Eyepiece... 2" or 1.25"

[ndastgir]

HI Forum,

I am thinking of spending some money on a few good quality eyepieces. And I was wondering if someone could tell me which size should I go with, 2" or 1.25"?

Thanks,

Naeim

[DirkSteele]

That really depends on what magnification / fields of view you are looking for with your scope. You will likely find that to cover a range of magnifications and field of views that you may well need both 1.25” and 2” eyepieces. To maximise the field of view at low powers, 2” EPs would be the way to go as they can have larger field stop diameters (up to 46mm in a 2” EP). However, for high power EPs, you likely find only 1.25” EP designs.

In case you are unaware, to calculate magnification achieved, take the telescope focal length and divide it by the EP focal length.

To calculate field of view, you divide the EP field stop diameter by the telescope focal length and multiply that result by 57.3. Or, take the apparent field of view of the EP (normally will be quoted by the manufacturer) and divide that by the magnification produced by that EP in your telescope.

Your telescope has a 150mm primary and a F5 focal ratio (focal length of 750mm).

So for example, a 5mm EP will produce an magnification of 150x (750/5).

One my favourite 2” EPs is the 35mm Televue Panoptic (quite expensive though). It has a quoted AFOV of 68^o. In your scope it would produce a magnification of 21x. Divide one (68) by the other (21) and you get an actual 3^o field of view, which is approximately 6x the diameter of the full moon.

So I would suggest you think about what range of fields and magnifications you want to cover and your budget and then ask the SGL community for recommendations in your price bracket.

Hope this helps,

Clear skies,

[DirkSteele]

Sorry I should have added one extra detail. You also need to be aware of exit pupil produced by EPs. You can calculate by dividing the aperture of your telescope by the magnification of the EP, or EP focal length (in mm) divided by telescope focal ratio. Some very low power EPs will produce exit pupils above 7.5mm which can be problematic for telescopes with a central obstruction such as your Newtonian. Exit pupils of less than 0.4mm are small enough to allow eye floaters to interfere with the image and generally indicates you are using too high a magnification.

[ndastgir]

Thanks DirkSteele for clear explanations, I am looking at 1.25" BST Exploreer 18mm and 5mm. Do you think that would be a good choice?

I also saw the 30mm Skywatcher Aero ED SWA 2" eyepiece and I am not sure if I will feel a difference between this 2" eyepiece and my current 1.25" 25mm Plossl.

[earth titan]

I use 2" EPS, for my 40 and 32mm eyepieces - both of which are wide angle. I then drop down to 1.25" although I have a few 1.25" EPS in the large sizes too. I enjoy the big views given by the 2" glass.

If you have a dob, then I would absolutely suggest a large 2".

Typed by me, using fumms...

[ndastgir]

Thanks Tom, I've got a 6" Newtonian and I'm not sure how much benefit a 2" eyepiece would give me over and above my 1.25" wide angle eyepiece.

Naeim

[jimmyjamjoejoe]

Thanks DirkSteele for clear explanations, I am looking at 1.25" BST Exploreer 18mm and 5mm. Do you think that would be a good choice?

I also saw the 30mm Skywatcher Aero ED SWA 2" eyepiece and I am not sure if I will feel a difference between this 2" eyepiece and my current 1.25" 25mm Plossl.

All great choices. I have a bst 8mm for my 200p and love it. Also, 2 inch eyepieces are worth it if you want to go above 55-60degrees afov. I have the hyperion aspheric 31mm, and feel like i could fall in it sometimes!

[Rob]

Thanks DirkSteele for clear explanations, I am looking at 1.25" BST Exploreer 18mm and 5mm. Do you think that would be a good choice?

I also saw the 30mm Skywatcher Aero ED SWA 2" eyepiece and I am not sure if I will feel a difference between this 2" eyepiece and my current 1.25" 25mm Plossl.

Yes!.. very good place to start. I'd also look at TMB 6mm & 9mm in addition. You can also never go wrong with owning a 10mm or 12.5mm, as they are nice EP's to barlow

[John]

Thanks Tom, I've got a 6" Newtonian and I'm not sure how much benefit a 2" eyepiece would give me over and above my 1.25" wide angle eyepiece.

Naeim

The main benefit of a 2" eyepiece is that it gives a wider field of view than a 1.25" one. Many folks end up with 1.25" eyepieces for high and medium magnifications and a 2" or two for lower power, wide field views.

If you are still using the eyepieces that came with the scope then the BST Explorers and Aero ED would be a significant step up in quality.

[ndastgir]

The main benefit of a 2" eyepiece is that it gives a wider field of view than a 1.25" one. Many folks end up with 1.25" eyepieces for high and medium magnifications and a 2" or two for lower power, wide field views.

If you are still using the eyepieces that came with the scope then the BST Explorers and Aero ED would be a significant step up in quality.

Yes, I am still using the 10mm and 25mm eyepieces that came with the scope. The quality of the 10mm one is not impressive at all, in fact I stopped using it long ago but the 25mm seems ok. I guess I can only tell after I buy a good quality eyepiece and do a proper comparison.

Naeim

[John]

Yes, I am still using the 10mm and 25mm eyepieces that came with the scope. The quality of the 10mm one is not impressive at all, in fact I stopped using it long ago but the 25mm seems ok. I guess I can only tell after I buy a good quality eyepiece and do a proper comparison.

Naeim

Why not look for a used one on the UK Astro Buy & Sell website ?:

http://www.astrobuysell.com/uk/

You can get the BST Explorers for around £30 used and if you don't like it you will almost certainly be able to get your money back if / when you re-sell it. It's a great way to see if something suits you

[ndastgir]

Why not look for a used one on the UK Astro Buy & Sell website ?:

http://www.astrobuysell.com/uk/

You can get the BST Explorers for around £30 used and if you don't like it you will almost certainly be able to get your money back if / when you re-sell it. It's a great way to see if something suits you

Great idea, I'm buying a 5mm BST from the website you mentioned. Thanks!

[Rob]

Here.. Also check out the 'Try & Buy' option. Alan is a very reasonable guy, and great to chat with.

http://www.skysthelimit.org.uk/telescope%20eyepieces.html

[rwilkey]

2" eyepieces are great step up if you like DSO's, my PanaView 32mm was the first ep I ever bought and to be honest I have never looked back. The Aero ED is good choice, the SW Nirvana's are also very good, good clear sharp views. As with others, I prefer to use 1.25" eyepieces for high magnification, and have a set of BST Explorers, which I thoroughly recommend.

[ndastgir]

Ok, after reading all the reviews and pros and cons, I bought a Baader Hyperion Zoom eyepiece. First thing that I noticed was the huge size compared with the plossls that came with my telescope. it also came with a 2" adapter.

I have not yet had a chance to take it out for a spin, thanks to the cloudy skies. so far the farthest object I've seen through this eyepiece is my neighbor's chimney bricks and even those look more crisp and clearer compared to my plossls. I'm now waiting for a clear night...

[ndastgir]

[rwilkey]

Thanks DirkSteele for clear explanations, I am looking at 1.25" BST Exploreer 18mm and 5mm. Do you think that would be a good choice?

I also saw the 30mm Skywatcher Aero ED SWA 2" eyepiece and I am not sure if I will feel a difference between this 2" eyepiece and my current 1.25" 25mm Plossl.

Excellent choices for your scope, you will love and appreciate the difference the 2" Aero ED will make, great for DSO's, a cracking ep.

[ndastgir]

Excellent choices for your scope, you will love and appreciate the difference the 2" Aero ED will make, great for DSO's, a cracking ep.

Thanks Robin, the 35mm Skywatcher Aero ED SWA 2" is on the list to purchase next.