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Questions and Answers

I frequently get questions via e-mail that I try to answer promptly.  I have included some of these below.

 

Question:

Hello,
Maybe you could help me.  I have a Nexstar 4, which has a 4" aperture and a 1300mm focal length, and I am trying to see some features of Mars.  Currently I only have a Celestron SMA 25mm eyepiece(51x), and a Celestron SMA 10mm eyepiece(135x).  With the 10mm I see Mars, but only as a dot a little bigger than the tip of a ballpoint pen.  What size eyepiece should I get for good magnification of Mars.  In the manual it said something to the effect of "your maximum useful magnification is 235x" so I figured I shouldn't go below a 6mm eyepiece which would give me 216x.  Would it be better if I got something in th 7-8mm range?  I also realize that the SMA models are not the best eyepieces, would it make a big difference if I got a Plossl, or a Lanthanum?

Thanks in advance,
Phil

 

Answer:

A good rule of thumb is that the best magnified view any earthbound telescope is able to produce is around 50 times the telescope's aperature in inches...in your telescope's case, it would be around 200 times  magnification.  The rule of thumb correlates pretty good with what your manual is stating, except I want to offer a couple of caveats to the rule.  You can only get this ideal magnification with a telescope that is properly collimated, and just as importantly, on a night with really good "seeing."  Every bit of optical distortion adds up quickly above this 50X/inch value.  Because of this, I'd suggest getting Plossl design eyepieces to get the best view possible.  I'd also suggest Televue as an eyepiece brand, or the Meade Series 4000.  With patience, I have found some great deals on eBay.com for these.  You also asked about the  Lanthanum eyepieces, and I have not used them, so I can't offer an opinion.  Plossl eyepieces will make a noticable difference to you - especially on objects that have lower contrast than the Moon or planets.

Surprisingly, your best views of Mars will be between a magnification of 50 - 100.  Yes, it will look very small in the field of view, but the contrast of the features will be high and you will even be able to see the fine sliver of the icecap with your scope - with patience and practice.  You will have to observe Mars for many minutes until the seeing steadies up, but you'll catch glimpses of Mars that will stick in your memory.  Many people I know sketch the features as they become visible.  I have to say that you will NOT have a view like the Hubble Telescope.  (Unless of course you are fabulously wealthy and can set up your own adaptive optics! :-)  Life is unfair.  You will however enjoy a "live" view of Mars better than anyone in history  ever had - even as recently as 200 years ago.  And that's pretty neat.  Not a picture of it, but a real image formed with your own eyes!

I mention patience in the preceding paragraph.  I can't stress this enough.  After you have spent several minutes studying the planet, watching the seeing come and go, you will begin to see detail that your eye overlooked entirely just a few moments before.  Your brain will begin to dissect the image in much more detail and you will be able to detect more and more features.

When I teach our club's beginning astronomy group, I let them in on an amateur astronomy secret:  Our human eyes are just not quite good enough to see amazing things throughout the night sky...A binocular's magnification of 7X will bring in incredible detail across the Milky Way and a telescope's view at 25X makes the Moon seem like you could reach out and touch it.  Unless I'm doing some seriously nerdy deep sky galaxy hunting, I keep my magnification well below 200X when I'm using my 8" even though in theory I could go up to 400X.

Sincerely,
Tom

This site is not sponsored by anyone except for me, and any opinions about the merits or demerits of any brands, telescopes, etc. are just that - my opinions based on experience.

 

11/2011

05/26/2017