telescope lens types

Ive been browsing looking for an explination of the different types of lens for a telescope, but i cant find any. i need explinations of the differences of plossil and what ever other lens types there are. anyone help here? thanks

Hi Fintan,

I'm no expert on this (not nearly) but I did alot of research on it when choosing my EPs so I'll jump in. It's a truly huge subject.

Plossl - Probably the most common type and great for general purpose viewing. Usually 4 elements. Quality varies greatly across brands and cost. Usually either 50 or 55 degrees field of view. Great high power piece. Low eye-relief at high powers.

Ortho - Never used one but they aren't too expensive and are supposed to be great for planetary work due to their small amount of elements (4) and high contrast. Small field of view.

Erfles - 5-6 elements, usually good at low powers but poor at high powers. Available 2 inch barrel only I think.

Kellner - Bright and sharp images. Cheap, but only about 40 degrees field of view.

Ultrawides & Premium EPs -
You could right a 10 page essay on this

You've probably heard of the expensive ones like the Pentax XWs and Televue (Nagler, Radian, Panoptic). You really need a premium scope to realise their potential. I haven't tried any of these.

There are cheaper 2" compound EPs though which are usually aimed towards larger fields of view at low magnifications. These cheaper EPs are great for long focal ratio scopes but often break down at the edge of the field for "fast" scopes.

And more still, there are mid price compound lenses like the excellent Orion Stratus and Baader Hyperion. Half the price of their Televue counterparts and offering 66 degrees field of view but also work well on 'fast' scopes. I love the Hyperions. They are still much more expensive than plossls though (even Televue plossls).

Out of all the EPs I have used so far my main used ones are my 21mm Hyperion for low powers and 10mm Plossl or 5mm Hyperion for planetary.

Why did I choose the Hyperions? Mainly because I had a fast scope at the time & these give good focus right to the edge of field + I wear glasses, requiring a decent eye-relief. I take the glasses off when uing the plossl.


The general consensus from the web was that Plossls represent the best value for money. If you don't mind 55 degrees field of view & short eye-relief at high powers they would be the one to choose.

I'm sure someone will chime in if I got anything wrong

Hope that helps,

Trev