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Please critique my recent efforts with M42 and M45.


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Hi all,

As a beginner to astrophotography, I have just bought an Altair Starwave 80 ED-R to go on my SW EQM-35 Pro GOTO mount. I also have the Starwave v3 0.8x reducer and attached my Canon EOS 70D. From my garden I can’t see Polaris, so I normally set up and polar align using PS Align Pro (and I can do this during daylight too). I didn’t run any star alignment routines with the mount and then tried to image both M42 and M45.

When I used the GOTO to get on target, I was a little off both targets so used the handset to get on target (which wasn’t too far off). Once on target I took some practice shoots with varying exposures. In the end I was getting 15 second exposures with no obvious star trailing (I’m sure if I had run a 2- or 3-star alignment routine I would have got longer exposures). These were all unguided too (this is potentially the next upgrade to my set up).

The images below were taken at ISO 800, and I managed to get a total of just over 50 mins exposure time for M45 and 61 mins for M42 with 15 sec exposures for both. I also took flats and biases (no darks as many here think darks aren’t useful for DSLRs).

I stacked the images in DSS using the intersection mode – I noticed when capturing the images that the EQM-35 wasn’t tracking properly as the star field of view of the individual images seemed to be moving from right to left between each exposure when viewed on my image capture software (Backyard EOS).

I then took the stacked images and processed them in Affinity Photo. The processing routine was very quick and simple as I only used a colour-preserving tone stretch macro developed by James Ritson and then used the ‘remove background’ tool to get rid of the gradient. That’s all I’ve done to them so far. I’m sure with more practice and ability I’ll be able to tease out a bit more detail and make them look reasonably acceptable, but I would welcome any thoughts, comments, or advice on what I’ve managed to achieve. I know the core of M42 is a bit overexposed so probably need to learn how to use mask layers in post-processing.

Obviously, I want to improve the EQM-35 tracking and have seen a few YouTube videos on how it can be tweaked to get it to perform better. I’ve also just bought an Optolong L-Pro filter to see if that will help with light pollution from my Bortle 7/8 location. I still need to try this filter out with my set up – when we get some clear skies again!

Thanks for any advice/comments. It’s still a steep learning curve for me 😊 

M42.jpg

M45.jpg

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Considering the short times they're pretty good. I struggle to get the nebulosity with m45, probably because the moon's always out when I attempt it. I'm not familiar with affinity but in PS I sometimes duplicate the layer and use the top one as a luminosity/soft light to enhance the gaseous regions a bit more.

Edited by Elp
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9 minutes ago, Elp said:

Considering the short times they're pretty good. I struggle to get the nebulosity with m45, probably because the moon's always out when I attempt it. I'm not familiar with affinity but in PS I sometimes duplicate the layer and use the top one as a luminosity/soft light to enhance the gaseous regions a bit more.

Thanks. I can try that in Affinity too. 

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Looking great for first tries with short integration!

Guiding is what will make your EQM35 work much more reliably, although still wont do miracles for you. My unit had a particularly nasty periodic error so unguided was not a good way to spend clear nights for me.

You can try and test how much periodic error you have by polar aligning as well as you can, orienting the camera so that RA is level left to right and shooting an exposure of at least 480s towards a low declination part of the sky. The image will be ruined of course but then you can measure how much periodic error you have by measuring the length of the trails in RA. Wont work if its windy though as the mount doesnt like that.

When you get this measurement you can make an educated guess as to how long could you shoot unguided. I would guess that 15s is already close to the max exposure time that is somewhat reliable, so you could just use that.

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2 minutes ago, ONIKKINEN said:

Looking great for first tries with short integration!

Guiding is what will make your EQM35 work much more reliably, although still wont do miracles for you. My unit had a particularly nasty periodic error so unguided was not a good way to spend clear nights for me.

You can try and test how much periodic error you have by polar aligning as well as you can, orienting the camera so that RA is level left to right and shooting an exposure of at least 480s towards a low declination part of the sky. The image will be ruined of course but then you can measure how much periodic error you have by measuring the length of the trails in RA. Wont work if its windy though as the mount doesnt like that.

When you get this measurement you can make an educated guess as to how long could you shoot unguided. I would guess that 15s is already close to the max exposure time that is somewhat reliable, so you could just use that.

Thanks. Would this periodic error cause the apparent movement of my field of view between each exposure? The movement is very small but noticeable when you move from one frame to the next.

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17 minutes ago, Steve143 said:

Thanks. Would this periodic error cause the apparent movement of my field of view between each exposure? The movement is very small but noticeable when you move from one frame to the next.

Steady drift to one direction is probably drift in declination due to poor polar alignment. Actually doesnt even have to be that poor if the session is long and you did not recenter. I found it necessary to babysit the mount and check the framing from time to time when i shot unguided.

Periodic error is back and forth where the tracking speed of your mount underperforms and overperforms periodically over one worm period (480s) but shouldnt result in steady drift for longer than one worm cycle. This motion is only in RA.

By the way doing the 3 star alignment will tell you how much youre off in polar alignment in the end, so you could use that to check how accurate it was. This does rely on you being very accurate when centering the alignment stars. It would make GO-TOs more accurate too, but not help with tracking accuracy.

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M42 is sort of a haiku of imaging -- anyone can put one together, but there is a great depth of subtlety and nuance available. You're well on your way!

The brightest area in the nebula, known as the Trapezium, is easy to "blow out" so that it's undifferentiated white. And it's actually rather hard to not do that, while still getting enough exposure to swamp the noise in the dimmer regions. There is actually an enormous cloud of dust and gas around the frequently-seen parts of the nebula, so that's another axis of difficulty even for experienced imagers.

Is the Trapezium blown white on your individual sub-exposures? If not, you may be able to retrieve some detail in it by masking it out as you stretch the contrast. In the past I've straight-up cheated by compositing with either a less-stretched version of the image, or an integration of much shorter sub-exposures, and masking in the bits with a soft brush in Photoshop.

A 2- or 3-star alignment, as onikkinen says, will not do anything for tracking accuracy. What that does is ground-truth the mount's sky model so that when you tell it to do a GOTO, it will be much more accurate. But polar alignment is an entirely physical thing, hoicking the mount's polar axis around until it points exactly at the Celestial Pole. There are several packages now that can align to within a few arcminutes using your imaging scope and camera, by taking a series of images at different RA positions, plate solving them, and back-calculating the axis error that would produce them. And several of them don't need to see the northern sky at all, much less Polaris.

You can also get a direct measurement of just how much DEC drift your alignment allows via the DARV method. Robert designed it as a means of actually polar aligning the scope via drift measurement, but it's also useful as a quick check. Basically you do a time exposure while (slowly) slewing the RA axis so that the image of the star reaches the edge of the frame in, say, two minutes, then slewing it back again. If you see a bright line, you're golden. If you see an elongated "V", you have DEC drift going on. He even thought of exposing for an extra interval at the start before beginning the slew, so one leg of the "V" ends in a bright dot -- that way you can tell which direction you're drifting.

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8 hours ago, rickwayne said:

There are several packages now that can align to within a few arcminutes using your imaging scope and camera, by taking a series of images at different RA positions, plate solving them, and back-calculating the axis error that would produce them. And several of them don't need to see the northern sky at all, much less Polaris.

Thanks. Can you tell me what these packages are? I was looking at the QHY PoleMaster as a solution - if I can get sight of Polaris! 

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2 hours ago, Steve143 said:

Thanks. Can you tell me what these packages are? I was looking at the QHY PoleMaster as a solution - if I can get sight of Polaris! 

Sharpcap Pro - need to be able see within about 5 degrees of the pole.

NINA (only in the beta at the moment I think)  - don't need to be able to see the pole.

With both of those they tell you the alt and az errors along with the total error and you adjust the alt and az of your mount until you get a small error.

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KStars/Ekos suite is what I use. I run it with StellarMate OS on a Raspberry Pi 4, but it can also run on Windows and Mac OS. It's a complete observatory-control system but you don't have to know all of it to use part of it. And it's all the same price (US$0.00).

Well, technically I paid $50 for mine, which was prepackaged to go onto a MicroSD card so I could just download it, burn it to a card, and boot the Pi with it. But KStars and Ekos are free to download.

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