Beginner with a Celestron CGEM 925 HD

[Asiddall]

Hi everyone,

After 40 years I've finally decided to follow my passion and take up astronomy as a hobby... I've spent weeks if not months looking at the different telescopes and whilst there are excellent choices out there I've decided to look into buying the Celestron cgem 925 HD... The main factors which influenced me is the relative portability against my limited storage space and future capacity to perform some photography. I would rather make the bulk investment now.

Does anyone have experience of this unit?

My firstt question is the old chestnut 'eye pieces'... I'm no expert on this... and just typing in 'eye pieces' in the search fields provides a wealth of information.... Could please you help me make a start on this..

What would a good beginners selection of good quality compatible eye pieces consist of for looking at the moon, planets, galaxies, maybe some deeper space objects... ?

I presume good eye relief and field of view are important?

The unit comes supplied with 'eye piece 1' of 102x (23mm?) and the spec stipulates a highest useful magnification of 555x (4mm?). I read on this forum that it's usually better to stick with twice the aperture (ie in this case 235x2 = 470mm = 5mm. Is this magnification useful for galaxies or just planets? Sorry - I haven't looked through a telescope foe 25 years!

Should I consider getting a good quality Barlow lense to cut down on the number of eye pieces? Or just stick with fixed lenses?

Thanks for your help...

Alan.

[RT65CB-SWL]

Hi Alan / 'Assidall' and welcome to SGL.

1. Congratulations on the choice of 'scope.

2. Don't believe the hype of 555x. On a 'good' night 200-230x is the maximum, especially in UK/GB.

3. SCT's do have narrow fields of view. I would personally stick to 'prime' e/p's (Plossl's, Ortho's, Wide Angle, etc). I have nothing against Barlow lenses, PowerMates, ImageMates etc, but I think they may cause more problems. That is what I found out when using my Barlow and/or ImageMate visually with my C6/SCT & ETX105, but ok in my Ranger. If you plan on astro-photography, (webcam or dedicated CCD imaging device than they maybe acceptable).

4. Don't go for a complete eyepiece set either. Eyepieces in my opinion are personal. AstroBoot has a bargain '18mm WA' http://www.astroboot.co.uk/AstroBoot/telescope-and-astronomy-stuff.html?highlight=AB7077#AB7077 for £9.00GBP + P&P. It is not in the same league of TeleVue or others, but adequate to good in my opinion for visual use if you are a beginner and want something 'cheap & cheerful' and better than some eyepieces that come supplied with the 'scope. I have yet to give mine its firstlight in my C6/SCT.

5. Enjoy!

[Coastliner]

Hi, you could take a look at the Facebook group "Uk Astronomy Network Imaging Group". There is a chap there called Nick Hunt that has the same scope. He took this image with it, using a Neximage 5 camera.

[ronin]

At 2350mm and f/10 you can use most eyepieces happily.

You can just get the BST Straguiders, basically the whole set except the 5mm is one idea.

That means the 8, 12, 15, 18 and 25mm. They are £49 each but do as most and get one or two at a time

The 5mm will likely be too short for the scope, it would give 470x, and I do not think there is a chance of using that much magnification.

Taking 200x an a practical max then that means the12mm as a minimum focal length.

With the focal length of the scope not sure a barlow will be of great use. The barlow (2x) and a 25mm will get you close to the "minimum" of 12mm so a barlow and 15mm is likely again to be too much and the extra glass may not help.

The 8mm BST will be for when conditions allow and if they do the view should be good at 294x.

Owing to the powers delieverd you may find yourself looking at planets more in which case consider the Celestron X-Cel eyepieces. They perform close to identical to the BST's but they have more focal lengths at the short end so a better selection for planets. Unfortunately they cost a bit more £59.

You can mix them but then you lose any parfocal attribute they have and it just makes things a little less easy. Also a set of BST's or X-Cels looks good.

You do have "bettter" options but I cannot see there being a great improvement over the ones mentioned.

[Asiddall]

Thanks to everyone for there advice... Not good weather at the moment, but guess I can practise putting it all together... May get chance to see the moon.... .:-)

My current wish list is as follows:

Cgem 925 edge HD

Selection of good eye pieces

Moon filter

Celestron own Nightscape CCD

http://www.celestron.com/browse-shop/astronomy/astroimaging-cameras/series/nightscape-ccd-camera

(not sure of the accessories .... I presume everything comes with it) -

Questions:

- this nightscape CCD camera appears to fit directly on to the eyepiece / prime focus , instead of replacing the secondary mirror, and sounds easier for a beginner and quicker than setting up a digital camera - however the website indicates 55mm w/ 2" barrel and only 26mm w/o barrel... Silly question, but how do I get say 12mm / 200x magnification. Or have I misunderstood this / it's not important for deeper space objects?

- how does this nightscape CCD differ from the type of having to remove the secondary mirror? Is it just for a faster exposure time?

- would the original counterweight still be sufficient for adding the nightscape CCD?

- would the current gem mount be adequate for astrophotography?

Do I need a lens shade / Dew shield (does this affect light levels or photography?)

Do light pollution filters really help?

Have I missed anything critical, other than a warm jacket and sleepiness nights?

I'm just trying to get a good idea for budgeting....

Thanks again for your help...:-)

[dannybgoode]

Hi there and welcome. Relatively new to the hobby myself (and just down the road from you in Sheffield).

My advice would be to ignore the imaging side of things for now and concentrate on the visual aspect .

I desperately want to get into imaging also but the more I read on the subject the more I realise I have so much to learn before investing any money in that side of things.

a good scope, good mount and some good eyepieces for now and get competent at the basics would be the way I go.

[Mr Spock]

As a C925 user I can offer practical advice on eyepieces.

For deep sky I use mainly a 22mm T4 Nagler. Your 23mm is similar in focal length so you already have a good start.

For planets my most used eyepiece is a Vixen NLV 10mm which gives x235. The newer SLV 10mm is £109 and would be a perfect choice for your scope.

I also have an 8mm I use on the moon and a 6mm I use for double stars. These are not essential and I could manage without them. I also have 13mm, 12mm, 9mm and 7mm - all luxuries I don't really need.

Additionally I have a 17mm T4 Nagler which I use on some clusters, such as globulars. I also have a 42mm LVW which is my widest available field of view.

I wouldn't use a Barlow for visual use, though one would help with planetary imaging. I would never use a C925 for deep sky imaging - that focal length is very demanding on tracking.

A dew shield is essential - I use an Astrozap.

[gnomus]

As to eyepieces, you could take a look at the Celestron Luminos range.

[Asiddall]

Thanks for this..

As suggested I will focus on the visual aspects, but I would like to further understand the implications of purchasing this scope for future applications / taking images (even if they are limited) etc...

Stupid question 1:

The description says:

"CGEM will track well past the Meridian for uninterrupted imaging through the most ideal part of the sky. The CGEM mount has a robust database with over 40,000 objects, 100 user defined programmable objects and enhanced information.."

Even if the sct has an f10 apparently unsuitable for dso imaging due to long exposure times, why can't I just keep the nightscape CCD imager connected to the eye piece for a longer period of time whilst the CGEM tracks a particular nebular or Galaxy in question whilst I go and have a coffee for an hour or so? I presume it's not that simple - but why?

What can the sct take good images of? Is it only planets? No chance of nebulas or m42?

Stupid question 2:

When would I use a wedge, is this needed with the CGEM mount?

Stupid question 3:

When would I need to use an off axis guider, guide scope, and an on axis guider? Are these only required for photography with an external slr camera? Erm... A little lamen terms won't go amiss.. :-)

[RT65CB-SWL]

Stupid question 2:

When would I use a wedge, is this needed with the CGEM mount?

In a nutshell, a wedge is to make an alt-az fork-mounted SCT, (and other OTA designs), as if it was an equatorial/polar aligned 'scope. As you have have a CGEM you do not need one.

http://www.astronomyasylum.com/telescopemountstutorial.htm

[Blazar]

Stupid question 1:

The description says:

"CGEM will track well past the Meridian for uninterrupted imaging through the most ideal part of the sky. The CGEM mount has a robust database with over 40,000 objects, 100 user defined programmable objects and enhanced information.."

Even if the sct has an f10 apparently unsuitable for dso imaging due to long exposure times, why can't I just keep the nightscape CCD imager connected to the eye piece for a longer period of time whilst the CGEM tracks a particular nebular or Galaxy in question whilst I go and have a coffee for an hour or so? I presume it's not that simple - but why?

What can the sct take good images of? Is it only planets? No chance of nebulas or m42?

Stupid question 2:

When would I use a wedge, is this needed with the CGEM mount?

Stupid question 3:

When would I need to use an off axis guider, guide scope, and an on axis guider? Are these only required for photography with an external slr camera? Erm... A little lamen terms won't go amiss.. :-)

Hi  Alan,

Welcome to SGL.

You have chosen a very nice scope and mount combination that would give you a great start , as well as lots of future room to grow into the hobby. I would ask if you have actually seen the size of the CGEM and 9.25? Might be worth getting along to a local club to see if anyone has one for you to look at. They are quite large, so was wondering about your comment on portability.

In answer to question 1: long focal length imaging is tricky as any inaccuracy is magnified, and as already noted the field of view means a lot of the larger objects won't fit on the cameras chip. You can add a reducer to raise the focal length, but this is more money. Guiding a mount can be done via two methods (1: a guidescope and smaller guide camera  2: via an Off Axis Guider (OAG). The best option for an SCT is usually the OAG. This sits in the light path and splits off some of the light via a small prism into the path of a guide camera.  I have only just started to try guiding using option 1, though I am not using my SCT. I would suggest before thinking of parting with any money on imaging you spend £20 on the book "making every photon count". This will help explain what equipment is used for imaging, and more importantly 'Why'. Guiding is also not a guarantee, so if a cloud gets in the way or the camera loses the guide star, then it all fails..whilst you are having your coffee probably....NOTE: the Celestron mounts do have an all star polar align feature to help polar align the mount (which I have found helpful).

In answer to question 2: (as already noted above...) you don't need one, as the CGEM is a German Equatorial Mount (GEM), so you set the mounts latitude  when setting up. Setting up an EQ mount can be quite daunting at first, but its gets easier. 

Question 3 should have been answered above. You don't need one for visual.

As previously noted, if you purchase a 9.25 then the most important piece of additional kit will be the dew shield. SCT's front corrector plates really do attract the dew. The Edge series are really nice scopes (I have the 800), and really do enjoy Lunar and Planetary imaging (And SCT's really are great for this)...with the 9.25 being an excellent performer. 

If you have not read it before I would also point you towards the excellent thread that does set expectations as to what you can actually see...its not exactly hubble...

What can I expect to see

I would have a look around ere at the lunar and planetary imaging forums and see what equipment is used....it really is a slippery slope..but well worth it ;-)

Good luck!

[gnomus]

You don't need a wedge for the CGEM.  You only need a wedge if using an Alt-Az mount - such as the CPC range from Celestron.

There are a number of issues with using a long focal length SCT for DSO imaging.  Many DSOs are larger than you think.  For example, you will not get all of the Orion Nebula or all of the Andromeda Galaxy within the field of view of the camera through your proposed scope.  You may well get quite pleasing visual views of these objects through the SCT, but that is because the eye cannot see as much as the camera will be able to.  

The long focal length also makes guiding more problematic.  Just as using a "long" lens on a camera is more difficult to stabilize than a "standard" camera lens.  

If you look in the Imaging Section under Deep Sky, you will see that most DSO imagers are using much shorter focal length scopes.  The Skywatcher ED80 is a very popular (and not too expensive) choice for this.  

I have been taking pictures for many years.  I have found astrophotography to be like starting out again as a fumbling beginner.  I have made, and continue to make, numerous mistakes.  I started out with a CGEM and an Edge HD 8".  I tried to do some DSO imaging.  It was a bit of an uphill struggle.  Eventually, I decided to get an ED80.  I do not claim great success, but at least I am getting some 'OK-ish' results, and  with much less effort.  I use my Edge for lunar and planetary work.  I use the ED80 (mounted on the CGEM) for DSO work.  

Once I get a bit better, I may try imaging some of the smaller DSOs with the Edge, but for now I'm sticking with the ED80.

If you get a C9.25 on a CGEM, I am sure this will be a superb scope (I'm happy with my CGEM and Edge HD 8).  If you want to get into imaging, then you could do some lunar and planetary work with your proposed scope and a 'video' camera such as the ZWO ASI 120.  You don't need to guide for lunar and planetary imaging.  The ZWO could, however, be used as a guide camera when you do start to get into the DSOs.

One thing to consider - if you went for a non-Edge C9.25, you could get a 9.25 and an ED80 (or something similar), and have some money to spare.  You could even get throw a 'vanilla' C11 into the mix.

If you are seriously thinking about getting into imaging, many people (me included) will recommend buying the book "Making Every Photon Count" http://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html.  I got another great book from Santa last year called simply "Astrophotography" http://www.amazon.co.uk/Astrophotography-Thierry-Legault/dp/1937538435/ref=sr_1_1?ie=UTF8&qid=1426354727&sr=8-1&keywords=astrophotography.  I would recommend either or both of these.  Have strong drink and an ice-pack (for your head) nearby as you read them.

I hope these somewhat meandering thoughts are of some use to you.

Good luck. 

[gnomus]

Oops ... looks like Blazar and I posted similar (though not identical) replies simultaneously.

Apologies.

[ollypenrice]

You are getting good advice. This scope is handy and excellent for visual use, though the long focal length might tempt you to go for a 2 inch visual back, diagonal and a good widefield 2 inch eyepiece. This will open up the view. It is a stunning planetary imager, highly rated by Damian Peach whom most would consider the best planetary imager in the world.

As a deep sky imaging scope it becomes difficult. The focal length is long, the demands on guiding are extreme, the pixel scale is optimistic. This may be Greek to you at the moment so, to put it succinctly, don't buy this scope as an introduction to deep sky imaging.

Beware of assuming that the Hyperstar system will be an easy fix. It goes too far. Coming down below F2 introduces new problems.

Olly

[Asiddall]

Thank you so so much for everyone's fantastic advice.... This is a great forum.. I really didn't expect so much help.

I don't yet have the sct... it is literally only a phone call / several hours away - last minute jitters / guidance required. My first reason for buying an sct was actually for planetary and general star gazing... I only thought about deep space photography after seeing some friends pictures... Guess it got me thinking... Been going backwards and forwards between a newt and sct for ages now...

I'll be travelling to Isle of Skye later this year, weather permitting I'm hoping to get some nice shots with whatever I get...

I'm happy if I can at least view deep space objects, even if I can't take pictures. Guess the universe isn't likely to go away anytime soon so don't need a souvenir yet..

I know the sct is a big scope, but it seemed like a good general purpose scope to invest in and easier to store away, separate, move around. Is it really easier to maintain and collimate than a newt?. If I'm wrong, sorry :-). My head is spinning with all the scopes and websites indicating the advantages and disadvantages...

Thinking about what everyone has said, I'm now going to only concentrate on the visual aspect of planets and dso's with the sct - I'll practice / try my luck just imaging videos and planets at a later date... BTW - are sct's ok for comets?

When the time is right for planetary imaging (not deep space objects lol), would you recommend the Celestron nightscape or just a standard slr camera with all the bits, pieces and attachments?

Decided that imaging dso will (quite rightly) be left with a different scope purchased at a later date (perhaps a 80-100mm refractor or 150mm newt) after I've enjoyed a few years of planetary imaging... Plus it will give me something to look forward to at a later date! No point opening all my presents at once!!

[Blazar]

Oops ... looks like Blazar and I posted similar (though not identical) replies simultaneously.

Apologies.

Guess we just know our stuff ;=)...well after a long and steep hill!

[gnomus]

....

When the time is right for planetary imaging (not deep space objects lol), would you recommend the Celestron nightscape or just a standard slr camera with all the bits, pieces and attachments?...!

Lunar and planetary imagers use 'webcams'. Some are actually modified webcams. There are, however, some dedicated 'webcam-type' cameras. As I said before, the ZWO ASI120 is quite popular. You are combatting variable seeing. The idea is that you shoot 3000-4000 frames of video. The sharpest of these frames are then selected (by the software program), and then 'stacked' (also in the software program). The good news is that most of the software to do this is free. Again, take a look at the Imaging forums for planetary and lunar work to see what folks are achieving using this technique. Indeed, take a look at some of Blazar's moon pictures. I think you will be quite impressed. You should be able to achieve these results with what you are going to buy.

[Blazar]

Thank you so so much for everyone's fantastic advice.... This is a great forum.. I really didn't expect so much help.

I don't yet have the sct... it is literally only a phone call / several hours away - last minute jitters / guidance required. My first reason for buying an sct was actually for planetary and general star gazing... I only thought about deep space photography after seeing some friends pictures... Guess it got me thinking... Been going backwards and forwards between a newt and sct for ages now...

I'll be travelling to Isle of Skye later this year, weather permitting I'm hoping to get some nice shots with whatever I get...

I'm happy if I can at least view deep space objects, even if I can't take pictures. Guess the universe isn't likely to go away anytime soon so don't need a souvenir yet..

I know the sct is a big scope, but it seemed like a good general purpose scope to invest in and easier to store away, separate, move around. Is it really easier to maintain and collimate than a newt?. If I'm wrong, sorry :-). My head is spinning with all the scopes and websites indicating the advantages and disadvantages...

Thinking about what everyone has said, I'm now going to only concentrate on the visual aspect of planets and dso's with the sct - I'll practice / try my luck just imaging videos and planets at a later date... BTW - are sct's ok for comets?

When the time is right for planetary imaging (not deep space objects lol), would you recommend the Celestron nightscape or just a standard slr camera with all the bits, pieces and attachments?

Decided that imaging dso will (quite rightly) be left with a different scope purchased at a later date (perhaps a 80-100mm refractor or 150mm newt) after I've enjoyed a few years of planetary imaging... Plus it will give me something to look forward to at a later date! No point opening all my presents at once!!

Alan,

No worries, we were all in the same boat! The planets are about all the time. At the moment you Venus in the west just before sunset, Jupiter then drifts trough the night sky, and if you are an early bird then Saturn is out and about. One of the most popular planetary cameras are the ZWO range (at the moment). You can have either colour or mono (greyscale) cameras. You connect it to a laptop with  a  piece of software (capture program, such as Firecapture) and then shoot a small video. You then process the video and stack only the best images out of the video. The camera can shoot up to 50Frames per second, and this speed helps capture the best moments of seeing (or when the atmosphere is at its best).  The same process is used for Lunar images. This obviously doe s mean having a laptop connected to the little camera, and powering it all.

Yes I remember the head spinning side of that first decision.To be honest I started without a scope. I bought some large binoculars and a small book to learn the constellations and then spent a year wandering around. I then brought a 100MM refractor (though now own three of those), then the SCT and then also the WOstar71....there is no one all round scope. they are all good in their own rights.

I started with doing Afocal imaging, so this is where you use a basic point and shoot camera and take an image through the eyepiece...it works well on the moon and is quite fun.

Hope we have not added to your confusion....it is a big first step....thats why I in the end stepped back (and got Bins).