Pentax 100mm Macro

i suppose if the beam was reflected by anything the camera would use that as the focus distance.

That's right just pointing out some of the latest methods of measuring distances that haven't yet found their way into cameras yet.

Thanks for the link Terry, I'll have a look later.

Rain or snow would be OK as long as the beam can get through. It's unlikely to bounce back off it.

Just as a matter of interest here's a youtube video showing a laser scan of a pub. Note this is a 3D drawing not a movie or photograph. If you wanted measurements of the building you could take it off these drawings you can zoom in as close as you want or walk through the building if the inside was scanned as well. The scanner takes millions of measurements in 3D costs 75-100k UKP.

shim

A beam system would be largely useless in a camera. If I take a photo of a beautiful wide view with lovely white clouds and a blue sky, what on earth would the beam reflect off? The reason surveying equipment uses a beam is that they need millimetric accuracy over long distances to a specific target. For a camera, once the lens hits infinity who cares if the object it is focusing on is 500m away or 1000m away or even 1267.452m away? AND the time taken for a Leica Total Station to take a reading, quick as it is, would have most photographers grumbling that they had missed the shot of the goal/bird/moving car etc.

The camera can, however, make use of a beam already although in a limited way. On the AF360FGZ flash (is that the right mix of letters?), one mode is to use the flash gun for low light focusing using an infrared beam. I guess the range is limited (I have never tested that out). I also assume its big brother will do the same, and probably some of the third party flashes.

If anyone is interested in how laser technology is moving things on, google LiDAR. This is airbourne laser scanning which is replacing more traditional land based survey. One of LiDARs great advantages is that it can survey through the tree canopy of woodland. Its disadvantage is that you have to process out of the survey the readings from the person walking the dog across the field...

Best wishes, Kris.

Infra-red autofocus systems have already been used in many compact film cameras.

These are "active" AF systems as opposed to the "passive" ones we use these days.

Presumably they work on the basis that if nothing comes back they set the lens to infinity :

Presumably, and of course focus point is less critical at longer distances. Even so, many cameras had Infinity Lock settings, or Landscape settings, which amounted to the same thing.

Also, depth-of-field is so great with compact cameras that precise focusing is often not so critical.

I have no complaint about the AF system Pentax DSLRs use, only that the manufacture or assembly of it doesn't always do it justice.

The infrared beam from the AF360 (or 560) is merely to provide sufficient illumination of the subject and has nothing to do with focusing as such.

"The AF360FGZ feature [sic.] a built-in red spotbeam projector to assist the autofocus system in dim light or low-contrast conditions... the AF360FGZ can be used exclusively as a focusing aid in dim light." The manual, page 55.

This is rather inconclusive as to how it works. It does also say, however:

"The AF spotbeam on the flash unit works accurately only when mounted onto the camera's hotshoe."

That suggests that it is doing a little more than "merely providing sufficient illumination" although I will agree the precise nature of how it functions is not clear just from the manual.

Cheers, Kris.

I may be getting confused again but doesn't the DOF issue only apply to digital compacts with their tiny sensors? With a 35mm compact the DOF would be the same as for a 35mm SLR, wouldn't it?

Best wishes, Kris.

I was looking around Amazon and just stumbled on this:
(Seems to be a current model)

Amazon.com Product Description
If you are looking for autofocus convenience and flash versatility, find it in the Olympus Trip XB-40 AF QD. In the XB-40, an infrared autofocus system with focus lock and a sharp lens combine for consistently clear shots. The auto- flash takes care of low-light situations, and fill-in flash helps minimize strong backlight and sidelight.

This camera offers precision autofocus with point-and-shoot simplicity. It automatically sets the film exposure so you don't have to remember to set it every time you reload. The motorized film load advances and rewinds in seconds. Focus lock is possible and enables accurate focus even when the subject of the photo is off-center. Quartz date and time recording make organizing your developed photographs a breeze.

shim

Yes, assumimg the focal length is the same. Compacts do tend to have slightly wider angle lenses.

The main factor is that compacts have lower quality lenses (usually) and are used to make smaller prints. So the requirement for resolution is lower. This is why I've never found one I was happy with.

Yes, fair enough. I was thinking of compacts with smaller formats.

Anyway, I think Pentax would have used IR beam focusing with the DLSRs if it was better than the passive system they have chosen - which I find adequately accurate and precise when setup properly, though a bit slow.

The flash projects a red grid pattern onto the target, thereby giving the AF system an area of high contrast to lock onto. It's an extremely simple idea but one that works very well.

*edit* PS. It has to be on the hot-shoe in order to (a) know when to cast its light and (b) be facing the same way as the lens.

The AF-assist spot beam (SB) works by illuminating the scene with a grid pattern of red light. This gives the camera a sufficiently contrasty area to achieve focus.

The flash has to be mounted to the camera (or connected via cable) to work at all. The SB function does not operate when the flash is electrically disconnected from the body. With a cable connected flash off-camera, you'd have to manually aim the SB correctly for the camera to 'see' it.