EP size basics

[starwonder]

There seems to be some conflicting statements going on here and I'm more confused than ever!!    - can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's.   Like give me the reasons why you bought a particular EP, it'll help me understand better I'm sure.

Thank you.

[AlexB67]

There seems to be some conflicting statements going on here and I'm more confused than ever!!    - can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's.   Like give me the reasons why you bought a particular EP, it'll help me understand better I'm sure.

Thank you.

Perhaps this useful guide will help you some more  http://www.swindonstargazers.com/beginners/eyepieces.htm

[Naemeth]

There seems to be some conflicting statements going on here and I'm more confused than ever!!    - can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's.   Like give me the reasons why you bought a particular EP, it'll help me understand better I'm sure.

Thank you.

Sorry if I confused you.

People buy 2" eyepieces for the larger apparent field of view they are able to provide. People buy 1.25" eyepieces more often, generally, because they are lighter and cheaper, but do not offer the same field of view that the 2" eyepieces offer.

[John]

There seems to be some conflicting statements going on here and I'm more confused than ever!!    - can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's.   Like give me the reasons why you bought a particular EP, it'll help me understand better I'm sure.

Thank you.

I wanted a large field of view in a longer focal length eyepiece. The only way to get this is to buy the 2" format eyepieces. As I realised that I wanted the large field of view I was getting to remain sharp to the edge even when the eyepiece was used in a fast focal ratio scope (fast = F/6, F/5 etc) I bought more expensive 2" eyepieces to get this. My Nagler 31mm eyepiece is I guess my ultimate expression of this as it delivers an 82 degree apparent field of view and has to be a big fat 2" eyepiece to do this.

[Moonshane]

my thread here explains why I bought my own eyepieces http://stargazerslounge.com/topic/188794-eyepiece-groups/

broadly I have one 2" eyepiece (26mm Nagler) and this serves as my widest field eyepiece. the rest provide higher magnifications at increasingly narrow fields of view although I do have a couple of 'repeats' for different purposes entirely. e.g. I have  32mm TV plossl which I use on the sun and the moon and a 25mm TV Plossl for the moon. I really am not keen on the 26mm Nagler on the moon and it has a field stop larger than my 6" secondary mirror so there's no point adding such a lump in that scope which is delicately balanced.

[Charic]

- can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's

In simple terms, You would buy  the 1.25" EP, as its the most popular choice. Not all telescopes have the 2" format.  You would   buy  a 2" eyepiece because of its longer focal length, wide-field  of view and low magnification, which may not available in the 1.25" format. (Longer focal lengths reach  physical limits in  1.25" format )

So your 2" lens will be larger & heavier , more expensive, because theres more in the construction.

To your original question ( depending on the brand of lenses you choose ) there may be no fundamental viewing difference between the two types.

lenses,  what asubject!

[Andrew*]

There seems to be some conflicting statements going on here and I'm more confused than ever!!    - can someone please tell me in simple lay mans terms the reasons behind buying either a 1.25" or 2" EP's.   Like give me the reasons why you bought a particular EP, it'll help me understand better I'm sure.

Thank you.

Usually one doesn't base eyepiece choice on whether it has a 2" or 1.25" barrel. The manufacturers decide that. They will usually design an eyepiece with a 1.25" because it's cheaper, but will use a 2" barrel if:

- the true field offered by the eyepiece is large. This means almost all eyepieces with fields larger than 24mm focal length and 68° AFOV or 32mm 50° etc.

- the lens design means it will be large and heavy

Usually manufacturers make good decisions in this respect, so unless you have a specific reason for choosing eyepieces with a particular barrel size, don't give it too much thought...

[bingevader]

Take a look at the picture at the bottom, of the line up of the new SkyWatcher SWA 70^o eyepieces.

This isn't a recommendation that you buy them, just for example.

They will all fit a 2" focuser/adapter. The 3.5mm to 17mm will also fit a 1.25" focuser/adapter. The 22mm and 32mm will only fit a 2" focuser/adapter.

You can achieve the same with all 1.25" eyepieces by buying a 1.25" to 2" adapter (I have one for my 14mm eyepiece for observing DSOs so that I can use it alongside the 2" eyepieces without changing anything else over).

To frame some of the larger DSOs completely you need a larger field of view that only larger pieces of glass can achieve. On the whole, the glass just wouldn't fit into a 1.25" eyepiece. So thy're bigger and more expensive!

It gets a little confusing because really, these two sizes are just to standardise the whole set up for manufacturers and users.

I don't know if this will help or make things more confusing, but Skywatcher do make a 1.25" 32mm plossl eyepiece with an apparent field of view of 50^o, that's about 1.3^o of the sky in my 'scope.

They also make the 2" Panaview 32mm with an apparent field of view 70^o with which I can see around 1.9^o of the sky. It's a big difference to me.

You can get small focal length eyepieces with large apparent fields of view, the magnification will be the same, on say jupiter for example, there'll just be a lot more sky around it!

Cheers

[starwonder]

This is great guys thank you, now I'm getting the picture why you'd not have just one set of all 1.25" or 2" EP's. 

You're all so knowledgeable in this and I'm not, not yet anyway.  I'm starting to wonder whether a newbie like me can actually be just a pure observer of the stars without being an expert in optics.

I look forward to the link's some of you have referenced, I need all the education in optics I can get at the moment.   Thank you.

[Naemeth]

This is great guys thank you, now I'm getting the picture why you'd not have just one set of all 1.25" or 2" EP's. 

You're all so knowledgeable in this and I'm not, not yet anyway.  I'm starting to wonder whether a newbie like me can actually be just a pure observer of the stars without being an expert in optics.

I look forward to the link's some of you have referenced, I need all the education in optics I can get at the moment.   Thank you.

Of course you can, the knowledge builds up over time. When I joined I had absolutely no clue, after my time here I understand quite a lot thanks to everyone here - you're in good company .

[Charic]

starwonder......... I reckon Patrick Moore  would still have  leaned towards reference materials, now and again?  Its such a vast subject. Collimation next when your scope arrives.

[starwonder]

It's really great to have so much support and despite being a complete numpty on this subject I haven't had any condescending comments at all.  A really amazing community this place, thanks everyone.  

Which EP I will start off with I'm not too sure now but I think I'm getting to understand the difference between the two sizes.

My choice of EP's will I think be partially be down to the quality of the 1/10 PV mirror I've ordered for my 10" OOUK Dob, I obviously don't want to buy an EP that doesn't do the mirror justice but on the other hand I haven't got a lot of brass left!  Any recommendations?

[ronin]

can actually be just a pure observer of the stars without being an expert in optics.

You can observe only, but in something like this that is based quite heavily on optics then some understanding what is happening makes a big difference.

[Moonshane]

you cannot go wrong with used televue plossls. you looked through a couple at mine. £50 each approx and as good as they come.

[Charic]

You kidding us?............. A mirror like that..........start saving for some eyepieces? Lol

[John]

you cannot go wrong with used televue plossls. you looked through a couple at mine. £50 each approx and as good as they come.

Agreed. These plus Baader Genuine Othoscopics (used) represent the best outright optical quality you can get for around £50 each in my opinion and are equal to eyepieces costing £hundreds more.

The ortho and plossl design does have what might be called "comfort compromises" in the shorter focal lengths but, unless you wear glasses when observing, they are still very usable 

[starwonder]

Nice one guys.  £50 you say for decent second hand EP's, might manage a couple of these okay.  Maybe a 7mm and 15mm 1.25" to start with?  I only wear glasses for reading so compromised focal length shouldn't be a problem.  Thanks everyone.

[Naemeth]

Nice one guys.  £50 you say for decent second hand EP's, might manage a couple of these okay.  Maybe a 7mm and 15mm 1.25" to start with?  I only wear glasses for reading so compromised focal length shouldn't be a problem.  Thanks everyone.

It'd be a 8mm and 15mm, TeleVue's highest power plossl is 8mm.

I can vouch for the quality of the TeleVue plossls by the way, brilliant EPs and will work well in any scope you put them in .

[starwonder]

But you can get the 7mm in other makes like the  Baader Classic Othoscopics - are they any good for my scope?

[Naemeth]

But you can get the 7mm in other makes like the  Baader Classic Othoscopics - are they any good for my scope?

The Baader Classic Orthos only come in 6,10 and 18mm (along with a 32mm Plossl). For a 7mm an Astro-Hutech ortho would be good, and yes they'd work well in your scope, as long as you could live with the small AFOV and short eye relief .

[John]

The Baader Classic Orthos are very nice eyepieces and very nearly as good as the Baader GO's, Astro Hutech's etc. Their mechanical construction is somewhat plainer and, while their field of view is 50 degrees rather than the normal 42 degrees of an ortho, that extra outer field is not entirely sharp. I wonder if it is intended to frame objects rather than to study them, which would be done in the centre of the field of view. ?. The Baader Classics are nice eyepieces but are only available in the 6mm, 10mm and 18mm focal lengths plus a 32mm plossl.

Edit: Jonathan beat me to it ! 

[michael.h.f.wilkinson]

It's really great to have so much support and despite being a complete numpty on this subject I haven't had any condescending comments at all.  A really amazing community this place, thanks everyone.  

Which EP I will start off with I'm not too sure now but I think I'm getting to understand the difference between the two sizes.

My choice of EP's will I think be partially be down to the quality of the 1/10 PV mirror I've ordered for my 10" OOUK Dob, I obviously don't want to buy an EP that doesn't do the mirror justice but on the other hand I haven't got a lot of brass left!  Any recommendations?

We all remember too well that we all started out as numpties

Besides, astronomy being an essentially infinite field (or at least unbounded), there are always new areas of numptiness awaiting anybody who has just "mastered" a certain area.

And maybe it is just spending time looking into the vastness of space that keeps us modest

[andyman]

I was also a numpty and still am but the eyepiece review section on sgl helped me out bigtime

It helped me to match certain eyepieces to my scope in terms of type of scope and fastness of mirrors

If it was not for these very helpfull reviews i wouldnt have had a clue.But whether its 45 degree fov or 100 degree fov

so long as the object i am viewing is clear and crisp in the eyepiece that will do for me and sgl has helped me achieve that

So thanks SGL for helping another numpty out 

[starwonder]

Perhaps this useful guide will help you some more  http://www.swindonstargazers.com/beginners/eyepieces.htm

Just finished reading the information on the link, very useful indeed, thank you.  Will definitely refer to this article when purchasing my EP's.  

One other question that arose from the link was the use of a Barlow to effectively double up a set of EP's, are they any particular drawbacks with this approach?  ie does introducing a Barlow into the chain cause reduced clarity?

[michael.h.f.wilkinson]

Just finished reading the information on the link, very useful indeed, thank you.  Will definitely refer to this article when purchasing my EP's.  

One other question that arose from the link was the use of a Barlow to effectively double up a set of EP's, are they any particular drawbacks with this approach?  ie does introducing a Barlow into the chain cause reduced clarity?

Another can of worms. A good barlow can provide extra magnification without a great deal of influence on image quality. A cheap barlow can degrade image quality visibly. In some cases Barlows get a bad name because people (ab)use them to push magnification beyond the capabilities of the scope or seeing conditions. If I use my (excellent) 2.5x TV PowerMate (not technically a Barlow, but does the same job) with my XW10mm to push my scope beyond 500x, I am bound to end up with a mushy view. Using the same combination in my F/6 scope to reach 120x with my 80mm scope works fine. It means I do not have to buy a 4mm EP. TV PowerMates and Meade TeleXtenders just "get out of the way" and do not appear to degrade quality.

An advantage of a Barlow is that you are effectively using the EP at slower F/ratio, which can help. Furthermore, a 2x barlowed 20mm Plossl gives a more comfortable eye relief than a 10mm EP of the same design. One downside I find annoying is the increased hassle when swapping barlow and EP, vs just swapping EPs. This means that in the end, I filled the gaps in my EP set, and use the PowerMates and TeleXtenders almost purely for planetary imaging.