Newbie - Hello and telescope advice

[Phil the lancs lad]

Hi everyone,

I became interested in astronomy as a hobby in my mid-teens which was many moons ago. Whilst career and family put the hobby on the back burner, i never lost interest and the flame has been rekindled.

These forums are excellent and i thought it was now time to say hello with some questions

1 I am looking for a telescope which has to be portable. During my reading I am not understanding how the focal ratio affects why planets maybe good through one particular model and not as good through another. The same applies for dso's

2 telescope choice - i like the look of the mak127, the nexstar 127 and the nexstar 8 se. I know that there is a huge leap in price for the latter but i am attracted to what looks a portable scope with large aperture. The budget i have would cover any of these choices.

Thanks reading and i look forward to being part of what is a fantastic forum

Phil

[sologuitarist61]

Hi Phil and welcome to SGL.

Think of focal length in this easy way - the shorter the focal length the less magnified will be the image, the longer the focal length, the more magnified. So if you had two 4" refractors side by side, the one of 600mm focal length will give a smaller image than one of 1500mm. This of course doesn't take into account the EP used, but the if a 25mm EP was used on both scopes, the same would apply, one would appear more magnified than the other, and so on, and that applies whatever the EP size.

[stevetynant]

Hi Phil and welcome to the forum

I'll let the more knowlegable guys talk to you about focal lengths etc but one thing I have found with scopes in my short experience is there is not one that is the best at everything - portability, planetary observing, A/P, DSO observing etc - it will always be a question of compromise - the 8SE does look a great piece of equipment mind you

welcome on board

Steve

[sologuitarist61]

Steve is absolutely right and you really need to think about what you really want to do with your scope when you have it. When you know what you want it to do then you can ask the right questions.

Very roughly, a short focal length is good for DSO's and the moon, yet not quite so good for planets and double stars. A longer focal length on the other hand does exactly the opposite - a little too powerful for many DSO's (but good for galaxies) and better for planets.

[Phil the lancs lad]

Thank you for your replies - further mulling required i think :-)

[Starlight 1]

Hi & Welcome to SGL , I say keep on reading and try to work out best for you.

[jonathan]

I have the 8SE, it is a very good tube, manageable, but to get the best out of it you really need to consider a better mount - the Goto that comes with it is OK but it wobbles quite a bit when focusing which makes life difficult.

I have gone for an NEQ6 mount to put mine on, which is as big and heavy I could go without spending a small fortune and drilling holes in the ground for a permanent pier. You could probably put an 8SE on an HEQ5 too. The NEQ6 mount is heavy but not too impractical if you are just carrying it to the garden or putting it in the boot of a car, it's weight means that you have to be very careful how you hold it as it will be easy to drop!

I have upgraded my 8SE with a dual-speed Crayford focuser, an upgrade I would recommend to any scope that can take it, 9x50 finder scope (more powerful than my binoculars! But not quite as practical. I still use the supplied red dot finder as well). That is another plus for the 8SE - the amount of stuff one can bolt on to it - I still have space for a DSLR piggy-back bracket.

Drawnback of the 8SE is the dew protection requirement, I have a dew shield, dew heater tapes, dew tape controller.. and this takes an extra power socket on the power pack (I now actually use two - one for the heater and another for the mount).

All of the gubbins adds up and it makes the 8SE or any other similar set up considerably less portable as, say, a simple refractor on an unmotorised EQ mount (no dew heater stuff, no batteries or wires, no Goto set up... just level the tripod, point the mount at the North Star and start gazing).

If I was buying again I would probably still buy the 8SE, it is a very nice scope, but would go straight for a better mount.

Consider including two additional eyepieces in your budget - a 10mm and a wide-angle one, such as the 38mm Skywatcher Panaview (opinions vary, but I have had some cracking views of the Orion Nebula and star clusters with this). The 38mm is a 2" fit so you would really need to purchase a 2" star diagonal in order to use it.

On focal length.. SCTs cheat a bit because they bounce the light inside the tube, but I find it easier to understand it with refractors - a long tube will offer a narrower field of view and higher contrast with less colour fringing, which is good for planetary viewing. Short tube refractors will offer wider field views but, unless fitted with more expensive glass etc, will show more colour fringing.

[Marki]

As another 8SE owner, I pretty much agree with Jonathan's assessment above - it is a bit wobbly on the standard mount, or even on my EQ5. I find the go-to ok, but the motors are quite noisy. It has good aperture, its easy to set-up, and physically reasonably manageable - the tube and mount fit in my little Polo fine in their cardboard boxes, and the tripod just sits on the back seat. I hated the red dot finder though... .

It has given me great views though - nice optics .

[JamesM]

Hi Phil, I believe in your question you asked about how focal 'ratios' effected the ability of a scope to perform on different targets. Focal ratio is a quoted figure that represent the relationship between aperture (the ability to collect light to reveal detail) and the focal length of the tube (potential magnification). The idea is that on bright planetary objects, there is less need for a large aperture (light gathering) but a greater need for a longer focal length (magnification). Also as focal length increase, the field of view gets smaller too (like looking through a very long tube) which again isn't a problem for planets as they occupy a relatively small area of sky. Conversely, when chasing very faint deep sky objects (DSO's) such as galaxies and nebulae, magnification is important but it is aperture (resolution of detail) that will be sought after in order to tease out faint structure and detail and as a consequence also providing a wider field. Over the years, the growing interest in astrophotography distorted scope production into providing shorter scopes known as 'fast' scopes (lower focal ratio numbers like F4) than say a 'normal' 'slow' scope that is typically F7 or higher. An important consideration to remember is that a scope with a low focal ratio, will require more precision from an eyepiece if it is to bring a wider light cone to focus in what is a relatively now a shorter tube. On 'slower' scopes (denoted by a high focal ratio) an eyepiece doesn't have to work so hard bringing a relatively narrower light cone to focus.

Reflector type scopes with very large apertures are inevitably going to be 'fast' scopes because of practical issues in both using and mounting them. A F4 scope with 400mm (16") aperture will be 1.6 metres long, at F7 will an impractical 2.8 meters! However the scopes you are intending to buy are of a Catadioptric design that both increases the field of view via the front corrector plate whilst internally reflecting the light in order to reduce the long focal length into a manageable sized tube. This explains why they are more expensive than reflectors. I hope my explanation helps or have I made it more confusing.

Clear skies

James

[M4lcs67]

I own the 127 SLT and it is a great scope for the money. I will be looking to upgrade at some point in the future and one of the Celestron 8"s is on my list, but for now my little mak is fine. As a newbie I didn't want to go out and spend a fortune until I had gained some experience first.

As the previous posters have said it is also down to what you want to do with the scope as well. You certainly have come to the right place for advice though. Thank goodness I found SGL when I was starting out.