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Equipment Discussions >> Eyepieces

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ponz
super member


Reged: 07/18/12

Loc: Kansas City, MO
Re: Help a Noob? new [Re: oo_void]
      #5627552 - 01/17/13 07:42 AM

Quote:

Just to warn you (and setting expectation accordingly) ... EP projection my give you usable results for bright objects like the moon and some of the planets, but you're going to be banging you head when it comes to DSO's. Even something bright like M13 takes hours of exposure time at prime with a good DSLR connected via t-ring, or a CCD.




Yes, I realize that. That's why I don't want to spend a fortune on eyepieces - at least not yet

Ponz


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ponz
super member


Reged: 07/18/12

Loc: Kansas City, MO
Re: Help a Noob? new [Re: CosmoSat]
      #5627553 - 01/17/13 07:43 AM

Quote:

Quote:

I was focused on a bird atop a tall tree two houses down and couldn't believe the light loss from the stock 20mm to the stock 5mm. Do the more expensive eyepieces exhibit the same light loss at shorter focal lengths?




Yes, all eyepieces will exhibit the light loss, With magnification, the brightness curve tends to drop off in any objects that you see because the concentrated light of the image in the low power eyepiece is now spread out in a larger area in the magnified image that you are viewing.

Clear Skies!




The same principle as most long camera lenses, huh.

Ponz


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CosmoSat
Pooh-Bah


Reged: 07/24/09

Loc: India
Re: Help a Noob? new [Re: ponz]
      #5627846 - 01/17/13 11:10 AM

No, in a camera, the aperture is stopped down by the inbuilt mechanical iris to control the light throughput.

In a telescope, the amount of light gathered by the primary to form an image is constant, what the eyepieces does is vary the size of the image so that with increase in magnification the amount of light in that image is spread out on an larger area, and hence it appears dimmer, in a lower magnified image, the light is concentrated in a smaller area and so it appears brighter.

Clear Skies!


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ponz
super member


Reged: 07/18/12

Loc: Kansas City, MO
Re: Help a Noob? new [Re: CosmoSat]
      #5630576 - 01/18/13 08:59 PM

I'm baaack!

I've been enjoying tracking Jupiter the past couple of nights with my SkyWatcher 600mm 80ED APO with the stock 5mm eyepiece.

How much magnification can I squeak out of this scope?

I realize, from reading here, that seeing/atmospheric conditions play THE primary role. However, I would like to get much closer and clearer with my scope, if that's at all possible.

If so, what will a couple of hundred bucks get me?

Should I purchase a barlow and attempt to magnify the stock 5mm?

Can I ever expect decent views of Mars with my scope?

So many questions - I know.

Thanks
Ponz


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dpwoos
Pooh-Bah
*****

Reged: 10/18/06

Loc: United States
Re: Help a Noob? new [Re: ponz]
      #5630723 - 01/18/13 10:33 PM

You can only squeeze so much out of an 80mm scope, and most folks won't get much more out of it than you are. However, everyone is different and so why not go for it? Rather than get a 4mm eyepiece, why not use/get an 8mm and a 2x barlow, or a 12mm and a 3x barlow? That way you will have much better eye relief, and the barlow to use with other eyepieces? The best advice is to observe with folks who have stuff that you can borrow to try these options for yourself.

Also, Mars is relatively small and so I think the best you will do is see an orange ball with small white polar cap(s). Very cool, but nowhere near as impressive as Jupiter or Saturn, at least for most folks.


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Rob55
member


Reged: 12/15/12

Loc: Fort Polk, LA USA
Re: Help a Noob? new [Re: dpwoos]
      #5630888 - 01/19/13 12:29 AM

So if I have a 13mm plossi; I'm better off with a 3x barlow than a 4.5 plossi?

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dpwoos
Pooh-Bah
*****

Reged: 10/18/06

Loc: United States
Re: Help a Noob? new [Re: Rob55]
      #5631221 - 01/19/13 09:47 AM

The eye relief on a (theoretical) 4.5mm plossl is really small (around 3mm), so you have to practically stick your eye on the top lens. A 13mm plossl has around 10mm eye relief, and barlowing it will increase that some. So, the result is much more comfortable viewing.

If you observe with your local astro club you will be able to try all kinds of combinations without spending any money - so I suggest doing that! If you were in my club I would pop your 13mm into my 3x TV barlow, and we would give it a try.

Edited by dpwoos (01/19/13 09:51 AM)


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bcuddihee
Carpal Tunnel
*****

Reged: 11/04/06

Loc: Cincinnati Ohio
Re: Help a Noob? new [Re: dpwoos]
      #5631246 - 01/19/13 10:13 AM

Ponz, you will most likely bottom out on aperture rather than atmospheric conditions. Your 80mm scope will max out at around 50x per inch of aperture so..around 160x. Even at that mag, images will start looking a bit dim. I would also suggest using a barlow for this set up, but instead of a plossl I would try something that will take advantage of the scopes wide fov. I might be inclined to try an explore scientific 6.7mm 82 degree ep for 89x and then get a 1-1/2x barlow to boost it to 135x. These ep's have very good eye relief for the fl.and are quite reasonable in price.
bc


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ponz
super member


Reged: 07/18/12

Loc: Kansas City, MO
Re: Help a Noob? new [Re: bcuddihee]
      #5631369 - 01/19/13 11:24 AM

OK - Given all the wonderful advice here, what do you guys think of this?

I have the stock 5mm and 20mm eyepieces that came with the SkyWatcher and I have an Explore Scientific 11mm 82 degree eyepiece on the way.

What about getting a decent 3x barlow to work with the three aforementioned eyepieces.

That'll give me 163x with new 11mm ES, 360x with the stock 5mm and 90x with the stock 20mm.

By the way, I still don't know the difference between a plossl and an an eyepiece Wikipedia says they're one and the same?

Now - to research plossls. Does it ever end?

Thanks,
Ponz


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bcuddihee
Carpal Tunnel
*****

Reged: 11/04/06

Loc: Cincinnati Ohio
Re: Help a Noob? new [Re: ponz]
      #5631652 - 01/19/13 02:13 PM

That sounds pretty good although you will probably never barlow the 5mm. 360x is way beyond the range of your 80 apo.
The 163 would probably be at the resolution limit. I'd be more excited about the views of open clusters and star fields with the 54x of the 11mm unbarlowed. Your best planetary views will most likely be in the 120x ish range.
bc


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Hermie
sage
*****

Reged: 04/20/05

Loc: Cloudy HKG
Re: Help a Noob? new [Re: bcuddihee]
      #5632569 - 01/20/13 02:18 AM

Ponz,

"Plossl" is simply the optical design for an eyepiece that Mr Plossl came up with a long time ago, and it is the basic eyepiece that everyone starts with. Most on the market are made in China and are fine, but there are more expensive better quality ones available (eg Televue). However, most of us move to other eyepieces for wider views or more eye relief.

I'd suggest to wait and use your ES 11mm before buying anymore eyepieces. After trying that you will understand more what other eyepieces offer.

Hermie


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