90D and Canon 300mm f4 L IS USM inconsistencies in exposure

[Wandalynn]

I wanted to see if (1) anyone else has had this problem and (2) if there are any fixes. First, let me say that my Canon 300mm lens has worked perfectly on my 70D, my 6Dii, and my R cameras. Add to that that all of my other Canon lenses perform perfectly with the 90D. I almost exclusively shoot in AV mode, mostly nature closeups, and mostly use evaluative metering, sometimes spot.  Taking pictures with the 90D + 300 through the VF, almost all of them are severely underexposed, almost black. Taking pictures with same lens using Live View, the exposure is fine. Again, that never happens with my other lenses on this camera, and I have no problems with this lens on my other cameras. Input appreciated.

[kvbarkley]

Does it work in manual mode?

I would try manual mode with the meter and then with the "sunny 16" rule.

[Wandalynn]

I haven't tried manual yet but will. Thanks.

[jrhoffman75]

"Taking pictures with same lens using Live View, the exposure is fine. "

Is the LCD showing the same exposure triangle setting (shutter speed, aperture and ISO) with Live View and optical view finder? Different exposure metering is taking place.

[Wandalynn]

The shutter speed has been slower in Live View but when using Auto ISO in AV, both VF and LV will mostly select 100, which I've been upping to 200-400 depending on what I think is more appropriate. The exposure will still compensate for the same dark exposure. Any adjustments in EV have to be guesses. I had a similar problem with a Sigma 105mm macro on my 6Dii, which is why I bought the Canon 100 macro.

[ebiggs1 · Accepted solution]

One of three things have got to have a problem. One, the camera. Two, the lens and three, you. First reset the camera to factory. Two if the lens works perfectly fine on all your other cameras, it is probably OK. So, that leaves, you!

Hopefully the reset will correct that issue. 

After rest, set the mode to P mode. ISO 200, One shot, do not use Ai-servo. Put the 300mm f4L in the AF position and go outside on a nice day and try it.  Select  different subject. If it works, it works!  You need to examine if you set something incorrectly either on purpose or by accident.

[Chris_N]

To rule out another possibility, you might want to clean the electrical contacts on the camera and the lens  lens with a q tip and a drop of alcohol. 

Check you do not have any negative exposure compensation dialed in on the camera. 

Check the aperture and shutter is opening and closing properly.  When indoors, dial in a 1/2 second exposure and try different apertures and look inside the lens to verify the correct aperture is being set.  

Kind regards

Chris

[ebiggs1]

Chris although I love your ideas to try, IME, cleaning the contacts rarely to never helps or works. The act of removing and mounting a lens is generally all the "cleaning" the contacts require. I avoid telling people do it because of the danger of making things worse. Although you clearly stated a drop of alcohol and a q-tip, I have seem folks use every means of cleaning.  A pencil eraser is a favorite. The gold plating is so thin, it can easily destroyed. 

The full camera reset will eliminate your the other issues.

[Wandalynn]

That's a great suggestion and I will try it! I'll write back with results. Thanks!

[Wandalynn]

It worked! Thank you, thank you, thank you!!!