topic Re: Canon T2i and 18 to 135 Lens Problem in EF & RF Lenses

Canon T2i and 18 to 135 Lens Problem

OrionNebula — Mon, 12 Oct 2015 03:37:11 GMT

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.

Re: Canon T2i and 18 to 135 Lens Problem

jrhoffman75 — Mon, 12 Oct 2015 11:48:17 GMT

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.

Re: Canon T2i and 18 to 135 Lens Problem

ebiggs1 — Mon, 12 Oct 2015 13:29:17 GMT

"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.

Re: Canon T2i and 18 to 135 Lens Problem

Waddizzle — Mon, 12 Oct 2015 16:49:20 GMT

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.

Re: Canon T2i and 18 to 135 Lens Problem

TCampbell — Wed, 14 Oct 2015 15:20:22 GMT

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.

Re: Canon T2i and 18 to 135 Lens Problem

OrionNebula — Sat, 17 Oct 2015 21:38:02 GMT

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.

Re: Canon T2i and 18 to 135 Lens Problem

jrhoffman75 — Sat, 17 Oct 2015 21:47:34 GMT

Is it a plastic mount lens? Could be damaged.

Re: Canon T2i and 18 to 135 Lens Problem

OrionNebula — Sat, 17 Oct 2015 22:54:15 GMT

How could it be damaged? I think it might be plastic. Is there a way to fix it?

Re: Canon T2i and 18 to 135 Lens Problem

jrhoffman75 — Sat, 17 Oct 2015 23:20:46 GMT

If you can twist the lens it means either the lens pin on the camera is sticking or the lens mount is loose. If you can hear a click when you mount lens and twist to install the pin is free and engaging.

Maybe the lens was bumped and the mount got damaged.

If it's the lens it's not worth fixing. Can you get to a camera store or with someone knowledgeable who can take a look at your gear?