My lens has a spot on it, is there anything I can do?

[Brian Drysdale]

It doesn't look like aperture ramping, that gets darker as you zoom in, it doesn't get lighter and you don't have variations. As Paul suggests, it's probably the auto exposure system on the camera.

[Ryan Elder]

Oh okay, but what auto exposure system would that be, or is there a way to turn that off perhaps? I know it's not the ISO cause I had it locked on 800. Is there a way to turn off that system?

[Chris Hurd]

What camera is this again? Are we talking about the Canon EOS Rebel T2i?

[Ryan Elder]

Sorry, yes that one. It appeared to have the same problem on the sony a7s II though.

[Brian Drysdale]

Check your auto exposure settings on both cameras, go through the menu settings to ensure that the exposure is totally on manual. You may need to go through the camera manuals to find the required menus.

[Ryan Elder]

Yep its totally on manual. I dont have the sony now but the t2i is. What now though if its on all manual yet it still does that when zooming?

[Brian Drysdale]

Don't create a problem that may not exist, that's the purpose of the test to prove, If the camera is totally on manual exposure the characteristics of the lens can be seen, rather than the inputs from the camera's exposure system.

The exposure variations match the exposure system making adjustments, either that or the lighting is changing during your shot.

[Paul R Johnson]

Don't zoom, move the camera. Something is clearly causing it. The lens is changing the iris aperture or the gain of the camera is doing it. Has to be one or the other. You need to find out which it is.

This lens does seem to be a very unfriendly and uncontrolled beastie - all things considered, you need to get something better.

[Ryan Elder]

Okay thanks. Well I know it's the lens changing the exposure, cause I just borrowed the Sony A7s II to try it, with a couple of adapters. One of the adapters communicates with the lens, and the other is not electronic and does not.

The one that doesn't communicate the lens with the camera, the aperture is constant throughout the zoom and doesn't change. But with the adapter that does communicate with the camera, the aperture changes, even though it's on the same f stop setting throughout the zoom. So the lens being powered by the camera is causing the exposure changes, cause if you cut off the power between camera and lens, then the aperture is constant.

[Brian Drysdale]

That sounds a good reason why you should use dumb lenses for drama or other video work where you want total control of the exposure. Cine lenses don't have such auto exposure features (with a couple exceptions for use on the Arri 16 SR film camera - the mechanical control pins could get jammed if you changed the lens mount. It happened to me on a new Zeiss zoom lens, so they were removed by the dealer) .

The alternative is to get a dumb lens adapter, so that the lens doesn't communicate with the camera.

[Ryan Elder]

Okay thanks. But the problem with a dumb lens adapter is that you cannot control the aperture, if you want to change it, since the lens does not have an aperture ring.

Are there any adapters, where the power can be switched on and off, so that I or a DP can switch the aperture with the lens, but then turn off the power to the lens after?

[Brian Drysdale]

That's one reason why people were telling you to buy manual lenses for video work, otherwise you have to fool your camera's auto exposure system to get the stop you want.

ND or neutral density filters are the standard tools for getting the stop you want, since they don't change the shutter speed or the sensitivity in the process.

[Paul R Johnson]

Indeed, and any lens you cannot control manually is a real limitation. Real video lenses have a manual or auto switch for a very good reason.

Come on Ryan - time to retire that lens and buy something that can do what you need.

[Ryan Elder]

Okay sure but i thought it was the camera changing the exposure since the lens does not change it when not attached. Shouldnt i get a new camera tgat doesn't change the lens's exposure as you zoom?

[Brian Drysdale]

Many people on a budget buy used lenses, some of them prefer the older glass because of the look. Plus you can get lenses with an aperture ring.

Buying from an established dealer reduces the risks and, as I mentioned, will usually have a short warranty.

We were discussing aperture ramping, which is different to what the camera auto exposure does. If you wish to buy a camera that's designed/useful for digital cinema, you'll need lenses with aperture rings.