mikeDnight

I like it too! What is it you don't like?

All telescopes, refractors and reflectors suffer from diffraction effects caused by anything in the light path. With a refractor the diffraction is caused by the edge of the lens cell. In a system with a secondary obstruction, both the edge of the mirror and the edge of the secondary produce diffraction paterns, hence the brighter first diffraction ring in reflectors and Cat's. I see diffraction spikes every time I use a Newtonian. It's simply the nature of the beast. A single vein spider will produce a spike that crosses the full field, and a double vein will create double the diffraction. A three vein will create six spikes, and a four vein, although appearing to produce four spikes, actually produces 8, they simply overlap. It's the edge of an object that produces the diffraction pattern, so thin vein spiders still produce the same diffraction effects, though the fractionally reduced distance between the diffraction effect may be less obvious. Even curved veins don't eradicate or reduce the effect, they just smear it. The glare around a planet can be produced by diffraction, but also by oil on the eye lens of the eyepiece from eyelashes, especially when there is minimal eye relief. Most often though it can be the result of mist or ice particles in the atmosphere.

Just a side note that might be helpful. When it comes to all my finished sketches, not including the rough eyepiece sketches, I always use a fixative spray to prevent smudging. That way the drawings should be safe for generations, bar for flood damage, fire or meteorite impact.

I'll often use pencil to position the stars, but then use fine tipped drawing pens of different sizes to cover the pencil marks. This enables me to then use graphite pencil to add nebulosity if needed, without smudging the stars. After that I'll usually image the sketch and turn it to a negative on my tablet, giving a life-like impression of the view through the eyepiece. And sometimes when drawing an interesting double star, I'll use watercolour pencil with a dark graphite background to give an eyepiece impression.

Thats very kind of you Stu, I'll pm you my bank details. I'm hoping to have an adventure to the Astronomy Show at Kettering in March, so your kind donation will be put to good use.

I bought my binoviewer in 2008 for £99 and have used it ever since. It's branded Revelation, but I'm pretty sure that its a generic binoviewer sold by many reputable companies. The eyepieces I used in the image were 16.8mm Kson Orthoscopics at around £40 each. They are excellent in a binoviewer, giving great eye relief and truly sharp detail. Using longer focal length eyepieces works really well in a binoviewer if a 2X barlow is used between the telescope and the binoviewer, and rather than 2X, the amplification factor becomes approximately 4X. In your case the 16.8mm's would give you around 108X, which is glorious on the moon. You can increase the power by changing to a 2.5X or 3X barlow while using the same eyepieces.

It depends on the magnification really. The Vixen HR's are great when I need very a high mag and the seeing allows, but I mainly use them for double stars. With the binoviewer im limited to 320X if I want to keep things comfortable, and then I'd only go so high with the Moon. I do feel that binoviewers somehow ease turbulence. The HR's can give me 500X, or 1000X with a barlow on double stars. I think I'd look like Marty Feldman if I tried such high power with my binoviewer.

It may sound strange that a cheap binoviewer with a 2x Barlow attached to its nose, and a couple of good plossl's or orthoscopics, could significantly improve the already great view through a high end eyepiece, but its true. When you think about it, its quite logical really, as you're using both retinas and therefore twice the receptor sensitivity. For the Moon and planets you'll not regret it, even with a small aperture scope. The Equinox 80ED below was a breathtakingly good lunar and planetary scope when used with a cheap binoviewer.

Exactly what Louis said!!

I found this fairly objective advice from an old Unitron advert shown in Sky & Telescope back in the 1950's that might help.

It looks fantastic to me Steve.

Ever since I started out in this hobby, a long lime ago now, I've tried to make sketches of the views I see through the eyepiece. One thing that always frightened me was the Moon as it was so complex. Where to start and where to finish a lunar sketch is difficult, as is how much detail to include in the sketch. To help myself overcome these problems, I decided to make simple sketches of crater floors and the floors of walled plane's. While sketching the floor of a crater named Werner using my 100mm refractor, I noticed what looked like a fine rille, so I drew it. The next time I came to Werner, I noticed another, and another, which I drew, but found that in conversation with more experienced selenographers, these rilles did not exist. They were not recorded on the maps I had, and images also failed to hint at them. Observing Werner through my 200mm Newtonian and also through a 10 Dob, revealed no hint of the rilles, yet each time I aimed my 100mm refractor at Werner, there they were, as fine as the lightest razor cut and visible even in full Sun. Was I imagining these rilles, or was I simply nuts? I can hear you now shouting "Yes"! Eventually I recieved an e-mail from a BAA member who had seen my sketches and decided to capture Werner. He sent me his images, and low and behold there were my fine little rilles. Just recently I've acquired a new Atlas, The Duplex Moon Atlas, which is highly detailed, and on map 18 there is Werner and with careful study there also are my little rilles. Seeing these rilles in the atlas will be a challenge in itself. They look like collapsed lava tubes and are far from obvious. So why are these rilles easier to see in a 4" refractor than in the Atlas, and why do the larger aperture reflectors not even hint at them? Then if a small refractor reveals detail not seen in scopes with greater theoretical resolution and light crasp, how can it be said that a large Dobsonian will always show more than a good refractor? My personal feeling is that with greater light grasp comes a reduction in fine definition with regard to already bright objects such as the Moon, and so the resolution gain which should make it easier to detect fine linear detail is hindered by the increase in light gathering. I've noticed a similar effect with regard the the rings of Saturn, where a superb view of the planet was presented through an 8" Dob, yet a 120ED standing alongside the 8" gave a much more intricate view of the ring detail. So the power of a refractor lies in its sharp, high contrast, high definition performance and not in its resolution and light gathering, and in this they can deliver beyond their presumed capabilities; and so Bigger Is Not Always Better.

I know it's a big decision, but when you think that many will pay what I consider a real fortune, just for an annual season ticket to home games, or for annual membership to a golf club; the price of a nice refractor pales into insignificance, especially when you can have it for life. You only pay once, unless you get bitten by the apo bug.

You're right Stu, but I did say "fluorite glass" and not fluorite crystal. I can't remember the percentages but I'm pretty sure FPL53 is composed of more than 90% fluorite. It doesn't have quite the same properties as the laboratory grown fluorite crystal though. I suppose there's a price to pay either way.

The FPL53 is fluorite glass, which when combined with the equally important mating element produces virtually no chromatic aberration. This means that pretty much all the light captured by the telescope will be concentrated in the Airy disc, leading to tight stars and bright images, even when viewing DSO's. What they lack in light grasp and resolution, refractors often make up for in fine definition and high contrast. An FPL53 scope should have a noticable edge over the FPL51, and on a different level of performance to the 130P-DS.

Very nice!

Yet another lunar atlas. 😁

Wow, that's a blast from the past. It looks like all it needs is a good prying clean and a polish with brasso. It's a very nice find!

Sometimes it's good to see a size comparison to help us realize what we are getting ourselves into. Here are two great refractors, a 5" F8.1 and a 4" F7.4. To give you an idea of scale, I'm 6ft tall. My FS128. Definitely a two handed job to carry just the tube assembly. Here with my FC100DC. The whole set-up, scope, mount & tripod can be carried with one arm.

If it makes you feel any better, you would only have spent it on something else of much less importance, such as fuel bills or council tax.

You'd better believe it! And just in case you want to say hello, here's who to look out for. As Paul said, he's "the handsome one".

Fantastic sketches Phil. I enjoyed looking at your observations so much that my wife asked me why I had a beaming smile on my face. I didn't realise I was smiling until she mentioned it. It's a real pleasure for me to see the observational sketches of others. Many thanks!!!

Lovely scopes Roy! I have to confess that I have a soft spot for the R, which I think stands for Rough, as it had a bit of a thistle finish. There was quite a buzz at the time because of the excellent Russian optics and the insanely low price, bringing a good 4" refractor within the grasp of many more people. Sky & Telescope liked them too, while at the same time having a downer on the Chinese achromatic refractors. Personally I liked the Chinese scopes too, and bought a lovely Helios 120 achromat in 1999 which came with three really nice plossl's, Barlow and diagonal, and a very nice EQ mount and tripod. All that for only £245. Happy days!

I went to the first one pre Covid and it was superb. I missed last year but looking forward to being there this year. ☺

I learned what sharp to the edge meant Dave, when at the age of 12, I decided to have a go with my dad's single blade Wilkinson Sword razer. All went well as I shaved the soap from my cheeks in a downward motion, but it was the single sideways stroke across my top lip and the lather suddenly turning red that made me think eek! That's got a sharp edge!!.