What has gone wrong with this stacked image/blue filter?

[oldannie]

This is just 8x300sec  blue stacked in DSS of the Leo Trio but something has  obviously gone wrong.  It only appears on the blue filter not the red, green or luminance.  Imaged with Takahashi 106ed and Atik 460ex.  I've just done a quick process using auto Camera Raw to show the large smudge!  I've no idea what has caused this and would appreciate some help!

 

Thanks

Annie

[carastro]

Cloud?

[ollypenrice]

Looks too focused for cloud, to me. Those would be very tiny clouds if you consider the size of the Triplet on the sky!  Blue is the filter most susceptible to artifacts because the short wavelength scatters most easily. A reflection from a nearby light source, possibly a very small one? Something bright in the light path? How do the individual subs look? Are they all the same?

I think it's most likely to be a reflection but can't be sure.

Olly

[oldannie]

I'll have a careful look at the individual subs Olly.  There's not much light pollution where I live so can't think where an external light source might come from but will have a good think about that. . perhaps it's something about my imaging train but wouldn't that affect all /most of my subs?

Thanks 

Annie

 

[oldannie]

Thanks Olly for reminding me to look at the obvious first!  Checked my subs and much to my embarrassment discovered the 'smudge' only appeared on the last sub!!!!!

 

Annie