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Hi All,

I had the first clear skies (for a couple of hours) since Christmas Eve yesterday so I seized the opportunity and took some snaps of what I could. Inevitably, I come back with more questions!

I'm using APT and for some reason, the images captured are being saved as "CR2" files rather than RAW files (imaging with a Canon 450D). I can't see where to change the saved image file type in APT, what am I missing?

The images I've posted below of Betelgeuse are the best I could get from yesterday, which are terrible! For me, just getting a reduction in star trails at 20-30 secs is quite the achievement. I'm also imaging through a scope with 660mm focal length (Achromat) on an EQ3, less than ideal until I get the right scope. 

I notice here that just on ISO 200-800 the images seem to be extremely bright.  Is this the result of light pollution or is there something else I'm missing?

I should also note that I'm using "Bulb mode" on APT, not sure if this has any bearing.

ISO 200 @ 30secs:

491306436_Single__0004_ISO200_30s__15C-JPG.thumb.jpg.de846d367bc0e98eed14745730bc81bf.jpg

ISO 400 @ 29 secs

1955733454_Single__0003_ISO400_29s__17C-JPG.thumb.jpg.d1976abd6b1caa9f44ec1e186bdb35c1.jpg

ISO 800 @ 29 secs

1681825897_Single__0002_ISO800_29s__17C-JPG.thumb.jpg.06602f452049158e75271db9f7e0d18c.jpg

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8 minutes ago, happy-kat said:

CR2 is Canon raw file format

What bortle number is your location where you captured these?

Thanks @happy-kat. Do you know how I can amend these file types so that DSS recognises them? When trying to open in DSS it doesn't recognise them at all.  

My Bortle area is 7/8 (Harrow, North London).

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You may be ok still with iso 800, check the light histogram to see where the histogram peak is, you will want it to the left of centre so as to not be clipping the light end.

Looks like it will be light pollution your lightness in your bortle level. 

What version of DSS are you using?

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5 minutes ago, happy-kat said:

You may be ok still with iso 800, check the light histogram to see where the histogram peak is, you will want it to the left of centre so as to not be clipping the light end.

Looks like it will be light pollution your lightness in your bortle level. 

What version of DSS are you using?

Okay, I'll keep my eyes on the Histogram in APT and make sure the peak stays to the left.

This seems like a lot of light pollution, no? Would a light pollution filter help or can most of this be dealt with in processing?

6 minutes ago, Paul779 said:

Hmmmm thats odd what version of DSS are you you using as CR2 s work fine for me

I think I've just figured this out; I was trying to open images via Processing>Open Picture File, which doesn't recognise CR2, rather than the Register and stacking>Open Picture files.  

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With the exposure length you are using I don't see a gain in using a light pollution filter as you can post process the images you have. But if you get to be able to take longer exposure lengths then there may be a gain as the filters help reduce over brightness so you can expose for longer.

Generally cameras have an optimum ISO, do you know what that is for your camera, it is likely ISO800 I think.

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2 minutes ago, happy-kat said:

With the exposure length you are using I don't see a gain in using a light pollution filter as you can post process the images you have. But if you get to be able to take longer exposure lengths then there may be a gain as the filters help reduce over brightness so you can expose for longer.

Generally cameras have an optimum ISO, do you know what that is for your camera, it is likely ISO800 I think.

Thanks @happy-kat, much appreciated!

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Im very new to AP myself and all my imaging is unguided and i ve found spending more time polar aligning getting it as spot on as i can has resulted in far less star trailing issues 👍

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32 minutes ago, Paul779 said:

Im very new to AP myself and all my imaging is unguided and i ve found spending more time polar aligning getting it as spot on as i can has resulted in far less star trailing issues 👍

Thanks @Paul779. I'm in quite a trick spot for PA; I have no sight of Polaris and am working form a covered balcony (see my viewing platform here and ongoing woes expressed here and here!) 

Once this is sorted I'm hoping my images will improve dramatically ;) 

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The problem with light pollution isn't so much the increased background level, which can be processed out, as is the noise that is left behind. The noise associated with any light source varies as the square root of the light intensity. The best ways to decrease noise is to take more exposures, or to block the light before it reaches the sensor. In a Bortle 7 or 8 location, I would definitely use some sort of filter on an osc camera, or go mono.

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3 hours ago, wimvb said:

The problem with light pollution isn't so much the increased background level, which can be processed out, as is the noise that is left behind. The noise associated with any light source varies as the square root of the light intensity. The best ways to decrease noise is to take more exposures, or to block the light before it reaches the sensor. In a Bortle 7 or 8 location, I would definitely use some sort of filter on an osc camera, or go mono.

Thanks @wimvb, very helpful.

Can you make any recommendations with regards to light pollution filters?

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If you image mostly nebulae with an osc camera, such as a dslr, then either an uhc filter or dual band filter, which only has transmission near Ha and Oiii, and a large gap inbetween will be best. If you image reflection nebulae, star clusters or galaxies, probably an IDAS lp suppression filter is best. The problem with lp suppression filters is always that you want to exclude as much light pollution as possible, while maintaining as much of the full spectrum as possible. Unfortunately you can't have both, and how effective a filter is, can depend very much on your local sky conditions.

Here are a few suggestions at least.

https://www.firstlightoptics.com/light-pollution-reduction-imaging/optolong-l-enhance-narrowband-deep-sky-imaging-filter.html

https://www.firstlightoptics.com/light-pollution-reduction-imaging/idas-d2-light-pollution-suppression-filter.html

https://www.firstlightoptics.com/light-pollution-reduction-imaging/idas-d1-light-pollution-suppression-filter.html

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