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(Not another!) Eyepiece Selection question!

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OK this should be a nice easy one. I have an OrionOptics (UK) 8" F5 scope. It has a 2" Focusser on it (I think it may not be original but not sure) and I am thinking about getting a 2" Eyepiece. The thing is I am wondering if it is wort it? Are 2" EP's only for low magnification widefield views? Most 2" ones seem to be around the 40mm mark, which would give me 1000/40=25 times magnification, surely not worth the bother? I am kind thinking it would be nice to get one of these 'space walk' type EP's so I can WOW! my friends but is a 2" the answer?

On a secondry note, why fit a 2" to an F5 'scope are they not really intended for slower 'scopes?

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Right, this very question has been on my wallet for the last few weeks, and I hope I can now answer it correctly.

Basically, 1.25" EPs are just as competent in most areas as 2" ones. Only 2" are more expensive. But when you start looking for low powered 1.25" EPs of 32mm upwards, the FOV becomes very limited. I imagine a 40mm 1.25" is a bit like looking through a key-hole - not very impressive. This is where 2" comes in. The larger barrel means a greater FOV is possible, and low power, wide FOV views of the Milky Way and DSOs are one of the main reasons I'm in this hobby!

The question is - which one should you buy? You need one that will cope with your fast scope and have the right FOV (too wide means you miss things outside your eye's vision) and of course PRICE! Generally, I think we (since we have a similar scope) shall expect to pay over £50 for a good enough EP between 32 and 40mm. Don't forget that the exit pupil may be a little to large in a 40mm.

HTH

Andrew

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The larger barrel means a greater FOV is possible, and low power, wide FOV views of the Milky Way and DSOs are one of the main reasons I'm in this hobby!

Nicely put Andrew :rolleyes:

Once an eyepiece focal length gets much above 24mm, its field of view becomes restricted by the 1.25" tube. So, focal lengths above 24mm are often given wider 2" tubes. Below 24mm, there is no optical advantage to having a 2" barrel. Also, a 2" barrel does not guarantee or even indicate that an eyepiece is especially good - that still depends on design, materials and manufacturing.

Wide-field 2" eyepieces are particularly popular with owners of fast, wide-field scopes because they have the most to gain from this eyepiece type.

Also, keep in mind that a FOV of 70 degrees(ish) is generally accepted as the widest the eye can see without tilting the head (to see the edges).

Scanning the Milky Way with a good, low magnification (30-40mm), wide-field eyepiece is a wonderful experience. If you ever get the opportunity (SGL Start Party?) grab it!

Hope that helps.

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So it is worth having such a low power EP in my collection, I was not sure if the magnification was way too low.

Now for my second question, what would be a good EP to give me that moon walking experience, and would I benefit from a 2" one here?

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Yes, it is definitely worth having a 2" low magnification wide-field in your collection. As for which one - what is your scopes f-ratio and how much are you thinking of spending?

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F5

and as little as possible!

Seriously though I am not (yet) in to critical observing so I dont want to spend a fortune.

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The cheapest good 2" wide-fields are the Revelation range from Telescope House:

http://tinyurl.com/9q7e3

(The 30mm is the one to go for).

Or, push the budget and consider one of these:

http://www.firstlightoptics.com/proddetail.php?prod=ms500032sp (not as wide but optically, very good)

Or, push it all the way for one of these:

http://www.firstlightoptics.com/proddetail.php?prod=pxw30

Eyepiece choice is subjective and there are a lot to choose from - I will be as interested as you to see what others recommend.

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2"? Hmmmm 31mm T5? Or cheaper is the QX range which are nice enough for the price. Or the GSO 2" stuff aka moonfish 30mm or 1rpd etc

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Or the GSO 2" stuff aka moonfish 30mm

I think the Revelations are the same GSO eyepieces...

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Eyepiece choice is subjective and there are a lot to choose from - I will be as interested as you to see what others recommend.

A cheap, 2" widefield eyepiece to use in a f5 scope? If you take out any one of those three criteria you have plenty of choice, unfortunatly all three together....... :rolleyes:

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Or the GSO 2" stuff aka moonfish 30mm

I think the Revelations are the same GSO eyepieces...

I think you are right if it's 80 degree or close

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I think the 70 deg Moonfish/ Revelation/ GSO are supposed to be OK at f5. The 80 deg version def. isn't, its fine at f9 or so but not much more than a 'finder' at f5.

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I have an 80 degree one and it's ok but not fantastic, never seen a 70 degree one. The 70 is probably much better as Gaz says.

80 degree is only good if you pay for the glass, and I brought mine for 30 squid hehe

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I use an Orion Optilux 40mm 62 degree field 2 inch EP in my Megrez 90 (F6.9) and Revelation 8 dob (F6) and it works very nicely in both. There is some loss of sharpness right at the edges of the field but stars are sharp across 80% of the field of view which is about as good as you can expect for the £45 that it cost me (used but mint condition). I think they are about £100 new though. The only "issue" I have with it is that the positioning of your eye is quite important - if you move away from the "right" spot the view tends to black out - this is quite a common issue with longer focal length eyepieces I understand.

This eyepiece gives a true field of 3.99 degrees with my Megrez 90 and just over 2.07 degrees with the Revelation 8 inch - there are slightly wider field eyepieces out there but not by much.

The Optilux 40mm is the same eyepiece as the University Optics Konig II 40mm which seems to have a good reputation in the USA.

John

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Having owned the 31mm type 5 nag i would say if you have the cash go for it, the other 1 would be the 30mm Pentax, i would also consider 35mm panoptic you can pick those up for around £ 180 second hand All are very good bits of kit. The 31mm nag could cause you problems with scope balance . :rolleyes:

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I think the revelations are the way to go for me. I dont want to spend over £100 on a single EP at this early stage of observing. I think the extra quality would be lost oin me :rolleyes:

Just need to scrimp together some cash now :wink::D :D

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The Antares Speers-WALER eps get good reviews from the people who have them, and I have heard them compared favorable to the much more expensive Naglers. I've just ordered the 24mm Speers, which has a FOV of 66 degrees. The shorter ones are 82 degrees, and said to give edge-to-edge sharpness. I plan to find out...

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Here is a link to an Australian web site review of the GSO 42mm 2 inch eyepiece which I believe is the same as the Revelation 42mm:

http://www.iceinspace.com.au/index.php?id=42,118,0,0,1,0

It seems to perform quite well in F6 and F5 Newtonians and at the end of the review the 30mm is mentioned positively as well.

For £50 delivered (Telescope House) IMHO I think you'd be hard pressed to find something better - you would probably have to spend double that, and a bit more to get significantly better performance.

John

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well, only positive comments about this EP now because I am the high bidder at £60!!

Andrew

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Sorry for the delay in getting back on this Andrew - don't whatever you do buy that Meade 32mm - they are made from radioactive glass which affects the brain causing a gradual increase in the desire to part with more money for increasingly better kit ....... too late !!!!!!!! :rolleyes:

John

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Sorry for the delay in getting back on this Andrew - don't whatever you do buy that Meade 32mm - they are made from radioactive glass which affects the brain causing a gradual increase in the desire to part with more money for increasingly better kit ....... too late !!!!!!!! :rolleyes:

John

Nevetheless, buy it WH's should 17mm be Antares a good Plossl bit he would of kit like for you. SWs instead! No subliminal coercion was used in this post... :wink:

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