HVX + Redrock: Losing focus towards edges of the screen (with footage/pics)

J

John Kary

Active member
One of my shooters has a Panasonic HVX200 + Redrock M2 combo and some Nikon lenses. I got some footage back from him and some of it gets very blurry towards the edges of the frame... does anybody know why this might be happening? Below is a frame-grab of one shot that it was particularly noticeable in the footlights near the bottom. This shot was using his 35mm Nikon lens.


35mmtestku8.jpg


What is most likely at fault: Bad glass? Not properly back-focusing? What can he do to fix this next time? Thanks for your input.

Video available upon request in MXF > CineForm HD > Xvid 10000Kbit.
 
To a certain extent corners will always be slightly softer with the Redrock or for that matter any of the 35mm adapters. The Brevis may tend to be somewhat more even.

However the main problem is usually that the HVX is not focused on the adapter imaging screen precisely at the best point for an optimum compromise between where the corners and the center are in best focus. My experience is that they are never in exactly the same spot but you can get very close.

There are 2 elements to this.
1 - There seems to be an optimum distance for the imaging screen to the HVX that takes some careful testing to get right. Too close or too far and the focus point for the center and corners seem to diverge more.
2 - It takes careful attention every time you set up any of these adapters to set the HVX focus at the ideal point. Just looking at the center can leave you off at the corners if you are not careful.
I suggest using a 3- 4 ' card with a blow up of a rtesolution chart and bringing it to the set all the time.

3- There is also the more gross question of whether the Camera is centered properly on Redrock screen so that all the corners are focusing at the same point. If that's off you will never get proper focus.

All the above come under the Rubric of Back Focus. It probably helps to have some depth of field at the HVX itself so you are not running the HVX iris wide open. Especially on an exterior it shopuld be easy to put the HVX @ f4 or 5.6.

4. The other issue is whether the lens mt on the Redrock itself is set properly. That's more of a long shot - less likely that is.
Some of the Redrock achromats a while ago were labeled backwards by the way and that is something to look at if you can't seem to improve it. Try turning it around and see if it improves radically.

My suspicion is that many people dopn't takle the time neccessary to set these up right. It took me 3 days at first.
Anyway that's my experience.

Sorry about all the typos.

Don't know if these issues are covered in the stickies above, but maybe they should be.


- Lenny Levy
 
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Those are some nice points, Lenny, thanks. I know we rushed this shot a bit due to losing daylight, so will have to take more time next time. That, and sticking with 1 lens for a good period of time would probably benefit also, so as to not needing to move it in and out of place on the rails.

Does anybody else have any tips about getting good focus from the HVX to the ground glass?
 
Also, with the M2 the HARDMOUNT should be STANDARD. A great deal of your M2 issues with sharpness, edge fall-off etc. will vanish when you hardmount the setup.

This will keep the camera aligned with the adapter at all times, no shifting means less focal issues on the ground glass.

You can find a hard mount for sale at the REDROCK website.
 
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