EX3 Flange to Focal Plane in-air distance. at DVinfo.net

Bob Hart · February 28th, 2009, 12:23 AM

Does anyone know the flange to focal plane "in-air" distance for the EX3 lens system?

Alastair Traill · February 28th, 2009, 05:32 AM

Hi Bob,
I recently made a Nikon adapter for for EX3 using a my shortest Nikon lens as a guide. The Nikon flange to EX3 flange distance ended up at ~ 16.61 mm. According to Wikipedia the Nikon flange to film plane distance is 46.5 mm. The "in air" distance for the EX3 flange to sensor distance will be the difference in the two measurements i.e. 29.89 mm. I do not know what you want the measurement for, if it is for a long focal length lens the distance is nothing like as critical as for a short lens where the depth of focus is next to zero. If you are making a mount i would recommend using a collimator to check your work. I can provide you with a simple formula, (if required) with which you can calculate how much too long your mount is if it is too long - this facilitates final machining.

Bob Hart · February 28th, 2009, 05:41 AM

Alistair.

Thanks you for your response.

I'm looking to make up a mount for the EX3 Letus relay for Letus Extreme to the SI2K's IMS mount system. I will provide for shim adjustment. The B4 Letus relay will be a turnkey solution for aquiring the standard movie frame from the groundglass on the Letus Ultimate.

My objective is to pull in a little more detail by going wider on the larger groundglass of the Extreme by using the wider view of a 2/3" sensor through this 1/2" relay. Hopefully the exit pupil will be wide enough and there won't be edge softness. It will be an abuse of the design for the Letus EX3 relay which is tailored for a 1/2" sensor but I may strike it lucky.

I'll be using a Mini35 with its own IMS mount system as a collimation projector, rough and ready method but the P+S build quality will get me by as it has already with modding other lenses. If anyone ever does this, do not run the projection lamp for any longer than about 30 seconds at a time over a five minute cycle, otherwise you may crack the prisms or the adjustable mirror in the flip enclosure.

February 28th, 2009, 12:23 AM	#1
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,477	EX3 Flange to Focal Plane in-air distance. Does anyone know the flange to focal plane "in-air" distance for the EX3 lens system?

February 28th, 2009, 05:41 AM	#3
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,477	Alistair. Thanks you for your response. I'm looking to make up a mount for the EX3 Letus relay for Letus Extreme to the SI2K's IMS mount system. I will provide for shim adjustment. The B4 Letus relay will be a turnkey solution for aquiring the standard movie frame from the groundglass on the Letus Ultimate. My objective is to pull in a little more detail by going wider on the larger groundglass of the Extreme by using the wider view of a 2/3" sensor through this 1/2" relay. Hopefully the exit pupil will be wide enough and there won't be edge softness. It will be an abuse of the design for the Letus EX3 relay which is tailored for a 1/2" sensor but I may strike it lucky. I'll be using a Mini35 with its own IMS mount system as a collimation projector, rough and ready method but the P+S build quality will get me by as it has already with modding other lenses. If anyone ever does this, do not run the projection lamp for any longer than about 30 seconds at a time over a five minute cycle, otherwise you may crack the prisms or the adjustable mirror in the flip enclosure. Last edited by Bob Hart; February 28th, 2009 at 05:46 AM. Reason: error

February 28th, 2009, 05:32 AM	#2
Alastair Traill Major Player Join Date: Nov 2008 Location: Melbourne Australia Posts: 626	Hi Bob, I recently made a Nikon adapter for for EX3 using a my shortest Nikon lens as a guide. The Nikon flange to EX3 flange distance ended up at ~ 16.61 mm. According to Wikipedia the Nikon flange to film plane distance is 46.5 mm. The "in air" distance for the EX3 flange to sensor distance will be the difference in the two measurements i.e. 29.89 mm. I do not know what you want the measurement for, if it is for a long focal length lens the distance is nothing like as critical as for a short lens where the depth of focus is next to zero. If you are making a mount i would recommend using a collimator to check your work. I can provide you with a simple formula, (if required) with which you can calculate how much too long your mount is if it is too long - this facilitates final machining.