2" or 1.25" eyepieces.

[weetooner]

I have a 8" Dob which has a 2" eyepiece holder and also a 1.25" adaptor. At the moment my eyepieces are all 1.25" which I am quite happy with but if I wanted to upgrade the eyepieces what, in your opinion, would be better 2" or 1.25" eyepieces? and what (apart from the diameter) are the differences between them.

Many thanks.

[RikM]

There is really no difference other than 2" eyepieces are able to give a wider apparent field of view for a given focal length than 1.25" but this depends on the optical design of the eyepiece rather than just the barrel size. Rather than thinking 'do I want 2" eyepieces?', think 'do I want 82° field of view at 30mm focal length?'. If you don't want that wider field of view, then you don't need 2" eyepieces.

[Zuben Elgenubi]

It depends on how you are wanting to upgrade/extend your eyepiece collection.

2" eyepieces allow a wider field of view so are suited to lower powers, focal lengths of 18mm plus. However if you want shorter focal lengths then I don't think that a 2" barrel offers any advantages - f you look at the different ranges available you'll find that even the premium brands produce higher power EPs in 1.25".

[Kirscovitch]

And usually from what I've seen shopping around for an EP that the 2" are usually a bit more expensive. 

[YKSE]

The main advantage of 2" eyepieces are the wider field of view, unless you're getting those hyper-wide eyepieces (100 deg e.g.), there's no need to get 2" eyepieces except the lowest magnification eyepiece, IMHO.

Assuming your dob is a f6(focal length 1200mm), the widest field of view you can get in 1.25" EP is like a 32mm 52-deg plössl, it shows about 52*32/1200=1.4 deg, but if you change it to a 2" EP, e.g. a Maxvision 34mm 68deg, you'll get 68*34/1200=1,9 deg, and it'll frame the Plejade (M45) nicely.

[weetooner]

Hi guys, thanks for the replies. Something for me to think about later if I decide to get new eyepieces. Cheers.

[ronin]

Have a look at a 2" eyepiece before you make a decision.

It sounds like a small step from 1.25 to 2.

They are big, much bigger then many expect.

I have a 20mm 2" sat in it's box next to some TV plossl's in their boxes.

I could get 4 TV boxes in the 2" eyepiece box.

[YKSE]

A very good point raised by ronin, all 2" EPs are much bigger and heavier than the stock EPs, the Maxvision 34mm 68deg, e.g. weighs over 800grams, some 20x of the stock EPs, I think.

The smallest wide field 2" EP weigh under 400 grams, such as Skywatcher Aero 35mm, Baader Aspheric 31mm.

[ronl]

The BST Starguider is 1.25 and has a 60 degree Fov, and is very popular

with members with the 200p, I find them very good and value for money,

this link http://www.swindonstargazers.com/beginners/eyepieces.htm is a very

good beginners guide to eyepieces, and is well worth a read. 

[earth titan]

I don't know if it's just me, or if there is any scientific proof (I'm sure someone will be along in a moment with an answer one way or another) but I find 2" eyepieces give a flatter field than 1.25" equivalents.

[Kirscovitch]

The 2 inch EP's are a lot bigger then u expect. Mine are bigger than a 12oz soda can. Didn't think that just going 3/4 inch bigger would make that much of a size difference but was I wrong!

[brantuk]

All good advice above - the main thing for me is that I can get larger objects in the fov at lower powers. On a good night it's fabulous to be able to scrutinise the Andromeda galaxy as a whole in the eyepiece and see all the intricate structure and pick out considerable detail in the dust lanes. Totally different kind of observing to high power views and narrower fields in order to see detail in Jupiter's banding or Saturn's rings.

I like to think of it as upgrading or changing the view rather than the eyepiece. Something around 30mm would be very nice in your 200P for a 2" eyepiece.

[Stu]

This thread has some size comparisons in in which put things in perspective. I know there are others out there, but I remembered I could search for 'chickpeas' and find this one.... You'll understand when you read it ;-)

http://stargazerslounge.com/index.php?/topic/183023-One-last-shot-before-the-band-breaks-up%2E%2E%2E%2E%2E%2E%21

Cheers,

Stu

[Paul73]

Fascinating thread. I'm hoping for 'first light' on my first 2" eyepiece tonight.

I am obviously exceedingly excited (worryingly) about this.

I was heading for a 32 or 34mm but in an f4.7 scope I would have ended up with a huge exit pupil so went for the much hyped 28mm max vision 68° 2". I have the 24mm 1/4" version so can do a pretty much side by side comparison. Await my post later........

On the size issue. The 2" makes my 10" Dob look a bit skinny and inadequate. Think that I need a bigger scope.....

Paul

[itmo]

I have a 34mm 2 inch MV , and it is picked to have the biggest exit pupil for my scope (around 7mm) , it is a huge handgrenade and I could possibly make do without it. It just gives me a VERY wide view with maximum pupil so it is nice to look at large clusters and wide targets and to use it as a finder eyepiece. 

[Paul73]

Paul

so went for the much hyped 28mm max vision 68° 2". I have the 24mm 1/4" version so can do a pretty much side by side comparison. Await my post later........

Well that was a fun hour with the new 2" eyepiece.

I'm sold.

The marginally wider field +0.25° did make a difference and the whole image felt more dynamic. Which is quite an achievement considering the quality of image across the 1 1/4" MV range. The field was reasonably flat across 80% of the view. The near 6mm exit pupil was no problem. I did keep smacking my head in the thing as I'm not used to having a lump of this size sticking out of the side of my scope. Changing between the 2" and the 1 1/4" is a pain which may limit its use a bit. But overall worth going for. Still can't get the whole of the Pleiades in my FOV.

Maybe I need the try the 40mm..... To go with the bigger scope....

Paul

[Stu]

40mm sounds like it might be interesting, but be careful because the exit pupil would be 8mm so it may appear very washed out. Not sure if you may also start to see the secondary shadow, perhaps not.

The FOV would be nice though, Pleiades fitting in completely. A larger scope may well have a longer focal length say 16" f4, although a 12" f4 would be the same, not sure what your plans are?

Often the best option for widefield is a nice short focal length apo frac, would give you 3 or 4 degrees and lovely for open clusters, with a dob giving you the aperture for the smaller deeper sky objects.

For reference, the three blue circles in this picture are the 24, 28 and 40mm 68 degree MV's, but watch the exit pupil as you look at the lower powers.

Cheers,

Stu

[Paul73]

Stu

Agreed, the 40mm would be too much. I was pleasantly surprised how well my 40 year old eyes coped with the 6mm exit pupil. I have the feeling that the 34mm at about 7.2mm would pushing it for all but the youngest observer under the darkest sky's.

Maybe we need to stop trying to make every scope do everything.

Paul

[Rich MedRev]

Most of the issues have already been covered already, in addition to size of the 2" EP's, given that your scope is an 8" Dob, balance with the larger and usually much heavier 2" EP's need serious consideration.

When I use the likes of my Meade 4000 UWA 14mm on my dob I have to make significant balance changes, even more so if a Barlow is used as well.

Therefore unless wide field low power views with as flat a field as possible are in order then you can probably stick with 1.25" EP's for a while yet.

[weetooner]

Most of the issues have already been covered already, in addition to size of the 2" EP's, given that your scope is an 8" Dob, balance with the larger and usually much heavier 2" EP's need serious consideration.

When I use the likes of my Meade 4000 UWA 14mm on my dob I have to make significant balance changes, even more so if a Barlow is used as well.

Therefore unless wide field low power views with as flat a field as possible are in order then you can probably stick with 1.25" EP's for a while yet.

I think I agree with Rich MedRev, after looking at the size of these eyepieces I thought wow, my scope is going to be a bit top heavy. Did not realise just how big the eyepieces were, just gonna stick with the 1.25" for the time being.

Cheers

[ChrisSJ]

Hi,

All I would add to the sound advice given above, is 2" EPs are heavy beast's, and you may struggle to adapt to a different type of nudging and balance in the first instance. This sometimes leads to frustration, and I've seen many a 2" EP sitting in peoples cases never used again.

Chris

Sent from my Hudl HT7S3 using Tapatalk

[brantuk]

Yup - weight can be an issue - just an Ethos in a Powermate can add 3lbs (1.5Kgs) to the front end of a dob and it'll nosedive without some form of counterbalance. I have a weighty magnet wrapped in foam packing and sealed with ductape that can fix in any position on the back of my dob. But there are other arrangements like variable, sliding weights, on a weight bar and radius blocks, screwed onto the ota. Hth

[Moonshane]

I have 16 eyepieces but only one is 2" (26mm Nagler). I rarely feel as though I want more field (max 1.8, 1.3, and 1.1 degrees in my three scopes) rather I sometimes wish the sky would allow more magnification.

[bingevader]

just an Ethos in a Powermate

That did make me chuckle! A mere trifle! 

Non of these problems is insurmountable though, except perhaps the cost element, but I know I'm a fan and can remember thinking, "Mmm, yes, that's splendid!" (I may well have said it out loud, not that anyone else was listening! ) the first time I popped in a 2" EP after using the stock 25mm (not that that is a particularly poor EP, just the difference between the 2)!

I have 16 eyepieces but only one is 2" (26mm Nagler). I rarely feel as though I want more field (max 1.8, 1.3, and 1.1 degrees in my three scopes) rather I sometimes wish the sky would allow more magnification.

But aren't they mostly 82^o and 100^o TVs? 

Cheers

[Moonshane]

not at all. OK, TVs and 3 bgos. but I have only three wide field

 I have

32mm plossl - 50 degrees

26mm Nagler - 82 deg

25mm plossl

20mm plossl

16mm Nagler

15mm plossl

13mm Ethos - 100 degrees

12.5mm BGO

11mm plossl

10mm Radian - 60 degrees

9mm BGO - 40 degrees

8mm Radian

7mm BGO

6-3mm Nagler zoom - 50 degrees

although I have realised it's 14 not 16! must buy some more LOL.