

 

thanks

Rory

[cctv_down_under 0]

The cheapest is the LTC0440, but this was originaly designed by Phillips and not much has changed, it still gives excellent colours and is still reasonably low lux, but it has only standard settings and you may find it compensates too heavily for areas with large saturation of colours.

 

The next step up is the Bosch made LTC0455 this is the old style D/N cam, not the IR filter one, it is only a few bucks more and has night sense, the night sense by defualt is pretty poor but if tweaked with gain it works out quite reasonable.

 

The step after that is the LTC0485 XF, and this is a real beauty, it still only has night sense and old style D/N, but the features list is rich and it is 15 bit, the picture quality is excellent.

 

After that you get to the LTC0495, the first of the true D/N, this is one of the best low light cameras I have ever seen, there are 1/2" versions of the XF and this camera but i doubt you would ever need it.

 

The last step is the IP camera, it is quite unique as it has smarts built into the camera for video content analysis etc, it also has bth IP and composite outputs and can send lots of different ways, it is still a little overpriced in my opinion.

 

The SDIII is awesome as well, but I find it hard to buy because of the prices.

[rory 0]

Yeah he doesnt want BW at all, its to pick up colors in the car park ..

The 485XF sounds like it, that has the WD also?

 

I want to try the coax thing also ..

 

thanks

Rory

[cctv_down_under 0]

Thats the one, you need the Bilinx tool though, it is a fair bit more expensive than the others.

 

http://www.boschsecurity.us/index.aspx