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The Warthog

Eyepieces - the very least you need.

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Hi I've just read your very informative piece about ep's which is quite enlightening but the problem is it doesn't cover my telescope my telescope is a skywatcher explorer 130 on a eq2 mount the focal length is 900 mm which equates to a ( f6.92) and your piece doesn't mention that I've just bought some plossal ep's for £80 in a case & I'm now wondering if I've done the right thing the lowest is 7.5 and the highest is 25 mm there are five altogether and I also bought three plossal's for viewing the planets only and they are stunning so what do you suggest I do now I also forgot to mention that I've got a x2 Barlow lens which I don't like using very much so if I get away without using I will thanx for incoming advice :-) Jimmy

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Hi Jimmy,

Your eyepiece set will work quite nicely with your 900mm focal length scope. They will give you a range of magnifications from 120x down to 36x. Your 2x barlow lens used with the 7.5mm eyepiece gives you 240x which is probably too much power much of the time although the barlow might provide a more useful power (say around 150x - 180x) used with the next shortest focal length eyepiece in the set.

So you are pretty well set for now I think :smiley:

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Hi I've just read your very informative piece about ep's which is quite enlightening but the problem is it doesn't cover my telescope my telescope is a skywatcher explorer 130 on a eq2 mount the focal length is 900 mm which equates to a ( f6.92) and your piece doesn't mention that I've just bought some plossal ep's for £80 in a case & I'm now wondering if I've done the right thing the lowest is 7.5 and the highest is 25 mm there are five altogether and I also bought three plossal's for viewing the planets only and they are stunning so what do you suggest I do now I also forgot to mention that I've got a x2 Barlow lens which I don't like using very much so if I get away without using I will thanx for incoming advice :-) Jimmy

I've got the same scope, I have the standard 10 and 25mm eps which came with it and also the skywatcher 3.6mm too.

Recently purchased the bst 8 and 15mm eps. Both give great views.

I'm thinking of investing in a 32mm ep and also a 4mm planetary ep.

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Hi I've just read your very informative piece about ep's which is quite enlightening but the problem is it doesn't cover my telescope my telescope is a skywatcher explorer 130 on a eq2 mount the focal length is 900 mm which equates to a ( f6.92) and your piece doesn't mention that I've just bought some plossal ep's for £80 in a case & I'm now wondering if I've done the right thing the lowest is 7.5 and the highest is 25 mm there are five altogether and I also bought three plossal's for viewing the planets only and they are stunning so what do you suggest I do now I also forgot to mention that I've got a x2 Barlow lens which I don't like using very much so if I get away without using I will thanx for incoming advice :-) Jimmy

I've got the same scope, I have the standard 10 and 25mm eps which came with it and also the skywatcher 3.6mm too.

Recently purchased the bst 8 and 15mm eps. Both give great views.

I'm thinking of investing in a 32mm ep and also a 4mm planetary ep.

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craigfoot......your  intended 4mm Planetary will be dimmer than a 7mm which would be more suited to your telescope? The 4mm will be pushing the limits. You could Barlow the 15mm to give 7.5mm!

Edited by Charic

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I have the standard Barlow that came with the scope, but should I get a better one to match the bst eps?

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I was recommended the Skywatcher Deluxe 2x Barlow. It works well for my eyes. You can, should you wish, just use the lens cell  as a 1.5x  Barlow?

Edited by Charic

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craigfoot......your intended 4mm Planetary will be dimmer than a 7mm which would be more suited to your telescope? The 4mm will be pushing the limits. You could Barlow the 15mm to give 7.5mm!

My standard 3.6 ep gave good views of Saturn last year and could clearly see the rings, I'm concerned I won't get the detail with a larger ep too

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I was recommended the Skywatcher Deluxe 2x Barlow. It works well for my eyes. You can, should you wish, just use the lens cell as a 1.5x Barlow?

Lens cell?

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lens cell = The bit at the base that holds the glass? On the deluxe Barlow, it unscrews allowing you to fit it directly onto an eyepiece.

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Oh I see. . I sorta figured with 32, 25, 15. 8 and 4mm eps I'd have a good range and no need for a Barlow. Which I think is sorta what this post suggested, although I think calculations for the high power piece suggests 5mm

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Oh I see. . I sorta figured with 32, 25, 15. 8 and 4mm eps I'd have a good range and no need for a Barlow. Which I think is sorta what this post suggested, although I think calculations for the high power piece suggests 5mm

Correct.......but a 4mm  alone will be pushing the limits of your telescope, and may only be useful for the Moon. My suggestion to Barlow the 10 or 8mm gives you 5 & 4mm if/ when  needed.  A good planetary eyepiece matching the equivalent focal ratio of your telescope will give an exit pupil of about 1.0mm giving better image quality. The Uk weather/atmospheric conditions limits what we can see. My telescope at 200mm is good for 200X power, any more is pushing it a bit, likewise a 130mm  is good for 130x power. This doesn't mean you can push to 200 and get away with good  views all the time?  The Moon Yes, throw whatever power you want at it, but everything else has limits, that we reach oh so quickly. and too much degrades the image.

a 5mm 10mm and a 35mm all hit the sweet spots of your telescope working off the focal ratio f/5. 

I said 7mm earlier, disregard. I believe your scope to be an f/5. 

Your standard SW 25mm should be ok to use. I chose the 32mm Panaview as my  highest focal length. The 8mm you have, as you know is just fine, so you may get some good use from a 5mm. Now my 6mm WO SPL is a fine EP for my Planetary use, but we have different scopes. I think between the 8mm(112.5x)  you have and possibly a 5mm (giving 180X power),  you should be ok.  So many combinations, and so much to absorb in decision making.

I said 4mm is pushing limits and 5mm ok!.......1mm can really make a big difference to the telescope

Edited by Charic
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The scope is f6.92

Would a specific planetary 5mm be a better choice than going for anther bst?

Not sure! When I enter your telescope details,  "Explorer 130 eq2" I see  F-650 and D-130 giving me an f/5 ratio telescope. I need to confirm I`m  looking at the same telescope, before recommending an exact size for the EP.

Off to work now, will get back later, unless someone else chips in to help you.

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Agree with charic, a 10mn barlowed or 5mm will be perfect for ur high end eyepiece. Look at the skywatcher planetary range or bst but i also think a 4mn will be over gunning it. Your 8 barlowed would cover the rare occasuon conditions allowed. You say you got good views of saturn with the 3.6mm but how much definition and contrast did you really get? Higher magnification often comes with a loss of definition, especially in scopes with smaller appertures. I found this out the hard way despite a lot of good advice. Anyway, charics advice stands good in my eyes for a 5mm or equivalent option. Steve (on holiday in Portugal :-) )

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The view was good, but was my first view, so I guess going with a bst 5mm May be a good idea, then look for an improved Barlow

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I've got the same scope, I have the standard 10 and 25mm eps which came with it and also the skywatcher 3.6mm too.

Recently purchased the bst 8 and 15mm eps. Both give great views.

I'm thinking of investing in a 32mm ep and also a 4mm planetary ep.

Ok.........SkyWatcher Explorer-130/900 EQ2 Telescope gives F900/D130=f/6.9 so your looking for an EP of approximately 7mm?  (My Skyliner is actually an f/5.9 rounded out to 6) So drop the 5mm suggestion in favour of the 8mm BST you already have or buy a dedicated EP of 7mm for your planetary use. 
The BST 8mm will give you  113x power and an exit pupil of 1.15mm If you Barlowed the 8mm, you would have 225x power and 0.58mm exit pupil. pushing the limits here. A 6mm EP would  give 150x and 0.87mm exit pupil. A 7mm EP giving 129x and 1.01 exit pupil. 
(f/6.92) rounded to f/7? look at your text above in yellow. You already have 8mm and 15mm ( only 1mm out on each EP!) and already getting great views. The reason being your just about on the mark with EP focal length and aperture. Match the f/ratio for your highest magnification ie. 6.9x  or 7x rounded  (the 8mm is closest)  double the f/ratio for the 'sweetspot' so say  13.84mm , rounded to 14mm ( close again with the 15mm EP)  I'd stick  with those EPs for now, and possibly just get something wider if you think you're 25mm is no good. The extra cost  now to change 1mm of  EP focal length may not be the most sensible use of your money.  You could still buy yourself a  dedicated 7mm or just put your money towards a bigger telescope? Your telescope has limits, which are quickly reached. Mine too. 
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I see. . Good advice. . I was already thinking of getting the bst 25mm, so maybe a planetary 7mm and a good a good Barlow is best?

Possibly a 32 once I've experimented more with the 25

Suppose I'm guilty of trying to rush into all options at once, where I should perhaps experiment more with what I got

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............from my garden, I find it hard to capture M31 Andromeda. Its there, but just a hazy small smudge? I go to a darker site and wow! the difference is staggering. The SW25mm I have is good (like yours) but now,  I feel,  just not  wide enough to take in M31, there's that much difference, so I needed the wider view.  I chose the Skywatcher Panaview 32mm for my wideview EP.  And during last Weekend, whilst comparing a TeleVue Plossl, I used the 32mm and located two new Galaxies M81 & M82, just not visible from my light polluted garden.

I chose the 32mm and my 6mm using help and advice from several SgL users, and for my f/6 telescope, and MY EYES only  these two EP's are very good indeed, they match my telescopes specifications,  and are comfortable  to use with my eyes. What works well on one scope, may not fare so well on another. But what you have at present seems to work quite  well. 

My first telescope was the Celestron 127EQ,  I see so much better with my 200P/8" and using my present EP's in the Celestron, doesn't  help the Celestron a great deal, I have needs that exceed the 127s ability,  so I just use the Skyliner.

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craigfoot......... I think you can manage without it? My replacement for the SW25mm was my BST 18mm?  The BST25mm came to me  second hand. The SW25 is a reasonable EP but with only 50° afov.

Whatever you buy will transfer to telescopes of the future? If you were to go down  the 200mm route the 32mm panaview would be a nice eyepiece, as would a 6mm WO SPL as your primary Planetary EP.

Only suggestions mind you. 

My 5mm BST came as a replacement to the 6mm TMB Planetary II which was not to my liking. The 6mm WO is nicer, but I really need to get  out one night soon,  to fully appreciate the EP. My new work is taking my spare time away whilst I study?

Edited by Charic

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