Eyepieces

[JM1311]

Hello

I have been using my skywatcher 200P for a little while now using the original 1.25" eyepieces supplied with it (10mm, 25mm, 2x Barlow).

I am now beginning to look around for some more eyepieces, i have tried searching for a while but I can't find an answer to this question:

What is the main advantage of a 2" eyepiece over a 1.25" eyepiece, and are these differences noticeable and worth the extra expense?

Thanks:icon_salut:

JM1311

[Nova]

I believe the main advantage is the additional field of view you get from a 2" also maybe the longer eye relief? but I dont own any yet there pretty darned expensive so dont know if the gain is worth the extra cost.

[NGC 1502]

As Steve has said, the main advantage if you get a low power 2" eyepiece is to get a much wider field of view. This is handy for finding objects, and viewing larger ones.

But be careful not to go too low. If you divide the magnification into the aperture size, that will give you the exit pupil. If that is too large, then it will be bigger than the dark adapted pupil of your eye, so not all of the light can enter your eye.

Example - my 27mm eyepiece gives 44x in my 10" Dob. 44/250 = 5.6mm. So it's just about ok for my approx 5mm dark adapted pupil ( I am 63 ) But that gives me a nice 1.5 degree field. A 25mm standard 1.25" eyepiece in my scope would give about a 1 degree field.

Regards, Ed.

[johninderby]

Basically a 2" eyepiece has no advantage at all over a 1.25"eyepiece in terms of the quality of the views. As mentioned above it just offers the possibility of a wider field of view at low powers.

OK this is a bit simplified and leaves out a lot of detail but essentially it's the diameter of the field stop inside the eyepiece that determines how wide a field of view you can get. However until you get to the 17mm - 20mm and over range the field stop will be smaller than 1.25" so there's no advantage in using a 2" barrel. It's a simple as that.

John

[damnut]

Good advice from Johninderby, see also link below - fill in the blanks, takes age into account which allows for exit pupil.

N.A.A. Telescope Math Calculator

You will find that most eps will be better than the ones that come with package scopes. Mid cost are the BST explorers at c£35, Hyperions c£100. Have both love em, the bsts are particularly good value for money.

Cheers

[Charon]

I recommend the Hyperions too. (Thanks for the great link Damian)

[damnut]

Hi Nereid3,

Dim trafferth!,

Hwyl

(taffy in Mansfield)

[crazyjedi]

I believe that EP's around the 25mm mark are the lowest wide angle lenses in the 1.25 inch format. The Meade 24mm SWA is a fabulous EP at around £100 (if you're sticking to 1.25 inch EP's. My filters are all 1.25 inch so i started a thread a short while ago trying to ascertain which would be a good (reasonably priced) low power EP @ 1.25 inch format. If i recall correctly the Meade SWA 24mm came out on top (The TV 24mm Panoptic being too expensive) The Meade SWA range seems to be vainshing from British retailers recently but Telescope experts Astroshop are selling them at very reasonable prices. It might be worth a thought

[Capricorn]

The disadvantage of a 2" eyepiece is they are BIG, if you haven't seen/used one you are in for a surprise.

Next they are expensive, all those bigger bits of glass cost money.

Finally they do not come in the range of focal lengths that 1.25" eyepieces do. You are not going to get a 10mm 2" eyepiece except if you pay lots of money. I suspect someone makes them but no idea who.

I have a 20mm 2"eyepiece, I can fit 4 TV eyepiece boxes in to it's box and it would need quite a bit of padding to prevent them rattling round.

[johninderby]

Not that I'd want to buy one myself but at about £50.00 or so:

WOLLENSAK 2in WF EYEPIECE 10mm

http://www.astrophoto.co.uk/surplus200eyepieces.php

John

[crazyjedi]

Not sure i'd want to buy an EP from a retailer with the word 'surplus' in the title. The ad states 60 degree + FOV - somewhat vague?

Anyone heard of Wollensak??

Are they as pants as they look or are we missing out. I am always interestedf in a bargain (but not at the expense of quality)

[John]

Wollensack is a brand name that is most often heard of in the USA. In the 50's and 60's it was a trusted name over there in cameras and audio visual products. Nowadays it seems to be used on re-branded versions of things like the chinese 30mm 80 degree field of view 2" eyepieces that are also branded Moonfish and others.

Browse through the Cloudynights forum and you will find the name cropping up from time to time but it's been a long time since the name was associated with actually making anything.

[great_bear]

Not sure i'd want to buy an EP from a retailer with the word 'surplus' in the title.

The "Surplus" name's there for a reason

Surplus Shed actually sell original/modified military surplus eyepieces - i.e. eyepieces made or modified from gunsights / periscopes etc. Military specifications often exceed consumer specifications for eyepieces, so you can get world-class optics for a fraction of the price of a brand name eyepiece.

Personally I think it's a bit of a lottery, and a game only worth playing if you've got a slow scope and know what you're looking for.

[crazyjedi]

Not for me then. My scope is fast and my pockets inadequately furnished.