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Improving tracking with CG-5

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#1 Deetrix

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Posted 08 October 2013 - 11:10 AM

I'm having to throw out about half my expsosures due to streaky stars. I'm imaging unguided at 560mm. I'm assuming that my polar alingment is good because some exposures are REALLY good and the framing of my subject does not change at all. I'm the first owner of the mount and have not taken it apart to de-burr or re-grease. Thanks in advance, Paul.

#2 Cliff Hipsher

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Posted 08 October 2013 - 11:51 AM

What camera? What OTA? What exposure time? What object?

If you are shooting DSOs unguided you will get star trails. Periodic Error in the worm gear is the prime suspect.

NEVER assume your alignment is "good"

#3 Mr Greybush

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Posted 08 October 2013 - 11:57 AM

Paul the simple answer is you can not image without a guide scope. I know you can get a few images without guiding I've seen it done but that is a very small percentage. Guide scopes are affordable and it is a must. Several different guide packages IMHO I have only used 2 methods for guiding. The first is my 80mm on a CG-5 with a 50mm scope and Meade DSI camera. My 8" sct has a 80mm guide scope using the same camera. I have separate setups and use the 8" with a ccd camera and the 80mm my T3i. These are housed at separate locations. I have a 8" sct also for planetary that doesn't need guiding but it has it. Sorry for a long drawn out answer but this what I use and I am still learning to use as everyone else is learning to

#4 Raginar

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Posted 08 October 2013 - 11:59 AM

I agree with John. That's why they invented guide cameras. You will be pleased with the results n

#5 Stelios

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Posted 08 October 2013 - 12:41 PM

I posted recently in Beginning and Intermediate imaging with the same problem--long stars in some exposures, good ones (or at least so-so) in others--and got the same answer: Periodic error.

The top suggestion for fixing was, of course, guiding.

Summarizing the advice:

0) Get an autoguider!
1) Be anal about the polar alignment. Learn to drift align.
2) Balance the mount--but give it an east bias. A trick to do this is to hang a weight (a couple of pounds) around the RA axis, so it always pulls to the correct side as you cross the meridian.
3) There are hypertuning kits and places that will hypertune the mount, making it exhibit less periodic error. [I personally feel dubious about that. Hypertune service is $425. Add 2-way shipping and you may as well sell the CG-5 and buy a better mount].
4) Make sure you discard your images with elongated stars before stacking.

#6 Cliff Hipsher

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Posted 08 October 2013 - 12:57 PM

3) There are hypertuning kits and places that will hypertune the mount, making it exhibit less periodic error. [I personally feel dubious about that. Hypertune service is $425. Add 2-way shipping and you may as well sell the CG-5 and buy a better mount].


Get the kit and do it yourself.

#7 Mr Greybush

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Posted 08 October 2013 - 01:00 PM

I posted recently in Beginning and Intermediate imaging with the same problem--long stars in some exposures, good ones (or at least so-so) in others--and got the same answer: Periodic error.

The top suggestion for fixing was, of course, guiding.

Summarizing the advice:

0) Get an autoguider!
1) Be anal about the polar alignment. Learn to drift align.
2) Balance the mount--but give it an east bias. A trick to do this is to hang a weight (a couple of pounds) around the RA axis, so it always pulls to the correct side as you cross the meridian.
3) There are hypertuning kits and places that will hypertune the mount, making it exhibit less periodic error. [I personally feel dubious about that. Hypertune service is $425. Add 2-way shipping and you may as well sell the CG-5 and buy a better mount].
4) Make sure you discard your images with elongated stars before stacking.


Polar alignment isn't so much about being anal about it everyone can get it close and the good one's have there setup on a pier. The drift alignment isn't so much so if your guiding is good both work hand in hand. I've done imaging both with drift and without with a good polar alignment. PHD has to be working well with a good calibration. Everyone does different things in different ways. I use what's best for me and may not be what you like. We are only human if we didn't think differently. The hypertune kit for the CG5 IMHO if the mount is good why would you mess with it. When something is going on with it then change out the parts. I have only HT 3 mounts among 30 mounts I've used. The reason for the 3 is because something was wore out and it was just as cheap or something quit all together. Why spend money tearing it down and void a warranty if its new let the sucker break during the warranty and have the manufacture fix or replace it. Save HT for after a warranty. I have a new 8" cpc that I'd like to defork but the warranty would be voided if I did. I will take the ota off of it after the warranty is dead that way I know I can mess with it.

#8 rmollise

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Posted 08 October 2013 - 01:01 PM

I'm having to throw out about half my expsosures due to streaky stars. I'm imaging unguided at 560mm. I'm assuming that my polar alingment is good because some exposures are REALLY good and the framing of my subject does not change at all. I'm the first owner of the mount and have not taken it apart to de-burr or re-grease. Thanks in advance, Paul.


It really depends on your requirements. The mount is capable of doing 30-second exposures unguided. Not every single sub will be a keeper, but most will. For a beginning CCDer, a stack of 30-second frames with a sensitive camera can get you started. I stuck with film and resisted CCDing for a long time, and when I decided to finally learn, I began with a CG5, a C8, a focal reducer, and Meade's original DSI. A stack of 30-second CG5 shots allowed me to get reasonable images, like the Dumbbell below. It was good enough to learn the ropes, at least. If you want to go much beyond this, you need a guidescope/guidecamera, yeah. One bonus? A polar alignment done with the hand control is more than good enough for 30-seconds. :cool:

Probably the most important thing with this mount? Keep the balance slightly east heavy all the time. ;)

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#9 Deetrix

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Posted 08 October 2013 - 02:24 PM

Thanks to everyone for the responses. So to sum it up, its unavoidable periodic error. I was hoping to go a little longer without auto-guiding. Funny thing is that I have a very nice astro tech 50mm guidescope. I think deep down I'm trying to avoid taking a laptop out with me. I hate to keep throwing out half my subs. Thanks again, Paul.

#10 gdd

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Posted 08 October 2013 - 04:07 PM

A focal reducer will help you get more out of your 30 second exposures and reduce the star trailing. A telephoto lens even more so. Specializing on targets near the polar regions will also help until you break down and start autoguiding.

Gale

#11 Stelios

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Posted 08 October 2013 - 04:34 PM

3) There are hypertuning kits and places that will hypertune the mount, making it exhibit less periodic error. [I personally feel dubious about that. Hypertune service is $425. Add 2-way shipping and you may as well sell the CG-5 and buy a better mount].


Get the kit and do it yourself.


My time is valuable too, and I'm hardly confident that

1) I would be able to do the job correctly with no experience or familiarity
2) It would make enough difference to justify the cost, given there are other alternatives.

#12 Deetrix

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Posted 08 October 2013 - 05:38 PM

Gdd, yes a focal reducer is definitely next.






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