Sh2-155 The Cave Nebula and surroundings

[MarkS]

Sh2-155 in Cepheus is probably the most challenging target I've tackled so far and I'm very pleased with the result.  
Taken in Riberac over 2 evenings (5 & 12 August).

The usual setup: H-alpha modified Canon 350D on Banana Scope (Tak Epsilon 180ED) with only an IR/UV filter.

65 x 5 minute exposures at ISO 800



Larger version here (scaled by 2/3):
http://gallery.orpington-astronomy.org.uk/albums/userpics/10046/cave12082010v2.jpg

It's a very interesting area of the sky with colourful stars, emission nebulae, reflection nebulae and some dark "blobs"

Enjoy!

Mark

[Rocket Pooch]

Hi,

Thats colourfull very nice, just think of what you could get with a good scope 

Why is the star in the bottom right over spiky?

Chris

[MarkS]

Why is the star in the bottom right over spiky?

I get this problem with stars at the bottom of all my images.  I'm pretty certain it is the DSLR's mirror - even though it flips up and tucks away when taking an exposure, it is still jutting slightly into the light path of the bottom pixels of the CCD when used at F2.8 on the scope.  It also causes severe vignetting (which the flats take care of).  I am seriously considering removing the mirror entirely but then I lose the convenience of the viewfinder.

I also get the same "surplus diffraction spikes" problem to a lesser extent with stars near the left and right edges - again due to the camera design obstructing the light path at F2.8 - again causing vignetting.  Stars near the corners get two sets of surplus spikes!

It's not a problem with camera lenses because, for a lens, the light cone finally emerges from a smaller area and closer to the CCD.

Mark

[Rocket Pooch]

Still a nice image.

[Fay]

Very nice indeed Mark, we will never catch up with you now!

[RobertM]

That's really lovely Mark, the linked image really shows the quality.  It also looks like you really did your homework in choosing a target.

I certainly think it's one of your best images to date.

Robert

[Fay]

I agree with Robert, the large image is wonderful

[Ian]

I wonder if careful use of a black marker on the edge of mirror might sort that spikyness out?

[Rocket Pooch]

What in the camera?  I'd flock the inside.

I can hear Mark thinking now

[MarkS]

I wonder if careful use of a black marker on the edge of mirror might sort that spikyness out?

I'd flock the inside.
I can hear Mark thinking now

I think the problem is that any straight edge interrupting the light cone causes a diffraction spike.  Nothing to do with internal reflections.

Mark

[RobertM]

I'd tend to agree, exactly the same thing happens with straight diaphragm blades when a lens is stopped down.

[Ian]

so not so much flocking as perhaps fur lining? You could use a tasteful leopard print.

[MarkS]

I've done a complete re-process of this and I'm happier with the result.

Here's a cropped half-size version:


Full version here:
http://www.markshelley.co.uk/Astronomy/2010/cave12082010v4.jpg

Mark

[Rocket Pooch]

Well its still a nice image and you seemed to have removed some of the gradient on the bottom.

[Daniel]

Fantastic Image Mark, star colours are incredible and those whisps of dark nebulosity really jump out of the background.

That new scope is really working out for you

Daniel
:O)