eyepiece suggestions please

[tsuken]

Hi all,

I had a great evening under the stars yesterday, but would like more magnification. Now I'm not at this point about to spend hundreds of dollars on the best eyepieces, but something that makes things bigger than 30x as the 25mm one I have in conjunction with my telescope (750mm focal length) would be A Good Thing.

If I were to get say 2 additional eyepieces, what would be my best bet for:

(a) focal lengths; do I go the whole hog and get a 4mm which would seem to be the highest useful magnification with my telescope, plus something in-between like maybe a 12.5mm? Or would I be best served with some lower power eyepieces (as I imagine with lower magnification, one gets a wider field of view, so there's a trade-off between magnification and how easy it is to find what you're after)?

(b) brands to look for with reasonable quality without spending too much post-Christmas money - especially considering I have a new iMac to buy in a few weeks ;)

Thanks very much in advance for any and all suggestions.

Raf

[tsuken]

hmmm - what do those who know about these things think about this: http://myastroshop.com.au/products/details.asp?id=MAS-188

On the face of it, it seems a good and cost-effective option. I worry though that it might be too inferior to a number of set focal length eyepieces...

Or this: http://myastroshop.com.au/products/details.asp?id=MAS-326 ? Too cheap to bother with realistically, or fine to be getting on with?

[wavelandscott]

As you can appreciate, this can be a difficult question to answer because it largely depends on what you want to see and how much you want to spend.

There are two schools of thought...(I've exaggerated a bit)

#1 Buy as many different cheap eyepieces as you can until you get a box full and then buy and sell eyepieces as you "grow" in the hobby.
or
#2 Buy few quality eyepieces that you will keep a lifetime.

http://www.televue.com/engine/page.asp?ID=131

I've attached a link to the Televue website and an article about eyepiece selection.

I tend to be of the opinion to buy a few of the best that you can...

But, I'd target 3 eyepieces low power (you have), medium power and high power. Some people would also advocate that a good barlow is important and it can effectively "double" the magnifications that are achievable with your existing eyepieces.

Before you buy anything, I'd suggest that you find someone near you and get together for a viewing night. This is a great way to try different gear in your scope. Depending on your strategy (#1 or #2) you can save yourself a whole heap of "learning" by trying gefore you buy.

Once you know what you want and how much you want to spend...there are many good options available for a wide range of budgets. However, generally speaking, you do get what you pay for...
Good Luck and Clear Skies!

[tsuken]

thanks for the thoughts, and the link :)

[Gargoyle_Steve]

Hi ..thought I'd throw in some of my own thoughts on this topic as I was a "green as they come" newbie in early 2006 when I bought my first scope (and I'm still pretty new in many ways). I do not have a lot of money to spend so I don't have any premium brand eyepieces, nothing much over $200 each. Perhaps some of my experiences and opinions may be relevant.

This may be tricky as we don't know anything about your scope except it's focal length, but reading between the lines it's about a 90mm or so aperture, which at 750mm focal length puts it around the f8 ratio.

PART 1 - Selecting Desired Magnification

Firstly you need to consider the field of view / magnification that you want to achive, selecting an appropriate brand and or model can follow after this.

My own scope has a focal length of 1500mm, ie exactly twice that of yours, and because:

Magnification = Focal length(scope) / Focal length (eyepiece)

each of the eyepieces I mention will give twice the magnification in my scope that they would give in your scope. For that reason I'm going to talk magnification factor for now, not ep focal length.

I own several eyepieces but basically use only 3 (a 4th on rare occasions).
These give me the following magnifications:
50x
88x
115x
(and 187.5x when I use the 4th)

The ep that gives me 50x also gives an 80° apparent fed of view, this one I use for looking around and "finding" things, or for taking in the size and/or surrounds of larger open clusters and or nebulae.

The ep that gives me 88x is probably my favourite ep in terms of the image quality in my 12" dob, but it is just slightly lacking in magnification for some objects. It does excel however in terms of "general" viewing of many "average sized" objects, but I don't use it for instance when viewing Jupiter or Saturn, or Planetary nebula, or when observing smaller stellar objects, double stars, and so on.

The 115x ep is THE eyepiece that I use the most, by far. It is good for planetary views (though it doesn't give "close" detailed views, but pleasant ones!). More importantly under normal sky conditions it gves me as much magnification as the atmospheric conditions usually allow before the image starts to deteriorate.

You mentioned the theoretical limit for your scope - keep in mind that any eyepiece that pushes your scope to that limit will almost never get used! You may get to use it on half a dozen nights a year, and that's only if you are availabe to view every night of the year.

That leads to the ep that gives me 187.5x, and the reason why I rarely use it at home. The theoritical limit in my scope is approx 5-600x. I sometimes use it when away from home at a good dark site, but from my suburban yard it remains almost unused.

(next post - Part 2)
=================================== =======

[Gargoyle_Steve]

Part 2 - Eyepiece Focal lengths, Makes & Models

So .... where does that leave us. I think that if you take the simpler path here (ie fewer ep's until you have more observing experience, and know what you want, and how much you're willing to spend to get it) I'd say Scott gave great advise - stick with 3 ep's for now. I've listed some possible suggestions here, trying to give you better (bigger) field of view than the basic ep's supplied with telescopes, and staying under $200 a pop. These are some of my suggestions only, and if you ask 10 other people you'd possibly get 10 different suegstions. Anyway, here goes....

Low Mag
The 30x (25mm) you already have may serve you well in the role of a low mag / wide field of view ep for now. If you decide that you absolutely do want to replace it as well, I'd look for something that would give around 50x give or take, ie 750mm/50x = 15mm ep, but for this one definitely get something that gives a wider apparent field of view as you'll be using this one to search around and find various objects, look for something with a 60-70° AFOV or wider.

Suggestion: read Mike's review here first of a 3 way shootout between "inexpensive" 15mm ep's
http://www.iceinspace.com.au/index.php?id=42,236,0,0,1,0

This will give you some idea of what can be good, and what can be bad, about less expensive ep's.

Having said that, peoples opinions of various ep's still comes down to personal preference. I'd strongly recommend trying to get to an observing night somewhere and have a look through various ep's in your scope and in other peoples scopes as well to see what you think of them before spending any money.

Better options? Televue 15mm Plossl, excellent quality, but only 50° AFOV
https://www.bintelshop.com.au/Product.aspx?ID=5268

or perhaps a Meade Series 5000 14mm Plossl with 60° AFOV, but very limited eye relief
https://www.bintelshop.com.au/Product.aspx?ID=6976

Alternately go up mag wise to a 13mm ep, or perhaps better still drop down to a 16 or 17mm. There are surprisingly few ep's around in the 14 to 15 mm range that are commonly available here and that price wise lay between the "very inexpensive" units, and the top of the line Pentax XW's, Televue Naglers, etc.


Mid range Mag
Something around the 90 to 100x - best choice possibly a 7 or 8mm ep, giving you approx 107x or 94x respectively.

Plossl ep's of shorter focal lengths also tend to have short eye relief, ie the distance that you need to hold your eye away from it to see properly. Plossls around the 7mm mark and lower can be a right pain this way, and if you need to wear your glasses when observing then forget these.

I own an 8mm Orion Stratus, which has a generously long eye relief and provides a 68° AFOV, but one of these new will cost you close to $200, and they are a relatively large and heavy ep.

(The Orion Stratus (https://www.bintelshop.com.au/Product.aspx?ID=7301)models are near identical to the Baader Hyperions, (http://www.myastroshop.com.au/products/baader-ep.asp)though a little cheaper, both of which however are cheaper (and I'm told lighter on performance) clones of the Vixen LVW (http://www.myastroshop.com.au/products/vixen-ep.asp?ProdID=MAS-078) range - though they all look very, very similar externally.

I own Stratus and Hyperion ep's, and I am very fond of them. I may perhaps replace them with "premium" ep's one day, but probably not anytime soon.


A possibly better contender for you may be the 8.5mm Pentax XF series
http://www.telescope-service.com/pentax/start/pentaxstart.html
http://www.frontieroptics.com.au/Planetary%20eyepieces.html

which gives a 60° AFOV and 18mm eye relief, and has been highly recommended by other members of this forum. It is also smaller & lighter than the Stratus, etc, models, and less expensive I believe too. At 8.5mm it will give you 88x magnification.


High Magnification
The 4mm ep you mention above to get maximum theoretical magnification would give you around 187x, lets drop that back a bit to be more usable, lets aim at 125 to 15ox instead. This translates to an ep in the 6 or 5mm range.

Orion Stratus 5mm - again 20mm eye relief, 68° AFOV
Burgess Planetary 6mm, 60° AFOV, great reputation, cheaper than the Stratus.
http://www.frontieroptics.com.au/Planetary%20eyepieces.html

I've included links here to several different suppliers, have a browse aroud on these sites as well. There's lots of eyepieces out there, some great, some not so, some inexpensive, some down right expensive.

I hope this has been of some assistance, best of luck with whatever you decide to go ahead with.
:thumbsup:

[Gargoyle_Steve]

I just had a quick look at the Buy and Sell area here, perhaps you ought to read this add:
http://www.iceinspace.com.au/forum/showthread.php?t=26880

;)

[tsuken]

Wow - thanks for that Steve :)

Sorry about the lacking details about my telescope in my question. It's a 150 mm Newtonian; a Celestron Omni XLT150 ... so f/5?

I'll go check out your links now. cheers

[Gargoyle_Steve]

Ah ok, bigger scope than I thought!

The maximum "theoretical" magnification for a scope is often quoted as being aprox 2x it's aperture in mm's, or approx 50x it's aperture in inches, so when you talked about a 4mm approaching that limit I divided 750mmm fl by 4mm giving 187x, or 90-ish mm's aperture.

Now that we know more we can say 2 things:

Having larger aperture means that you will get more use from the higher magnifications.

Knowing that your scope is an f5 (same as mine) means that some cheaper ep's that will work in an f8, f10, etc scope will give distorted views in a faster scope like your f5, which sadly means that you may have to spend a bit more on ep's at times to get satisfactory results.
(read that ep shootout article that Mike wrote for more info)

I'm sure that there will be plenty of other postings to this thread to help guide you along the way.
Cheers!