Bad result with Lens Projection technique

[maksovnik]

Hi there, I tried to take an image of the M42 Orion Nebula using 20mm Wide Angle eyepiece projection with a T ring adapter on my Nikon D3200 and my SkyWatcher 130/900 telescope. I managed to get the core of the nebula mostly in focus however upon observing the images I noticed that the stars nearer the edges of the image are completely blurred and out of focus. This meant that when I tried to put my images into Deep Sky Stacker the result was not what I wanted.

As a sidenote I have tried prime focus and I can not move the focuser in enough to get into focus via this method. I can use a barlow but again the same issue as mentioned in the previous paragraph occurs where things near the outside of the image because blurred.

One of the exposures(20 second for each)
[img]https:/ /i.imgur.com/RNDNMbY.jpg[/img]


Deep Sky Stacker result


How can I fix this??

Thanks
Maks

[sdbodin]

Try the Afocal method as described in this article:

app.php/article/basic-astrophotography-4

This should be easier than trying projection and result in a better correction of the edge of field.

Clear skies,
Steve

[maksovnik]

Hi there, I did some research and am struggling to see the difference between Afocal and Eyepiece projection. I can't just hold my camera to the eyepiece because I need it to stay there for 20 second exposure minimum.

[sdbodin]

The difference is that your camera lens should be removed for eyepiece projection. However, eyepieces are not corrected for projection, we all had slide projectors back in the day and those lenses were designed for that, but none are around today. But, Barlow lenses are corrected for projection, that is their lot in life. The Afocal method has the eyepiece at its designed placement in the optical train and should not add extra field curvature from what is already present in the telescope. However, other than those cell phone adapters out there in the market place, placing a real digital camera in Afocal configuration is problematic. And all that glass in the way does strange things, this is why I prefer the Prime focus placement which you cannot access, I guess.

BTW, you image displays a lot of field curvature or coma, I can't remember, is your scope a basic reflector? If so, then this is to be expected with out a coma corrector, another couple hundred bucks.

Good luck,
Steve

[JimMinCT]

Hi there, I did some research and am struggling to see the difference between Afocal and Eyepiece projection. I can't just hold my camera to the eyepiece because I need it to stay there for 20 second exposure minimum.

They sell phone adapters for just that purpose.
Do a search for telescope phone brackets.
This will not fix the extended curvature you are seeing. As was mentioned, a coma corrector is required to fix that.