A little over two years ago, I first began exploring the potential of a 130mm f/5 Newtonian reflector. As you may recall, I was really quite impressed with what the telescope delivered for its very modest price tag, something I had come to expect after the very positive experiences I had had with a larger 204mm f/6 Newtonian for a whole year. Both telescopes were made by SkyWatcher, and had excellently figured parabolic mirrors with smooth, colour free optics. These collective experiences transformed my opinion of Newtonian reflectors, so much so that I have come to prefer them to my erstwhile favourite type of telescope; refractors.
The 130mm f/5 Newtonian is a very convenient telescope for travel and quick grab ‘n’ go excursions. Indeed, in one form or another, this telescope has travelled the length and breadth of the country with me and has never failed to deliver excellent views on all classes of celestial real estate. Over the 25 months I have owned it, it has clocked up well over 100 hours under the stars. Indeed, it was so easy and comfortable to use that I invested in making an already good ‘scope into a great one. I upgraded the flat to one of higher quality and had both mirrors treated with the best coatings money could buy. In previous blogs, I have described how I re−housed the open tube configuration into a more stable closed tube configuration with a better focuser. I also described how I lined the inside of the tube with cork before covering it with standard flocking material. All of the modifications were very cost−effective and, all in, set me back just a few hundred pounds.
I have enjoyed extraordinary success with the 130mm f/5 in my pursuit of double stars. It has resolved double stars down to 1.0” and elongated 0.9” pairs. And in recent months, I have been able to add a few more strings to my bow, including Iota Leonis and Eta Geminorum to name but two; systems that I found to be very difficult with top quality refractors of 4− and 5−inch pedigree under good, stable skies. Indeed, my notes confirm that on these and other high−resolution targets, the 130mm f/5 was more proficient than a 4−inch f/15 classical achromat, in violation of a tradition that hearkens back to the 19th century, and shattering forever the myth that good Newtonian reflectors cannot serve as first rate double star telescopes.
I can reaffirm the beneficial effects of insulating the tube of my 130mm reflector. My ongoing studies have shown that it significantly reduces tube currents while the ‘scope is acclimating, and in use, I have seen with my own eyes the beautiful, ultra−high magnification views of various tricky double and multiple stars. I would estimate that the insulating material consistently provides text book perfect images at the highest powers I have used with this telescope (over 400x on some objects during spells of good seeing) about 30 per cent more frequently. In addition, and as previously noted, the instrument is also an excellent lunar and planetary telescope for its size, as well as being a very satisfying deep sky instrument.
My success with double stars is particularly noteworthy, and I wanted to communicate another surprising advantage of using a small aperture Newtonian reflector like this. Anyone reasonably well acquainted with optics will tell you that as the f ratio of the primary mirror decreases, so too will the size of the field that is free of coma (an aberration that is particularly important to consider in high resolution double star work). So, conventional wisdom would say that an f/6 ‘scope will have a larger coma free field than an f/5 instrument and so on. But is this true? Surprisingly, the answer is “not exactly.” Let’s do the math to see what I mean.
The coma free field of a Newtonian system in millimetres, scales directly as the cube of focal ratio. Specifically;
The coma free field = 0.022 x f^3.
So, for my f/5 Newtonian we obtain a coma free field = 0.022 x 5^3 = 2.75mm.
Next, consider how this translates into true field.
True field in radians is given by; coma free field/ focal length.
Thus, expressed in radians, the true coma free field in the 650mm Newtonian will be:
(2.75/650) = 0.0042, and converting to angular degrees gives 0.0042 x 360/2pi = 0.24 degrees.
Consider next a typical high−power eyepiece used in double star divination. A popular choice I like to use is a Parks Gold series 7.5mm, coupled to a 3x Barlow lens, with an AFOV of about 50 degrees. This yields a power of 260 diameters in the 130mm f/5, so the coma free field at this enlargement is: 260 x 0.24 = 62.6 degrees!
This means that there is no coma to worry about across the entire field of view using this particular configuration. In contrast, if I were to use a 2.5mm Nagler or some such, offering an AFOV of 82 degrees, the periphery of the field would have some coma. This observation helps explain why I have done so well using comparatively simple eyepieces!
Curiously, we can do the same calculation for my 8” f/6 Newtonian, which has a focal length of about 1200mm, yielding 0.23 degrees; slightly smaller than offered by the 130mm f/5!
Another consequence of this result is that the coma free field will be proportionally smaller in larger instruments of the same f ratio. Consider my 12” f/5 Newtonian, for example. In comparative terms, a power of 260x will only deliver a coma free field of 26 degrees, which is only about 27 percent of the true field delivered by an ordinary 50 degree AFOV eyepiece.
This agrees with experience; to get the best images at 260x from my 12” f/5 , I have to keep the objects in the centre of the field to derive the best images.
On the Road
I’m a sentimental observer, and I have grown to love my 130mm f/5. I hope to travel further afield with it this coming summer, God willing, when our family will visit the south of Ireland. Here, I’ll hopefully be able to view Jupiter fully 5 degrees higher in the sky than I can at my adopted home here in Scotland. This will be about 8 weeks after it reaches opposition in May, but with the return of truly dark skies for a few hours at this more southerly latitude, I’m hoping that it will make a significant difference to the views. Fingers crossed eh!
For travel, as well as for just general storage of the instrument, I decided it was high time that I invested in a sturdy case for my “Fastnewt 130 F5.” I pulled the trigger earlier today by purchasing a decently priced aluminium flight case, with dimensions of 850 x 295 x 270mm. Here’s the link. I’m hoping this will give me enough room to store the telescope, finderscope, various eyepieces and Barlows, guide and note books etc for hassle free conveyance to our various destinations. As soon as it arrives, I’ll chime in again with news on how I get on with it.
March 9 2018
Well, the package containing my carry case finally arrived today after a delay of a few days owing to the dreadful weather of late. I’m delighted with it. It’s light weight and sturdy, and should fit the instrument as well as other stuff as I had planned. All I need to do now is cut the foam to size and I’m in business!
After supper I set to cut the foam. Here is the final result. I think it looks dapper!
My new case has brought instant domestic dividends! You what mate? It’s got my wife off my case lol. You see, she’s always nagging me about how the Fastnewt 130 F5 clutters up our hallway. It was more or less permanently mounted on my Vixen Porta II from the day I acquired it. Now it has its very own space; a place prepared for it.
I was a bit over ambitious about just how much I expected to pack into the case. My guide and note books didn’t make the cut (excuse the pun lol); they’ll go with the general luggage; no sweat. There’s a silvery (foam) lining though; my home made flexi dew shield just sits ’round the optical tube, and the deep incisions I made to accommodate the finder ‘scope can also carry filters; a variety of kinds; polariser, colour and planetary. Because Jupiter will be low in the sky, colour filters, in particular, will help clean up the images. The polariser will serve me by day, cutting through glare.
March 10 2018
I am lucky enough to have acquired some very nice oculars over the years and have come to appreciate many of them. The f/5 optical system serves up very good images with fairly simple eyepieces, such as orthoscopics, Plossls and even Kellners (on axis). Some of my favourite eyepieces include my 32mm SkyWatcher Plossl, which is my main wide field eyepiece with the Fastnewt F 5, delivering a well corrected 2.5 degree true field; plenty big enough for the vast majority of deep sky objects. For medium power work, I enjoy the widefield options delivered by my Mark III Baader zoom (particularly at the 8 and 10mm settings), but also appreciate the more contrasty views served up by 6mm Baader orthoscopic as well as a 7.5mm Parks Gold eyepiece and a 10mm Orion Explorer II Kellner. For high power work, I am fully sated by amplifying these eyepieces using either a 2.25x or 3x Barlow.
The extra aperture afforded by the 130mm parabolic primary mirror takes grab ‘n’ go to a whole new level of experience; and that’s not a hyperbola! Five years ago, I may have been cajoled by articles like this, but having owned and used many small aperture refractors (including a Zenithstar 66 SD doublet & triplet, SkyWatcher ED 80, Takahashi FS 60C, TeleVue 76, Tele Vue Genesis (original f/5 fluorite model), Tele Vue 102, Skywatcher ED100, and even long (but still small apertured) Skylight 4″ f/15 and Moonraker 80mm f/15 achromats), to name a sizeable fraction, they were all vanities of sorts.
Newtonians alerted me to this rose−tinted, but ultimately delusional state. I just sensed something was wrong. In contrast, I discovered an honesty in the Newtonian reflector that simply wasn’t there in other telescopes. You do get what you pay for, that’s for sure. But from a purely visual perspective, you get a whole lot more with the Newtonian! I was seeing more details, capturing more light and extending my target base with the 130mm reflector. Denying or dismissing these facts is a vanity!
Faster, cheaper, better!
As stated in previous blogs, the Fastnewt 130 F5 is truly fast in other regards; most especially cool down. Indeed, (and unlike the Fastmax 180 F4.5) its open tube configuration and small mirrors ensure rapid acclimation without the need for fans and other active cooling systems. The provision of Bob’s Knobs on both the primary and secondary mirrors means I can fine tune collimation in seconds when the most exacting optical ‘syncing’ is called for.
As you may know, I am especially passionate about observing double stars. And the 130 F/5 Newtonian has turned out to be a fine instrument for teasing out pairs down to the theoretical limit imposed by its aperture. I enjoy watching such pairs and triplets moving through the field at ultra high powers. Here are a few sketches of systems I’ve just recently visited.
The first drawing shows Iota Leonis, resolved using a 6mm Baader orthoscopic coupled to a Meade 3x Barlow delivering 318 diameters. The second set of drawings are of Mu Bootis(Alkalurops), a most delicate triple system, and Delta Geminorum (Wasat). These were imaged using my 7.5mm Parks Gold and 10mm Kellner, respectively, coupled to the same 3x Barlow. Over the last couple of years, I’ve managed a whole suite of difficult pairs with this telescope and it continues to go from strength to strength.
March 12 2018
I gave up on equatorial mounts after I quit doing CCD imaging and film astrophotography. I felt liberated in being able to find things using muscle power, eye and brain. No wires, battery packs, heavy counterweights and finicky cameras to think about. There is great virtue in such simplicity; it brings peace and joy in equal measure.
The Fastnewt 130 F5 sits pretty astride the Vixen Porta II mount. I have owned this piece of kit for about six years now and it has carried all manner of small and medium sized telescopes. It is an excellent match for this instrument and is gifted with slow motion controls. Over the years I’ve trained myself to use these controls to follow targets, even at very high powers. For example, during a recent excursion, I was following a double star target at 406x fairly comfortably While looking through the telescope, I grasp both controls and make very gentle adjustments so as to keep the object centred, even in a very narrow field!
This kind of work is equally amenable to sitting or standing modes. And it’s made possible by virtue of the close proximity of the focuser to both the azimuth and altitude controls. Such a configuration confers maximum stability for exacting, high power work.
Mechanically it’s been sound; strong, light−weight and modular, breaking down into easily stored and transportable components. It works in all seasons, and here in Scotland you really can experience all four in one day! But like any ole jenny, the Porta can have its moments. The plastic knobs of the slow motion controls have a habit of coming loose…..sometimes during very critical observing moments. That’s why I always check ’em over before beginning a vigil. Having said that, I am now looking into ways of improving these also. That said, there is such a thing as overdoing it; check out what this bloke did with his Porta lol.
The clever design of the Porta enables it to used in spotting ‘scope mode during daylight. I am enjoying my 10mm erecting eyepiece, which delivers a correctly orientated view at 65x with a 2mm exit pupil, but I’m equally enthralled at seeing the details of nature at super high powers, thanks to its superior light gathering power and resolution over a conventional spotter. When you’re using 150x and upwards, it matters little whether an object is upside down or rightside up. This is possible because my climate here does not (as a general rule) endure large diurnal temperature variations and that leads to stable air masses, allowing me to capture wonderful details of nature over distances up to a few hundred yards.
March 14 2018
Stephen Hawking has gone to meet his Maker. The poor man suffered for so long, trapped in the prison of his wheelchair. May the Lord have mercy on his soul.
Once upon a time, I entertained a dream to have my very own observatory, but now that I’ve matured as an observer, I have little desire to create one. I’ll always have a mancave of sorts though, but not an observatory. My modus operandi is open air observing, using telescopes I can manage; so that confines me to instruments of 12 inches or smaller. I own all the telescopes I could possibly wish for in life. As I get older, I will likely use smaller telescopes more frequently, and the ultraportable Fastnewt 130 F5 will thus remain an important instrument in my arsenal. Right now, I’m in the prime of my life and can enjoy my 8 and 12 inch telescopes just as much as the 130. As good as the latter telescope is, there are many things in the firmament that are beyond its reach. There is a time and a place for them all.
Acquiring a solid tube for the optics at the heart of the 130mm f/5 has proven to be a good move. I can remove the instrument from its case and mount it with little in the way of collimation adjustment. Certainly, it is a great step up from the original Skywatcher Heritage 130P (open tube) in this regard, but with very little additional mass.
I am very much enjoying using the telescope as my new spotting ‘scope for nature studies. It’s a pure joy to watch the noisy corbies that make their nests in the conifer trees near my house. The telescope produces beautiful, sharp images and even on a dull day like today its generous light gathering power makes such observations very worthwhile. You don’t miss a trick with a telescope like this! Sometimes they look straight at you and you can see the light in their eyes. I sometimes wonder whether they see me better than I see them!
The telescope also allows me to monitor the buds on the trees as Spring progresses. Horsechestnuts are among the first to bring forth their leaves ’round these parts. I can tell you that they’re well on their way, but will need a few warm, sunny days before we will see their full glory, draped in harlequin green.
Nature waits for no man.
I understand that some folk are reluctant to use Newtonians in terrestrial mode because the tube is open to the elements. But this too is a vanity. As I’ve described in a previous blog, Newtonian optics are easy to clean, and any dust that falls inside the telescope can be easily removed. I find cleaning the optics once or twice a year is plenty often enough. It’s not afraid of pollen, or dust, moisture or even an adventurous spider! Whatever makes its home on the optics or in the tube can be removed; no sweat.
March 15 2018
Well, the weather has taken another down turn. Hoping for some more clear skies, but no go, unfortunately. I do however have a wee treat for you; I found this review of a close kin of my 130mm Newtonian; enter the Vixen R130SF. This lady provided a good review of this telescope on a Porta II mount no less. The reader will note that no mods of any kind were made in this report, but I think you’ll agree that she ticks many of the boxes I have covered in my own exploration of this telescope.
March 17 2018
Lá ‘le Pádraig sona daoibh!
The Fastnewt 130 F5 has been tested in all weathers. I’ve enjoyed it at temperatures as low as minus 10C and as high as +25C. In general, the telescope performs better in milder weather but I have encountered textbook perfect images on many freezing cold nights.
When the weather is settled, I usually bring the instrument out from a warm, indoor environment and let it cool off to ambient temperature. Low powers can be enjoyed pretty much immediately, whereas medium power views (up to 100x say) are fine to explore after about 10 minutes. But for the most critical observations at very high powers, I usually give it at least 30 minutes.
In unsettled spells, such as those we are experiencing just now, I leave the telescope in a dry, unheated outhouse, so that it can be deployed at a moment’s notice. This is a strategy that works well for all kinds of telescopes. That way, I can enjoy the telescopic heavens even during the briefest of clear spells.
Like any other activity, preparation will always be your friend.
Time: 22:10 UT
The great French scientist, Louis Pasteur, was fond of saying, “chance favours the prepared mind.” I think this is true. Though the heavens declare that Spring is here; the weather says otherwise. Indeed, this is the coldest St. Patrick’s Day I can remember in many years. A biting easterly wind brought in more snow and temperatures struggled to rise above zero today. But I did get a short half hour spell this evening with the telescope between snow showers, and to my sheer delight I discovered that conditions were excellent. Northerly winds almost invariably bring turbulent air in this location, and quite often, those from the east are little better. But there are always exceptions. Shortly after 9 pm local time, I was able to visit a few of my favourite double stars; Polaris A & B, Theta Aurigae and Iota Cassiopeiae; old friends from the depths of space. Indeed the images served up were so good when the wind died down, I was able to make a recording of what the 130mm f/5 showed me at 183x. A telescope of this size will show a very delicate 1st Fraunhofer diffraction ring ’round Polaris A, a magnitude 2.0 star, together with its tiny spark of a companion. A similar looking system; Theta Aurigae, is significantly fainter; just +2.6. In contrast to brighter Polaris though, the first diffraction ring is much more subdued. It follows that fainter systems will show even less of their diffractive effects; a good thing when it comes to observing these beautiful, delicate wonders of nature.
Below is a pair of drawings I made to show these differences.
By 9:45 pm, the situation had deteriorated. The clear sky was gone and another snow shower had begun.
Still, it was good to get out, if only for a wee while!
To be continued………..