Canon T2i brightness shifting

Shane Ross

Shane Ross

Veteran
I have the camera in full manual mode...even the ISO is set to a manual setting. But still, when I zoom in and out the brightness of the image shifts, and not smoothly. Noticeable STEP-STEP-STEP in brightness shifting. Now, originally I thought it was the f-stop shifting, because wide open it will have a different setting then zoomed in. So I zoom in and set the F-Stop to that setting. But still, I zoom out and step-step-step of brightness shifting.

Anyone else notice this? Is there a setting I am missing? Shutter speed, F-Stop, ISO...those are all locked off.
 
Its the lens. What lens are you using? Some zoom lenses have a physical aperture shift when you zoom. The camera can't do anything about it.

Here are a few ways to avoid it:
1)Don't zoom during your shots
2)Use a constant aperture lens
3)Use a prime lens
 
The steps should be the camera re-adjusting the aperture. Canon hasn't implemented this in a smooth fashion and it might be because the aperture servos in their lenses aren't designed for smooth operation. If you rotate the lens enough for the electrical contacts to disengage but still leaving the lens attached to the camera, you should be able to zoom and get a gradual shift in exposure since the camera will no longer be actively trying to adjust the aperture. Even in manual aperture mode, the camera will adjust the aperture when it detects a zoom change. Canon should really change that for video as it makes no sense. For stills it works though.
 
It's the stock 18-55 lens. And this makes sense. So, ANY zoom lens will do this? That's BAD. In video settings, we need to ZOOM.

Thanks,
 
Shane Ross said:
It's the stock 18-55 lens. And this makes sense. So, ANY zoom lens will do this? That's BAD. In video settings, we need to ZOOM.

Thanks,
Click to expand...
Not all zoom lenses, just the ones with variable aperture and autofocus and native EOS mount. For instance, a variable aperture manual focus Nikon lens adapted to EF mount will gradually change exposure as you zoom.

Also, you don't need to zoom during your shots. There are plenty of folks here who have high end zoom lenses that don't have this problems and yet choose not to zoom due to personal taste.
 
I have the same lens. This is just how lens operates. What is happening is when you are at 18mm you can have a 3.5 aperture, when you zoom in there is a minimum on the lens at each focal length for the aperture. So when you are totally zoomed in at 55mm you cannot have a 3.5 aperture opening it has to be closed at a minimum of 5.6f. This is just the way the lens works. You cannot have a 3.5f at 55mm on that lens. Nothing wrong with it or the camera. Correct me anybody if I am wrong.
 
Grab a Tamron 17-50 f2.8 or Canon 70-200 f4L/f2.8L lens if zoom is absolutely necessary. They are constant aperture and shouldn't result in problems with brightness.
 
Thanks guys. Since this is my home video camera too, zooming is necessary. BUT, because it is a home video camera, I can live with the brightness shift too.
 
Here's another extremely important thing that you need to know about zoom lenses: There are two different kinds that are casually called "zoom." A true zoom lens is a "parfocal lens," which will maintain focus throughout its range. But there's also the "varifocal" lens, which does not maintain focus as you change focal length. In the still photo world, most "zoom" lenses are varifocal. Varifocal lenses are easier and cheaper to design and make. Photographers don't generally care about this, since they don't need to change focus in the middle of a shot, and autofocus helps them quickly find focus for a still.

BTW, Shane: You didn't notice the aperture value changing on the LCD display? Or did you have the overlay disabled for video recording?
 
Has anyone put together a list of Parfocal lenses? And for that matter, how can you tell? Obviously if you have the lens you can check, but I mean when looking at new lenses? I've been looking on the sigma site and I can't see any mention of it. I have a 24 - 70mm f2.8 from sigma that is parafocal, but I don't know about the 70 -200mm f2.8

thanks.
 
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