Cleaning My Primary Mirror

Cleaning your primary optics is something they say you should only do as a last resort. I admit I haven't really noticed a degradation of optical performance, but my primary mirror has become quite dirty lately. Even though I'm good about keeping the dust covers on, dust gets in (likely some gets in when I'm imaging), and even though I rarely have dew issues here in desert Utah, I do get frost in the winter, which tends to concentrate the dirt. On top of that, I even had some dead bugs and airborne seeds down on the primary I couldn't just shake out, so a while back I decided to do some cleaning. It isn't hard to remove the primary mirror cell on the AstroTech 8" Imaging Newtonian; you just remove 6 screws around the base of the optical tube and slide out the mirror cell. It fits snugly in the tube so it takes a little prying to get it out. Here's the dirty mirror on the mounting cell after I removed it:

I've cleaned this mirror once before, after I left the telescope out the same night my sprinklers came on. That time I was extremely worried about scratching the mirror or removing coatings, so I used only distilled water applied with a spray bottle and some isopropanol to help in drying it out. I do think you need to avoid scratching your mirror, but I was a lot less cautious this time. I rinsed the mirror with tap water, applied a few drops of dish soap to the water-filled "dish" formed by the concave surface of the mirror, and after carefully washing my hands, rubbed the surface with my fingers. This took off the dust deposits nicely, with no apparent damage to the surface. I then thoroughly rinsed off the soap with tap and distilled water, and finished off with isopropanol to assist in drying, as before. Here's the resulting cleaned mirror:

I ran into a little difficulty getting the mirror cell back into the optical tube. As I noted above, the fit is pretty snug so it took some prying to get the cell back into place, with the screw holes in the cell aligned with the holes in the mounting tube. After a little effort, I got that done without dropping anything. I used a laser collimator to line up all my optics, and was ready to get back to imaging. To be honest, I have not noticed a difference in my images after going through the cleaning procedure. I imagine it would be manifest in higher image contrast, but with the galaxies I've been trying to image recently I think the darkness of the background sky is a much more important factor.

The Season of Galaxies

I've had a very busy winter term and haven't taken the time to post in quite a while. But now the term is over and I've got the urge to write a bit.  This time of year is known as "galaxy season" among amateur astronomers, because in the Northern Hemisphere the galaxy-rich constellations of Ursa Major, Leo, Virgo, and Coma Berenices are all well-placed for viewing and astrophotography. As a result, I've been imaging galaxies during most of the time since my last post, and have stepped away from narrowband H-α for a bit because most galaxies are not best photographed in H-α (although it can certainly help in some cases). Most of what I've been doing is just one-shot color imaging, going as deep with the subexposures as I can (currently my longest are 600 s). I'm getting a lot more integration time these days than in past seasons (I almost always image up to the meridian, do a meridian flip, and continue until dawn or the setting of the target, whichever comes first), and this has allowed me to stretch the data more aggressively without bringing up as much noise. I'm also routinely trying both Nebulosity stacking and Deep Sky Stacker 2x drizzle stacking (using subframes preprocessed and prealigned in Nebulosity) for every image. Sometimes drizzling helps, and sometimes it doesn't.  Anyway, here are a few galaxies. M81 is a personal favorite, and I'm getting better at imaging it:

A beautiful moonless night, so I decided to go back to one of my favorite and most-attempted targets, M81. Because I'm routinely doing 600-s subframes now in Hα, I decided to try to go deeper with M81 by using 600-s subs and the UHC-S filter. Finding was via synch on α UMa followed by PicGoto acquisition. I had some trouble initiating guiding; calibration went OK, but then the guide star started drifting off in Dec. I think my Dec gear clutch was just loose. Imaged up to the meridian, then re-synched with Astrotortilla and reacquired and imaged until dawn. I was thrilled to pick up what appears to be a small satellite galaxy at top center. I wasn’t sure that wasn’t an artifact, but now I’ve seen it in others’ images so it must be real.

Date: 16 Feb 2015

Subject: M81, Bode’s Galaxy

Scope: Astrotech AT8IN+High Point Scientific Coma Corrector

Filter: Baader UHC-S

Mount: CG-5 (Synta motors, PicGoto Simplificado)

Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.4.1 (Win 7 ASCOM)

Camera: DSI IIc no cooling (about 0 °C)

Acquisition: Nebulosity 3.3, no dither

Exposure: 41x600 s

Stacking: Neb 3.3.2, bad pixel map, bias included, 33 flats, histogram match, deBayer & square, trans+rot align, 40-60% median combine.

Processing: StarTools 1.3.5.289 Crop; Wipe; Develop 87.49%; HDR:Optimize; Color: Scientific, 300%; Deconvolute 2.5 pix; Track 3.5 pix; Magic: 1 pix. Photoshop CC 2014 + Carboni Astronomy Tools Deep space noise reduction; Increase star color; Layer masked unsharp mask for dust lane enhancement; Astroframe.

M82 is nearby and also a favorite. This is one where I thought maybe adding in some Hα would help pick up the jets streaming from the galaxy, so I tried that too. I'm not sure it helped, but here are the results.

Since I was already in the neighborhood the night before (imaging M81), I decided to try and get a better image of M82 by using similar tactics. Began by synching on α UMa with a PicGoto slew to the target; it was in the field of view. Used the UHC-S filter because I'm looking north toward the Provo light dome, and used 600-sec subframes again to try and go as deep as possible. Started imaging, refocused a couple of times, and took a nap, with an alarm set for transit time. Got up and did the meridian flip and refocused, then went to bed.

Date: 17 Feb 2015

Subject: M82, Cigar Galaxy

Scope: Astrotech AT8IN+High Point Scientific Coma Corrector

Filter: Baader UHC-S

Mount: CG-5 (Synta motors, PicGoto Simplificado)

Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.4.1 (Win 7 ASCOM)

Camera: DSI IIc no cooling (about 0 °C)

Acquisition: Nebulosity 3.3.2, no dither

Exposure: 43x600 s

Stacking: Neb 3.3.2, bad pixel map, bias included, 33 flats, histogram match, deBayer & square, trans+rot align, 40-60% median combine.

Processing: StarTools 1.3.5.289 Crop; Wipe; Develop 87.49%; HDR:Reveal core; Color: Scientific, 230%; Deconvolute 2.5 pix; Life:Moderate; Track 4.0 pix; Magic: 1 pix. Photoshop CC 2014 + Carboni Astronomy Tools Deep space noise reduction; Increase star color; Layer masked unsharp mask for dust lane enhancement; Astroframe.

Here it is with Hα added:

I'm filling in these notes almost a week after the fact because I was so dissatisfied with the results that I wasn’t going to post them. There was a lot of moon the night these were taken, so I decided to see how M82 looks in Hα, thinking that might enhance the filaments that emanate from the galaxy. It didn't work very well, but it was fun to give it a shot. I had some guiding issues and also didn’t do a very good job of focusing, so the galaxy Hα experiment was not too successful. I did drizzle process these Hα images (in Nebulosity 3), and also tried drizzling my earlier (17 Feb 2015) UHC-S images (using Deep Sky Stacker; I couldn’t get it to look good using Nebulosity—DSS was just better for this image). Finally I scaled the two images in Nebulosity 3 and used a 50:50 combination of the R channel from the UHC-S image and the Hα as R in this final image, with most of the background from the UHC-S. Here it is for what it’s worth.

And then a few other galaxies:

Found very easily by initially synching on ψ UMa and using the PicGoto. This is a beautiful little galaxy. I'm wondering if I would have been better off withouth the UHC-S filter. I had a lot of guiding issues as well, probably due to non-optimal balance (balance is critical with my finicky old mount). Finally, my primary mirror has gotten absolutely filthy so I really do need to clean it. Nevertheless, the image turned out OK but not great. 

Date: 19 Mar 2015

Subject: NGC 3198, spiral galaxy in UMa

Scope: Astrotech AT8IN+High Point Scientific coma corrector

Filter: Baader UHC-S

Mount: CG-5 (Synta motors, PicGoto Simplificado)

Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.4.1 (Win 7 ASCOM)

Camera: DSI IIc no cooling (about 10 °C)

Acquisition: Nebulosity 3.3.3, no dither

Exposure: 23x600 s

Stacking: Neb 3.3.3, bad pixel map, bias included, 33 flats, histogram match, deBayer & square, trans+rot align, 40-60% median combine.

Processing: StarTools 1.3.5.289 Crop; Wipe: Develop: 87.49%; HDR:Optimize; Color:Scientific 248%; Deconvolute 3.0 pix; Life:Moderate; Track 5.4 pix; Magic:Shrink 1 pix. Photoshop CC 2014 + Carboni Astronomy Tools Deep space nr; layer masked space nr; Increase star color; Astroframe.

This galactic cluster always proves challenging for me. I thought I'd try it on an extremely dark night, go to 600-s subs, and use only the UV-IR cut filter. It is still challenging. I continue to have guiding problems; it is just hard to guide well enough with my rickety old mount when using my tightest imaging scale. I tried both my "normal" workflow in Nebulosity and using 2x drizzle stacking in Deep Sky Stacker; I think the DSS drizzling worked better, and here is the result. I didn’t want to darken the background too much, because the ring galaxy at upper left has a faint outer ring I didn’t want to disappear.

Date: 20 Mar 2015

Subject: HCG 44 / Arp 316, Galaxy Cluster in Leo

Scope: Astrotech AT8IN+High Point Scientific coma corrector

Filter: Baader Fringe Killer

Mount: CG-5 (Synta motors, PicGoto Simplificado)

Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.4.1 (Win 7 ASCOM)

Camera: DSI IIc no cooling (about 0 °C)

Acquisition: Nebulosity 3.3.3, no dither

Exposure: 29x600 s

Stacking: Neb 3.3.3, bad pixel map, bias included, 33 flats, histogram match, deBayer & square. DSS 2x drizzle app (1.5)-sigma combine.

Processing: StarTools 1.3.5.289 Crop; Wipe:76%; Develop: 83.33%; HDR:Reveal core; Color:Scientific, 200%, cap green to yellow; Deconvolute 2.0 pix; Track 6.7 pix; Magic:Shrink 2 pix. Photoshop CC 2014 + Carboni Astronomy Tools Deep space noise reduction (2x); Star color enhance; GradientXterminator; Astroframe.

More galaxies coming in future posts!