Eyepieces 2" vs 1.25"

[Pixies]

Hi guys,

Just about to pull the trigger on a Bresser Messier 8". I see that it can take 2" eyepieces but comes with an adapter and a 1.25" eyepiece (25mm plossl).

I'll need to decide on which size I stick with, for future purchases. I assume I wouldn't want to mix things up, so that I won't have to double-up on filters, etc. So which is best? 2" or 1.25"?

Could you let me know the advantages and disadvantages of both - when considering the 'scope I'm likely to be using them with?

 

Many thanks.

[johninderby]

35 minutes ago, Pixies said:

Hi guys,

Just about to pull the trigger on a Bresser Messier 8". I see that it can take 2" eyepieces but comes with an adapter and a 1.25" eyepiece (25mm plossl).

I'll need to decide on which size I stick with, for future purchases. I assume I wouldn't want to mix things up, so that I won't have to double-up on filters, etc. So which is best? 2" or 1.25"?

Could you let me know the advantages and disadvantages of both - when considering the 'scope I'm likely to be using them with?

 

Many thanks.

1.25” for most of your eyepieces and a low power 2” is the normal thing.

In general the lowerr mm (higher mag) eyepieces come in 1.25” and  the higher mm (low mag) eyepieces are 2”. There are good reasons for this. So get moon and planetary filters in the 1.25”. With the low mag 2” eyepiece you will be looking at widefield views so a filter more suited to that.

So basicly you will need both sizes of eyepieces. 

Edited April 25, 2020 by johninderby

[Ricochet]

15 hours ago, Pixies said:

so that I won't have to double-up on filters

Reportedly, the current model is shipped with a 2"-1.25" adaptor that is threaded to take 2" filters. This means that you can buy 2" UHC and OIII filters, and use them with both your 2" and 1.25" eyepieces. 

For planetary and lunar you only want a neodymium filter, which could be either size, and possibly a couple of polarising filters, 1.25" on the eyepiece and 2" in the adaptor, so that you can turn the eyepiece to adjust the brightness.

The reason for 2" eyepieces existing is to allow wider fields of view that the barrel of a 1.25" eyepiece would impede. This means that generally speaking, 2" eyepieces are limited to long focal length, wide field of view eyepieces. However, there are also some short focal length, wide field of view eyepieces that are fitted with a 2" barrel as they are very heavy and the 2" fitting is possibly more secure.

[Pixies]

Thanks everyone. Another question (sorry - but I guess if you are commenting on posts in the 'Beginners' section, then that's cool)

I've seen comments here and elsewhere that with a fast 'scope (this one is f6), one needs better quality eyepieces. Could anyone elaborate on what causes this and also, what one would differentiate a 'better quality' eyepiece. Well, as far a the budget would stretch for a beginner scope.

 

Cheers

[johninderby]

A fast scope is one with a lower f number f/5 vs f/10 for instance. Slow scopes are more tolerant of aberations in eyepieces so you don’t need as high quality eyepieces. Fast scopes do show up distorions and aberations in eyepieces and it costs more to produce one with better quality lenses and coatings. 

Price is a pretty good guide to eyepiece quality but if your scope is only say f/6 a merely good eyepiece will do. Also the wider the fov of the eyepiece the more expensive in general. 

I have over simplied things a bit but hope it gives you the general idea.

[Pixies]

Does a barlow have an impact on viewing angle? Say - would a 60deg 25mm EP become equivalent to a 60deg 12.5mm EP when barlowed?

[jonathan]

I have a really nice PanaView 2" wide field eyepiece which is brilliant for things like the Orion Nebula, clusters, and also the moon, so I have a couple of 2" filters which I only use for this one eyepiece - one is an ND filter for the moon (fits entirely in the eyepiece) and the other is for the nebula, it brings out the glow of the dust just a tad, makes the stars shine green.  I forget which filter it is right now, probably OIII.  The PanaVIew may not be the best 2" wide field eyepiece out there but it certainly has the Wow! factor compared to regular 1.25" eyepieces, it just has so much glass that you can't fail.

I also have a 1.25" ND filter for any other eyepiece I own.

Like on a racing car, you need to use the right tyres for the current situation - so use the best eyepiece for the job at hand!  If that means 2" (and it's an option) then do it.

Edited April 28, 2020 by jonathan

[JOC]

As a general comment I guess it depends on your budget.  I get the distinct impression that you can get 2" and 1.25" EP's in most sizes, I can easily believe that 2" will consistently be better than an equivalent 1.25".  However, I bet more amateur observers like me tend to stick with 1.25" purely because they will often/always? be the cheaper option.  Until you find out if astronomy is going to be 'your thing' and I'd give it 6-9 months I'd be inclined to start off with a few moderately priced 1.25" EP's picked up second hand from the SGL classifieds or the astro 2nd hand web sites.  You will find out if it's going to be your 'thing' and then if you want to invest and upgrade to 2" EP's you will find you can sell on the 1.25" EP's for very much what you paid for them (assuming you look after them).

[John]

8 hours ago, Pixies said:

Does a barlow have an impact on viewing angle? Say - would a 60deg 25mm EP become equivalent to a 60deg 12.5mm EP when barlowed?

A barlow lens can reduce the field of view of very wide angle eyepieces, ie: those with the widest field stops that the barrel size can accommodate, eg: in the 1.25 inch format a 32mm 52 degrees, 24mm 68 degrees etc. A 1.25 inch eyepiece 25mm with a 60 degree field might be affected as the field stop size is quite large.

 

 

 

[johninderby]

Genearlly 2” eyepieces are available in the over 25mm focal lengths. Very little choice in the shorter lengths. The are some 2” eyepieces in the shorter lengths but these tend to be actually 1.25” with an additional 2”” barrel. Ethos, Morpheus etc. 

Edited April 28, 2020 by johninderby

[JOC]

1 hour ago, johninderby said:

Genearlly 2” eyepieces are available in the over 25mm focal lengths. Very little choice in the shorter lengths. The are some 2” eyepieces in the shorter lengths but these tend to be actually 1.25” with an additional 2”” barrel. Ethos, Morpheus etc. 

How about the Baader hyperions John?  I've got a 31mm hyperion aspheric and you can unscrew the 1.25" barrel and put in place a 2" one to make full use of the width of the glass they go down to 5mm - I get the impression that the full range might function in a similar manner?  https://www.rothervalleyoptics.co.uk/baader-hyperion-1252-modular-eyepiece.html  The ones that link talks about.  I don't know how good they are, but they seem to cover a range of lengths??

[johninderby]

The Hyperions don’t seem to work well in 2”.. Found this quote from some one who wasn’t impressed.

” While Baader claims you can remove the lower lens group entirely from the standard Hyperions and use them as 2” wide-field eyepieces, doing so results in a rather aberration-filled eyepiece with almost no eye relief, rendering it almost useless. Don’t try it. “