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tboconnor
member


Reged: 01/14/10

CGEM not suitable for serious astrophotography?
      #5647690 - 01/28/13 09:44 AM

Hi all

Came across this blog post:

http://www.photodady.com/blog/2012/10/08/cgem-final-thoughts/

I was about to start to give astrophotography a more serious go, but it sounds like I might be in for some serious frustrations.

How do other CGEM owners feel about this?


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jrcrillyAdministrator
Refractor wienie no more
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Reged: 04/30/03

Loc: NE Ohio
Re: CGEM not suitable for serious astrophotography? new [Re: tboconnor]
      #5647754 - 01/28/13 10:27 AM

The orthogonality issues described make the mount less than ideal for unguided imaging. With guiding, they wouldn't be significant.

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neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: CGEM not suitable for serious astrophotography? new [Re: jrcrilly]
      #5647773 - 01/28/13 10:41 AM

I have seen many good pictures made by CGEM owners. It is relatively cheap mount so you can't expect level of precision and tracking like a mount that costs 4 times more money but if you do not overload it and have autoguiding i don't see any reason not to try astrophotography.

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RogerRZ
Whatta you lookin' at?
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Reged: 01/09/06

Loc: West Collette, NB, Canada
Re: CGEM not suitable for serious astrophotography? new [Re: jrcrilly]
      #5647799 - 01/28/13 10:55 AM

I don't know what "serious" astrophotography is, but I would wager a guess that most "serious" (and a lot of not so serious) astrophotography rigs incorporate autoguiding as a part of their equipment.

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Footbag
Postmaster
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Reged: 04/13/09

Loc: Scranton, PA
Re: CGEM not suitable for serious astrophotography? new [Re: RogerRZ]
      #5647836 - 01/28/13 11:10 AM

After reading through a lot of his posts, I realized a few things. First, he's well over the weight capacity for visual observing. In addition, he's using a long FL SCT.

In one of his early posts, he says that he would expect the CGEM to get 5m unguided exposures. If he means with the SCT, then he's expecting too much from the mount. My Mach 1 cannot do that.

I belive that drift alignment doesn't require orthogonality or initial leveling. He seems to think otherwise. Unless I'm misunderstanding.



Every mount is going to have every type of error. The closer you look, the more you will see. That doesn't mean all of your problems are stemming from the error you are observing.

Edited by Footbag (01/28/13 11:44 AM)


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bunyon
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Reged: 10/23/10

Loc: Winston-Salem, NC
Re: CGEM not suitable for serious astrophotography? new [Re: Footbag]
      #5647841 - 01/28/13 11:12 AM

5 minute unguided exposures? Does any mount do that?

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: RogerRZ]
      #5647847 - 01/28/13 11:14 AM

"Serious" is all in the user. Loaded to the max at f/10 or higher will be problematic as it can be for many mounts (and more important, many users). Unguided imaging is a waste of time and effort even on some much more expensive mounts.

Can the CGEM be used for some great astrophotography? You bet! I took images from a CGEM user this last year and blew them up to eight feet wide for backgrounds for my PATS/ASAE boths and they were stunning. They were taken with an FSQ106 at f/5. It takes a lot more to be able to do that with good results, even at f/5, than to just look at an image on a small computer screen. In my book that does make the CGEM suitable for "serious" AP.


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: neptun2]
      #5647856 - 01/28/13 11:17 AM

Wow, this guy is tough, but he might be right. I was surprised recently, after two stars align and polar align routines, to still get a fast drift in declination. I was at f20 and autoguiding was powerless. I am still new to the mount so i still keep my judgement for latter, but, since ddady did an extensive work on the mount, i expect him to be right.
Bottom line: spending lots of time in polar alignment to fix dec drift might not be a solution. But, can we hope to be saved by the imaging software? stacking AND derotation of subs when two stars are selected for stacking should fix a slight polar misalignment, correct?

PS: sorry f/20 for me is c9.25 x2, that is 4700 mm. At bthis fl, i could see a star drifting in declination immediately (and RA too)

Edited by dickbill (01/28/13 11:23 AM)


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jrcrillyAdministrator
Refractor wienie no more
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Reged: 04/30/03

Loc: NE Ohio
Re: CGEM not suitable for serious astrophotography? new [Re: bunyon]
      #5647863 - 01/28/13 11:21 AM

Quote:

5 minute unguided exposures? Does any mount do that?



You'd need a perfect polar alignment (the blog entry linked to in the first post is complaining about the difficulty of achieving that with this mount). Then you'd need to limit the focal length to that for which the corrected PE is less than one pixel. Then you'd need to be using something more internally stable than SCT. My old EM-200 (with its excellent polar alignment scope) worked well unguided at 500mm.


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AstroRick
member


Reged: 08/13/12

Loc: Ohio
Re: CGEM not suitable for serious astrophotography? new [Re: tboconnor]
      #5647894 - 01/28/13 11:36 AM

Hi,

When I got into astronomy and astrophotography in 2010 I bought a CGEM mount and have gone through trials and tribulations to learn how to take astrophotographs. It is an ongoing process. I am indeed "serious" about learning how to do prime focus AP, but I am far from the level of someone at the professional level. So I would say that answering the question of whether the CGEM is suitable for serious astrophotography does depend on your definition of "serious".

In my ongoing learning process, I have tried to eliminate possible problems with the hardware so I could figure out what areas in my process and technique were in need of improvement.

* I purchased and installed a Hypertune kit from Deep Space Products to make it easier to balance the mount and to improve tracking.

* I purchased reticle eyepieces to better center alignment and calibration stars.

* I purchased a polar alignment scope to get the initial setup closer.

* I purchased a digital level as an independent measure of level. The bubble level on the mount is not accurate, when compared with the digital level. I also use the digital level to adjust the altitude by placing the level on the saddle and adjusting it to the observing latitude.

* Finally, I purchased some ultrahigh molecular weight polyethylene and cut a washer-shaped ring to sit between the tripod and the base of the mount. The ring decreases the friction which allows adjustment of the azimuth during polar alignment even when the mount is securely fastened to the tripod.

In a perfect world my ~$1500 would have bought me a mount that did not these enhancements to get it to work acceptably. In fairness to Celestron, some of it may not have been necessary, but I did it anyway in order to eliminate any hardware issues that may have existed in order to uncover flaws in my techniques.

As a result of all of the above, and I am now able to diagnose and correct issues that affect image quality and to collect images with round stars from edge to edge.

In hindsight, some of the struggle may not have been necessary if I had purchased a more expensive, higher quality mount. However it is equally likely that the cost of that mount would have prevented me from ever getting into astronomy to begin with.

I hope this explanation is of value to you.


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: jrcrilly]
      #5647925 - 01/28/13 11:48 AM

yeah well, i guess a mount of a quinzillion dollar can always do great unguided imaging at 500 mm, but so can do a cg5.
But i don't think anybody can expect a 5 min unguided at 2300 mm for any mount. I was well warned in these forums, when the cgem came a couple of years ago, that the PE of the cgem would not be any better than the older Atlas, but worse, maybe even no better than the cg5!
Several times i asked "2 min unguided at 2300 mm right?"
and the answer always was "nope, 20 seconds like the good ol' cg5'. So it's not reallistic expectation to ask for these kind of unguided performances. The deal was always that the cgem can autoguide a heavy load better than the cg5 at ~2000 mm. Now if that was not true, it would be very disapointing since that means going adaptive optics and more dollars spent.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5647926 - 01/28/13 11:48 AM

I would also have to question the "work" that he did on the mount. While he states that "you get what you pay for" his expectations were far above what he paid for and would probably be above his next choice of a G11. Expectations (along with experience) are very important here. The CGEM is far from a perfect mount in both design and quality, but in the hands of the right person, it is an amazing piece of equipment. For those with the money, I always recommend going higher end, but a high end mount in the hands of someone less experienced can also provide poor results. There is an inherent amount of talent in astrophotography and some people just have it while others don't. Some people aquire the talent with hard work while others never seem to.

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Stew57
Carpal Tunnel
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Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5647968 - 01/28/13 12:04 PM

The two biggest problems that plague the CGEM are motor related. The dec cogging effect and the 8/3 PE that makes pec ineffective. Both are currently being activly woked on by celestron. They have been working on it for awhile and have no firm timetable for completion. If you are the impatient type......

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corpusse
scholastic sledgehammer


Reged: 04/11/10

Loc: Mississauga, Ontario, Canada
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5647970 - 01/28/13 12:05 PM

I don't see why unguided images is even important at all. As long as it can take unguided images for the 2 second exposures I take as I align that's good enough for me. The CGEM was the first mount I ever had and got it up to 10 minute exposures with a 8" and even 2 and a half minutes with an 11" scope.

While I consider myself a "serious" imager my picture quality may not be "serious" but I'd rank my location, then my skillset above the mount as being the reasons.


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5647989 - 01/28/13 12:13 PM

Yes experience and patience is mandatory in this hobby and sometimes talent too. But at the amateur level i hope two things (beside adaptive optics).
Using software and smarter ccd: the soft would correct for evrything: drift, derotation, and perhaps ignore or substract some photons that fall into the ccd well during a single accumulation period.
Or Electron Multiplication CCD for the masses, so that subs of a few seconds can replace minutes-long exposure.


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rmollise
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Reged: 07/06/07

Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5648086 - 01/28/13 12:49 PM

OK...to put it as kindly as I can, the person who started that thread was...uh..."barking up the wrong tree." The CGEM is quite suited for serious astrohphotography.

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TxStars
Pooh-Bah
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Reged: 10/01/05

Loc: Lost In Space
Re: CGEM not suitable for serious astrophotography? new [Re: rmollise]
      #5648127 - 01/28/13 01:07 PM

Please define the following:
1) "Serious"
2) "Is"

"Seriously though", would'nt any type of astrophotography be "Serious" compared to casual visual?


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rmollise
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Reged: 07/06/07

Re: CGEM not suitable for serious astrophotography? new [Re: TxStars]
      #5648363 - 01/28/13 02:34 PM

Not sure I follow you...but...

_I_ define "serious" as one's primary pursuit in amateur astronomy.


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photodady
journeyman


Reged: 09/03/12

Re: CGEM not suitable for serious astrophotography? new [Re: bunyon]
      #5648477 - 01/28/13 03:22 PM

ABSOLUTELY!
The Astro-Physics 3600GTOPE cans easily do 20 minute unguided sessions tracking accurately to within ONE arc-second of a degree over the entire period.

http://www.astro-physics.com/products/mounts/3600gto/precision-encoder-comple...

I'm not claiming that this is in any way an affordable mount, just that it is possible and commercially available.


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RogerRZ
Whatta you lookin' at?
*****

Reged: 01/09/06

Loc: West Collette, NB, Canada
Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5648506 - 01/28/13 03:32 PM

It is possible and commercially available to go 240mph with a car, it just isn't fair to expect a $30000 Honda Accord to do so.

A CGEM is a lot like an Accord. Pretty capable, pretty affordable, widely available...


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korborh
scholastic sledgehammer
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Reged: 01/29/11

Loc: Arizona
Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5648519 - 01/28/13 03:39 PM

Within 1" may not be enough for un-guided where the image scale may be 0.5"/px or less. So 1" on RA and DEC will show up as resolution loss compared to a well auto-guided one
.
Usually when un-guided performance is claimed, it is without quantifying the actual star FWHM compared to if it were guided. Un-guided long exposure for doing high-res does not make sense - auto-guiding is much easier, predictable, cheaper and will give better results with much less effort.


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: CGEM not suitable for serious astrophotography? new [Re: RogerRZ]
      #5648522 - 01/28/13 03:40 PM

This guy turned up on the CGEM Yahoo group and gave the impression that he had an axe to grind. There were a lot of flaws in his claims.

He had a TPoint plot that alleged to show a mount orthogonality error but he had disabled cone error and I think that the cone error had been transferred to the mount orthogonality term - with a huge error term.

He flounced off when we pointed this out.

Chris


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: RogerRZ]
      #5648589 - 01/28/13 04:10 PM

Photodaddy, if you had been reading cn forums around 2005 when the mount began, you'd have seen plenty of threads on the expected performances and endless comparisons to the Atlas.
Me among others were plenty hopefull of better gear, ie better PE and longer unguided subs than the cg5, but even before the mount was available, the replies in the post were clear that it was not going to be the case.


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tboconnor
member


Reged: 01/14/10

Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5648606 - 01/28/13 04:16 PM

Wow, thanks for the amazing information everyone! Ill get stuck into imaging with my CGEM now...Or at least when the clouds clear up

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Patrick
Postmaster
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: CGEM not suitable for serious astrophotography? new [Re: tboconnor]
      #5648639 - 01/28/13 04:31 PM

I was looking through "Dady's" photo galleries and noticed he doesn't have a single gallery devoted to astrophotography. Hmmm....sort of puts a damper on his credibility in my mind. It looks to me like he's basically a photographer, not an astrophotographer.

Patrick


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tboconnor
member


Reged: 01/14/10

Re: CGEM not suitable for serious astrophotography? new [Re: Patrick]
      #5648699 - 01/28/13 04:56 PM

I should also mention - I currently have two scopes - a Meade 12 inch ACF that Im using for visual and some lunar/planetary imaging, and a WO Megrez 90, which is what I want to use for deepsky dabbling.

I dont currently have any auto-guiding gear, but was intending to add something inexpensive like the Orion miniguider - kind of just to dip my toe in the water.

Just for fun, I tried some unguided shots with the Meade on the CGEM - I used the polar alignment routine, and managed to get one or two shots that showed it can guide for around 20 seconds - although it was very hit and miss - some shots showed trails with 15 second exposures, while some where fine with 30 seconds. I really need to drift align, but I wanted to see how good the all-star alignment system was

I really dont expect to be able to get much joy out of shots from the Meade - its way over the payload of the CGEM, although for visual it works just fine.


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orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: CGEM not suitable for serious astrophotography? new [Re: tboconnor]
      #5648776 - 01/28/13 05:28 PM

No, of course not.
CGEM is not suitable for unguided astrophotography.
If you want unguided AP then buy some high end Direct Drive Mount.
Also CGEM is not suitable for long FL AP.
Also CGEM is not suitable for heavy scope AP.

But under 900mm and up to lets say 12-14 kg equipment?
Well that is another story. Of course there are CGEMs that are not working correctly and that has to be said. But if you get a good one you actually don't have to hypertune...

99% of my images are made from 30min guided subs with refractor @ 765-900mm.
Do you know how many of those 30min subs I had to toss after I got OAG?
None.
And my CGEM has never been hypertuned.

Is this serious enough for you?


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kbastro
scholastic sledgehammer
*****

Reged: 04/20/08

Loc: Running from Clouds
Re: CGEM not suitable for serious astrophotography? new [Re: orion69]
      #5648827 - 01/28/13 05:51 PM

I have ta agree with orion69 on this one,, cgem's including one that I used, was ok,, but no where near exceptional and didn't have chance in hell of producing good astrophotos unguided at anything over 800mm f.l.

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WadeH237
Pooh-Bah


Reged: 02/24/07

Loc: Snohomish, WA
Re: CGEM not suitable for serious astrophotography? new [Re: kbastro]
      #5648881 - 01/28/13 06:15 PM

It looks like it hasn't been mentioned, but this has been discussed before.

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Jay Wise
sage


Reged: 11/21/08

Loc: Near Williamsburg VA
Re: CGEM not suitable for serious astrophotography? new [Re: WadeH237]
      #5648946 - 01/28/13 06:44 PM

One look at orion69's website puts an end to this discussion about the cgem's ability in the right hands. It is said that some of Ancell Adams photos were taken with a modified Brownie! It is frequently the master not the instrument that counts.

JayW


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: WadeH237]
      #5648965 - 01/28/13 06:51 PM

However, is it confirmed that PEC in the cgem is inefficient as ddady mentioned?
I used the PEC once with no great result but my drift in declination indicated that i was not very well polar aligned. So i'd like to know from those who are well aligned.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5648986 - 01/28/13 07:03 PM

Quote:

However, is it confirmed that PEC in the cgem is inefficient as ddady mentioned?
I used the PEC once with no great result but my drift in declination indicated that i was not very well polar aligned. So i'd like to know from those who are well aligned.




My understanding of the problem with the Celestron PEC is that it does not cover enough cycles to account for the 8/3 error from the motor gearbox. That is an issue for some people but not all. But PEC has supporters and detractors in general as well as disagreement on whether it should be used with guiding or not, so just like guiding, it is not a universal fix and will not magically turn a $1500 mount into a $15,000 mount.


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orlyandico
Postmaster
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Reged: 08/10/09

Loc: Singapore
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649001 - 01/28/13 07:14 PM

this horse has been beat to death before.

and "daddy's" claims are imho specious. you don't buy something for $1500 and expect it to perform like $6000. you get what you pay for as he himself said.

with that out of the way... a good PEC training on a mount that has small non-periodic terms (i.e. Celestron AVX!) will reduce the native PE by at least a factor of 4. If you accept that a normal CGEM has around 25" to 30" of PE, a good PEC (if there were no 8/3) would reduce that to perhaps 8".

your typical user with a DSLR or 8300 class CCD and imaging with a refractor would have perhaps 2.5" per pixel image scale. with 8" of corrected PE remaining, you could go unguided up to perhaps 2-3 minutes? not much more than that. but it is what it is.

unfortunately most CGEMs have at least 7" to 8" of 8/3.. in some cases much worse. so PEC training won't get you much below 15". long story short - you have to guide. all the time.

most folks are using CCDs anyway so guiding is not a huge extra chore.

funny story: I was puttering around last night with this:

and guess what. I was still guiding.

It's just too much effort to do the perfect polar align to go unguided for any length of time. Not to mention you need to factor in atmospheric refraction and all that. But with an eyeball polar align (mount in Park 3, I put a scope on and ensure it's pointed at this church stained glass rosette a couple miles away) i can do subs as long as i want, with guiding.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: Jay Wise]
      #5649009 - 01/28/13 07:16 PM

Quote:

One look at orion69's website puts an end to this discussion about the cgem's ability in the right hands. It is said that some of Ancell Adams photos were taken with a modified Brownie! It is frequently the master not the instrument that counts.

JayW




Absolutely correct. If you need images better than those, then just download the Hubble shots. A tremendous amount of AP is time and talent (of which I am lacking in at least one ).

Here are some more amazing shots with a CGEM and a CGEM DX: http://jwalk.smugmug.com/.

The raw AP talent of Jimmy Walker and Orion69 simply leaves me in awe. Their photos are every bit as good as the ones that are done by one of my club's members and he has spent probably 5 to 10 times as much on his system.


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orlyandico
Postmaster
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Reged: 08/10/09

Loc: Singapore
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649024 - 01/28/13 07:25 PM

Ed, you forgot Jeff over on the CGEM yahoo group. I also greatly admire his long FL work. but he has a leg up with the SX AO.

One thing you do get with the spendy mounts though is less hair loss. Less tweaking etc. If you have to drive 200km to get to dark skies like I do, and the weather is uncooperative most of the time, actual clear imaging time is precious and at some point you'll tear your hair out trying to deal with the mount...


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5649044 - 01/28/13 07:32 PM

Yes. There are definitely other's out there. Too many for me to keep track of. Jimmy's photos are the ones I blew up to 8 feet wide by 8 feet tall.

What the people with the bigger bucks are doing is no longer driving anywhere. They just buy a plot over in southern New Mexico or Arizona at one of the new astro communities, build a remote observatory, and do all their imaging from many miles away. The CGEM is not particularly suited to that, but I know people who do it with everything from Meade classic LX200s to top end AP and Bisque gear.


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ghataa
professor emeritus


Reged: 06/20/11

Loc: Central, NJ
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649067 - 01/28/13 07:43 PM

Maybe I should then just take my CG5 out back and shoot it.

George


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wolfman_4_ever
Pooh-Bah


Reged: 07/15/11

Loc: El Segundo, Ca, So. Cal
Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649083 - 01/28/13 07:49 PM

New firmware should be coming out soon for the CGEM DEC guiding bug.. but....There might..MIGHT... be new motors coming out for the CGEM.. similar to the VX line..

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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM not suitable for serious astrophotography? new [Re: wolfman_4_ever]
      #5649110 - 01/28/13 07:59 PM

Quote:

New firmware should be coming out soon for the CGEM DEC guiding bug.. but....There might..MIGHT... be new motors coming out for the CGEM.. similar to the VX line..




It is pretty likely that the new motors in the VX could simply be dropped into the CGEM if they changed the firmware to account for the new gear ratios. That's the only reason that we can't dump something else in there already. The big problem will be if they will be willing to supply enough motors for sale to satisfy everyone that might want to make the switch. Actually, if they would just allow us to change the gear ratios in the firmware that would allow anyone to drop in any motor that would fit.


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649117 - 01/28/13 08:02 PM

.. and for that reason (the promise of sweet, sweet AVX motors ) I am holding on to my CGEM. Even though every time I turn it on, I find something annoying (like my recent problem with the ASCOM drivers).

but it is just so darn easy to use! ASPA is great, the pointing model is great... AP doesn't have a pointing model (simple 1-star align). Unless you bolt up a PC with APCC.


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gmartin02
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Re: CGEM not suitable for serious astrophotography? new [Re: Stew57]
      #5649146 - 01/28/13 08:10 PM

Quote:

The two biggest problems that plague the CGEM are motor related. The dec cogging effect and the 8/3 PE that makes pec ineffective. Both are currently being activly woked on by celestron. They have been working on it for awhile and have no firm timetable for completion. If you are the impatient type......




+1 on the dec cogging problem. I have a CGEM with the dec guiding issue (some CGEM mounts do this, others do not). I am unable to shoot astrophotos with my AT8RC because of this problem, but am able to use my Tak FS-60 & Orion 110 ED because of their shorter focal lengths (although I still have to "nudge" the dec axis sometimes to unstick it when shooting with the shorter f/l scopes).

I am patiently waiting for the firmware or firmware+motors/motorboard solution from Celestron for the CGEM (this fix is already in the new VX mount).

Greg


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wolfman_4_ever
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Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649153 - 01/28/13 08:13 PM

Quote:

Quote:

New firmware should be coming out soon for the CGEM DEC guiding bug.. but....There might..MIGHT... be new motors coming out for the CGEM.. similar to the VX line..




It is pretty likely that the new motors in the VX could simply be dropped into the CGEM if they changed the firmware to account for the new gear ratios. That's the only reason that we can't dump something else in there already. The big problem will be if they will be willing to supply enough motors for sale to satisfy everyone that might want to make the switch. Actually, if they would just allow us to change the gear ratios in the firmware that would allow anyone to drop in any motor that would fit.




The issue is that the new motors are is very short supply right now..

Also...

It isn't the motors that makes the Dec Guiding issue go away. It is the firmware, and the firmware WILL work on existing mounts as well. The VX mount has the new firmware. The issue is during all the hoopla to fix the cgem bug, which was fixed in a beta release, the vx firmware took precedence.. Then somehow the fixed cgem/cge-pro firmware got fubared..

The new motors have different gear ratios, and would also require different feedback loop parameters. That could be overcome with a software update and an update to the PRN value. The latter requires you send in your motor board to Celestron. There is also a voltage issue. The voltage issue could be worked around by reworking a few resistors to your motor board (after you sent it in) but it is better for most consumers to get a new motor board if (and only if) you want the new motors.

The new motors have a bit more torque and integer gearing.


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dickbill
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Re: CGEM not suitable for serious astrophotography? new [Re: EFT]
      #5649171 - 01/28/13 08:21 PM

Quote:

Quote:

However, is it confirmed that PEC in the cgem is inefficient as ddady mentioned?
I used the PEC once with no great result but my drift in declination indicated that i was not very well polar aligned. So i'd like to know from those who are well aligned.




My understanding of the problem with the Celestron PEC is that it does not cover enough cycles to account for the 8/3 error from the motor gearbox. That is an issue for some people but not all. But PEC has supporters and detractors in general as well as disagreement on whether it should be used with guiding or not, so just like guiding, it is not a universal fix and will not magically turn a $1500 mount into a $15,000 mount.




Knowing that all the cgem errors (whatever their sources are) during a worm cycle are not perfectly periodic, my expectation is still that some of them must be periodic and the PEC routine must correct for them. So at least some smoothness must be obtained during the play back of the reccord even if non periodic glitches remain. In short the PEC can not be totally inefficient.


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5649196 - 01/28/13 08:31 PM

it's not. you can get rid of most of the fundamental, i.e. if you have 25" of fundamental and 8" of 8/3, you can get rid of maybe 15" to 20" of the fundamental. this will drop the PE of course, but the 8/3 is untouched.

i.e. you cannot get less than 10" corrected PE.


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WarmWeatherGuy
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5649217 - 01/28/13 08:43 PM

I love my CGEM. I take 10 minute exposures at 2000mm with my C8 (f/10) all the time. I can get polar alignment down to 15" (1/4') using the All Star Polar Align, after a few lengthy iterations. I use a C5 (1280mm) for my guide scope though. If you use some tiny 50mm finderscope lens for guiding you may have trouble.

Here is a single 10 minute exposure I took of the Sculptor Galaxy using the CGEM in strong gusty wind:
http://www.astrobin.com/5015/

It really is a matter of what is meant by "serious astrophotography." Many people are thrilled with a blurry picture of M42 that they got with their 6" DOB. NASA would be unhappy with what you can do with a $50,000 mount.

The proof is in the pudding. Browse Astrobin to see what you can do with different mounts.


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EFT
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Re: CGEM not suitable for serious astrophotography? new [Re: wolfman_4_ever]
      #5649231 - 01/28/13 08:50 PM

Quote:

Quote:

Quote:

New firmware should be coming out soon for the CGEM DEC guiding bug.. but....There might..MIGHT... be new motors coming out for the CGEM.. similar to the VX line..




It is pretty likely that the new motors in the VX could simply be dropped into the CGEM if they changed the firmware to account for the new gear ratios. That's the only reason that we can't dump something else in there already. The big problem will be if they will be willing to supply enough motors for sale to satisfy everyone that might want to make the switch. Actually, if they would just allow us to change the gear ratios in the firmware that would allow anyone to drop in any motor that would fit.




The issue is that the new motors are is very short supply right now..

Also...

It isn't the motors that makes the Dec Guiding issue go away. It is the firmware, and the firmware WILL work on existing mounts as well. The VX mount has the new firmware. The issue is during all the hoopla to fix the cgem bug, which was fixed in a beta release, the vx firmware took precedence.. Then somehow the fixed cgem/cge-pro firmware got fubared..

The new motors have different gear ratios, and would also require different feedback loop parameters. That could be overcome with a software update and an update to the PRN value. The latter requires you send in your motor board to Celestron. There is also a voltage issue. The voltage issue could be worked around by reworking a few resistors to your motor board (after you sent it in) but it is better for most consumers to get a new motor board if (and only if) you want the new motors.

The new motors have a bit more torque and integer gearing.




Yes, the DEC cogging issue is different than the 8/3 issue that I was thinking of.

What is the source of information on the new motors? From the looks of them, I would be very surprised if they are not 12VDC motors (it would be silly to use anything else). From the photos I've seen, I would expect the new motors to be the same Igarashi motors with different gearboxes. A fix that would require not only new motors but a new motor board at a total cost of somewhere around $500 would be pretty useless. Even having to buy motors at the current $128 is outrageous. These motors can be obtained in the many thousands easily (actually that's really the only way to buy them) and any shortage would be because of a lack of desire to purchase them, not because they are unavailable.


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Stew57
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Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5649319 - 01/28/13 09:43 PM

The efficiency of the PEC depends on the amount of 8/3 error. For some the 8/3 error is the largest error so pec is pretty much useless. My 8/3 is 75% of the first harmonic so PEC will only get that far at best. I have no cogging problemthough so it is not all bad.

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photodady
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Re: CGEM not suitable for serious astrophotography? new [Re: RogerRZ]
      #5650219 - 01/29/13 12:35 PM

OK, you have a point. The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.

This is 1/60th of the performance of the Astro-Physics mount, so then I should be satisfied if my Accord has a top speed of only 4 MHP?

Five minutes of accurate unguided performance is not that unreasonable.


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650276 - 01/29/13 01:02 PM

cars aren't mounts.

while it is true that 5 minutes unguided is not that unreasonable - at what focal length? an AP can't do 5 minutes at 3000mm.

if we take your statement as 5 minutes at 600mm - a reasonable focal length - then yes a CGEM still can't do that. i don't know if there's any mount less than the G11 that can. it simply is. you don't get that performance for $1500.


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Mike X.
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650278 - 01/29/13 01:03 PM

Quote:

OK, you have a point. The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.

This is 1/60th of the performance of the Astro-Physics mount, so then I should be satisfied if my Accord has a top speed of only 4 MHP?

Five minutes of accurate unguided performance is not that unreasonable.



No it's not but it depends on the focal length someone wishes to photograph with and the results that is satisfied with.

Here are my two cents of thought for what they count...I find it a little exaggerated to put a mass produced,budget mount with.an industrial sample quality control against a high end, expensive and highly refined mount with piece per piece quality control and customization.

The only thing the mass produced mounts have in common with some other mounts like the mach1 or the ddm60 etc...in my humble opinion is that they are...mounts...period.

Said that...I'm happy doing dso ap with a cg5....and I bet is way worst than the Cgem.

Edited by Mike X. (01/29/13 02:06 PM)


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EFT
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650295 - 01/29/13 01:13 PM

Quote:

OK, you have a point. The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.

This is 1/60th of the performance of the Astro-Physics mount, so then I should be satisfied if my Accord has a top speed of only 4 MHP?

Five minutes of accurate unguided performance is not that unreasonable.




Unguided AP for anything but the brightest objects, fastest focal lengths and shortest exposures, particularly at this price point, is unreasonable. Depending on the scope and imaging setup, it can be unreasonable for even a much more expensive mount. Any amount of research on the CGEM would show that. I agree that about the only thing the CGEM and an AP mount have in common is that they are both telescope mounts.


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freestar8n
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650311 - 01/29/13 01:20 PM

Quote:

The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.




Non-orthogonality of the axes has no connection with dec. drift at all. The axes could be off by 20 degrees and it would certainly affect GoTo accuracy - but once you had the scope somehow aimed at an object, and if the polar axis is aligned, and if you are smoothly rotating around that polar axis, then the tracking will be no different from that of a perfectly orthogonal mount.

Polar tracking just involves rotation around a single axis. As long as the rest of the geometry is fixed relative to that axis - there is no way to induce additional rotation in a different direction.

Frank


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jrcrillyAdministrator
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650366 - 01/29/13 01:48 PM

Quote:

OK, you have a point. The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.




That would amaze me; I've never heard of orthogonality issues causing drift of that magnitude. Sounds more like a severe polar alignment error.


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rmollise
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650369 - 01/29/13 01:49 PM

Quote:

OK, you have a point. The CGEM drifts about one arc-second every twenty seconds, just in the declination axis, due to non orthogonality.

This is 1/60th of the performance of the Astro-Physics mount, so then I should be satisfied if my Accord has a top speed of only 4 MHP?

Five minutes of accurate unguided performance is not that unreasonable.




Your problems, whatever they are, are not caused by "non-orthogonality." Look to your polar alignment. How did you perform it?


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wolfman_4_ever
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Re: CGEM not suitable for serious astrophotography? new [Re: rmollise]
      #5650476 - 01/29/13 02:46 PM

That's exactly what I was going to say Rod.

This guys blog post screams user error..

The mount is only going to be as good, or as smart, as the user is.. I don't care what mount you are using.. As they say.. "stupid is as stupid does"


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gdd
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Re: CGEM not suitable for serious astrophotography? new [Re: rmollise]
      #5650550 - 01/29/13 03:15 PM

Quote:

Your problems, whatever they are, are not caused by "non-orthogonality." Look to your polar alignment. How did you perform it?






I don't understand what non-orthoganality has to do with tracking accuracy though I can see it messing up goto accuracy. You don't even need to have a dec axis to track (think of AstroTrac).

Gale

Edited by gdd (01/29/13 03:16 PM)


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jrcrillyAdministrator
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Re: CGEM not suitable for serious astrophotography? new [Re: gdd]
      #5650567 - 01/29/13 03:21 PM

Quote:

I don't understand what non-orthoganality has to do with tracking accuracy though




If it were off by tens of degrees you'd see drift. If it were critical in small amounts, folks would have to worry about alignment of the optical axis of the telescope to the mount. Some do worry about that, but most do not.


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photodady
journeyman


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Re: CGEM not suitable for serious astrophotography? new [Re: freestar8n]
      #5650625 - 01/29/13 03:47 PM

"Non-orthogonality of the axes has no connection with dec. drift at all."

This is completely untrue, you are conflating optical axis-RA non-orthogonality with non-orthogonality of the RA-Dec axis.

For the former misalignment your statement is true and is called Cone Error, but for RA-DEC nonorthogonality the error is not constant, rather the scope will travel both below and above the intended path. The two extrema will be 90 degrees from the zero crossings. When the path traveled is viewed from the side it will form a lissajous pattern, or a figure eight.

The periodic error for the corrections using a guiding system in the declination axis will have a period of 24 hours. For my particular scope the peek-to-peek error is about 1/2 degree, or about the angular width of the Sun or Moon.

A similar effect occurs when viewing the Sun at the same time every day and plotting its position, I think this is called the Sun's analemma. This is also due to the nonorthogonality of the rotation of the earth's axis in relation to its orbital plane.

Sorry I just assumed that those outspoken in an astronomy forum would have at least had a basic course in astronomy.


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dickbill
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Re: CGEM not suitable for serious astrophotography? new [Re: jrcrilly]
      #5650653 - 01/29/13 04:09 PM

Misalignement also translates into field rotation, that's easy to see.
The simplest think to explain a dec drift, as Rod said, is inaccurate polar alignment. Do not assume it is good just because 'before' it was good. My experience is that if you are going to image, check it, even if two days before it was indeed very good and you havn't move the mount.

First using the polar routine after top notch 2stars align + 2, the mount put the Esquimo dead center of the C925 at f10, 120X. So then i did the routine for polar alignement and had little drift in RA and dec thereafter.
Well, 2 days later i thought i should not realign since it was good before and i didn't move the mount. And this is when my declination drift showed up. In between I had lots of winds. I think the altitude can not change so easily under transversal winds so it's perhaps just the azimuth that has shifted, or perhaps something about the central spreader and screws that get loose, I'll know next time i realign, but anyways, as long your mount is not on a solid permanent pier shielded from the winds, polar alignement should be checked regularly IMO.


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rmollise
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650683 - 01/29/13 04:24 PM

Quote:

"Non-orthogonality of the axes has no connection with dec. drift at all."

This is completely untrue, you are conflating optical axis-RA non-orthogonality with non-orthogonality of the RA-Dec axis.

For the former misalignment your statement is true and is called Cone Error, but for RA-DEC nonorthogonality the error is not constant, rather the scope will travel both below and above the intended path. The two extrema will be 90 degrees from the zero crossings. When the path traveled is viewed from the side it will form a lissajous pattern, or a figure eight.

The periodic error for the corrections using a guiding system in the declination axis will have a period of 24 hours. For my particular scope the peek-to-peek error is about 1/2 degree, or about the angular width of the Sun or Moon.

A similar effect occurs when viewing the Sun at the same time every day and plotting its position, I think this is called the Sun's analemma. This is also due to the nonorthogonality of the rotation of the earth's axis in relation to its orbital plane.

Sorry I just assumed that those outspoken in an astronomy forum would have at least had a basic course in astronomy.




The telescope is only being driven in RA. If it is properly polar aligned, you won't get drift. Forget this as the source of your problem.


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freestar8n
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650699 - 01/29/13 04:31 PM

Quote:

This is completely untrue, you are conflating optical axis-RA non-orthogonality with non-orthogonality of the RA-Dec axis.




No - I am not conflating anything. It's unfortunate that apparently some people on CN also don't realize that orthogonality has nothing to do with dec. drift, but one person above agrees with my perspective. I am extremely familiar with pointing models and cone and so forth - and they do affect the pointing model - but once you have a telescope rigidly attached to a single rotating axis - orthogonality plays no role at all. The dec. axis shouldn't be moving in the first place - so you can bend and weld the entire system - except for the polar axis - and it will track perfectly.

I rather doubt that you had the telescope outside tracking a star and you did a proper drift alignment and determined that no matter what you did, the star would drift away.

You are certainly in a "write-only" mode when it comes to these matters, and I think CN could have been a good place for you to ask questions and learn how to get the best out of your mount. But I think that was a lost cause when last you dismissed the CN community, and I don't expect it to change during this unfortunate rehash.

Frank


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jrcrillyAdministrator
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Re: CGEM not suitable for serious astrophotography? new [Re: photodady]
      #5650702 - 01/29/13 04:32 PM

Quote:

Sorry I just assumed that those outspoken in an astronomy forum would have at least had a basic course in astronomy.




Ad hominem attacks won't improve your understanding of how EQ mounts work. A careful reading of comments by those who do know might.


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Stew57
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Re: CGEM not suitable for serious astrophotography? new [Re: jrcrilly]
      #5650730 - 01/29/13 04:51 PM

Are we discussing euler angle?

One thing besides the poining accuracy that a nonorthogonal dec/ra axis would affect is ASPA.

Edited by Stew57 (01/29/13 05:05 PM)


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gdd
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Re: CGEM not suitable for serious astrophotography? new [Re: rmollise]
      #5650755 - 01/29/13 05:06 PM

Non-orthogonality will cause ra and dec drift only for GOTO slews and may prevent you from doing a GOTO to the area around the celestial pole. The mount's modeling features should compensate for this to some degree. However, once the imaging target is found tracking accuracy depends only on the correctness of the RA polar alignment, not on the cone error, orthogonality of the DEC axis to the RA axis or the OTA axis. Rotational error is caused by using a guide star that is not in the center of the image, again nothing to do with orthogality. What about RA single axis equatorial mounts? They have no concept of orthogonality yet they can track. This is strictly a GOTO issue for finding the imaging target, important for automated sessions but not so much of a problem for manual sessions.

Gale


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: gdd]
      #5651100 - 01/29/13 08:26 PM

perhaps dady is insisting on his lissajous pattern tracking because he is guiding in both RA and DEC.

but then he says he wants unguided.

i find it really hard to wrap my brain around his concept of tracking errors in both axes when the DEC is not moving!


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guyroch
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5651322 - 01/29/13 10:49 PM

Ah, we should all write a blog entry on the blog the OP posted

The CGEM is very capable.

Guylain


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Patrick
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5651336 - 01/29/13 11:00 PM

With modern camera's we DON'T NEED to track for hours on end. In my suburban area, a 2 minute sub with my DSLR pushes the skyfog mountain a third of the way from the left side of the histogram...and that's with a light pollution filter. Longer subs will not increase the SN significantly, so it's better to take a lot of shorter subs and stack them. With CCD camera's having 60 to 70% QE values it's possible to grasp a lot of light in a short amount of time and that only helps the situation. That takes a lot of pressure off the mount.

One other comment for Photodady...for most of us, this astronomical pursuit is a hobby. We are mainly "amateur" astronomers. Most of us have families and other things to spend our hard earned money on instead of very expensive astro imaging gear. We generally try to eek out as much as we can from what we can afford. It's pretty amazing what some of our more serious members here can do with 'cheap' gear.

I'd still like to see some of your astro images, sir. Perhaps you expected to be obtaining dazzling images of deep sky objects and are dismayed at what you're actually getting. You know you still have to go through the learning curve of actually using your gear, right? Astrophotography may be a subset of photography, but it has very different requirements from general photography. There is a steep learning curve and quite a few people give up because it's too tough. In my experience only those who are really serious continue in this part of the hobby.

Patrick

Edited by Patrick (01/30/13 09:45 AM)


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: Patrick]
      #5651349 - 01/29/13 11:10 PM

Patrick, I wish that were true. In my location light pollution is so bad. And I'm using an IDAS LPS V4 filter. Was trying for the Horse head last night. At 1880mm and f8. 20 minute subs weren't cutting it. I figure I need 40 minute subs. And - surprise? - the Mach1 can't do 40 minute guided subs with a C9.25 consistently...

So its a matter of expectation. Certainly the Mach 1 is a great mount - but it also has its limits. And I'm realistic about it.

Dady's blog post and responses seem to be a combination of inadequate practice, and unrealistically high expectations. Dec drift induced from the RA movement points to polar misalignment..


Guess I should go back to my f6 refractor. That one pulls in decent detail with 20 minute subs... But the horse is small...


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Patrick
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5651383 - 01/29/13 11:25 PM

Singapore? Yes, I get that. You would be doing good to image the moon.

What camera are you using?

Patrick


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Bowmoreman
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5651693 - 01/30/13 07:07 AM

Quote:

Patrick, I wish that were true. In my location light pollution is so bad. And I'm using an IDAS LPS V4 filter. Was trying for the Horse head last night. At 1880mm and f8. 20 minute subs weren't cutting it. I figure I need 40 minute subs. And - surprise? - the Mach1 can't do 40 minute guided subs with a C9.25 consistently...

So its a matter of expectation. Certainly the Mach 1 is a great mount - but it also has its limits. And I'm realistic about it.

Dady's blog post and responses seem to be a combination of inadequate practice, and unrealistically high expectations. Dec drift induced from the RA movement points to polar misalignment..


Guess I should go back to my f6 refractor. That one pulls in decent detail with 20 minute subs... But the horse is small...




Horse head is tough at best, try an Ha filter...

If you have bad LP, longer exposures will just drown it in the sky fog otherwise... It's all about signal to noise, if the signal, in this cas HH, is dimmer than your LP, then longer does nothing...


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Patrick
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Re: CGEM not suitable for serious astrophotography? new [Re: Bowmoreman]
      #5651870 - 01/30/13 09:24 AM

Samir's Discussion on Optimal Subframe Exposures is a pretty good treatise on short vs long exposures using a DSLR in light polluted environs with less than ideal mounts. It's a good read, btw.

Here's the math for determining the most efficient Signal to Noise Ratio and Subexposure Duration.

Here's one on Measuring Skyfog and one on using LP Filters...very good stuff!

The bottom line here for me is that technique is a big part of the imaging process. Knowing how to use one's equipment with all it's inherent flaws is part of the process.

Patrick


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dickbill
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Reged: 09/30/08

Re: CGEM not suitable for serious astrophotography? new [Re: Patrick]
      #5653943 - 01/31/13 09:48 AM

Well, i realigned last night and it turn out that it was still very close from the previous polar alignment, so the mount didn't loose it as i thought.
The gotos were excellent, near the center of the field at 240X, so i proceeded anyway to gain maybe a few arc minutes in the polar alignment.
The problem is that i still got declination drift on the ccd during imaging. I believe it is possibly because of the inability of PHD to correct in south declination during calibration. During guiding, the guide star was actually excentered in the guide box.

I had another incident unfortunatly which is worth opening a new thread, for the other cgem users.


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dickbill
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Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5660685 - 02/03/13 08:41 PM

I come back to this thread because i think the title was a bit harsh.
Well, with some patience I managed to autoguide my cgem for 4 min at...4700 mm, C9.25 plus barlow. It was not easy and still is not perfect (still some drift, soft focus, no darks, piggyback scope not parallel, i was in a rush etc) but it's a testimony to the mount. Needless to mention it would not have been possible with a cg5.

4 minutes in H-alpha on NGC2392, the Eskimo.


Edited by dickbill (02/03/13 08:42 PM)


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5660765 - 02/03/13 09:24 PM

Dick, that is pretty darn good. Didn't think it was possible with a CGEM.

Question, what is the % keeper rate on those 4 minute subs...


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dickbill
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Re: CGEM not suitable for serious astrophotography? new [Re: orlyandico]
      #5660803 - 02/03/13 10:00 PM

Question, what is the % keeper rate on those 4 minute subs...

answer: 100% because it is only 4 subs. i didn't have time to do more before i hit the dreaded meridian.
i posted the full composite in the ccd section


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tboconnor
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Re: CGEM not suitable for serious astrophotography? new [Re: dickbill]
      #5678747 - 02/14/13 03:19 AM

just a mini followup - Im having a ball with the CGEM Unguided So far only 30 sec - 1 minute with my refractor. (a megrez 90) I havent tried too much longer, because LP kills it anyway. No signs of trails at these exposures, so Im sure I could go longer.

Im only using the All-Star alignment routine for polar alignment, and its good enough for the above.

Im sure under dark skies and with an autoguider I could do some 'serious' astrophotography


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orlyandico
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Re: CGEM not suitable for serious astrophotography? new [Re: tboconnor]
      #5678820 - 02/14/13 06:20 AM

i can do anywhere from 4-6 minutes unguided with my CGEM using the ASPA. but only at 336mm focal length. it is kinda fun.

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