M51 and pacman nebula

[ckp82]

I finally managed to get out last night to get reacquainted with my setup and see what I could see. I'm still new to eaa so my images aren't as good as some on here, but I'm happy with what I can see and hopefully with more experience I'll be able to tweak and ease out some more detail.

I used a bahtinov mask to focus. In hindsight I think Vega was too bright to do this on as in preview mode it looked spot on but I've got some strange looking stars, maybe it's the tracking? Any advice would be greatly appreciated on how to make a better image. I think I may also have some dust or dew marks on one of the lenses which can be seen in the images?

I'm waiting for my dual narrowband filter to arrive but had a go at the pacman filter anyway. I took 55 x 30 seconds images and can start to see the colour and shape come through, I'm guessing with the filter I'll see more in the same time frame?

M51 was 15 x 30 seconds

Equipment used were as follows:

Skywatcher st80

Skywatcher azgti and wedge

Asiair plus

Asi585mc 

Svbony ir/cut filter (I heard this filter stops star bloat?)

Thanks.

[PeterC65]

I don't think you're out of focus. The star shapes look like you have a problem with field flatness. I get this around the edges of my refractor images but with the widening smudges pointing outwards towards the edges of the image, so with stars on the left the smudge is to their left and with stars on the right the smudge is to their right. You have these smudges right across your image and all pointing to the right, so I'd say you have an issue with camera tilt.

The dark circles on your M51 image are caused by dust. You can get rid of this sort of thing by taking flat frames but taking flats is quite a bit of effort. I would check your optical train for any obvious signs of dust and try to remove it. It could be anywhere in the optical chain, from the camera window to the scope objective lens.

The M51 image has quite a bright background, particularly in the lower left quadrant. This might be caused by dew on the telescope objective lens. The dew scatters light from other sources, such as nearby terrestrial lights or the Moon, which brightens the background. In this case the brighter background is also making the dust spots more obvious.

When you get your narrowband filter it will make the background darker so that you will see the Pacman Nebula more clearly but even without the filter you can make out the shape.

 

[ckp82]

1 hour ago, PeterC65 said:

I don't think you're out of focus. The star shapes look like you have a problem with field flatness. I get this around the edges of my refractor images but with the widening smudges pointing outwards towards the edges of the image, so with stars on the left the smudge is to their left and with stars on the right the smudge is to their right. You have these smudges right across your image and all pointing to the right, so I'd say you have an issue with camera tilt.

The dark circles on your M51 image are caused by dust. You can get rid of this sort of thing by taking flat frames but taking flats is quite a bit of effort. I would check your optical train for any obvious signs of dust and try to remove it. It could be anywhere in the optical chain, from the camera window to the scope objective lens.

The M51 image has quite a bright background, particularly in the lower left quadrant. This might be caused by dew on the telescope objective lens. The dew scatters light from other sources, such as nearby terrestrial lights or the Moon, which brightens the background. In this case the brighter background is also making the dust spots more obvious.

When you get your narrowband filter it will make the background darker so that you will see the Pacman Nebula more clearly but even without the filter you can make out the shape.

 

Thanks @PeterC65

How would I go about fixing the camera tilt? Is the only way buying a camera tilt unit? I can screw the camera and extender tube onto the end of the scope but if I add a filter I have to use a nose piece for the filter to screw into. This is then held in place place with the grub screws. Could this be the problem?

I haven't a clue about flats, darks and bias yet. Is the flats where you put a white t shirt or light panel over the lens and then shoot so many shots at the same exposure? I'll give the optical train a good look over for any dust or marks.

Thanks again.

[TiffsAndAstro]

20 minutes ago, ckp82 said:

Thanks @PeterC65

How would I go about fixing the camera tilt? Is the only way buying a camera tilt unit? I can screw the camera and extender tube onto the end of the scope but if I add a filter I have to use a nose piece for the filter to screw into. This is then held in place place with the grub screws. Could this be the problem?

I haven't a clue about flats, darks and bias yet. Is the flats where you put a white t shirt or light panel over the lens and then shoot so many shots at the same exposure? I'll give the optical train a good look over for any dust or marks.

Thanks again.

You will be shocked by what calibration frames will do for your results.

[PeterC65]

1 hour ago, ckp82 said:

Thanks @PeterC65

How would I go about fixing the camera tilt? Is the only way buying a camera tilt unit? I can screw the camera and extender tube onto the end of the scope but if I add a filter I have to use a nose piece for the filter to screw into. This is then held in place place with the grub screws. Could this be the problem?

I haven't a clue about flats, darks and bias yet. Is the flats where you put a white t shirt or light panel over the lens and then shoot so many shots at the same exposure? I'll give the optical train a good look over for any dust or marks.

Thanks again.

The camera tilt is probably fixable without a tilt unit. You could screw together the optical train and if you do this there are adapters (like this one) that allow a 1.25" filter to be fitted to the camera while still using the M42 screw connection. Screw connections are the most accurate, but you should be able to fit the optical train together with nosepiece / clamp connections and have no tilt (this is what I do). Make sure the clamps all have compression rings with two thumb screws as these are less prone to tilt. I would also check the focuser on your ST80 (this will also need a compression ring fitting). When you fit each nosepiece / clamp, make sure you turn it an check that it is home properly square as you tighten the thumb screws.

Yes, flats are taken with a white T-shirt or light panel over the scope objective lens. I sometimes use them but mostly I don't. Flats are quick to take but quite fiddly to get right and they need to be taken with the optical train you are using on the night (and re-taken if you change anything). As I understand it, flats also need to be used with darks (taken with an opaque cover over the scope objective lens). Darks are not so fiddly and you can take a set at different camera temperatures and use them across sessions, but they take longer to take.

I use SharpCap for EAA which has a hot pixel removal and a background removal feature, and used together these do almost as good a job as dark frames but with much less fuss. Then if I'm not using darks I don't use flats. In my (relatively limited and EAA only) experience, darks and flats only make a worthwhile difference if you are pushing your optics, so using high magnification or observing difficult objects. For example, I only take darks and flats when I'm using the Explorer 200 with a Barlow and am trying to observe faint galaxies or nebulae.

I'm sure its a different story for AP.

[bosun21]

5 minutes ago, PeterC65 said:

you do this there are adapters (like this one) that allow a 1.25" filter to be fitted to the camera while still using the M42 screw

I have found these to be too thick as they take up most of the M42 thread leaving the camera barely hanging on by a single turn.

[ckp82]

1 hour ago, TiffsAndAstro said:

You will be shocked by what calibration frames will do for your results.

I've just watched a video on what calibration frames are and see that bias frames are taken with the quickest exposure possible and darks are the same as lights but nothing about the exposure time of flats. What should these be?

[ckp82]

34 minutes ago, PeterC65 said:

The camera tilt is probably fixable without a tilt unit. You could screw together the optical train and if you do this there are adapters (like this one) that allow a 1.25" filter to be fitted to the camera while still using the M42 screw connection. Screw connections are the most accurate, but you should be able to fit the optical train together with nosepiece / clamp connections and have no tilt (this is what I do). Make sure the clamps all have compression rings with two thumb screws as these are less prone to tilt. I would also check the focuser on your ST80 (this will also need a compression ring fitting). When you fit each nosepiece / clamp, make sure you turn it an check that it is home properly square as you tighten the thumb screws.

Yes, flats are taken with a white T-shirt or light panel over the scope objective lens. I sometimes use them but mostly I don't. Flats are quick to take but quite fiddly to get right and they need to be taken with the optical train you are using on the night (and re-taken if you change anything). As I understand it, flats also need to be used with darks (taken with an opaque cover over the scope objective lens). Darks are not so fiddly and you can take a set at different camera temperatures and use them across sessions, but they take longer to take.

I use SharpCap for EAA which has a hot pixel removal and a background removal feature, and used together these do almost as good a job as dark frames but with much less fuss. Then if I'm not using darks I don't use flats. In my (relatively limited and EAA only) experience, darks and flats only make a worthwhile difference if you are pushing your optics, so using high magnification or observing difficult objects. For example, I only take darks and flats when I'm using the Explorer 200 with a Barlow and am trying to observe faint galaxies or nebulae.

I'm sure its a different story for AP.

I never knew these adaptors existed. I've ordered one as I like the extender tube screwed into the focuser tube rather than the grub screw holding it.

I'll have to have a play about with the different type of frames.

[ckp82]

30 minutes ago, bosun21 said:

I have found these to be too thick as they take up most of the M42 thread leaving the camera barely hanging on by a single turn.

I did see the reviews were varied but I thought I'd try it

[bosun21]

3 minutes ago, ckp82 said:

I did see the reviews were varied but I thought I'd try it

They are ideal for screwing into an extension. It's just when used directly in the camera I found that they use up the threads.

[TiffsAndAstro]

9 minutes ago, ckp82 said:

I've just watched a video on what calibration frames are and see that bias frames are taken with the quickest exposure possible and darks are the same as lights but nothing about the exposure time of flats. What should these be?

I use Nina flat wizard and it's incredibly simple and reliable.

Before I used Nina flat wizard, I would just switch my dslr from manual to aperture priority and take my flats (white t-shirt, tablet displaying white screen, histogram 1/3 from left). Worked a treat on my canon 600d.

I would recommend looking at some introduction to Nina videos. Nina should work with your Nikon.

[daz]

Flats:
Don't worry about the temperature of flats. They need to be long enough of an exposure to give somewhere between 40% and 60% of your histogram brightness. You might need to experiment with the exposure length to get the right value. Aim for 20-25 frames that you will stack to produce a master

Darks:
Same duration as the light frames, and if possible, same temperature. Aim for more frames - 40 to 50, but again might need experimentation with your camera.
You will need TWO sets of darks - one for the light frames and one for the flat frames (these are sometimes called flat darks or dark flats, but are just darks!) The ones for the flat frames will be at the same duration as the flat frames.

Bias:
Don't worry about these. Unless you plan on scaling your darks, you won't need them. Take darks for the flat frames instead.

 

So, you will end up with:

Light frames
Flat frames
Darks for the flat frames
Darks for the light frames

Good first images though! Welcome to the slippery slope!

 

[ckp82]

2 hours ago, TiffsAndAstro said:

Nina should work with your Nikon.

I'm using an Asi585mc and the asiair plus.

Thanks for your reply though.

[TiffsAndAstro]

3 minutes ago, ckp82 said:

I'm using an Asi585mc and the asiair plus.

Thanks for your reply though.

Doh apologies. It's a quality camera and deserves flat frames though

[ckp82]

2 hours ago, daz said:

Darks:
Same duration as the light frames, and if possible, same temperature. Aim for more frames - 40 to 50, but again might need experimentation with your camera.
You will need TWO sets of darks - one for the light frames and one for the flat frames (these are sometimes called flat darks or dark flats, but are just darks!) The ones for the flat frames will be at the same duration as the flat frames.

 

Thanks for the explanation.

As I'm using asiair software it gives me options for lights, flats, dark and bias if I remember right. Would I just make another set of darks in the bias folder?