Jump to content


Help a Noob?

  • Please log in to reply
30 replies to this topic

#26 Rob55



  • -----
  • Posts: 35
  • Joined: 15 Dec 2012
  • Loc: Fort Polk, LA USA

Posted 19 January 2013 - 12:29 AM

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

#27 dpwoos


    Surveyor 1

  • *****
  • Posts: 1540
  • Joined: 18 Oct 2006
  • Loc: United States

Posted 19 January 2013 - 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.

#28 bcuddihee



  • *****
  • Posts: 2119
  • Joined: 04 Nov 2006
  • Loc: Cincinnati Ohio

Posted 19 January 2013 - 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.

#29 ponz


    Vostok 1

  • -----
  • Posts: 144
  • Joined: 18 Jul 2012
  • Loc: Kansas City, MO

Posted 19 January 2013 - 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 :confused: Wikipedia says they're one and the same?

Now - to research plossls. Does it ever end? :tonofbricks:


#30 bcuddihee



  • *****
  • Posts: 2119
  • Joined: 04 Nov 2006
  • Loc: Cincinnati Ohio

Posted 19 January 2013 - 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.

#31 Hermie


    Ranger 4

  • *****
  • Posts: 338
  • Joined: 20 Apr 2005
  • Loc: Cloudy HKG

Posted 20 January 2013 - 02:18 AM


"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.


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics