07-23-2015 01:32 AM
I've been using the t2i for about a year now, and it has been working great for me. Quite recently I've bought a Rokinon 85M-C 85mm F1.4 lens. I've used it for one whole day, and it worked great. The next day my cmaera have been taking overexposed pictures everytime I use the lens, yet the problem doesn't happen whenever I use my other lenses like my Canon 50mm f1.8.
I ALWAYS use the manual mode. I always keep track of my ISO, shutter speed, and aperature. I use the histogram constantly. I point to the subject, properly adjust the exposure, check the histogram, and snap the picture. Then I check my picture to see that it is more exposed than it should be. Given the histogram of that resulting picture shows that it got over exposed. In order to get the proper picture with the Rokinon lens, I will have to underexpose in the preview and GUESS if it will be right or not. Setting the ISO or shutter speed to auto can work, but I hate using auto settings.
I have reset my camera settings, but the problem presist. My metering mode is set to evaluative, so I don't think that the mode is the problem. My camera itself does not control the aperture of the Rokinon lens. The lens itself has the aperature ring.
07-23-2015 05:22 AM - edited 07-23-2015 05:26 AM
07-23-2015 08:28 AM - edited 07-23-2015 08:32 AM
This sounds like the aperture blades aren't working. When you rotate the aperture ring on the lens, do you see the blades constricting (you can likely see it if you look into the front of the lens.) Also... if you're looking through the viewfinder while you do this, you should notice the iamge is getting darker.
With an EOS lens you can press the "depth-of-field preveiw" button on the camera (the DOF Preview is on the front of the camera located just below the lens release button.) The blades will only constrict while you keep the button pressed. But since the Rokinon doesn't have electronics to control that, it wont respond to the DOF Preview button.
Incidentally, since you are using the Rokinon manual lens... be very careful about trusting the meter. Is the lens chipped at all (are there electronics?) Does the camera actually know and report the f-stop that the lens is using? If not, then you can't trust metering. If one lens' "wide open" is f/4 and a different lens' "wide open" is f/2.8 ... but the shot actually calls for using f/8 at your chosen shutter and ISO, the camera needs to be able to know what the current f-stop is when it is tryng to meter.
I take images with my camera through the telescope, but when doing so I realize there is aboslutely no communication to the telescope ... you can't use the meter at all. It's completely manual. If the Rokinon lens isn't chipped and can't report it's current f-stop to the camera (e.g. when you look at the camera's f-stop while changing the aperture, do you see the f-stop value updating on the camera's display screen?) then you can't trust the meter.
07-23-2015 12:35 PM
07-23-2015 03:07 PM
I'm guessing that the observed behavior is a function of whether the Rokinon is or isn't a preset lens, of whether the camera knows that it is or isn't, and of whether the camera is or isn't triggering the preset mechanism correctly in live view mode and/or when using the viewfinder. Answering those questions may provide a path to understanding what's going on.