SW Exp 200P Newt - Equipement

[Kahl]

Hi Everyone,

I've spent the last few days doing some research into new equipment (specifically EP's); although I've expanded my overall knowledge, there's a few gaps that need filling.

So, I've gathered that the BST & X-Cel-LX ranges come highly rated and are within my price range.

Firstly, If I understand correctly, a 8mm is (roughly) optimal for planetary viewing with my scope? I've had good results with the stock 10mm looking at Jupiter, though I'd like to get a little closer. Would a 8mm suffice for Saturn?

8mm would give 250x (barlowed) which is close to my limit considering my location (SW England).

Secondly, I've also been reading that 25-40mm is (roughly) optimal for DSO? I've not been graced with a chance at the Orion Nebula (a good starting point) but I'm curious how 'close' I would get at this level of magnification? Would the Orion Nebula fill the scope with a 25mm?

Also, how would wide-angle EPs effect both of the above? I see that BST make 8mm wide-angle EPs. I don't quite understand the difference between them, or why the wide-angle EPs are equal .mm to the standard EPs? 

Sincere apologies if these questions have been answered elsewhere. I did spend several hours reading old posts but I couldn't find much clarity regarding these specifics.

Many thanks in advance,

[Kahl]

Edit: I also understand that trial and error will most likely answer these questions; I'm looking for some general guidance.

[LouisJB]

If you download Stellarium you can set up your telescope and eyepieces in there and then it will show you exactly what you will see in terms of FoV etc. It's a good way to consider new equipment before getting it.

The mm is the focal length. The tubes focal length divided by the EP focal length gives magnification. For example 25mm on 1000mm FL tube = 1000/25 = 40x.

The EP field of view is how wide or narrow the image is, i.e. imagine seeing the same image down a kitchen roll tube, a drainpipe and a dustbin sized tube... it's the same size image (same magnification), but you'll see more or less of it depending on the field of the EP. Wider field EPs are normally more expensive because a wider field is better than a narrower one...

Just to add, I'm not sure 25mm is ideal for DSO's - some DSOs but not all DSOs are very similar. For example M42, M45, M31 are 'massive' compared to say M57, the latter would need a low mm eyepiece, say a 6mm or whatever and the former may require >25mm to see it all. On M31 it's so big maybe even a 32mm wouldn't be enough. It would also depend on the focal length of the tube it's used with and the aFoV of the EP you're using.

[Kahl]

Thanks LouisJB. I'm all over Stellarium, its just what I was looking for!

One final question; I've noticed that the standard 8mm BST offers 60^o FOV, whilst the wide angle offers 58^o FOV. Surely the wide angle should offer a better FOV?

[LouisJB]

well what exactly constitutes wide-angle isn't really that well defined.

Is the 'wide angle' a high mm eyepiece, if so then they are referring to the size of the patch of sky you will see with it. i.e. a 25 or 32mm EP is wide-angle, regardless of the field of view, even if it were only say 52 degrees. The focal length and EP fov are separate variables, although there is a relationship between them of course. So you could have a 80 degree 6mm and a 52 degree 25mm EP or vice versa. Generally wider field of view of eyepieces is more desirable, but independent to the focal length/magnification an EP might offer. Also the eye relief / exit pupil sizes can be worth considering, I think this gets more of an issue as the EP focal length gets lower - but I'm no expert here, just mentioning it as something to consider, esp. if you wear glasses.

The BSTs seem to get good reviews, I'm thinking to get some myself. I have 1 Celestron X-Cel LX (7mm) and it's nice also.

I think for the cost either would be a good purchase, just make sure you're getting the right focal lengths to suite what you want to view.

[Kahl]

Thanks again LouisJB.

In case anyone else had the same questions regarding Wide-Angle EPs, here's Alan's response (from Skies Unlimited):

The main difference is that the Explorer is an ED eyepiece that uses low dispersion glass in its construction and the Wide Angle doesn't.  The effect of using the ED glass is that it tends to make the image brighter (and some say sharper) that the other eyepiece.  The effect of not using ED glass in the Wide Angle is that it appears to give greater contrast to the colours of planets.

So, if it is mainly going to be the planets that you will be looking at then the Wide Angle will have the edge whereas if it is stars, clusters and nebulae then I would recommend that the ED eyepiece would be the better one.