SLR: Is what you see really what you get?

[JayGannon]

Would a lens that does not hold focus when the focal length is changed truly be a zoom lens? I was always told that lenses that do this are technically called "variable focal length lenses," and that "zoom lenses" hold focus.

Ask the lens tech's and they will agree wholeheartedly, ask the marketing department and they will say 'What the hell is a variable focal length lens? Its a zoom ffs!'

 

[lxdude]

I sharp blow on the side of the head usually re-collimates the brain Jeff.

Of course that's often what caused the problem in the first place!

 

[SilverGlow]

No one has brought up the possibility of human error. If one shoots with a fast lens, close to the subject, wide or nearly wide open, and has the bad habit of doing the Lock-Focus-Recompose dance, one will often get images that lack critical sharpness.

Most Canon SLR's have multi-focus points and for good reason. It is best to use them, picking the best one manually for a given composition, and NOT recomposing after locking focus. This bad habit can often cause lenses to be thought of as "bad", as us humans hate to blame ourselves.

Now of course, there does exist lenses that are out of calibration or just plain dogs.

Additionally, doing the Lock-Focus-Recompose dance can cause metering issues, when using zoned/matrix metering mode. Not much good will come out of that bad practice.

 

[markbarendt]

No one has brought up the possibility of human error. If one shoots with a fast lens, close to the subject, wide or nearly wide open, and has the bad habit of doing the Lock-Focus-Recompose dance, one will often get images that lack critical sharpness.

Most Canon SLR's have multi-focus points and for good reason. It is best to use them, picking the best one manually for a given composition, and NOT recomposing after locking focus. This bad habit can often cause lenses to be thought of as "bad", as us humans hate to blame ourselves.

Now of course, there does exist lenses that are out of calibration or just plain dogs.

Additionally, doing the Lock-Focus-Recompose dance can cause metering issues, when using zoned/matrix metering mode. Not much good will come out of that bad practice.

Oh get off your high horse SilverGlow, this isn't a bad habit it's an advanced technique, well proven over time, and highly useful and if one is paying attention and if one is setting the camera manually or locking there's no exposure problem regardless of the metering method.

In the skilled hands of someone who understands how to use it and has practiced this technique it is fast and accurate and beats the hell out of trying to switch focus dots in the middle of a quick series of shots.

Hell in street and many other forms of people photography it's darn near the best way to be able to keep up and catch a great expression.

 

[film_man]

I've been using focus-and-recompose for ever. I just cannot be bothered to play with focus points. I have never lost a single shot because of focus errors and I've had a lot of close-ups at f/1.4.

 

[Rol_Lei Nut]

Most Canon SLR's have multi-focus points and for good reason.

Yes, so they can sell more to gadget-obessed consumers who are led to believe that such things are necessary...

A good manual viewfinder system (used skillfully) is fast, effective and still the most accurate way to focus.

 

[Markster]

This would be on an AE-1P. Manual focus. 1 focus point (center split with ring around the split) to aid in focusing. Focusing done wide open, lens stops down to proper aperature as the shutter is tripped.

It's not an issue of focus so much. Or... maybe it is... What I mean is that from my end-user perspective when I've done similar things in the past they've been in focus. The question is: is it my film my lens or myself?

Right now I'm going to eliminate the third possibility. Oh, I admit I'm no expert and I do make mistakes. I don't think that's the case here, though.