Back focus slipping at DVinfo.net

Calvin Bellows · October 25th, 2011, 12:34 AM

I just wanted to know if there are other HM 700 users that have noticed that they need to adjust their back focus often. I have the Fuji 17x lens and I have to adjust it almost every time I take it out of my bag lately and I crank the screw tight. I have talked with another HM 700 user in my area and he is experiencing the same problem. Any one seeing the same thing or have any suggestions. Thanks.

Adam Letch · October 25th, 2011, 02:33 AM

it should be something you do for every professional shoot, variances in temperature cause metal to expand an contract, this causes the back focus to move slightly. Nothing major.

Keith Marley · October 25th, 2011, 04:39 AM

Yes Calvin,
I am having the same problem with my Canon lens. I always make sure that screw is tight, but it seems like I have to do it every time I get it out of the bag.
Not much help, I know, but at least you know you are certainly not alone!

Antony Michael Wilson · October 25th, 2011, 07:44 AM

I've had this problem on all 1/3" bayonet lenses I've ever used on the JVC ProHD cameras. I would expect to check back focus regularly anyway but you really do have to be vigilant on these cameras. The new(er) bundled Canon lens seems to be the worst culprit but the Fujis (new and old) seem to be pretty dodgy in this regard as well.

Shaun Roemich · October 25th, 2011, 05:23 PM

Had an issue with one of my HD200s with stock 16x5.5 last week as well. Seem to be slipping more than any other lenses I have used.

Michael Delagarza · October 26th, 2011, 09:33 AM

We have had the same issue with the Canon 14x. I spent considerable time trouble shooting the issue and found an interesting problem.
The Macro ring is connected to the back focus ring. When you set the back focus the Macro ring turns with it. Makes sense. The problem is that when everything is locked down (thumbscrew tight, macro ring locked in place) there is a small amount of play in the macro ring. Enough play to affect back focus. So, if the back focus is perfect and you twist the macro ring for some reason it can make the back focus go out of whack.
Just a little bit and difficult to catch in the viewfinder but very soft on wide shots when you see it on a monitor.
I don't know if this is the same issue others have, but I sent the lens off to Canon for service and replacement of the Macro ring. Due back this week. It will be interesting to see if the problem is fixed!

Calvin Bellows · October 30th, 2011, 09:26 PM

I do agree that the macro can be very loose and it does affect the sharpness of the picture. I wonder if this is because it is the lenses are less expensive then most

October 25th, 2011, 12:34 AM	#1
Calvin Bellows Major Player Join Date: Feb 2009 Location: Red Deer, Alberta Posts: 215	Back focus slipping I just wanted to know if there are other HM 700 users that have noticed that they need to adjust their back focus often. I have the Fuji 17x lens and I have to adjust it almost every time I take it out of my bag lately and I crank the screw tight. I have talked with another HM 700 user in my area and he is experiencing the same problem. Any one seeing the same thing or have any suggestions. Thanks. __________________ Calvin Bellows www.exposureproductions.ca

October 25th, 2011, 02:33 AM	#2
Adam Letch Major Player Join Date: Feb 2006 Location: Perth, Western Australia Posts: 414	Re: Back focus slipping it should be something you do for every professional shoot, variances in temperature cause metal to expand an contract, this causes the back focus to move slightly. Nothing major.

October 25th, 2011, 04:39 AM	#3
Keith Marley Regular Crew Join Date: Jun 2010 Location: Liverpool UK Posts: 37	Re: Back focus slipping Yes Calvin, I am having the same problem with my Canon lens. I always make sure that screw is tight, but it seems like I have to do it every time I get it out of the bag. Not much help, I know, but at least you know you are certainly not alone!

October 25th, 2011, 07:44 AM	#4
Antony Michael Wilson Major Player Join Date: Sep 2005 Location: London, UK Posts: 343	Re: Back focus slipping I've had this problem on all 1/3" bayonet lenses I've ever used on the JVC ProHD cameras. I would expect to check back focus regularly anyway but you really do have to be vigilant on these cameras. The new(er) bundled Canon lens seems to be the worst culprit but the Fujis (new and old) seem to be pretty dodgy in this regard as well.

October 25th, 2011, 05:23 PM	#5
Shaun Roemich Inner Circle Join Date: Sep 2002 Location: Vancouver, British Columbia (formerly Winnipeg, Manitoba) Canada Posts: 4,088	Re: Back focus slipping Had an issue with one of my HD200s with stock 16x5.5 last week as well. Seem to be slipping more than any other lenses I have used. __________________ Shaun C. Roemich Road Dog Media - Vancouver, BC - Videographer - Webcaster www.roaddogmedia.ca Blog: http://roaddogmedia.wordpress.com/

October 26th, 2011, 09:33 AM	#6
Michael Delagarza New Boot Join Date: Oct 2009 Location: Port Townsend, Wa Posts: 5	Re: Back focus slipping We have had the same issue with the Canon 14x. I spent considerable time trouble shooting the issue and found an interesting problem. The Macro ring is connected to the back focus ring. When you set the back focus the Macro ring turns with it. Makes sense. The problem is that when everything is locked down (thumbscrew tight, macro ring locked in place) there is a small amount of play in the macro ring. Enough play to affect back focus. So, if the back focus is perfect and you twist the macro ring for some reason it can make the back focus go out of whack. Just a little bit and difficult to catch in the viewfinder but very soft on wide shots when you see it on a monitor. I don't know if this is the same issue others have, but I sent the lens off to Canon for service and replacement of the Macro ring. Due back this week. It will be interesting to see if the problem is fixed!

October 30th, 2011, 09:26 PM	#7
Calvin Bellows Major Player Join Date: Feb 2009 Location: Red Deer, Alberta Posts: 215	Re: Back focus slipping I do agree that the macro can be very loose and it does affect the sharpness of the picture. I wonder if this is because it is the lenses are less expensive then most __________________ Calvin Bellows www.exposureproductions.ca