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  #21  
Old 10-10-2018, 08:34 AM
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mental4astro (Alexander)
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Stephen, to finish answering your question about a numerical value that quantifies the ultimate quality of your optics, this can be approximated by visual techniques, but it is only possible following a lot of experience and knowing how to conduct bench tests, the various tests required and how to interpret the information these tests provide.

An example of this is the testing carried out by a Russian optical lab. They have the necessary equipment to thoroughly investigate a set of optics that access the different values and provide the ultimate quality value that is provided in a series of values, such as Strehl, RMS, P-V, and a few others. These all tell slightly different things about the optics, though not contradictory. Of these different values, the Strehl rating is the one that's most significant as it is the overall quality rating, as a ratio where 1.0 is "perfection", exceptional quality would be something like 0.974, mediocre quality is 0.767.

I'll chase up a link to this Russian lab.

Alex.
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  #22  
Old 10-10-2018, 10:51 AM
Wavytone (Nick)
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http://fidgor.ru/Observers/test.html

Back up your PC and make sure it has malware defences BEFORE you try that link as it is known to dish up some real nasty stuff.
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  #23  
Old 10-10-2018, 11:18 AM
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Quote:
Originally Posted by mental4astro View Post
your 60mm refractor
Alex.
What about the really small table top reflectors, like the 76mm reflector (Orion FunScope 76mm, Celestron FirstScope, Sky-Watcher Heritage 3 inch, Saxon Mini Dobsonian, ect) ?
Such supermarket/department store priced 76mm reflectors have even been sold by Aldi.
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  #24  
Old 10-10-2018, 12:01 PM
Saturnine (Jeff)
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Wavy, why provide a link that has known malware issues !!!

This thread is something that I'm sure that would be useful to a lot of amateurs, old and new, about how telescopes perform and what we are actually seeing through them and how to interpret what we are seeing. When it comes to fine lunar features it is obvious that they exceed the supposed resolution of the telescope in use, in good seeing of course.
Have had a few memorable nights where I've pushed the old Jaegers 4" f9 to 75X per/ inch on the planets and moon and double stars. My NG 5" triplet does perform better than the old achro by are fair margin even taking the extra aperture into account.

Alex and yourself have provided a great resource with your knowledge and insights, thank you.
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  #25  
Old 10-10-2018, 01:39 PM
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Quote:
Originally Posted by JeniSkunk View Post
What about the really small table top reflectors, like the 76mm reflector (Orion FunScope 76mm, Celestron FirstScope, Sky-Watcher Heritage 3 inch, Saxon Mini Dobsonian, ect) ?
Such supermarket/department store priced 76mm reflectors have even been sold by Aldi.
Jenifur,

Now we head into the Dark Side of astro - the cheap.

What Nick and I have been discussing so far has been in relation to GOOD astro gear. To be able to push a scope to its theoretical limits, it needs to be a quality instrument. Sadly, the majority of what newcomers to astro buy is not good.

Before I go into tearing shreds off any item, I need to make something very clear, and something that is VERY CLOSE TO BOTH NICK AND MINE HEARTS:

"The best telescope is the one that gets used. If all you can afford is an inexpensive item, and you use it all the time, then it is just as good as the finest, most exquisite instruments humans have ever devised! And Damned be anyone who dismisses this."

So, knowing that cheap supermarket scopes are poor, we can discuss the Good, the Bad and the Ugly.

To make a scope cheap, then cheap and crude manufacturing techniques need to be used. And in turn, cheap scopes appeal to those people who unfortunately on a whole don't understand what they are buying. There's no right or wrong here, just a merge of two different forces - ignorance and market.

The requirements needed of an astronomical telescope are very stringent, and to produce such a high standard of instrument needs high quality materials and highly controlled manufacturing processes. And this costs money. Don't make the mistake of blaming China for cheap and nasty stuff. The Chinese are also very capable of making outrageously fine equipment, and today can rival and even surpass many traditional manufacturing powerhouses! Don't forget, some high profile Japanese and American brands have their entire product line now manufactured in China, and no one blinks an eye.

Those supermarket telescopes are not made using the optimal processes for a good astro telescope. They can't. These cheap scopes are entirely made to a price, and quality is only skin deep. Those 76mm reflectors are made with a poor quality spherical mirror, not a parabolic one. The eyepieces use plastic lenses, or uncoated glass lenses. This means that they are very poor at high magnification. These cheap scopes are best for low power wide field viewing, and they can deliver a very nice low power image. But they do not deliver a good high power image at all. They can't, and many people end up very disappointed with astronomy within 5 minutes and take it no further. And it's not just the figure of the primary mirror, but the cell it sits in, the focuser, the secondary mirror and its holder and the stalk that holds it. These can be altered to an extent to improve the little scopes performance, but these mods should not be something that the end consumer should be responsible for. These scopes are made to a price after all.

I have owned 3 of the Celestron FirstScope table top reflectors. All have been terrible at high power. I suspected this when I purchased my first, but I bought it as a had a particular use in mind with it, as big aperture finder scope, which meant I was exploiting its greatest strength - low power. And these scopes proved to be great for this. I had one mounted on my 17.5" dob!

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Would I recommend these cheap little scopes to anyone? It depends. These would not be my first or second suggestion, but for better or worse they do fill a niche. As a first telescope, they may work out to be a wonderful introduction to astronomy for a little kids - my own children when little enjoyed this little FirstScope. For older, more discerning kids and for adults, not a chance.

Last edited by mental4astro; 10-10-2018 at 01:58 PM.
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  #26  
Old 10-10-2018, 01:58 PM
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Quote:
Originally Posted by mental4astro View Post
Jenifur,

Now we head into the Dark Side of astro - the cheap.
Thank you very much for the reply, Alex.


In my case, getting the 130P reflector, price was important, but the physical size of the telescope mattered more due to where it would be set up.
Block of flats with small patio, and not much front to back depth. You can get an idea of how shallow a depth, from my avatar pic.
There's no way I could use a refractor here.
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  #27  
Old 10-10-2018, 02:06 PM
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Jen (I hope you don't mind me calling you Jen), I have only heard good things about that scope of yours. It is a clever design! Despite its price, you thought about it more than a lot of people to make sure you got something that suited your situation. That's blooming brilliant!

Don't get me wrong, some inexpensive scopes are real gems. Your's is one of those gems. You didn't buy that scope at Aldi. There's a few things you can do improve your experience with this little scope too. I'd be happy to PM you about some of these as this goes beyond the scope of this thread. Drop me a PM if you like

Alex.
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  #28  
Old 10-10-2018, 02:43 PM
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For buying a scope, the display of scopes in the window of my local Australian Geographic, caught my attention back in March. I had cash to spare and I could have all too easily bought a scope right there and then. Thankfully, I didn't.
At home, I started looking up info on beginner scopes, thinking about where I'd be using the scope, it's portability, storage size, the stuff that really matters when you're wanting to use a scope, and you live in a block of flats which only has stairs. I was thorough in doing the homework before heading to my nearest specialist astronomy shop here in Brisbane, Astro Anarchy, to 'kick tyres'. I wasn't going to spend a cent till I could actually see the scope, to be certain if it'd fit. I was lucky when I bought mine, as at the time it was on sale for about 40% off its usual RRP, so not expensive to start with and then sale price to make things even better.
In terms of what I've bought since getting the scope, that I use pretty well every viewing session, it's listed in my sig.
And that brings things right back to topic, on a point you raised. Eyepieces.
The stock ones with my scope would basically be a good way to dissuade anyone from astronomy. The 25mm has a nice wide field of view, but not enough magnification. The 10mm has better magnification, and bad chromatic aberration.
That meant getting better eyepieces was a must.
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  #29  
Old 11-10-2018, 06:30 AM
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Should this very useful Beginners thread be stickied?
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  #30  
Old 11-10-2018, 07:07 AM
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Jen, changing the stickies situation is one of the many things on the Administrator's list of "things to do"...

Ok, I've been asked to supply a few more challenges, so here goes

CHALLENGE NO. 3

Martian Clouds!
With the Martian global dust storm finally showing signs of breaking, it gives us an opportunity to chase down not just the polar caps (YES! Snow on another planet! And you can see it from here on Earth) which is easy, but the real teaser that is Martian clouds!

Steady seeing is a must. And another thing that helps is an #80A colour filter, or a #8 filter as it helps to tone down the glare of the red surface and allows the white clouds to show up more easily. But be patient! These clouds are not as dense as our Terrestrial ones. They are also best seen close to the limb of the disk (outer edge) as this is where they will be most dense in line-of-sight.

NOTE ABOUT COLOUR FILTERS:

Using colour filters with the planets will not necessarily make those features you seek stand out more obviously or how you expect them! Many features are very difficult to spot, and may appear in a way opposite to how you might expect. So be patient, understand what you are trying to see and give yourself time to interpret the image you are seeing.

Alex.
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  #31  
Old 11-10-2018, 07:23 AM
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Quote:
Originally Posted by mental4astro View Post
Jen, changing the stickies situation is one of the many things on the Administrator's list of "things to do"...
Thanks Alex, I didn't know of the state of play for the to-do list.

Quote:
Ok, I've been asked to supply a few more challenges, so here goes
Right now, Brisbane is stuck with ugly stormy weather. Getting a long enough break to see anything is a challenge.

Quote:
CHALLENGE NO. 3

Martian Clouds!
With the Martian global dust storm finally showing signs of breaking, it gives us an opportunity to chase down not just the polar caps (YES! Snow on another planet! And you can see it from here on Earth) which is easy, but the real teaser that is Martian clouds!

Steady seeing is a must. And another thing that helps is an #80A colour filter, or a #8 filter as it helps to tone down the glare of the red surface and allows the white clouds to show up more easily. But be patient! These clouds are not as dense as our Terrestrial ones. They are also best seen close to the limb of the disk (outer edge) as this is where they will be most dense in line-of-sight.
This challenge is something I've wanted to be able to observe since getting my scope.
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  #32  
Old 12-10-2018, 07:27 PM
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CHALLENGE NO. 4

A cluster of volcanoes!

From just finding out that there are volcanoes on the Moon, this challenge is to spot one of the easiest clusters of lunar volcanoes, the Hortensius Omega cluster, also known as the Hortensius Domes.

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NASA photo

This is not so much of a "can you see this feature" sort of challenge, but one of teaching yourself how to distinguish run-of-the-mill-mountains vs shield volcanoes on the lunar surface. But note the individual domes are small, the largest about 12km in diameter, so it will be a challenge for scopes under 3" in aperture.

Unless you knew what to look for, if you happened to come across this cluster of volcanoes you would just dismiss them as just a cluster of mountains. Instead, there's a couple of distinguishing features that go to help identify these as shield volcanoes.

Because these are not particularly high features, timing of the lunar phase is important, two days after first quarter or a day or two after last quarter.

What is most remarkable about this region is that there are literally dozens of volcanic domes that dot the entire area. The above NASA photo shows how wide spread they are. Making it easier to identify this area is it lies due west of Copernicus.

Happy hunting!

Alex.
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  #33  
Old 12-10-2018, 09:27 PM
morls (Stephen)
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Great stuff, thanks Alex.

I've found some great moon maps, published by the US Geological Survey:

https://pubs.er.usgs.gov/publication/sim3316

Stephen
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  #34  
Old 20-10-2018, 08:09 AM
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You've excelled again, Alex! Such helpful info...

Just out of interest, Mars and Neptune will be within one degree of each other on December 7...will make Neptune easy to find 😁 Alex, do you have any observing tips for finding Neptune - it is still a real challenge 🤔
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  #35  
Old 20-10-2018, 01:48 PM
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Thanks Stephen and Shaun

Stephen, great link mate!

Shaun, Neptune and Uranus are not difficult to spot. Both can be easily found using binos, even under urban skies. From a dark site, Uranus is also visible to the naked eye, but it does also require a transparent sky. I've seen Uranus many times where I go in the Blue Mountains west of Sydney, and there were also fainter stars visible than Uranus.

What distinguishes both Neptune and Uranus is their distinct intense colour. Neptune an intense blue, Uranus a bluish-green. Don't bother too much to resolve a disk with either as both are really small, and no surface features can be made out either. You could use their disk to help distinguish them from surrounding stars, but you will require very, very good seeing conditions so that you don't have bloated stars to contend with.

Actually, thanks to you Shaun, I nearly forgot that I have another challenge, this time not just involving ALL the planets, but EVERY major body in the solar system that orbits the Sun. I'll make my next post about this. There's only a few days left this year from today's date (20th of October), and then two more opportunities to see the same next year, and then that's it for several hundred years: The Massey Alignment! Read all about it in the next post!
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  #36  
Old 20-10-2018, 02:10 PM
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Challenge No. 5

The Massey Alignment

Firstly, I am not so arrogant as to name something after myself! Instead, this name was given to this most unique apparition by some of my friends, so why not go with the flow

For the next few days from the writing of this post, and on two more occasions next year, it will be possible to view ALL the planets, plus the Moon and Pluto all in the sky at the one time!

This is not a linear alignment as the planets will be spread out across 180 east to west. Linear alignments also won't show all the planets in the sky at the one time - Venus and Mercury will be between the Earth and Sun.

I chanced upon this whole of planetary alignment by chance a few months ago while researching possible dates for outreach. This apparition is only visible for about half an hour to 45 min as Venus and Mercury disappear below the western horizon these next few days, and Uranus is just rising in the east at the same time. No one had noticed this alignment of every major body in the sky all at the one time, not individuals or professional astronomers. Me!

There will be three opportunities all up that this apparition will happen. This October just after sunset, in late April next year (2019) just before sunrise, and end of October/start of November next year (2019) again just after sunset. This apparition is only visible for a couple of weeks during these dates. And then that's it for several hundred years!

I started a thread here in IIS about this:

http://www.iceinspace.com.au/forum/s...d.php?t=167278

I've also made a post entry on my blog about this event too:

http://alexanderastrosketching.blogs...ing-up-in.html

Oh, and a mate of mine started a thread about the current Massey Alignment here in IIS. I managed to complete the Massey Alignment last night! Crazy really as last night was the first clear night in Sydney for the last two weeks and the only clear night forcast for the next week too:

http://www.iceinspace.com.au/forum/s...d.php?t=170866

Below are two Sky Safari screen shots of this October's apparition, looking West and looking East at 7:57 pm.

So, if you miss this October's apparition, you'll have two more next year. Then that's it for a very, VERY long time.
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  #37  
Old 20-10-2018, 08:02 PM
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wow, that's awesome! Pity I won't be able to see Pluto with my 8" Dob 😏 Or for that matter, see through the clouds here in Shellharbour...better wait until next year 😊 Maybe you could patent the Massey Alignment 😜
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  #38  
Old 23-10-2018, 07:23 PM
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I'd hoped we'd have good clear skies this evening in Brisbane, like BOM predicted.
This eveing, after being driven back upstairs from the back yard by the mozzies, I remembered Challenge number 4. Figured I'd have a go at seeing if I could see it.
Set up the scope on the patio, then checked what I was looking for, and returned to the scope, and in those scant 5 to 10 minutes of looking up what I needed, clouds had rolled in and there was no chance of seeing the Moon.
Damnably frustrating.

edit: fix typo

Last edited by JeniSkunk; 23-10-2018 at 07:24 PM. Reason: fix typo
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  #39  
Old 06-11-2018, 08:17 AM
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Challenge No. 6

Naked eye observation of Uranus!

I mentioned earlier that Uranus can be seen naked eye. I've seen it on many occasions myself.

So, the challenge is to do it yourself!

Reckon it's easy? Here's what you need:

* Mk 1 pair of eyeballs - no telescope or binos - eyeglasses permitted...
* Dark site - Uranus shines at around magnitude 5.8, so forget seeing it from Sydney's CBD...
* Good transparency - this is the deal maker/breaker! You may be under the darkest of skies, with no light pollution anywhere other than that created by the stars themselves. But unless the sky is VERY TRANSPARENT, you won't stand a chance. Transparency is how clear and clean the atmosphere is. Any hint of mist or fog (heavy dew is a tell-tale sign of dodgy transparency), smoke, dust, or any other type of haze inducing muck, then the sky will lack transparency, and the faintest stars that are actually visible will not be. Being able to see Uranus naked eye is a good indicator of good transparency.

TIP: If you manage a night and site that ticks all of the three conditions above, you will also be able to see star fainter than Uranus, even pushing magnitude 7.

With Uranus being visible naked eye, it means 7 out of our Solar System's planets are visible naked eye.

There are many good apps that will show the current location of all the planets, some of which are also free.

Have a shot!

Alex.
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  #40  
Old 06-11-2018, 01:17 PM
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Doubt I'll get a chance to try to do this one.
With the space needed for my wheelie walker (Post a photo of yourself thread), and the kitchen chair I use as a stand for my telescope, being able to get a lift out to any dark site seems quite unlikely, so I'll have to endure the grey haze of bad light pollution, and pass up on dark site challenges.
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