Sky Hunting with Small Refractors

[MistrBadgr]

As I mentioned in other posts, I am curious to find out just what can be seen with the small refractors one might purchase for a son or daughter, if not for oneself, to start finding out about astronomy.  I purchased an older model 60mm diameter by 700mm focal length NG-60 and a newer style 70mm f/10 NG-70 to try out.  The smaller one uses 0.965 eyepieces and the larger 1.25.

A few nights ago, I took them out for a trial run.  Both handled reasonably well.  I have discovered a few glitches that I will discuss later in another post.  The thrust of this one is what I could see in this first hunting expedition in my yard.

I live in a light pollution red zone in general, with an artificial sun on the front of a neighbor's garage that has no off switch.  I can, with effort, read parts of a newspaper with no additional light, when I have a fairly strong moon.


I first set up on Polaris.  I normally like to look at Polaris as a test for both sky and telescope.  I could only see one other Little Dipper star, so there was not much hope of seeing Polaris B.  For those that do not know, Polaris is actually a triple star system.  With small scopes, Polaris A and B should be visible.  Well...Polaris A looked yellower than usual and was wobbling around like a bowl of jello.  Forget Polaris B until I have a better night.  I did not have much trouble finding Polaris A with the 70mm.  Its eyepieces have a 50 degree fiield of view.  The sixty mm with the smaller eyepieces had an apparent field of view of at best 40 degrees and was much more difficult.

I then looked a Jupiter.  The nice thing about these Alt/Azimuth mounts is that I can just pick them up and move around.  No worries about messing up polar alignment.  I saw Jupiter as a squashed ball, a little more squashed than normal, due to its position near the western horizon.  It is also on its side by my perspective, with the orbits of its four moons traveling almost up and down.  I could not see any bands on the planet itself, due to having to look through too much atmosphere.  (A light fog high up was not helping any either.)  I could, however, see all four of the big moons.  At least three of the four, if not all four, are bigger than our moon.  I like to watch their dance around Jupiter over several nights.  Jupiter will be fun, with these scopes,  when it makes its way around to the morning side of things.  (Assuming I feel like getting up early in the morning.)  Well 1 out of 2 so far isn't too bad for a night like this.

The next item was a general look at the moon.  This is where both of these scopes really perform!  The light gathering power is low enough that I did not need any neutral filter, which can hurt the view some.  After all, it is another piece of glass to get in the way.  Later this year, I plan on starting a program of viewing a few different things on the moon each month and talking about them.  Both scopes can do well with shorter focal length eyepieces, or higher  power.  I was surprised at what I could see with the little eyepieces on the 60mm...barring a narrow field of view.  It naturally could have been better, but it was not bad.  Even the 4mm SR eyepiece showed me more than I thought it would.  The top end with these scopes and the moon is the equivalent of a 6mm or maybe a 5mm eyepiece.  After that, I think I would be magnififying fuzz and not seeing anything more. I had no luck with the 60mm scope's 3X barlow with any eyepiece.  I probably need to put it between the diagonal and the telescope.  I could not focus at all with it after the diagonal.

The 70mm was pleasant, but with most eyepieces, I think the 60mm can do just as well if the field was the same in terms of eyepieces.  Just for grins, I brought out a 4mm TMB planetary and had a look.  Not bad!.  It was pushing the little scope too far.  I will try some longer eyepieces later to see just how far it can be pushed and not go over the edge.

Next, I looked at the Great Orion Nebula.  For anyone unfamiliar with this nebula, look at Orion, which is in the Southeastern sky at about 8 PM in the middle of January from my house in Northeastern Oklahoma.  Look for his belt and then his sword hanging at an angle below it.  If you have much light polution, you may only see the middle and bottom of the three stars in the sword.  What looks like the middle star is actually the great Orion Nebula.  It is known to most astronomers as M-42.

There is a whole swathe of nebula material across Orion.  The great Orion Nebula is an area with bright young stars illuminating it.  In the little scope, I could see a vertical bar of the nebula that was slightly bent in a C shape.  This is the emmission nebula.  The bright stars push a lot of radiation into this part of the nebula and excite the hydrogen atoms there, which causes them to get all excited and start emitting light themselves.

   To the right of the C shaped part, there is another part of the nebula that is not radiating on its own, but reflects light from the stars back at us.  This is considered a seperate nebula called a reflection nebula.  With the 70mm, I could just begin to see this reflection portion.  In better lighting conditions, I believe both telescopes can too a good job with this object.  Certainly, it will not be the emotional or artistic experience that one can have with a ten inch or larger telescope.  It will still be very pretty anyway and a lot of fun to examine. 

From that point, I looked at the top cluster of stars in the nebula.  This is call the trapezium.  This is a double set of multiple stars and the two sets may revolve around each other as well.  I am not sure.  At first, I could only see three of the four main stars. As the evening progressed and visibility improved, I began to see the top star as a very tiny, very intense point of light.  With larger telescopes and good atmosphere, more stars can be seen.  With these little scopes, I think the challenge will be to see all four of the major trapezium stars and the reflection nebula.

I tried several different eyepieces on Orion.  The best view seemed to be with 12mm.  I tried the 6mm MA that I have  with the larger scope.  Things just got ugly.  Everything was fuzzy and the top star in the trapezium went out again.  I think the highest magnification for things like the Orion Nebula with these scopes will probably be in the the 60 to 80X range, unless you want a lower power to take in more of its surroundings.

The last item of the night is what is called an open cluster.  This particular one is one of my favorites.  It is so near the earth that it can be seen with the naked eye.  In ancient times, this was called the seven sisters or the Pleiades.  (I probably did not spell that right.  But, it is late and the audience I am writing to mostly will not be able to spell it either.) Now, it has a number like most things.  These days, most people will see six or eight stars, not seven.  Because of that, some people think one of the stars may have been brighter or at least shined different centuries ago compared to now.  What we see now is six very bright, large blue white stars that are burning at a very rapid rate.  There is some nebulosity in their area.  But, it is not thought to be the original mebula material of their birth.  It is just some gas that is drifting by or they are drifting through.

Where is this cluster?  At about 8 PM, from my yard, in the middle of January, it is an oblong fuzzy group of stars almost straight overhead.

Most people look at this cluster with binoclulars.  I like a low power telescope with maybe a 2 degree true field of view. 

With the little 60mm telescope with its 25mm eyepiece that has a 40 degree apparent field of view (how wide the view looks to you when looking through the eyepiece) , the true field of view (how wide a piece of the sky you are really looking at) is maybe one and a quarter degrees.  I could look at a sizable chunk of the cluster, but not all of it, much less viewing the whole thing with extra space around it  to see it in its surrounding setting.  I could see many of the stars and ponder which ones were double or multiple star systems.  However, I could not get a good sense of the cluster itself. 

With the 70mm scope and its 25mm eyepiece that has roughly a 50 degree apparent field of view, the true field of view is about 1.8 degrees.  I could just barely get in the wholee cluster and start to get a sense of what it is about.  I slipped into the garage and came out with a 32mm plossl.  If I were to recommend any additional eyepiece for this scope, it would be a 32mm plossle.  This gives a 2.4 degree true field of view.  This allows the Pleiades to really stand out.  As far as I am concerned, a 32 mm plossle is the best finder eyepiece made, regardless of what telesope you have with a focal ratio of 5 or more. (focal length divided by the diameter)  Shorter scopes are pretty much limited to 25mm and shorter eyepieces.  The little 70mm scope and the 32mm plossl seemed to be made for each other.  If I could have fit the 32mm eyepiece on the 60mm scope, I would probably say the same thing.  Unfortunately, a 1.25 inch diameter eyepiece does not fit into a 0.965 inch hole.

Well, I ran out of time and had to go in and get some rest.  I had to go to work the next day.  Over all, I would consider four of the five objects at least a reasonable success.  The one that was a miss was due, I think, to the weather.  Astronomy is a lot like hunting or fishing.  It depends a lot on things the person has no control over.  Sometimes you find a lot.  Other times you do not do so well.  That is why I am calling this series Sky Hunting.  I tried for a multiple star and missed, saw a major planet and its moons, looked at our moon, looked at two different kinds of nebula and a couple different open star clusters, these had multiple stars in them, so I saw some multiple stars anyway.  I had a lot of fun this night, exploring the sky and seeing what these little scopes can do.  I plan on doing it off and on through this yearof 2010.  I hope to have just as much fun on those occasions as well as I hope you have fun with your scope too.

Good Luck and Clear Skies!

Bill Steen

[MistrBadgr]

Well, I have been tinkering with Mars some with the 70mm refractor, trying out different entry level eyepieces.  We have had a lot of light fog high up.  I am not sure if it is that or the fact that either that size of a scope or that level of eyepieces cannot make it.  I had a lot of glare and really only had a fuzzy bright redish spot to look at.

I plan on trying again, with the entry level eyepieces and some others as well.  I am curious to find out what can be seen of Mars with some good planetary eyepieces.  The ones I will be trying are University Optics HD Orthoscopics, TMB Planetaries, and a combination of 2X and 3X APO barlows and some University Optics 70 degree eyepieces.  I have had some luck with wide angle eyepieces and conservative focal length telescopes for pulling out subtle details on lunar surfaces. 

It is a long shot all the way around.  But, maybe I can see something.


I also want to try and see the Andromeda Galaxy, a few open clusters, and maybe another nebula this next time out.  If I can pick out a pretty double star, I will include that also.

For anyone interested, I am using the AutoStar software that you can download from Meade to find things.  It seems to be better than the software that comes with the small scopes.

Hopefully, later this week the skies will clear and I can have some fun.

Clear Skies!

Bill Steen

[PapaJ]

MistrBadgr,I've been reading your posts because I,myself,have a small scope (90mm mac/cass)and am curious about what I might find with my different eyepieces (9.7,12.4,26 sp),which all are Meade. Please keep the info coming, because I'm also finding objects from my back yard, in the night skies, that  when they come into view, I go wow,I did'nt even know mine could that.

clear skies

PS,I before E except after C, but not in this case. (Pleiades)

[MistrBadgr]

I took out the 70mm refractor for another attempt at Mars.  Again, the uncoated entroductory eyepieces by themselves were overwhelmed.  Using a Meade #140 2X APO Barlow in front of the 25mm MA did a little better....maybe.  I was able to see the redish disk with what appeared to be a bluish white area around the upper left of my image.  Allowing for the left and right reversal in the image using a diagonal, the bluish white area was actually on the upper right.  Either it was a polar ice cap area or some kind of chromatic aberation.  If anyone knows where the visible polar ice cap is, please speak up.

With the coated W70 series and the #140 barlow, I was able to see consistent mottling between redish and bluish areas.  There was one bluish area in particular in the upper right of my image that kept showing up as well as some lesser areas in the bottom.

I saw roughly the same thing with the UO HD Orthoscopics.  With the large amount of light to play with, I was able pretty much to work up to the equivalent of a 5mm eyepiece.  This gives about the maximum magnification for the telescope of 140X.


No mater which set of eyepieces or barlows I used, I consistently was battling one major reflection that was off to the lower left.  Since this happened with all eyepieces, it was either the diagonal or something related to objective lenses or collimation.

In any event, with an elevated level of eyepieces, I could see some detail on Mars.  Does this mean that beginners should rush out and buy a bunch of better eyepieces?  You must remember that most of the eyepieces and barlows I was using cost each as much as the whole scope, tripod, original eyepieces, and all.  Getting a good look at Mars is just one of those things a beginner will have to wait for in terms of equipment.  There are many other things to observe with an entry level scope.  The point in this excersize was to determin if the 70mm scope could see anything of Mars at all with good eypieces.  Though not a high quality image, I belive the answer is yes.

I plan on getting the 70mm out again when the ground gets dryer and I can roll out my 14.25 inch f/6.7 reflector.  I should then be able to verify what I am seeing in the little scope.

I do recommend that you try looking at Mars.  Do not expect much, because that is most likely what you will get.  Then, if you see anything at all you can be happy about it.

Good Luck!

Bill Steen

[Philip Pugh]

OK, I have a bias but I don't know of any other book that covers this ground. Most astronomy books are aimed at total beginners or experts/specialists. This one is firmly aimed at those with some knowledge and gives realistic descriptions of what can be seen with small to medium instruments:

http://philippugh.fortunecity.com/ScienceAndArt.html

Quite often, you can improve the performance of modest instruments by suitable use of eyepieces/accessories. That's all covered, too.

[MistrBadgr]

Thanks, Philip!  I just ordered one.  You are right.  Such books are rare.  This is the kind of thing I do a lot with small scopes of one kind or another and plan on doing so with these two refractors after I get through seeing what they can do with the tools provided and in their original state.

I am working out what I can and cannot do with the basic entry level refractor the mom or dad will buy to start a young person in astronomy.  Possibly, mom or dad may be interested themselves.

Most books scoff at this level of telescope, saying not to buy them.  However, this is what mom or dad is going to see and not what is said in a book somewhere.  Secondly, mom or dad will most likely not be able or willing to pay for a larger or better made scope when the youngster may only show interest a time or two and then use the scope for a ball bat or some other such thing.

This level of scope has its purpose, which is to "introduce" someone to astronomy and not to fulfill the needs of an astute observer.  Hopefully, with this series of posts some light can be shed that can help a person new to astronomy use their new scope to the full and neigher be discouraged by what it cannot do or simply dismiss astronomy because of these initial limitations.


With your experience, any and all input you might care to make is very welcome.

Thanks,

Bill Steen

[MistrBadgr]

About a week and a half ago, I was away from home, working at a power station in Southwestern Oklahoma, near the town of Anadarko.  The plant has a water reservoir a couple of miles North and I decided to go there one evening and see what I could with the NG-70 refractor.

This area has, from my perspective, very dark skies.  They are not black, by the colored light pollution maps....probably on the border of blue and dark gray.

I arrived before sun down.  The wind slowly died until the reservoir surface was like glass.  The spot I picked protected me from any lights from the power plant and there were no others around.  It was just me, some giant Canadian geese, and a pack of coyotes howling in the distance.  The nearest town, Anadarko, is maybe eight miles away.

I first looked for the moon as the sun was sinking.  It was maybe three days past full moon and I thought I should be able to see a little of it before the sun went completely down.  I was wrong.  However, immediately as the last bit of the sun dropped below the horizon....pop! There it was!.  I had a lot of fun just watching things show up on the moon at maybe 60X.  I would look for a while, then rest my eyes for a moment.  When I looked back, there would be something new there and I would say to myself, "That is so plain!  Why could I not see that a moment ago?!"

Mare Crisium was just about right in terms of terminator location.  Not only were several small creators visible, so were several dorsa (ridges) that are hard to see at any time except when the terminator is near.  The craters Picard, SWift, and Peirce were all readily visible.  I could see the peaks of some mountains starting to get light, probably the Montes Taurus.

From there, I went looking for the double cluster in Perseus.  After a little searching, I found them.  Man!   with no real light pollution, they were quite a site.  I happened to look up from the telescope at Persius and there were the two clusters!  I could see them just with my eyes and no scope.

The double cluster is located between the star that I think of as the point of Perseus's cap and the two western-most stars of Cassiopeia.  Cassiopeia is a zig-zaggy constellation that looks like a lop-sided crown.  From the line connecting the last to major stars in Cassiopeia and Nu Perseus (the point of his cap), the Double Cluster is about one-third of the way from the point to the line.

I spent a little time looking at Mars.  From that location, it looked about the same or actually a little worse than at home.  I really do not know why.

Next...M-31...The Great Andromeda Galaxy.  I cannot see this from home, with the aritficial sun on the front of my neighbors house, and red zone light pollutin otherwise, except for an occasional hint of the center......with ANY scope.  Here, it was plainly visible to the naked eye and impressive through the little scope.  With the 70mm refractor I could see disk about half way to M-110, the satelite spiral galaxy.  I could just barely make out the center of that one.  There was an odd dark area along where I thought I should see M-32, the little eliptical galaxy satelite of M-31.  I was surprised not to see it.  Possibly there was a small cloud in the way.  There were a few tiny ones around in an otherwise clear, stable sky.

The way I find Andromeda is to think of the constellation as a long dress of the queen.  There is a star at the top or point, then three sets of pairs that go wider and wider from the point.  If you draw a line through the second pair of stars and head Northeasterly about the same distance as between the two stars, you will find M-31.  If you follow the same line in the other direction about double the distance between the two stars and then jog a little bit  to the west, you should find M-33, the Triangulum galaxy.  That one is hard for me to see anywhere.

By the time I finished with Andromeda it was getting a little too cold and was time for me to go to the hotel.  It was only 8:00 PM.  But, I had a big day planned for tomorrow.  It was a good thing to go anyway.  The pack of coyootes were getting pretty close.  They normally shy away from people.  But, with no fire arm with me (not allowed on company property) I really did not want to stay and debate the point if a large number of them showed up.

I did look around a little for M-33.  But, I did not find it.  That one is probably not in the cards for this scope....at least for me.

As I was packing up to go, I looked to the east, about half way up in the sky,  and identified M-44, the beehive cluster, just sitting there!  I thought, "Wow, I wonder what this place is like after the moon goes down?"

[Philip Pugh]

About a week and a half ago, I was away from home, working at a power station in Southwestern Oklahoma, near the town of Anadarko.  The plant has a water reservoir a couple of miles North and I decided to go there one evening and see what I could with the NG-70 refractor.

This area has, from my perspective, very dark skies.  They are not black, by the colored light pollution maps....probably on the border of blue and dark gray.

I arrived before sun down.  The wind slowly died until the reservoir surface was like glass.  The spot I picked protected me from any lights from the power plant and there were no others around.  It was just me, some giant Canadian geese, and a pack of coyotes howling in the distance.  The nearest town, Anadarko, is maybe eight miles away.

I first looked for the moon as the sun was sinking.  It was maybe three days past full moon and I thought I should be able to see a little of it before the sun went completely down.  I was wrong.  However, immediately as the last bit of the sun dropped below the horizon....pop! There it was!.  I had a lot of fun just watching things show up on the moon at maybe 60X.  I would look for a while, then rest my eyes for a moment.  When I looked back, there would be something new there and I would say to myself, "That is so plain!  Why could I not see that a moment ago?!"

Mare Crisium was just about right in terms of terminator location.  Not only were several small creators visible, so were several dorsa (ridges) that are hard to see at any time except when the terminator is near.  The craters Picard, SWift, and Peirce were all readily visible.  I could see the peaks of some mountains starting to get light, probably the Montes Taurus.

From there, I went looking for the double cluster in Perseus.  After a little searching, I found them.  Man!   with no real light pollution, they were quite a site.  I happened to look up from the telescope at Persius and there were the two clusters!  I could see them just with my eyes and no scope.

The double cluster is located between the star that I think of as the point of Perseus's cap and the two western-most stars of Cassiopeia.  Cassiopeia is a zig-zaggy constellation that looks like a lop-sided crown.  From the line connecting the last to major stars in Cassiopeia and Nu Perseus (the point of his cap), the Double Cluster is about one-third of the way from the point to the line.

I spent a little time looking at Mars.  From that location, it looked about the same or actually a little worse than at home.  I really do not know why.

Next...M-31...The Great Andromeda Galaxy.  I cannot see this from home, with the aritficial sun on the front of my neighbors house, and red zone light pollutin otherwise, except for an occasional hint of the center......with ANY scope.  Here, it was plainly visible to the naked eye and impressive through the little scope.  With the 70mm refractor I could see disk about half way to M-110, the satelite spiral galaxy.  I could just barely make out the center of that one.  There was an odd dark area along where I thought I should see M-32, the little eliptical galaxy satelite of M-31.  I was surprised not to see it.  Possibly there was a small cloud in the way.  There were a few tiny ones around in an otherwise clear, stable sky.

The way I find Andromeda is to think of the constellation as a long dress of the queen.  There is a star at the top or point, then three sets of pairs that go wider and wider from the point.  If you draw a line through the second pair of stars and head Northeasterly about the same distance as between the two stars, you will find M-31.  If you follow the same line in the other direction about double the distance between the two stars and then jog a little bit  to the west, you should find M-33, the Triangulum galaxy.  That one is hard for me to see anywhere.

By the time I finished with Andromeda it was getting a little too cold and was time for me to go to the hotel.  It was only 8:00 PM.  But, I had a big day planned for tomorrow.  It was a good thing to go anyway.  The pack of coyootes were getting pretty close.  They normally shy away from people.  But, with no fire arm with me (not allowed on company property) I really did not want to stay and debate the point if a large number of them showed up.

I did look around a little for M-33.  But, I did not find it.  That one is probably not in the cards for this scope....at least for me.

As I was packing up to go, I looked to the east, about half way up in the sky,  and identified M-44, the beehive cluster, just sitting there!  I thought, "Wow, I wonder what this place is like after the moon goes down?"

A light pollution reduction filter helps when you can't get a dark site. Revolutionised my viewing!

[MistrBadgr]

I purchased a book entitled, The Moon and How to Observe It by Peter Grego, published by Springer.  It appears to be what I needed to help me understand more of what is on the Moon and why.  It also has a section on equipment, which I read with considerable attention.  There is a table in it that tells what will most likely be the highest usable magnification for a particular size of telescope and the size of the smallest object that should be detectable.

The same standard that I have used before of 2X the diameter of the objective in milimeters seems to apply as well, even though I have used magnifications higher than that when viewing through a higher quality telescope than the NG series telescopes.

Mr Grego also give information on what the smallest size object that should be detectible with various sizes.  For a 60mm, the smallest object that should be dissernable is 3.6 km and for an 80mm, that number is 2.7.  Taking the average of the two, the 70mm comes out near 3.2 km.

Taking out the NG-70 a couple of times this last week, I studiedMare Humorium.  I could see some of the dorsa as well as some fairly small craters.  Three that I can remember distinctly are Gaswsendi O, J, and Y.  Gassendi Y was of interest to me as the smallest of the three.  When I looked up the size of that crater, it showed to be 3 moles or 5 m across.  From what I could see of that crater, I beleve the NG-70 could indeed discern a lunar object in the range of 3.2 km or very nearly that.

With a telescope of that size seeing what it can, I believe it can be used to make a relatively in-depth study of the moon.  By the time the observer sees all the things that can be seen with this scope well enough to identify the objects.  That person will be a lunar expert with more knowledge of the moon than many people who have been into astronomy for decades.

Observing the moon is definitely a strong suit for small refractors.

Sky and Telescope has a field map of the moon that I would recommend to you.  I personally bought what I think is a better copy, that is illustrated by Antionin Rukl.  I bought both the straight forward version and the reversed version, thinking that both would come in handy.  So far, I have only used the straight forward version.  This particular item, that I have bought is more expensive than another set that I believe may be based on photographs.  The lower priced version, I sells for $4.50 per copy, if I remember correctly.  The version I bought sells for $11.00.  Most likely either one can do the job.

I have tried any number of filters, including a polarizer.  Possibly, it is just me.  With this small of a telescope, I am not really seeing any improvement in what I can see enough to warrant the purchase of addition equipment, except a 2X barlow to use with a 9 or 10mm eyepiece to get the maximum magnification the scopes can handle.  Near full moon, a neutral density filter might be helpful.  However, you can still see the things you want to see, assuming they are visible at all with no shadows.  The high light level will simply mess up your night vision for a while for other things.

During those observing sessions, I did a little more work trying to see what I can of Mars, the Double Cluster, and "The Horse and Rider" in Ursa Major.  I will talk about that in another post to this string.

[MistrBadgr]

Mizar and Alcor, the Horse and Rider, is the first known double star.  This couple was known in antiquity and was considered a test for good eyesight.  If you could see the two stars, then you had good eyesight.

Looking at the the Big Dipper, (I think it is called the Plow in Europe), Mizar is the second star from the end of the handle.  Training a small refractor on this pair, you suddenly find that there are not two, but three stars!  Mizar is a double all by itself!.  There is another little secret here.  Mizar A, Mizar B, and Alcor are all close doubles themselves.  That makes this a six star system.  It is located about 78 light years away.  Look up Mizar on Google and look at a wikkipedia and another article from a university website.  I will not steal the thunder from these articles.  Go read them and then look at this system with your telescope.  Knowing what I was looking at added excitement for me.

Being back home in my normal red zone back yard, I took a look at the double cluster to make sure I could find it with a little refractor.  Sure enough, it was there.....just not as sensational as in a dark sky.  If I had not know where to look or what I was looking for, I probably would have missed it.

I did a little playing with filters, looking at Mars.  Already, Mars is starting to fade for a little scope.  I believe that Mars, at its brightest is most likely helped with an orange filter (Wratten 21) with possibly a single polarizer on top.  With the planet fading a little, I think it was a best with a dark yellow or Wratten 15.  With an 82A (light blue), the polar ice cap area stood out a little better.  In order for Mars to be of much interest with a small refractor, the disk probably needs to be at least 10 arcseconds across.  Or, in other words, near opposition.

In general, I do not think filters will help a small refractor much.  Filters only subtract light and not add any.  With the light gathering limitations of a small refractor, filters are best left alone.  The moon, Mars, and maybe Venus are exceptions.  This of course assumes you can see anything at all of Venus other than a white ball.  Supposedly, a violet filter can aid in seeing faint patterns in the Venusian atmosphere.  A violet filter lets only about 3% of the light through.  I have not tried one and probably will sometime.  For a very small refractor, I doubt that it will help much if any.  I do not think it would be worth the money to purchase a violet filter for a small refractor.

Well, that is all I have been able to see to date.  With rolling cloud covers, it has been hard to get time outside.  Hopefully, if I am clouded in, then maybe some of you have clear skies.

Bill Steen

[Philip Pugh]

I purchased a book entitled, The Moon and How to Observe It by Peter Grego, published by Springer.  It appears to be what I needed to help me understand more of what is on the Moon and why.  It also has a section on equipment, which I read with considerable attention.  There is a table in it that tells what will most likely be the highest usable magnification for a particular size of telescope and the size of the smallest object that should be detectable.

The same standard that I have used before of 2X the diameter of the objective in milimeters seems to apply as well, even though I have used magnifications higher than that when viewing through a higher quality telescope than the NG series telescopes.

Mr Grego also give information on what the smallest size object that should be detectible with various sizes.  For a 60mm, the smallest object that should be dissernable is 3.6 km and for an 80mm, that number is 2.7.  Taking the average of the two, the 70mm comes out near 3.2 km.

Taking out the NG-70 a couple of times this last week, I studiedMare Humorium.  I could see some of the dorsa as well as some fairly small craters.  Three that I can remember distinctly are Gaswsendi O, J, and Y.  Gassendi Y was of interest to me as the smallest of the three.  When I looked up the size of that crater, it showed to be 3 moles or 5 m across.  From what I could see of that crater, I beleve the NG-70 could indeed discern a lunar object in the range of 3.2 km or very nearly that.

With a telescope of that size seeing what it can, I believe it can be used to make a relatively in-depth study of the moon.  By the time the observer sees all the things that can be seen with this scope well enough to identify the objects.  That person will be a lunar expert with more knowledge of the moon than many people who have been into astronomy for decades.

Observing the moon is definitely a strong suit for small refractors.

Sky and Telescope has a field map of the moon that I would recommend to you.  I personally bought what I think is a better copy, that is illustrated by Antionin Rukl.  I bought both the straight forward version and the reversed version, thinking that both would come in handy.  So far, I have only used the straight forward version.  This particular item, that I have bought is more expensive than another set that I believe may be based on photographs.  The lower priced version, I sells for $4.50 per copy, if I remember correctly.  The version I bought sells for $11.00.  Most likely either one can do the job.

I have tried any number of filters, including a polarizer.  Possibly, it is just me.  With this small of a telescope, I am not really seeing any improvement in what I can see enough to warrant the purchase of addition equipment, except a 2X barlow to use with a 9 or 10mm eyepiece to get the maximum magnification the scopes can handle.  Near full moon, a neutral density filter might be helpful.  However, you can still see the things you want to see, assuming they are visible at all with no shadows.  The high light level will simply mess up your night vision for a while for other things.

During those observing sessions, I did a little more work trying to see what I can of Mars, the Double Cluster, and "The Horse and Rider" in Ursa Major.  I will talk about that in another post to this string.

I don't totally believe the 2xaperture in mm room. With a wonky mount, you'll be lucky to get 1x and on brighter objects and a decent telescope/mount, you can push it up to 4xaperture. Needs a bit of trial and error. By "decent", I'm thinking of an APO, Maksutov or really high quality Newtonian.

[MistrBadgr]

With an NG-70 and NG-60, looking at the moon, 2X is about what I am able to push to.  For the weight of the scope, the mounts and tripods are fairly stable.  The 140X for the NG-70 really is about the end of the road due to manually pushing the scope around with no fine adjustments.  For a really top end refractor in this size, I think the mount and motion controls would also have to be really top notch to go much higher.

[Philip Pugh]

With an NG-70 and NG-60, looking at the moon, 2X is about what I am able to push to.  For the weight of the scope, the mounts and tripods are fairly stable.  The 140X for the NG-70 really is about the end of the road due to manually pushing the scope around with no fine adjustments.  For a really top end refractor in this size, I think the mount and motion controls would also have to be really top notch to go much higher.

For achromats that's not unreasonable, although I have managed 240x with a 60mm achromat. Good mount, though. If you have a Maksutov or Apochromat (and probably an Advanced Coma Free, too but I've never looked though one) you can push it a bit. Indeed, I've snapped crater close-ups at nearly 500x but I've also got the EQ3/2 mount, which is rather solid.

Peter's book is rather good. I have to admit a certain bias, as I've worked on a revision of Tony Buick's "How to Photograph the Moon and Planets...", which I hope will be out later this year.



I have added a lot in my lunar section of "The Science and Art of using telescopes" which is aimed at the astronomers who are just emerging from the beginner phase.