Can someone advise me please?

Hi Dave,

One possibility is Residual Bulk Image, a memory effect in front-illuminated CCD chips. This can be particularly noticeable at red and longer wavelengths. I find if I image a bright star for centring purposes, there is a ghost of the star in subsequent images.

John

JohnONeill wrote: Hi Dave,

One possibility is Residual Bulk Image, a memory effect in front-illuminated CCD chips. This can be particularly noticeable at red and longer wavelengths. I find if I image a bright star for centring purposes, there is a ghost of the star in subsequent images.

John

I have seen this before on other peoples CCD Chips, however he is using the KAF-8300 chip which is not affected by this, it's the same CCD Chip as I have in my ATIK383L+

My guess here is that this has been introduced during processing, the image where there is no evidence is a Mono image yet where the problem resides is a colour image

Hi Folks,

I'm very grateful for the ideas here. I've tried the following;

1. Went back to the raw data and re stacked the images
2. I did notice the gradient on the raw images, although obviously not as pronounced as in the final image
3. To be sure, I took the master the 1st Feb image master flat and calibrated the 16th Feb image
4. Then I reprocessed again in PIXINSIGHT, gradient is still there
5. The flats are collected using a Gerd Nuemann EF source...so I'm pretty confident in those

I have also reprocessed the data from the 1st Feb and there is no sign of this gradient. I have a theory though...

I keep a log of my photo shoots because I'm still very much a novice deep sky imager. I've learned so much since October it is almost unbelievable. But I haven't been recording anything on light pollution. I only noticed recently that a sodium street lamp is on within 50m of my observatory (not direct line of site though). This has not been working in so long I can't remember.

I noticed lately that this has been repaired but I am not sure when (i.e. last week or month). Also, I do not have an LPR filter for my camera. Would this be a plausible source for the light gradient? Is it worth my while buying an LPR filter? any recommendations?


Thanks for all of the ideas so far...I'm learning loads!


Clear skies


Dave

In my opinion because of the way the gradients are in the frame a Light Pollution Filter is not going to help, LPF are more geared towards a "General" light pollution in the whole frame rather than blotches like you have

It might well be that you are getting some "Reflection" or "Light Leakage" entering the imaging train which it what you need to solve, I had a similar issue a few years back whenever I imaged in a certain direction, I had some weird light hitting the sensor

Hi Simon,

Many thanks for your advice, I've eliminated flats and spurious light from a nearby street lamp. I managed to successfully shoot M81 again on Friday the 13th without any major issues (except leaving the imaging run in 2x2 bin mode...oh how I laughed when I realised that). Anyway, not withstanding it was a monochrome image, the end result had no spurious light in it. To be honest, I'm quite pleased with the image even though it is mono. The exact imaging position would have been different since the last shot 16th Feb. So, light leakage looks like a good contender for now. I think it's time I moved onto other targets now...thanks everyone for their ideas!


Clear skies


dave

Hi Folks,

I think I've isolated the problem to light leakage from my laptop...there are blue status LED's blinking even when the screen is off (Thanks Carl in S&S for putting me onto that one!). So I've reshot M81 for 1 hr with a thick towel over the computer and the result was much better.

Also, I did some PIXINSIGHT training and applied improved processing methods which overall gave a much more pleasing image. I just wanted to say thanks to everyone who contributed, I've listened to everything you all said and have been busy applying the lessons...I hope you like the result of your experience!

Clear skies


Dave

www.astrobin.com/168813/