OT: How I get 'perfect' focus with my HDV cam

Ben1000 wrote on 7/1/2006, 1:59 PM

Howdy...

Like many, I was initially stumped with how hard it is to get a perfect focus with many HDV camcorders. I have a Z1, and found that quite often, even with the auto-assist, I would get slightly soft images. This is especially true if you don't have an HD monitor, and are relying on SD or the VF or LCD.

So, I have since developed a technique that's simple, but might help anyone else who has this issue. Since I started using this, my focus has been razor sharp.

Basically, my new rule is: Don't focus on people. People are soft. They have soft edges. Clothes are soft.

Here's what I do: I have printed a white sheet of paper with some text on it, in point sizes ranging from 9 point to around 30 point. Any font will do, and it's just black on white from a crisp laser printer.

Once my subject is set, I get him/her to hold the paper at eye level, essentially covering their face. I then zoom in all the way, hit the focus assist button (which doubles the image size on my Z1), and then use my eyeballs and peaking to get the text razor sharp in the VF. Once the text is sharp, the subject ditches the paper, and we shoot...

I've used this quite often recently, and found it to be the best, cheapest, easiest way to get a great focus everytime..

Hope that helps you.

Best,

Benjamin

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Comments

farss wrote on 7/3/2006, 7:39 AM

This might hep a little:
http://en.wikipedia.org/wiki/Zoom_lens

However thinking about what Serena is quoting I'd have some doubts. All the ENG lenses I've come accross only have a servo for focal length so clearly no argy bargy would be possible. I guess anything's possible on fixed lenses but the only use I can find for varifocal lenses is in security cameras where they're simply used to have adjustable focal length i.e. set focal length, set focus and don't touch.

Certainly some zooms have a lot of elements, there was a white paper written by Canon that goes into the difficulty of designing good zooms for HD.
All that aside though even 35mm expensive glass can breath, in fact some seem to see this as desirable (???).

BTW Dave, did you see my post above, I think your camera may have a problem.

Just thinking about this some more, if the lenses were actually varifocal with electronic intervention you'd think it'd be simple enough to have them do an auto backfocus calibrate.

Bob.

Serena wrote on 7/3/2006, 4:29 PM

epirb, actually that CML discussion was the first thing to alert me to that. I had assumed otherwise. I'll have to check with Sony. The difference seems to be in the mechanism for controlling focus - mechanical or servo-motor.

Serena wrote on 7/3/2006, 8:00 PM

Checked that question with the Sony service guys and they confirm that the FX and Z1 are fitted with varifocal lenses (as defined above). That is, the mechanics of the zoom are handled by servo motors and not by mechanical coupling, the latter being regarded as more precise and certainly more expensive. They hear that the Z1 (and presumably the FX) do have a bit of a focus drift problem but they've had only a few in specifically for lens problems (I didn't note the statistics but they've serviced several hundred of the cameras), so this indicates that the focus matter isn't being regarded as unusual by operators. They hadn't seen anything to confirm that rumour. The cost of cleaning etc and "back-focus" adjustment is about A$160 here.

farss wrote on 7/3/2006, 8:18 PM

Interesting.
That might explain why there's a menu setting to tell the camera that you've fitted a WA adaptor. Which then leads to the question of how well that works with 3rd party WA adaptors.

I guess one could argue the semantics of 'varifocal', technically I'm wearing varifocal glasses at the moment and in general 'varifocal' seems to refer to a lens that has no mechanism for adjusting focus as focal length changes so one could argue that the servoed focus adjustment negates the moniker of 'varifocal'. However I think the way it's been defined here is perhaps more meaningful otherwise there's be no distinction between the two systems.

Bob.

Serena wrote on 7/4/2006, 1:02 AM

The test procedure I flagged previously is OK but it was really a procedure for checking the focusing function. I think this chart is rather more use if you're wanting to check that your lens holds focus during zooming. focus test chart

I've just repeated checking my FX (in light of these discussions) and it holds well throughout the zoom.