Telescope Tuesday - Eyepieces

It's been a couple of weeks since our last Telescope Tuesday.  Let's just all be glad this one is actually on a Tuesday.  Last time I wrote about the mechanics of reflector telescopes and the optical path within the tube.  Today I'll cover the last bit that path which is the eyepiece.

There is the old astronomers saying "The light travels for millions of miles only to get blocked in the last one".  This is of course a reference to the bane of all astronomers, both professional and amateur, which is weather and clouds.  Seriously, clouds suck.

So lets take an easy example...Polaris (The North Star).  Assuming you can see it (difficult in Chicago at best), the photons from the surface of that star have traveled a distance of 434 light years.  434 light years = 4,105,957,025,100,067.5  (4.1 Quadrillion) Kilometers...which is a very long distance by any standard.  The photons you have managed to capture with your telescope now travel down the optical path of the tube assembly (a focal length of 650mm in my case) and get reflected by the secondary mirror into the eyepiece assembly.  This last little bit is one of the most critical portions of the photons journey.  That last little 2-25mm makes all the difference.

There are scads of different types of eyepieces, each type having a specific use; normal viewing, wide-angle viewing, comma-correction, etc...

The fancier they are, the more expensive they are because of the increase in the optic quality as well as the number of lenses contained within, ranging from $50-$500.  Personally, I only have the two eyepieces that came with my scope *sadtrombone*   The image focusing and other special effects depends on the types and arrangement of lenses inside the eyepiece.

Apart from all the special functions that a high end eyepiece can do, the most basic function of the lenses is to magnify the image so that the observer can make out fine details.  The calculation of magnification is simple and depends only on the focal length of the optical assembly and the eyepiece itself.

So in my case I have a focal length of 650mm in the reflector telescope.  With my two eyepieces; 25mm and 10mm this gives me a magnification of 26x and 65x respectively.  It is a common misconception that the higher the magnification the better.  While this is true to some extent every telescope has an upper theoretical magnification which is 50-60 (depending on your source) times the aperture of the telescope in Inches.  Since my scope is 130mm=5.125 inches, that means there is an upper limit of 256x-307x that I could expect to achieve.  This limit is due to the fact that the higher the magnification is, you are not only magnifying the object you are looking at you are also magnifying the imperfections in the optics, as well as atmospheric disturbances.  At very high magnifications, even air currents inside the scope will cause distortions in the image (which is why you are always advised to cool your scope to the ambient outside temperature).

In addition, the higher the magnification, the smaller the apparent field of view and the dimmer an object will be.  Since I am severely limited to planets and the moon due to Chicago's light pollution, I don't have to worry about this too much as of yet, but when I finally make it to a dark-sky site...a lower power eyepiece will allow me to see more of the overall structure of nebula.  Lastly, if like me you don't have a mount that can track, any object is going to whip across the field of view due to the earths rotation.  When I am able to get Saturn centered in my 10mm it is gone from view in about 7-8 seconds.

I will close this with a segue into next weeks (hopefully) topic...CCD Cameras.   The CCD Camera I have has a focal length of about 5mm as best as I have been able to calculate.  This then means that I have an effective magnification of about 130x.  Needless to say this provides some excellent close-up views of the Moon.

Telescope Tuesday: Friday Edition

Welcome to Telescope Tuesday, where I will be rambling about a) My Telescope, and b) Things I Do With My Telescope.

Since this is the first in a series, I'll take some time to give an explanation of what the equipment is:

This is the scope I picked up earlier this year.  It's an Orion Space Probe 130 ST Newtonian Reflector.  Unlike a Refractor Telescope, the Newtonian Reflectors 'fold' the light beam so as to increase the focal length while still having a decent aperture.

As you can see, the light comes in through the front of the scope, is focused by the primary mirror at the back of the optical assembly, reflects off the secondary mirror and is sent to the eyepiece.  As with most things, bigger is (often) better.  The larger your aperture, the more light the scope will gather.

With my scope, the aperture is 130mm, or just under 5"...which is pretty decent for a high-end starter scope.  The focal length is the total distance the light travels from the front end of the tube to the exit at the eyepiece, which in this case is 650mm.  You then divide the focal length by the aperture to get the focal ratio which is an f/5 in this case.

The focal ratio determines the image magnification, field size (how much of the sky you can see at one time), and the brightness of an image; all depending on the eyepiece used.  'Fast' telescopes with ratios around f/4-f/5 give a wide field of view, but are not specifically designed for high-magnification planetary viewing.  For that you want a 'slow' telescope with a f/11-f/15 ratio.

Since my scope was a 130 ST (the ST stand for 'Short Tube') I sacrificed a bit of power for portability.  The standard Orion 130 has a 900mm focal length and a f/6.9 ratio.  But since I will be lugging this thing around, I needed something manageable.

Lastly, the eyepieces determine the viewing field and magnification.  Each eyepiece has its own focal length which you divide into the scope focal length to determine the magnification.  My scope came with a set of 25mm and 10mm eyepieces.  This gives a magnification of 26x and 65x respectively.  While you might think that more magnification is always better, this is not always the case.

Since I don't have a mount that has automatic tracking, I have to manually move the telescope to keep whatever it is I am looking at (so far only the Moon and Saturn) centered in the eyepiece.  With the 25mm eyepiece, the views of the moon are great, and you can make out the rings of Saturn.  However, with the 10mm eyepiece, the views of the moon are fantastic, but Saturn whips across the field of view in under a minute (so it's hard to track)...but you can make out the gap between the rings and the planet itself, and I have managed to spot Saturn's moon Titan every time.  It's really pretty fantastic.

Living in the city, I'm fairly limited in what I can see due to the light pollution.  I can only imagine what I would be able to spot once I can get this thing out under some nice, dark skies.  Saturn will soon be setting for the season, but I think Jupiter will be in a good spot in a few months.  Right now, Jupiter and Mars are in the East right before sunrise, and there is no way I am dragging myself out of bed at 3am...I'll wait a few more months.

Bitter Dregs...

I had to spend a lot of the last week or so processing this shift in direction for my life, giving up (for now) the plan of the PhD in Astrophysics and transitioning into something slightly more reasonable based on my current situation...changing my Major to Communications.

There was a lot of this going on the past week (and over the summer as well)

It was a very tough decision to make, but I just had to realize my limitations.  The intense course load of Calculus, Chemistry, and Physics classes was taking its toll and I was barely holding my head above water...as it were.  As much as I love all of those topics, I just felt like I wasn't actually learning anything, just scrambling to go from assignment to assignment, exam to exam, and just getting by.

The switch to Communications was a major relief.  Currently I am now in the Professional & Technical Communications (PTC) program with a Chemistry minor.  The Chem minor is already complete, and I'm sure that down the road I will eventually finish it up in my spare time...being a lifelong learner is just a part of who I am.  The communications department here at IIT is planing on offering a Degree in the Journalism of Science, which is what I will switch to once it become official later in the Academic year.

So this semester is going to be very writing intensive obviously.  My classes are vastly different from what I've had before, but I've gradually grown excited about them.

This semester is:  Editing, Document Design, Verbal Visual Communications, Intro to Journalism, and Web Design.  3 of the 5 are internet classes, of which I am no fan...but it does mean I only have 1 class Monday-Thursday which is nice.  Next semester will be a couple of Philosophy of Science Classes, more Tech Communication classes, and Web Application Development.

When it's all said & done, I will still get out on time in the Spring of 2015, but there is a chance I might be able to graduate next Dec.   I don't even want to think about graduation right now, since the only option I have (unless I manage to get a job immediately after I graduate) is to move back to Michigan and live with my 70 year old parents until I can find a job.   Not something I am looking forward to.

So expect more regular postings now that I need to write, write, write.  Later this week I'll talk about the Curiosity Rover's 1 year 'Marsiversery', and introduce "Telescope Tuesdays" where I ramble about my struggle with my Telescope.  Note:  This weeks 'Telescope Tuesday' will be on Thursday...at least the both begin with a 'T'

Science!