1.25" vs 2" What's better? and suggestions please.

[Screwdriverone]

Hi Everyone,

I have been reviewing some threads discussing the pros and cons of certain eyepieces and was wondering;

1) Why do most high power eyepieces only come in 1.25" barrels? Is it the weight of the extra lenses? Is 2" better than 1.25"?

2) I have one 80 deg 30mm WA 2" eyepiece (Andrews) and enjoy the view and the larger barrel, so I would like to select another eyepiece of the 2" variety to complement my scope's power. What would you suggest and furthermore, does it need to be 2" barrel?

3) The theoretical limit to my scope on exceptional nights (the 12" dob that is) is probably around 300x to 400x which means I need about a 5mm eyepiece considering my FL is 1500mm. Is this possible or just too difficult to see with such a small exit pupil and a dobsonian platform.

4) Considering I enjoy the Wide FOV of the 68 deg 2" at 50x magnification, perhaps it is better to buy a nice Vixen LVW 13 or 17mm EP and use this and the other favourite 12.5mm and the 2" 30mm and be done with it all?

5) Am I better off using a quality ED type small-FL high power EP than barlowing a crappy one and introducing too much glass in the way?

5) I have listed my current eyepieces and their standard non barlowed magnifications below;

Barlows: 2.5x ED Achro and 3x APO GSO.

10mm standard SW Plossl = 150x (good general EP)
12.5mm ED Andrews = 120x (best one I have for quality and FOV clarity) - use this one when the 2" doesnt get close enough.
15mm WA = 100x (not very good quality and views are horrid most of the time)
20mm Standard SW Plossl = 75x (good general EP)
30mm 80 deg WA Andrews 2" = 50x (nice wide FOV but suffers from bad coma at the edge) - one I use most at the moment coz the view is immersive compared to the others.

Any suggestions you have would be most welcome to complement this motley crew of EP's, no doubt some of these will never get used if I get a scorching EP so I have no qualms about selling or giving them away to make room in the EP case.

Thanks in advance

Cheers

Chris

[ColHut]

1 - very roughly, the light cone is so narrow at high powers that the barrel does not need to be 2" wide. It varies a bit with the focal ratio of the scope - faster scopes need wider barrels before slower scopes. Manufacturers seem to choose 26mm as the transitional point between 1.25" and 2".

2 - maybe add a barlows to provide more use for your existing eyepieces. a 1.25" X2 barlows will effectively add a 6.5 and 5 etc - although you might want something in the 20mm range.

3 - on those rare nights of really good seeing you can really up the power, a 5mm planetary with good eye relief or barlowed existing 10 or 12.5mm eyepiece will certainly give you the possibility of some great views of Jupiter etc. The problem with a dob is that you have to tap it round and then let the planet drift across the view (you cannot follow it manually), rinse and repeat. It only take 10-20 seconds to cross your view at high mag.

4 - sorry I do not follow your question here

cheers

[Screwdriverone]

Hi Colin,

Thanks for the input, what I meant by question 4 was, if I have a good 12.5mm 1.25" and a good 30mm 2", should I just get a good 17mm Vixen LVW EP and thats it?

This would give me a good range of magnifications for visual as I hardly use the other FL anyway because of their lower quality and FOV.

As a side question, to most people who have 2" focusers end up using 1.25" EPs anyway? seems a bit of a waste unless there is some other reason to do so?

Cheers

Chris

[koputai]

I wouldn't bother going for a 5mm, you'll never use it with that scope in the 'burbs, as you might get one night a year when you can actually see through it. I'd recommend a good wide 9mm. I have a similar scope, and absolutely love the Nag 9mm, use it all the time. I've tried a couple of 5mm but none were useable, and also a budget (Seibert 2") 7mm and the viewing was crap, but I think that was the crappy quality of the eyepiece. Next I want to try a premium 7mm, but wouldn't bother going shorter than that.

Cheers,
Jason.

[Screwdriverone]

Hmmm, Thanks Jason.

Are we looking at the $300-$400 dollar mark for a "good" Nagler 9mm (about the same as a Vixen LVW of the same quality?)

Cheers

Chris