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  #21  
Old 18-03-2017, 06:24 PM
astro744
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Quote:
Originally Posted by AussieBill View Post
Thanks Astro,

Thats very helpful and will have another go tonight - too cloudy last night.

Bill

Astro Said : "I then tried a 7mm T6 Nagler (51x) with and without the Planetary filter. The GRS was small but just visible with and without filter but again it was only there in moments of good seeing and was very tiny and if I had not know that it was there I may not have identified it at this power. The two equatorial bands were easy at this power and the north polar region was more grey and less bright than the south polar region. The image was noticeably larger than at 40x. In fact each 10x power jump makes for a noticeable and significant image size jump. Especially between 40x, 51x, 60x, 72x."
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Originally Posted by mental4astro View Post
Astro744,

Brilliant report mate!

Thanks for taking the time to actually do this, The forecast for the this week in Sydney is terrible, and I have no idea when I'll be able to get any scope time, so it is fantastic that you should do this. It is excellent that you saw the details that you did, as it shows what a good small instrument is capable of doing with good eyepieces. Blooming good benchmark
No worries guys. I'm enjoying my morning observing sessions and was limiting them the the weekend but a 1/2 hour session before heading off to work is great. I find I'm too tired in the evening especially by the time twilight ends and I'm usually up early anyway. Weather was a bit iffy this morning but I had another go this time on Saturn but there was too much moving cloud to do anything serious. A grab and go small refractor is great for short sessions as it cools quick and can bet setup and taken down fast.
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  #22  
Old 18-03-2017, 07:15 PM
astro744
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One more thing about Jupiter. It is currently just over 43 arc seconds in angular size. In Sep 2022 it will be over over 49 arc seconds; about 15% larger in appearance. This is significant and noticeable in the details seen.

43 arc seconds is still larger than the 25 arc seconds Mars is capable of and that only every 15-17 years or so (next two oppositions are good). Mars comes around every 2 years and 2 months but only every 15-17 years us it favourable near 25 arc sec or at least over 20 arc sec.

You can get info at Calsky or USNO.
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  #23  
Old 19-03-2017, 07:13 AM
astro744
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Addendum: 19 March 2017 between 6am and 7am.

Seeing was much better this morning than two days ago but easterly cloud did drift in and kept forming providing intermittent viewing. Air was steady though much better than previous session.

Telescope use was Tele Vue 60. I always start off with 24mm Panoptic as my finder and switch to the Nagler zoom at the 6mm setting giving 60x.

Almost immediately I saw a very thin North Temperate Belt (NTeB) separated from the North Equatorial Belt (NEB) by an also thin North Tropical Zone (NTrZ).

On the south I saw a broader and whiter STrZ and a darkening at the northern edge of the South Polar Region (SPR) which was likely the South South Temperate Belt (SSTeB) but I could not distinctly see the South South Temperate Zone (SSTeZ).

Overall the SPR was grey as was the NPR The north side didn't appear as bright immediately north of the NEB and NTeB as it did on the south side immediately south of the SEB.

I then added an 80A filter to the 6mm setting and immediately noticed the SEB had its 'pimple' back with the GRS perhaps 60min from the eastern limb. I didn't notice this without the filter but then when I removed the filter it was visible just stood out more in the light blue light of the filter. This was a good test this morning because I didn't check when the GRS was next visible and found it this time by actually seeing it first.

The purpose of this whole exercise was to see how small an image can be and still provide views of the two main belts and the spot. In the better seeing conditions this morning I was able to discern the NTeB at 40x although it was only just resolved. At 45x and 51x it was a little easier but obvious at 60x. I would not normally observe Jupiter at such low powers and I would start at 60x with the zoom and move up to 120x and if seeing permitted I would switch to the 4-2mm zoom and move up to 180x. However I have found about the 2.5mm setting (144x and 0.42mm exit pupil) is about optimal for me with this 'scope before floaters in my eye interrupt the image as I begin to run out of light. Jupiter is best in slightly larger 'scopes between 150x and 250x as seeing permits but higher powers are of course possible.

I was going to add a note referring to this addendum in my original post but as I typed it up in Word and then copied it always comes up completely blank when I edit.

Last edited by astro744; 19-03-2017 at 07:16 AM. Reason: Last sentance changed.
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  #24  
Old 19-03-2017, 01:00 PM
AussieBill (Bill)
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Had another go with the Aldi telescope last night with Jupiter higher in the sky.

20mm eyepeice and a 2x Barlow lens gave me the best crisp views of Jupiter and Moons - thats only 35x magnification. Jupiter was a well focussed discrete disc and the moons were tiny specks bu clearly visible.

The image from the 4mm eyepiece wasnt quite so clearly defined and 4mm plus 2x Barlow was hopeless - unable to focus the basic disc with any degree of clarity - it was always just a white blob.

So final verdict - $50 75mm x 350mm telescope has been fabulous for this newbie to see the moon + craters and then Jupiter and its moons.

The optics not good enough to see the bands and the red spot - but that doesnt matter am still chuffed.

I suspect that a single decent quality eyepiece for a quality scope would cost twice as much as what I paid for this entire scope and eyepieces.

Thanks for the many responses and clarifications to my understandings.

Bill
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  #25  
Old 19-03-2017, 06:08 PM
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LaughingBeagles (Peter)
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Great stuff Bill and really well done. Nothing like those "oh wow!" moments.
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  #26  
Old 19-03-2017, 08:39 PM
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mental4astro (Alexander)
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Bill,

Alas a scope like yours uses a spherical mirror, not a parabolic one. With its fast focal ratio, it just won't focus well at high magnification. A parabolic mirror will. It is also made very cheaply and the with quality as its paramount interest - this again goes to a degradation of the image. Scopes like yours can provide a good image, but it needs to be within its strengths. A decent plossl eyepiece is better than what these scopes are supplied with, but again they are better than nothing and use them to their strengths with those of your scope and you will get respectable results.

My 76mm FirstScope I know has a poor primary mirror. But for low power work its is fine. Even knowing its limitations, I am still having a good go with it to become more familiar with what it is capable of, and what I can see through its problematic high power image.

I always say "any scope is better than no scope at all". Don't be discouraged. I actually use one of these FirstScope's as a big finder on my 17.5" scope. I use another f/4.4 114mm Newt, also with a spherical mirror, for video astronomy. Again, I'm making use of the strengths of both scopes - low power.

I've just found a set of notes i made after viewing Saturn with my ED80 refractor. It was late in its season, so it was far from its opposition best. But I still did manage to see the Cassini division with it. Something that absolutely amazed and thrilled me!

Alex
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