John
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Posts posted by John
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Hi David,
It should not make much difference but when buying and selling used but expensive eyepieces, I've found that having the original box, internal packaging, paperwork and original dust caps does make a difference to what you can actually get in practice.
Obviously optical and cosmetic condition is of more importance though.
As to how much of a difference in the price, it's difficult to say precisely. In the case of Ethos and similar eyepieces, the market is not saturated with them so, if it's one that someone is particularly looking for, the impact on price might be small.
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Looks like you got Uranus there. It does not vary much in apparant size - it's always a long, long way away !
There are 4 Uranian moons that it is possible, though challenging, to see with amateur telescopes. I've managed 2 of them with my 12 inch dobsonian - Titania and Oberon.
Neptunes disk is smaller again but it's largest moon, Triton, is visible with moderate aperture telescopes at high magnfications. Triton is a little easier to see than the brightest Uranian moons.
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37 minutes ago, Piero said:
Yes, but my real challenge is to catch the huge nebula in M33: NGC 604 (my user image)! A real monster compared to M42. Hope to see it one day - with a filter of course.
You don't need a filter for NGC 604. I can see it with my ED120 without a filter. It's away from the core of the galaxy that is visible visually and next to a prominent foreground star:
https://www.skyandtelescope.com/observing/triple-treasure-in-triangulums-pinwheel110320150311/
Nice report of your haul - thanks for posting it
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1 hour ago, markse68 said:
....Nice to think of us all out there separately looking up- connected in some way.....
Yep - all slightly nuts, but in a good way !
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Interesting. Is the white stuff PTFE I wonder ?
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1 hour ago, jock1958 said:
Thought I was in for a good night but high level wispy cloud interrupted viewing constantly.
Started off with Jupiter which was ok at best, Saturn was crisp and detailed before cloud came over.
Managed a glimpse of the eastern side of the Veil with my OIII filter & 24mm pan, thinking I will have to invest in a lower power eyepiece (35mm pan?) to see the whole nebula instead of bite sized chunks.
M13 was an absolute delight with my 3-6 zoom, like opening a box of jewels.
Finished off with Zeta Herculis, not convinced I managed to split it at x225 it seems like a wobbling miss shaped airy disc on one side? 🤔 apologies for poor description!
I had that wispy cloud issue as well. Dodging those showed some nice dark skies though.
Your description of a nearly split zeta hercules sounds right.
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Great report - I agree that the Skyliner 200Ps are super and versatile scopes.
An adjustable ironing chair can make a decent observing seat. Often found in charity shops for low prices
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Nice report Mark - proves that the ST80 can turn it's hand to all sorts of things
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13 minutes ago, Stu said:
Saturn looking as good as I've seen it this apparition. Cassini etched black against the rings, A, B and C rings clear and lovely surface banding on the planet. A number of moons around too, need to check which ones in a bit.
Saturn the highlight for me too so far. 200x (Ethos 6mm) is so crisp and sharp. 5 moons and I think I've glimpsed Enceladus a couple of times but it's close to the N side of the planet so it's a little doused in glare.
Got some thin, stringy cloud drifting about just now around the S horizon which is mildly annoying.
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7 minutes ago, Marvin Jenkins said:
What does that thing weigh? I recently borrowed a William Optics 66mm frac (baby) to compare against my 130 newt. Supprised by how heavy it was. Nice bit of kit thought, very well made.
9.5kg with tube rings, finder and diagonal. 3 lens elements weigh a bit but the scope is quite well balanced.
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Shorts, t-shirt and a big refractor
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21 minutes ago, Buzzard75 said:
Hopefully you folks in foreign lands can see this video. Take a look at the eyepiece being used at 3:16 in the video.
Nice movie and I did see the Apollo 11 eyepiece, briefly. I wonder if the young man is connected with the Tele Vue company in any way ?
The reactions were great - thats why I love doing outreach
Mind you, they react like that when more ordinary eyepieces being used as well !
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19 minutes ago, JamesF said:
Hmmm. KStars is showing it as between Aries and Taurus (and I've just updated the comet data), and rather close to the Moon. Perhaps I'll see if Stellarium says anything different.
James
This is what The Sky Live shows:
https://theskylive.com/where-is-168p
Assuming we are talking about the same comet 168p !
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3 minutes ago, Galen Gilmore said:
Correct me if I am wrong, but a small dot of dust on the photo like that would have to be directly on the sensor of the camera. A spot on the lens/mirror probably wouldn't even be visible because of the long focal lengths involved in telescopes.
I agree - most likely debris or dust on the sensor.
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I might pop my 12 inch dob out this evening to look for this one. It's between Perseus and Auriga from the charts that I've seen. Not expecting anything bright though - maybe mag 11ish but the Sky Live website is saying mag 13.5 ???
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9 minutes ago, Piero said:
John, the formula that you referred to is the linear coma free region. That is 0.022*F^3 where F is the F-ratio. As you said, in an F4 that is ~1.4mm, in a F5.3 that is ~3.3mm. This is evaluated with the eyepiece field stop.
I find that formula rather difficult to use though as coma does not increase with magnification. While magnifying, the FOV decreases (=>less coma), but the Airy disk increases (=>more coma), so coma remains the same basically. I tend to prefer a formula that describes the angular coma free region, instead. There are a few, but an easy one to remember is 1*F^2, which is 16 deg for F4, 25 deg for F5, 36 deg for F6, 49 deg for F7, etc. Basically, for an F7 telescope, the coma free region is like a Plossl eyepiece. This is independent of magnification.
For collimating primary and focuser axial alignments, the numbers in my previous post are about error tolerances. Roughly speaking how much the collimation error can be large before we lose the "sweet spot" completely (=miscollimated telescope). The formulas are 0.005 * F^3 for the primary mirror axial alignment, and 0.03 * D for the focuser axial alignment (without parrcor). A coma corrector reduces the tolerance to 0.005 * D. These are evaluated with a collimator.
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As you said, outside the coma free region (of a collimated telescope), the telescope still works and can provide good views. The best ones are on-axis though.
Thanks Piero - I'm afraid that formulae and maths leave me rather cold but I'm sure this is all excellent stuff
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The Travelscope 70 is an F/5.8 achromat refractor so it's mainly designed for low to medium power observing. Using short focal length eyepieces will give more magnification but the view is unlikely to be crisp and clear over around 60x-70x and the chromatic aberration that the scope produces (in common with other scopes of similar spec) will become more and more apparent.
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The info that I've seen suggests the collimation "sweet spot" of an F/4 mirror is 1.4mm compared to 3mm for an F/5.3. Outside of this the scope still works of course but it's not giving diffraction limited performance, apparently.
An F/8 mirror has a wacking great 11mm sweet spot !
Edit: Piero's post contains much more detail !
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I also agree with vlaiv and Louis D - my 12 inch dob is as quick or quicker to set up than my refractors, all of which are also used on alt-azimuth mounts.
Perhaps you could expand a bit on what you find awkward with your current 8 inch dobsonian to ensure that any suggestions steer clear of the issues that trouble you.
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I didn't realise that your scope was F/4. It needs somewhat more precise collimation than my F/5.3. The collimation "sweet spot" will be a lot smaller.
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I put a Moonlite on my Orion Optics 12" F/5.3. The original was a single speed Chinese unit probably made by GSO. It didn't sag but I felt that the dual speed was desirable with this scope. I'm very pleased with the Moonlite. I've used both the spacers in the Moonlite fitting kit. I found that the 10 inch one fitted the Orion Optics tube - it's slimmer than the Chinese 12 inch dobs use.
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Thats great to hear Gerry but why should it surprise you ?
Even your average skies are pretty dark and 24 inches is a whopping increase in terms of light gathering area over 15 inches. Similar to the difference between my 12 inch and a 20 inch and I've been left in no doubt about the additional capabilities of that additional 8 inches of aperture when I've had the chance to observe with a 20
It's good for kit to make you pleasantly surprised though - much better than the other way around !
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Its interesting that the Skytee II load capacity is listed as lower than the Ercole but nevertheless, having compared the way that these mounts handle my 130mm F/9.2 triplet, I'm convinced that the Skytee II is steadier at higher magnifications and any vibrations that happen dampen a little faster. Thats not the result I expected by the way, but there it is.
I wonder if FLOs figure for the Skytee II is influenced by the rather poor stock dovetail clamps fitted to the mount ?. My Skytee II has an ADM clamp fitted which is much, much better than the stock item and also I use a Berlebach Uni 28 tripod which is very stable. I do like the Ercole though which is why I also have one of those !.
It is not just the tube weight that creates the challenge for the mount of course, the length of the tube, in the case of these large refractors, is a major contributary factor as well.
It would be great if the Discmounts were more readily available here:
The DM6 in particular seems to be very popular in the USA for use with heavy and relatively long refractors.
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Skywatcher do one that is 1.85kg. It's normally sold paired with a 3.4kg one for the EQ3-2 mount but it will fit on EQ5 and HEQ5 mount C/W bars.
Vixen do a 1kg weight for their AP, GP or SX mounts that I think will fit the 20mm EQ5 C/W bar.
An August clear sky beckons ......
in Observing - Discussion
Posted
The widest I've got with my Tak 100 DL is 3.1 degrees using a 40mm 70 degree eyepiece in the 2 inch fitting which is not quite wide enough to squeeze in the E & W segements of the Veil nebula. I rarely use my DL with 2 inch eyepieces though probably because, as Stu says, my Vixen 102 ED F/6.5 is a more useful wide field scope.