2" vs 1.25"

[Dyptorden]

Hi again,

Could anyone tell me if there are other differences between 2" and 1.25" besides the 2" offering a bit less vignetting when making photos and a bit wider FoV when watching DSO's? If I start buying eyepieces...filters... I need to know whether it is worth investing in 2" or not.

And... does the 2" offer any advantage when observing planets?

Thank you,

[MiguelMJr]

Good question. I would like to know the same.

Miguel

[Lowjiber]

There is no real advantage of using a 2" eyepiece below about 24mm, as the field stop of the eyepiece basically eliminates any extra light at higher magnifications.

That said, I use 2" eyepieces (31mm, 24mm, and 18mm) for my wide field DSO searches (the three in the middle of my case below).  Everything else is 1.25" format.

Clear, Dark Skies

[John]

The principle advantage of the 2" eyepiece format is that a wider field of view can be offered with the larger barrel size. There is no advantage to the larger format at medium or shorter focal lengths and therefore the manufacturers stick to the 1.25" format there. Many folks end up with an eyepiece set that is mostly 1.25" but with a 2" or two for lower power / wider angle viewing.

My own set comprises:

31mm = 2"

21mm = 2"

13mm, 8mm, 6mm, 5mm, 4mm, 3.5mm and 3mm = all 1.25".

[Dyptorden]

I asked this because of... filters .. I am kind of forced to buy both 1.25" and 2" filters this way...

Or could I somehow adapt the 2" filters to the 1.25" eyepieces?

[John]

Most 1.25" - 2"  eyepiece fitting adapters have a 2" filter thread cut into the scope side. As long as the barrels of your 1.25" eyepieces don't project too far down the adapter (do check this !) you can put 2" filters onto the end of the adapter and use 1.25" eyepieces with them.

Alternatively, if you are using a refractor or schmidt or maksutov-cassegrain, you can usually screw a 2" filter onto the end of the 2" diagonal barrel.

[Floater]

There is no real advantage of using a 2" eyepiece below about 24mm, as the field stop of the eyepiece basically eliminates any extra light at higher magnifications.

That said, I use 2" eyepieces (31mm, 24mm, and 18mm) for my wide field DSO searches (the three in the middle of my case below).  Everything else is 1.25" format.

Clear, Dark Skies

Aw man! Love that case!

[bingevader]

Like Lowjiber, I have 3 2" eyepieces for DSO work.

The advantage, other than the extra field of view, in them all being 2" is that I don't have to change over the 2" eyepiece holder during the session.

As John has said, if I want to go for a little higher magnification, I add a 1.25" to 2" adapter to my 14mm eyepiece and then just slot this in.

It can be fitted with my 2" filter, so I don't need a 1.25" filter as well.

[Peter Drew]

Another advantage of 2" fit is that it provides a beefier platform for heavy items. 

[Ruud]

There is no real advantage of using a 2" eyepiece below about 24mm, as the field stop of the eyepiece basically eliminates any extra light at higher magnifications.

That said, I use 2" eyepieces (31mm, 24mm, and 18mm) for my wide field DSO searches (the three in the middle of my case below).  Everything else is 1.25" format.

Clear, Dark Skies

 That's a great eyepiece case, John. Have you already posted it in the eyepiece case thread? Nice cat too. 

I have two 2" eyepieces that I use for very low power wide field views. The first is a 28mm which gives  a 3.7° true field of view at 18x. The other is a 34mm which shows a 4.6°  TFOV at 14.7x.  

In a 500mm fl telescope,  a 1.25" fitting allows views of 3.3°. With a scope as short as this you may never feel the need for 2" eyepieces. But in a 2000mm fl SCT, a 1.25" barrel can only show a 0.83° circle of sky, and if you want to see more you have no choice but to move to 2". 

[Dyptorden]

As long as the barrels of your 1.25" eyepieces don't project too far down the adapter (do check this !)

Many 2"-1.25" adapters don't have threads to attach filters, but I guess I could go (for example) for a 8mm eypiece and a 2x 2" TeleVue Powermate (that has threads), to obtain the effect of a 4mm.

Looking for 2" mainly because these items "never die", and in future I might get into astrophotograpy.

Could you confirm if I'm right?

[Earl]

One of the issues you need o loog out for with 2 to 1,25 adapters is making sure there is enough depth to prevent 1.25 inch eyepieces bottoming out on a 2" filter, not a cheap accident to happen.

[Lowjiber]

 That's a great eyepiece case, John. Have you already posted it in the eyepiece case thread? Nice cat too. 

...

I don't think I have posted it.

Here are a couple of pics.  It has a small string of red LED's that can come on when you open the case.  There's a knob to turn them off or dim them.

I had the guy at Wood Wonders build it for me.  I got to pick the stain color and design my own eyepiece tray.  (He has several trays as standard, but will build whatever you want.)  It's made of solid oak, and his craftsmanship is incredible.

Here's the link: http://www.wood-wonders.com/Eyepiece.htm

Clear, Dark Skies

[Donkeiller]

2" is a lot heavier and unwieldy than 1.25".

More expensive too.

When do you need more than a 2.7 degree FOV?

That's what I get with a (1.25") 32mm Plossl.

[bingevader]

Lucky you!

I don't have a 'scope in which a 32mm plossl will deliver 2.7 degree FOV! 

[Stu]

2" is a lot heavier and unwieldy than 1.25".

More expensive too.

When do you need more than a 2.7 degree FOV?

That's what I get with a (1.25") 32mm Plossl.

When you want to see the whole of the Veil nebula in one field of view. You need over 3.5 degrees for that

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[nicoscy]

When you want to see the whole of the Veil nebula in one field of view. You need over 3.5 degrees for that

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Or when you really want to enjoy Andromeda Galaxy or the North American Nebula.

However, most DSO fit just fine in 1'25" eyepieces but again, I am a big fan of wide field views as framing of objects is as important to me as the actual objects themselves!

[acey]

The true field of view of a telescope is determined by the field stop of the eyepiece and the focal length of the telescope. The field stop is limited by the diameter of the eyepiece, which is limited by the diameter of the focuser. So a 2" eyepiece potentially allows for a wider true FOV, and a 3" would offer even wider. Is it any use for planets? Only if you really want to see lots of dark sky around a planet. Is it useful for DSOs? Only if you want to look at extrememly large DSOs (of which there are very few), or lots of DSOs in one field, or see DSOs surrounded by lots of background sky. I only use 1.25" eyepieces and don't feel the need for anything else. Once you go to 2" it all gets more expensive - eyepieces and filters alike.

[Charic]

acey mentions............." Once you go to 2" it all gets more expensive - eyepieces and filters alike " ...........  this was a concern that I thought through  before venturing into 2" EPs. But what did persuade me to buy a 2" EP was the feeling that  my 25mm  was not wide enough (M31)? hence the purchase of the Panaview.. This EP is unlikely to get any additional help from any filters, or any need to Barlow.

Any objects I  view  are  framed  to get the best view,  if everything had a lot of space around the target, it just wouldn't look right. 

[Moonshane]

When you want to see the whole of the Veil nebula in one field of view. You need over 3.5 degrees for that

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for which you need a scope of focal length less than about 480mm for a 32mm plossl. This is where 2" eyepieces come into their own although off the top of my head there are less than 10 well known objects that won't fit even in a 1 degree true field.

[John]

Lots of common sense in this thread

Given that, it's amazing how popular the 2" format is and how many wide, ultra-wide and now hyper-wide eyepieces are owned.

The motivation for me is some of these handful of extensive objects are, to my eyes, the most beautiful sights in visual astronomy and something that draws me back to the scope season after season

[LeeB]

I have all three sizes in my eyepiece box, 0.925, 1.25 and 2 inch. I use the 1.25's most of the time, and therefore invested in 1.25 filters, as they cost less and have only missed having them in 2 inch on very odd occasions.

[Stu]

It's whatever works for you, doesn't really matter which.

I most often use 1.25" eyepieces from home these days, either Orthos, Plossls or a 24mm Panoptic for wider views.

That said, I invested in 2" Lumicon filters for those occasions at dark sites where I can really benefit from Widefield views. Seeing the entire Veil complex in a 5 degree field of view in the Genesis/31mm Nag is a wonderful experience. Of course it is totally difference to the close up, detailed (and bright!!) views you get in a big dob, but I love it none the less

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