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T3i metering with preset long telephoto


I have a Canon T31 and a very good preset 500mm preset lens. In "live view" (mirror up) it exposes correctly. In normal (mirror down) overexposes by 1 or 2 stops. Metering mode is set to "evaluative" and everything else is equal. [Tripod and wired remote shutter release].

Any ideas?



I'd like to weigh in, if I may? 

Seeing as the lens is a Vivitar T-mount lens, the Rebel T3i has no idea what lens is connected to it (or that a lens is even connected). Even if you were to use an EF-adapter, my guess is that there are no electronics in this lens to communicate with the camera. In most cases, the camera will read "F00", like Wadizzle said above. That means either no lens is attached, or the camera doesn't recognize the lens.

We obviously haven't tested these lenses, so we can't guarantee anything, but we've found that they work best in fully manual mode, so  you can tell the camera what you're doing. Remember, the camera doesn't even know a lens is attached when you're looking through the viewfinder. 

On the flip side, when you use Live View, the camera's electronics doesn't know about the lens, however, it can tell optically that *something* is there. That means that it will expose the shot to the best of its ability.


That's why the "automatic" settings will be all over the map, and remember, we guarantee nothing when you're using a non-Canon, non-EF/EF-S lens. 

I hope that helps!

View solution in original post



What is the minimum aperture?

f8, but I was shooting at f11

oops. minimum aperture is f32


and shooting in AV mode.  Also, I noted that the 'live view' shot was iso 100, 1/100th, while the 'normal' shot was iso 120, 1/60th


iso was auto


If it is a 'preset' lens the aperture is fixed at f/8. So setting the camera to f/11 would throw themail metering of. Camera would meter expecting to lose a stop of light when the aperture stops down, but, it never does.

this is a preset Vivitar 500mm t-mount lens. I set the focus and the aperture manually, it was set to f11 and I was shooting at a subject that was effectively at infinity [3500 feet away] (the camera cannot change the aperture nor focus) & the live view image was perfectly exposed.

In live view the camera sets the amount of light without opening the lens to the max. In regular mode, the camera expects the lens to stop down *after* it sets the exposure, which is what fools the camera.


Add some exposure compensation to get pleasing results.

This raises a question:

I always thought that the exosure was set with the lens wide open, but how does the camera know the maximum aperture of the lens? Nowadays that is easy since the lens tells the camera the maximum aperture. But lenses have *always* worked this way, even before electronics. How did the all manual SLR's know that you had installed an F/1.8 vs an F/1.4?

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