Using Tape Measure For Precise Focus at DVinfo.net

Go Back   DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XH Series HDV Camcorders

Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


Reply
 
Thread Tools Search this Thread
Old April 3rd, 2009, 08:44 AM   #1
Major Player
 
Join Date: Aug 2008
Location: Belfast Northern Ireland
Posts: 261
Using Tape Measure For Precise Focus

After some slightly soft results (fully zoomed out on an interview subject who's standing approx 4 feet away) having used Magnify and Peaking, I've resorted to a tape measure to keep my mind at ease. I tried a 'laser tape measure' today but the results weren't completely accurate - the instructions also say it's not to be used where precise measurements are required.

I've just filmed some tests on my XHA1 using a normal tape measure and am looking forward to seeing how sharp they are when I play them back shortly.

However, I'd just like to ask, does anyone else here use a tape measure with their XHA1 for interviews or filmmaking?

If so, what's the ideal spot to place the beginning of the tape measure (I'm thinking that perhaps the tape measure might need to begin a bit further back on the A1)?

At the moment I'm placing the beginning of my tape measure immediately just behind the little screw that holds the sensor at the front of the camera.

I'll describe my findings once I watch my footage.
Peter Dunphy is offline   Reply With Quote
Old April 3rd, 2009, 01:24 PM   #2
Trustee
 
Join Date: Dec 2007
Location: Glasgow, Scotland
Posts: 1,521
http://www.dvinfo.net/conf/canon-xh-...e-readout.html

I wondered that too in post #3 in above thread. Do let us know if you find out where to measure from.
Colin McDonald is offline   Reply With Quote
Old April 3rd, 2009, 01:43 PM   #3
New Boot
 
Join Date: Sep 2008
Location: Simi Valley, California
Posts: 8
Once you have measured the distance from the subject to the camera, are you going to set the focus based on the distance indication on the display? Because if you are, be aware that the distance displayed is not that accurate. I have two identical XHA1s that provide distances as much 6 feet different from each other when focused at a distance of approximately 60 feet.
Larry Shilkoff is offline   Reply With Quote
Old April 3rd, 2009, 02:05 PM   #4
Tourist
 
Join Date: Mar 2009
Location: Los Angeles, California
Posts: 4
Measure from the front of the glass on the lens. Yeah, I know it's weird, since with older cameras the measurement is from the film plane, but I've heard (more than once) to use the front glass.
G. Scott Campbell is offline   Reply With Quote
Old April 3rd, 2009, 02:16 PM   #5
Trustee
 
Join Date: Dec 2007
Location: Glasgow, Scotland
Posts: 1,521
Quote:
Originally Posted by G. Scott Campbell View Post
Measure from the front of the glass on the lens. Yeah, I know it's weird, since with older cameras the measurement is from the film plane, but I've heard (more than once) to use the front glass.
Interesting - where did this information come from?

Last edited by Colin McDonald; April 3rd, 2009 at 02:18 PM. Reason: clarification
Colin McDonald is offline   Reply With Quote
Old April 3rd, 2009, 02:19 PM   #6
Inner Circle
 
Join Date: Feb 2006
Location: Belfast, UK
Posts: 4,121
Quote:
Originally Posted by G. Scott Campbell View Post
Measure from the front of the glass on the lens. Yeah, I know it's weird, since with older cameras the measurement is from the film plane, but I've heard (more than once) to use the front glass.
With ENG style video lenses you measure from the front, with Cine style video lenses you measure from image plane like a film camera.

If you're planning to use tape measurements the Cine style lenses are much better because they have the stretched focus scale that film camera lenses use. The ENG style video lens usually only rotate a 1/3rd of the way and have a more compressed focus scale.

I doubt you can get any Cine style lenses for 1/3" cameras, although they're available for 2/3" cameras and are commonly used on dramas etc.

Of course, you can make your own focus scale for your ENG style lens, in fact that would be good idea because the manufacturer's original markings may not be accurate. You also need a manual zoom lens, rather than one of those continuously rotating focus ring jobs found on most consumer/prosumer cameras.
Brian Drysdale is offline   Reply With Quote
Old April 3rd, 2009, 02:54 PM   #7
Trustee
 
Join Date: Dec 2007
Location: Glasgow, Scotland
Posts: 1,521
And?...

Brian, given that we are stuck with the lens supplied with the XH series (should have gone to Specsavers and bought an XL series), where do we measure from - the glass or the focal plane (and if the latter where is it)?
Colin McDonald is offline   Reply With Quote
Old April 3rd, 2009, 03:29 PM   #8
Inner Circle
 
Join Date: Feb 2006
Location: Belfast, UK
Posts: 4,121
Quote:
Originally Posted by Colin McDonald View Post
Brian, given that we are stuck with the lens supplied with the XH series (should have gone to Specsavers and bought an XL series), where do we measure from - the glass or the focal plane (and if the latter where is it)?
It's easy enough to find out.

For the front element, using a tape measure set up a flat chart that easy to eye focus on at a distance that matches a measurement on your focus scale. With the lens aperture wide open, zoom in and eye focus it - if the scale's distances matches the measured distance from your front element, that's your reference point. I suspect this will be the case, since it's pretty standard on video cameras.

However, if it's not you can find your focal plane marking by using the tape measure. If you set up the chart so that it in focus at a locked off focus marking on the lens and then measure that distance back to the camera you should find your focal plane. You can put a reference mark on your camera body and ideally a tape hook.

Also, I'd check that tape measurement works with a range focal lengths. The focus rings on the software controlled varifocal length zooms found on 1/3" cameras often tend not to hit repeatable marks. You should also check that the focus scale on the lens is accurate, the markings can be pretty rough settings and they won't have witness lines that give you the exact position on the focus scale, only numbers.
Brian Drysdale is offline   Reply With Quote
Old April 3rd, 2009, 03:59 PM   #9
Regular Crew
 
Join Date: Aug 2008
Location: Burlington, VT
Posts: 33
Have you tried getting in really tight on your subjects face, setting the focus and then zooming out? When you are in tight, you can use the magnification and peaking to really get a sharp focus. I typically set the focus using my subjects nose.
Joe Gaetani is offline   Reply With Quote
Old April 3rd, 2009, 06:10 PM   #10
Inner Circle
 
Join Date: Feb 2006
Location: Belfast, UK
Posts: 4,121
Quote:
Originally Posted by Joe Gaetani View Post
Have you tried getting in really tight on your subjects face, setting the focus and then zooming out? When you are in tight, you can use the magnification and peaking to really get a sharp focus. I typically set the focus using my subjects nose.
The eyes are better, they are the main points of interest in the typical frame sizes used in interviews.
Brian Drysdale is offline   Reply With Quote
Old April 3rd, 2009, 11:14 PM   #11
Inner Circle
 
Join Date: Feb 2007
Location: Fairfield, Dunedin, New Zealand
Posts: 3,634
Images: 18
Think this may be of interest.........

http://www.dvinfo.net/conf/open-dv-d...an-i-sure.html.

Sure works for me.


CS
Chris Soucy is offline   Reply With Quote
Old April 4th, 2009, 03:06 AM   #12
Major Player
 
Join Date: Oct 2007
Location: London, UK
Posts: 792
I never have time for tape measures or the magnify button (which requires you to stop shooting) and I don't find the peaking button to be very helpful either.
I zoom in and centre the image on what I want in focus, press the instant focus button and zoom out.
It seems to work.
__________________
http://www.gooderick.com
Richard Gooderick is offline   Reply With Quote
Old April 8th, 2009, 09:12 AM   #13
Major Player
 
Join Date: Sep 2006
Location: Virginia Beach, VA
Posts: 656
Dosen't the XH-A1 have an electronic focus mechanism rather than mechanical?

I would think an electronic focus mechanism would require a qualitative focus adjustment, as on an external monitor.

A true mechanical focus would offer repeatable focus results and quantitative focus measures would actually work well there.

Sometimes the XH-A1 focus can be very frustrating. Shots you make every possible effort to focus later appear to be soft for no apparent reason. I believe it's a very infrequent image processing snafu of some kind that causes this occasional poor focus. I say that because it sometimes looks like there is a little more wrong with the image than just mis-focus if you look very closely at the image.
__________________
Panasonic HMC150/Canon A1/JVC HD1/Sony Vegas 8.0c
Jeff Kellam is offline   Reply With Quote
Old April 8th, 2009, 09:26 AM   #14
Trustee
 
Join Date: Dec 2004
Location: Lipa City Batangas, Philippines
Posts: 1,110
Quote:
Originally Posted by Jeff Kellam View Post
Sometimes the XH-A1 focus can be very frustrating. Shots you make every possible effort to focus later appear to be soft for no apparent reason. I believe it's a very infrequent image processing snafu of some kind that causes this occasional poor focus. I say that because it sometimes looks like there is a little more wrong with the image than just mis-focus if you look very closely at the image.
This is affected a lot by how you set the exposure. If you use small apertures you are likely to get a soft image even when the focus is spot on. Try shooting everything at F4 for a while to see the XH-A1 at its best, (in terms of sharpness).

Richard
Richard Hunter is offline   Reply With Quote
Old April 8th, 2009, 02:36 PM   #15
Regular Crew
 
Join Date: Feb 2007
Location: Warrington England
Posts: 143
Peter, if you look at your lens there is a red line around it as I think there is on all canon lenses I Think jvc rings are green and I am sure that that is your focal plane and that is where you take measurements from but don't take that for gospel I have never used a tape to focus.

Alan
Alan Craig is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XH Series HDV Camcorders

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 11:56 PM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network