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-   -   wide angle and back focus (https://www.dvinfo.net/forum/jvc-gy-hd-series-camera-systems/69486-wide-angle-back-focus.html)

James Daniels June 13th, 2006 05:04 PM

wide angle and back focus
 
Hi, I just bought a used hd100ua and it came bundled with a clamp-on century optics WA adapter. This is the non-zoom-through variety and is only useful at full wide (5.5). However, I have found my back focus no longer seems accurate with it mounted - does this make sense? I have to adjust back focus when I add/remove it.
I have noted another thing, though, which is I can zoom with it on and then bring it into focus by adjusting the back-focus.
Anyway, am I missing something here?
thanks for reading.

Carl Martin June 13th, 2006 07:30 PM

Quote:

Originally Posted by James Daniels
Hi, I just bought a used hd100ua and it came bundled with a clamp-on century optics WA adapter. This is the non-zoom-through variety and is only useful at full wide (5.5). However, I have found my back focus no longer seems accurate with it mounted - does this make sense? I have to adjust back focus when I add/remove it.
I have noted another thing, though, which is I can zoom with it on and then bring it into focus by adjusting the back-focus.
Anyway, am I missing something here?
thanks for reading.

James,

When using non zoom through wide angle lenses, set the lens at infinity and use the macro to set focus along with, although only slightly the zoom triger.

Once the back focus is set, it should not be a problem, make sure that the locking screw is tight.

Gary Morris McBeath June 13th, 2006 07:52 PM

Even the zoom through WA adapter requires re-setting the back focus; you've changed your wide end focal length, so the back focus has to be set each time that is changed: WA on, WA off.

As a JVC owner, you might consider yourself fortunate; another HD camera I used to own necessated resetting the back focus with every built-in ND filter change. (unless you bought the $1300 set of good ones from the after market) At least the JVC's filters on my camera are ground with precision, and no back focus change is necessary. Something you should test on your camera to be sure.

Gary Morris McBeath
SaltAire Cinema Productions

Carl Martin June 13th, 2006 08:19 PM

Quote:

Originally Posted by Gary Morris McBeath
Even the zoom through WA adapter requires re-setting the back focus; you've changed your wide end focal length, so the back focus has to be set each time that is changed: WA on, WA off.

As a JVC owner, you might consider yourself fortunate; another HD camera I used to own necessated resetting the back focus with every built-in ND filter change. (unless you bought the $1300 set of good ones from the after market) At least the JVC's filters on my camera are ground with precision, and no back focus change is necessary. Something you should test on your camera to be sure.

Gary Morris McBeath
SaltAire Cinema Productions

This is news to me. I very rarely if ever have to reset my back focus no matter what lens adapter I use. I use zoom through, fish eye, wide angle, and all kinds of filters and never have to rest my BF. I have the hd100, Sony digibeta, and beta sp.

Gary Morris McBeath June 13th, 2006 09:56 PM

Carl,

Didn't used to be an issue with my std def cameras either. Have you done any testing with a hi-def star chart (like the DSC labs chart, not the older style we all used for std def)? The setting is much more critical than it was with std def cameras. Real easy to go past the focus point unless you have the finer resolution chart. Also, best to get the chart as close to the camera as possible so you can see the focus at the wide end. Jeff Cree, formerly of Sony, now with Band Pro, made a believer out of me in a class he taught some years ago.

And I always thought you New Yorkers always got your news before we bumpkins on the west coast did. Heh, heh.

Carl Martin June 14th, 2006 09:15 AM

Quote:

Originally Posted by Gary Morris McBeath
Carl,

Didn't used to be an issue with my std def cameras either. Have you done any testing with a hi-def star chart (like the DSC labs chart, not the older style we all used for std def)? The setting is much more critical than it was with std def cameras. Real easy to go past the focus point unless you have the finer resolution chart. Also, best to get the chart as close to the camera as possible so you can see the focus at the wide end. Jeff Cree, formerly of Sony, now with Band Pro, made a believer out of me in a class he taught some years ago.

And I always thought you New Yorkers always got your news before we bumpkins on the west coast did. Heh, heh.

Hi Gary,

I use that very chart, and still no BF issues. To be honest, I do check it once a week to be sure. I also have a 2/3 HD lens on my camera with the 2/3 10 1/3 lens adapter. Maybe this makes it not as critical as with the standard lens that was shipped with the HD100.

Carl

Paolo Ciccone June 14th, 2006 10:04 AM

Quote:

Originally Posted by Carl Martin
This is news to me. I very rarely if ever have to reset my back focus no matter what lens adapter I use. I use zoom through, fish eye, wide angle, and all kinds of filters and never have to rest my BF. I have the hd100, Sony digibeta, and beta sp.

Carl, not arguing with what you said but you should check backfocus every time you move the camera from one location to another. Backfocus has been known to be very sensitive for HD.
I generally check it before a shoot, even temperature changes can affect it.

Carl Martin June 14th, 2006 12:34 PM

Quote:

Originally Posted by Paolo Ciccone
Carl, not arguing with what you said but you should check backfocus every time you move the camera from one location to another. Backfocus has been known to be very sensitive for HD.
I generally check it before a shoot, even temperature changes can affect it.

I think I will. Thanks.

James Daniels June 14th, 2006 01:33 PM

thanks
 
This forum rocks.
Thanks for clearing this up and saving me much time.


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