8 edge8d vs. non-edge 9.25 (both cgem II) = same price

[Venzen]

Celestron CGEM II 8 EdgeHD vs. Celestron CGEM II 9.25 standard SC (SAME PRICE)

Is this "6 one way, half a dozen another" situation?

I'm buying a telescope for my wife for Christmas. It will be our first telescope. These two telescopes/mounts are in the price range I'm looking to spend. 

I've done enough research to know I don't have time to self-research this topic, and I realize that telescopes are NOT one-size-fits-all-purposes, however, I'm going to ask anyway...

Is one of these better if the criteria were general "all-around" usefulness, not just out-of-the-box, but considering potential future accessory purchases.

Thanks, I'll hang up and listen. 😃

 

 

Edited December 11, 2020 by Venzen

[vlaiv]

Hi and welcome to SGL.

If you were astrophotographer doing long exposure deep sky astrophotography or experienced amateur observer of deep sky that enjoys pin point stars in their widest 2" eyepieces, then I would say - obviously 8" EdgeHD version.

On the other hand if you were keep planetary observer or imager - then I would say, without a doubt - C9.25.

For someone about to use telescope for the first time - I simply can't say one way or the other. Both scopes are not really suited for all round use as they have very long focal lengths, and I can't help but recommend something like 8" dob mounted newtonian (maybe even motorized) as much better all around scope that will cost much less than two above but provide the same level of enjoyment and very similar views to scopes you suggested (in areas where two said scopes excel).

Maybe some more background, expectations and possible future interests could help give better recommendation?

[CraigT82]

I think the C8 will be a better all-rounder, having a slightly shorter focal length but still with decent aperture, but I agree with Vlaiv in that neither are actually allrounders really.  An 8" or 10" goto dob would be much more of an all round do it all scope and more user friendly too. Not to mention cheaper. 

[michael.h.f.wilkinson]

I have had the much older GP-C8 (C8, on Vixen Great Polaris mount) for just over 25 years now, and it is an awesome allround visual scope, and cracking planetary and lunar imager. It has a maximum FOW of about 1.33 deg, which fits most DSOs. It is not and Edge-HD (didn't exist in the day), but I still get lovely views of galaxies, nebulae, most clusters, etc. An 8" Dob is just as good visually, and provides wider views, certainly, but it is not as good a planetary and lunar imager, even with motors. My C8 is also way easier to transport in a small car to carry it to dark sites, or take with me on holidays (and still fit the kids, the tent or skis, and the shoes of the missus ).  It gave me breathtaking views of the 1999 eclipse in France. As said before, the C9.25 SCT will be better on planets, but it is a much heavier beast to set up, compared to the C8 (Edge-HD or otherwise).

For real wide-field observing and DSO imaging, later added a small refractor (APM 80mm F/6), which is much better in that role.

[Venzen]

2 hours ago, vlaiv said:

Maybe some more background, expectations and possible future interests could help give better recommendation?

I know she'll want to take photographs of what she finds. She takes photographs of everything already. I suspect the technical aspects of figuring out the scopes will give her some difficultly (she's sharp, though, a nurse anesthetist). I definitely don't want to create a frustrating situation (I can help her with the technical aspects of it, if necessary). I'd like something that can function pretty intuitively to start for basic viewing and photography, with the fine-tuning and more advanced features being nice to have once that learning is achieved. 

 

 

[vlaiv]

17 minutes ago, Venzen said:

I know she'll want to take photographs of what she finds. She takes photographs of everything already. I suspect the technical aspects of figuring out the scopes will give her some difficultly (she's sharp, though, a nurse anesthetist). I definitely don't want to create a frustrating situation (I can help her with the technical aspects of it, if necessary). I'd like something that can function pretty intuitively to start for basic viewing and photography, with the fine-tuning and more advanced features being nice to have once that learning is achieved. 

 

 

In that case, I'd say, ok, why not, go with EdgeHD version.

Keep in mind that astrophotograpy is very difficult and demanding. It's really not - attach a camera and snap what you are looking at. Even very modest images require at least dozen minutes of exposure as things in space are very very dim. Exception to this rule is the Moon and planets, but imaging those requires radically different approach (it consists of recording a video sequence with specialist cameras and then cherry picking good frames - software does that for you. In planetary it is all about catching that moment in time when atmosphere is stable enough to offer sharp view). Starting AP with 2000mm focal length scope is not something that I would recommend though.

Only drawback of having EdgeHD 8" is relatively narrow field of view / high magnification, otherwise it will be very nice scope. Computerized version will find objects for you once properly aligned so narrow field of view is not that much of issue.

Before you decide, do look at few videos featuring that scope. Pay attention to size of the mount and factor in that you need to set it up each time you observe. It is Equatorial type mount that weighs 40lbs for mount head, 20lbs for tripod and another 17lbs for counterweight.

Telescope weighs another 14lbs. In total that is 90lbs or about 41kg that need to be assembled in order to observe.

Best telescope is the one you use most often. If setting up each time feels like a chore or takes too much of your time - you'll be wanting to watch your favorite TV show rather to go out and observe.

[Venzen]

3 minutes ago, vlaiv said:

Best telescope is the one you use most often.

I think this is a critical observation.

In terms of reducing weight, I have the opportunity to pick up a lighter Celestron advanced VX mount with the 9.25 standard SCT, throwing in some extras like 3xbarlow, 12mm 1.25 ep, 25mm plossl, a 1.25 lighted recticle finder, and a skyportal, all for a decent price. (from a situation where a person wanted a telescope and got way more than they were interested in - they had in mind the stereotypical brass tube sort).

My understanding is that the EdgeHD offsets fuzziness as the images or eye travels toward the periphery of the view, is that right?

 

[vlaiv]

1 minute ago, Venzen said:

In terms of reducing weight, I have the opportunity to pick up a lighter Celestron advanced VX mount with the 9.25 standard SCT, throwing in some extras like 3xbarlow, 12mm 1.25 ep, 25mm plossl, a 1.25 lighted recticle finder, and a skyportal, all for a decent price. (from a situation where a person wanted a telescope and got way more than they were interested in - they had in mind the stereotypical brass tube sort).

Yes, one of the greatest problems with telescopes is managing expectations.

People want to see more, see better and one way to improve what you can see is size of telescope, or more precise - aperture of telescope. Larger aperture gathers more light and resolves finer detail (as long as atmosphere is cooperative) but also weighs more - and is hence harder to use because of that.

My personal view is that for beginner scope 8" size should be really only used in dobsonian configuration. Mount with tripod (either EQ or Alt-Az) to hold 8" of scope will simply be very large and very heavy. Dobsonian base for 8" scope is no light weight category either - 8" dob weighs in at about 25-26kg total, 10-11kg being the telescope tube and additional 15Kg for the base.

Advantage to dob mount is that base is as low tech as can possibly get - no precision gear that need to be handled with care - you just lug it around like luggage, drop it onto flat ground and just carefully carry OTA (optical telescope assembly - or telescope tube) and place it on the base. That is only time you have to be careful with dobsonian type telescope assembly - handling the OTA.

Otherwise, if looking at Catadioptric type scope - 6" is probably much more manageable.

9 minutes ago, Venzen said:

My understanding is that the EdgeHD offsets fuzziness as the images or eye travels toward the periphery of the view, is that right?

Yes, EdgeHD has special optical elements that make sharp view over all of the field. This is very important for astrophotography, but not as much for visual.

With visual observation, couple of things happen that lessen the effect. First is - we tend to place objects of interest in center of the field of view - where image is the sharpest and we concentrate on that part. Since our vision is such that we can only concentrate on one part of the image - we don't notice blurry image at the edges as much if we don't look intentionally there.

Second thing that happens is that we are not nearly as sensitive to this at low magnifications - as these imperfections tend to be very small and only become noticeable when magnified. With low power views where these tend to show - they are small and much less intrusive.

At higher magnifications - we are simply looking at central part of the image and image is sharp in that region and when we have magnification that would otherwise obviously show optical issues - there are no issues to be shown (they are outside of field of view since we are "zoomed in").

Standard SCT suffers from two most obvious aberrations - coma and field curvature. Coma in F/10 SCT is comparable to F/6 Newtonian.

I have 8" F/6 Newtonian scope and never really noticed coma, even in wide field eyepieces. Mind you - once you start searching for these and you see it - you can't really unsee it later. So if it's not obvious - don't go looking for it . Point being - for visual, you won't be much bothered by off axis aberrations from telescope, but they do show up in images and you need correctors to take good images with such scopes.

 

[Cosmic Geoff]

Either scope would serve well if you want to cover visual observing and also planetary imaging.   If for visual only, there are other solutions that would be a lot cheaper and lighter.  And if you want to do wider field deep sky imaging, you need a different scope.

The expensive and heavy CGEMII equatorial mount will only come into its own if you want to do long exposure astrophotography, an enterprise which requires a lot of skill and patience, as well as deep pockets. 

If you just want to do visual observing and planetary imaging, you could consider an alt-azimuth mount like that in the Celestron CPC range, which would be somewhat lighter, cheaper and easier to set up compared with the CGEMII.

 

[Ken82]

Some excellent points from Vlaiv !

I started with a edgehd scope but wouldn’t start that way again given the choice. Excellent scopes but certainly not for starting out. I only ever get mine out now during galaxy season. 
 

Using an avx mount I wouldn’t really consider photography with a sct apart from planetary, although it can and has been done. I would agree a 6” sct is much more manageable. 
 

Personally  I’d be looking for a 130mm Newtonian or 80mm refractor with EQ mount for photography. And if I just wanted to do visuals I’d get a dobsonian. 

[Venzen]

Update:

So, if I want something in hand for Christmas (the place that appeared to actually have them, didn't , sad face), it looks like I need to decide between:

A Nexstar 8 SE, or

Standard 9.25 advanced VX with some extras (from the person I mentioned in an earlier response). 

Price difference is about $800, not really an issue, but I mention it in case it sways any opinions.

I know she'll want to take pictures of the moon and the planets, and I'd like her to have the potential, should she decide to go down that road later, of trying her hand and patience with other images.

Does that rule out the 8SE? Again, I'm dealing now in terms of what appears to be available for Christmas, which I admit isn't the smartest way to go about choosing a telescope. But, unless I'm absolutely going wrong here, I'm probably going to choose something. 

Edited December 12, 2020 by Venzen

[Cosmic Geoff]

The Nexstar 8SE is a visual scope in a portable setup. You can do planetary imaging with it, but it's a pain to do because there is too much wobble and backlash in the mount, and you would soon be wanting a mount upgrade.  I find that I have to actively guide to keep the planet's image on the cropped region-of-interest even with a short 60 second video run.

Since you can obviously afford the extra, I'd suggest the C9.25 on the AVX.  Despite some negative comments about this mount's suitability for deep sky astrophotography, it should be perfectly adequate for planetary imaging and general visual observing.

I'd quite like a C9.25 myself, but I'd need another mount and...

[GreyArea10]

Sorry for hijacking this a little, I’m new and trying to identify which telescope to go for and had landed on these two as well. I suppose it’s driven by trying to find a scope that is as close to an allrounder as possible. I see everyone here saying no for imaging for these two however they both state faststar as reducing the focal length and f number, why are people disregarding this? I assume there’s a reason I’m not aware of?

[vlaiv]

2 minutes ago, GreyArea10 said:

Sorry for hijacking this a little, I’m new and trying to identify which telescope to go for and had landed on these two as well. I suppose it’s driven by trying to find a scope that is as close to an allrounder as possible. I see everyone here saying no for imaging for these two however they both state faststar as reducing the focal length and f number, why are people disregarding this? I assume there’s a reason I’m not aware of?

As far as I've heard (not tried Faststar myself) - it is sort of a nightmare to operate

To begin with - it is not diffraction limited, it is very sensitive to tilt and collimation. Camera goes in front of the scope so you are limited in choice of camera - you want round / slim model in order not to cause diffraction effects. Since you need to route cables (cooling / data cables) - you'll end up with diffraction spikes anyway.

Flat fielding is rather difficult to do - you can't use simple flat panel that goes over the aperture of the telescope - you need something much larger.

While you can use Faststar / Hyperstar - you really don't want to do that when you can get RASA now which is much better optically.