HD Focus, what's going on here?

[Chris Keth]

That's why the back-focus has to be adjusted -- for one thing, temperature changes cause the aluminum block holding the prism & CCD's to expand or contract. This is a reason why Clairmont Cameras replaced the block with a stainless steel one, and why Sony is going to do the same for their future replacement to the F950.

 

Also, these cameras are basically heat generators, so all sorts of little problems can happen as they overheat, including more noise in the image.

 

 

Perhaps they should take a hint from the high-end PC gaming world and liquid-cool their cameras. I had a liquid-cooler in a dual processor PC that hardly made any noise at all, so I'm sure someone could make it essentially silent if they were striving towards that end.

[Laurent Andrieux]

That would only work when the camera is on... It's not like a computer that doesn't mecanichally keeps the memory of an instable state... If a camera mount or CCD expends or moves while the camera is off, it won't at once go back to it's perfect state when you just turn it back on...

[Jamie Metzger]

Since we're talking about focusing in HD, do you guys use a tape measure or focus by eye, BTW ? Do you use the monitor just as a check or focus with it ?

 

Would your focusing technics be different according to the lenses you use ?

 

 

Hard to say... the first few days I was using tape measure, because the lens was so sensitive, and we double checked with eye focus. I finally put markings on the lens, and my own wittness mark so I knew the inbetweens for pulling focus, which helped tons.

 

After a week of shooting and noticing the focus slightly getting worse (nothing considerably bad), I checked the lens and bumped the Back Focus out of alignment tightening the PL mount. So we had to check back focus, and it was a lot easier than I thought. The focus was much better and it was a quick fix.

 

Why sony still puts a hand mount on an HD lens is past my understanding.

 

Thanks for all the help guys. I kept my DP updated, and we made it just fine.

[Chris Keth]

That would only work when the camera is on... It's not like a computer that doesn't mecanichally keeps the memory of an instable state... If a camera mount or CCD expends or moves while the camera is off, it won't at once go back to it's perfect state when you just turn it back on...

 

 

You've done very well stating the obvious, Laurent! :D

 

I just meant it to perhaps solve the problem of the camera-produced-heat causing the backfocus problems. True, environmental temperature would still affect it, but at least the camera heating up wouldn't make you check the backfocus a ton during shooting. A well-done cooling system could make it a morning routine/company move thing rather than a constant annoyance.

 

On the other hand, you can check and set backfocus very quickly once you have your own method down and you're used to doing it. It's not a big deal to constantly check it once you're good at it.

[Michael Nash]

Why sony still puts a hand mount on an HD lens is past my understanding.

 

Then it's an "ENG" lens, not a "cine" lens. ENG lenses are designed so that a single operator can control focus and zoom easily, and the focus rotation is much smaller so that a simple finger adjustment covers a longer pull. When shooting ENG-style HD, you need these features plus the sharper glass of an HD lens.

 

ENG lenses are also typically focus calibrated from the front of the lens, not from the focal plane. But you'd have to check your lens (which is likely Fujinon, not Sony, BTW ;) ).

[Brian Drysdale]

After a week of shooting and noticing the focus slightly getting worse (nothing considerably bad), I checked the lens and bumped the Back Focus out of alignment tightening the PL mount. So we had to check back focus, and it was a lot easier than I thought. The focus was much better and it was a quick fix.

 

On HD you should check the back focus every day, every time you remove/change lens or if the temperature changes. You could end up checking it several times in a day.

 

Camera assistants are always double checking it throughout the day.

[Laurent Andrieux]

I just meant it to perhaps solve the problem of the camera-produced-heat causing the backfocus problems. True, environmental temperature would still affect it, but at least the camera heating up wouldn't make you check the backfocus a ton during shooting. A well-done cooling system could make it a morning routine/company move thing rather than a constant annoyance.

 

On the other hand, you can check and set backfocus very quickly once you have your own method down and you're used to doing it. It's not a big deal to constantly check it once you're good at it.

 

That sounds clever to me, you must be right stating it's more the camera-produced heat that is an issue.