Beta 6.0 NGC 891

[Jim McMillan]

There's nothing particularly unique about this image - other than to say that it was acquired with ACP Beta 6! I'm posting it just for fun since there haven't been many images posted lately. (33 x 10 min; star spikes are added by software)

A couple of notable things:

1) NGC 891 happens to be one of the targets where the focus star (findbrightstar) selects a bad (undocumented double) in the GSC catalogue. I was able to identify the bad star and put it into the "BadBrightStars.txt" file. ACP recognized the bad star and selected another one (new 6.0 feature).

2) For some weird, unknown reason, MaxIm "held" one exposure in the camera buffers about 40 seconds after the exposure was done. The effect is the image won't calibrate properly because all the extra time it sits in the camera, it gathers more noise which won't get dark-subtracted out.

3) For some weird, unknown reason, a couple of minutes before reaching the meridian, the scope decided to slew a few degrees to the east. The result was that when ACP initiated the flip procedure, the mount didn't flip (because it hadn't reached the meridian yet). The mount was lost. The mount did flip a few exposures later, but the mount was still lost. Once I stopped and restored proper pointing, things ran fine thereafter.

4) I did have one guiding incident where, between exposures, the mount moved such that the star was about 6 arcsec off where it had been once guiding restarted. Fortunately, the guide star got recentered back to where it belonged at the 19th guide cycle retry. I have no idea what caused that to happen.

5) For me, this was the first time using MaxIm 5.x (5.12). I don't know what to attribute these 3 glitches to - MaxIm or hardware. I'm sure it's not ACP though.

6) I discovered and already reported in the hardware section that the AP driver may have up to a 5 second delay after a slew before properly reporting the pierside.

All in all, not a bad result for the first time out with a new version of MaxIm and beta ACP software!

Jim

[Russell Archer]

Hi Jim

All I can say is Wow - beautiful image!

I know this was something of a "test image" for you with ACP 6, but it shows me just how much I need to learn
I took an image of NGC 891 about a month ago and on a scale of 1 - 10, your image would be at 10 and mine would struggle to reach zero!

Thanks for sharing the image.

Russ

[Bob Denny]

Yeah, that's wonderful!! If only people knew what can be done with a modest setup and a high degree of skill!!!

[Jim McMillan]

Thanks Bob and Russ for your kind words.

Russ, I was thinking about what useful advice I might give and thought it consisted of only 2 main points. But, after rethinking, there's probably a bit more. Here's some thoughts:

1) Pay attention to your hardware setup. What are the things that can cause results to be inconsistent? You need to deal with issues like things that can shift, cords that can get hung up, etc. This NGC 891 image consists of 33 of 36 images taken. I described the 3 images I had to throw out that were due to unknown operating problems. Usually, I lose 0 images due to operating problems, so I've got some figuring out to do. (I do lose images to satellites/planes though!)

2) Gets the details right. FocusMax works wonders with focusing, but make sure the v-curves are doing their best job; the near focus HFD you're using works well, etc. Collimation needs to be spot on. For example, with my LX200, mirror flop affects both collimation and focusing. I've actually put set screws in the sleeve/baffle to "fix" the primary and focus using an external focuser (Clement).

3) Internal reflections in the OTA and imaging train can cause all kinds of gradient problems. I've flocked and painted every surface I can to minimize the problem. I image from a suburban environment about 2 miles south of a major mall, so doing what I can to deal with light pollution gradients during image acquisition makes post processing easier.

4) Get your calibration (reduction) process working well. You want your images to be as clean as possible with the highest S/N ratio possible. Doing this process poorly can actually add noise to an image.

And here are the 2 key points I originally thought about once you get the above stuff conquered:

1) Guiding has got to be very, very good. If you don't have a very good mount, you need to use an AOx device. Otherwise, you will never achieve decent image resolution. In fact, before I got an AP1200, I imaged with an LX200 Classic and AO7. That worked extremely well. (I'm still using the same OTA.)

2) Take lots of images to combine. There's formulas around to figure out the optimum individual exposure length, but for most people, something around 10 min should work. It's all about achieving the best S/N ratio possible. The brighter your skys, the more important this is. For me, anything less than about 6 hrs for the luminance alone just won't cut it. My typical LRGB images will have about 24 hrs. total - 12 hrs luminance and 4 hrs each R,G,B.

Hopefully this is helpful.

Regards,

Jim

[Bob Denny]

Great info, Jim. You'd be a good speaker at one of the astro-imaging conferences. Too many people bet the farm on expensive equipment and are disappointed with the results... they don't pay attention to the details.

[Russell Archer]

Jim

This is wonderful advice for someone like me who's 'learning the trade'!
Thank you so much for taking the trouble to write it all down, I really do appreciate it.

I've been interested in astronomy since I was about 5 years old (I'm coming up for 52 now!), and have done casual visual observing with small refractors on and off over the years. I seriously got the imaging bug about a year ago when I bought a 12" LX200 (ACF). Boy, have I had some fun getting to grips with that! I thought my day job as a computer programer was hard until I tried astro imaging

I'm certainly progressing however, and given my badly light-polluted location on the outskirts of London, I've been able to produce some quite nice (to me) images which give me hope that I'll do better as I master all the different variables (wobbly mount, good polar alignment, PEC, focusing, etc.).

Your comments on guiding were very interesting. I've got a Starlight Xpress off-axis guider and Lodestar, in combination with a SXVR-H9 as my main imager. And I've also recently been using PEMPro to both refine polar alignment and tackle periodic error in the mount. So far I've had reasonable success, but I do reject quite a few images due to trailing. As you mention, I'm seriously thinking of getting the SX adaptive optics unit. At the moment it's a toss-up between getting an SX AO or replacing the Meade microfocuser with something better with a proper stepper motor (like one of those shiny Moonlite focusers or the Optec TCF-S).

I'm also interested to see the large number of images you're combining for a typical LRGB image (24hrs in total). That's quite a revelation to me and something I'll pursue in future (2hrs or less would be typical of what I'm doing right now).

Thanks for tips about internal reflections, that's something I never even considered. I'd be reluctant to open-up my LX200 though

So, I shall be taking your list of advice, putting it on my wall, and working through it over the next few months (or years!).

Once again Jim, thank you very much for taking the time and trouble to pass on your advice and experience.

Best wishes

Russ

[Dick Berg]

Jim,

I really like this image, too. You have such good skill working as you do from the distant "outskirts" of Cleveland.

Seeing this picture brings back a vivid, wonderful remembrance of walking around the halls of Chicago's Adler Planetarium when I was a boy (about 60) years ago. Around the central hub that held the Zeiss planetarium, a dark marble corridor had lit-from-behind black-and-white transparencies (positives) mounted on the walls that looked just like your picture. One of them could have been your picture. They were probably taken at Lick Observatory or Yerkes Observatory with much larger instruments, darker skies and shorter photographic exposures, but they were no better.

Thanks for the memories.

[Jim McMillan]

Hi Dick & Russ,

Dick, I'm glad my image brought back some fond memories for you. That makes me smile.

Russ, I'm glad you found my note useful. I don't really consider myself all that skilled an imager. Having said that, I think my data capture skills are stronger than my processing skills. I find it intellectually challenging and satifsying when everything just works! It's certainly fun and satisfying when Bob incorporates one of my suggestions to make imaging better/more reliable/easier into ACP.

Regarding your next purchase, if it were my choice, I'd go with the AO first versus the focuser - although I'm sure you'll end up with both eventually! (I don't have any experience with SX cameras, sorry. But, I think others using ACP do.)

I'm not sure you've seen my guiding paper written a few years ago. Bob distributes it with ACP in the DOC subdirectory. It basically captures all I learned while trying to get my LX200 to guide, followed by AO7 guiding on an LX200, followed by conventional guiding with my AP1200. If you're throwing out too many images due to trailed stars, perhaps we can figure out what's happening and make some improvements. Even if we never can overcome the LX200's faults, we will still learn a lot about guiding in the process.

I actually lived in London for a couple of years (1988 - 1990) in Hampstead. In fact, I visited London this past May. Light pollution will be a difficult problem for you. More exposures will cut through a lot of that though. Having said that, a while back, I did a calculation to figure out how much longer I needed to image with my skys and 10" scope to duplicate what a 20" scope in darks skys could do. I forget the exact numbers, but I think I need to do 8+ hrs for each hour with a 20". Practically speaking, 12 hrs (luminance) is about the limit. Beyond that, I don't see much difference. The difference between 6 hrs and 12 hrs is actually pretty subtle. I usually do 6 hrs on a target per night - 3 hrs on each side of the meridian. So, it takes 2 nights to get 6 hrs L and 2 hrs each RGB. From there, I just keep repeating the process until I feel I can't make any more improvements. Usually, that means 2 more nights.

Anyway, as you progress, please post your images. It's fun to see someone's progress!

Regards,

Jim

[Russell Archer]

Hi Jim

I don't really consider myself all that skilled an imager

Well, from what I've seen in the (com center) and heard (from speaking with Bob) everybody else seems to think very highly indeed of you

if it were my choice, I'd go with the AO first versus the focuser

Splendid! It's always nice when somebody else backs-up that little money-spending devil that whispers 'go on, you need an AO, the wife really won't mind at all if you spend $1000's on another incomprehensible astronomy gizmo'

I'm not sure you've seen my guiding paper written a few years ago

Actually, I found it a couple of days ago and have been reading it bit-by-bit - it's a real treasure trove of info!! Reading your document gives me hope that I might be able to get good results with the LX200's mount.

I actually lived in London for a couple of years (1988 - 1990) in Hampstead.

Ah! I was born very close to Hampstead. It's one of the nicest parts of London. You get a great view over the city from the top of Hampstead Heath! I now live in Teddington, near Richmond in the south-west of London. A lovely place to live (very close to the Thames), but the backyards are tiny, which means a permanent observatory is out for me (I keep the scope in a wooden shed on a 'ScopeBuggy'). Unfortunately, the lights from neighbouring houses (particularly 'security' lighting) is a major problem. 5-minute exposures are the absolute maximum I can do I think....

Anyway, as you progress, please post your images. It's fun to see someone's progress!

I will! Although I'm rather hesitant given how many 'proper' astronomers there are in the DC-3 com center

Thanks once again for all your encouragement!

Best wishes

Russ

[Bob Denny]

I now live in Teddington

Ah! I've made several visits to the Southwest London area, where everything is "just off the A3" :-) I have friends that live in the area (New Malden, Sunbury). It's been almost 20 years since I've been there though.