Re-Naming the Forum

Got a beginners' question? No matter how elementary, our friendly forum community and magazine writers will answer it.

Re-Naming the Forum

Postby david48 » Thu Mar 19, 2015 7:17 pm

Shouldn't this forum be re-named the "Ask a Silly Equipment Question"

Because most of the questions posted recently, don't have much to do with Astronomy.

They're more concerned about buying equipment.
david48
 
Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

Re: Re-Naming the Forum

Postby The Man with the Corrugated Iron Roof » Tue Apr 28, 2015 9:55 pm

I think the forum name's OK. Some questions aren't really all that "silly". We're all still learning.
How can I be one with the universe when we don't know what 96% of it is.

About Me: https://www.amazon.com/Philip-Pugh/e/B0034NTCJK

My blog: http://sungazer127mak.blogspot.com/

Photos: https://www.flickr.com/photos/philippughastronomer/
The Man with the Corrugated Iron Roof
 
Posts: 501
Joined: Sat Nov 23, 2013 1:53 pm
Location: Wiltshire but can be just about anywhere up to 41 000 feet

Re: Re-Naming the Forum

Postby david48 » Mon May 25, 2015 7:50 pm

The Man with the Corrugated Iron Roof wrote:I think the forum name's OK. Some questions aren't really all that "silly". We're all still learning.


Well, we're all learning. And what I've learned is this:
Most posters here have no real interest in actually observing anything.

What they want to know is - what's the "coolest" bit of kit. Is that true?
david48
 
Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

Re: Re-Naming the Forum

Postby SkyWatcher17 » Mon May 25, 2015 8:13 pm

I'm not so sure, neither of my telescopes are anything special and were relatively inexpensive, although I am rather limited to size and weight of OTA and mount as I have a physical disability. Investing in some decent quality eyepieces seems eminently practical to me. The results can actually be seen lol.
Sky-Watcher Explorer 130M, EQ5 Deluxe, AZ5 Deluxe, SkyMax 102mm, SkyMax 127mm, Orion/SW ST80s (both modified), Vixen Porta II/Vixen SXG Hal-130, Orion 90mm StarMax , Celestron NexStar Evolution 9.25", TS Optics/GSO: SVD series 150mm, f/6.
SkyWatcher17
 
Posts: 36
Joined: Mon May 04, 2015 1:31 pm

Re: Re-Naming the Forum

Postby david48 » Mon May 25, 2015 10:25 pm

Well it's "eyepieces" again, like I said!
The function of the eyepiece, is to magnify the image produced by the primary OG or mirror.

This magnification can be produced by a simple convex lens. Or by an achromatic lens, composed of 2 flint and crown glass components, to reduce chromatic aberration.
david48
 
Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

Re: Re-Naming the Forum

Postby SkyWatcher17 » Mon May 25, 2015 10:47 pm

david48 wrote:Well it's "eyepieces" again, like I said!
The function of the eyepiece, is to magnify the image produced by the primary OG or mirror.

This magnification can be produced by a simple convex lens. Or by an achromatic lens, composed of 2 flint and crown glass components, to reduce chromatic aberration.


Yes, I know a little about eyepiece types. Most of mine are Plossl (symmetrical designs with two doublets of lenses) although I have a couple of Kellner (achromatic doublet) EP's. It would be interesting to know if they have any real differences in usage. I have two Celestron 15mm, one a Plossl, the other a Kellner. All I really know is they both give me a 60x magnification with my Newtonian telescope and around an 87x with my Mak. I used my Mak to view the gibbous moon recently with both. I got some great views of the seas and some dramatic crater shadows. The moon never fails to wow me. I thought the Plossl gave slightly brighter views (with or without a 2x Barlow) but it may just be higher quality. Sometimes it's useful to know how equipment works observing certain things. General star observations don't need huge magnification, unless you're trying to separate binaries or something. Planetary observing is another thing however. Magnification and detail seen are often dependent on objective mirror size, eyepiece combination utilised and weather conditions (thermals).
Sky-Watcher Explorer 130M, EQ5 Deluxe, AZ5 Deluxe, SkyMax 102mm, SkyMax 127mm, Orion/SW ST80s (both modified), Vixen Porta II/Vixen SXG Hal-130, Orion 90mm StarMax , Celestron NexStar Evolution 9.25", TS Optics/GSO: SVD series 150mm, f/6.
SkyWatcher17
 
Posts: 36
Joined: Mon May 04, 2015 1:31 pm

Re: Re-Naming the Forum

Postby david48 » Mon May 25, 2015 11:19 pm

Thanks Sky for your intelligent and informative reply. What a pleasure it is, to hear from an a person such as yourself! However, I still think that the simplest eyepiece, ie a convex lens, is probably the best for definition.

Because If more lens elements are introduced, surely the image must deteriorate. Owing to the reflections and aberrations, which the increased number of air/glass surfaces will inevitably produce.
david48
 
Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

Re: Re-Naming the Forum

Postby SkyWatcher17 » Tue May 26, 2015 12:31 am

Yes, I would assume the simpler the eyepiece design, the more light would get through to the observer.

EyepiecesDiagram.jpg
EyepiecesDiagram.jpg (65.59 KiB) Viewed 3016 times


There does seem to be a bewildering array of designs prevalent now however. I believe Plossl eyepieces have only become economical to mass produce since the 1980's, before that their unit price was prohibitive for most amateur astronomers.
Sky-Watcher Explorer 130M, EQ5 Deluxe, AZ5 Deluxe, SkyMax 102mm, SkyMax 127mm, Orion/SW ST80s (both modified), Vixen Porta II/Vixen SXG Hal-130, Orion 90mm StarMax , Celestron NexStar Evolution 9.25", TS Optics/GSO: SVD series 150mm, f/6.
SkyWatcher17
 
Posts: 36
Joined: Mon May 04, 2015 1:31 pm

Re: Re-Naming the Forum

Postby dave.b » Tue May 26, 2015 11:08 pm

david48 wrote:Because If more lens elements are introduced, surely the image must deteriorate. Owing to the reflections and aberrations, which the increased number of air/glass surfaces will inevitably produce.


The short answer is that a well designed and manufactured multi element eye piece will out perform a simpler design. The only thing that having more elements will have is the potential for increased light transmission losses. But as simpler designs tend to suffer from spherical aberrations (such as coma; an in ability to produce a focused image across the entire field without distortion) and chromatic aberrations (the inability to produce a co-focused image across the visible spectrum). Which is the design problem the complex designs try to solve.
Internal reflections result in a loss of contrast or ghosting when observing bright objects. This is mostly controlled with anti reflective coatings and tube baffling.
Finally, the lens-air refractive index is controlled in some designs by the use of an inert gas fill such as argon or nitrogen.
dave.b
 
Posts: 803
Joined: Mon Feb 13, 2012 6:35 pm
Location: Staffordshire

Re: Re-Naming the Forum

Postby SkyWatcher17 » Wed May 27, 2015 3:00 am

Earlier I got a pretty good view of the rings of Saturn with my Mak from around transit at 00:50 BST to around 02:00. The weather conditions precluded a really sharp image but I could see colour detail and the Cassini division quite well. I used a 12.5mm and 15mm Plossl plus a Barlow 2x at one stage. Although, as I have no batteries for my clock-drive, it moved pretty quickly at 208x magnification! :lol:
Sky-Watcher Explorer 130M, EQ5 Deluxe, AZ5 Deluxe, SkyMax 102mm, SkyMax 127mm, Orion/SW ST80s (both modified), Vixen Porta II/Vixen SXG Hal-130, Orion 90mm StarMax , Celestron NexStar Evolution 9.25", TS Optics/GSO: SVD series 150mm, f/6.
SkyWatcher17
 
Posts: 36
Joined: Mon May 04, 2015 1:31 pm

Next

Return to Ask a silly (astronomy) question

Who is online

Users browsing this forum: No registered users and 1 guest