I miss depth of field indicator on 7D

[markkubis]

Does anybody know why KM neglected in the 7D (also 5D and A100?) to keep the wonderful graphic DOF indicator as on the back panel of the film 7? It's not easy to check the DOF on a picture on the LCD panel nor is it always easy to see what you are doing through the lens whilst it is stopped down. It was a brilliant innovation.

Mark

[David Kilpatrick]

We can just hope that Sony might spot it and put something like it on the review screen of new models - sort of focus equivalent of what the histogram does for exposure. I just think that the focus point of the lenses is so inaccurate it would be meaningless. If I aim my CZ 16-80 at a landscape, at 16mm it may focus anywhere between infinity and six feet and still say 'yes' for AF confirmation. There is obviously high enough contrast and fine enough detail for the AF to be happy.

It would be extremely useful to have the function, because it would display the actual focus point of your lens. You would look at the back, and see that the readout said you were focused on 5ft when you know full well it should have been 8ft - or whatever. Maybe it would be too revealing.

David

[markkubis]

The film 7 DOF display does not indicate what the camera has decided the focus distance should be. It just tells you what the distance in front of and behind the focus distance that will be reasonably sharp given your selected focal length and aperture. Of course it would be better if it also told you the focus distance for the reason you describe. It would be better still if you could set an aperture and the camera automatically set the hyperfocal distance and tell you the distance of the near point of sharpness. The camera has all the necessary information to do all this if you are using a D lens. Of course it's a joke trying to establish the focus distance from the readings on the lens barrel of an AF lens, more so if it is a varifocal zoom.

SLR/DSLR focus systems have always been bad at automatic focusing when using wide angle lenses, more difficult still if they are slow lenses. Even manual focusing using split screens is problematic as there is not much differentiation between sharp and not sharp. The crop factor on the 7D sensor that gives rise to a greater depth of field for the same aperture, focus distance and field of view makes the problem more pronounced with this camera. Rangefinder cameras having manual focus systems are much easier than SLRs/DSLRs to focus accurately under wide angle conditions.

With a film 7 and a D lens it is possible to hyperfocus the lens. Select an aperture and focus on an object in your frame. Check that the point of far sharpness on the DOF display shows infinity. Then focus on another object a little closer and check again. Keep doing this until the infinity value changes to a distance reading. Then focus on an object a little behind until it shows infinity again. Look at the distance indicated on the DOF display that defines the distance of reasonable sharpness in front of the (undefined) focus distance. Look at the object you have just focused on (without your camera) and mentally subtract this distance. If the distance of closest focus is not acceptable then reselect your aperture and try again. The film 7 also displays changes in DOF in real time as you alter the aperture. The 7D could also be made to do this. So as fine adjustment for the lazy, when you have approximately established your focus distance, just adjust the aperture a little until the point of far focus just changes to infinity as indicated on the DOF display and check that the front focus point is still acceptable to you.

This procedure is easier done than said once you have trained yourself. It is less convenient and less accurate to do it the old fashioned way with DOF tables. I have written a hyperfocal DOF chart for my non-D Tamron 19-35 and the greatest inaccuracy lies in estimating the given hyperfocal distance from your chart so that you can find an object at this distance to focus on. With the 7D, even with a D lens, you are automatically forced to do things this old way, every time.

David, I think that you are absolutely right about the reason Minolta engineers don't want you to see what distance the camera has decided to focus on. People would be alarmed when the camera gets it wrong under certain conditions such as very wide angle. But the 5D/7D/A100 could have a DOF indicator similar to the film 7 that does not reveal focus distance. Better still both cameras could reveal focus distance, depth of field and even automatically set the lens at the hyperfocal distance. The display could include a warning during conditions of difficult focus telling the user that the data may be inaccurate.

[David Kilpatrick]

In theory, the A100 already has the hyperfocal distance auto-setting in place - it is the Landscape mode on the picture styles of the mode dial, marked with the Mountains symbol. The workings were carried over from the old Creative Expansion card system, built in to later cameras, may have changed a bit but should still adjust the lens so that infinity is at the end of the depth of field. The firmware exists, it's just access to it and displaying what is going on which is missing.

David