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Hi all,

I have a 6-inch Newtonian reflector with equatorial mount but would like something with a bit more magnifying power. I can never get to grips with focal length versus mag and light collection etc etc, so will need some help. Yes, I'm still a beginner and I know I shouldn't move up yet, but I've been so frustrated with my current scope.

Can anyone suggest a good all-round 8 or 10 inch, motorised, pref with go-to. I have dyspraxia so find it hard to locate objects when the image is upside down and swings the opposite way from where I move the scope, so a go-to would be helpful!

My requirements: my interest is in both planets and deep sky objects. I would like eventually to take pics. It would be good if the scope and tripod are not too heavy as it would need to be transportable, but also stable.

Am I asking too much?!!

Alex

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Howdy Astrosurf,

you say you are not getting on with your current scope, can you be a bit more specific? Oh, and what is your current scope? And if you really want to get a bigger scope what would your budget be?

re focal length, the longer the F ratio then the higher the mag you will get with any given EP, so a 10mm EP in an F5 scope will give lower mag than the 10mm EP in an F15. So for planetary viewing you are generally better with a londer F ratio scope as you get higher mag. For DSO's you are better with shorter F ratio scopes as they generally have a wider field of view and can therefor show you a bigger area of the sky.

As for a good value all-rounder, you could do a lot worse than one of these......

http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=30877&CatalogueID=272&CategoryID=3812

or, if you wanted to spread your costs then you could get one of these.......

http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=30622&CatalogueID=272&CategoryID=3766 and then when your budget allows upgrade it with one of these............. http://www.astronomica.co.uk/GOTOkits.php?product=223&action=moreinfo&offset=0

I ahve read that buying the C8N and then upgrading is a better way to go than buying the C8NGT as many people think the C8NGT is too noisy. I have a C8NGT and, although it is a bit noisy, I dont think it is too bad.

Hope that helps,

Gary

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If your budget will allow it, I'd recommend one of the Celestron Nexstar SCT scopes, which all have goto. I've got the 8 inch double-fork arm version and its great - very easy to set up and use in Alt Az mode, and you can upgrade it to a wedge if you decide to get a bit more serious with astrophotography (I've used it for nearly a year in Alt Az, including taking photos and been very pleased). The Nexstar SE range are lighter though, so if you want portability, they may suit better. As always there's a trade off, and they aren't as stable for taking photos I understand.

HTH

Helen

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Hi Astrosurf,

As a dyspraxic myself I’ve found that the finderscope tends to be the weak link in the system for me. If you know you’re in the right area you can bang in your lowest magnification eyepiece and start looking for landmarks in your field of view; if you’re nowhere near and trying to scan wide areas of sky with your main scope you’re only going to be finding what you want to find by pure luck. So before you start spending big money on a scope have you got a half decent finderscope? If you have got a decent finder, have you considered one of the telrad or red dot finders as an additional finder as it might get you in the general area to start with.

Having said that I must admit my non-goto 10” Newtonian is now much neglected in favour of my Nexstar 11 GPS...I align on a couple of stars and I’m viewing without hassle all night. If you’ve got the pennies I’d wholeheartedly recommend anything from the Nexstar stable and also Skywatcher have an excellent reputation, however you’re starting to talk serious money if you want to upgrade your scope at the same time as moving to goto (for new kit start off at £600 and work up to any number you care to think of). Aperture is the prime factor in buying a scope when you’ve an interest in DSO’s...bigger is better if you can use it, but goto (when it works well) makes a nights viewing a lot easier.

Phil

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Hi Alex

Focal Length/Aperture = f Ratio

Focal Length/f Ratio = Aperture

f Ratio x Aperture = Focal Length

Focal Length/Eyepiece FL (mm) = magnification factor. Therefore a 10mm eyepiece attached to a scope of Focal Length 1000mm will give a magnification of x100.

Magnification is of far less importance than light gathering ability, and the times that we actually need high mag, or the 'seeing' allows us to use it, are quite few.

In general, long focal lengths and slow f ratios (f 20 to f 40) will provide a smaller field of view (FOV) which is ideal for Planets, where when the 'seeing' permits, we can 'crank up' the magnification.

Short focal lengths, with faster f ratios (f4 to f6) are ideal for deep sky objects (DSO's), where we need a wider FOV and good light gathering ability.

A good compromise, is to have a long focal length scope, with an f ratio of say f/10. With this we can use a x2 Barlow to raise the ratio to f/20 or higher, using a higher power Barlow or Power Mate, and then use it for planets.

Conversely, we can use a Focal Reducer, to shorten the focal length, and speed up the f ratio, to make it more suitable for DSO's.

Whatever scope you choose, will be governed by your budget.

Dave

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Can anyone suggest a good all-round 8 or 10 inch, motorised, pref with go-to. I have dyspraxia so find it hard to locate objects when the image is upside down and swings the opposite way from where I move the scope, so a go-to would be helpful!

My requirements: my interest is in both planets and deep sky objects. I would like eventually to take pics. It would be good if the scope and tripod are not too heavy as it would need to be transportable, but also stable.

The Skywatcher Explorer 200P with HEQ5 is one of the best all-rounders available and GOTO can be added at a later date, or there is the HEQ5 PRO option with GOTO pre-fitted.

You could fit a right-angled erecting finderscope or a 1x red-dot finder.

HTH

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Howdy Astrosurf,

you say you are not getting on with your current scope, can you be a bit more specific? Oh, and what is your current scope? And if you really want to get a bigger scope what would your budget be?

re focal length, the longer the F ratio then the higher the mag you will get with any given EP, so a 10mm EP in an F5 scope will give lower mag than the 10mm EP in an F15. So for planetary viewing you are generally better with a londer F ratio scope as you get higher mag. For DSO's you are better with shorter F ratio scopes as they generally have a wider field of view and can therefor show you a bigger area of the sky.

As for a good value all-rounder, you could do a lot worse than one of these......

http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=30877&CatalogueID=272&CategoryID=3812

or, if you wanted to spread your costs then you could get one of these.......

http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=30622&CatalogueID=272&CategoryID=3766 and then when your budget allows upgrade it with one of these............. http://www.astronomica.co.uk/GOTOkits.php?product=223&action=moreinfo&offset=0

I ahve read that buying the C8N and then upgrading is a better way to go than buying the C8NGT as many people think the C8NGT is too noisy. I have a C8NGT and, although it is a bit noisy, I dont think it is too bad.

Hope that helps,

Gary

Many thanks for your help Gary

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So many thanks to you all. What brilliant replies! I will now have to print this off and mull it all over!

I have been recommended an alt-azimuth but have never used one before and don't understand what the wedge does. I guess I would have to see one in action!

I will start a thread on the pros and cons of alt-az and equatorial as I'm stumped!

Many thanks again.

Alexxx

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The probs I've been having with the scope are:

Blue and red hues around the object - I've had the scope checked for mal-alignment and it seems OK.

Loads of grease on the focuser but it's still stiff and wobbles so focussing on high mag is nearly impossible.

A metal plug has fallen out of the RA knob so it won't tighten. I'm getting someone to cut a bit of metal for me.

The rest is user error!

Alex

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Hi Alex,

Blue and red hues around the object - I've had the scope checked for mal-alignment and it seems OK.

Got to be any eyepiece problem I think as newtonians are usually colour free - unless yours is one of those with a barlow-type lens at the bottom of the focusser drawtube to give a longer focal length in a compact tube - those have been known to have problems I believe

Loads of grease on the focuser but it's still stiff and wobbles so focussing on high mag is nearly impossible.

De-grease the focusser using a little white spirit on a rag and re-grease with lithium grease. tweak the 2 small grub screws on the top of the foccusser to reduce the tension while not introducing wobble. Tweak the 4 small screws underneath holding the focusser pinion and focus knobs in place in a similar fashion.

A metal plug has fallen out of the RA knob so it won't tighten. I'm getting someone to cut a bit of metal for me.

You can replace the RA/DEC knobs with other suitable knobs - I got some from a 2nd hand electrical goods dealer (radio knobs I think he called them) - as long as they will fit on the shaft and have a grub screw to tighten down on the flat area of the shaft they will work.

Just some suggestions :D

John

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Hi Alex,

Blue and red hues around the object - I've had the scope checked for mal-alignment and it seems OK.

Got to be any eyepiece problem I think as newtonians are usually colour free - unless yours is one of those with a barlow-type lens at the bottom of the focusser drawtube to give a longer focal length in a compact tube - those have been known to have problems I believe

Loads of grease on the focuser but it's still stiff and wobbles so focussing on high mag is nearly impossible.

De-grease the focusser using a little white spirit on a rag and re-grease with lithium grease. tweak the 2 small grub screws on the top of the foccusser to reduce the tension while not introducing wobble. Tweak the 4 small screws underneath holding the focusser pinion and focus knobs in place in a similar fashion.

A metal plug has fallen out of the RA knob so it won't tighten. I'm getting someone to cut a bit of metal for me.

You can replace the RA/DEC knobs with other suitable knobs - I got some from a 2nd hand electrical goods dealer (radio knobs I think he called them) - as long as they will fit on the shaft and have a grub screw to tighten down on the flat area of the shaft they will work.

Just some suggestions :D

John

Great John, thanks.

Grub screw - that's what it's called! Ta.

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I have been recommended an alt-azimuth but have never used one before and don't understand what the wedge does. I guess I would have to see one in action!

Here is my NS8GPS (An AltAz mount) on my wedge:

ns8gps_20070827.jpg

It tilts the vertical rotation axis so it can be aligned at the celestial pole.

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I have been recommended an alt-azimuth but have never used one before and don't understand what the wedge does. I guess I would have to see one in action!

Here is my NS8GPS (An AltAz mount) on my wedge:

ns8gps_20070827.jpg

It tilts the vertical rotation axis so it can be aligned at the celestial pole.

Um . . . I'm dead thick so I'd still need to see it in operation. Wot a loada wires! . . . Um.

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I have been recommended an alt-azimuth but have never used one before and don't understand what the wedge does. I guess I would have to see one in action!

Here is my NS8GPS (An AltAz mount) on my wedge:

ns8gps_20070827.jpg

It tilts the vertical rotation axis so it can be aligned at the celestial pole.

Wot a loada wires! . . . Um.

:laughing6:

That surely is an awesome setup! :D

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I have been recommended an alt-azimuth but have never used one before and don't understand what the wedge does. I guess I would have to see one in action!

Here is my NS8GPS (An AltAz mount) on my wedge:

ns8gps_20070827.jpg

It tilts the vertical rotation axis so it can be aligned at the celestial pole.

Um . . . I'm dead thick so I'd still need to see it in operation. Wot a loada wires! . . . Um.

Oh Steve that looks like ot was stolen from a Borg Cube....................... :D

Gary

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Oh its grown more cables since then, but I now have some cable tidies and clips to hold the cables in check... kind of :D

Anyway back to what a wedge does for an AltAz mount.....

On a GEM, its primary function to to point the rotational axis at the celestial pole, so as the sky "rotates" from east to west above you head, the OTA only needs to track from east to west one one set of motors. It doesnt need to track north/south while imaging... just the constant sidereal rate of the RA motors will keep the object in view at all times.

A normal AltAz mount, while tracking an object, needs to track not only east to weat, but also north/south as the object rises from the horizon, and takes a long graceful curve as it heads up then down towards the west. This involves both sets of motors, and can causes "staircasing" steps (up, right, up some more, right some more, etc). AltAz also creates what is called field rotation, where the object will appear to rotate over time, which for visual observing isnt really a problem, but is a nightmare for astrophotography. Let the following image load (might take a while). This is M13 taken on an AltAz mount in May 2007 (my first ever deep sky object!), 20 x 30 seconds, so this is pretty much the rotation you can expect to see in 10 minutes

m13-altaz-rotation.gif

What you need to do with an AltAz mount is to make the vertical rotation axis (theline that comes directly up the middle of themount) is pointing at the celestial pole. That way, any object's movements will only ever be east to west, and never north/south. That what a wedge does... it allows you to point that central rotaton axisof the AltAz mount at the celestial pole.

A GEM and a AltAz+Wedge have the same end result, but do it slightly differently. I love my setup, it does the job as required, but would I choose it again if I had to start from scratch? That I am unsure of. An AltAz mount limits your upgrade path, requiring you to change the entire mount and OTA, whereas with a GEM mount, you just change the OTA and away you go like nothing ever happened.

The cost most also be looked at:

AltAz Mount+OTA plus the price of a wedge (and wedges are not cheap, not even the cheapest ones!)

versus

HEQ5/6(Pro) plus just an OTA plus the cost of dovetail bars or mounting plates/rails

Personally, I will *HAVE* to move to a GEM if I ever upgrade.... not that I am planning anything ike that just yet, I`m having too much fun with my current setup, but who knows...

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