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Equipment Discussions >> Mounts

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korborh
professor emeritus
*****

Reged: 01/29/11

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
*****

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
*****

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
Post Laureate
*****

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
*****

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
Post Laureate
*****

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
*****

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
Post Laureate
*****

Reged: 08/10/09

Loc: Singapore
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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