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BST/Starguider Explorers - f/4.6?

gooseholla

By gooseholla
in Discussions - Eyepieces

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Bart

Bart

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Posted

John

Can't say for sure on f4.8 but they worked very well at f5. They won't be bad I'd say. Someone else must be using them at that ratio and should be able to confirm for you. I'm guessing that will be reasonably high power you'll be using it. I use to use a BST 5mm for x250 and got some great views

Barry

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gooseholla

gooseholla

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Thanks for the replies.

I use a telescope house branded orthoscopic at 5mm and it is quite reasonable. 4mm is too much on my scope - it'd gives c.325 - 350x, depending on what my true focal length is (still trying to work that one out for sure!), which for most nights isn't useable.

Just hoping they are fine, as a 5mm Hyperion was, frankly, the worst eyepiece I had ever used! Was a shame really.

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rwilkey

rwilkey

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Hi John, the BST Explorers/StarGuiders should work OK at that f/ratio, but unfortunately they only come in 5mm or 8mm ie. outside the focal ranges you are looking for.  I think you would be better off with Explore Scientific 82 degree series, 4.7mm and 6.7mm, website here: http://www.explorescientific.com/eyepieces/82_degree_series1.html.  Alternatively, Agena Astro in the US is a good supplier to buy from: http://agenaastro.com/eyepieces.html?camptype=homepage-btn

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Reeny

Reeny

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Posted

Didn't they used to come in more sizes?! Or is it the TMB designed etc. that I am thinking of?

Those ES look cracking eyepieces... but a lot of money! :sad:

The ES 82 degrees are £90 delivered, with pre-paid import duty.

That's only £41 more than the 60-degree BST.

Edge effects on my 11mm are minimal (8-inch dob at F5.9)

Viewing the moon at 240x in the Barlow is amazing at 82-degrees.

I got mine through hands on optics on Ebay - but their stock is very limited.

Agena's Ebay shop works out about £10 more due to the higher postage costs.

Germany sells them for 120-euro plus 10-euro postage. http://www.explorescientific.co.uk/en/Eyepieces/

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AlexB67

AlexB67

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Posted

Didn't they used to come in more sizes?! Or is it the TMB designed etc. that I am thinking of?

Those ES look cracking eyepieces... but a lot of money! :sad:

It is the BST starguiders that come in 5 and 8mm and offer 60 degrees. The others you mention are a different type.  As said you'll probably find they'll work okay for you, it is all in the eye of the beholder and expectation I guess ?.

Do note though you are buying an eyepeiece rated for f/5, so with that in mind expect off axis performance to drop a bit.  Certainly in my Dob at f4.7 with the 8mm BST I find this to be the case, planetary details on Jupiter is notably best on axis, but it has taken me several months of Jupiter observing doing long hours to discover the more subtle details to learn some of these things.

For the price though the BSTs offer a lovely contrast level and given me nice views, and on axis views are nice and scatter levels reasonably good. If cost is an issue and you can tolerate the reduction in comfort an orthosopic would be a better choice I think, that being said the BST are so comfortable and easy to use, there is a lot to be said for that, and ortho is not comfortable with very tight eye relief and therefore not for everyone, also they offer a much smaller FOV round 40 - 42 degrees and that will frustrate some. 

Personally I'd go ortho route or TV plossls for an 8mm perhaps second hand if I bought now for similar money, though never tried the latter in such faster scopes that is my feeling anyway. 

The other thing to consider, I thought to throw it in the pot seeing it is rarely mentioned , but with the wider angles eyepieces at that sort focal ratio coma will also begin to degrade planetary detail a bit as well off axis. I've never been privy to trying with a coma corrector. Suffice it to say there are quite few experienced observers that swear by them for retaining good planetary detail going much further off axis if you want those wider views past 60 - 70 degrees in faster newts at that ratio. Opinions on this will vary, but with that in mind given the ratio of your scope  perhaps 60 degrees or thereabouts is not a bad limit to stick to anyway for best details,  and you would need a well corrected eyepiece in every other area to use that FOV. I found myself not using the full 60 degrees of the 8mm BST for best results in teasing out details on Jupiter, that being said it has given me much pleasure on Jupiter. At 6mm, 200x in my case the TV Radian with 60 degrees has been my first eyepiece for panets where I am happy to let it sail through the FOV.

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