Can anyone explain?

[cutepetgroomer]

So as I been looking at different eyepieces to purchase (monsoon season now where I live) and I see planetary eps and plossls. I know more or less what a plossl ep is but I am unfamiliar with planetary eps. I think from the name they are designed for planet viewing, but is thts all they are limited to?

[Peter Drew]

You can use "planetary eyepieces for most purposes except perhaps solar projection. They are usually fairly unsophisticated in design and have few optical components, this configuration gives good light throughput and contrast. The downside for other than planetary viewing is that they tend to have rather small fields of view.      

[ronin]

They tend to be designed for good contrast so that planetary features stand out more.

However I suspect that people would like good contrast on all eyepieces, so not sure why they are "different".

To keep contrast high they should have good coatings to pass light through the system and to reduce scatter.

The "planetary" of general reference is the TMB, actually unaware of anything else that is specifically called a "planetary". It is fairly good but not outstanding. At the first production it was actually poor. It underwent a number of improvements, I think 7, in order to rectify problems. However it still never seemed to perform as many hoped it would or should.

Similar in some ways are the Astro-Tech Paradigm and the Celestron X-Cel.

I think a post on CN summed it up nicely:

The TMB planetary performs like a $60 eyepiece, the Astro Tech Paradigm performs well above a $60 eyepiece.

Many use Ortho's for planetary observing.

One aspect of eyepieces used for planetary observing is they tend to have smaller fields of view.

[cutepetgroomer]

Other than when in class I've never done solar observing and I doubt I will anytime soon. I tend to love the moon and planets more . I do like dso gazing as well.

[Jim Steele]

Can't go wrong with a set of orthos, narrow fov, but crisp detail to the edge of view and high light transmission allowing brighter fuzzies. The BCO range are good value for around the £50 mark.

[cutepetgroomer]

I have my eyes set on some good plossls to start with that come with some filters (I figured out through trial and error that I got some strange vision at night ) . I do have one ep already that is. Wide view and i enjoy that one a lot, next full moon I plan on using the barlow with that one.

[ronin]

I would sit quiet and wait to make up your mind what to get once you have the scope.

Plossls are the easy option, and I have been there, but I gave most of mine away, many were given away unused.

Anything down at 8mm or less is questionable - they just do not have the eye relief to make them easy to use and get on with. Ease of use is a factor to be considered. If you look at ones like the TV plossl (excsllent items) they do not make a plossl less then 8mm and I suspect there is a good reason for this.

Even with a set I find there are still ones missing and a few are simply too short. A 4mm plossl is as close to a waste of time as I can think of.

There will be alternatives to plossls around at good prices, Barsta make a range of eyepieces that many retailers sell under a brand name. The Astro-Tech Paradigm being one, it is sold by Agena Astro under the Agena name, here it is available with about 4  different names and costs, but all the same Barsta eyepiece.

Plossl are a step up from many of the supplied items but equally many companies produce a cheap plossl that just doesn't perform. You need to be a little selective these days.

The other aspect is that getting plossl's as an step before better means you spend out twice.

[Alkaid]

I have found that the term 'planetary eyepiece' is as much to do with the scope being used, rather than the design of the eyepiece.  Any eyepiece which gives a high power in your set up would be a planetary eyepiece.  Generally speaking, the planetary eyepieces are of shorter focal lengths, say less than 10mm. 

For example a 10mm eyepiece used in an SCT or Maksutov with 2000mm focal length would give a magnification of x200, good for the planets.  In your 50/700 model, a 7mm eyepiece would give x100.  (That's really the max for a 50mm scope).  But as it's the highest power you can use with that scope, you could therefore describe it as your planetary eyepiece.

As the others have said, some eyepieces are better than others for contrast and field of view.  Eye relief is a biggie for me as I wear spectacles.  Even if you have normal vision, you really don't want to be pressing your eyeball right up to the lens as it's a pain.  Avoid short focal length plossls for this reason.