Warning on Flange Focus Adjust - Page 2 at DVinfo.net
DV Info Net

Go Back   DV Info Net > Sony XAVC / XDCAM / NXCAM / AVCHD / HDV / DV Camera Systems > Sony XDCAM EX Pro Handhelds
Register FAQ Today's Posts Buyer's Guides

Sony XDCAM EX Pro Handhelds
Sony PXW-Z280, Z190, X180 etc. (going back to EX3 & EX1) recording to SxS flash memory.

Reply
 
Thread Tools Search this Thread
Old September 2nd, 2009, 05:15 AM   #16
Major Player
 
Join Date: Nov 2008
Location: Melbourne Australia
Posts: 626
[QUOTE=Vincent Oliver;1086317]Daniel, you are right in sating the backfocus should be set up correctly. However, at the wide setting of the lens there is a lot of depth of field which makes manual focus very difficult.


Vincent,
It is true that at the there is a lot of depth of field at the wide angle end of the focal length range however the depth of focus is much less. That is to say that the lens/film plane or lens/sensor plane distance is much more critical at short focal lengths than longer focal lengths. The long focal length lens is bringing the light rays to a focus over a much greater distance than the wide lens that has much less distance to do so. i.e With the wide lens the light rays are refracted more sharply as they pass through the focus making the distance setting more critical. Draw yourself some ray diagrams one with the gently converging rays of a long lens and one with steeply converging rays. You will find that you have to be more precise placing the film plane with the wide lens if you want exact focussing.
Alastair Traill is offline   Reply With Quote
Old September 2nd, 2009, 10:24 PM   #17
Trustee
 
Join Date: Sep 2004
Location: Chislehurst, London
Posts: 1,724
[QUOTE=Alastair Traill;1301565]
Quote:
Originally Posted by Vincent Oliver View Post
Daniel, you are right in sating the backfocus should be set up correctly. However, at the wide setting of the lens there is a lot of depth of field which makes manual focus very difficult.

Quote:
Vincent,
It is true that at the there is a lot of depth of field at the wide angle end of the focal length range however the depth of focus is much less.
I wondered if anyone would pick up on this. You are absolutely correct in your reply, the depth of rear focus (nodal point) does need to be more precise with wide angle lenses. The depth of field (whats in front of the lens) will be greater, hence my statement that focusing doesn't need to be as critical.

Like most other things, to get the best results your kit does need to be in balance, i.e. setting the back focus is just as important as setting the focus on your subject.
__________________
Eyes are a deaf man’s ears. Ears are a blind man’s eyes
Vincent Oliver is offline   Reply With Quote
Old September 3rd, 2009, 03:38 AM   #18
Trustee
 
Join Date: Dec 2003
Location: Malvern UK
Posts: 1,931
It would be nice if the stock fuji lens had a manual back focus. However I believe that the reason why is because even in full manual mode the focus ring is still operating a servo with no mechanical connection. So any back focus adjustment has to be servo operated too.
Simon Wyndham is offline   Reply With Quote
Old September 3rd, 2009, 05:57 AM   #19
Major Player
 
Join Date: Nov 2008
Location: Melbourne Australia
Posts: 626
In my post above I said that the depth of focus of a wide-angle lens is much less than for a longer lens. Here is an example that shows what a slight change in lens/sensor distance would be expected to make. The calculation is based on a simple formula that relates the focal length of a lens, the focusing distance and the extension of the lens from its infinity setting. It is a very useful formula to use when making a lens adaptor and you do not know how long the mount should be.

If for some reason such as a build up of dust etc or some damage causes the EX3 lens to be 0.1 mm further from the sensor than the correct adjustment, and the lens is set to infinity one could expect the following: -

At a focal length of 5.8 mm the lens would focus on a subject about 3.3 m away.
At a focal length of 81.2 mm the lens would focus on a subject at about 660 m away.

I.e. in this case the change at the long end would not be noticeable whereas at the wide end there may be a problem
Alastair Traill is offline   Reply With Quote
Old September 4th, 2009, 08:20 AM   #20
Regular Crew
 
Join Date: Feb 2009
Location: Australia
Posts: 119
can someone explan depth of focus?

Also, I believe the Z7 has manual back focus adjustment, I didn't think the Zeiss lens on that camera was fully manual even on full manual? (i.e. was using a servo). You just pressed a button when it was in focus at Tele and at wide and it would set it. Sounded pretty sweet to me.
Glynn Morgan is offline   Reply With Quote
Old September 4th, 2009, 09:07 AM   #21
Trustee
 
Join Date: Sep 2004
Location: Chislehurst, London
Posts: 1,724
Depth of focus is the point that the lens projects the image on the CMOS,CCD or film plane. This a very small but critical distance. Think of using a magnifying glass on a sunny day to project the suns rays onto a piece of paper, if it is in focus then it will burn, if not then it won't. Then think of the small distance you have to move the magnifying glass in order to make it work, and then compare that to the distance you are away from the sun. Extreme I know, but I hope it makes the point clear.

Depth of field is the area in front of your lens, i.e. your subject matter, this varies according to which aperture is in use.

Th
__________________
Eyes are a deaf man’s ears. Ears are a blind man’s eyes
Vincent Oliver is offline   Reply With Quote
Old September 4th, 2009, 10:14 AM   #22
Regular Crew
 
Join Date: Feb 2009
Location: Australia
Posts: 119
learn something new everyday, cheers.
Glynn Morgan 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...

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

Scan Computers Int. Ltd.
+44 0871-472-4747
Bolton, Lancashire UK


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 > Sony XAVC / XDCAM / NXCAM / AVCHD / HDV / DV Camera Systems > Sony XDCAM EX Pro Handhelds


 



All times are GMT -6. The time now is 11:25 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2024 The Digital Video Information Network