Eyepiece Set

The SkyWatcher Explorer 130P is, in my opinion, a very good entry level telescope for someone who wants to get into astronomy on a fairly limited budget. Priced in the range £180 to £200 (UK Sterling), the telescope should hopefully be affordable to most people.

Unpacking and setting up the telescope was very easy - I had everything assembled within about half an hour. There is a one-off requirement to set up the latitude where the telescope is going to be used, which would only need to be re-done if you move the scope several miles from this location. The user guide provides clear instructions on how to do this.

Each time you switch on the auto-tracking Alt-Azimuth mount, the scope needs to be horizontal (zero on the mount's scale) and pointing north. This enables the scope to track objects in the sky. This is really useful because objects have a tendency to move out of the scope's field of view very quickly if you are not tracking them using a motorized mount. The only thing I don't like about the motorized mount is that the power pack does not have an on-off button, meaning that it needs to be switched on or off by screwing or unscrewing it from the mount.

The telescope has a focal length of 650mm and comes with two eyepieces (I guess this might be different in different countries) and a Barlow lens. One eyepiece has a focal length of 25mm, giving a magnification of x26 (650mm / 25mm), and one has a focal length of 10mm, giving a magnification of x65 (650mm / 10mm). The Barlow lens can be inserted in front of the eyepiece to double the magnification, giving a magnification of x52 (2 x 26) and x130 (2 x 65).

The 130mm aperture captures quite a bit of light, producing bright, sharp images. One thing to remember though is that viewing an object through a 130mm telescope is not going to produce images like those we see in books. For example, viewing Saturn at a magnification of x130 will produce an image that is about 2mm at arm's length. So, hold a ruler at arm's length and look at, say, the distance between the 150mm mark and the 152mm mark - this is how big Saturn will appear through the SkyWatcher Explorer telescope at a magnification of x130.

The highest practical magnification is x260 (2 x the aperture (130mm)), but it is really difficult to get sharp images at this level of magnification unless the viewing conditions are really good. (I bought a 5mm eyepiece which, in conjunction with the Barlow lens, gives me a magnification of x260.)

The SkyWatcher Explorer is easy to pick up and move about, which is essential if like me you store your telescope in the house. I normally use my telescope in the back garden, and I never have any problems moving it around.

All in all I'm really pleased with my purchase and would recommend the telescope to anyone who is just starting out in astronomy.

About the Author: John Dixon is a web developer working through his own company John Dixon Technology Limited. The company also develops and supplies a free accounting software tool called Earnings Tracker. The company's web site contains various articles, tutorials, news feeds, and a finance and business blog.

eyepiece collection?

noticed similar question and I'm curious bout mine.

I also have a Celestron Starhopper 8 inch f/6 (strange eh?) focal length 1219mm

Eyepieces:all 1.25" format

28mm Meade Orthoscopic

26mm Super Plossl Series 4000

25mm Plossl (came with telescope)

12mm DSO Super Plossl

9.7mm Super Plossl Series 4000

9mm TMB Planetary Eyepiece

What do you think? How is it? I think it is pretty decent but I know that I do indeed need a wide field low powered eyepiece. Orthos have a narrow FOV and SP will not suffice.
Suggestions? Thinking about a 1.25" Nagler or Panoptic. Going for 1.25 format because i don't want to buy an entire new set of expensive 2inchers. And too lazy to take out 1.25 adapter while observing. Any suggestions?

Most reasonable gets five points. Thanks and clear skies!

If you want to stick to wide field format the maximum field of view achievable will be with the 24mm Pan Optic. This will give you 1.35 degrees which is the largest field your scope can provide in 1.25 inch format.

A 20mm Nagler would have the same field of view but it will be a two inch eyepiece and so is not in contention according to the rules stated, which require 1.25 inch format only. The largest of the 1.25 inch Naglers is the 16mm. It will give you a tad under 1.1 degrees which is substantially less, in area, than the Pan Optic. It will be better corrected.

The question states "wide field low powered." Note that while low power is equated with wide field, it depends on the design. The Pan 24mm will give you 51x magnification. You can get the same field of view, not bigger, not smaller, by getting the Televue 32mm plossl (1.25 inch). The TV32mm will cost about 1/2 to 1/3 the Pan Optic. Its field of view will be identical to the Pan Optic but the magnification will be only 38x.

The Pan Optic's biggest problem is that it is poorly corrected off axis which can lead to some weird effects if you are paying attention on certain objects, such as turning the full moon from a round circle to a football when you move it to the side of the field. It is nonetheless extremely popular among dob owners because it is one of the lightest options out there.

The Pan Optic's major benefit relative to the TV 32mm plossl is that it will make the sky look darker and blacker--more like outer space. The lower your magnification, the more the background sky tends to look gray.

So if you have the funds and want to stay with 1.25" format, and also want the widest possible field of view for your scope in 1.25 inch format, then the Pan 24 is probably the best choice save for the off-axis aberration mentioned. The color correction on the Pan 24 is also poor, a lot of lateral color which shows up as a lime green fringe on the moon as you move off-axis. But you will only notice on Jupiter and the Moon, and chances are you will switch to higher power viewing and not have to deal with it.

People in the know sometimes sacrifice some field of view to get the Pan Optic 22 which is a better corrected piece of glass. That would give you 1.24 degrees at 55x and is probably the best compromise among these options.

Your current maximum field of view with the 28mm is a bit under 1.2 degrees at 43x. So again you'd have LESS field of view with the 16mm Nagler. But you won't get a lot more field of view by moving to the Pan 22. Just a bit more. So you have a lot of trade offs to consider.

I have to point out that by staying with 1.25 inch you are cutting back your field of view quite dramatically. A 40mm two inch eyepiece with 70 degrees like the University Optics MK70 ($225) or the Pentax XW ($500) or the 41mm Pan Optic (around $600) would give you a whopping 2.3 degrees and get some very nice views. There are some "UWAN" offerings that are less expensive from William Optics. Of the three mentioned above the University Optics is the lightest and best suited for a dob (for balance issues). The stream of light coming out of your focuser would be fairly wide however, over 6mm, which is bigger than your pupil will likely be. So you will lose some light at 40mm wide field and your 8 inch scope will perform like a 6 inch scope. But many people consider that a worth while trade off for a wide field view of objects that can't be seen well any other way. I'm not sure why getting a two inch eyepiece will make you get a whole set of 2 inchers. You can have the two inch eyepiece and use the rest. Even those of us who have three or four two inch eyepieces are using 1.25 inch at higher magnifications (the break point between 2" and 1.25 inch is usually 20mm, but 17mm for the Naglers). So basically you'd have a wide field eyepiece and then your regular 1.25 inch selections.

Good luck,
GN




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