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Monday, March 15th, 2010
The agony of the mask.

Soooo... with the ED103S, I was not happy with the spikes coming off of the bright stars due to what I've learned are spacers mentioned in the last entry. The first thing I thought when I saw them was, "I guess I can't shoot the Horsehead". Or any other objects with bright stars in the field. I'm trying to get away from diffraction spikes by using a refractor to begin with, but I prefer the crosses of a Newtonian to the spikes produced by the shiny obstructive spacers in this scope. Grrrrr...

The first thing I tried was to just blacken the spacers. I did this by removing the top lens from the cell and using a Sharpie to color them black. In the process, as careful as I was, I ended up leaving a small Sharpie mark on the lens. That was annoying, but more annoying was the fact that in the end, blackening the spacers made no difference. So, the fact that the spacers are silver wasn't so much the issue as they were in the light path.

A friend told me that I could clean up the Sharpie mark on the lens with alcohol. So I took the top lens off again and sure enough the mark came right of with just a quick dab.

The downside was that as I was putting the lens back where it goes, I nicked the edge and both chipped and scratched the top lens. MAJOR Grrrrr... It's a small chip and a small scratch, but will definitely be a problem to both the image quality as it will scatter light and to the scope's value. Lesson learned.

Bailing on the whole "take it apart and fix it" thing, I went to Tap Plastics and got a matte black acrylic ring to use as a mask. Unfortunately, to really hide the spacers (and the scratch), it masks the scope down to 90mm making it now 90mm f/8.8. More grrrr...

I also see that the halos are no longer centered on the stars like they were in my first light shot which tells me that collimation is now likely out a bit. At the moment I'm not exactly sure what to do about that and we're a few days away from clear skies again. So, more to come on that...

The significant thing learned here is that if I ever get another apo:
1) It MUST NOT have anything obstructing the light path.
2) I won't take the cell apart again

In the gallery below are 2 screenshots of the scope with and without the mask. These are single two minute shots of Arcturus.

Also included is a 30 minute (3x600) shot of M3 while I was in the vicinity. Clouds were looming the entire time and passed the 2nd shot and covered M3 during the third shot. So it's really not much more then a 10 minute shot really.

Info on the night
Date: 3/15/2010
Temp: 47F
Seeing: 5/10
Transparency: 3/10
Location: Vancouver, WA
Bortle Scale: 5

M3 Image
Scope: Vixen ED103S @ 90mm & f/8.8
Mount: Orion Sirius EQ-G with GoTo
Guiding:  Meade DSI Pro and PHD Guiding
Guide Scope: William Optics ZenithStar 66 SD
Camera: Canon EOS 1000D (Modified)
Special Settings: None
ISO: 800
Exposure: 30 minutes (3 x 600s)
Processing Software: Acquired in Nebulosity with high dithering, Stacked in Deep Sky Stacker (Kappa-Sigma Clipping for all frames), Levels, Curves, Astronomy Tools, Gradient XTerminator and Noise Ninja in Photoshop
Support Files: 40 flats, 40 bias, one dark used as a bad pixel map
See Gallery below for image

M101 - The Pinwheel Galaxy Image
Scope: Vixen ED103S @ 90mm & f/8.8
Mount: Orion Sirius EQ-G with GoTo
Guiding:  Meade DSI Pro and PHD Guiding
Guide Scope: William Optics ZenithStar 66 SD
Camera: Canon EOS 1000D (Modified)
Special Settings: None
ISO: 800
Exposure: 30 minutes (3 x 600s)
Processing Software: Acquired in Nebulosity with high dithering, Stacked in Deep Sky Stacker (Kappa-Sigma Clipping for all frames), Levels, Curves, Astronomy Tools, Gradient XTerminator and Noise Ninja in Photoshop
Support Files: 40 flats, 40 bias, one dark used as a bad pixel map
See Gallery below for image


Image Gallery For This Session
01 Arcturus Spikes 02 Arcturus No Spikes
03 M3 30m 04 M101 30m
   

01-Arcturus-Spikes.jpg
Click picture above for larger version
If the picture seems too bright or too dark, try adjusting the brightness below.
Brightness:
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Comments:
On 03/18/10 at 11:52am Anonymous wrote:
so i guess you will be keeping your reflector after all?
kd7
mark



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