Eye Pieces and Focal Ratios?

[rob1]

im looking to buy a some eyepieces in the near future to upgrade my standard skywatcher eyepieces i got with my scope, i only have the 2 at the moment and when looking at them on flos website i noticed in the descriptions some say better suited to telescopes with f/6 and up. my telescope is a skywatcher 200p f/5 witch is a fast scope apparently, i was wondering how diffrent focal ratios affect different eyepieces? and if you guys have any recommendations on what to get next, i currently have the 25mm and 10mm standard ones and a 2x barlow, any help would be greatly appreciated

[Naemeth]

im looking to buy a some eyepieces in the near future to upgrade my standard skywatcher eyepieces i got with my scope, i only have the 2 at the moment and when looking at them on flos website i noticed in the descriptions some say better suited to telescopes with f/6 and up. my telescope is a skywatcher 200p f/5 witch is a fast scope apparently, i was wondering how diffrent focal ratios affect different eyepieces? and if you guys have any recommendations on what to get next, i currently have the 25mm and 10mm standard ones and a 2x barlow, any help would be greatly appreciated

An idea of budget would help

Essentially, as the focal ratio increases (from a starting point of, say, F/1), the aberrations of the eyepiece (and indeed, whole optical system) become less and less difficult to control, so the end result gets better and better as focal ratio increases. If an eyepiece is very well corrected (e.g. TeleVue), then you will get a completely sharp field at F/4 (and they even test at this focal ratio). When you get a large focal ratio (say, F/15), most eyepieces perform very well indeed, because they don't have to 'work' much.

Recommendations, budget per eyepiece:

~£50 - BST Explorers / Starguider EDs (http://www.skysthelimit.org.uk/bst%20ed%20eyepieces.html)

~£70 - TeleVue Plössls (2nd hand)

etc..

Let me know what budget you've got and that will help immensely

[damnut]

Hi Rob,

Could you give some idea of budget??. The BST explorers around £50 are well respected, Next Baader Hyperion, celestron Xcels and Vixen Lanthanums c £100.. After this it is deep pockets. There is an excellent guide to ep's by warthog on the forum.

If you want to have a bit of fun & see what you may view have a go at these, just type in your scope & ep details...

http://www.stargazing.net/naa/scopemath.htm

http://www.12dstring.me.uk/fov.htm

Cheers

[E621Keith]

Like others said, a budget will be useful.

A good alternative to the Vixen Lanthanum (NLV) is the Meade Series 5000 UWA. They cost about the same as a NLV, but has much wider field, which can be a very useful feature in a undriven scope such as a dob.

[rwilkey]

The Baader Hyperion's are bit soft on fast scopes, I would suggest the BST/StarGuiders as the best way forward.

[russ.will]

The Baader Hyperion's are bit soft on fast scopes.

I would agree with that. The couple I looked through didn't float my boat and I was living with a case full of BST Explorers at the time, so I considered it money well saved.

Russell

[alan potts]

Having read the posts I tend to agree with Kieth, he recommended the Meade UWA amoung others

I have had almost all of the Meade UWA range and still have 4 of them, I have only used them at F5.26 and they are very good at that speed. The other good thing is the older ones of these are now only picked up secondhand as they have been discontinued. The UWA available now are not from the same source company that is the 5.5mm, 8.8mm 14mm 20mm (only seen in US) the others 24mm and 30mm are old stock. Because these focal lenghts under 14mm are in competition with ExSc they can be picked up for 75-95 pounds. At that price I would say they are cracking good value.

They made the following range, 4.7mm, 6.7mm,8.8mm, 14mm, 18mm, 24mm and 30mm. The longer ones will cost more due to the new cost being much greater.

Alan