How come no DOF info on view finder??

qtaran111 wrote in post #3979154
How? The camera only knows/records the focal length not distance to subject.

The camera knows how far as the lens reports it.

It might not be perfectly accurate but many lenses today have a distance gauge so with some clever software it should be possible to extrapolate the distance base on the position of the focus mechanism. The camera also knows what lens is attached and if it’s a zoom, what position the zoom is in. Couple that with the aperture and it seems everything is there to pop up a DOF number.

Sorry to be a pain in the you know what, but where is this distance to subject reported? And where is this distance gauge?

I believe that not all lenses pass distance information the camera. I think this is why only 29 lenses are in the list for those than can have CA corrections with DPP 3.2

As I said a few posts back not all lens will 'transmit' the actual distance information.

Not sure if I still have the link but it was a Canon pdf I downloaded that indicated which lenses did so when the ETTL-II needed it to perform certain additional functions of flash & distance calculations.



PS I think I have found the chart again here http://www.usa.canon.c​om …tegoryid=156&mo​delid=7328 download thelink on the right "Lens Chart". Ther are more lenses than I thought by by no means all all of them.

Thanks Box Brownie,

Do you know how they acheive this measurement? I assume it is some sort of feedback mechanism from the lens' focus ring (rather than an actual distance measurement)?

about 1/2 of the EOS lenses report distance information back to the camera thru the electrical contacts. This is used by the ETTL-2 flash system to help compute the right amount of underexposure for your flash photos. Those lenses that do are marked with a bullet on the far left on >>>this chart<<< which is a canon download.

DavidEB wrote in post #3979384
Those lenses that do are marked with a bullet on the far left on >>>this chart<<< which is a canon download.

I get "Referral Denied" on that link.

-js

The link to the chart doesn't work for me.

You don't have permission to access "/=/879/8842/5m/canonf​tp.download.akamai.com​/8842/cpr/software/cam​era/Lens_chart_091707.​pdf" on this server.

Try this one:

http://www.usa.canon.c​om …ns_Extender_cha​rt_new.pdf

Much better. Thanks!

All my Canon lenses report distance info. Wonder if my Sigma 70-300 APO DG does...

-js

qtaran111 wrote in post #3979383
Thanks Box Brownie,

Do you know how they acheive this measurement? I assume it is some sort of feedback mechanism from the lens' focus ring (rather than an actual distance measurement)?

I think most of those that do are the USM driven ones so I suppose combined with the right "chips" in the lens it can tell by the motor position what the focus distance is??? There will be a specific total amount of travel of the motor to get it from min to max distance and the finer the degrees of measurement of the range the more accurate it will be but the lens must surely have the 'right' added harware onboard to be able to interpret the info.

You do not have to kill to get this camera. It exists on one of the defunct Minolta digital SLR cameras. The DOF readout was seen on the rear LCD.

I think you are right. Take a look at this: http://www.canon.com …um/tech/room/f_​index.html

I'm guessing the drive quantity detector knows how far the focus ring has been moved (quantity) which it communicates to the lens microprocessor which is then fed back to the main processor which does the AF range calc. Phew!

Erm, what's the fuss?

The bodies have a *button* that stops the lens down to the relevant f-stop. You can actually (woo!) *see* what's in/out of focus rather than have lens-info. converted into some meaningless number....