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Focus Drift Shooting Birds-Eye?

PostPosted: Fri Sep 04, 2015 8:40 pm
by Gary2
Using a Phase camera, has anyone had issues using lenses pointed straight down for a long time? Or more importantly, if so, does anyone have a solution?

We have stuck with Contax for a long time. But, the hassle factor is getting too big. One reason we have held off getting a Phase camera is that we heard that there was a focus change when the lens was shooting down from overhead for a long time. Then, our eqpt rental service said they thought it was now not an issue.

So we tried an XF with Schneider 80 mm lens. It sat all day high on a tripod pointed down at the set. And the focus would shift.

We really want to leave Contax behind. Does anyone have a sense of the scope of this problem or how to address it? Was this an issue with a prior series of lenses and we had just been given one to test with?

Thanks,

Gary

Re: Focus Drift Shooting Birds-Eye?

PostPosted: Sat Sep 05, 2015 3:24 pm
by Paul_Steunebrink
The old Zeiss for Hassellblad V lenses with leaf shutter, a.k.a. CF lenses are known for their focussing stiffness and often used for this task.

More in general manual focus lenses are less prone to drift when 'looking down'.

Re: Focus Drift Shooting Birds-Eye?

PostPosted: Wed Oct 07, 2015 10:04 am
by Jim_DK
As long as you are not using extension tubes, you can engage AF, but disable AF pre focus from the release button via the custom functions. That way the lens is braked by the body motor but will not autofocus when you invoke capture.

Re: Focus Drift Shooting Birds-Eye?

PostPosted: Thu Oct 08, 2015 2:31 pm
by Digital Transitions, Doug
The above suggestion will help you up the stiffness to the max it can go with the body.

If you need something even stiffer then I'd suggest one of Phase One's dedicated repro bodies which is designed explicitly for shooting straight down for long periods of time. These bodies provide zero slippage across weeks of use pointed directly down.
http://dtdch.com/dt-rcam-reprographic-camera-system/

Or you can add a stiff rubber band around the barrel of the XF, provided that you don't need to change the focus often.