Celestron Nexstar 5 with a 6mm EP.

[LukeSkywatcher]

Hi all

Forgive this most stupid of questions, but my brain has decided to take the night off. I know someone who has a Nexstar 5 (f/l 1250mm.........i think). I gave them a couple of EP's (Celestron Plossl's 10mm and 6mm). I know the 10mm will work fine on any night of the week. I'm just wondering about the 6mm.

1250/6=208X.

That should be ok for use most nights also?. It will deliver fine views of the Moon and planets?.

I ask because i have rarely used the 6mm on a 5" scope (i have a Heritage 130p in my collection).

Did i do ok by giving them the 6mm EP or will they get little to no use out of it?

Thanks in advance.

Paul.

[Stargazer_00]

Excel doesnt paste every well, 1 moment...

there we go!

the 6mm will show 208x with a 0.6mm exit pupil. this is close to the highest practical exit pupil of 0,5mm so the view wont be perfect and will require good seeing conditions to get a pleasing view in my opinion. it'll work well as a dedicated eyepiece which shows the highest mag the scope can give. On this basis I wouldnt bother barlowing the 10mm to a 5mm as the exit pupil will be tiny and therefore the views dipleasing.

Hope that helps

[John]

I think they will get some use out of the 6mm provided they understand that it's towards the upper end of whats feasible and may not always show sharp views, depending on the viewing conditions / target. It should work well on Saturn, the Moon and binary stars, with the caveat of decent seeing conditions as already said.

The Nexstar 5 will need to be in good collimation and well cooled to get the best high power views.

[LukeSkywatcher]

I think they will get some use out of the 6mm provided they understand that it's towards the upper end of whats feasible and may not always show sharp views, depending on the viewing conditions / target. It should work well on Saturn, the Moon and binary stars, with the caveat of decent seeing conditions as already said.

The Nexstar 5 will need to be in good collimation and well cooled to get the best high power views.

That's pretty much what i was thinking. Usable, but close to the edge. So not a complete waste.

[michael.h.f.wilkinson]

I used a 5mm Ortho in my 6" F/8 in the past, which pushed that scope even further (though the small CO made it a very sharp 6" indeed). 240x was useful on nights of really good seeing, but the near non-existent eye relief prevented me from using it that often. A 6" Plossl should be OK for those who can observe without glasses.

[LukeSkywatcher]

I used a 5mm Ortho in my 6" F/8 in the past, which pushed that scope even further (though the small CO made it a very sharp 6" indeed). 240x was useful on nights of really good seeing, but the near non-existent eye relief prevented me from using it that often. A 6" Plossl should be OK for those who can observe without glasses.

Even if it has a rubber flip-up top. That allows glass wearers to use it also.

[michael.h.f.wilkinson]

Even if it has a rubber flip-up top. That allows glass wearers to use it also.

No: a 6mm plossl (not 6" ) cannot be used by people with specs, because even with the rubber eye shield turned down you cannot put your eye at the exit pupil with your glasses on (the Pauli exclusion principle sees to that). My kids have a 6.3 Plossl, and it is impossible for me to use that with glasses.

[LukeSkywatcher]

I never wear my glasses when observing. I am not sure if the rubber eye shield should be up or down for people wearing glasses, i always assumed up.