First light with LL and X2 + questions

[aparker]

At risk of redundancy with CN, I'm going to post here since this seems to be the center (or centre as you'll have it over there) of the Lodestar universe.  I took my first try at running my new X2 with LL v0.10 last night (I'll upgrade to 0.11 before trying again).  and got some OK results.  Here's two

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which should be familiar to all and sundry this time of year :-)

[aparker]

My questions are many, as you might expect.

1. I found the white point/black point sliders very hard to adjust.  Doing 10 sec exposures, with mean stacking, I needed to have both WAY down toward the low end, like 700 for black and 3000 for white.  The jumps in value with mouse movement are large, and I could not find a way to arrow key or type in values.  Is there a better way to get fine control over these guys?

2. The sliders below (gamma, brightness, contrast, I believe) are super-sensitive.  Any attempt to tweak one experimentally ended up blowing the image out in sold green or yellow.  After a few tries I just left them alone.  I note that there is channel selection via radio button for these - are they only useful for color cameras?  Mine is monochrome.

3. I tried sum stacking but found myself having to "chase" the image up the white/black histogram constantly.  What do people normally do for stacking?  Is there any use case for the sum stacking that I'm missing?  Do you sum stack a series of images then stop acquiring new ones and play with the processing settings from there?

4. I am using a c8 edge HD with a 0.5X GSO focal reducer and Astronomik CLS filter.  As can be seen in the images above, there's quite a bit of coma present.  Can I tweak anything about FR placement to help that?  Based on my reading about the FR, I think I got the distance from the lens to sensor about exactly right (1/2 of FL or 79mm) - certainly the image scale I'm seeing of about 30x24 arcmin fits with the calculation for the sensor size and ~1000mm FL for the overall optical system with reduction.  

5. Any tips and tricks for finding objects?  I can tell that with the "approximate" go to capabilities of the Celestron CGEM mount I'm going to need to get good at star-hopping and get friendly with Stellarium, since I need to land my object in that 30x24 arcmin field to see it.  Scanning around the sky is tough when you have to wait for each new exposure to refresh before you can move on - definitely a change from visual observing.  

6. What about electronic finders?  I have a decent 50mm RACI optical finder on the scope now, which gives me about a 4 degree field for visual finding/starhopping, but with the Boston LP there are precious few stars to be seen through it in some parts of the sky...

Thanks in advance for any/all of your collective wisdom...

[aparker]

Oh and I should note that I'm running LL on a Macbook Pro with OSX 10.10.2

[HiloDon]

Hi Alex,

Welcome to the world of Lodestar. You have a lot of questions there and I'm sure that you can get all your answers here. I'll start with what I know and others can chime in. I run a MacBook Pro as well, so at least we have that same viewpoint.

The first thing you need to do is download LL v0.11. Paul recognized the control problems and corrected much of that. The stacking also is easier to follow. Gamma is gone now and you only have brightness and contrast, although you still need to adjust the white and black levels. Paul will be coming out with some tutorials soon that should help us all.

Your question on stacking is interesting. I have learned from some very knowledgeable people that sum and mean stacking are mathematically the same. My testing confirmed that with LL, so it makes sense to just use mean because it's so much easier. With sum, additional adjustment is necessary. Dom also found that stacking improves noise for about five stacks with each stack progressively getting smaller and smaller. No improvement is perceptible after five.

I'm not an expert on scope aberrations, but I do know that collimation is critical, especially when using a focal reducer. Here's a good reference on collimating an SCT that I use. I didn't realized the need to use such high magnification with a very small amount of defocusing. Once I did that my results were much improved.

https://www.astromart.com/articles/article.asp?article_id=548

At a focal length of 1000mm, it's tough to find objects. I use SkySafari and try to align near the object I'm looking for by finding a bright star in the same region. Then I see where it is in my target bullseye and move it in the same position for the desired object. I also have two Lodestars, so sometimes I run one as an efinder in a wide field scope or finder scope. I do have an old MacBook with OS 10.6 that will run LL. So I have two computers going along with my Thunderbolt 27" monitor.

Hope this helps. I'm sure there will be others that can add or correct what I started.

Good luck. You have an excellent start.

Don

[Dom543]

Alex,

I have been using a flip mirror with long focal length SCT's. Here is a thread with photos about it

http://stargazerslounge.com/topic/227032-flip-mirror-with-two-stage-focal-reducer/

It not only facilitates finding and centering objects but also helps to alleviate my wife's suspicion of anything displayed on a computer screen. She can convince herself, by looking into the eyepiece, that the object is really out there in the space and not just created by an app or downloaded from a website.

An alternative that I myself am planning to implement is to have a 50mm finderscope with a 1.25" eyepiece attached to the main OTA. I can then use the findescope to find and center the targets. But I can also move my Lodestar from the main OTA into the ep holder of the finderscope for widefild views. There are many beautiful large nebulae that require the wide field provided by a scope with less than 200mm focal length.

Clear Skies!

--Dom

[Paul81]

Welcome to the world of Lodestar! haha!

Always good to get first light under the belt, and looks like you are off to a good start. The other guys have pretty much answered the questions I was going to address, so there is not much more I can add on that front.

Keep up the good work and look forward to hearing about your next observing session!

[aparker]

So the second time out I grabbed LL 0.11 first before starting, and have to say the white/black sliders are very much improved.  I also learned some things about how to finesse stacking (set a wider pixel shift allowance, but not too wide, for example).  I also found that I can only go up to about 45 sec subs before the stacking tends to fail pretty often.  I'll need to get the mount on a pier and drift align to get better tracking, I think.  Nevertheless, definitely better results on round 2.  For a nearly full moon, capturing even a wisp of a mag 15.1 galaxy is pretty cool!

[aparker]

Definitely a few hot pixels in there.  That was 3 x 45sec; stacking failed after three subs so I stopped there.

Also got an improved M81 by stacking 8 x 10 sec.  Both of these were with the arcsin gamma function, which seems better to me that the original linear or the other new option.

Much better view of the spiral structure than I got the first time out.

[aparker]

I need next to work on the coma issue - it's distracting.  I'm wondering if an 8" f4 Newt with coma corrector might not be a better solution for this enterprise than trying to push the c8 to f5 with a focal reducer.

[arkosg]

Hi there,

I use an Edge HD 8" scope, and I have it reduced to about f4; there is a bit of coma, but nothing too bad (in fact, it may be collimation rather than reduction).  

Have a look at my gallery shots for some examples of pics with this combination of scope/reduction.

As Don mentioned, the spacing between components is critical, as is having a fairly rigid imaging train - I use threaded components when at all possible.

Cheers,

- Greg A

[HiloDon]

Hi Alex,

Your C8 Edge is a great scope, and I agree with Greg that the scope isn't the issue. If anything, the Edge should be the best for eliminating coma.

I suspect it has something to do with your reducer. If everything is collimated properly and centered in the optical train you should see minimal coma even at F3.3. I looked up one of my old captures with my Meade 8" SCT and my 3.3 FR. Here's NGC253 and there's minimal coma present. And this Meade is just the standard version, not the ACF. Before I would invest in a newt, why not try a 2" 3.3 reducer? There is the Optec, or you might find a used Meade. The one I have is a China version, and I don't see the problems with it others have claimed. As I said before, collimation is critical when using a reducer. Probably more so with a newt.

Getting your mount polar aligned will help a great deal with the stacking. Sounds like you're already on that. You can't beat drift aligning, and the more you do it, the easier it gets.

[aparker]

Thanks for the suggestions, gentlemen. I think the collimation is pretty good as it came from the factory. I have checked it against a star with the highest power eyepiece I have with what look like perfect results. I agree also that the EdgeHD optics are great - using the scope visually at f10 there's no hint of coma even with an eyepiece that yields a >1 degree TFOV. I am using screw together or screw type compression fittings on the whole optical train - no thumbscrew compression fittings anywhere, so I don't think its wobbling excessively. That seems to be narrowing the issue to the reducer (GSO component, the cheapest piece in the whole system...). I guess the next step is to play with spacing from FR to sensor. I suspect that going farther away (more reduction) will only make things worse, but experiment is called for. Maybe I just need a better reducer. Unfortunately the weatherman says we're in for a string of cloudy days here, so it may be awhile until I can test this...

[stash_old]

Alex,

I have been using a flip mirror with long focal length SCT's. Here is a thread with photos about it

http://stargazerslounge.com/topic/227032-flip-mirror-with-two-stage-focal-reducer/

It not only facilitates finding and centering objects but also helps to alleviate my wife's suspicion of anything displayed on a computer screen. She can convince herself, by looking into the eyepiece, that the object is really out there in the space and not just created by an app or downloaded from a website.

An alternative that I myself am planning to implement is to have a 50mm finderscope with a 1.25" eyepiece attached to the main OTA. I can then use the findescope to find and center the targets. But I can also move my Lodestar from the main OTA into the ep holder of the finderscope for widefild views. There are many beautiful large nebulae that require the wide field provided by a scope with less than 200mm focal length.

Clear Skies!

--Dom

"but also helps to alleviate my wife's suspicion of anything displayed on a computer screen. She can convince herself, by looking into the eyepiece, that the object is really out there in the space and not just created by an app or downloaded from a website"   

[aparker]

So the second time out I grabbed LL 0.11 first before starting, and have to say the white/black sliders are very much improved.  I also learned some things about how to finesse stacking (set a wider pixel shift allowance, but not too wide, for example).  I also found that I can only go up to about 45 sec subs before the stacking tends to fail pretty often.  I'll need to get the mount on a pier and drift align to get better tracking, I think.  Nevertheless, definitely better results on round 2.  For a nearly full moon, capturing even a wisp of a mag 15.1 galaxy is pretty cool!

best M106 01APR15.png

Looking again at this capture, I was just playing around in Sky Safari configuring scopes and sensor dimensions, and realized that I can't be getting 0.5X reduction with my present setup, or I would not be able to get all four of these galaxies in frame.  It looks like around 0.38X to get the FOV demonstrated by the photo.  So, it looks like my sensor to reducer spacing is pretty far off (too distant), which may explain the severe coma.  For my next time out (hopefully clear skies Sunday night) I'm going to step through adjusting the spacing to find the fastest system that is agreeably coma-free.  Wish I did not have to reduce the already-small FOV, though.  Maybe I need to look into the Hyperstar option afterall.

[HiloDon]

Hi Alex,

I took one of your images (hope that was ok) and put it into Astrometry.net. The FOV I got gives a focal reduction of about .35 with the C8 HD and the LS. You're at about 700mm. Here's the link:

http://nova.astrometry.net/user_images/631629#annotated

You're correct, this could be the cause of your severe coma.

Hope this helps.

Don

[aparker]

Hi Alex,

I took one of your images (hope that was ok) and put it into Astrometry.net. The FOV I got gives a focal reduction of about .35 with the C8 HD and the LS. You're at about 700mm. Here's the link:

http://nova.astrometry.net/user_images/631629#annotated

You're correct, this could be the cause of your severe coma.

Hope this helps.

Don

Don - that's great, thanks for the confirmatory data and the pointer to the astrometry site. For my spacing adjustment exercise I was thinking about pointing at Mizar / Alcor. At 0.5 X that "pair" should be pretty exactly half of my diagonal FOV. I hope I can stay a little faster than that and still banish the coma....

[aparker]

I had an interesting opportunity to contrast EAA with visual last night. I was up at my "dark" site (yellow to green zone, by no means pristine). I had my 18" f4.8 Newtonian out with pretty good skies, except for marginal seeing (seeing is never great here). I was mostly focused on galaxy hunting in Leo and Virgo, but decided to check out M106 and friends that I posted a screenshot of above. Interesting contrast. M106 was a more satisfying view visually, since you get all the fancy post-processing your visual cortex does implemented in realtime. The 12th mag adjacent to it was obviouly there but very faint. The two faint fuzzies were maybe popping in at the limit of averted vision, but without knowing exactly where to look, there's no chance I ever would have thought there was something there. Contrast that to EAA with an 8" scope from white zone Boston on a moonlit night, where it was immediately obvious that there were four objects on the screen as soon as the second frame stacked. Amazing delta in sensitivity. Although for bright (eg 8-10 mag) objects, the eyeball view from a dark site still is hard to beat. I am really pleased though that this EAA thing gives me an avenue to do DS observing from Boston. Of course, eventually I will have to explore the combination of dark site, 18" scope, and digital sensor...

[aparker]

Some progress tonite. Got the FR spacing adjusted to give true 0.5x reduction, and guess what? No more coma. Plus got my old guide scope and camera out and set up, running with PHD. Curious that LL will connect to its camera on either usb port on my macbook, while PHD only likes the lefthand one.