Stephen Hamilton's Astronomy Blog

My thoughts on Astronomy, Imaging, and just about anything else I may come up with.

<June 2017>



Meade 6.3 Focal Reducer Test and Setup

Why Write this article:

There has been a lot of discussion concerning the use of standard Meade (and other's) focal reducers with the DSI cameras including questions of optimal distance, expected performance, etc.  I conducted the test below in February of 2006 along with testing several other focal reducers.  Since many people have the Meade 6.3 focal reducer and are copnsidering using it with thier cameras and various scopes, I though it was appropriate to post my findings on the use of this focal reducer and the results.  While I attemtped to be very precise and careful in my measurements, you may find that your particular setup may differ as may your results.  This is not a conclusive article on the use of the reducers in all situations but should give yo a good idea of what you may expect when using them with a DSI camera.


This article documents tests conducted using the Meade 6.3 focal reducer.  Where applicable, images and photometric data will be supplied along with detailed measurements to support my findings.  Overall, a few tests were conducted utilizing the focal reducer in various configurations.  The details of each test primary test are documented here

Test Conditions:

These tests were conducted on the night of Friday, February 24, 2006 between 8:00 and 11:00 PM.  During the tests, the sky conditions were generally very good with seeing around 8/10ths and transparency about 7-8/10ths.  Outside temperature range was between 3.8C at 8:00 PM and -0.9C at 11:00 PM.  DSI-Pro II chip temperature ranged from 9.0C to 7.5C throughout the evening.  Dark Frames were captured at 8.5C and used for all images utilizing the auto-dark subtract sub-routines in Envisage.

Equipment Setup:

Scope:      Meade 8” LX90 UHTC
Mount:      Equatorially mounted on the Meade Super Wedge
Camera:   DSI-Pro II
Filters:     ATIK Filter Wheel used during 6.3 tests, no filters (or wheel) during 3.3 tests
Guiding:   DSI-Pro thru ETX-90 mounted on the LX90 – Envisage controlled guiding
Alignment:Polar aligned using Kochab’s Clock method, no drift or iterative alignment required
PEC:        Off

Focal Length Measurements:

In order to accurately measure the focal length and hence the focal reduction of each image, the following formulas were utilized:

Distance between known stars – 
            D = Cos (A) = sin(d1)*sin(d2) + cos (d1)*cos(d2)*cos (ra1-ra2)
            (where d= Declination and ra = Right Ascension)

Pixel Distance between known stars – 
            S = SQR{(x1-x2)2 + (y1-y2)2}
            (where x and y are the coordinates of the stars in the image)

Pixels to mm – 
            L = S * .0083 
            (8.3 microns per pixel in DSI Pro II)

Focal length = (L)/(D) * (180)/P

Stars selected for measurements in all images do not necessarily equate the best stars to be used for optimal measurements based purely on their location in the image but instead are based on available information for any given star in the image.   Standard SAO catalogued stars were used for all measurements and thus, at times, may not be as far from each other in the image as other available stars.   With this in mind, stars utilized for measurements were based on their available data and then selected based on their distance from each other to ensure accuracy.

Star Measurements:

In order to effectively measure the actual shape and characteristic of the stars, I chose to use the Star Image Tool in AIP4WIN v2.  This tool delivers detailed information on each star selected including Size, Star Profile, elongation, diagonal and other characteristics.  The information is provided as textual data and a graph as can be seen in the images below:


The image on the left shows a star that is nearly perfectly round, having no perceptible elongation and the graph indicates the pixel values vs. the radius from the center of the star being very smooth to the outer boundaries. 

The image on the right depicts what would be seen for a very elongated star.  It also depicts what would be expected in a star that is flared strongly due to vignetting at the edge of an image as the pixel values disperse near the outer points of the star with no smooth transitions.

Meade 6.3 Focal Reducer Test

The test conducted was with the Meade 6.3 focal reducer and was mounted as seen in the diagram below:

As seen in the image, this setup places the CCD chip 62mm behind the glass of the focal reducer.  Based on past usage of these focal reducers, it is my belief that this is a very effective length that provides the best results.

While the ATiK filter wheel was used for this test, the filter wheel is very narrow at 19mm and closely replicates the same setup using the standard DSI-Pro II filter slide.

The object selected for this test was NGC1977, the Running Man Nebula in Orion, located approximately 1 degree north of M42.  This object was selected due to its size being nearly perfect for the expected focal length.  The image below is the Luminance layer taken thru the Meade IR blocking filter.  This image is composed of 30 x 1 minute exposures with no processing.

As can be seen from this image, the stars are nearly perfectly round edge to edge with only minimal vignetting apparent in the far corners.  Note:  The “Lens Flare” that can be seen around the 3 brightest stars in the lower section of the image is common in images of this object and is no reflection on the equipment being utilized.

The stars noted as S1 and S2 were selected for measuring the focal length.  Using the equations stated earlier in this article, the following measurements were calculated:

Angular Distance between the two stars:  0° 12” 3.52’

Pixel Distance between the two stars:  440.07 pixels or 3.652581 mm on the chip

Calculated Focal Length (L/D)*180/P) = 1041.30 mm with a focal ratio of 5.12

These results were very surprising and several measurements were made using different star sets to ensure the accuracy of the findings.  The average of all measurements was within statistical standards and differed by no more then 10mm in focal length or .1 in focal ratio.  It should be noted that even when using the exact same stars for multiple measurements, deviation in the determination of the centeroid of a given star will often times cause the results to differ by as much as 5 pixels at any time though generally less depending on the size of the star selected.

Star Measurements for 6.3 Focal Reducer

The image below depicts the stars that were utilized for measurements and their results:

As can be seen, the stars are virtually identical in each test with only a slightly higher diagonal measurement at the edges, a nearly perfect flat field.

Final Analysis of the 6.3 Reducer

Focal Reduction – This was the biggest surprise in the measurements but those measurements bear out that this is an excellent focal reducer going well beyond the manufacturers indicated values

Flat Field – The stars from the center and edges of the image were close to perfect in their measurements and visually can not be distinguishes in their elongation or diagonal.  This focal reducer in this configuration provides excellent field flattening.

Vignetting - The corners of the image show only the slightest amount of vignetting.  In a highly stretched image, this is more evident and the user would need to take that into consideration when processing. 

Overall, this focal reducer in this configuration provides excellent results and versatility.  The focal reduction achieved with this setup, while probably near the edge of the capabilities of this reducer, is outstanding and should provide similar or even better results when used closer to its 6.3 stated resolution. 


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A Funny Thing Happened on the way to Prague

This is indeed, a momentous occasion. I believe that the 2,500 members that attended this years meeting of the International Astronomical Union should all be given an award, a memento of some sort, at least a plaque, signifying the great event they were part of. Yes folks, for the first time in human history, a group of scientist got together and at the end of their meeting, discovered that somewhere along the line, they lost a planet. And I'm not talking about a "I misplaced my keys and will find them if I retrace my steps" kind of lost. I talking about, lost-lost, gone, completely missing, as in "I went out last night and now don't remember where my car is (forget the keys)" kind of lost. Yup, it's true, good old Pluto has gone missing.

Now then, while they celebrate their new enlightenment, I believe I would be remiss if I didn't at least offer to jump in and help them find their lost planet.  If I'm not mistaken, there are probably hundreds of millions of school children around the world, all under the age of 10,  who could probably find it for them again without so much as a second thought.  After all they have "My Very Energetic Mother Just Served Us Nine Pizzas" to use as a guide.   While the scientists and astronomers of the world work out complicated equations and definitions of exactly what constitutes a planet, the rest of us take the easier approach, Pluto is a planet, plain and simple.  Always has been, always will be.

But why, what is the justification, what can possibly cause an uproar from folks over the classification of something that most have never even see a picture of and will probably never see thru a telescope?  Well, I’m sure if most non-astronomers were asked, it might be because of that cute little dog we all love.  There is something just wrong with the idea of Mickey’s pet being named after a planet that, well, isn’t a planet any more.  After all, Walt Disney loved the idea of the new planet so much that he named one of the most famous cartoon characters after it (not the other way around as many people think).  There has to be something to that!

But, science isn’t based on our love for cartoon characters nor is it based on “that’s the way it has always been” either.  If that were true, despite all evidence to the contrary, we would still consider the earth flat and blood letting might still be in vogue.  But there are real differences though in comparing the idea of Pluto as a planet to either of the previous examples.  Obviously, there are real implications to ignoring true scientific fact and continuing to say the earth is flat, not true of Pluto.  Leaving Pluto as a planet, if for no other reason then it always has been, and with no strong scientific findings to the contrary (especially some empirical data that will immediately affect our lives), is of little consequence to the scientific community.  It changes nothing, violates no laws of nature, and I am fairly certain no one is going to fall off the edge of anything over it still being in the list of sacred spheres (said tongue in cheek) revolving about our sun.

For amateur astronomers especially, there may be other reasons for leaving Pluto in the planetary list.  For many of us, this is a target which we search for diligently in our telescopes, taking a certain amount of self satisfaction at being able to say you have seen or photographed all of the 9 planets, especially something as elusive and difficult to see as Pluto.  We are part of a community that has been taking pot shots as this poor little isolated rock in space for years and yet we hang on, doggedly fighting the opposition because it is holds meaning to us.  We appreciate the time and sacrifices made by Clyde Tombaugh in searching for and finding it.  We applaud NASA’s latest exploration to find out more about it (even though it will take 9 years to get there).  In Pluto, like so many other objects in the heavens, we find something that we know so little about, but, since it is a “close” space object and one of our neighbors, we somehow expand our own “world” by visiting our farthest-closest neighbor.  It’s a member of the club, and even if it were to be only an honorary member, once a member, always a member.  One of our greatest astronomers alive today, Sir Patrick Moore, in a recent interview, put it this way “Pluto, such a shame, such a lovely planet”.  That probably sums it up quite elegantly for the rest of us.

I think in the end though, there is something more elementary here, something deeper inside of us that causes us to question the dismissal of this small planet.  In an era in which we are constantly looking for other worlds, the possibility that life exists, could exist, or at one time existed in other places, and where we continue to expand our astronomical horizons, there is something about removing Pluto as a planet that seems to instead limit us in some way.  It is as though some imaginary dotted line has been drawn in space beyond which our little universe (our solar system) ends or at least stops providing us with objects with which we stand on some common ground.  The demotion of Pluto leaves us all feeling just a little smaller, our neighborhood somewhat diminished, and possibly even feeling a little more insignificant in this giant universe. 

In a couple of generations, if this ruling stands, millions of children will have been taught in school about our 8 planets in the solar system.  They will probably be told of how up until 2006, even Pluto was considered a planet, and the children, with their new planetary mnemonic, will not give it a second thought.  The idea of only eight planets will survive and those of us that remember there being nine will talk about the old days and remember that “it wasn’t always that way”.  Our relics of the past, such as a solar system model including good old Pluto, will be viewed in much the same way we view maps that showed the earth dropping off suddenly at some unknown border.  But we will know, we will remember, that at one time, for a little over 70 years, a small icy orb in space called Pluto, held our fascination and was included in this greatest of clubs, the Planets.

To quote my good friend and fellow astronomer Kent Blackwell, “I wonder if Pluto looks as bright as it did previously?”.  Hm, I wonder…


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You've Come a Long Way Baby

This month, October 2005, we will be celebrating one year since the introduction of the Meade DSI family of cameras.  As you may know, one of the things we have going on to note this occasion is the First Annual DSI Imaging Contest which will conclude this month.  Our sponsors, Meade Instruments, Anacortes Telescope and Wildbird, and Willman-Bell have generously contributed soem wonderful prizes and the entries we have received so far have been amazing.

Last Week, Matt Taylor posted a message to the Meade_DSI Yahoo Group pertaining to how far he has personally come this past year in his imaging skills, understanding of processes, and general capabilities.  He posted this awesome image of the Crab Nebula (M1) which shows just how far he has come in one year.  Nice Job Matt.

Following suit, I began to look back thru my images and see what improvements, if any, I have made in that time as well.  I started to look back thru my images and actually found quite a few that qualify but the one below of M33 stood out the most to me.  The first one, taken in September of 2004 (on the right) was one of the first galaxy images I had ever taken with the DSI.  I recall being very pleased with the results at the time in looking back, with the level of experience I had at the time with this camera, I am still pleased with the results.  Of course, I must admit that when I compared the two, I was really amazed at what I considered acceptable then vs. what I consider acceptable today.  Perhaps next year I will be able to post 3 images, I certainly hope there is a significant difference once again, we'll see.

Sometimes, (like the frog in the water) we don't really see change occurring,  I suppose that as astro-photographers, we are probably much more critcal and harder on ourselves then others are and it is generally others that tend to see the improvements over time that we don't see.  I guess it just helps to take a step back every now and then and really look at where we are vs. where we have been.  For example, I was just looking thru some of my favorite galleries here on AutoStarSuite.Net and was amazed at some of the absolutely beautiful images that are here.  Most of these folks would have been considered "beginning imagers" back when these groups first started but you certainly can't tell it by their postings here.  Some of my favorites include Chuck Reese, JP Longchamp (Polo), Matt Taylor, and too many others to mention.  I personally consider these folks to be the experts in this field and definitely with these cameras, we are certainly fortunate to have them and so many others as members. 

Of course, this makes another point doesn't it?  How far would any of us have gotten in this past year without the help of the group members as a whole?  They say no man is an island unto himself and these groups really typify that statement.  I am constantly amazed at the generosity and selfless dedication of so many folks here and on the Yahoo! Groups.  These groups have grown (combined) over the past two years to close to 5,000 people, all willing to jump in and help, share a thought or experience, or just post a friendly "Good Job" when someone throws a new image up on the site.  Yes, we have all come a long way in our abilities to take images, but along the way, we have made some new friends, learned a few lessons, and hopefully, made this hobby of our just a little bit better for those that stop by.

by E2Pilot | 1 Comments

Summertime Lemonade

OK, I admit it, I really hate summer.  Now, this wasn't always true, I used to love summer. Long days on the beach, the breeze blowing in off the ocean at night.  There was something magical about summer.  Now a days, I consider it magical if I am actually able to get the once in a blue moon night with low humidity, cool temps, good transparency, and no mosquitoes.  Yes, that would be the astronomer talking instead of that young kid walking down the beach.

So, what can change my perception so much?  Well, quite possibly it could have something to do with the fact that there is less night time to view or image, or maybe the fact that I can always bundle up in the winter while removing layers in the summer means only that there is more of me to be attacked by the vicious mosquitoes.  Or maybe, it is the fact that here on the east coast of the USA, summer nights mean that while you may have great seeing, your transparency will go to the dogs due to all the moisture in the air.  Yes folks, I do hate summer...   or do I?

The other night, I decided to go to one of our dark sky sites to try some imaging.  As I stepped out of the car, there was no surprise, rising humidity, hot air, and a hazy sky.  I dutifully set up my scope, did my hour long alignments, sprayed copious amounts of bug spray on myself, and tried my hand at imaging a few targets.  As the evening wore on, I became more and more convinced that the summer bug had bitten me again and this evening’s efforts were for naught.  Suddenly, as I looked up at the sky, the Milky-Way, which had been there all the time, seemed to simply jump out at me.  I stood there in amazement taking in this glorious site.  What would I give for a camera that could take a shot of that at that moment.

Just a few short months ago, I remember the posts and statements by many folks proclaiming the glories of the DSI and DSI-Pro and how they didn't need cooling apparently.  Well, they didn’t, not when it was 25 degrees F outside and ice was building up on the back of the camera.   Having been in this situation before, I was waiting for the other show to drop (per say), for the reality of the situation to set in and the discovery by everyone that indeed, yes, even this great camera's performance is degraded when the outside temperature is still above 90 degrees F at midnight. 

Lately, the many conversations on the boards have turned to the fact that yes, it is quite possible, that our DSI cameras could use a good dose of cold on these hot summer nights.  Folks such as Steve Mogg have stepped up to bat and created a product for us to purchase and add onto our cameras for cooling.  But, being the stingy type, I decided to try and work out the problem myself.  So, here I sit, a pile of electronic parts, fans, coolers, etc waiting to be turned into this glorious cooling savior for my camera.  Do I have a clue what I am doing?  Absolutely not, never touched anything like this before in my life.  But, here I sit, on and off the phone with my good friend Michael as we throw ideas back and forth.  What is the best approach, how can we control the cooling, condensation, regulate voltage, etc.  Somewhere along the way, we suddenly found ourselves talking the lingo, doing actual tests, measuring the effectiveness of various configurations, and guess what else... Learning!!! Yup, it's true, we are learning something new.  Suddenly, I am excited about all of this, how cool (no pun intended) to create a project from scratch, solve a problem, and learn something new along the way. 

I guess there are all sorts of opportunities to learn during your life.  Sometimes, you simply have to take a different look at the situation and instead of just complaining, find a solution.  You may even learn something along the way and, heaven forbid, have fun doing it.  You know something; the nights will still be just as short, the temperatures just as hot, and the air just as humid.  But on clear nights, that Milky-Way will still be just as beautiful and now, my camera will be nice and cool inside.  Yes folks, I hate summer, but as the old saying goes, "When life gives you lemons, make lemonade".

Stephen P Hamilton
Chillin' in Chesapeake

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