Celestron X-Cel 2.3 mm

[burger]

Hi

I have a skywatcher 130M.

Is this going to give me a reasonable image or better using lower mag with a barlow ?

Many thanks

Mark

[John]

I think your scope has a focal length of 900mm in which case a 2.3mm eyepiece gives 391x magnification. The theoretical max for a 130mm scope is around 260x and the practical max would be closer to 200x. I don't think the 2.3mm will be a lot of use I'm afraid to say.

[alan potts]

John is absolutely correct a 2.3mm eyepiece will be of no use what so ever unless you know how to completely remove the Earths atmostphere and even then I would think we are pushing things a bit. Great minds think alike so go for something in the X200 area max or an eyepiece around 5-6mm, you will get much more use from it as the image will be better and you will see more. I don't think I have ever used that magnification on my 12 inch scope.

Alan.

[burger]

many thanks, that is what i was thinking, its just too much for the scope to handle.

Thanks so much for your comments.

[Naemeth]

I agree entirely. I've barlowed a 4mm (giving effectively a 2mm eyepiece) and it's only really of any use on the Moon. My scope is F/5, and the 2mm gives 325x, so 391x would certainly be too high.

A 2.3mm eyepiece will give the maximum (theoretical) magnification with an F/4.6 scope, a 2.5mm eyepiece for a F/5, and a 4.5mm eyepiece for an F/9 (so the shortest FL eyepiece you should use is half of the focal ratio in mm )

HTH

[Pig]

A 4 to 5mm would be your realistic highest magnification or an 10mm with a 2 X Barlow

[Stargazer_00]

To Make it clear why. If you divide the aperture of your scope in mm by the magnification you calculate the diameter of the exit pupil. This is the shaft of light that comes out the eyepiece. If it's too small then the image is dim and unpleasing. I Find less than 1mm unpleasing and 1mm is effectively your aperture as magnification. So On a130mm I'd aim for 130x max to get tolerable views. Hope that helps

[Stargazer_00]

Just following up on my post above, I want to make it clearer how important exit pupil is.

I found this very informative post on CN (hope cross foruming posting is OK? - if not sorry!)

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4987165/page/116/view/collapsed/sb/5/o/all/fpart/1

The telescope retailers will quote maximum practical magnification of a scope at 0.5mm exit pupils, in reality you should be thinking the diameter in mm is the maxmum magnification you should be looking to achieve and further to that the BEST detail view you are likely to get is half your diameter in mm as magnification (giving a 2mm exit pupil).

[RMcCallum]

I too have a SW 130M and the best magnification I can get is 180x with a 5mm BST and this is with good conditions mind. As people have alread mentioned, bigger is not better (in terms of magnification anyway!).

[burger]

Just following up on my post above, I want to make it clearer how important exit pupil is.

I found this very informative post on CN (hope cross foruming posting is OK? - if not sorry!)

http://www.cloudynig...5/o/all/fpart/1

The telescope retailers will quote maximum practical magnification of a scope at 0.5mm exit pupils, in reality you should be thinking the diameter in mm is the maxmum magnification you should be looking to achieve and further to that the BEST detail view you are likely to get is half your diameter in mm as magnification (giving a 2mm exit pupil).

superb, many thanks for the info, I have been looking for a while for an easy guide to the suitable EP's I can use.

I even understood most of it, it must be sinking in after all

[Stargazer_00]

No worries mate. As soon as the penny drops it all makes a world more sense and you know exactly what you're buying and what you will get.