what went wrong with my image

I took this picture on Sunday and brought to the local professional lab here in NYC. I made two exposures one of the river and one of a street corner. The one from the river turned out fine, but the one from the street corner looks like it had fog right in the middle, it is a bit dark to see but it is around the center of the image.

My question is: did I screw up by letting light come in? Did the lab screwed up? My previous picture was fine so camera bellows are tight and it is a brand new camera. I am posting the two pictures, the bad and the good.

http://farm3.static.flickr.com/2486/3987164502_4028439a1e_o.jpg

http://farm3.static.flickr.com/2620/3986337229_ac40c2c28f_o.jpg

Technical information:
Chamonix 4x5 with 210mm lens
Efke (4x5) PL100 film
1 sec Bulb exposure

Maybe when you put the dark-slide (film holder) in the camera back it wasn't fully in place. It's fogging and the light's coming from the top edge when in the camera back. If the darkslide isn't fully inserted it sits on the ridge and a very slight bit of light creeps around the edge.

Unlikely to be the lab, as the other is OK. Something you did somewhere.

Ian

Ian

Thanks Ian, I thought I was being careful, but I guess something happened there? I even put some tape between the slide and the holder.

Thanks.

Don't worry about it, the river photograph is a better photograph. In the future, leave the fog for the weather and not the film.

Steve