Alan64

I read somewhere, recently, someone saying not to let Sky-Watcher know just how wonderful the 100ED really is.

If you didn't have a fast 102mm refractor, I'd say go with the 102mm ED.  What about a 150mm Maksutov; that for lunar and planetary, and the fast refractor for wide-field deep-sky?

2 hours ago, baggywrinkle said:

I have the SW Mak 127 on the goto mount. It is an excellent wee scope, good views and great for exactly what you are looking for.

Though the mount is a tad lightweight a mass placed in the EP tray make it more stable. It is easy to set up.

The only downside are the poor quality ep's and star diagonal. Below two images (not the highest quality) taken with the Mak 127...

Those are actually quite, quite good.

Our eyes, as humans, are weak, compared to an animal of the night equipped with tapetum lucida.  For them, the same dark site as described must appear as an overcast day does to ourselves, and at high noon even.

...wise decision.  The AZ4 will provide a solid, stable and lasting platform for the refractor. 

"'Another nice feature is the altitude and azimuth scales marked in one-degree divisions — a nice aid to locating celestial objects if you have a Palm or Pocket-PC planetarium program.'  Ade Ashford - Astronomy Now, Dec 08"

This is the manual for the AZ4, for both: the steel-legged and aluminum-legged variants....

http://www.opticalvision.co.uk/documents/163.pdf

The aluminum-legged version is lighter, of course, but it also sits closer to the ground when the legs are not extended, albeit with less stability overall perhaps compared to the steel-legged.  The 120mm f/5 has a short tube, but only in relation to its considerable aperture, and when compared to an 80mm.  One of the benefits of refractors and corrected-Cassegrains(SCTs and MCTs) is the ability to sit, and remain seated whilst observing.  Therefore, before purchasing either one, get out what you might anticipate as being your favourite observing chair, and a rule, make measurements, and according to the specs on the last page of the manual.  Several variables require consideration before deciding on which one to get.

3 hours ago, menacegtr said:

Is it ok to use the  Skywatcher 2" Di-Electric Star Diagonal which Includes 2"-1.25" adapter, can I use 1.25 eyepiece's as stated above for my ST 120mm, I hope so as I have purchased one from FLO. I did not want to have to buy 2 diagonals (2" and 1.25") as I want to get a PanaView 2" eyepiece so was informed a good 2" diagonal with adaptor would be the ticket for both types of eyepieces. Thanks again for all your help.

                                                                      Regards. Dave:

...splendid choice...

A 2" diagonal with a 1.25" adaptor accommodates 1.25" eyepieces as well...

In addition, by inserting a .965" adaptor into the 1.25" adaptor, one can use old-school .965" eyepieces even...

A short-tube 120mm refractor is a bit much for the included AZ3 alt-azimuth mount within said kit, and when extra weight is added in the form of eyepieces and accessories, well.  Give it a go with the AZ3 for a spell, and see how it works out.  There is the option, however, of getting the OTA separately...

http://www.firstlightoptics.com/startravel/skywatcher-startravel-120t-ota.html

The OTA is £30 less than the kit, therefore the AZ3 is thrown in at a £67 discount.

A more robust alt-azimuth mount... http://www.rothervalleyoptics.co.uk/skywatcher-az4-1-alt-az-mount-with-aluminium-tripod.html

Whilst that one would easily handle the refractor, and any and all eyepieces and accessories, it does not have slow-motion controls, as the AZ3 does, for some inexplicable reason.

http://www.teleskop-express.de/shop/product_info.php/info/p8069_TS-Altazimuth-Mount-with-Fine-Adjustment-and-Quick-Release.html 

...and ideal, but for yet another inexplicable reason, it's not sold in the UK.  It's very popular for smaller telescopes throughout the rest of the world.

Hello Dave,

A 2" 32mm, as described, would probably be the only 2" eyepiece in your collection.  Some get a 2" ocular in the 25mm-ish range, too.  But the 1.25" oculars are more than adequate from 4mm to 25mm, for most people.  My 2" 32mm is the only one I have, and I don't really feel the need for any more.  If you plan on getting that 2" 70° 32mm eyepiece in future, then it would need a 2" mirrored star-diagonal, and with a 1.25" adaptor as it never hurts to have a spare.  Although I'm unaware of 2" diagonals being sold without 1.25" adaptors.  Most come with one in any event.

On the other hand, if you decide on the 1.25" Vixen NPL 50° 30mm instead as your lowest-power eyepiece, then consider a 1.25" mirrored star-diagonal.

Yes, one doesn't have to spend a fortune on eyepieces to have a rewarding experience 'neath the starry void. 

6 hours ago, menacegtr said:

I have been doing some research and trying to learn about eyepieces and overpowering the telescope. Is this equation right as I understand. The ST 120 is a 600mm focal length and 120mm aperture? so to get an eyepiece to work inside the scopes capacity is to A x the 120 by 2 to give the maximum magnification at 240x. So the standard aperture of the ST 120mm is 600mm, so do I divide that by the 10mm lens that comes with it to get 60x and the 25mm lens would be 24x so there is massive room for improvement. Now if I add a good 2 or three element 2x Barlow does that effectively give me double the focal length now, so I should have 1200mm focal length so a 10mm lens should now give me 120x. So from that I can squeeze out more mag and go to 1200% by a 7mm lens to give me around 171x magnification, if I go to a 6mm lens I would get 200x mag so still not going over the 240x mag with the 2x Barlow but maybe to strong for the scope. Is this how it works out so as not to overpower your telescope. And if I take the Barlow out and just use eyepieces I would get at the extreme end, 600 aperture % a 3mm lens would get me I would think an unusable 200x magnification.  I don't want people saying that the scope is Rubbish with a Barlow or just use a 3mm lens to get 200x mag is bad, I just want to no is this how you work it out

                                                                                         Regards. Dave

The 120mm f/5 will gather a lot of light, and the Baader semi-apo filter sounds to be effective, per research: win-win.   

The achromat has a focal-length of 600mm.  That's all that's needed when choosing eyepieces and a barlow.  The lowest-power eyepiece, and for great wide-field views, will be a 32mm, and since the focusser is able to accept 2" eyepieces, this 2" 70° 32mm, combined with a 2" 90° mirrored star-diagonal, would be a great performer, and pictured at right...

http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-panaview-2-eyepieces.html

600mm ÷ 32mm = 19x, and quite close to that of a pair of 20x80(20x) binoculars.

I have the same 32mm, and illustrated here alongside my Synta 1.25" 25mm...

Just by looking at it, one can get a sense of its performance.  The 1.25" 45° Amici-prism terrestrial/daytime diagonal supplied with the kit can be used at night, but it is not designed for astronomical use, therefore its performance will be lacking.  The kit is sold with one, and in a terrestrial/daytime configuration.  A 90° mirrored star-diagonal is recommended for fast refractors, for astronomical/nighttime use, and for best performance...

http://www.firstlightoptics.com/diagonals/skywatcher-di-electric-star-diagonal.html

A 2" eyepiece and diagonal is not required however.  For examples...

A 1.25" 50° 30mm(20x) Plossl... http://www.firstlightoptics.com/vixen-eyepieces/vixen-npl-eyepieces.html

I have it, too, and it's a great performer.  I chose it over the GSO and Baader 32mm Plossls, and after careful research...

...and a 1.25" 90° mirrored star-diagonal, for example... http://www.rothervalleyoptics.co.uk/altair-astro-125-dielectric-star-diagonal.html

600mm ÷ 30mm = 20x(2x barlow: simulated 15mm/40x), (3x: 10mm/60x)

600mm ÷ 25mm = 24x(2x barlow: 12.5mm/48x), (3x: 8.3mm/72x)

600mm ÷ 10mm = 60x(2x barlow: 5mm/120x), (3x: 3.3mm/180x)

Examples of better-quality barlows...

2x:  http://www.rothervalleyoptics.co.uk/antares-x2-twist-lock-barlow-lens-125.html

2.25x: http://www.firstlightoptics.com/baader-planetarium/baader-classic-q-225x-barlow.html

3x:  http://www.rothervalleyoptics.co.uk/antares-x3-twist-lock-barlow-lens-125.html

A barlow is placed into the optical train, and therefore needs to at least match the quality of the refractor's doublet-lens and the eyepieces, and for better performance.  The lens element of the Baader Classic Q 2.25x, listed above, is removable, and at 1.3x.  I recently read of a fellow amateur with a GSO 2x/1.5x.  As he removed the element to place it on an eyepiece, he dropped it and chipped the lens, therefore extra care is needed when handling.

Barlows are used for visual, and imaging.  For visual, its use is two-fold...

1. To multiply the number focal-lengths within a small eyepiece set, as demonstrated above.

2. To reach a higher magnification without having to resort to using an eyepiece with a tiny eye-lens and short eye-relief.  For example, this is a 4mm orthoscopic...

You know that one has to be difficult and even painful to look through, eh?

Instead of using it, 3x-barlowing a 12mm, and for a simulated 4mm, makes for much greater eye comfort...

That combination of a 60° 12mm and a 2.8x barlow actually simulates a 4.3mm; but close enough, and O! the wonderful things I've seen with it!

Then, there are eyepieces that have a built-in barlow, with said greater eye comfort, and when compared to a standard 4mm orthoscopic or Plossl...

http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

4 hours ago, Linda said:

Is a 180mm Mak also suitable for Deep Sky? In the sense that it could be a better alternative then a 8 inch reflector? Or is again the narrow FOV very limiting?

An 180mm Maksutov-Cassegrain would make for a splendid celestial "microscope"; for the Moon and the planets and double-stars, and would simulate a 140mm f/19 refractor.  Observing quite a few of the smaller, single deep-sky objects should be possible, too.  Now, a 30mm ocular, which gives a wide-field low-powered view at 25x via my 6" f/5 Newtonian, would realise 90x with said Maksutov: a considerable magnification, and one of the lowest practical powers.  Perhaps more people than we know look upon the short tubes of the Cassegrains thinking that one would make for a capable deep-sky instrument, until it's there before them.  Notice how the 2700mm focal-length of the 180mm Maksutov is folded into three sections within the optical tube...

Therein, its true nature is revealed.

6 hours ago, Bobby1970 said:

I think some of this is a little unfair. There are several members who have owned or do own fast achromat scopes and I for one would not say it exhibited "oodles and gobs" of false colour. 

If you went down the reflector route, be advised you will need to be more careful when transporting the scope and it will also need collimating now and then. 

Some people do not find CA a problem. Some find it more so. I got myself a semi apo filter for next to nothing second hand and it does diminish the CA somewhat. But the flip side is a slightly yellow cast to the objects you are viewing. 

The best course of action is to try one of the scopes for yourself and decide if you find it acceptable. I do think that ultimately you will end up with more than one scope though. Most people seem to   

Physics is incapable of being "unfair".  It is what it is....

I have an 80mm f/6 achromat.  It even came with its own vampire-star...

At f/6, the aberration is well controlled, up to a moderate magnification...

However, research the colour-suppression performance of the faster Synta 80mm f/5 achromats(Orion, Sky-Watcher, iOptron, et al).  Then, add an extra 40mm to said f-stop.  The aberration increases with aperture when the same f-stop is maintained.  Again, a 120mm f/5 achromat should offer, at times, wonderful if not stellar deep-sky performance, and that is its strong suit.

A 120mm f/5 achromat is going to exhibit oodles and gobs of false colour on every bright object you observe.  Do you remember kaleidoscopes as a kid, and it gets worse as the magnification is increased.  A fast achromat however excels at observing the dimmer deep-sky objects; not too terribly bright, mind you.  If you want to observe mostly at higher magnifications, then go with either a 150mm f/12 Maksutov, or a 150mm f/5 Newtonian combined with a barlow.  The Maksutov would be a near-simulation of a 120mm f/15 planetary refractor, and perfect for observing everything up close.  Similarly, a 127mm Maksutov would mock a 90-100mm long-focus refractor.  On the other hand, a 150mm f/5 Newtonian would imitate a 120mm f/6 apochromatic refractor...

http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-ds-ota.html

Newtonians are apochromatic, meaning "totally without colour"; that being false colour, or chromatic aberration.  With a better-quality 2x barlow, the 150mm f/5 would enable magnifications up to 250x and beyond, in good and better seeing conditions; and all the way down to 23x with a 32mm ocular for wide-field deep-sky objects and vistas. 

As a spectacle wearer I can vouch for the fact that the eye/brain combination is very good at doing on-the-fly RGB alignment. It can be fooled, illuminated TESCO signs in red and blue and the HSBC logo on a computer screen both show movement of the two coloured parts when I move my head - in fact the red spelling wiggle under TESCO moves side to side as I shake my head! But when the colours are overlaid, the eye correct (e.g. the word TESCO in white doesn't split into RGB except at the extreme edge of my vision, even though the red bit must be moving as much as the wiggle!)

I'm near-sighted, and have worn glasses since my relative youth. 

In any event, what I had meant by my statement regarding the camera's shortcomings, is in that it fails to capture the sharpness of a live view.  This is a photograph I took with the Tanzutsu 60mm f/15...

It appears nice and sharp, eh?  Ah, but not nearly as sharp as the live view at the time the photograph was taken.  Here's a close-up...

During the live view, within the circled portion, I saw what appeared to be dozens if not hundreds of what I term "hills and dales", within that ridge.  The event has me almost convinced that the achromatic doublet was not manufactured by Tanzutsu, but by the Japanese optical house, Towa, instead.  The two companies were in collaboration with one another at some point in the past.  I wouldn't be surprised if the doublet was a part of Towa's old stock, and possibly from at least a decade prior to the refractor's manufacture.

A 5" Zeiss apochromat might exhibit only one thing: perfektion.

Nice pics of the scopes

In that last one of the moon, it looks like the CA around the limb varies in tint from the top (greenish) to the bottom (blueish). I've not seen that before. Usually you see it as per your other two photos, a consistent colour around the limb, changing colour, again consistently, as you rack through the focus point.

Does the Antares show that visually or is it a photographic artifact ?

At f/6, 480mm, the Antares will indeed exhibit its fair share of false colouration, and the camera only accentuates it further in the resulting photograph.  I've been told that the camera itself, even, will introduce colours, particularly when held at an angle.  Here's another shot through the Antares, and at a higher magnification.  However the colour wasn't as strong when observing with the eye...

That's quite a strong colour cast through the Tak. Was it a TeleVue ep by any chance?

The Moon was almost full, waning I think, when I took that photograph, thus the use a variable polariser to dim down the brightness.

Refractive family portraits...

Takahashi FS-102, a 102mm f/8 apochromat...

Purchased new in 2003, it is a consummate "pupil", my having split Sirius in the same year when it and its companion, "The Pup", were practically adjacent to each other; said companion having blinked in and out, but never having disappeared entirely within the Dog's intense glare.  The separation between the two has steadily increased since that time.  I attribute said feat to the refractor's exquisite calcium-fluorite doublet, known for its relative absence of light-scattering...

Tanzutsu 60mm f/15 achromat, and upgraded to a 1.25" focusser...

Made in Japan in 1987 or '88, this example was purchased as new old-stock earlier this year.  Almost 5" had to be cut off of the optical tube, from the front, and in order to effect the new 1.25" format.  An extra tube-baffle was added, and ultra-flat black spray paint applied throughout the optical path where necessary, from the front edge of the dew shield to the 1.25" visual back.  I had always wanted a long-focal achromat, albeit only a 60mm.

Lastly, the most recent acquisition: an Antares 805 80mm f/6 fast-achromat...

It, too, will need enhancing, but as it stands I was able to view the Airy disc of the brightest star within Orion's Trapezium, designated "C", rather distinctly and under high magnification.  Nonetheless I consider it to be little better than a guidescope with less than stellar optical quality.

An afocal image via the Takahashi, and simply by holding a point-and-shoot camera up to the eyepiece...

Likewise, via the Tanzutsu...

...and via the Antares...

Chromatic abberation is well-controlled with this example, but present nevertheless.

In every instance, the Canon S110 always falls short of that seen during a live session.