Focal Length Test

As I progress through building my telescope, it is important to know and understand the focal length, or distance where all of the light from the star forms into an actual image at one point.  There is a simple yet effective way to do this.  You don’t need much, but a checklist is helpful.

When I perform this test, I use:

a bucket  halfway full with clean water

a tape measure that extends to about 100 inches

the mirror (duh)

a piece of chalk or card to mark the distance

and a white poster board (optional but it helps)

Here is the setup:

So here’s the steps from Building a Reflecting Telescope:


As you can see, the process is so simple and straight to the point that I will agree not to explain what is being depicted.  My results came out well as expected.  I was aiming for an f/12 telescope, which would yield a 48 inch focal length, and it came in at 47 inches.  No harm done, as an inch will not effect the performance in the least bit.

As I was grinding on the weekend, I am on the last 2 abrasives; aluminum oxide 9 and 5 micron.  It is said that when grinding has been successfully completed, the mirror will feel like the finest satin to the touch, and newsprint can be read through it.  It’s already unbelievably smooth, and not quite able to read through, but nevermind.

I caught a snag while finishing my abrasive: I scratched the mirror’s surface near the edge.  I’m not quite sure how it happened, but my best guess is that somehow, dirt of some sort got between the glasses, and scratched.  If this furrow was near the center, I wouldn’t be stressing over it as much.  It takes about 3 times as long to remove such a thing at the edge than one near the center, as the glass naturally grinds out fastest at the center.  Oh well.  I knew that I would get a scratch at some point, but I’m happy it wasn’t during polishing, or I would have been in some serious trouble.

Hope to be finishing this project soon, because I’m itchy to look through this telescope!



Deep Sky with Binoculars and Mirror Grinding

Grinding is wrapping up for my telescope mirror project.  I only have 3 more abrasives left to grind through, and the on to polishing.  The project is going very well, and the abrasive is like a powder.  It has been rainy the past few days, so that ruled out most of the observing, but before I get into the project, I had a spectacular night with binoculars.

I have a decent pair of Barska 10×50 binoculars, and there were clearings from the clouds and the rain late at night.  Cassiopeia is getting pretty high up in the sky now, so that means prime observing time for the Double Cluster, NGC 869.  Through the binos, it is  large, bright, and resolves approximately 40 stars with an unresolved background of stars.  This large bright grouping could even be sen with my unaided eye, as 2 faint small patches of light.

My next target was another Cassiopeia cluster- NGC 7789.  It was faint, but there as an irregular glow of unresolved stars.  It was nice to see a non-Messier object with binoculars.

Next was M31, Andromeda galaxy.  It is easily seen in the binoculars, but not naked eye.  The core was bright and obvious and was very large.  I could not detect M32 nor M110.

My last target was M33, Triangulum.  If you observe in skies similar to mine, you know how difficult of an object this is.  I started scanning the area several times, and I detected a faint oval patch of light.  I had finally found M33!  It was not an impressive view, but It was certainly visible.

It turned out to be a great night, and was good enough for me.  Sometimes, small optical devices are all you need to enjoy the night sky.  The clouds came and went as the night wore on, but I was satisfied to have my look at the heavens.

In the last post I set up a grinding schedule to accomplish one grade of abrasive every week.  It looks like that plan is going to work.  I set up my equipment and got to work.  I always find it interesting to feel and study the surface of the glass closely and then grind the next finer abrasive for 30 minutes or so and then look and feel the difference.  This was apparent after transitioning from Silicon Carbide #80 to #120.  These are very coarse grains, but there is a big difference.

It seems impossible that there are still 3 more grades left, because the surface is so smooth to the touch.  I opened up the 5 micron container and sampled its size.  I detected no difference in texture from the 5 micron to the 15 micron.  As I was cleaning up shop for the day, I thought about just putting a layer of plastic wrap over the top of the workstand, then removing it when it is time to change abrasive sizes.  That way, I don’t  have to clean it outside and re-level the stand each time which would save a huge amount of time.



Theory of Distance and Visual Limits

Early on in my astronomy career, I was looking at a rather nice astronomy book and it had wonderful high quality large photo prints.  They were obviously at the Hubble level, and they showed an excellent amount of detail.

I had left the book on my bed propped up, and upon my return, I noticed something.  I stood back a few feet, and noticed that there was less detail than being up close to it.  It seems like a rather oridinary thing, but I studied this for a while, and I started to formulate a scientific theory.

This theory states that there is a limit at which the human eye can detect color, and this varies to the person.  Plain and simple, at a certain distance, you can no longer detect color in an object.  I believe that this is possible in not just photographs, but as well live objects.

Step 1: Acquire a large, visual, preferably not very filtered astronomical picture.  The Orion Nebula and Andromeda galaxy are perfect.  Prop them up on a chair outside.

Step 2: Walk up to the photograph, and note the definite color and detail in the deep sky object.  Note and remember what you see.

Step 3:  Now walk back 10 feet, and study the photograph.  It now appears smaller, and with less striking colors and details.  What were beautifully detailed and cloudy objects are reduced to a smoother, mottled appearence.Note and remember what you see.

Step 4: Walk back another 10-15 feet and study the picture now.  It has most of it’s defined detail gone.  Now, when I got to this point, I came upon a problem.  Galaxies and nebulae emit their own light, and a photograph does not.  The solution I found was to have the picture be printed on a translucent piece of bendable plastic.  Now take a light, and shine it through the back, but scatter the light with a thin fabric sheet to make the light distribution equal over all diameters.  I probabily should have told you this before, so my apologies.

Step 5:  Now walk back again and again, repeating the process until which there is no more color detected by your eye.  This distance varies for everyone and generally, the view will be very similar to the view through a telescope.  You have now found your visual limit; but now what?

I am no math wizard, so there must be some kind of number system for the visual limit.  And if so, the object, distance of that object for real and the exposure time must also be accounted for.  This requires one big equation that I am definitely not up for.


This experiment actually works too! I tried it and there is something to this, try it yourself, it should only take a few minutes.  If you can’t have it printed on translucent plastic, another possible method is to print it out on regular paper or a poster and tape the paper to the plastic.  A decent astronomy poster that is somewhat large can be had for under 10 dollars on amazon.

Good luck and clear skies.




Less than Transparent Skies

The growing dilema in amateur astronomy is light pollution and other related sources.  In the mid city, forget about all of the NGC’s or IC’s you’ll be lucky to see all of the Messiers.  I have faced this problem everytime I go out with my telescope.  The LA county fair is in full swing right now, and that pretty much rules out the entire southern sky.

I don’t have any problem with the fair, it’s just that it turns an already not transparent sky into something that can’t be described without seeing it firsthand.  If you live far away in the country, you don’t have much problem with this.

Anyway, I am finishing up the Mesier project, 70 objects are very close now! I need only about 15 more Messiers, but this is hardly any compared to how many I have observed.  Pretty much all of these were observed in town, in badly polluted skies.  Before going out with the telescope, I look at the color of the daytime sky.  If it is a deep blue, it will be a decent night.  However, if it is pale blue and the area above the horizon is a dirty smog color, it will not be worth going out for deep sky.  I have been limited to planets and the moon on nights like that.

I can’t wait to see dark skies, even acceptably dark sites like Mount Baldy are well worth the trip.  By the way, the blog appearence and theme has been changing a lot lately and I have finally found a look that I am satisfied with.  I haven’t observed too much as school is really in full swing now.  I have also been blogging less, like one to two posts a week.

If you ever get the chance to pull the trigger on one of Astro league, programs, it is HIGHLY reccomended you start one.  Mesier one is awesome for learning and taking notes on these bright and detailed astronomical objects.

Clear Skies

Astronomical Sketches: Old And New

I’ve been going through some of my old observing notes lately and pulled out my very first astronomical sketch book.  I took a few minutes and looked through every page.  If you’ve seen my recent sketches, they are perfect representations of what you would see through the eyepiece, except they are negatives.  All of the sketches in my first book were all made with #2 pencil.

My first sketches were made on lined paper and the sketching circle representing the field of view in a telescope eyepiece was just merely hand drawn.  These first sketches were crude, and they were not descriptive or an accurate sketch either.  I the went to taping circular pieces of sketching paper which proved much better.

I was still not very satisfied with my results, and wanted more oomph from the sketches.  I read Steve Coe’s Deep Sky Observing, which is one of the best deep sky/ sketching books I have ever read.  Then came the perfect set up.  I has ample room for notes, including dates; times; and telescopes used plus a 3 inch circle complete with North and East markings.  These could be made on the computer and were used with ease.For an example of what these sketches look like versus the real thing: I have a picture of the real object and one of the sketch I made.











This object is a planetary nebula- the Dumbbell Nebula (M27).  See the Dumbbell? The sketch was made using my small 70mm Refractor, and the view would have been much more impressive from a darker sky.  For those who live in light polluted skies, you feel my pain and know what I am talking about.  There is one other type of deep sky object I like to sketch: globular clusters.  At first I thought this was not possible but once again, referring back to Deep Sky Observing, it shows how to sketch these stellar nodules of stars in space.

The view through a small telescope is dramatically less impressive than looking at a high quality photograph.  A strip of 35mm film can capture much more light than your eye.











You can really see the difference in globular clusters obviously.  By the way, Hi Digi Com and Media!

The Moon: A Tribute to Armstrong

The celebrated life of world famous astronaut Neil Armstrong has passed last weekend.  As a tribute, all weekend I observed the moon.  From Friday to Sunday, I viewed the moon on every night using my dad’s 6 inch reflector and my regular- 70mm f/10.

My dad had just gotten one of those sky and telescope moon maps and he was using his little 4 1/2 inch reflector.  It was the day after first quarter, so it was pretty bright by then.  My dad was busy with the moon, I looked up and noticed how transparent the sky was!  If you remember me talking about seeing the central star in M57, this night was 10 times better than that.  Honestly, I think pretty much any night would be better that that one, but the Milky was seen, it was not bright, but it was there.

I viewed M31, Andromeda Galaxy, and countless others.  The 2 other days were remarkably clear, in fact, I actually logged in many Messier objects for the program from the Astronomical League.  Only 22 left!



Whenever I observe the moon, I always have to try to take some decent pictures.  I took more than I should, but I guess that’s not a bad thing.  They actually come out pretty good in the 70mm.  I’ll share some of the best ones:



I have also been encountering severe moisture in the air late at night.  After 2 or 3 hours of observing, I come in and it looks like my equipment was just sprayed with a garden hose.  I guess that means that fall and winter are on the horizon, because it’s been cooling down more lately.  More recently, it barely cools at all. At 11:00 last night, it was still something like 83 degrees.  So I guess the heat is still to stick around for a little longer.

Regarding small scopes, the 70mm has become quite a performer.  One thing to add before I go into a small discussion of moon scopes, I just cleaned my telescope lenses last night.  The telescope is a second, meaning that it had minor imperfections   There are a couple scratches here and there on the tube, but after thoroughly cleaning each lens, They were pristine.  They actually looked better than when I first got the telescope.

On to the moon scopes.  The 70mm f/10 is an excellent choice.  It pulls in a fair amount of light, and has a long focal length for that size (700mm).  For example, Sunday night I counted 5 crate-lets on the floor of Plato in full sunlight.  It seems that refractors have an advantage over reflectors because there is no central obstruction.  For that reason, refractors will always have sharper crisper images than reflectors.  Virtually any decent Refractor will prove to be an excellent lunar scope.  I love medium to large scopes too, and my serious aperture is Orion’s 10″ classic dob.  I probably said that before, but it’s such a cool scope.

Don’t forget that observing with your telescope is supposed to be an enjoyable experience.  I know that many astronomers take all their “observations” as pictures, but try to just observe.  It’s a lot easier to set up too.  Try sidewalk astronomy, it is really interesting as well

By the way, I didn’t take this picture of Plato!

Meteor Shower Bust

As many of you have heard of the meteor shower the past 3 days, I had been up on the second day, thinking that it was the peak of the show.  The weather has been pretty iffy lately and these clouds come in from the east.  Then they stay right where they are because there is no breeze to blow them away.

Anyway,  it wasn’t very good at my house, which is heavily light polluted.  But I did have PVAA’s loaner 8 inch scope handy and used that most of the time.  I was up ’til about 1:30 in the morning, and by that time, M31 (Andromeda galaxy) and M33 (Triangulum Galaxy) had come up pretty high.  M31 was a cinch, and was glimpsed naked eye.  Nearby was M110, which was very bright.  M32, which is right on M31 was not visible, I have never seen the dark lanes or globular clusters in M31.

The next target was Stephan’s Quintet, I hope that’s spelled right.  I was unable to snag the grouping of galaxies.  By that time, Scorpius was below the horizon and the teapot was practically invisible.  All in all it was a great night, except for the main attraction, I counted a lousy 20 meteors.  I have thought it would be interesting to sketch them, so at some point, I will attempt to.  I have seen some with double tails, in all different colors.


I have been looking online for some UHC filters, I don’t care what brand it is, and I have found a site where they sell pretty cheap.  Kson Optics has been around since the 80’s and make telescopes, mounts, rifle scopes, and scope accessories.  I have not found the actual filter on their site, but it does come in a filter wheel along with planetary and other DS filters.  I checked on Amazon for them, and the cheapest model is around $40.  So it seems like that’s the cheapest I can find anywhere online.

I just wanted to say a few words about 10minuteastronomy and his recent post on “What’s on you bucket list?”  Somebody wrote a comment saying some of the stuff that he has seen.  I think its worth some words:

For years I thought an 8″ scope was a “lifetime” scope. Probably around 15000 DSOs are reachable, and pretty much all star clusters. You could spend a lifetime with one and become quite an accomplished observer.
But my interests shifted more to galaxies so I moved up “a magnitude” to a 12.5″. And while I certainly can see more galaxies and details therein, the biggest difference in appearance came with the mundane, easily visible, brighter objects.
I’ve seen (and it wasn’t possible in an 8″):
–individual stars in M31 (NGC206 stars)
–stars across the face of M14
–tons of H-II regions in most of the nearer galaxies
–white swirls inside the GRS on Jupiter
–brightness variations on Ganymede
–differential colors in the Galilean moons
–the Keeler Gap in Saturn’s rings
–the outer spiral arms of M81 and NGC7331
–to-the-core resolution on M15
–red giants in M13
–dark lanes in tons of edge-on galaxies
–M17 and M16 as part of the same nebula
–wonderful striations across the face of NGC6888
–B33 (Horsehead), both with and without a filter
–galaxies in some faint Abell Galaxy clusters
–several Abell planetaries


After reading this list myself I thought hey, I want to see that stuff too it sounded like lot’s of cool things are reachable in telescopes of modest aperture.  I have something to add that’s possible in scopes of a minimum of 8 inches: the moons of Mars.  Everybody’s all excited about Curiosity landing and all, but I found out how to view it.

It involves “occulting” the eyepiece.  The process is to take a piece of foil, painted black and cover half the lens of the eyepiece (on the inside).  This effect when positioned correctly will block out the light of the red planet and allow the Moons Phobos and Deimos to be seen. This must be done on a telescope with perfectly clean optics, perfect collimation, and a reasonably good night.  I found out about this in a booked called Astronomy Hacks available through amazon.  Mars is getting low in the sky, but why not give it a try?






Some Great Books…

I have noticed on the right sidebar of this blog that there was a significant jump in the views yesterday.  From the first  10 minutes of my previous post there was at least 10 views.  It brought the total to 79.  Now as I am making this post, it is  up to 85!  I really thank all of you that visit my blog.  I would like to hear what you think of it.  Please send me a comment at the top of this post by the title.  When you comment, you will have to enter your email ( it won’t let me change that).  When you do comment, it will be sent to me via email and I will put it on the blog with a reply from me.

Anyway, today I’m talking all about books.  If you want to become really successful astronomer, you’ll find you accumulate many books.  Books about astronomy come in many forms.  They vary from subjects suitable for beginners or equations regarding quantum physics.  It just depends on what you need or want.  For example, in the deep sky observing catagory, I recieved the book,  Deep Sky Observing, by Steven R. Coe.  He is a very accomplished astronomer and makes gorgeous astronomical sketches.  Basically, his entire life’s work is in that book.  He uses an array  of different instruments as well!  Telescope sizes range from 6inches to 36inches!  I is all explained well in Coe’s notes.  Highly recommended.













One of the best deep sky observing books I have heard about but don’t have is Burnham’s Celestial Handbook  by Robert Burnham Jr.  It is kind of an old book, but covers the entire sky and shows what to look at.  His 3 volume set is one massive work.  Steve Coe, recently observed every object in Burnham’s book.

There is one more book I would like to share on today’s post and that book is called Universe: the Definitive Visual Guide edited by Martin Rees.  The book shares many authors, too numerous to mention.  There are 2 versions available, A large hardback edition or a smaller paperback edition.  This book covers everything having to do with astronomy.  Each page has beautiful high contrast color photos on it.  The last 20 pages or so has some exceptional star charts that I have used many times before.  If you want a big book covering countless topics, you need this book.

All of these books are available through and can be purchased reasonably cheap.


All of these books are  really great for astronomy and you will be impressed with all of them.  Also, tonight there is an astronomy meeting tonight for my astronomy club, here’s the link again:  I will bring my observing notes and sketches as I haven’t had time to post them on the blog yet.  Hopefully sometime soon in the future would be nice.