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Planets with a Reflector

Planet SCT Reflector Visual
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#26 EsaT

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Posted 23 November 2022 - 10:02 AM

Avoid windy nights -- these have poor seeing and the scope may shake or vibrate.

Telescope getting shaked by the wind is certain risk without some cover, but seeing isn't necessarily always bad.
 
Ten days ago had blackout because of "normally bad" autumn weather and with first good break in clouds for many many weeks and nothing better to do decided to check the moon.
96x was perfectly usable and 169x was quite decent.
While in next evening in completely calm weather already 96x was rather bad and 169x completely hopeless.
Image was literally like watching over some black parking lot in hot summer day.

 

And weather was like this:
Saturday.JPG

Did that first observing session during that pre 20:00 gust spike.

Second visit was around 22:00 and last session after mid night.

(just double the number to get knots, if that's more familiar speed unit)



#27 ngc7319_20

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Posted 23 November 2022 - 01:03 PM

 Ten days ago had blackout because of "normally bad" autumn weather and with first good break in clouds for many many weeks and nothing better to do decided to check the moon.
96x was perfectly usable and 169x was quite decent.
While in next evening in completely calm weather already 96x was rather bad and 169x completely hopeless.
Image was literally like watching over some black parking lot in hot summer day...

 

Well when I say "avoid windy nights" ... these are generalizations.  There tends to be a lot of turbulence and rapidly moving patterns where I live, when you get over about 10 mph.  Yes, maybe on a windy night 100x looks good.  But on a really good night you should be able to get to 400x to 600x in an 8" reflector.  

 

The converse is not necessarily true -- calm winds don't guarantee good seeing.  You can still have rising thermals if the terrain around you is cooling.  Scope optics might be cooling, too.



#28 Nightskyman

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Posted 24 November 2022 - 08:52 PM

Can you use a Barlow along with the zoom piece? Just bought the celestron 8-24 zoom from Amazon. Price was on sale for 89.00 plus a coupon for an extra 10.00 off!



#29 vtornado

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Posted 24 November 2022 - 09:00 PM

Yes you can use a barlow with a zoom eyepiece.

GSO 2x barlow is a good value.

There are other barlows that are better but come at a higher price.



#30 Asbytec

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Posted 25 November 2022 - 10:54 AM

Any advice on viewing the planets using a 8” dobsonian and which eye pieces and magnifications I should use?

It depends on your seeing conditions, or how willing you are to wait for those good moments. For Jupiter, I am thinking 300 to 400x works. Mars can take 400x easily enough, and probably more. Saturn is normally good at around 400x without losing much. Saturn's rings are brighter with some high (and low) contrast detail, I've been up to 600x on the rings in descent seeing. The Crepe ring, Enke minimum, brighter ringlets, and of course Cassini division are to be had. 

 

Saturn 27 Sep 2019 Small.png


Edited by Asbytec, 25 November 2022 - 10:56 AM.

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#31 areyoukiddingme

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Posted 25 November 2022 - 03:31 PM

I agree with Norme. It very much depends on the seeing and target. When very stable, I find my 8" F7 will easily go beyond 300x with a good stable image, and I do have some floaters to contend with.

 

A night where 120x is all I can get. . . I'd not bother with the planets that night for more than a quick look. A mediocre night for me is typically a 200x night--e.g., last night. 200x was pushing my luck with Jupiter, but later in the night Mars looked decent at that power.

 

Mars and Saturn both tend to benefit more from higher powers than Jupiter. 


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#32 Dave Mitsky

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Posted 25 November 2022 - 04:16 PM

Mars and Saturn both tend to benefit more from higher powers than Jupiter.

That's been my experience too.  Jupiter's features tend to be low contrast.


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#33 Asbytec

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Posted 25 November 2022 - 05:38 PM

That's been my experience too.  Jupiter's features tend to be low contrast.

Yes, Jupiter is awash in low contrast detail that rolls into view during times when seeing is steady and disappears at the slightest flap of a butterfly's wings. Observing Jupiter is observing its low contrast detail. It has higher contrast detail, too, like the equatorial bands themselves, the GRS, eclipse shadows, etc. Interestingly, in my understanding and experience, Jupiter's low contrast detail tends to fade at some point at higher magnification and smaller exit pupils while the high contrast detail remains (and the limb is still sharp). I believe this occurs on our eye (afocal) and not on the focal plane because we're observing he same fine image we saw at lower magnification where detail is much easier on the eye.

 

Actually, most of Saturn's cloud structures are low already bright low contrast at all magnifications, so they are more difficult to see anyway. So, Saturn can take some magnification without significant degradation, especially the rings. Mars has bright low and high contrast detail, too. The latter can take magnification, too, and I believe Mars is a little brighter per unit area than Jupiter. Bright high contrast detail can take magnification a little better than low contrast detail. Good optics and no obstruction help a little but seeing rules all who observe through the atmosphere above us, and the proper magnification is important along with a scope prepped for observing. An 8" is a capable scope at the right magnification. 

 

So is a 6" aperture. Below I cherry picked on of my better observations of Jupiter near the zenith in good seeing through a 6" at 240x. My 8" is noticeably better resolved. It's not like this stuff jumps out at you. It takes a while for detail to briefly roll into view and you have to be there to see it when it does. It takes a good while, maybe 30 to 45 minutes, to see everything we can see even in better seeing conditions and before Jupiter's rotation causes it to change significantly. Color takes some skill because it's low contrast and just a shade or two from grey scale in small apertures, but we can learn to discern faint differences in hue.

 

The sketch is embellished in terms of contrast and color saturation, so others do not have to work as hard as I did. You should not have to "observe" a sketch, but that would be cool and more realistic if we did. smile.gif

 

Jupiter 6 Feb 1330UT Final.jpg


Edited by Asbytec, 25 November 2022 - 05:46 PM.

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#34 Nightskyman

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Posted 25 November 2022 - 09:49 PM

Ok, so I returned my starter eyepiece kit and purchased the following individually since the earlier posts indicated kits were not good investments. I bought a 6mm, 9mm, 15mm, and 20mm Orion expanse plossls with 66 degree field of views and eye relief enough for glasses. Also a 32mm Meade 4000 series super plossl with 52 degree field of view and extra eye relief and a Orion High-Power 1.25" 2x 4-Element Barlow Lens. I hope this is now a good selection and of decent quality. Would a 40mm be of any use?


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#35 Asbytec

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Posted 25 November 2022 - 11:35 PM

A 40mm will give you 30x and a 6.6mm exit pupil. That'll work. Also consider a 25mm eyepiece for about 50x and a 4mm exit pupil. Both for larger nebulae.

I'd try your 6mm for 200x and 1mm exit pupil on Jove. Even if seeing doesn't "allow" it because you will get some better moments in average seeing and Jupiter is just better when it's big. You might even push your 9mm with the 2x Barlow for about 265x for the same reason.

For Mars, try pushing your 6mm with the Barlow. Mars is small at less than half the diameter of Jupiter. It's easier (and dimmer) when Mars is bigger on our eye. Seeing may not "allow", but it might. It has high contrast details that may not be erased by seeing conditions.

Edited by Asbytec, 25 November 2022 - 11:37 PM.

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#36 Dave Mitsky

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Posted 26 November 2022 - 01:48 AM

Ok, so I returned my starter eyepiece kit and purchased the following individually since the earlier posts indicated kits were not good investments. I bought a 6mm, 9mm, 15mm, and 20mm Orion expanse plossls with 66 degree field of views and eye relief enough for glasses. Also a 32mm Meade 4000 series super plossl with 52 degree field of view and extra eye relief and a Orion High-Power 1.25" 2x 4-Element Barlow Lens. I hope this is now a good selection and of decent quality. Would a 40mm be of any use?

The Orion Expanse eyepieces are not Plössls.  They are a different design with the 6 and 9mm models employing a so-called built-in Barlow lens.

I don't recommend a 40mm Plössl, if that's what you're thinking about getting.  It will produce almost the same true field of view as a 32mm Plössl but with a narrower apparent field of view.  

If you want a larger true field of view, you'll have to get a 2" eyepiece.  The 70-degree AFOV 38mm Agena SWA will show some field-edge astigmatism at f/5.9 but should be useable.  There are better options but they will cost $200 or more. 

 

https://agenaastro.c...a-eyepiece.html


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#37 Nightskyman

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Posted 26 November 2022 - 04:05 AM

Are the Orion expanse and the Meade 4000 series better than the plossls? Is the Orion High-Power 1.25" 2x 4-Element Barlow Lens a decent choice? 



#38 Nightskyman

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Posted 26 November 2022 - 04:09 AM

As a beginner, I want to watch my budget but wanted to have a good basic range of sizes and Barlow that would be a step up from entry level eye pieces.


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#39 Asbytec

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Posted 26 November 2022 - 04:24 AM

Orion Expanse get descent reviews. I am sure the Meade 4000 series Plossl is fine. 

 

I'd go with Dave's recommendation of the 38mm Agena SWA (Super Wide Angle) for the reasons he mentioned. 



#40 Sky Muse

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Posted 26 November 2022 - 05:25 AM

Ok, so I returned my starter eyepiece kit and purchased the following individually since the earlier posts indicated kits were not good investments. I bought a 6mm, 9mm, 15mm, and 20mm Orion expanse plossls with 66 degree field of views and eye relief enough for glasses. Also a 32mm Meade 4000 series super plossl with 52 degree field of view and extra eye relief and a Orion High-Power 1.25" 2x 4-Element Barlow Lens. I hope this is now a good selection and of decent quality. Would a 40mm be of any use?

A 32mm and 40mm have about the same field-of-view, but the view through the 32mm will be more contrasty, with the background sky a deeper black; and that's what we want, a jet-black background, to where the illuminated objects themselves pop out at us.

 

The Orion "Expanse" eyepieces are the exact same eyepieces as these, just in different "clothes"...

 

https://agenaastro.c.../agena_ewa.html

 

...which, in turn, may, most likely, be the same as these...

 

https://www.aliexpre...id=vJ8eluTytiDg


Edited by Sky Muse, 26 November 2022 - 06:12 AM.

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#41 JohnBear

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Posted 26 November 2022 - 01:55 PM

+1

With your current set of Expanse EPs, you should be in good shape for viewing celestial wonders for quite a few more years.  Test and compare them to your factory plossls to develop you understanding of what EP specs are of significance to YOUR eyeballs and biological image processor - some of us see things differently!  With use you will start to learn and notice what specs work best for You, especially things like eye relief, exit pupil, and AFOV. You will also learn that the sky viewing conditions (as well as the quality of your OTA and mounts) set the real limits on EP performance.  Thus, ALL EPs can be expected to perform pretty much the same under terrible viewing conditions - regardless of how much they cost, or what specs they have!  This is why astronomers are willing to travel hundreds of miles to get to good dark sites when the conditions warrant (it is also why we build space telescopes). 

 

As always, try to get to the some astronomy events (star parties, gatherings and such) to see and compare what other experienced astronomers use. 


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#42 Nightskyman

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Posted 26 November 2022 - 11:19 PM

Is the thought that the above mentioned agenda eye pieces are better than the Orion expanse? Any Opinions about the Orion High-Power 1.25" 2x 4-Element Barlow Lens?


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#43 KWB

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Posted 27 November 2022 - 12:29 AM

Is the thought that the above mentioned agenda eye pieces are better than the Orion expanse? Any Opinions about the Orion High-Power 1.25" 2x 4-Element Barlow Lens?

The Expanse and the 2 inch SWA are so different that they are not really comparable as to which is "better". The Expanse are 1.25 high and medium powered eyepieces and the 32 or 38mm SWA is a 2 inch low powered eyepiece. Each eyepiece design does something the other design can't - higher magnifications versus low power and a considerable wider TFOV capability.

 

They are both entry level budget aftermarket eyepiece designs.


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#44 Sky Muse

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Posted 27 November 2022 - 12:31 AM

Is the thought that the above mentioned agenda eye pieces are better than the Orion expanse? Any Opinions about the Orion High-Power 1.25" 2x 4-Element Barlow Lens?

No, it's only that those at Agena are less expensive, and if ordered from their country of manufacture, cheaper still, but a bit longer to wait until they arrived.  

 

I don't have that Orion barlow.  I had gotten Antares 2x and 3x barlows from Agena at the time, years ago.  Through the 2x and an eyepiece, I saw my first perfect start-test, both sides of focus being identical, and through my 4" refractor.  With the 3x and an old-school, mid-grade eyepiece, I witnessed snap-to focussing through a basic, mass-produced 6" f/5 Newtonian.  I had never seen either event with just an eyepiece before, nor since.

 

Agena no longer sells Antares products, but ScopeStuff does.



#45 Nightskyman

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Posted 28 November 2022 - 11:59 AM

I have an 8” dobsonian with a focal length of 1200 and focal ratio of 5.9. Which 3 eye piece sizes would you recommend for viewing planets?


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#46 Nightskyman

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Posted 28 November 2022 - 12:02 PM

Already have a 2x Barlow 



#47 Nightskyman

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Posted 28 November 2022 - 04:42 PM

My scope came with a 2” extension piece and a 2” to 1.25 adapter. Is the 2” extension ever used with a 1.25 eyepiece? If so when and if not, should I not be using it at all?



#48 Sky Muse

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Posted 28 November 2022 - 05:35 PM

I have an 8” dobsonian with a focal length of 1200 and focal ratio of 5.9. Which 3 eye piece sizes would you recommend for viewing planets?

Anything that results in 150x and up.


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#49 ngc7319_20

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Posted 28 November 2022 - 06:42 PM

My scope came with a 2” extension piece and a 2” to 1.25 adapter. Is the 2” extension ever used with a 1.25 eyepiece? If so when and if not, should I not be using it at all?

Yes. the 2" extension is sometimes used with 1.25" eyepieces.   If you cannot move the focuser out far enough to reach focus, then try the 2" extension.



#50 ngc7319_20

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Posted 28 November 2022 - 06:47 PM

Ok, so I returned my starter eyepiece kit and purchased the following individually since the earlier posts indicated kits were not good investments. I bought a 6mm, 9mm, 15mm, and 20mm Orion expanse plossls with 66 degree field of views and eye relief enough for glasses. Also a 32mm Meade 4000 series super plossl with 52 degree field of view and extra eye relief and a Orion High-Power 1.25" 2x 4-Element Barlow Lens. I hope this is now a good selection and of decent quality. Would a 40mm be of any use?

 

I have an 8” dobsonian with a focal length of 1200 and focal ratio of 5.9. Which 3 eye piece sizes would you recommend for viewing planets?

I think the eyepieces you mention -- especially the 6mm and 9mm Orion Expanse -- should be good for planets.  You can Barlow these to get effectively 3mm and 4.5mm, which are also good.


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