10-11-2015 11:37 PM
I have a Canon T2i with 18 to 135 mm lens. I recently noticed it does not go below f/5.6. The widest aperture is f/3.5 at 18mm. I can narrow the aperture without any problems. I removed the lens from the camera and screwed it back in, but the problem is still there. I wonder what is causing the problem.
10-12-2015 07:48 AM
It isn't a f/3.5 lens. It's a f/3.5 - 5.6 lens. As you zoom out the minimum f/stop opening decreases.
It has always been like that; it's just that you just noticed it. Nothing wrong with lens or camera.
10-12-2015 09:29 AM
"The widest aperture is f/3.5 at 18mm."
And it is not a 20mm as jrhoffman says. It quickly loses that f-ratio as you zoom.
10-12-2015 12:49 PM
You can see the effect on the f/stop in "M" mode on the LCD. Adjust the zoom lens to its' minimum setting, and set the f/stop to its' minimum setting. Now re-adjust the zoom from minimum to maximum, and you should see the f/stop value change as you increase/decrease the zoom.
10-14-2015 11:20 AM
Whenever you see a lens' focal ratio listed as a "range" (e.g. f/3.5-5.6) instead of a single value (e.g. f/4) it means the lowest possible focal ratio really depends on the focal length (how far have you "zoomed" the lens.)
That means that at the 18mm end it can go as low as f/3.5. But at the 135mm end it can only go as low as f/5.6.
But it's not quite that even. It turns out variable zooms QUICKLY increase their focal ratio as you zoom in from the lowest focal length and roughly by the time you're half-way through the zoom range they are already at the high-end of the focal ratio range. In other words, you can use f/3.5 at 18mm... but probably by the time you make it to 60mm you'll already be at f/5.6 as your lowest possible focal ratio.
High end zooms can provide a constant focal ratio at any focal length. For example there's the EF-S 17-55mm f/2.8 IS USM which can provide an f/2.8 focal ratio at any focal length in the zoom range. There are lots of lenses that can do this, but they tend to be more expensive lenses. Less expensive zoom lenses are usually always variable focal ratio lenses.
10-17-2015 05:32 PM - edited 10-17-2015 05:38 PM
When the lens is attached to the camera, I can twist it around a little bit. When I do that, I can get the aperture down to f/3.5. I think there is some issue with the connector.
10-17-2015 07:20 PM