Is backfocus more stable on 17x, 18x, 20x ? at DVinfo.net

George Strother · June 9th, 2007, 09:26 AM

Has anyone noticed if the backfocus is more stable using one of the upgrade lenses than it is using the the stock 16x?

Probably no one has enough experience with all of these to know, but is there a most stable choice between the 17x, 18x and 20x?

I have read that these lenses are easier to back focus, but haven't seen anything about frequency of readjustment.

Paolo Ciccone · June 9th, 2007, 09:59 AM

George, I used the 18x and didn't notice anything different about the backfocus. I doubt that there is a stability issue associated with the lens unless the backfocus ring has a problem in the locking mechanism. Backfocus needs to be adjusted frequently with any removable lens. Temperature changes can affect it. In fact many cinematographers advice to check the backfocus any time you move the camera. It's not the lens, it's the nature of the device.

William Hess · June 9th, 2007, 10:26 AM

It seems that some of the people who've upgraded to the 17x or 18x have reported that the backfocus ring is much better machined, and that they have fewer backfocus issues after upgrading their lens. If you do a search for 17x or 18x I believe you'll find many posts on the subject.

I've just discovered that my 16x has issues with the macro ring. It has some "play" in the locked position, and if touched it moves back and forth very slightly, which in turn affects the focus when zoomed out wide. I've never had problems with the backfocus ring itself.

George Strother · June 9th, 2007, 01:51 PM

[QUOTE=Backfocus needs to be adjusted frequently with any removable lens. Temperature changes can affect it. In fact many cinematographers advice to check the backfocus any time you move the camera. It's not the lens, it's the nature of the device.[/QUOTE]

Paolo -

I think you are right. I was just wondering if anyone had found an improvement in stablility.

My usual practice is to carry eight 3-4 hour batteries, turn the camera on before I leave for a shoot, leave it turned on all day - even lunch, and always check the backfocus on a bigger screen at each setup.

I know the main issue is the small chips, short backfocus distance, high camera temps and high thermal expansion of the camera casing/optical block mount material.

I thought the only chance for an improvement in backfocus stability with these lenses would be if they were more thermally stable than the stock lens, but that seems unlikely if they use more metal and less plastic.

But hey, you never know if you don't ask.

[QUOTE=I've just discovered that my 16x has issues with the macro ring. It has some "play" in the locked position, and if touched it moves back and forth very slightly, which in turn affects the focus when zoomed out wide./QUOTE]

I have found some Macro play in all of the 16x's I've used. I try to turn it lightly to the OFF direction while adjusting (think of pinching the backfocus adjusting screw and the top of the macro button surround toward each other while adjusting) and before hitting record. At least it keeps everything in some kind of standard reference position. If I was smarter, maybe I would be using gaffer tape.

But then, I also wasn't smart enough to remember to check this play on the 20x I shot with for a few minutes a couple months ago. Nice glass btw.

Maybe some owners can chime in on this.

Does the macro ring on your 17x, 18x, 20x have free play when in the locked/off position?

June 9th, 2007, 09:26 AM	#1
George Strother Major Player Join Date: Jun 2006 Location: San Diego, CA Posts: 204	Is backfocus more stable on 17x, 18x, 20x ? Has anyone noticed if the backfocus is more stable using one of the upgrade lenses than it is using the the stock 16x? Probably no one has enough experience with all of these to know, but is there a most stable choice between the 17x, 18x and 20x? I have read that these lenses are easier to back focus, but haven't seen anything about frequency of readjustment.

June 9th, 2007, 09:59 AM	#2
Paolo Ciccone Trustee Join Date: Apr 2005 Location: Santa Cruz, CA Posts: 1,116	George, I used the 18x and didn't notice anything different about the backfocus. I doubt that there is a stability issue associated with the lens unless the backfocus ring has a problem in the locking mechanism. Backfocus needs to be adjusted frequently with any removable lens. Temperature changes can affect it. In fact many cinematographers advice to check the backfocus any time you move the camera. It's not the lens, it's the nature of the device. __________________ Paolo http://www.paolociccone.com Demo Reel

June 9th, 2007, 10:26 AM	#3
William Hess New Boot Join Date: Feb 2006 Posts: 20	It seems that some of the people who've upgraded to the 17x or 18x have reported that the backfocus ring is much better machined, and that they have fewer backfocus issues after upgrading their lens. If you do a search for 17x or 18x I believe you'll find many posts on the subject. I've just discovered that my 16x has issues with the macro ring. It has some "play" in the locked position, and if touched it moves back and forth very slightly, which in turn affects the focus when zoomed out wide. I've never had problems with the backfocus ring itself.

June 9th, 2007, 01:51 PM	#4
George Strother Major Player Join Date: Jun 2006 Location: San Diego, CA Posts: 204	[QUOTE=Backfocus needs to be adjusted frequently with any removable lens. Temperature changes can affect it. In fact many cinematographers advice to check the backfocus any time you move the camera. It's not the lens, it's the nature of the device.[/QUOTE] Paolo - I think you are right. I was just wondering if anyone had found an improvement in stablility. My usual practice is to carry eight 3-4 hour batteries, turn the camera on before I leave for a shoot, leave it turned on all day - even lunch, and always check the backfocus on a bigger screen at each setup. I know the main issue is the small chips, short backfocus distance, high camera temps and high thermal expansion of the camera casing/optical block mount material. I thought the only chance for an improvement in backfocus stability with these lenses would be if they were more thermally stable than the stock lens, but that seems unlikely if they use more metal and less plastic. But hey, you never know if you don't ask. [QUOTE=I've just discovered that my 16x has issues with the macro ring. It has some "play" in the locked position, and if touched it moves back and forth very slightly, which in turn affects the focus when zoomed out wide./QUOTE] I have found some Macro play in all of the 16x's I've used. I try to turn it lightly to the OFF direction while adjusting (think of pinching the backfocus adjusting screw and the top of the macro button surround toward each other while adjusting) and before hitting record. At least it keeps everything in some kind of standard reference position. If I was smarter, maybe I would be using gaffer tape. But then, I also wasn't smart enough to remember to check this play on the 20x I shot with for a few minutes a couple months ago. Nice glass btw. Maybe some owners can chime in on this. Does the macro ring on your 17x, 18x, 20x have free play when in the locked/off position?