M81 (first time)

[vineyard]

Hello,

Hope everyone staying safe & well.  Finally had a chance to process some images from 27 March.  Have been ill most of the clear nights (so only managed to get 2 nights of capturing done) but mustn't grumble given the circumstances!

This is the best 47 of 60 lights of 60 secs.  Taken with an ASI178MC.  I'm actually quite enjoying AP, although the picture quality is very basic (need more data & better processing skills).  Still it gives something to do!  (And I'm starting to think about whether an ASI294MC might be something for Santa this year )

Stay safe all,

Vin

 

Edited April 2, 2020 by vineyard
added camera type

[vineyard]

Hello, hope everyone healthy. So I went back to M81 earlier this month with my 4", and took longer exposures (and more of them) with guiding.  Still not a great image - too grainy for my liking & not a patch on some of the amazing M81 posted earlier today by @lux eterna (that's just incredible).

Stay safe,

Vin

[wimvb]

You're getting there. In all fairness, that other image had 15 hours of data.

[vineyard]

For sure re the other image - its beautiful.  I find images of that calibre really motivating - I know my processing skills will likely never reach those levels but its all about continuous improvement .  Hope you get some good nights before the permanent twilight arrives!  Cheers, Vin

[wimvb]

When I was new at this, I tried to capture several objects in one night, getting just about 1 - 2 h of data on each. Now, I'm not even starting to look at the data before I have abt 8 hours. Processing gets a lot easier when you don't have to worry about noise. Good data takes time, and access to dark skies helps a lot.

[MarkAR]

Much better second time round.

[lux eterna]

14 hours ago, vineyard said:

Hello, hope everyone healthy. So I went back to M81 earlier this month with my 4", and took longer exposures (and more of them) with guiding.  Still not a great image - too grainy for my liking & not a patch on some of the amazing M81 posted earlier today by @lux eterna (that's just incredible).

Stay safe,

Vin

 

Thank you Vin. One of the good things with this hobby is that you never reach any kind of finishing line, there is almost always room for improvement. My M81 is collected over several years, without intention when I started, but this time I just got the idea to add some more data to it. Because I had so many subs now, I could reject those with very small imperfections and still have 15 hours to stack.

So keep collecting, you have good data that deserves more company.

Ragnar

 

[vineyard]

Hello,

So I went back to M81 again during the week, and took more data (almost doubled it to 101 lights of 120s each, so about 3h20 of data).  And I used a different processing workflow in PI.  So while I can't really disentangle the comparative effects of the extra data vs the new workflow, I definitely prefer this newest image out of the three above.  So I suppose that's progress

Will try this new workflow on a couple of other targets that I grabbed some data for this week too, and see what transpires.

Stay safe all,

Vin

[wimvb]

👍

What gain do you use for the asi178?

[vineyard]

Most of those lights were zero gain. On some (I think about 20-40 mins worth of lights, I can't remember precisely) it was gain 102.  The darks are also not at the right temperature in the above image (I took them but stupidly forgot to check their bit-size so they got taken as 8-bit which DSS won't let me use with 16-bit files - hey ho, another lesson learnt!)

[vlaiv]

11 minutes ago, vineyard said:

Hello,

So I went back to M81 again during the week, and took more data (almost doubled it to 101 lights of 120s each, so about 3h20 of data).  And I used a different processing workflow in PI.  So while I can't really disentangle the comparative effects of the extra data vs the new workflow, I definitely prefer this newest image out of the three above.  So I suppose that's progress

Will try this new workflow on a couple of other targets that I grabbed some data for this week too, and see what transpires.

Stay safe all,

Vin

Image is taken with 178mc?

As far as I remember, 178mc is 3000x2000px camera, how did you get your image to be 4936 × 2976 pixels? Did you do multiple panels and make image out of mosaic?

Quick search online gives TV102iis as 880mm scope, did you use any reducers with it? If not, you were sampling at 0.56"/px - far away from what is optimal for 4" scope on Heq5. You should really aim for 2"/px or there about.

[vineyard]

HI vlaiv, yes re the camera (the only other one I have is an ASI120MM mini for mono lunar & guiding).  I didn't take mosaics (not yet brave enough for that w EKOS) - I just set M81 as the target and took lots of lights over probably about 3 nights.  And then stacked them in DSS, and worked on the TIF file in PI.  Hmm, I did then open the post-PI TIF file in GIMP & GIMP did ask about a colour conversion - could that have been where the pixels changed?  Or maybe when I exported it as a TIF & a JPG from GIMP?  (On my DSS it shows as 3096x2080, but obviously something then happened afterwards in the chain but I'm not sure where)

No I don't have any reducers.  Ah re the ideal sampling resolution - I didn't appreciate that, as that is a whole area I have not yet got my head around.  I have played with the CCD Suitability calculator on astronomy.tools & I can see that it gives different recommendations.  But, must admit I don't know what that means in terms of image quality though (ideally I guess I could compare with a similar rig, two different resolutions & cameras and see the difference but don't have that hardware).

As it happens, b/c I am enjoying AP way more than I thought I would, I am planning to save towards a cooled camera now.  My current working hypothesis is that the ASI294MC might be the best one to step up to from where I am currently?  The CCD calculator says that would give about 1.1"/pixel which is still below the 2" that you recommend though?  I haven't yet decided that (even whether OSC vs mono) b/c that's a whole other area of research (well, it is lockdown ).  Are filters pointless with OSC?

Anyway, thanks for the tip on the resolution - could that also explain why my images always feel slightly less crisp & clean to me?

Stay safe,

Vin

 

[wimvb]

46 minutes ago, vineyard said:

about 1.1"/pixel

That's just in your sweet spot. Stick with that. Imo, it's easier to process images that are (moderately) oversampled than undersampled.

[vlaiv]

49 minutes ago, vineyard said:

HI vlaiv, yes re the camera (the only other one I have is an ASI120MM mini for mono lunar & guiding).  I didn't take mosaics (not yet brave enough for that w EKOS) - I just set M81 as the target and took lots of lights over probably about 3 nights.  And then stacked them in DSS, and worked on the TIF file in PI.  Hmm, I did then open the post-PI TIF file in GIMP & GIMP did ask about a colour conversion - could that have been where the pixels changed?  Or maybe when I exported it as a TIF & a JPG from GIMP?  (On my DSS it shows as 3096x2080, but obviously something then happened afterwards in the chain but I'm not sure where)

No I don't have any reducers.  Ah re the ideal sampling resolution - I didn't appreciate that, as that is a whole area I have not yet got my head around.  I have played with the CCD Suitability calculator on astronomy.tools & I can see that it gives different recommendations.  But, must admit I don't know what that means in terms of image quality though (ideally I guess I could compare with a similar rig, two different resolutions & cameras and see the difference but don't have that hardware).

As it happens, b/c I am enjoying AP way more than I thought I would, I am planning to save towards a cooled camera now.  My current working hypothesis is that the ASI294MC might be the best one to step up to from where I am currently?  The CCD calculator says that would give about 1.1"/pixel which is still below the 2" that you recommend though?  I haven't yet decided that (even whether OSC vs mono) b/c that's a whole other area of research (well, it is lockdown ).  Are filters pointless with OSC?

Anyway, thanks for the tip on the resolution - could that also explain why my images always feel slightly less crisp & clean to me?

Stay safe,

Vin

 

Could have happened in DSS if you checked option for drizzle.

You should not drizzle your data. Let's see if we can manage to work it out. Could be x2 drizzle and then some crop due to alignment. In any case - that is something that you should not use - drizzle option.

Neither of these two should be checked. Drizzle has the same effect as oversampling - it just spreads values thin over many pixels without actually producing resolution. This lowers signal per pixel and your SNR - which is bad thing.

It is most obvious when you look at image 1:1 or 100% zoom level:

There are not stars - these are some white "Orbs" in space. Or rather - that is empty resolution. We could say that image actually supports this much resolution:

Now stars look like points - but another thing happens - noise goes down and overall impression of the object goes up. I did not do any further processing on this except resizing it to x6 smaller size than original.

Doing that on still linear data will let you process image much better. Anyway - that was the point with proper sampling - it renders nice looking sharp image with best SNR in comparison to any oversampled image.

On the matter of ASI294MC-PRO - yes that is probably best choice of sensible priced color sensor, and I would go with that myself.

[vineyard]

Thanks vlaiv that is hugely helpful.  And yes you're spot on - I checked my DSS settings and it was 2x drizzle!  That will remain unchecked now  and I'll try again on the linear workflow.

This is probably another stupid Q: when you say you resized to x6 smaller, do you mean the dimensions of the picture (just by changing the rectangle size by dragging)?  Or is there a sizing function that's hiding in plain daylight in front of me?

And thanks both vlaiv & wimvb for the feedback on the 294MC - I think that will be this year's treat.

Stay safe,

Vin

[vlaiv]

1 hour ago, vineyard said:

This is probably another stupid Q: when you say you resized to x6 smaller, do you mean the dimensions of the picture (just by changing the rectangle size by dragging)?  Or is there a sizing function that's hiding in plain daylight in front of me?

In this particular case I used IrfanView and resize image to 16.666% (or one sixth). It uses Lanczos resampling (which is excellent resampling method).

Any down sizing of the image will improve SNR, but different methods my different amount. Here I wanted to show you what properly sampled image looks like - stars are small even when you look image at 1:1 or 100% zoom level. Here image is small so it is already at 1:1 / 100% zoom level but it shows what stars should look like when you open image in viewer and zoom to actual size.

As consequence of resizing - we got some noise reduction although that was not my primary intention. Best noise reduction (or rather SNR improvement) comes when data is still linear, prior to processing, and when you bin data instead of just resampling it.

 

[vineyard]

Ah, I think I see. Thanks. I tried the undrizzled data, and tried to replicate the PI & GIMP workflow as much as possible (from memory rather than having written it down first time!).  I think this image does seem sharper than the previous drizzled one (but I'm never sure about my eyes at the end of a long day) - the centre seems more blown out but I'm hoping much of that is my clumsiness.  I tried to scale it to 2/3 size (using GIMP's image scale function) but I'm also never sure what that looks like on a screen until uploaded so fingers crossed.

Lots of learning today, so cheers again!

Vin

[wimvb]

46 minutes ago, vineyard said:

 I tried to scale it to 2/3 size

Pixinsight: process - geometry - resample

[vlaiv]

Better yet PI - integer resample x2 average