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Kash26
2011-Jan-11, 08:37 AM
I recently found a decently priced imaging bundle from Orion telescopes but wanted to see if I could get some opinions on what quality of Astro-imaging I might yield with this equipment.

-Orion 6in newtonian reflector f/5 150mm
-EQ G go to mount
-Starshoot CCD pro camera 2.0
-Autoguider refractor

My underlying question is will I get good deep space images with long exposure, tracking and stacking with a 6 inch like this and a good rated CCD chip as this one. When I see Astro images I usually notice people are sporting an 8 inch or a refractor. So I'm curious. If any one can provide some insight I would greatly appreciate it.


As always, clear skies mates!

Hornblower
2011-Jan-11, 04:55 PM
I recently found a decently priced imaging bundle from Orion telescopes but wanted to see if I could get some opinions on what quality of Astro-imaging I might yield with this equipment.

-Orion 6in newtonian reflector f/5 150mm
-EQ G go to mount
-Starshoot CCD pro camera 2.0
-Autoguider refractor

My underlying question is will I get good deep space images with long exposure, tracking and stacking with a 6 inch like this and a good rated CCD chip as this one. When I see Astro images I usually notice people are sporting an 8 inch or a refractor. So I'm curious. If any one can provide some insight I would greatly appreciate it.


As always, clear skies mates!I would venture a guess that the results in deep sky work depend about 1% on having good equipment and 99% on the skill and experience of the operator. The learning curve is pretty steep. There are some experienced astrophotographers in this forum, and perhaps you could find an astronomy club in or near your area and pick their brains about deep sky imaging.

RickJ
2011-Jan-12, 08:13 PM
A 6" f/5 isn't a bad way to start imaging. You want to start with a short focal length scope. As Hornblower says, the learning curve is very steep. Nearly vertical if you have had no simpler imaging experience. The mount is by far the most important element. The one in this list is a very minimum mount for that scope. Any slight wind and you'll be in trouble very fast. I recommend 60% or more of the budget go to the mount. I can take rather good images with crappy scopes and cameras but I'm dead without a good mount.

Next think about the guiding system. A separate guide refractor must be super solid. Any flex of the system anyplace means the guide scope isn't seeing the stars in the same place as the imaging scope and your stars will be lines. Also be sure, once you do have it solid enough (usually requires separate support for focuser and camera besides the tube of the scope itself) that you guide very close to or inside the field of the camera. This will reduce image rotation caused by imperfect polar alignment. Most beginners mistakenly believe if they guide on a star polar alignment isn't all that important. This is very wrong. What happens is the star you guide on is fine. A nice point, but everything else rotates around the star! So you get arcs for stars across the image. The worse the alignment the faster the arcs develop. Also the further you are away from the guide star the longer the arcs are. You will need alignment to be within a couple minutes of arc for imaging with the field of the guide scope right by that that is imaged. Further away you need even higher accuracy. A skill that takes some time to learn. At least for me.

Rather than a guide scope I much prefer an off axis guider. One that uses the same scope for both imaging and guiding. This way there is no flex and you are forced to use a guide star very close to the imaging field. Yes it takes longer to set up but the results are far superior. Flex in a separate guider is a very difficult problem for the experienced imager to correct. A beginner has virtually no chance, most give up and quit. When I started 50 years ago guide scopes were the only option. I was lucky to get 1 in 20 images to come out due to this issue. Somehow I hung in there while all others I knew at the time gave up. Then off axis guiders became available and things went much better.

Add to the list a Bahtinov focusing mask. Until this came along recently beginners had a terrible time finding focus. This mask will make this super easy. Though if your temperature drops you will need to refocus rather often. An f/5 scope has a focus range of less than 50 microns! (formula often say 80 but I've found this way too generous, even at my f/10 which the formula put at up to 300 microns I find 25 microns makes a difference. So did an article in a recent Sky and Telescope magazine. I don't know where the formula goes wrong but it does.) Usually a good dual speed manual or electric focuser is needed to achieve this. Doubt the package includes either. Focus and focusers are a common problem for beginners.

Starting with a short focus scope helps with the guiding issues but if the f ratio is low focus becomes difficult. I started my digital work with a 6" f/4 and a JMI electric focuser as I knew I had no chance with the manual focuser on the scope at the time. While I could find a usable focus I was surprised that every once in a while my images were far better than normal. I originally blamed this on seeing. Nope, it was my inability to find that perfect focus except by pure luck once in a while. The Bahtinov focusing mask hadn't been invented yet. I finally got software to measure my average FWHM of the stars in the image and used that. Slow but worked. The mask was still years in the future. You're fortunate its around. Buy or make one. No I still don't use one as I now use FocusMax. Fine for an automated system like I use but for manual focusing go with the mask.

A good source of additional information:
http://starizona.com/acb/ccd/ccd.aspx

Rick

Kash26
2011-Jan-17, 01:44 PM
Sorry, actually I will be getting the Orion Atlas EQ-G Computerized Go To Telescope Mount. Apparently it comes with the only Deep Space Astro-Imaging bundle I can afford.

I looked into off axis guiders and found some good ones available from Orion, and that sounds interesting in order to reduce flex.

In the interim I've been tinkering with getting better focus on my solar and planetary imager with my 10" inch.

So, let's say with experience and luck will I be able to get nebula and galaxy images with a 6" inch imaging Newtonian. Is it possible with good skill and long exposure? Given the limitations of telescope itself? Particularly it's size.

Thanks for your help. Glad I'll be thinking of many of these things long before I receive any of my equipment.

RickJ
2011-Jan-17, 08:09 PM
The answer is yes the scope is fine for what you want. My main worry is the mount. It is your weakest link by far though I've seen some good images with it. Just expect to do a lot of fine tuning to get the guiding stabilized.

This was my very first attempt at a galaxy with my $100 6" f/4 with $300 electric focuser. Only 20 minutes so very under exposed. At the time I had no decent processing software able to do anything but 8 bit processing and no non linear ability at all. This greatly limited my processing though I was too ignorant at the time to know this. Also collimation was off so the stars go out of focus across the image. In other words nearly everything but the tracking went wrong. Still, I was thrilled with the results at the time. Pretty sick by today's standards.

Your camera has 6.1 micron pixels with color filter overlays. Mine used 9 micron pixels. Smaller pixels are far less sensitive in that they pick up photons over a smaller area and being filtered only about 30% are recorded while my unfiltered pick pixels up 80% and with more area are far "faster". While your pixels are smaller and each therefore has higher resolution the combining of pixels to get color data as well as luminance data through various filters results resolution is likely very similar to my 9 micron pixels so the major difference in resolution would be my 6" shorter focal length, 24" vs 30". I use a minimum exposure time of an hour total, 2 would be better. Subs as long as mount and sky conditions allow.

Rick

Kash26
2011-Jan-29, 10:54 AM
Thanks for the information. Let's talk a little bit about the mount again. See the package I discussed is roughly 2,500 and is the only way I could ever afford these items since I would be getting huge savings by buying the so called bundle solution.

Here is the mount information:

Orion Sirius EQ-G GoTo Mount and Tripod (more info)
"With its computerized GoTo system and hand controller, the included Orion Sirius EQ-G mount and tripod is ideal for virtually any astrophotographic applications. The internal dual-axis stepper motors slew your telescope at up to 3.4-degrees per second, and keep the target object centered for extended exposures, so deep-space objects will reveal more colorful and dynamic features. The Orion Sirius EQ-G mount includes an illuminated polar-axis telescope, 8.3-inch dovetail mounting bar, and one 11-lb. counterweight. The tripod is remarkably sturdy, as evidenced by the 1.75-inch diameter stainless steel legs and cast-metal spreader plate. The mount requires a 12-volt DC power source, like our Orion Dynamo Pro, or an AC-to-DC adapter for GoTo operation and motorized tracking."

When we talk about a lot of fine tuning being necessary with this scope, are we talking about electronic focusers, plenty of focusing, and so forth. Can you briefly touch a little more in the weaknesses of the mount and ever so briefly on ideas for overcoming it's weakness.

As always thanks!c :-)

RickJ
2011-Jan-29, 07:17 PM
Of course much of what they say is puffery and has little real meaning as to imaging abilities. It doesn't talk about backlash in gears, vibration damping, wind loading, gear accuracy, ease of polar alignment, etc. These are the important things, but not what they talk about! Imagers do successfully use the mount and, in fact it is superior to the one I started with 50 years ago. But then only one in 20 images came out!

The camera and scope would image at an image scale of about 1.7" of arc per pixel. This means the mount must track the equivalent of a slowly rolling golf ball at one mile and keep that on one of those pixels through the entire imaging run!!! Otherwise the golf ball will trail into a line. You will use a guide camera to see any deviation and send corrections to the mount. But a telescope and counterweights as well as other moving parts of the mount have inertia. The mount's drive must accept the correction and over come this inertia moving the mount a distance of less than the diameter of that golf ball at one mile without over or under shooting the mark and do this many times a minute. This is the demands we put on a mount when doing deep sky imaging through a scope! It is severe and why the mount is by far the weakest link in any imaging chain.

By tuning I mean both hardware and software. Work to eliminate backlash in gears for instance is a hardware tune. Usually with a mount like the one you are considering it is best to mis align on the pole a bit so the declination correction is in one direction only and then disable guiding, if the software can, in that direction you shouldn't have to move. Seeing will move the star the "wrong" way but you want to ignore such corrections as backlash in a mount of this price range would just make things worse than not guiding that way for the short time period seeing moves it the wrong way. Not a perfect solution but best for this mount and mounts like it. Tuning also means finding and eliminating gear errors that cause sudden tracking errors a guider can't follow, sagging focusers and guide scope if you use one. And many more things. It also means tuning the guiding software parameters. How much error to correct at a time, how often, how quickly (too fast and momentum will kill you -- too slow and you never get caught up), what errors to ignore etc. are all controlled by software settings in the guiding software. RA backlash can be a problem if you correct too fast. Get the mount moving a bit faster than sidereal rate to make a correction means you have to slow it down again. Momentum keeps it going and will pull the gears apart slightly if there's any backlash. Slow down to make the correction means it has to instantly speed up after the correction which is impossible. Thus not making the full correction may in fact make the full correction when the mount overshoots or undershoots due to this momentum issue. By balancing the scope so it is always a bit heavy (counterweights too light) makes the mount work uphill and lets gravity help prevent this backlash overshoot error. But as you reach the meridian this gravity assist is greatly reduced. You may find it necessary not to image too close to the meridian because of this unless you can really adjust the worm to remove the backlash. When I used a similar mount this was a weekly adjustment.

It all depends on how critical you are of your images. A beginner is thrilled with any result but as time goes on becomes aware of the problems and elation can turn to severe disappointment. I've seen this happen many times. You will, most likely, quickly outgrow the mount. I did, but back then there was nothing better out there that was portable so I stuck with it for years, greatly improving my four letter vocabulary.

If you don't guide, with that camera and scope a 30 second to 1 minute exposure is all you can achieve with the mount. This means stacking many frames to get a reasonable image (60 to 120 minimum). Each has read noise degrading the image quality. With guiding you would likely need 6 10 minute frames rather than 120 30 second ones. This reduces signal to noise ratio of the 10 minute subs over the 30 second ones by the square root of 120/6= ~4.5 times. This makes for a far superior image.

I'm not saying don't get the package. Just realize you are in for a much harder job than they want you to believe from their ads. You will become an expert on the tricks needed to get good images out of that mount and likely "improve" your vocabulary along the way. I certainly did.

Rick