Jump to content


Photo

Using a Small Refractor for Lunar Observing?

refractor
  • Please log in to reply
18 replies to this topic

#1 cwilson

cwilson

    Mariner 2

  • -----
  • Posts: 211
  • Joined: 01 Oct 2012
  • Loc: SW Oklahoma

Posted 12 August 2014 - 03:06 PM

For a number of reasons I'm considering a small refractor (100mm to 120mm) as a future purchase. I've never owned one before, and previously I've owned an 8" f/6 Newt and a 6" f/12 Mak. Should I get a small refractor, how well will it do for lunar observing?

 

With my previous scopes I rarely ever observed the moon - just a glance now and then. But I'm thinking of doing a lot more lunar observing in the future.



#2 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5360
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 12 August 2014 - 03:29 PM

Personally, I consider a 4" - 5" refractor to be medium size, with the 5" bordering on the large side. The smallest scope I routinely use for lunar observing is a 63mm Zeiss Telemator and I can spend hours with it. My 85mm Zeiss is a VERY noticeably step up in performance and will show me a LOT of details. my 5" f/9.4 will show even more. 

 

An 8" f/6 newtonian or a 6" f/12 mak should both be fantastic lunar scopes. What makes you think a 4" - 5" refractor would be better? It will be better for quick sessions, but both the 6" mak and the 8" should outperform them, when cooled and the seeing is any good. 

 

If your observing sessions are often short and you need to set up quickly, you'll probably find a refractor to be extremely useful. 

 

 

 

Clear skies!

Thomas, Denmark


Edited by Astrojensen, 12 August 2014 - 03:31 PM.


#3 Pricewool

Pricewool

    Sputnik

  • *****
  • Posts: 48
  • Joined: 10 Apr 2013

Posted 12 August 2014 - 05:40 PM

Agreeing with Thomas, 100 to 120mm refractors are more "medium" to me. Semantics aside, I regularly view luna with 80 and 110mm refractors, both f7. I consider them ideal for the job, easy to set up, and very quick to come to temperature. Views with my Ortho's and Plossls are just stunning. Highly recommended.

 

Price



#4 JimK

JimK

    Skygazer

  • *****
  • Posts: 839
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 12 August 2014 - 08:41 PM

If you are going to use the refractor just for "grab-and-go" lunar viewing, it will work fine.  I have done so many times.  The 100 objects in the Astronomical League Lunar Program (I) can easily be seen using using an 80mm refractor, having viewed them myself.

 

However, to go much past that level of detail in viewing Luna may require a larger aperture telescope.  As I mentioned in a recent thread ( http://www.cloudynig...rmediate-level/ ) the issue is one of optics (tiny details cannot be seen/are blurred in small apertures) and a small eyepiece exit pupil (where eyeball floaters detract from the view of a large bright lunar surface), and both of these issues are less of a concern with a larger telescope aperture.

 

A small refractor that is often used is well worth it.  But if you are going to do a LOT of detailed lunar viewing, then you may (either now, or later) wish to consider what you used to have (8-inch f/6 Newt or a 6inch f/12 Mak) as a better choice for lunar viewing.



#5 cwilson

cwilson

    Mariner 2

  • -----
  • Posts: 211
  • Joined: 01 Oct 2012
  • Loc: SW Oklahoma

Posted 12 August 2014 - 08:47 PM

I guess in my mind I was splitting them into two camps: small being up to 120mm and anything over that as a "large" refractor. :waytogo: 

 

The main reason I'm interested in a refractor is quicker setup and cool down. I don't have as much time to observe as I used to, and I'm getting to the point where lugging around a heavy or bulky scope and mount is getting to be too much for me. The 8" Newt and the 6" Mak were great scopes, but the Newt needed frequent collimation and the Mak needed a long cool down.



#6 Sarkikos

Sarkikos

    Hubble

  • *****
  • Posts: 17148
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 13 August 2014 - 06:24 AM

My C80ED is becoming my favorite grab-n-go Moon scope. It has enough aperture to show me many features and has a sharp image with virtually no CA.  I don't like CA when viewing the Moon or planets. Up to now, my favorite grab-n-go Moon scopes have been my C90 or C5 on a 501HDV head and Bogen tripod.  They lack CA as well, but both of those take a little time to acclimate. The C80ED is always ready to go.  I bought mine from Astronomers Without Borders at a nice price.  My first APO/ED scope.

 

On the other hand, I don't like viewing the Moon at narrow exit pupils due to my eye floaters. A 1mm exit pupil is about ideal for me, though I will push it to 0.8mm if necessary to see fine detail.  This is where larger aperture will have an advantage, since I can push the power higher before eye floaters become aggravating. Of course, a bigger scope will also provide greater resolution.  I used to take out my 8" or 10" Dob for intense Moon observation. But I have a feeling that my new EdgeHD 8" with NexStar tracking will become my favorite Moon scope for extended viewing to catch the more difficult lunar features.

 

Mike


Edited by Sarkikos, 13 August 2014 - 06:30 AM.


#7 bvillebob

bvillebob

    Vostok 1

  • -----
  • Posts: 187
  • Joined: 19 Jan 2014

Posted 13 August 2014 - 11:08 AM

I can't comment on a 4" refractor, but I do have a good 6" reflector *(an RV-6)  I've been using as a comparison.  I also have a good 12" dob and I just finished an 8" dob with an excellent mirror.

 

The 8" is a BIG step up from the 6", the difference is striking.  Much brighter images and much better detail, an obvious difference, just a more pleasant viewing experience all around.

 

On the other hand, the difference between the 8" and the 12" (for lunar viewing) is minimal.  Going back and forth it's really hard to pick out any difference between the two, which I suspect simply means that I'm limited by seeing and that the 8" is performing near the top of its ability while the 12" is being hindered by the seeing.  I have yet to get a night of "perfect" seeing since finished the 8".

 

Based on what I've seen I have to think that the difference will be significant going from an 8" to a 4" refractor.  I know refractors are supposed to outperform refractors, but you're talking 1/4 the area of the objective.



#8 JimK

JimK

    Skygazer

  • *****
  • Posts: 839
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 13 August 2014 - 02:44 PM

...  quicker setup and cool down. I don't have as much time to observe as I used to, and I'm getting to the point where lugging around a heavy or bulky scope and mount is getting to be too much for me. The 8" Newt and the 6" Mak were great scopes, but the Newt needed frequent collimation and the Mak needed a long cool down.

 

Yes indeed -- many of us would LOVE to have an ultra-lightweight grab-and-go 8-inch aperture telescope that requires no collimation, minimal setup time, and requires only a couple of minutes to cool and thermally equalize.

 

Some observers have compromised with a 5- or 6-inch SCT, avoiding the mount issue for a similarly sized refractor.  Everyone has to choose the tradeoffs that matter most to them -- there is NO single correct answer to fit all needs.



#9 cwilson

cwilson

    Mariner 2

  • -----
  • Posts: 211
  • Joined: 01 Oct 2012
  • Loc: SW Oklahoma

Posted 13 August 2014 - 05:08 PM

 

...  quicker setup and cool down. I don't have as much time to observe as I used to, and I'm getting to the point where lugging around a heavy or bulky scope and mount is getting to be too much for me. The 8" Newt and the 6" Mak were great scopes, but the Newt needed frequent collimation and the Mak needed a long cool down.

 

Yes indeed -- many of us would LOVE to have an ultra-lightweight grab-and-go 8-inch aperture telescope that requires no collimation, minimal setup time, and requires only a couple of minutes to cool and thermally equalize.

 

Some observers have compromised with a 5- or 6-inch SCT, avoiding the mount issue for a similarly sized refractor.  Everyone has to choose the tradeoffs that matter most to them -- there is NO single correct answer to fit all needs.

 

 

How fast do the smaller SCTs cool down? My 6" Mak (Intes MK66 DX) had great optics, but it took forever to cool down, and on nights where the temperature dropped fast, it never caught up.



#10 RazvanUnderStars

RazvanUnderStars

    Sputnik

  • -----
  • Posts: 26
  • Joined: 15 Jul 2014
  • Loc: Toronto, Canada

Posted 14 August 2014 - 06:47 AM

I'm using an 80mm refractor as grab & go and will work well during wintertime. It's not of concern for Oklahoma where you live, but here in Canada it makes life easier on a really cold night. Quick set up and the tripod works better in snow than a dob.



#11 Sarkikos

Sarkikos

    Hubble

  • *****
  • Posts: 17148
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 14 August 2014 - 07:46 AM

In general I dislike the ergonomics of refractors, especially ones with longish OTAs. There is a long range of eyepiece altitudes. Also, IME refractors are less comfortable when looking near zenith than are Newts or even Cats.  I discovered this again last night when viewing Delta Cygni and the Double Double through my C80ED on a photo tripod.

 

But things change when the object is the Moon or a planet. These run along the ecliptic and at my latitude they never quite get up to zenith. In any case, the Moon or a bright planet is easy to sight and center in a nontracking scope for a long observing session. Last night after struggling with doubles, M13 and other objects near zenith, I was wishing I could stay up later to observe the Moon with my C80ED. But I couldn't. Not yet retired!

 

Mike


Edited by Sarkikos, 14 August 2014 - 07:47 AM.


#12 JimK

JimK

    Skygazer

  • *****
  • Posts: 839
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 14 August 2014 - 10:13 AM

 


How fast do the smaller SCTs cool down? My 6" Mak (Intes MK66 DX) had great optics, but it took forever to cool down, and on nights where the temperature dropped fast, it never caught up.

 

 

Perhaps the Cats & Casses forum is a better place to find an answer, as indicated in the links below.

 

Here's one link on C5 SCT cooling:  http://www.cloudynig...wn#entry5273269

 

Here's another on a C6 SCT vs 6-inch Mak regarding cooling, et al:  http://www.cloudynig...n#entry4955069 

 

And here's a link on a C5 SCT vs C102 refractor:  http://www.cloudynig...2-any-advantage

 ==> note the comment by Sarkikos on page 2 regarding cooling

 

In short, more aperture gives more detail, but less aperture is better for quick grab-and-go/casual views.


  • cwilson likes this

#13 cwilson

cwilson

    Mariner 2

  • -----
  • Posts: 211
  • Joined: 01 Oct 2012
  • Loc: SW Oklahoma

Posted 15 August 2014 - 12:06 AM

 

 


How fast do the smaller SCTs cool down? My 6" Mak (Intes MK66 DX) had great optics, but it took forever to cool down, and on nights where the temperature dropped fast, it never caught up.

 

 

Perhaps the Cats & Casses forum is a better place to find an answer, as indicated in the links below.

 

Here's one link on C5 SCT cooling:  http://www.cloudynig...wn#entry5273269

 

Here's another on a C6 SCT vs 6-inch Mak regarding cooling, et al:  http://www.cloudynig...n#entry4955069 

 

And here's a link on a C5 SCT vs C102 refractor:  http://www.cloudynig...2-any-advantage

 ==> note the comment by Sarkikos on page 2 regarding cooling

 

In short, more aperture gives more detail, but less aperture is better for quick grab-and-go/casual views.

 

 

Hmmm.... Maybe I should be considering a small refractor for those quick observing sessions, and a 6" or 8" SCT for those nights when I can observe all night? The 6" SCTs aren't very costly either. :hmm:



#14 Sarkikos

Sarkikos

    Hubble

  • *****
  • Posts: 17148
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 15 August 2014 - 06:02 AM

 

 

 


How fast do the smaller SCTs cool down? My 6" Mak (Intes MK66 DX) had great optics, but it took forever to cool down, and on nights where the temperature dropped fast, it never caught up.

 

 

Perhaps the Cats & Casses forum is a better place to find an answer, as indicated in the links below.

 

Here's one link on C5 SCT cooling:  http://www.cloudynig...wn#entry5273269

 

Here's another on a C6 SCT vs 6-inch Mak regarding cooling, et al:  http://www.cloudynig...n#entry4955069 

 

And here's a link on a C5 SCT vs C102 refractor:  http://www.cloudynig...2-any-advantage

 ==> note the comment by Sarkikos on page 2 regarding cooling

 

In short, more aperture gives more detail, but less aperture is better for quick grab-and-go/casual views.

 

 

Hmmm.... Maybe I should be considering a small refractor for those quick observing sessions, and a 6" or 8" SCT for those nights when I can observe all night? The 6" SCTs aren't very costly either. :hmm:

 

That's pretty much what I've done. But the C90 and C5 aren't bad for grab-n-go if you allow them to cool-down.

 

Mike


  • cwilson likes this

#15 Glen A W

Glen A W

    Viking 1

  • -----
  • Posts: 948
  • Joined: 04 Jul 2008
  • Loc: USA

Posted 15 August 2014 - 10:35 AM

I observed so much with a 4" achromat in years past that I still think the Moon should have a blue fringe!  It is like the way the old Star Wars movies used processes that put blue fringes around the space ships - it looked right to me.  I could go up to around 400x on the terminator, and maintain sharpness, though the image was dimming and yellowing a lot.

 

After I moved on to a Meade 8" f/6, I still missed the refractor's views.  The Meade could go higher in magnification, and it provided color free views which were also high in contrast.  I think the f/6 ratio helps over the short f/4 Dobs which are so common.  However, the old 4 inch would nearly hold its own, as it had a very good lens.  The old refractor made even the Full Moon interesting.  The shading in the maria and rays was just extraordinary.  My newer SW100ED cannot match the old achro in this respect.  On the reflector scale, I would rate the 4-inch achro as like a 6 or 6.5 inch reflector, with better contrast.

 

Glen



#16 cwilson

cwilson

    Mariner 2

  • -----
  • Posts: 211
  • Joined: 01 Oct 2012
  • Loc: SW Oklahoma

Posted 15 August 2014 - 11:18 PM

I observed so much with a 4" achromat in years past that I still think the Moon should have a blue fringe!  It is like the way the old Star Wars movies used processes that put blue fringes around the space ships - it looked right to me.  I could go up to around 400x on the terminator, and maintain sharpness, though the image was dimming and yellowing a lot.

 

After I moved on to a Meade 8" f/6, I still missed the refractor's views.  The Meade could go higher in magnification, and it provided color free views which were also high in contrast.  I think the f/6 ratio helps over the short f/4 Dobs which are so common.  However, the old 4 inch would nearly hold its own, as it had a very good lens.  The old refractor made even the Full Moon interesting.  The shading in the maria and rays was just extraordinary.  My newer SW100ED cannot match the old achro in this respect.  On the reflector scale, I would rate the 4-inch achro as like a 6 or 6.5 inch reflector, with better contrast.

 

Glen

 

Glen, how do you like the SW100ED overall? That's one of the scopes on my short list that I'm considering, along with the SW120ED.



#17 Glen A W

Glen A W

    Viking 1

  • -----
  • Posts: 948
  • Joined: 04 Jul 2008
  • Loc: USA

Posted 16 August 2014 - 05:22 PM

The SW100ED is an excellent scope, especially considering the low price.  It is certainly superior to the achro on Jupiter, maybe even on Saturn.  I think the reason I liked the achro so well on the full Moon is that the chromatic aberration made the bright white rings of highly-lit craters stand out.  I have not seen this effect with any other scope, yet it was very nice.  But the SW100ED is just amazing, for its size.  It gives remarkable views of Jupiter for a 4", and deep sky views are really superb.  I use it all the time because on a smaller mount, like the old Vixen regular Polaris I have it on, it can be taken outside in one piece.  It too can go up to crazy powers on the lunar terminator, like at least 400x.  A good 2" ED Barlow is a must.  I use the GSO model.  Glen


  • cwilson likes this

#18 Glen A W

Glen A W

    Viking 1

  • -----
  • Posts: 948
  • Joined: 04 Jul 2008
  • Loc: USA

Posted 16 August 2014 - 05:24 PM

By the way, the 4" achro I had was only a Chinese one, a Celestron CH102, which I bought nearly twenty years ago when they first starting bringing them over.  The lens was superb.  You should not rule out one of these because you can just about get them for free!   I didn't like it on Jupiter but it was just a fantastic lunar scope.  The contrast was awesome.  The SW100ED is a better scope, but doesn't have the "soul" the achro had.  On the Moon, I honestly would take the achro, but I gave it away to a beginner last year. 

 

Between 2000 and 2006, I observed the Moon most every night... or morning!  That 4" achro was a Lunar go-getter.  It was really atmospheric to be using a refractor, which is the kind of scope you see in old books.  And the detail and contrast that scope gave on the Moon - I mean, I can still remember the views like they are etched into my memory.

 

Don't forget to observe in mornings too, if you can.  Having the lighting from the other way makes things look different.  And, in the Fall, we get the crescent up high in the morning, at least here in the Northern Hemisphere.  I remember looking forward to sunset on Aristarchus and the Schroter Valley, in particular.  You don't need to spend a lot of money to get good Lunar views.  Get some books if you don't have them, and explore!

 

Glen


Edited by Glen A W, 16 August 2014 - 05:33 PM.

  • cwilson likes this

#19 karstenkoch

karstenkoch

    Viking 1

  • -----
  • Posts: 647
  • Joined: 21 Apr 2012
  • Loc: GMT+9

Posted 17 August 2014 - 12:51 AM

You don't need to spend a lot of money to get good Lunar views. Get some books if you don't have them, and explore!


Thank goodness for the moon! It's easily accessible with inexpensive equipment from heavily light polluted areas for two weeks every month, clouds permitting.

However, better equipment does improve the view ... better contrast, less scatter. I love browsing it's features on short notice with my 80mm APO. I usually don't go higher than an 8mm LVW with a 3x focal extender (180x) with this scope.

In any case, the moon usually looks great through just about anything. Enjoy it!





Also tagged with one or more of these keywords: refractor



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics