Newbie needing help with M31

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julietdiane
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Joined: Fri Nov 17, 2017 11:17 am

Newbie needing help with M31

Post by julietdiane » Fri Nov 17, 2017 11:58 am

Image

This is my first ever imaging attempt, up to now I was visual only.
Equipment Stats:
Skywatcher startravel 150 (F/750) apochromatic refractor with ZWO 150mm (USB 2.0) colour camera.

Sharpcap Stats:
I used Livestack.
Capture Area=1280x960, Colour Space=RGB24, Gain=100, Exposure=23.5, White Bal (B)=79(Auto), White Bal (R)=63(Auto), Brightness=3, Gamma=55
Apply Flat=None, Subtract Dark=None, TotalExposure(s)=471.0, StackedFrames=20

Apology:
The grey grainy background blurs is my telescope lens needing a clean. ( Never spotted this in visual sessions).

Any Tips Please:
I am not sure if this is a good attempt or not.
Also I cannot see M32 or M110 is this because I'm zoomed in too much?
Last edited by julietdiane on Fri Nov 17, 2017 6:05 pm, edited 2 times in total.

robrj
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Re: Newbie needing help with M31

Post by robrj » Fri Nov 17, 2017 4:31 pm

I get a 404 page not found with your link.

robrj
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Re: Newbie needing help with M31

Post by robrj » Fri Nov 17, 2017 4:40 pm

As for M110 & M32, I think you'll need a wider field of view, so either a small, fast telescope, a focal reducer or a much larger sensor on your camera.

Here is M31/M32/M110 in one image using an Orion 50mm Guidescope. You can see how far away they are (hover your mouse over the image to see them marked:
Image


Here it is in an 8" with a similar focal length and sensor size:
Image

julietdiane
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Joined: Fri Nov 17, 2017 11:17 am

Re: Newbie needing help with M31

Post by julietdiane » Fri Nov 17, 2017 5:47 pm

You suggested a focal reducer - I just read up about it and yes looks like it does give a wider view. I will need to get one.

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admin
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Re: Newbie needing help with M31

Post by admin » Fri Nov 17, 2017 7:08 pm

Hi,

while a focal reducer will give you a wider view, you can improve your image quite a bit by fixing a couple of simple problems the next time you image...

1) Focus - your focus is a bit soft - getting this right will be the biggest change you can make. SharpCap has a number of focus assistance tools, and for M31, I'd suggest using the 'Multi Star FWHM' tool (find it by clicking on the magnifying glass on the toolbar). This tool finds stars on the image and measures their widths - the smaller the better. As you adjust the focus, SharpCap will show a rolling graph of the average star width and you just adjust to make that score as small as possible.

2) Hot Pixels - the grey worm trails running horizontally are caused by hot pixels from your camera - these are reading out at a very high level in every frame due to the long exposures. Sadly the sensor in the 120MM is quite prone to them. There are a few ways to get rid of them or reduce them

a) Dark subtraction - you can use SharpCap for this - take dark frames of the same exposure time just before you start imaging and then subtract those to remove most of the hot pixels (best to do new darks every time as they depend on the sensor temperature which will change from day to day with the weather)

b) Cooling - the ZWO cameras are relatively easy to add DIY coolers to using a 12V peltier cooler (£6 or so from ebay) and an old PC heatsink/fan.

c) If you can't do either of the above, try stacking more but shorter exposures (at some point going shorter will start hitting problems with noise build up, so this may not be applicable).

Hope this is helpful,

Robin

julietdiane
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Joined: Fri Nov 17, 2017 11:17 am

Re: Newbie needing help with M31

Post by julietdiane » Fri Nov 17, 2017 7:57 pm

Robin,

Wow you have given a lot to think about and I look forward in looking into your tips.

I am wondering have I over-blown the white centre?

And finally what I thought was dust on my lens, second look at the background "Noise" - it is to regular to be dust. I am wondering if I am having
problems with my AZ-EQ6 mount - possible vibration. Any thoughts on what this horrible noise maybe?.

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admin
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Re: Newbie needing help with M31

Post by admin » Fri Nov 17, 2017 8:07 pm

Hi,

I think the noise you are talking about (the little white horizontal wiggly lines) are the hot pixel tracks I am talking about. What's happening is that your mount is not quite tracking perfectly (PA may be slightly off). SharpCap live stacking fixes that by aligning every frame using the stars, but that means that the hot pixels which stay in the same place on every frame create little trails across the image. Dark subtraction or cooling should get rid of those.

The center is a bit over exposed - you'll get more dynamic range (the ratio between the brightest and dimmest things) by switching into MONO16 mode (RAW16 for a colour camera). This will help keep detail in the faint stuff when you reduce exposures to avoid blowing out the core.

cheers,

Robin

julietdiane
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Joined: Fri Nov 17, 2017 11:17 am

Re: Newbie needing help with M31

Post by julietdiane » Sat Nov 18, 2017 9:54 am

Thanks again, I will take on board your hints and "I'll be back" with something better.

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turfpit
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Re: Newbie needing help with M31

Post by turfpit » Sat Nov 18, 2017 12:59 pm

Have a look at these viewtopic.php?f=16&t=353 . They were captured with a ZWO ASI120MC. I captured dark frames (just put the cap on the camera and follow the instruction from the menu in SharpCap). The dark frames were subtracted 'on the fly' as the images were captured.

Dave

julietdiane
Posts: 6
Joined: Fri Nov 17, 2017 11:17 am

Re: Newbie needing help with M31

Post by julietdiane » Sat Nov 18, 2017 3:26 pm

Great pics Dave, just goes to show even with the cheapest ZWO camera you can get some good images.

I want to limit my time on the computer (not do any post processing..) that is why Livestack is ideal for me.

Robin,
See the blank vertical black bar on the left hand side of my image (you have to look carefully), I think this is the misalignment between frames that you talked about.?

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