Jump to content


Photo

Meade Lightbridge for Planetary

  • Please log in to reply
11 replies to this topic

#1 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 19 November 2012 - 02:34 PM

Hi All,

I'm looking to buy a planetary eyepiece for my Lightbridge...
Thought I might look towards a Baader Genuine Orthoscopic 5mm.

Is there anything I should steer away from and anything you can recommend (I do wear glasses).

Many thanks in advance for your help.

#2 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22578
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 19 November 2012 - 05:09 PM

Hi All,

I'm looking to buy a planetary eyepiece for my Lightbridge...
Thought I might look towards a Baader Genuine Orthoscopic 5mm.

Is there anything I should steer away from and anything you can recommend (I do wear glasses).

Many thanks in advance for your help.

Well, that eyepiece, though excellent, will have too small an eye relief for you to observe wearing glasses.
But then, will you need glasses to use the eyepiece?
In your f/5 scope, that yields a 1mm exit pupil. Most astigmatisms are not severe enough when such small portions of the cornea and retina are engaged to require correction of astigmatism, and near-sightedness or far-sightedness can simply be corrected by re-focusing.

I think, though, that you would be better served by having an eyepieces of, say, twice that focal length (which you would use a LOT) and then getting a really good Barlow to create the 5mm.
First, because the Barlow actually improves the images at the edge of the field in a typical Plossl or Orthoscopic, and second because the Barlow would be usable with all your eyepieces, effectively doubling your eyepiece collection. Third, that way you get to partake of the eye relief of a ten millimeter eyepiece instead of the reduced eye relief of a five.
And I say "good Barlow" because the light loss and light scatter in a good one is so negligible as to be essentially non-existent.
Bear in mind that people who wear glasses tend to prefer eye reliefs larger than 12-15mm (depending on the apparent field of the eyepiece), and that usually rules out most simple design eyepieces.
However, there are a fair number of excellent 6-element designs that are extremely sharp, and which have longer eye relief if you feel you must use glasses at this exit pupil.
Myself, I'm so presbyopic I can't see anything sharply that's closer than 20' from my eye. So I view without glasses on, but put glasses on to read charts, books, DSC, or even EP focal lengths. So my glasses go on and off 500x a night when I'm viewing. The solution? A lanyard around the neck. I take them off and let them fall and they don't hit the ground and i always know where they are. You could do that too as long as you're viewing alone. But if everyone in the family is taking turns at the eyepiece, you kind of have to use your glasses to at least have the focus close when the next person sits down.
Hope that helps you make a decision.

#3 SeattleScott

SeattleScott

    Apollo

  • -----
  • Posts: 1361
  • Joined: 14 Oct 2011

Posted 19 November 2012 - 10:54 PM

a 5mm will give you 300x in a non-tracking scope. How good is your manual tracking? I would be tempted to go with an UWA even if you lose a tiny bit of contrast.

#4 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5082
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 20 November 2012 - 03:46 AM

I have a 12" Lightbridge, which I use for planetary observing. A couple of observations:

The mirrors need to be close to ambient. Keep the primary fan running. Is your local seeing often very good? If not, you may find the scope limited to 150x-200x on most nights, just like I do. A dedicated 5mm eyepiece will be a waste, unless you can use it often or if you already have a decent collection of good eyepieces and merely want to have something to use on excellent nights.

Already 150x shows a LOT of stuff on Jupiter, but the view is FAR better if you can use both eyes. I have a binoviewer and the planetary views are much better than with a single eyepiece. Mine uses a 2.6x corrector and two 25mm eyepieces for 160x magnification. The view is vastly superior to what my 10mm eyepiece delivers and it's a very good 10mm.

Also, I find that tracking the dob at 300x begins to get tiresome and I'm using a 10mm eyepiece with 70° AFOV and a 2x barlow. The difficulties are only getting larger with a 5mm eyepiece that has only 45° AFOV. You may find it extremely difficult to always keep the planet in the sweet spot of such a tiny field or even to just keep it in the field. The sky turns extremely fast at 300x. You may also find that edge performance of the ortho at f/5 is not so hot and that this will increase the problems. It may be wiser to go with a 10mm and a 2x barlow. Or a 15mm and 3x barlow. Or 25mm and 5x PowerMate... Or a 5mm eyepiece with internal barlow. All will show improved edge correction over a 5mm ortho and thus keep the planet sharper for a longer time as it zips across the field. Personally, I strongly prefer the barlowed binoviewer for planets. I use orthos or Königs with it and get ultra crisp images across the whole field.


Clear skies!
Thomas, Denmark

#5 coutleef

coutleef

    Soyuz

  • *****
  • Posts: 3964
  • Joined: 21 Feb 2008
  • Loc: Saint-Donat, Quebec, Canada

Posted 20 November 2012 - 03:06 PM

i have a dob similar to yours and at this magnification, i really appreciate my wider field EPs. since my skies do not often allow that level of magnification, i went the way of the barlow and am very satisfied.

#6 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 21 November 2012 - 12:44 PM

Hi Starman1

My eyesight is not all that bad and I can go without the glasses, but prefer not to.
Great idea to use a lanyard though.
I'll think carefully then about eye relief before I choose.

Thanks for great advice as usual.

#7 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 21 November 2012 - 12:48 PM

Hi SeattleScott

That's not the first time I've heard someone sing the praises of the UWAs.

My tracking is alright I suppose, but it is a lot easier to see detail for longer if one is not constantly nudging the scope... absolutely.

Thanks for that. There's a 6.7mm Mead UWA. Any good?

#8 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 21 November 2012 - 01:00 PM

Hi Astrojensen

Night skies are darker now the street lamps go off at 1am, but I've always used a light shroud and the enclosed tube can amplify the tube air currents.
How's the image distortion with the fan running? Is it noticeable?

Very interesting. Thanks for your advice. I like the idea of the binoviewer a lot and I'll look into the Powermate - I don't have one currently.

Also, I welcome the opportunity to discuss collimation since we both have the exact same scope!

Many thanks.

#9 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 21 November 2012 - 01:04 PM

Hi coutleef,

Thanks for your reply.
Are you saying that you are using the UWAs and then add the Barlow when the conditions allow?
What focal length UWAs are you using? Does it give around the 120x without the Barlow?
Which UWA do you favour most?

Many thanks,

#10 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5082
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 21 November 2012 - 01:26 PM

Hi Brummell

Unless it's very windy, I use the shroud when observing planets, to keep body and ground heat out of the light path. It has a visible, positive effect. I also keep the fan running, which also has a visible, positive effect. The image gets a little bit sharper and steadier.

My scope holds collimation well during use and usually only requires minor tweaking at the start of each night. I use a laser for collimating the secondary and barlow it, when collimating the primary. Works well. I want to change the springs around the primary collimation screws. They are too weak and if I don't have the screws threaded almost all the way in, the mirror cell can flop, as the scope moves. Do make it a point to understand and master collimation. It makes a huge difference at the eyepiece.


Clear skies!
Thomas, Denmark

#11 B Brummell

B Brummell

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jun 2012

Posted 22 November 2012 - 02:46 PM

Hi Astrojensen

If you're using a barlowed laser for collimation how did you make the screen to project the donut image onto and how did you affix this screen?

I'm using this method now together with a Cheshire eyepiece: Cheshire eyepiece first for rough adjustment and then the barlowed laser and screen for micro adjustments.
I found that a circular casing for plumbers PTFE tape fits snugly over the focuser draw tube and then I was able to fit some white card for a screen inside this casing with a punched out hole exactly in the centre.

It has the desired effect, but I worry it's too "home made" to be totally accurate enough.

Best regards...

#12 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5082
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 24 November 2012 - 03:56 PM

Hi Brummell

The laser I use has a built in screen. It's one of these:

http://www.teleskop-...tion-TS-Newt...

These are no doubt also available in the states and other countries under different brand names. I like it. It seems to be accurate and well collimated. I use a cheap GSO 2x barlow for barlowing a la Nils Olof Carlin.


Clear skies!
Thomas, Denmark






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics