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thanks! i meant if i could use it effectively because of the eye relief effect,also , is there a big difference between the 25mm provided by skywatcher and the bst one?

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I would say yes. The SkyWatcher one (Super 25) is a very basic eyepiece, while the BST is a definite step up in quality and will show you a bit wider field.

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It depends on which SW 25mm you get.

I've purchased several SW scopes, and got different kit eyepieces with them. They were in 10mm and 25mm focal lengths but different types.

There is SW Super RK - which is reversed Kellner (that is what RK stands for) - 3 element eyepiece, and there is SW SP Plossl - Super Plossl, which is 4 element eyepiece - of classical Plossl design.

In my opinion both 25mm are usable eyepieces and I never felt the need to replace that exact focal length. With longer focal lengths change in magnification is small when you make significant step in focal length of eyepiece, so you don't have to be closely spaced. If I've got for example 32mm plossl and 17mm plossl for 8" dob - I've found that I don't really use 25 or 20mm plossl. I'll use 32mm because it offers more field and will act as wide field eyepiece / finder eyepiece better than 25mm. If I want higher mag and smaller exit pupil - I'll jump straight down to 17mm.

Even now, with more expensive eyepieces I tend to do the same. I've got ES68 28mm and ES68 16mm. I have not thought about needing anything in 20-24mm range. With shorter focal lengths you will want closer spacing because magnification starts to jump suddenly (for example 6mm and 4mm is only 2mm apart, but magnifications they offer in 8" F/6 will be x200 and x300, so 50% increase, while 24mm and 20mm are 4mm apart, but magnifications are x50 and x60 - only 20% difference).

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Occasionally you get a plossl eyepiece with these scopes but most often they are 3 element "cheapies" which get you going but thats about it. If you got a Skywatcher 25mm plossl you won't find that the BST Starguider 25mm much of an improvement (I've just sold one so I know what they are like) but replacing the cheaper 25mm would be more of a priority.

If you are lucky, you might get the eyepiece on the left with your scope but more likely it will be the one on the right :smiley:

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