A Brief Pause

The seasons have changed again, at least according to the calendar if not the thermometer. Despite the pleasant autumn I managed to be lazy and not haul my imaging gear out. I think an early cold snap convinced me it was winter. The reality is it's almost the new year, so time for a look ahead to 2024.

C9.25 and TV-102 back in service

As a last gasp of 2023 activity I did do a little bit of scope maintenance. First it was the turn of my old Celestron C9.25 to get collimated; I had cleverly manage to mess up its alignment to the point it was useless. This time I was very careful. Only small adjustments were made until I had it close to correct. I'll still have to do a finer tuning in the spring/summer when I can get the scope out under some decent stars.

The other bit of work was for my TV-102. Some years ago (nine? Amazing how time flies!) when imaging  IC 348 in Perseus, I noticed an irregularity in the flare around 4th magnitude omicron Persei. You can see it as a notch at about 5 o'clock.  

Omicron Persei with a mysterious dark notch

Here's a link to the full image on AstroBin. For comparison, here is Gamma Cas with my FSQ106, showing what a flood of starlight should look like.

Gamma Cas (FSQ-106EDX4)

The dark notch isn't awful, but it is a serious distraction. The primary suspect was something in the optical path. It was a simple thing to point the scope at a light surface and look through the objective from the focuser end. Clearly apparent was a sort of bump protruding into the circle of the objective. But what was it? Had something fallen into the OTA?

In the dangerous tradition of "monkey see, monkey disassemble," I took off the objective cell and discovered the problem. A bit of the TeleVue flocking paper inside the telescope tube had blistered up and gotten into the way of light. The fix was obvious to this monkey so I carefully filed down the petrified bump, put the objective cell back in place, and called it a done deal. 

Then something amazing happened: I had a thought. I wondered if I had gotten the cell back in place correctly, and was the scope still optically aligned? Dashing to the Internet I started reading posts about the travails people had collimating TV-102s. Also how they often had to fabricate clever jigs to do the alignment. Said jigs were far beyond my technical skill to create, so I was depressed. Not wanting to admit to myself that I might have made more trouble than I had remedied I set the scope aside and moved on to  imaging with my C9.25 (not yet misaligned), AT65EDQ, and eventually FSQ-106. I'd revisit the potential damage later.

Fast forward nine years to the other night when I put the TV-102 on the mount and actually looked through it at a star. It wasn't a complete star test, but at 90X Polaris A and B looked like pinpoints. At  450X racking in and out a touch gave decently symmetric airy disks. So maybe I got really lucky and it's fine. The old scope can rejoin the fleet now. I would like it functional for that eventual time when I return to visual observing. It works wonderfully with my 31mm Nagler Type 5 hand grenade, and to me it looks like the classic telescope. A picture of it from 2008 still graces the WhiteRock Conservancy (home of the Iowa Star party) web site.

AT65EDQ

After adding the FSQ-106 for imaging my poor AT65 has languished. It's an imaging scope that's corrected to provide astrograph flatness, meaning it's not a so great for visual use. Its FL of 420mm (f/6.5) is close to that of the FSQ with the 0.73X reducer (f/3.65 and 387mm) so it's somewhat redundant. But it is small and light and could easily sit on something less substantial than my G11. 

All it really needs to be a little sibling to the FSQ is electronic focusing, so that's what I'll be adding to it. And a nice Seahorse hard case for travel. Then I only need to rig a way to mount the Pegasus powerbox to it. More about that next time.

Veil Mosaic

I have all the data, I've been delaying processing until snowy winter hibernation mode starts. In the Twin Cities in a given year a "white Christmas" with 1" of snow or more on the ground has a chance of about 71%. But that won't happen this year!  The ground is bare and the forecast is for a record-warm 53 on Christmas Eve with a possible thunderstorm. The non-winter of 2023-24 is on track to continue into January.

When the snow finally arrives I'll start with a mosaic of the luminance data first to see what I've got, then repeat for each of the color channels.

 AstroBin Voting

I like to post my better pictures on AstroBin. It's mostly a vanity exercise but I think that posting technical details about images can be helpful to others. I know I've learned some things by seeing how other people acquire their data. 

Because AstroBin is a sort of social medium members are allowed to vote for images and there are best image designations. Some people complain that it's highly subjective, motivated by people trying to build their posse of followers, get votes in return, etc. All of that is possible but I don't care. It's fun, and I like it when I get up-votes. Although I admit I don't often understand why some of my images get more votes than others I've posted.

I've noticed something odd in the last year or so, though. Some of my dusty old posts that have been sitting quietly will suddenly get a flurry of votes from unfamiliar people. An example is this image of Jones 1 from 2015. Earlier this month it got four new votes within a few minutes of each other. Other people have imaged this object and created far better images than mine, so I have to ask why I got those votes.

Possibly it's people fishing for votes, but why would they reach back to an image from eight years ago? Why not take the time-honored approach of following someone so that they'll reciprocate and build your posse?  The near-simultaneity of the votes makes me think it might be something more devious.

Oh well, maybe the applicable adage is "don't look a gift horse in the mouth." So I say: Thank you  for your votes, mysterious time-lagged strangers! Maybe next time don't wait 8 years!

Messier Marathon Night Results

"Mission Accomplished!" to use a cliched phrase. "Goal Reached" might be a little better, or maybe "Dumbness Overcome."

This was one of my first attempts to use my DSLR in quite a while, and I managed to make a lot of mistakes early on:

• Forgetting to return to ISO 1600 from the composing setting of 6400
• Forgetting to set the shutter control to bulb
• Forgetting to increase the number of frames on the DSLR controller from the dark frame to light frame counts

And so on. The evening began with starts and restarts, but once it got going it went well. The time I lost meant I wouldn't go after the dimmer planetary nebula I had included on my object list in the last post, but that was okay.

All the hardware worked perfectly, although some went untested. The dry air and the gusty to breezy conditions meant the dew preventers weren't needed. It was only around 2 A.M. that frost began to appear, and my scopes stayed clean until the end a little before 3 A.M. The DSLR power supply worked perfectly and the 35Ah battery was barely tested running that and the mount. I used my laptop for PHD with its power supplied by it's own battery augmented with a Duracell 600 battery pack. The Duracell ran down pretty far in the five or so hours, so this might not be a good option for multi-night imaging. For more power conservation I need to find a way to turn off the laptop's display, not simply dim it.

The evening tally was six Arp galaxies and one planetary. In terms of Messier objects it was 9 1/2. Let's see some marathon images:

Leo Triplet (clockwise from NGC 3526 at top, M65, and M66) Together these are Arp 317. M66 is Arp 16.

M49 (right of center, Arp 134)

M60 (left of center, Arp 116) and M59 (right of center)

M87 (Arp 152)

M90 (Arp 76) and M89 at bottom edge

M97 (Owl Nebula) and M108 at bottom edge

All the images are based on 10 three minute exposures with a Canon T2i (at ISO 1600) riding on a TV 102 operating at f/7--except the image of M90, which was 5 three minute exposures at ISO 6400 (see list of mistakes above). These were calibrated with 20 dark frames collected throughout the night as the temperature fell from around 30°to 20°F. They obviously haven't been flatted. I reprocessed them to include synthetic flattening, and now they look a lot nicer!



An inspection of single light frames shows that they surpass visual observations, so why not bring back the idea of an Imaging Messier Marathon? Three minutes at ISO 1600 is about the same as 45 seconds at ISO 6400. 3/4 minute times 110 objects is only 82 minutes; out of a six hour marathon night that leaves four and a half hours for acquisition and composing images. Definitely doable.

That aside, the evening bumped my Arp list count to 26 and my planetary list count to 23. Both lists are about 1/4 done!

Onward to warmer weather!

Two images from last weekend: M17, M20/21; Processing workflow.

I'm REALLY pleased with how this image of M17 came out:

Messier 17 (Omega or Swan Nebula), click for full size

The previous night's image was not quite as successful--M20 and 21. More about why in the next blog entry.

M20 (Triffid) and M21

Both images are full-frame. For all the gory details of acquisition, look at my gallery on AstroBin. By way of a quick summary, both are LRGB images made with an SBIG ST8300M CCD, TeleVue 102 apo and autoguided CGEM mount under mag 6+ skies. Dark and bias frames only, no flats.

Imaging is SO much faster doing LRGB in the dark than it is to use narrowband filters under light-polluted skies. 

I realize that the colors in the M17 image may look a little muted to you, but I kind of like them this way. What's particularly pleasing about the image from my standpoint is three-fold: The stars are nice and round right out to the edge of the field, meaning that my field flattener is doing its job perfectly; The merging of the LRGB channels seems to be spot-on. And finally, guiding with the Orion mini-guider works great at the 700mm focal length of the TV102 to correct mount errors. I'll eventually try out the mini on my C925.

My processing workflow continues to evolve. These two images were made by ping-ponging back and forth between Images Plus and Photoshop:

• Calibrate, align and stack using IP
• Stretch using PS
• Noise cleanup and star size reduction in IP
• LRGB combine in PS using Annie's Actions
• Color balance in IP
• Masked sharpening in PS

Yes, I know that's a mess, and some will say that all can be done in IP or PS or Maxim or whatever. Good for you if you can function with only one software package, but at this point I can't. I'm using IP 4.5, so probably some of the changes that have gone into later versions would make it a better processing tool. 

Are Baader filters Parfocal?

At a recent star party I made an offhand statement that I doubted that my narrowband filters were parfocal. That set me wondering if I was correct and how would I go about determining this for all my filters. So I did a little experimenting one night by imaging Betelgeuse through all my filters.

I decided to set focus with the luminosity filter in place, and then cycle through all my filters seeing if the focus changed. Sorry, but I don't have a focuser with a digital readout. To get some sense of any focal shift I put a Bahtinov mask on my scope and imaged the results. I used three stars of different spectral types (O, A, and M), just in case the results would be influenced by wavelength. (I was imaging through my TV-102, so I didn't expect to see any significant wavelength dependence.) Here is a test strip for Betelgeuse (click to see full scale image):

Betelgeuse imaged through various filter configurations with no adjustment of focus

I used 5 and 25 s exposures for the broadband and narrowband filters, respectively, and processed only using ImagesPlus digital development. It looks like the central spike produced by the mask moves little if at all as the filter is changed. As expected, the focus shifts significantly when changing to no filter in use. So how much shift is significant? Here is an image resulting from 1/12th turn of my fine-focus knob away from focus:

Appearance when defocused by about 0.3mm

This is approximately an adjustment of 0.3 mm in focus and the central Bahtinov spike has shifted quite a bit. From past imaging experience, I think my final focusing "tweaks" are about 1/5 of this in magnitude.

So are the filters (Baader LRGB and 7 to 8.5 nm Ha/S-II/O-III) parfocal? They look close to being so. To my surprise, the broadband and narrowband filter sets seem to be almost, but not quite, parfocal with each other. The results were the same for the other two stars, Sirius and Altinak. But I'll probably still refocus every time I change filters in the future, particularly when using anything less than an apochromatic telescope or there's been a change in temperature.

Waiting Time

One week since I sent in my CCD to SBIG, and one week to go to the Heart of America Star Party 2012. I didn't expect to hear anything from SBIG this week; my impression is that the repair queue is about two weeks long. After that--in a few short days--you hear from them, they do the repair, and it's on its way back to you. So I'm guessing that I'll get it back sometime around the last week of October.

On the HOASP front, there's good and bad news. A friend who also owns an ST-8300M has agreed to loan me his for the trip. CCD imaging is back on the menu. I'm still waffling about which scope to bring, the TV102 or C925. Today, I'm favoring the TV102. Stand by.

Bad news is the weather forecast. At this time it has all three days of HOASP as showers and thunderstorms, so the whole CCD issue may very well end up moot. I've picked three targets as if there will be three nights of clear sky. The helix nebula (NGC 7293), The sculptor galaxy (NGC 253), and The foxface nebula (NGC 1788, a reflection and dark nebulae in Orion) Will any get imaged? Or will I come home having collected only mildew?

Clip and Save

I'll admit to being a very frugal person. I have very few hobbies, and the only one on which I've spent an appreciable amount of money is Astronomy. Which you probably could already guess.

Back somewhere around 2003 I went to a local star party hosted by the MNAA. If you know the MNAA, "star party" is probably too formal a phrase for their get-togethers. I took along my Orion XT-10 Dob. One of the MNAA members let me try his Tele-Vue 31mm Type 5 Nagler with an OIII filter. At that point I had neither. If you know your eyepieces, you know that around then the 31 was one of the most expensive eyepieces around, and possibly one of  the heaviest. When I used it to look at the Veil Nebula, I was blown away. He and I decided that the 31 was made for the XT-10. Actually, given that back then they were both around $640, perhaps the XT-10 was made for the 31.

The hook had been set, and I realized the value of the 31.  There was no going back to my relatively inexpensive eyepieces, the best of which was a Panoptic 19. The 19 was a darn good eyepiece, but the 31 was something special. I had to have one.

But—how to pay for it? The Sunday advertisements gave the answer: By clipping grocery coupons. I held to a rule that I would only use coupons for things we normally used, not junk or extravagances. And several years later, I had saved up all the money I needed to buy the 31.  In fact, I kept clipping until I had enough for the OIII filter, too.

But wait, there's more to the story.  The person who hooked me on the 31 had sold his TV-102 a couple of years earlier to someone I knew from the annual star party at the Jeffers Petroglyphs. I had seen the 102 at that star party and greatly admired the views it provided. I became the 102's third owner in 2004. And yes, it works with the 31 as if the two were made for each other.

So why do I bring this up now? I've started clipping again, saving for a Canon EOS lens-to-ST-8300M adapter (about $300!).