Flange focal length

Jun Tang · October 22nd, 2005, 10:15 AM

Now that I'm experimenting with the 35mm adapter, and with different lenses, I've run into terms such as flange focal length.

I'm trying to get a better understanding. Is there a website or books that can help explain it in detail?

Joshua Provost · October 24th, 2005, 01:34 PM

The flange focal length is the distance from the backplane of the lens to the plane of the film.

A. J. deLange · October 25th, 2005, 05:51 AM

The flange focal length is the distance from the lens rear flange to the point at which the lens focuses. The object is to get that point coincident with the film plane or CCD plane and that's what back focus adjustment is all about. The best place to learn about stuff like this is a good text like Sidney Ray's "Applied Photographic Optics" (Focal Press) which isn't too geeky.

Jun Tang · October 25th, 2005, 05:58 AM

Hey Joshua and A.J.

Thanks.

I want to know or find out the ffl length of each lens that I am looking to buy. Of course I can get that on the manufacture website/info. I'm trying to learn what happens when the flange focal length doesn't match.

I read that you can use a lens that require a longer ffl on a mount (in my case micro35, not a film camera) with an extender or adapter. While if your lens had a shorter ffl, you can't use it on a longer distant.

tHanks for the book.

I'm looking to experiment a few different lenses using the micro and see what are the results. thanks for your help. I'm waiting for the andromeda to do some lens testing.

Joshua Provost · October 25th, 2005, 10:46 AM

JT,

Try this camera mounts & registers page. Register is the same as flang focal length.

Yes, you are correct, you can usually extend the FFL, but you cannot shorten it. If you move it at all, the focus markings on the lens will not be accurate, but you can still manually focus.

Josh

A. J. deLange · October 25th, 2005, 12:40 PM

You can use lenses with shorter FFL's than the camera but an adapter with a relay lens is required. Example: the Mini35.

Jun Tang · October 25th, 2005, 12:45 PM

Hey Joshua and A.J.

Once again, thanks. Very much appreciated.

Where did you get the link Joshua... did you Super Google that site. I tried, but nothing like that came up. It is now bookmarked.

A.J, that is definitely something I don't know about. I've never worked with the mini. Is that something you can use and adopt for say the micro35?

A. J. deLange · October 25th, 2005, 07:44 PM

Actually it is a competing device. It works by using a 35 mm lens to project an image onto a ground glass. A relay lens then transfers that image to the CCDs in the video camera. I don't know enough about the micro35 to figure out what it does but it appears to be similar.

To make such devices useful with a combination of lenses and cameras it would be necessary to have adapters for the taking lenses to bring their focal points to the proper position with respect to the relay system in whatever form that might take and adapters for the cameras to bring the relayed image onto the CCD's. The adapters could, theoretically in the case of a very short BFD lens, contain relay lenses or, in the case of longer BFD lenses be essentially nothing more than spacers. I would expect the manufacturer of the micro35 to have a list of taking lenses and cameras with which the device can be used. A quick look at their website was not too revealing in this regard.

October 22nd, 2005, 10:15 AM	#1
Jun Tang Regular Crew Join Date: Sep 2004 Location: West LA Posts: 135	Flange focal length - resources? Now that I'm experimenting with the 35mm adapter, and with different lenses, I've run into terms such as flange focal length. I'm trying to get a better understanding. Is there a website or books that can help explain it in detail?

October 24th, 2005, 01:34 PM	#2
Joshua Provost Major Player Join Date: Sep 2004 Location: Phoenix, AZ Posts: 493	The flange focal length is the distance from the backplane of the lens to the plane of the film. __________________ Owner/Operator, 727 Records Co-Founder, Matter of Chance Productions Blogger, Try Avoidance

October 25th, 2005, 10:46 AM	#5
Joshua Provost Major Player Join Date: Sep 2004 Location: Phoenix, AZ Posts: 493	JT, Try this camera mounts & registers page. Register is the same as flang focal length. Yes, you are correct, you can usually extend the FFL, but you cannot shorten it. If you move it at all, the focus markings on the lens will not be accurate, but you can still manually focus. Josh __________________ Owner/Operator, 727 Records Co-Founder, Matter of Chance Productions Blogger, Try Avoidance

October 25th, 2005, 05:51 AM	#3
A. J. deLange Major Player Join Date: Jun 2004 Location: McLean, VA United States Posts: 749	The flange focal length is the distance from the lens rear flange to the point at which the lens focuses. The object is to get that point coincident with the film plane or CCD plane and that's what back focus adjustment is all about. The best place to learn about stuff like this is a good text like Sidney Ray's "Applied Photographic Optics" (Focal Press) which isn't too geeky.

October 25th, 2005, 05:58 AM	#4
Jun Tang Regular Crew Join Date: Sep 2004 Location: West LA Posts: 135	Hey Joshua and A.J. Thanks. I want to know or find out the ffl length of each lens that I am looking to buy. Of course I can get that on the manufacture website/info. I'm trying to learn what happens when the flange focal length doesn't match. I read that you can use a lens that require a longer ffl on a mount (in my case micro35, not a film camera) with an extender or adapter. While if your lens had a shorter ffl, you can't use it on a longer distant. tHanks for the book. I'm looking to experiment a few different lenses using the micro and see what are the results. thanks for your help. I'm waiting for the andromeda to do some lens testing.

October 25th, 2005, 12:40 PM	#6
A. J. deLange Major Player Join Date: Jun 2004 Location: McLean, VA United States Posts: 749	You can use lenses with shorter FFL's than the camera but an adapter with a relay lens is required. Example: the Mini35.

October 25th, 2005, 12:45 PM	#7
Jun Tang Regular Crew Join Date: Sep 2004 Location: West LA Posts: 135	Hey Joshua and A.J. Once again, thanks. Very much appreciated. Where did you get the link Joshua... did you Super Google that site. I tried, but nothing like that came up. It is now bookmarked. A.J, that is definitely something I don't know about. I've never worked with the mini. Is that something you can use and adopt for say the micro35?

October 25th, 2005, 07:44 PM	#8
A. J. deLange Major Player Join Date: Jun 2004 Location: McLean, VA United States Posts: 749	Actually it is a competing device. It works by using a 35 mm lens to project an image onto a ground glass. A relay lens then transfers that image to the CCDs in the video camera. I don't know enough about the micro35 to figure out what it does but it appears to be similar. To make such devices useful with a combination of lenses and cameras it would be necessary to have adapters for the taking lenses to bring their focal points to the proper position with respect to the relay system in whatever form that might take and adapters for the cameras to bring the relayed image onto the CCD's. The adapters could, theoretically in the case of a very short BFD lens, contain relay lenses or, in the case of longer BFD lenses be essentially nothing more than spacers. I would expect the manufacturer of the micro35 to have a list of taking lenses and cameras with which the device can be used. A quick look at their website was not too revealing in this regard.