Celestron Firstscope

[Alan64]

A 150mm f/8 Dobsonian is a long-focus Newtonian on a Dobson-style mount, and a tried-and-true design.  The 150mm f/8 Newtonian itself has been around for quite some time.  Here's an ad from 1960...

http://www.company7.com/library/graphics/criterion_rv6-1960_733964.jpg

Back then, there were no short, low-power telescopes to really speak of, nor Dobsonians.  Newtonians in general were more expensive at that time, and many came with large and heavy equatorial mounts...

http://www.philharrington.net/coaststore.jpg

Then, enter John Dobson, and the amateurs suddenly had large apertures with which to observe, at nigh a moment's notice; and without a heavy, cumbersome equatorial...

https://en.wikipedia.org/wiki/Dobsonian_telescope

For the most part, the shorter the telescope, or f-stop, for a given aperture, say, a 150mm, the more difficult and more costly the mirrors or lenses are to produce, as they require more work by the optician in generating the steeper geometric curves required when grinding and figuring them.

Eyepieces are static, unchanging; whilst telescopes are dynamic, and with a wide range of apertures and focal-lengths.  Take a 15mm eyepiece.  It will always be 15mm, but then insert the eyepiece into a 150mm f/5 with a focal-length of 750mm...

750mm ÷ 15mm = 50x

Take that same eyepiece, and with a 150mm f/8 with a focal-length of 1200mm...

1200mm ÷ 15mm = 80x

F/5 and f/8 are the telescopes'  focal-ratios, or f-stops...

750mm ÷ 150mm = f/5(750 ÷ 150 = 5)

1200mm ÷ 150mm = f/8

A 150mm f/8 Dobsonian is chosen for moderate-to-high powered observations of the Moon and planets, double-stars, and a goodly smattering of deep-space objects...

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html

A 150mm f/5 tabletop Dobsonian, or Newtonian, is chosen for low-to-high powered observations of same; versatility never had it so good...

A standard 2x barlow will effectively make the 150mm f/5 even longer than the 150mm at its native f/8, and at f/10 instead, with a new effective focal-length of 1500mm, and therefore quite suitable for higher-powered observations.  Take an 8mm ocular, insert it into the barlow... 

1500mm ÷ 8mm = 188x, and at about the highest power practical on most nights for general observations.  Keep in mind that the Earth's atmosphere must cooperate when ramping up the power.  Such is called the quality of "seeing" when so doing.

Remove the barlow, then the f/5 instrument allows for low-power wide-field views, and binocular-like, as low as 19x, or perhaps even less if determined.  As a bonus, the optical-tube is shorter, compact and portable.

If you place a 2x barlow into a 150mm f/8 Dobsonian, it is then transformed into an effective f/16, and with a new focal-length of 2400mm.  Said 8mm eyepiece would then realise a magnification of...

...2400mm ÷ 8mm = 300x, and certainly within the capabilities of the telescope's aperture, but success would depend on the optical quality of the mirrors or lenses received, and with the finicky atmosphere ever present.  Also, since the 150mm f/8 is on a manual mount, it will become more difficult to keep an object in the eyepiece's field-of-view at high powers, for that portion of the sky is highly magnified, and therefore much smaller, with the objects tending to race out of sight, as you may have noticed when inserting that 4mm into the FirstScope.  Many users of manual mounts then choose eyepieces with wide fields-of-view themselves, and to extend the viewing time before having to bump and nudge the telescope to recapture the object, and with actual fields-of-view, or AFOV, of 82°; for example...

https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-82-degree-series-eyepieces.html

Then, some turn to motorised mounts, tracking-only or go-to, which makes the objects stand still there in the eyepiece, and as if time itself had stopped.  Therefore, wide fields-of-view are unnecessary, and with most any high-power ocular.

With a motorised tracking mount, if one desires some perspective, like the view through a "picture window", with the object of interest surrounded by a large backdrop, then the wide-field high-power oculars will serve in that instance, as will the wide-field low-power eyepieces when viewing large expanses of the sky.   In the case of high-powered views, some do not like that however, preferring instead to concentrate upon and study just the object at hand, with a little bit of sky surrounding it, and at the higher and highest of magnifications.

[SAW]

Thank you Alan. There is a nice big moon tonight so my little firstscope is working ok for this.

So am I right in thinking Refractors or better for planets ?

Dobsonions are are cheap way to get good size scope but it's going to be big and I'll have to manually find anything I want to look at ?

Reflectors are smaller than the Dobsonions but will give give the equivalent focal but cost more, it can also be available as a go to ?

Would it be better for me to buy a good quality 2x and 3x barlow lenses as I can use them on more scopes that I get ?

I'm not sure if i want to go Dobsonion or better Reflector that I can upgrade ?

[Alan64]

"So am I right in thinking Refractors or better for planets ?"

Longer focal-lengths are better for planets, in the splitting of double-stars, at the higher magnifications, and regardless of the design of telescope.  Refractors do provide, however, centimeter to centimeter-and-a half, and with their clear, unobstructed apertures, the sharpest and most contrasty views over all other designs.  Here, a comparison of the apertures of a refractor, a Newtonian, and a modified-Cassegrain(Maksutov)...

Note how similar the apertures of the refractor(far left) and the Maksutov(far right) appear.  A Maksutov is the only mirrored design that has been described as being "refractor-like", and in their performance under the night sky.  In addition, refractors generally do not require collimation, nor on a regular basis as is common with Newtonians.  Maksutovs are a very close second to refractors in that regard.  Refractors are also the most costly per inch of aperture, particularly in apertures of 130mm and up.  Again, Maksutovs are a close second to that as well, and starting at 150mm.  Newtonians, on the other hand, start getting pricey at apertures of 300mm to 400mm and up.

Now, when you look at the optical-tubes of refractors and Newtonians, what you see is what you get.  This 150mm Newtonian and this 150mm refractor are long, and therefore have long focal-lengths, and purposed for moderate-to-high magnifications, and higher still...

https://www.rit.edu/cos/observatory/images/tel/k01.jpg

http://www.rtmcastronomyexpo.org/archives/photos/2006/tel1 copy.jpg

There are no low-power wide-field views to be had with those two, and they require large mounts to support them.  But they are ideal for planetary and double-stars.

Then you have somewhat shorter ones; and then the really short ones...

http://www.teleskop-express.de/shop/Bilder/shop/GSO/Newtons/gsn1506/ts-imaging-newton-150-f4.jpg

http://www.cloudynights.com/uploads/monthly_12_2014/post-7901-0-77311000-1418681336.jpg

...and again, what you see is what you get: short focal-lengths for low-power wide-field views; for scanning the Milky Way in summer, and observing the galaxy in Andromeda and the Pleiades in the fall and winter.  Also, the mounts required to support them are much smaller.

Now we come to the "smoke and mirrors".  With the Schmidt and Maksutov Cassegrains, which use both a lens and two mirrors, what you see can be a bit deceiving.  The optical tubes are short and compact, but the focal-lengths are long, like the long Newtonian and refractor shown in the above.  Take these 5" f/12 Maksutovs on go-to mounts, for examples...

https://www.firstlightoptics.com/maksutov/skywatcher-skymax-127-synscan-az-goto.html

https://www.firstlightoptics.com/slt-series/celestron-nexstar-127-slt.html

If either one was suddenly transformed into a refractor, it would be this long...

http://www.astromart.com/images/classifieds/527000-527999/527559-1.jpg

As a result, Schmidts and Maksutovs are very popular, not only for those old-timey views at high magnifications, but they are also exquisitely portable and relatively maintenance-free.  Folks tend to like that sort of thing a lot these days, and in valuing ergonomics over observational versatility.  Incidentally, as for myself, I would overwhelming prefer a Maksutov over a Schmidt, but that's just me.

"Reflectors are smaller than the Dobsonions but will give give the equivalent focal but cost more, it can also be available as a go to ?"

A 150mm f/5 Newtonian on a go-to mount will cost more than a 150mm f/8 Dobsonian, yes.  The focal lengths between the two are not equivalent, however, and as explained previously.  In so far as the cost of a 150mm f/5 OTA versus a 150mm f/8 OTA, without mounts, I've found that the cost is equivalent, despite the fact that it's more difficult for an optician to grind and figure an f/5 primary mirror, the parabola, compared to that of an f/8.

Here's a 150mm f/5 Newtonian, somewhat similar to my own, on a go-to mount, and quite popular...

https://www.firstlightoptics.com/reflectors/sky-watcher-star-discovery-150p.html

...and one of better build-quality, but much heavier than the go-to kit...

https://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-eq3-2.html

"Dobsonions are are cheap way to get good size scope but it's going to be big and I'll have to manually find anything I want to look at ?"

A 150mm f/8 dobsonian is not as large as you may be thinking; the base, the mount, however is almost twice as heavy as the tube.  There are also go-to Dobsonians, but starting at a minimum aperture of 200mm...

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-flextube-goto.html

" Would it be better for me to buy a good quality 2x and 3x barlow lenses as I can use them on more scopes that I get ?"

It's always an option for the buyer to get anything of better quality, but it doesn't have to break the bank, albeit though perhaps with a small crack...

http://www.rothervalleyoptics.co.uk/antares-x2-twist-lock-barlow-lens-125.html

http://www.rothervalleyoptics.co.uk/antares-x3-twist-lock-barlow-lens-125.html

I have the Antares models, the 2x and 3x, that just preceded those two listed above, but without the twist-lock feature, and they're very, very, very good, if not excellent...

I've witnessed snap-to focussing with the 3x combined with an average eyepiece, and with my mass-production 150mm f/5 Newtonian.  With the 2x, I witnessed the first acceptable star-test of my 4" f/8 refractor, and after a few failed attempts otherwise over the years. 

You don't have to get both at once; and yes, they only have to be acquired one time, for use with telescope to telescope in future.

[SAW]

Took this tonight, I know it's not much but I thought it's not bad using the little FirstScope my iPhone 6 and a cheap universal mount from eBay which does not really stay on the eye piece unless I hold it lol.