What is going on in this image?

[Andyk93]

Hi, I would like some help with imaging, I can't figure out what's going on in the photos that I'm taking. Here is the full spec list, equipment used and settings.

SW 200pds, neq6, auto focuser, Baader 13mm Hyperion, extension tube, SW coma corrector

Camera is a Nikon d3300 (i know this isn't ideal)

settings for this image: iso800, 1 x 30second exposure.

the picture is of Deneb in the Cygnus region. It was taken today when the full moon was out and I would say below average LP.

the main thing is the stars are teardrop shaped, some stars are multi coloured red/blue/white.

it is well polar aligned, the scope is perfectly collimated, there was no wind, vibration or movement in the mount. I don't touch the mount to focus or take pictures and I used a Bahtinov mask to focus this.

Any help really appreciated.

 

 

[Uranium235]

Proabably best to convert it to a jpg with a little stretch, then repost the image so people can make a quicker diagnosis of what may be the issue.

[Andyk93]

6 minutes ago, Uranium235 said:

Proabably best to convert it to a jpg with a little stretch, then repost the image so people can make a quicker diagnosis of what may be the issue.

I'll do that now, thanks

[Demonperformer]

At the risk of stating the obvious, all the 'tails' on the stars are going from the centre to the edge (so it isn't guiding) with the red fringe is towards the centre and the blue fringe to the edge.

According to MEPC p182, "Reflectors produce a pretty 'pure' image, free from chromatic aberration" - which yours appears not to be and it does have coma.

I would therefore guess that it is something to do with the coma-corrector. Maybe something to do with its spacing? If the spacing is critical then, because it contains lenses, this may introduce the colour fringes as well as not correcting the coma properly if the spacing is out.

[I'm no imaging expert, neither do I use a newt/coma corrector, so others may have more informed opinions].

HTH

[alacant]

 

8 hours ago, Andyk93 said:

Baader 13mm Hyperion, extension tube, SW coma corrector

Hi. You have an eyepiece in the light path (?). That should explain the colour. The coma may be that the extension tube is throwing the cc to sensor distance. I think the cc should be right up against the camera flange. Can you post a photo or some measurements of what's in the focuser and in what order? HTH.

[Andyk93]

Okay so I've taken some pictures of exactly how it was setup. Camera - eyepiece - cc - extension. Thinking about it now I probably didn't need the extension. 

From camera to the end of the extension is 180mm and without the extension it's 120mm

[Chris-A]

As Alacant says, it's the eyepiece that's the problem - you don't need an eyepiece for astrophotography, just for visual.

[Andyk93]

10 minutes ago, Chris-A said:

As Alacant says, it's the eyepiece that's the problem - you don't need an eyepiece for astrophotography, just for visual.

Surely I'm not going to get any magnification without the eyepiece? I just assumed you needed it. I will give it another go tonight. Thanks for the help

[Chris-A]

5 minutes ago, Andyk93 said:

Surely I'm not going to get any magnification without the eyepiece? I just assumed you needed it. I will give it another go tonight. Thanks for the help

For imaging the magnification comes from the native focal length of the telescope, not from any optical elements such as eyepieces (although it is possible to use Barlow lenses to extend that effective focal length in certain circumstances, especially for planetary imaging).

[alacant]

Hi. The first element up against the camera flange must be the cc. Unless you're going for planets, lose the eyepiece -and hence the colour-, the extension tube -or you're not going to reach focus- and you're good to go. Clear skies and HTH.

[Uranium235]

Its definietly the EP causing this, I did the same when I first started and the resulting images were horrendous. If you want a lot more magnification for planetary, just use a barlow (3, 4 or 5x). Or, you can stack a couple of 2x barlows.... but thats not as good as having one powerful barlow.

[Andyk93]

Thank you all very much for the help. It should be clear tonight so I will post up an image of the same area for reference

[ollypenrice]

There is no such thing as magnification in imaging. Nothing is being magnified. (Consider the true size of M31... You ain't about to magnify it!!!) In visual observing the image on the retina is being magnified so the image has a 'natural' size and a magnified one. There is no natural sized image to be magnified in AP.

Instead think of focal length. The longer the focal length the larger the projected image will be on the chip. If you want to get the whole of M31 onto an APSc sized chip the longest possible focal length will be around 300mm. A scope with more FL than that will not allow M31 to fit on your chip.

As the others have said, forget the eyepiece! Shoot at native FL.

Olly

[Andyk93]

I've had another go tonight. i was figuring out how to guide more than image but thought I would do a comparison of Deneb. The moon was up so it's not the best but it's definitely better than the first image. Any pointers would be much appreciated ? There is a purple halo next to Deneb, I don't have a clue what that would be

 

[wornish]

Definitely fixed the original problem  no sign of the coma.  Your focus is spot on.

Had to look really close on the full size image  to see the purple halo is it to the right of Deneb ?

Don't think its sensor noise because of its shape.

Could be some light pollution possibly,

or a very small flaw in the coma corrector or on one of the mirrors in the scope.

 

[Andyk93]

yes it is. It looks to me like a water droplet with light pollution shining on to it. I'm going to try again tomorrow, thanks for the advice

[Knight of Clear Skies]

It might just be a reflection from the very bright Deneb. If you can dither when imaging (move the scope a few pixels between each exposure) and use a statistical stacking method then most artifacts like this will vanish.

[alacant]

On 21/10/2016 at 19:10, Andyk93 said:

a water droplet

Hi. My money is on the cc. Can you test shoot without? IAC it's unlikely you'll be imaging with anything as bright as Deneb in the fov so no worries even if you find positive. HTH.

[Andyk93]

4 hours ago, Knight of Clear Skies said:

It might just be a reflection from the very bright Deneb. If you can dither when imaging (move the scope a few pixels between each exposure) and use a statistical stacking method then most artifacts like this will vanish.

Is there a tutorial for dithering? It's something else I've got to learn to do. Thanks

[Andyk93]

2 hours ago, alacant said:

Hi. My money is on the cc. Can you test shoot without? IAC it's unlikely you'll be imaging with anything as bright as Deneb in the fov so no worries even if you find positive. HTH.

Yeah I will do that tonight as it should be clear again. This is my first stacked image of andromeda, I think I'm on the right track it just obviously needs more data. 11x20second images. It's not been processed at all. Appreciate the help

[alacant]

49 minutes ago, Andyk93 said:

Is there a tutorial for dithering?

Hi. You don't really need a tutorial. With most camera apps such as APT, it's a simple one click option. With your setup I'd suggest starting at a dither of around 15 pixels. There's a but however; APT also needs to control your camera and mount. I don't think you've mentioned how you're doing that ATM so I don't think we'll be able to answer fully. HTH.

[alacant]

48 minutes ago, Andyk93 said:

It's not been processed at all.

Stretch it anyway just to see what's there but I think you're gonna need longer exposures -I'd start at e.g. 2 minutes ISO 1600-. Also with a telescope, you're not gonna get much of the galaxy; you'd do better with a 200-300mm camera lens. HTH.

[Andyk93]

20 minutes ago, alacant said:

Hi. You don't really need a tutorial. With most camera apps such as APT, it's a simple one click option. With your setup I'd suggest starting at a dither of around 15 pixels. There's a but however; APT also needs to control your camera and mount. I don't think you've mentioned how you're doing that ATM so I don't think we'll be able to answer fully. HTH.

I use eqmod + cartes du ciel with phd2 for guiding. I have a qhy5 and 9x50 scope for guiding and a Nikon d3300 and use an intervalometer to control it. I have got apt but I assumed the Nikon wouldn't connect to it. I'm looking at getting an Astro modded canon next

[Andyk93]

I did image the ring nebula and dumbbell nebula last night too. The dumbbell was 20x30seconds and the ring was 51x30seconds. Just stacked nothing else.