Karl in NY 0 Posted January 27, 2007 I just got my first network camera capable of using interchangeable CS- or C-Mount lenses. (Arecont 2100). However, when I mount any of my older C-mount zoom lenses (using the necessary 5mm spacer, of course, to convert to the CS mount), the zooms behave as varifocals...whenever I zoom, I have to refocus. I'm not talking about a slight correction, but a major refocus. All of my 2/3" and 1/2" format C-Mount zoom lenses (mostly older models like the Canon 17-102mm V6x17) are acting as varifocals. I can focus at any focal length, but without focus-tracking while zooming... Is this typical of using C-Mount zooms on a CS-mount camera with a 5mm spacer? Any wisdom would be appreciated. Share this post Link to post Share on other sites
kensplace 0 Posted January 27, 2007 Sounds like you need to backfocus, do a search on back focusing on the forum and or google and you should find some guides on how to do it. Once you have backfocused the lens, the problem should go away, unless the lens is dodgy... Share this post Link to post Share on other sites
Karl in NY 0 Posted January 27, 2007 The camera does not have any lens-mount adjustment...my only recourse is to use shims, like 0.5 mm, which permits focus from both least to greatest focal length, but still without focus-tracking as the lens is zoomed... Share this post Link to post Share on other sites
kensplace 0 Posted January 27, 2007 No lens mount adjustment? How do they expect people to backfocus lenses? Its a pretty basic requirement. Have you checked the manual, maybe its software controlled or something, find it hard a camera wont allow lens adjustment. But then again its a megapixel cam, so maybe they have not heard of it.. Share this post Link to post Share on other sites
Karl in NY 0 Posted January 28, 2007 The Arecont camera has no hardware or software backfocus provision...the OEM lens (a CS-Mount Computar 4.5-12.5 f1.2) had a shim ring behind it, less than a mm in thickness. Share this post Link to post Share on other sites
kensplace 0 Posted January 28, 2007 I would send a email to the manufacturers, ask them how to backfocus a lens. Would be interesting to see what they reply. They advertise it as having a c/cs mount, and if it cant be back focused I would say that they are selling goods not fit for purpose, so you would have a right to complain - loudly... Share this post Link to post Share on other sites
CollinR 0 Posted January 28, 2007 I have had to use shims before. Share this post Link to post Share on other sites
rory 0 Posted January 28, 2007 ask them what lens the camera takes, and buy the right one .. It may not work with an (old) C Mount lens regardless of advertising. I dont think the camera is cheap ... quality of the camera will depend on the quality of the lens.. if the lens is old it is best to replace it. How old are these lenses exactly? If it were 5 years or more older, id definitely change it. Share this post Link to post Share on other sites
Karl in NY 0 Posted January 28, 2007 I'm coming to the conclusion that C-mount zoom lenses, when mounted on a CS-mount camera (with the necessary 5 mm ring) behave as varifocals and not true zooms. Of the three I have tried, all have done the same thing, but at least they will focus over their entire zoom range. The lenses are very usable that way, but just not as convenient having to refocus after each zoom. Share this post Link to post Share on other sites
vitHoward 0 Posted February 8, 2007 The engineers at Arecont are great technology people. (I love their cameras.) But they failed to check with the folks in the real world to see how we live. If properly back-focused, a zoom lens focused on a object will stay in focus throughout the range of the focal length. In practice, a very minor change in the distance from the imager to the lens will greatly effect the back-focus. Arecont has promised to address the situation. Unfortutely, when it comes to zoom lenses, we're pretty much screwed unless we're lucky enough to grab the right shim. By the way, I found an assortment of "shims" at a plumbing store. They're the washers used around faucet stems. They come in a lot of sizes and thicknesses. I grabbed a handfull last time I was in... just in case. Hope this helps, Howard Kohnstamm www.videoguardit.com Share this post Link to post Share on other sites
