Recommended first accessories for starblast 4.5

Question

My son got an orion starblast 4.5 for Christmas. It comes with orion explorer II 17mm and 6mm eyepieces. We are looking at some additional accessories and wondering what you would recommend as "first accessories" to get the most out of the telescope. Our initial inclination is towards:

1. A barlow lens. Probably the orion shorty 2x barlow. Is the shorty-plus twice as good? (It is twice the price.)
2. A 25mm eye piece. From what we've read, a reflector with these specs is best for wide field views.
3. A solar filter. We think it would be cool to look at the sun.

Answer 1

I'd recommend getting to know the telescope before adding a bunch of accessories. A few things I'd recommend:

• NightWatch by Terence Dickinson (Firefly). This is by far the best beginner's book on astronomy, and contains an excellent set of star charts for finding objects in the night sky.

• 10x50 binoculars. Useful in themselves, but also excellent to scout a new part of the sky before exploring with the telescope. I use my 10x50s as much as I use my telescope. Orion Scenix 10x50s are excellent, and are currently on sale.

• A good star atlas. My favourite is the Sky & Telescope Pocket Sky Atlas (Sky).

• A red flashlight.

• A solar filter. The best ones are made by Jim Kendrick using Baader AstroSolar film, better optically than Orion's glass filters: http://www.kendrickastro.com/astro/solarfilters.html

• The supplied eyepieces are a good match for this telescope. There isn't much to look at that requires a wider field of view than the 17mm, and the 6mm is about as high as you can go with a 4.5" telescope. Any more magnification than 75x would be "empty magnification." For the same reason, I wouldn't recommend a Barlow. By the way, the "Shorty Plus" is twice as good as the "Shorty"!

Answer 2

I don't think splurging on accessories is the best strategy in this case. This is a small scope, the design cuts quite a few corners, there's not much room for improvement via accessories. It's a very aggressive F/4 that is hard on the eyepiece. Maybe save that money and get an 8" dob.

I know it's customary for most new users to just "get a barlow", but often that doesn't make a lot of sense.

Before you get any accessories, make sure the scope is very well collimated. That will make a large difference in performance. It's more important than any accessory. There are many collimation techniques, this is worth spending the time learning.

Anyway, let's talk accessories if you like.

The scope has 114mm of aperture, and an F/4 focal ratio, with parabolic primary 450mm focal length.

The short eyepiece

Theory says that a 2mm eyepiece will provide 225x magnification, or a 0.5m exit pupil - both are the maximum (and minimum) theoretical values for an ideal scope with these parameters. So either the 6mm with a 3x barlow, or a plain 2mm eyepiece (assuming you could afford one) would be more than enough.

OTOH, I have my doubts that this scope will do well at such a high magnification. It's the combination of small aperture, steep focal ratio (it's only F/4 which is very aggressive) and cheap optics that are not friendly to high mags - you'll get plenty of aberrations and a washed out image.

See if you can borrow a zoom eyepiece and a barlow, and explore the 3mm ... 8mm range. Two things to look for: A) Jupiter and Saturn looking washed out; and B) Stars looking like formless blobs, or bizarre shapes due to aberrations, instead of tight points (or regular figures of diffraction). As you're pushing the mags higher and higher, at some point the planets will look washed out - indeed, it will be harder to see Jupiter's stripes past a certain magnification, not easier.

My hunch is - you can't get much more than 100x ... 150x out of this scope. But it's hard to do an arm chair prediction as to how far can you push it.

The long eyepiece

It all boils down to the exit pupil. Young kids' eyes can dilate up to 7mm in full darkness. Old folks can only expect 5mm or so of pupil diameter. If the exit pupil of the scope exceeds the pupil diameter of the eye, you're wasting light. A 24mm eyepiece will provide a 6mm exit pupil; 20mm eyepiece - 5mm exit pupil; 28mm eyepiece - 7mm exit pupil. So there isn't much point in using an eyepiece longer than that; 25mm or nearby is okay, or anything in the 20s really.

But this assumes your eyes are dark-adapted when you observe. If there are sources of light nearby, your pupil will constrict a little.

Solar filter

You MUST use a solar filter if you want to look at the Sun. It MUST be the full aperture kind, the one that goes over the entry point in the tube (on top of the tube, where the light comes in). Do not use "solar filters" that go in the eyepiece!!! Those are not really solar filters, and are very dangerous. Permanent eye damage is very likely to occur when the "filter" breaks due to excessive heat and lets the full blast of solar energy hit your eye.

Make sure the filter is attached solid to the tube. You don't want the wind to blow the filter away, or a careless nudge to the scope to send the filter flying - you'll go blind in a second. There are filters that fit snugly to a given scope diameter; ask the vendor if not sure. You may even want to provide additional safety by taping it to the tube; better err on the side of caution.

In broad daylight, the big tube must be either covered with its vendor-provided cap, or the solar filter must be installed - at all times. Do not take the scope outside under sunlight with the top end uncovered, ever. If you own firearms and you know a little about trigger discipline, this is a bit similar.

With a good solar filter at the entry point of the tube, feel free to watch the Sun. There are additional hydrogen filters that go in the eyepiece (so those are optional, besides the main solar filter on top which is mandatory) but worry about that later.

Answer 3

I think Geoff nailed it. The nice thing about a good set of binoculars is that they are always with you and have close to zero setup time. The best scope is the one you can count on being there when the moment arises. Now....if you have an iPad, the astronomy apps are outstanding and are a tremendous aid, particularly to a beginner. Probably, the best thing an iPad does.

Answer 4

The biggest problem with a telescope is actually finding something to look at. Assuming you are an urban astronomer, the next thing would be a starfinder. It will be enough to get you oriented. Pocket Sky Atlas is now a reference and would be of great follow on choice.

I am with Geoff. Books will likely help the most. Beside Nightwatch I would also look for a and Backyard Astronomer's Guide which is also an excellent (but more advanced) choice. It will explain what kind of other observations you can do with a scope.

Considering that budding astronomers need success, I would look for some ways to find the planets in the sky. This used to come in the form of planetarium software but you can now get some of that for free from the Internet. Jupiter is nice right now in the evening but this will change soon enough. Planets offer the nicest, most rewarding views in a small scope with Jupiter and the moons or Saturn and the rings being top contenders. A good way to find them will definitely help.