black line on my photos

[Marilynne]

Thank you for the welcome Danno after I uploaded the photo, I couldn't see what I was describing either.

Welcome!

Glad you responded back, because I don't see a white line either.

 

[Bob Blaylock]

It almost looks to me like the mirror isn't going up all the way. But I'm just making an uneducated guess, I'm pretty new to DSLR's. I have to agree with stmv, see if you have a local shop that can take a quick look at it. Maybe they have seen this before and can give you an estimate.

I'm with bobonit. Shutter curtain issues tend not to be so completely horizontal. And the fact that you don't get it when no lens is attached leads me to believe that somehow the mirror may be getting stuck against something actuated by the lens attachment (though now that I think about it, with no lens attached unfocused light sneaks in from all angles so you wouldn't see it.

With a lens off, select a long shutter speed or put it in bulb or mirror lock for cleaning mode and see if the mirror goes up all the way?

Then it sounds like the timing of your mirror is off. Put your D3100's shutter release in "Quiet Mode" and see if you can take pictures that way, using the viewfinder.

It wouldn't be the mirror.

Keep in mind that the image is inverted on the sensor. The mirror not being up all the way would shade the upper edge of the sensor, but that would be the lower edge of the image.