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An artifact has started appearing in my subframes. Here is an example of one frame, 900 secs in OIII on the Jellyfish. I have just given it the STF stretch in Pixinsight. I am talking about the dark area at "3 o'clock" on the edge of the frame. It is not like my usuall dust bunnies (of which there are some, but they don't show up under this stretch)

My equipment is 102 F7 Triplet, Atik 460 EX Mono and Paramount MX Mount, operated remotely.

TIA for any input.

post-7711-0-90724800-1450908868_thumb.jp

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Might be a bit of dust on the filter or reducer (if you are using one). Luckily, its in a place that can either be cropped out - or healed with the delicate use of a clone brush.

One thing thats of more concern however, is that you seem to have some sort of blooming spike on a few of the larger stars.

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The spikes look like the scope was knocked to me - or perhaps a sudden gust of wind, it doesn't look like an optical defect.

ChrisH

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If it's an OAG shadow, which is potentially possible, then the OAG is on the wrong side of the chip. It should be at 90 degrees so as to enter the light cone on the chip's short axis.

The symmetry of the artefact, if it isn't an OAG shadow, is remarkable!

Olly

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Thanks for the answers everyone. There is no OAG on this, and it does appear on all the subs, this is not a one off. It just appeared overnight. It seems a bit severe to be a dust bunny... there are other dust bunnies in there but they don't show up under these conditions (this is just an STF stretch in p/i).

C

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Just a chance it could be ice on the ccd if it changes shape between subs but I would have expected a bigger artefact

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It's not a spider or insect that has taken up residence somewhere in your imaging train??

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Try changing the dessicant and putting the camera somewhere it can dry out, just in case it's the problem as it is growing.

Carole 

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