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M81 test stack to play with please as I cannot get close to what I was achieving last year and I'm not sure why.


FaB-Bo-Peep

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Hi everyone,

The attached is about 30 minutes of RAW files taken with a Skywatcher 250PDS, AZ-EQ6, Canon Rebel XS, (1000D), and Optolong L-PRO filter, stacked in DSS.

This is very similar to my total integration time per target from previous years but no mater what target I attempt I'm simply just not getting results comparable to last year and the only thing I've added in the optical train is the Optolong LPRO which I can't think for one minute is my issue but next session I will try without it just as a test.

Anyway, just in case I am messing up with the latest version of Startools, I would be very grateful if some of you could please have a quick play with the attached and post your end result.

 

Thanks in advance

🙂

M81-DSS-FITS.FTS

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Hi,

I had a quick look at your dataset, but it there are several pre-processing and acquisition issues that really need to be addressed.

  • If using StarTools, please use the recommended settings for DSS.
  • The dataset has been drizzled for no good reason
  • There is severe pattern/correlated noise visible (probably due to drizzling)
  • The dataset was not calibrated with flats - they are really not optional.
  • The dataset was color balanced.

Particularly the lack of flats will keep you from progressing.

For recommended DSS settings for use with StarTools, see here.

For further recommendations and do's and don'ts, see here.

I hope this helps!

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Thanks for the above reply, while I am always looking to progress, I am none the less confused as to why I cannot at least equal what I have previously achieved.

Taking the points you mention:

  • I will certainly look at this.
  • Interesting, I am certainly drizzling for the first time this year, (using an ASIAIR PRO), and thought it only had positive impact but maybe not.  ****Correction, I am "dithering" with the ASIAIR PRO, not even sure what drizzling is so need to check how this is happening****
  • I fully understand that flats would have a positive effect but to date I have not ventured into using them so as I have never used them I would expect my results from this year to be similar to previous years.
  • I have not changed anything on the camera so is the "colour balancing" something that is occurring in DSS? I have re-installed a new version on a new computer so maybe it's an option I have inadvertently enabled?
Edited by FaB-Bo-Peep
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Stars are sharp but I think you just need much more data/exposure time. Make sure you dither between every 2nd or 3rd exposure to help reduce noise. Then add appropriate bias, darks and flats if you can. If you've had success without the LPro then remove it - its just an extra piece of glass that will further limit light getting to your sensor. Good luck. 

ps. I'd also double check you are getting the exposure time you think you are as it doesn't look like 30 mins of data from a 250mm newtonian. With my DSLR I regularly think I'm taking 1min exposures only to find they are 1 second - easily done in the dark (by me anyway). 

Edited by AbsolutelyN
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Thanks for all the advice, all very helpful for further development but sorting out the DSS settings has got me back to where I thought I should be.

Here's a couple of very rough + ready DSS stacks onward processed with my very limited knowledge in Startools. While I fully appreciate they will not win any awards, I can at least say they are now better than my previous attempts which with the addition of the LPRO filter is exactly where I thought I should be 🙂

p.s. please don't bother trying to process the stack in my original post, as jager945 points out, it has multiple issues largely due to incorrect stacking settings in DSS.

M81-DSS-FITS-3RD-STARTOOLS-JPEG.JPEG

CROSEYE-3RD GO-DSS-FITS-STARTOOLS-JPEG.JPEG

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Good to hear you're back on track. 👍

@AbsolutelyN brings up a good point; the L-Pro filter will block some light pollution, which will help record targets with specific emissions that are not in the same part of the filtered spectrum (Ha, Hb, O-III, etc.). However galaxies in particular, emit at all wavelengths so you are definitely filtering out some "useful" light. Whether that is worth it vs blocking the unwanted light from light pollution is dependent on the situation of course. Spectrum response at the Optolong site;

https://www.optolong.com/uploads/images/20191111/8b905545f314b530f408a27ce76b4b73.png

 

 

 

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