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# Best eyepiece sizes for viewing Moon close up?

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### #1 Dave12345

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Posted 11 January 2013 - 06:50 PM

Hi

I am just wondering if anyone has any general advice and experience of what the best sized eyepiece would be to get for viewing the Moon close up. Maybe a 4mm?

### #2 Tim2723

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Posted 11 January 2013 - 07:13 PM

Dave, you need to make the calculations pertinent to the scope you choose. You can't really accomplish much before you decide on the scope you're buying. For the Moon I sometimes start with the maximum magnification my skies allow on good nights and work backward.

Does this mean you've decided on the scope?

### #3 GlennLeDrew

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Posted 11 January 2013 - 07:20 PM

What telescope do you have; what's the diameter of the main lens or mirror, and what's the focal length or f/ratio? This will determine the range of eyepieces which will be useful, where you want to achieve a range of exit pupils between about 5-6mm down to 0.7mm. Bigger exit pupils are low power, and smaller exit pupils are high power.

Let's say you want to determine the highest useful magnification, where the exit pupil is 0.7mm. If your scope is a 6" f/8, the eyepiece focal length delivering a 0.7mm exit pupil equals the f/ratio times the exit pupil. And so f/8 * 0.7mm = 5.6mm. A 6mm focal length eyepiece would be the closest 'standard' focal length.

### #4 Dave12345

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Posted 11 January 2013 - 07:27 PM

Yes, it was between the Skymax 90 (EQ1) 90mm (3.5") Maksutov-Cassegrain an the Celestron Astromaster 90EQ... I am choosing the Skymax, becaus of portability etc, and it's suggested a few times by people, i've seen a picture of the Moon through that particular scope and i wes pleased with it, and because of it's potential stability for the purpose of photography. On the other hand the 90 eq has a slightly higher usefull magnification...
The Skymax 90

### #5 Dave12345

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Posted 11 January 2013 - 07:33 PM

Hi
The telescope focal length is 1250mm (f/13.88)

### #6 Dave12345

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Posted 11 January 2013 - 07:34 PM

Or maybe a 2x barlow?

### #7 mogur

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Posted 11 January 2013 - 07:59 PM

IMHO, a 7mm EP would give you pretty much the maximum (180x) power you will be able to use with that scope. Most times probably not that much even. A 9 or 10mm would also be a good companion.

### #8 Jon Isaacs

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Posted 11 January 2013 - 08:05 PM

Hi
The telescope focal length is 1250mm (f/13.88)

Typical wisdom is 2x per millimeter of aperture, with a 90mm scope, that would be 180x. In your scope, that would be a 7mm. Short focal length Plossls, Orthos and the like, often have short eye relief, that can be uncomfortable.

Eyepieces like the TMB Planetary eyepieces have what amounts to a built in Barlow and maintain a reasonable amount of eye relief.

I like to have a number of magnifications available for viewing the planets.. some nights the atmosphere is stable, the images are stable and you can increase the magnification, some nights it's turbulent and lower magnifications are best. For a single higher power eyepiece, a 9mm would provide a reasonable magnification (140X) that could be used effectively most nights.

Jon

### #9 Dave12345

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Posted 11 January 2013 - 08:24 PM

### #10 Dave12345

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Posted 11 January 2013 - 08:42 PM

How about 7.5? do ou know how the barlow efect is achieved?

### #11 Dave12345

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Posted 11 January 2013 - 08:44 PM

### #12 Tim2723

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Posted 12 January 2013 - 01:56 AM

With mine, specifically on the Moon, I spend most of my time at 125x. The scope is especially comfortable there, sort of a 'sweet spot' for this particular scope (besides being a really nice view of the Moon). I think it comes with a 10mm, so don't spend a lot up front. You'll be surprised how little you need with this scope. I prefer a long eye relief EP, so I use an old Vixen Lanthanum, but the one it comes with is pretty nice for the price. Maks work well with the simpler designs too, so you don't really have to spend tons on the elaborate stuff unless you want something special like eye relief. Live with the scope for a while at first. Learn what it can do, learn what your skies are like. You'll be surprised how well you can do with just the set up as it comes.

I've taken the scope to 250x on good nights with perfectly acceptable results. It's 'empty magnification', but the scope can take it. At least on the Moon where there's enough light. Don't run out and spend money to do that, but if you end up with a 2x Barlow one day don't be afraid to try it.

### #13 Quinn

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Posted 12 January 2013 - 02:22 AM

G'Day Dave

The pictures of the Moon taken with a Orion starmax 90mm I posted in your

http://www.cloudynig...5613806/page...

were taken through a Plossl 10mm 52mm aFOV EP. Using a 25MM Plossl EP would show the entire Moon.

### #14 CosmoSat

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Posted 12 January 2013 - 02:45 AM

Pictures of the moon look great taken through almost any telescope irrespective of the design.

The EQ1 mount you are considering is definitely not stable enough for any descent astrophotography.

A telescopes potential magnification depends upon its aperture size, So both the 90mm scopes are capable of achieving the same magnification thought in the refractor the images may look sharper because of no central obstruction.

A 15mm eyepiece with a 2x barlow lens will will effectively act as a 7.5mm eyepiece.

I would suggest u have a look at this on too.. Celestron Powerseeker 114/900mm newtonian telescope.

Clear Skies!

### #15 Dave12345

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Posted 12 January 2013 - 11:37 AM

Hi i didn'r realise you posted them, but i had a look, very nice, didn't know where the thread had gone. Thank's for posting, if i take any pictures i'lle upload them ;-)

### #16 Dave12345

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Posted 12 January 2013 - 11:40 AM

With mine, specifically on the Moon, I spend most of my time at 125x. The scope is especially comfortable there, sort of a 'sweet spot' for this particular scope (besides being a really nice view of the Moon). I think it comes with a 10mm, so don't spend a lot up front. You'll be surprised how little you need with this scope. I prefer a long eye relief EP, so I use an old Vixen Lanthanum, but the one it comes with is pretty nice for the price. Maks work well with the simpler designs too, so you don't really have to spend tons on the elaborate stuff unless you want something special like eye relief. Live with the scope for a while at first. Learn what it can do, learn what your skies are like. You'll be surprised how well you can do with just the set up as it comes.

I've taken the scope to 250x on good nights with perfectly acceptable results. It's 'empty magnification', but the scope can take it. At least on the Moon where there's enough light. Don't run out and spend money to do that, but if you end up with a 2x Barlow one day don't be afraid to try it.

Great ;-)

### #17 Dave12345

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Posted 12 January 2013 - 11:43 AM

Pictures of the moon look great taken through almost any telescope irrespective of the design.

The EQ1 mount you are considering is definitely not stable enough for any descent astrophotography.

A telescopes potential magnification depends upon its aperture size, So both the 90mm scopes are capable of achieving the same magnification thought in the refractor the images may look sharper because of no central obstruction.

A 15mm eyepiece with a 2x barlow lens will will effectively act as a 7.5mm eyepiece.

I would suggest u have a look at this on too.. Celestron Powerseeker 114/900mm newtonian telescope.

Clear Skies!

Thank's for the reply, the only problem with the Powerseeker is the size, and portabilty, or it deafinatley would be a consideration. What mount would you suggest?

### #18 Jon Isaacs

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Posted 12 January 2013 - 05:05 PM

What mount would you suggest?

Dave:

If I am not mistaken you are planning on purchasing the SkyWatcher Skymax 90 EQ1 90mm Maksutov Cassegrain Telescope. As I recall, you are hoping to take photos as well as just view the moon through the eyepiece and need a reasonably compact, portable telescope for under 200 pounds.

I think that the 90mm Mak is a very good choice. Maks are well suited for viewing the moon, there will be plenty to see. The EQ-1 is not a heavy duty mount but the StarMax 90mm is a nice, compact telescope, under 4 lbs and only 10 inches long, it does not tax the mount the way a longer, heavier Newtonian or refractor would. The Powerseeker 114 uses the same EQ-1 mount for a telescope that it about 36 inch long and much heavier.

As far as taking photos, it's always difficult but the moon is one of the easiest targets, its bright enough that you can use short exposures, I am sure that with time and practice, you will be able to take some satisfying photos of the moon.

As far another eyepiece, the Starmax comes with 25mm and 10mm eyepieces. That would provide you with 50x and 125x, those are actually quite nice magnifications for a 90mm scope. I would start with those.

Jon

### #19 Tim2723

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Posted 12 January 2013 - 06:40 PM

One of the nice features of this little 90mm Mak is that it has a Vixen-style dovetail and a 1/4" socket, so it can go a lot of places. Even if the EQ-1 isn't the very best photo mount, the scope can still last a lifetime.

### #20 CosmoSat

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Posted 12 January 2013 - 10:24 PM

Thank's for the reply, the only problem with the Powerseeker is the size, and portabilty, or it deafinatley would be a consideration. What mount would you suggest?

I would always suggest an alt-az mount, easy to setup and use. Taking good pics of the moon is not difficult in a alt-az mounted scope even with a hand held digi cam.

And yes I am aware the 114 comes with the same eq-1 mount like the others u mentioned, but along with them, I just wanted u to have a look at(and maybe consider) the reflector too which has more light gathering power.

Clear Skies!

### #21 azure1961p

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Posted 12 January 2013 - 10:34 PM

I think you've gotten great advice. A high power of 180x via a 7mm ocular sounds accurate. Mind you on the best nights as mentioned you can probably hit 250x and still have a sharp view but at the penalty of no added detail and probably a slight contrast loss. It's the big picture though and all in fun the 250x sounds ok. My 70mm refractor has been pushed to 300x in good seeing on the moon again, excessive but startlingly good for such a small scope being pushed that hard. Typically though in good seeing the rule used is about 40x per inch on the moon putting 140x as a higher power working magnification. In a more relaxed but profitable setup, 100x to 120x is nice. The call on 180x with the 7mm is probably as good as profitable will allow tho again not to say it isn't fun to fatten the image up, penalties and all.

Good luck.

Pete

### #22 John Carruthers

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Posted 13 January 2013 - 05:34 AM

Hi Dave, before you buy, join your local astronomical society (if you haven't already). They will have scopes you can try out or borrow and you can see what suits you best.
As for magnification, the rules of thumb are very general, the maximum you can use depends very much on the sky conditions, how steady the 'seeing' is.
If more magnification reveals more detail then it is justified.

here's a list of UK societies;

http://fedastro.org....rapper&Itemid=8

edit;
PS, don't forget a humble webcam is often the weapon of choice for lunar and planetary imaging.

### #23 Dave12345

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Posted 13 January 2013 - 12:58 PM

Well great, this is even more comfirmation.

### #24 Dave12345

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Posted 13 January 2013 - 12:59 PM

Thank's i will check that out.

### #25 drewp

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Posted 13 January 2013 - 01:01 PM

your going to get a 10 and 25 with that scope according to what ive seen. that should get you to 125x or so, get used to your new scope a bit before racing to buy the highest mag ep possible for a scope you dont know or even own yet.The 10mm that comes with it will give you quite a good view of the moon as is .with that mount you will probubly have trouble with shake with the higher power so considering ways to weigh down the mount for higer powers might be another consideration.

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