Best Mix, Eyepieces

[Zuts]

Hi All,

I am after a bit of advice. I have a number of eyepieces and am wondering if anyone can tell me if i should have a better mix. I may sell or trade to get a better mix.

I have a Nexstar 11 GPS, 2 by Televue powermate

and the following eyepieces

35mm Panoptic = 80, 160 by with barlow
16mm Nagler = 175, 350 by with barlow
11mm Nagler = 254, 508 by with barlow
5mm Radian = 560, 1120 by with barlow (probably not useful with barlow)

Thanks all

[acropolite (Phil)]

I reckon you should sell them all and get some Series 500 plossles...

Seriously good mix of EP's you have there, maybe something to fill the gap between the 16mm and the 35 Pan. I doubt you would get much use out of the 5mm Radian, 560x is pushing it and you can get almost that if the conditions ever warrant it with the 11mm barlowed, but I'd keep it anyway just in case you get one of those push to dobby thingys or maybe a nice refractor (5mm = 120x on an ED80).

[janoskiss (Steve H)]

Agree with Phil the 5mm will have little or no use. If it was me I'd ditch the 5mm and be looking at getting something at 300x and 400x to give better selection at the high power end. Also a 20mm T5 for general purpose deep sky. The 16mm is probably just a little too much power for many faint fuzzies, esp galaxies, IMO.

[rmcpb (Rob)]

Good advice given above. Swap the 5mm for an eyepiece between the 16 and 35.

Cheers

[janoskiss (Steve H)]

Another thing to keep in mind is that the f.l. and hence the f-ratio of a Cassegrain is not fixed and depends on how far the EP is placed from the back. A 2" diagonal will slow it down some. So e.g. instead of 20mm you might want to go with 22-24mm. For same reason, you might also find that the 2x powermate is greater than 2x.

[Mr. Subatomic]

I agree, consider maybe 1, 2 or 3 eyepieces in that gap between 16 and 35 for some of the faint DSO's, but you've got a really broad, quality mix there, should provide you with some good viewing.

[Zuts]

Originally Posted by janoskiss

Another thing to keep in mind is that the f.l. and hence the f-ratio of a Cassegrain is not fixed and depends on how far the EP is placed from the back. A 2" diagonal will slow it down some. So e.g. instead of 20mm you might want to go with 22-24mm. For same reason, you might also find that the 2x powermate is greater than 2x.

Hi

I never realised this. Thanks for that information. Do you know how i can calculate the actual focal length of the scope with a 2 inch diagonal. Also i am thinking of a Crayford focuser which may slow it even more?

Thanks for all your replies

[Zuts]

Originally Posted by janoskiss

Agree with Phil the 5mm will have little or no use. If it was me I'd ditch the 5mm and be looking at getting something at 300x and 400x to give better selection at the high power end. Also a 20mm T5 for general purpose deep sky. The 16mm is probably just a little too much power for many faint fuzzies, esp galaxies, IMO.

Hi,

In this case i agree with Janokiss. On an outstanding night, maybe once a year if i am lucky my scope should reach 60 per inch of aperture. So the 5mm radian in this case would be ideal for planetary views (although the barlowed 11mm is much the same).

Still I may get another scope. I used to have some vixens and they lasted for years. Maybe since i already have the radian i may keep it if i get a slower scope.

[Zuts]

Originally Posted by rmcpb

Good advice given above. Swap the 5mm for an eyepiece between the 16 and 35.

Cheers

Hi,

If i was going to get some more eyepieces i guess i may get rid of the radian 5mm. Anyway i can look at the following to round out my collection, assuming i decide to fork out the money .

Option 1

24 mm panoptic, 116, 232 barlowed
OR
26 mm nagler, 107, 214 barlowed

AND

55 mm televue plossl, 50 by, nearly a bino mag view

AND

maybe swap the 5mm radian for a 6mm radian

Option 2

Get a F6.3 focal reducer, this would give me

5mm radian, effectively 7.9 mm with reducer
11mm nagler, effectively 17 with reducer
16 mm nagler, effectively 25 with reducer
35 mm panoptic, effectively 55 with reducer

so option 2 gives me the 25 and 55 mm more cheaply

Option 3

Bankrupt myself and get

7mm nagler
26 mm nagler
55 mm plossl

Wha do you guys think?

[janoskiss (Steve H)]

Do you know how i can calculate the actual focal length of the scope with a 2 inch diagonal. Also i am thinking of a Crayford focuser which may slow it even more?

Sorry, don't know how to calculate the f.l. but you can do drift timing with an EP of known field stop diameter to figure it out.

[Mr. Subatomic]

do you mean focal ratio?

[janoskiss (Steve H)]

same thing really. focal length = primary diameter * focal ratio; and primary diameter is fixed so f.l. goes like f.r.