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The "No EQ" DSO Challenge!


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Well, here's early sight of my integration of the Ha images. I only managed 34 x 30s and 22 x 60s, all taken at 300 gain, 50 offset and -20C. I haven't inspected them, rejected any images, or applied any calibration. This is uncropped and only stretched with levels and curves. I have to say, Ha data is so much cleaner to work with than LRGB! I'll be taking flats tomorrow and doing a proper integration of this, and my LRGB data (not that I got much before it went behind the steam vent). I also took a quick peek at M81 and it's a breath taking galaxy (but that one really does need calibrating!).

NGC2239_H_40m.jpg

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I'm still fairly new to imaging, but have had a good start with Planetary and Wide Field images. Obviously, like most of us, it's the Deep Sky stuff I'd like to glimpse, but time, location and more im

Assorted shots with a Nexstar 102SLT and a Canon 1000D. 30sec subs at ISO1600. Total exposures range from 5 mins (M20)  to ~1hr (M31). NigelM

this was taken a couple years ago on my AZGOTO mount with 130p...... about 50 x 5 sec subs, no calibration frames

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9 hours ago, Filroden said:

I'll be taking flats tomorrow

Nice. I'm envious of your FoV! Ha does seem to give a 3-dimensional effect.

Does Ha present particular problems in this regard? I'm thinking in terms of the emission spectrum of the source used. I use an led light, others laptop screens etc. and I wonder what they emit at 654nm.

Ian

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1 hour ago, The Admiral said:

Nice. I'm envious of your FoV! Ha does seem to give a 3-dimensional effect.

Does Ha present particular problems in this regard? I'm thinking in terms of the emission spectrum of the source used. I use an led light, others laptop screens etc. and I wonder what they emit at 654nm.

Ian

Thank you. It is such a richer image than the original luminance that I used. I'm going to have to study the tutorials about blending it into L and into R. I may try three versions:

1. Mono Ha with stars removed and tinted red

2. LHaRGB

3. HaRGB

The latter to see if it retains more detail without the L channel.

I've just taken flats using a white image on my LED TV. The Ha flat took 32s compared to between 1s and 2s for the LRGB. I can't see much difference between the results yet but I've somehow managed to put more dust onto the camera having (I though) given the whole system a good going over with the blower when I fitted the Ha filter.

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It wouldn't surprise me if the dust is emphasised because of the narrowness of the passband, leading to interference effects. I guess that's the purpose of taking flats to correct for it!

I had a solar 'scope once and it would have been interesting to have done narrow-band imaging of the night sky. I sold it though in order to acquire my current 'scope, and in any event I soon realised that I really needed a monochrome astro-camera for it rather than my mirrorless, which was more than I was prepared to invest at the time.

Ian

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11 minutes ago, The Admiral said:

It wouldn't surprise me if the dust is emphasised because of the narrowness of the passband

When I did some quick integrations of my M81/82 images last night the dust was clear in the L channel but was invisible in the Ha. I think it's because there is so little background in the Ha and the signal is weaker that it's just harder to spot. Now I have time to properly calibrate all the files it will be interesting to see the difference.

I will also see if I can balance the flats and subtract the Ha from the L to see if there is any real difference. Given it's a new filter, I would hope it is clean so the flat should mainly be dealing with dust near the sensor and the vignetting of the optics. If so, I could possibly be lazy in the future and correct Ha using the L flat.

That, or I have to figure out how to get my light box working so I can increase the intensity when doing Ha flats and reduce the exposure time. 32s exposures means I also need to correct for darks. With 1s exposures I could get away with using the bias as a dark.

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Would you believe it...the only filter with any discernible difference is the Ha filter which has two nice blobs in the centre. There's quite a bit of dust on the sensor. It's a design flaw with the first two versions of the ZWO ASI1600 camera. ZWO included 4 desiccant tablets inside the camera next to the sensor window so any time you unscrew the camera body there is a risk it grinds the tables, spreading dust everywhere. The third version removes this flaw. Looks like I need to open it again.

 Flats.jpg

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That certainly is a design flaw. It would have been good if ASI had offered to replace/upgrade earlier models.

I'm pleased to say that I don't seem to have a great deal of problem with my camera; I think the sensor 'cleaning' cycle it invokes each time I switch off is doing a fair job.

I'm surprised at the amount of vignetting you are getting Ken. Is that because the filters are only just large enough, or did you get that with your 'scope prior to use of the ASI?

This is how mine turn out, which I'm very pleased with.

M42 flat.jpg

Ian

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4 minutes ago, The Admiral said:

That certainly is a design flaw. It would have been good if ASI had offered to replace/upgrade earlier models.

I'm pleased to say that I don't seem to have a great deal of problem with my camera; I think the sensor 'cleaning' cycle it invokes each time I switch off is doing a fair job.

I'm surprised at the amount of vignetting you are getting Ken. Is that because the filters are only just large enough, or did you get that with your 'scope prior to use of the ASI?

It's a complete redesign of the body so they can't offer an upgrade kit. They have offered $200 off a new camera if you owned the previous version. Given the camera's popularity, resale value of the older versions should be high, so it wouldn't be too much of a loss. I just need to be more careful.

My flats above have been stretched to highlight the variations. The "flat" flats look more like yours (example of the L filter below). I've always had about that much vignetting but the flats seem to fully correct it, so I've not been too bothered by it.

Flat_L_20170124_g300o50_-20C.jpg

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15 minutes ago, JohnSadlerAstro said:

Hi,

Nice pic, mate! Perhaps some photoshop to bring out the details?  :D:D:D

John

Yeah, well you see, I'm only a beginner :wink2:. This darned light pollution!

Well here's what I got after a bit of stretching. This is the green channel, other channels are much the same, that is, a couple of bits of crap visible and vignetting at the extreme corners. Top more than the bottom, so I'm thinking there's a bit of focuser droop, which wouldn't surprise me as I get some elongation of stars towards one edge.

Ian

Edit. Oh hang on, you're referring to Ken's flat not mine. Ha Ha!

Flats stretch.jpg

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On a serious note, (not wanting my humour to get me banned)!

What would you suggest as the best method for taking white frames? I've been having trouble with vignette, but as my sensor is large, its more one-sided. (I'm ok with dust as my DSLR auto cleans the sensor every time it turns on or off).

John

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4 minutes ago, JohnSadlerAstro said:

On a serious note, (not wanting my humour to get me banned)!

What would you suggest as the best method for taking white frames? I've been having trouble with vignette, but as my sensor is large, its more one-sided. (I'm ok with dust as my DSLR auto cleans the sensor every time it turns on or off).

John

I fold about half a dozen sheets of white paper so they hand from the end of the scope and act as a diffuser then I put up a completely white image on my TV screen. So long as you expose for long enough to not capture the screen refresh then it seems to work well.

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4 minutes ago, JohnSadlerAstro said:

On a serious note, (not wanting my humour to get me banned)!

What would you suggest as the best method for taking white frames? I've been having trouble with vignette, but as my sensor is large, its more one-sided. (I'm ok with dust as my DSLR auto cleans the sensor every time it turns on or off).

John

There seem to be a multitude of ways, just search on SGL. I've used a laptop screen to provide the uniform light before now, others recommend stretching a T-shirt over the dew shield and expose to a uniformly lit sky, but in the end I went down the route of using a home-constructed LED light which I've described on the forum (See https://stargazerslounge.com/topic/274057-flats-light-final-chapter/). It's worked out very well because I can  slip it over the end of the 'scope without disturbing it, and so can run off flats any time during the session.

Ian

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13 hours ago, Filroden said:

Well, here's early sight of my integration of the Ha images. I only managed 34 x 30s and 22 x 60s, all taken at 300 gain, 50 offset and -20C. I haven't inspected them, rejected any images, or applied any calibration. This is uncropped and only stretched with levels and curves. I have to say, Ha data is so much cleaner to work with than LRGB! I'll be taking flats tomorrow and doing a proper integration of this, and my LRGB data (not that I got much before it went behind the steam vent). I also took a quick peek at M81 and it's a breath taking galaxy (but that one really does need calibrating!).

NGC2239_H_40m.jpg

Fantastic! You are on your way to the par with that one:

It's already just as fine. Can't wait for color :)

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2 hours ago, Filroden said:

3. HaRGB

The latter to see if it retains more detail without the L channel.

I'm tempted to suggest just HaGB or rather LHaGB, because I wonder if Ha could completely replace R.

I also wonder if L can replace G, so that you could also try HaLB. Anyway that's a lot of tries :)

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Very little detail carries into the image from the RGB. It is used to add colour to another layer, which could be L, Ha or a blend of both. I could use the colour of Ha instead of red but I would need to also use Ha instead of L or with L. So more like LHa-HaGB

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44 minutes ago, Filroden said:

Very little detail carries into the image from the RGB. It is used to add colour to another layer, which could be L, Ha or a blend of both. I could use the colour of Ha instead of red but I would need to also use Ha instead of L or with L. So more like LHa-HaGB

Correct me if I'm wrong, but can't L be extracted from RGB? Otherwise it wouldn't be possible for Bayer arrays to work, would it? I'm not sure where the practise of doing a separate L channel exposure in astro imaging has come from. So why can't Ha just be used in place of R, why do you need to add an L channel replaced by Ha? I don't understand how that would add anything. This is an area where I know little, so I'm happy to be educated.

Ian

PS. There's a lot of detail in you Ha image already.

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It's just how my workflow works. Because I capture L i don't need to carry detail from RGB (so I collect less and I can apply a lot of blurring to reduce noise). I only use its colour information. If you collected enough RGB on its own it does become like a OSC. But I gather L much quicker than RGB so I prefer it for detail. If I don't have a lot of L I have extracted L from RGB and combined it with real L. Sometimes it improves the image, sometimes not.

So the suggestions are possible but given I have L data I would end up throwing away detail. That said, the Ha is so clear I think I could use it instead of L. 

The other reason not to replace R with Ha is you would get false star colours.

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39 minutes ago, JohnSadlerAstro said:

Hi,

OK, so this is rather an ignoramus question, but would I be able to capture the Rosette Nebula with an unmodded Canon DSLR on a 900mm focal length scope with an expo length of say, 1:00-1:30?

John

Well, a question worth asking, and the quick answer is anything's worth a try!

A couple of points to note. Un-modded cameras vary in their red sensitivity, I can't comment specifically about the EOS 1000d, but there are plenty of folk on here who can. We tend to use 'scopes with a FL around 500mm and even so the Rosette's a tight fit. The Rosette is 1.3° in diameter, so I think you'd have problems imaging the whole object. As happy-kat suggests, you'd probably have more luck with your camera lens at 200mm.

I'm not sure what you mean by 1:00-1:30. Do you mean 60-90s per sub, or an hour to 1-1/2 hours total? Presumably, if the former I guess you'll be using your EQ mount (off-topic for this thread :icon_biggrin: ). But I'd certainly aim for a minimum of an hours total exposure, though I've revealed it with as little as 20m (see https://stargazerslounge.com/topic/261523-the-glorious-orion-and-rosette-nebulae/ though I've come on a bit since then!).

Ian

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4 hours ago, The Admiral said:

I think the sensor 'cleaning' cycle it invokes each time I switch off is doing a fair job.

I've turned this off on my camera, as if it self-cleans between me taking photos and making my flats...

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1 hour ago, JohnSadlerAstro said:

Hi,

OK, so this is rather an ignoramus question, but would I be able to capture the Rosette Nebula with an unmodded Canon DSLR on a 900mm focal length scope with an expo length of say, 1:00-1:30?

John

I got the Rosette on my (modded) 10D last year using a 135mm lens.

Bearing in mind that the 10D is only 10bit so I is much less sensitive than even an unmodded camera I would say. I can't post the pic as it's taken on an EQ tripod ;'-)

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22 minutes ago, Stub Mandrel said:

I've turned this off on my camera, as if it self-cleans between me taking photos and making my flats...

Yes, a point worth remembering, though I've not been that diligent in this regards I must admit! I've been lucky in that the dust hasn't been that troublesome. It'd be worth doing a sensor clean at the beginning of an imaging session I'd have thought.

Ian

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