T2i Taking Overexposed Pictures than Previewed

[soulmaster846]

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.

Please help!

[ScottyP]

I don't think the Rokinon lens communicates its aperture to the camera, does it? I mean, they actually sell little chips you can glue onto the metal mount that add that capability.

If the lens can't tell the camera what aperture it is on, that will make a false histogram, right? I considered buying their 14mm and in researching I've seen google and Google videos about the add-on chip. I'd suggest checking Google and see if that is the answer. The chips are only like $20 or so and I am not kidding when I say you just glue it on.

[TCampbell]

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.

[soulmaster846]

Thank you guys for the quick response!

So my Rokinon lens is not electronically linked with my camera. It doesn't even have any electronics on it. Yes, the aperture blades are still functional. I see them moving whenever I turn the aperture ring. The screen still does change in accordance to how I switch the f-stop, though it is not as "sensitive" to the change as much as the first day I've shot with it.

This is so weird because the screen was giving me the right exposed picture throughout all the first day I was shooting it. In other words, I was able to trust my screen and histogram on the first day. Then the next day, every picture that was displayed ON the screen was too dark. So in the result of that, the histogram OF the screen shows an underexposed graph.

For example: let's say that I am shooting a subject that will be properly exposed at a shutter speed of 1/60th, f2.8, and ISO 400 (I'm throwing random numbers for the sake of it). Then I set my camera to those factors. Instead of showing a properly exposed subject, my screen and its histogram shows a very underexposed preview instead. Once I snap the picture, the resulting photo will be properly exposed. It wasn't like this the first day. The screen on the first day always showed the accurate depiction.

The meter on the viewfinder seems correct, but I don't like using the viewfinder. The screen seems to display accurately whenever I set the ISO or shutter to auto, but again-I hate auto.

I hope this hones down the possible problem!

[RobertTheFat]

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.