Backfocus

[k_jensen 0]

It started with a kiss, never thought it would come to this...

initally, I just wanted to know if you guys used a ND filter to focus a domecamera. We had a little discussion about it.

 

wow, we have been around - thats nice with a forum like this.

[jisaac 0]

thats good because you get a good thorough answer. What I like about this forum is in alot of topics there might not be one specific answer only to a question/problem and its good to get every ones answer on how they do that.

[Cooperman 0]

It's certainly been an interesting thread with lots of useful discussion, but as AVCONSULTING so accurately pointed out, there has been a slight degree of confusion regarding Back Focus and implied Depth of Field.

 

In practice, for perhaps 75% of camera installations, Back Focus is not an issue simply because it is still possible to bring an image into sharp focus using the lens' focus ring, albeit that the imager may actually be sitting x/tenths of a millimetre, from where it should ideally be.

 

Setting the back focus on a camera fitted with a fixed focal length lens, should take no more than a minute or two, and for a zoom lens, perhaps a couple of minutes extra just to be sure. The trick is to set Back Focus against a constant, which in optical terms is always infinity. Trying to set it against a measured point or the 'Minimum Object Distance, can waste a lot of time unnecessarily.

 

Generally speaking, it's usually cameras fitted with fixed focus (maybe ultra wides) or zoom type lenses which may well need to be back focussed.

 

I often find that cameras used in very low light with the lens aperture set to maximum, are the ones to worry about. Personally, I usually do the set ups, only after the camera has been running for an hour or two (in other words, operating at normal temperatures).

 

I've actually seen quite a few cameras in the past, where the internal heat generated actually causes the chassis to expand a few thousandths of a millimeter, and that can be enough to lose critical focus, if the adjustments were initially made immediately after the unit was switched on from cold.

 

Relying on technology to solve basic technical problems (like Back Focus) may be a nice easy way get through the working day, but in practice, there really is no substitute for learning how to do something properly, just so you don't get caught out when the technology isn't there, or it fails at a critical moment.

[VJD 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

I have seen the kit for sale which includes the usb adapter and software for over $300 and the usb adapter by itself for under $100. Why are they selling the kit and charging $200 for the software when you can download it for free?

[cctv_down_under 0]

You are indeed correct, the Bilinx software comes for free on the XF Promo cd, therefore you only need the adapter!