Camera problems

[Barry65]

I have had problems with 70D and 90D. A black streak goes across the image making the camera unusable. What am I doing wrong?

[jrhoffman75]

I suspect you have an intermittent problem with a sticking  aperture blade. 

[Barry65]

With having 3 Canon cameras have a similar problem, I am just trying to see if I'm doing something wrong.

[jrhoffman75]

With lens off camera look through rear element. Do you see anything other than a clear view through?

Set the Av to f/8. 

Look through the lens and cycle the DoF button. See anything amiss?

[rs-eos]

As another test, if you use your lens at the widest aperture (f/2.8) on all three cameras, does the problem still exist?  If not, it's then highly likely it's indeed an aperture blade in the lens that is failing.

Also agree that the likelihood of three cameras all having failing shutters is extremely low.

[Barry65]

Using my Sigma 17-50 mm lens, I still have a problem with a horizontal white bar and a diagonal black bar at right.

[Barry65]

I no longer have the two earlier 70D cameras that had problems. The 90D started having problems last night. I have a used 70D backup which is working fine right now. I just want to figure out if I'm doing something to cause this.

[jrhoffman75]

While it is unlikely that three cameras have failed shutters, the additional info seems important.

Now it seems you are saying that one camera has a problem and one doesn't. And it happens with two different lenses.

That would seem to be a camera problem.