Back focus adjustment on the F3 at DVinfo.net

Pieter de Vries · March 30th, 2011, 12:42 AM

The flange depth of the F3 can be tweaked with an allen key using the adjustment screw by the lens mount. I presume that this distance has been set in the factory. PL mount lenses, being top of the pile are calibrated to a set distance before they go out so that they all back focus correctly regardless of the camera used ie. Arri and Aaton film cameras.

With say a Sony HDCAM using a 2/3 inch sensor, there is a requirement to fine-tune the backfocus at the rear of the zoom lens itself on a regular basis. I've found that hot or cold conditions can affect back focus notably with lenses using softer lens compounds like Flourite glass.

Can I mount a swag of different lenses with a dog's breakfast of mounts; PL, F mount, Nikon, Canon, Voigtlander onto the F3 and be confident that they are all back focussing absolutely spot on? At this level of rez there is no room for doubt - wide angle lenses at T2 are very prone to back focus error as we know.

I'm aware that large sensors are less prone to back focus error, but will this mean that the flange depth on the camera body may have to adjusted for some lenses if they don't find infinity? There are a lot of variables in an video camera body especially when using lens mount adaptors which introduce another point for error.

Alister Chapman · March 30th, 2011, 01:29 AM

Backfocus adjustment is required for zoom lenses. With prime lenses, provided the flange back distance is reasonably accurate then any small error only shows up in a very slight difference in the position of the focus ring relative to the focus marks on the lens. After all, the only thing the focus ring is doing with most primes is altering the distance between the lens and the sensor, ie adjusting the flange back distance.
However with a zoom lens, back focus must be adjusted to match the lens as if it is wrong then focus will alter through the zoom range. So it is only really an issue with parfocal zoom lenses.

Brian Drysdale · March 30th, 2011, 01:32 AM

Mount adapters have been used for many years on film cameras. but these have been manufactured to tight tolerances. However, I wouldn't hold my breath over $20 adapters on ebay matching the required standard, so buy quality adapters.

You should test your lenses, so that you know if any have back focus issues and then get that particular lens set up by a lens technician if there's a problem. You should be able to switch your lenses without touching the back focus on the camera.

I expect we'll hear if the F3 mount itself is prone to drifting due to temperature variations etc as people start to use them. I know people use the RED without touching its back focus after it's set at the rental house.

Tony Partamian · March 30th, 2011, 05:33 AM

Hi Alister

it was really a pleasure meeting you last week in Dubai...and the session very helpful.

I just received a old Lomo 200mm lens from a friend and it's a nice lens by what i read.
Problem is it's not PL mount, does a PL to Lomo exist? is it really worth it?

I attached the pictures of the lens, your thoughts are very valuable.

David C. Williams · March 30th, 2011, 06:08 AM

PL to OCT-19 doesn't exist, flange depth and diameter are too great on the OCT-19. BUT, F3 to OCT-19 does exist. I can't vouch for the quality though...

Konvas LOMO OCT19 OCT 19 to Sony PMW-F3 F3 adapter | eBay

Tony Partamian · March 30th, 2011, 10:42 AM

Thanks David, seems a good quality product.

But the question remains....is the 200mm Lomo worth it?

March 30th, 2011, 12:42 AM	#1
Pieter de Vries New Boot Join Date: Mar 2011 Location: Sydney AUSTRALIA Posts: 22	Back focus adjustment on the F3 The flange depth of the F3 can be tweaked with an allen key using the adjustment screw by the lens mount. I presume that this distance has been set in the factory. PL mount lenses, being top of the pile are calibrated to a set distance before they go out so that they all back focus correctly regardless of the camera used ie. Arri and Aaton film cameras. With say a Sony HDCAM using a 2/3 inch sensor, there is a requirement to fine-tune the backfocus at the rear of the zoom lens itself on a regular basis. I've found that hot or cold conditions can affect back focus notably with lenses using softer lens compounds like Flourite glass. Can I mount a swag of different lenses with a dog's breakfast of mounts; PL, F mount, Nikon, Canon, Voigtlander onto the F3 and be confident that they are all back focussing absolutely spot on? At this level of rez there is no room for doubt - wide angle lenses at T2 are very prone to back focus error as we know. I'm aware that large sensors are less prone to back focus error, but will this mean that the flange depth on the camera body may have to adjusted for some lenses if they don't find infinity? There are a lot of variables in an video camera body especially when using lens mount adaptors which introduce another point for error. Last edited by Pieter de Vries; March 30th, 2011 at 02:00 PM.

March 30th, 2011, 01:29 AM	#2
Alister Chapman Inner Circle Join Date: Dec 2005 Location: Bracknell, Berkshire, UK Posts: 4,957	Re: Back focus adjustment on the F3 Backfocus adjustment is required for zoom lenses. With prime lenses, provided the flange back distance is reasonably accurate then any small error only shows up in a very slight difference in the position of the focus ring relative to the focus marks on the lens. After all, the only thing the focus ring is doing with most primes is altering the distance between the lens and the sensor, ie adjusting the flange back distance. However with a zoom lens, back focus must be adjusted to match the lens as if it is wrong then focus will alter through the zoom range. So it is only really an issue with parfocal zoom lenses. __________________ Alister Chapman, Film-Maker/Stormchaser http://www.xdcam-user.com/alisters-blog/ My XDCAM site and blog. http://www.hurricane-rig.com

March 30th, 2011, 01:32 AM	#3
Brian Drysdale Inner Circle Join Date: Feb 2006 Location: Belfast, UK Posts: 6,154	Re: Back focus adjustment on the F3 Mount adapters have been used for many years on film cameras. but these have been manufactured to tight tolerances. However, I wouldn't hold my breath over $20 adapters on ebay matching the required standard, so buy quality adapters. You should test your lenses, so that you know if any have back focus issues and then get that particular lens set up by a lens technician if there's a problem. You should be able to switch your lenses without touching the back focus on the camera. I expect we'll hear if the F3 mount itself is prone to drifting due to temperature variations etc as people start to use them. I know people use the RED without touching its back focus after it's set at the rental house.

March 30th, 2011, 05:33 AM	#4
Tony Partamian Regular Crew Join Date: Oct 2006 Location: Lebanon Posts: 51	Re: Back focus adjustment on the F3 Hi Alister it was really a pleasure meeting you last week in Dubai...and the session very helpful. I just received a old Lomo 200mm lens from a friend and it's a nice lens by what i read. Problem is it's not PL mount, does a PL to Lomo exist? is it really worth it? I attached the pictures of the lens, your thoughts are very valuable. Attached Thumbnails

March 30th, 2011, 06:08 AM	#5
David C. Williams Major Player Join Date: Jun 2008 Location: melb.vic.au Posts: 447	Re: Back focus adjustment on the F3 PL to OCT-19 doesn't exist, flange depth and diameter are too great on the OCT-19. BUT, F3 to OCT-19 does exist. I can't vouch for the quality though... Konvas LOMO OCT19 OCT 19 to Sony PMW-F3 F3 adapter \| eBay __________________ www.davidwilliams.com.au

March 30th, 2011, 10:42 AM	#6
Tony Partamian Regular Crew Join Date: Oct 2006 Location: Lebanon Posts: 51	Re: Back focus adjustment on the F3 Thanks David, seems a good quality product. But the question remains....is the 200mm Lomo worth it?