rob_x2004 Posted March 31, 2008 Share #1 Posted March 31, 2008 Advertisement (gone after registration) Two questions. Can anyone recomend an R lens adaptor for the 20D that will provide focus confirmation, presumably with the flash of the red rectangle or whatever canon use? Does the adaptor hold open the lens for exposure metering and focusing or does the lens close down as you roll through the apertures. Some members have mentioned pretty wild exposures when using adaptors. Link to post Share on other sites More sharing options...
Advertisement Posted March 31, 2008 Posted March 31, 2008 Hi rob_x2004, Take a look here EOS 20D bayonet adaptor. . I'm sure you'll find what you were looking for!
stunsworth Posted March 31, 2008 Share #2 Posted March 31, 2008 The lens closes down as you change the aperture. I'm not so sure about the 'wild' exposure claim, I used R lenses with Canon DSLRs for 3 years or so. The 5D did have some minor issues with overexposure as the lens was stopped down, but that was cured by dialling in a permanent -2/3 stop compensation. I never noticed any issues with a 300D or 20D. The only focus confirmation adaptor I bought fell apart after a couple of weeks, so I can't offer any advice in that area. Link to post Share on other sites More sharing options...
rob_x2004 Posted March 31, 2008 Author Share #3 Posted March 31, 2008 The on board camera meter would be used to reading the light coming through a canon lens held open at widest aperture. If the lens stops down down isnt the camera going to assume it is darker than it actually is, leading to overexposure, specially at f/8,16? Is something else going on I dont understand? Dialing in negative EV seems a pretty meatball sort of solution? Link to post Share on other sites More sharing options...
stunsworth Posted March 31, 2008 Share #4 Posted March 31, 2008 No, asuming the camera is being used in aperture priority mode the meter reads the light when the shutter is pressed, so the fact that the aperture is open or closed is irrelevant. It's the amount of light falling on the meter that's important, not the aperture. Since there's no mechanical or electrical linkage the body doesn't have a clue what aperture has been selected, it only knows how much light it's seeing and adjusts the shutter accordingly. Similarly if shooting manually, you need to take a meter reading with the lens stopped down. I agree that in fully manual mode if you metered with the lens wide open and then stopped down you'd get an underexposed image. Not sure if a 'meatball solution' is meant to be good or bad, but it worked and meatballs can be tasty. Link to post Share on other sites More sharing options...
rob_x2004 Posted March 31, 2008 Author Share #5 Posted March 31, 2008 ....the meter reads the light when the shutter is pressed, ......Similarly if shooting manually, you need to take a meter reading with the lens stopped down. I agree it is nothing to do with the f/stop per se, but I figured the meter was working and computing exposures based on available light while the lens was wide open, and while there is enough area to properly expose teh on board meter at wider apetures, and I figured that once you close way down meter readings might be problematic. Good to hear, if that is not the case. How come in any mode, when you reach the shutter detent it will give you meter readings, and display shutter and f/stop, or, in the case of manual mode, tell you what your exposure is and whether you have to dial in more or less aperture or shutter speed. All this is done with the lens held fully open untill the iris closes down and the shutter is released. The lens only closes down after you press teh shutter relase. Be good to find an adaptor with confirmation. I dont think the 20D has a split screen or if it has, whether you can see it. You dont need an overly bright finder with autromanticfocus. A good canon lens is probably cheaper than an adaptor anyway;)...but I would like to give my R lenses something to do. Link to post Share on other sites More sharing options...
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