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Joerg
24-Aug-2017, 11:13
Hi,
I'm brand new to large format photography and am looking at camera options. In the description of a Chinese rangefinder camera vendor, there is mention of a "Lens Knife." Googling the term doesn't lead to results. I gather it's a metal piece that matches the focus and/or field of view of the rangefinder camera to the lens as the bellows is adjusted. Since there is nothing on Google I'm guessing that "lens knife" is possibly not the correct term. Does above description sound familiar to anyone? Is there a different name? Is this something one has to make or have made for each focal lenght lens?
Thank you for any feedback!

Leigh
24-Aug-2017, 11:27
Hi Joerg, and Welcome Aboard.

I've never heard the term "lens knife", nor anything that might resemble that in translation.

Some rangefinders do rely on cams to control the movement of one of the mirrors.

- Leigh

Tracy Storer
24-Aug-2017, 12:01
Very probably a rangefinder cam specific to each lens focal length.

domaz
24-Aug-2017, 12:14
If Linhof rangefinder cams were actually knifes they would probably be illegal in some states. And forget getting on an airplane with it!

Oren Grad
24-Aug-2017, 12:29
Some rangefinders do rely on cams to control the movement of one of the mirrors.


Very probably a rangefinder cam specific to each lens focal length.

What Leigh and Tracy said - it's almost certainly referring to rangefinder cams. If you use plenty of imagination, the shape of the cams for the Linhof Technika rangefinder could arguably be described as resembling a knife.

Joerg
24-Aug-2017, 12:42
I was able to find a picture (see link below). Apparently, this brass part is made specifically to a focal length. The person who posted this picture called it a "focusing blade". The google result for "focusing blade" is the same as it is for "lens knife". I understand what this thing does (kinda), but I am trying to figure out how hard (if not impossible) it is to get something like this for a different focal length. It may be unique to just one camera though I'm thinking there are probably more out there using something like this.

http://photobucket.com/gallery/user/keechoon15/media/cGF0aDovMThfMDNfenBzdHprd2g5anAuanBn/?ref=
Any thoughts?

Oren Grad
24-Aug-2017, 13:03
There are repair technicians who are willing and able to carve cams for custom focal lengths. This is easiest to do if you want a cam for an existing system like Linhof or Horseman where cams in a wide range of focal lengths have been provided by the manufacturer, and matching a new focal length requires only modest adjustment to an existing blank or finished cam. If you have to start from scratch to come up with a cam for a very different focal length in a camera that is not based on an existing cam system, it will likely be more difficult, time consuming and expensive.

djdister
24-Aug-2017, 13:08
What Leigh and Tracy said - it's almost certainly referring to rangefinder cams. If you use plenty of imagination, the shape of the cams for the Linhof Technika rangefinder could arguably be described as resembling a knife.

Actually doesn't take too much imagination to think of it as a knife...
168743

John Layton
24-Aug-2017, 13:30
...now how about that lens sharpener?

Jim Andrada
24-Aug-2017, 13:56
Lens sharpener??? Isn't that what digicams do???

John Kasaian
24-Aug-2017, 16:03
What you'd use to turn a Dogmar into an Artar, perhaps?

Nodda Duma
24-Aug-2017, 16:32
...now how about that lens sharpener?

I once made a lens sharp by dropping an 8 inch calcium fluoride objective on the shop floor, but I don't think that's what you were referring to

Joerg
24-Aug-2017, 17:31
Thank you! Apparently "focusing cam" was the term I was looking for. Unfortunately neither Linhof nor Horseman cams look anything like the one in the picture, but clearly, that's what it is.