Any idea what is causing this glow ?

[bigal1]

Hi all i purchased a canon 1000d camera over christmas but have not had chance to use it on my scopes yet but lastnight was the clearest night ive seen in a long time here in manchester so i piggyback mounted the camera and just used the kit 18-55 lense to test . The results were ok but i seem to have a strange light area ( glow ) coming from somewhere but im not certain where , this effect is present no matter what area of the sky i shoot so was wondering if anyone has any ideas what could be causing this issue thanks .

Regards Alan

[Psychobilly]

Its not glow but is shadow an effect known as Vignetting... caused by the sensor not being evenly illuminated by the lens.

http://en.wikipedia.org/wiki/Vignetting

Stopping the lens down a couple of stops will help give more even illumination but will require longer exposures... the other option is taking a trip into the wonderful world of "flats" which are used to help correct for the light fall off across the frame...

Billy...

[bigal1]

Great thanks billy didnt realise you can get vignetting with lenses knew about it using scopes , guess i should take some flats

[Psychobilly]

I tend to use lenses that are designed for Full frame rather than ones that are designed for APS-C sized sensors (so for the Canon EF lenses not EF-S) these are essential if your using a clip in filter system... and also give much better corner to corner illumination of the smaller APS-C sized sensor.

Billy...

[bigal1]

cheers billy only just getting into dslr astrophotography so thats good to know , i'll be picking up some lenses soon for widefield so ill be on the lookout for the ef ones .

[ollypenrice]

I find I certainly need flats with camera lenses.

Olly