31 replies to this topic

[SeattleScott]

So you would use a low power 2inch to find an object, then put in the 2-1.25 reducer and use 1.25 for the other powers? Are there reasons why you wouldn't want a 2 inch at higher powers (besides weight and cost?) I might do that for now and then in the future look for good deals used for a full set of 2s.

That is correct. The only reason to have a 2” barrel at higher magnification is eliminating the need to mess with the adapter. Baader Morpheus/Hyperion eyepieces are one of several examples. The 2” barrel isn’t a functional part of the optical system of the eyepiece. It is only there for convenience.

[Dave Mitsky]

So you would use a low power 2inch to find an object, then put in the 2-1.25 reducer and use 1.25 for the other powers? Are there reasons why you wouldn't want a 2 inch at higher powers (besides weight and cost?) I might do that for now and then in the future look for good deals used for a full set of 2s. 

Below a focal length of about 17mm there's no optical advantage in having a 2" barrel.  Hybrid 1.25"/2" barrels such as the ones on the Tele Vue Ethos eyepieces exist for convenience and safety.

[Aaron Zhang]

Well I was hoping to spend somewhere around $2-300 on a full set of eyepieces (my previous telescope only used 1.25 so I was hoping to get a full set of 2s). Starting to seem like that may have been unrealistic for decent 2 inch eyepieces, at least new. My plan was to buy budget pieces just to get me going, and slowly replace them over time by hunting down good deals used as my wallet allowed.

You can get quite a nice starter set with that budget. For example:

38mm Agena SWA

15mm Agena Starguider/Astro-Tech Paradigm

8mm Agena Starguider/Astro-Tech Paradigm

5mm Agena Starguider/Astro-Tech Paradigm

[Starman1]

Also, I've read that a good range for eyepieces would be as follows:

 

low: 8-20 power

medium: ~50 power

high: ~100 power

very high: 160 - 200 power

 

Does that seem like a good range to aim for? Could be easily doable with 2 eyepieces and a barlow. I have also heard good things about zoom eyepieces so maybe I should look into those.

I have the same size scope. Unless there is a particular reason to go lower than ~25-30, I would skip the ultra-low powers.

--the background sky will be bright and light polluted and yield poor contrast on most objects.

--powers below about 6X/inch of aperture are poor at resolving seep sky objects like star clusters.

 

Over the long haul with a 4" aperture, I've found powers of

16-40 to be low power

40-80 to be medium power

80-120 to be high power

120-200x to be ultra high powers.

A great place to start is with 30x/60x/90x/120x, which will cover most of the use you give the scope.

Higher magnifications will be used on small objects, mostly, and lower magnifications will be confined to the very largest objects in superbly dark skies.

(like a large faint nebula when using a nebula filter, or a huge star cluster).

A 24mm 82° eyepiece makes a great low power.

An alternative 28mm 82° at 26x makes an OK substitute if you regularly observe in dark skies.

If you have severely light polluted skies at home, it's more likely you'll use the scope at 60x and higher 99% of the time.

[Starman1]

Well I was hoping to spend somewhere around $2-300 on a full set of eyepieces (my previous telescope only used 1.25 so I was hoping to get a full set of 2s). Starting to seem like that may have been unrealistic for decent 2 inch eyepieces, at least new. My plan was to buy budget pieces just to get me going, and slowly replace them over time by hunting down good deals used as my wallet allowed.

And you can have a full set for that price with 1.25" 60° eyepieces like the Astrotech Paradigms or BST Starguider ED.

They'll work great in your scope.

 

Inside every eyepiece is an iris called the field stop that determines the true field you see through the eyepiece.

That field stop gets smaller with shorter focal lengths.

So there is no reason for an eyepiece longer than 16mm to be 2" in general because the field stops fit inside a 1.25" barrel--it doesn't gain you any field.

The 13mm TeleVue Ethos is a 100° eyepiece, and it is 1.25".  There was no reason to make it 2". [it is a dual-fit eyepiece, basically a 1.25" eyepiece that has a 2" skirt to use it that way if desired.]

[Jon Isaacs]

So you would use a low power 2inch to find an object, then put in the 2-1.25 reducer and use 1.25 for the other powers? Are there reasons why you wouldn't want a 2 inch at higher powers (besides weight and cost?) I might do that for now and then in the future look for good deals used for a full set of 2s. 

 

As has been said, you really only need one 2 inch eyepiece to maximize the field of view. Using adapters is not a big deal, you just do it once after you've located the object.

 

Jon

[Jon Isaacs]

 

I have the same size scope. Unless there is a particular reason to go lower than ~25-30, I would skip the ultra-low powers.

 

--the background sky will be bright and light polluted and yield poor contrast on most objects.

 

--powers below about 6X/inch of aperture are poor at resolving seep sky objects like star clusters

I also have a 4 inch refractor. 

 

For star hopping without a finder, lower powers are helpful because they will generally provide a wider field of view. The 28 mm UWA would provide 3.27° at 25.5x, that is workable.

 

As far as I know, the sky brightness of the OPs observing site is not known. The 38 mm might be a better choice if skies are dark. As a finder it does provide a fields that's about 0.4° wider with less of the in the peripheral vision. 

 

Large exit pupils are useful under dark skies when using deep sky filters.

 

On a budget, the 32 mm Q70 has advantages. Currently, it's on sale for $80.  It has a 40.0 mm field stop and provides a 3.21° field of view at 22x with a 4.6 mm exit pupil. It's not sharp across the field like the 28 mm UWA or the 30 mm UFF but its only $80.

 

Jon

 

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