small eyepiece?

[DazC]

Hi all.

I have a celestron 130eq md and am wanting to get an eyepiece smaller than my 10mm. My scope is an F/5 with a focal length of 650mm.

Can i go as small as 2mm or is this too small for my scope? Any surgestions please.

Thanks.

[Peter Drew]

Hello Dazc.

I think, realistically, your next choice of higher power eyepiece that will see most use is a 6mm, the scope would be useable at higher magnifications but less often due to seeing conditions. A 2X Barlow lens might be worth considering, a 2mm eyepiece would definitely be OTT for your scope. .

[Capricorn]

Cannot think of any scope that will be able to use a 2mm eyepiece, and any good 2mm eyepiece will I suspect cost a lot more then a 130 f/5 scope.

At the small end you will find that you could easily need a 4mm, 5mm, 6mm and 8mm.

I usually find I can use the 6mm, not 100% however, occasionally the 5mm is usable and rarely the 4mm is.

So you could get a 5mm then find you do not have the chance to use it often. The 6mm is a safer option and would give you about 108x.

Not sure how they work in your scope but for small increments like this you are looking at something like the TMB planetary's. Plossls come in the smaller sizes but the 5mm and small will be like using the eyepiece as a contact lens.

[Double Kick Drum]

I have a similar size 127mm F5 refractor.

My second additional EP purchase was a skywatcher 6mm with good eye relief. Viewing is easy but it does not have particularly sharp focus.

I am getting a 8mm Celestron X-Cel for Christmas. If that gives gives improved viewing sharpness as I believe it will (going on SGL recommendations), I will get a 5mm too but anything smaller will be almost unusable.

[damnut]

Hi DazC,

A 2mm ep would give 325x, the theoretical limit for your scope is 260x. As you approach this you will need to realis that the image will darken significantly and you may loose contrast. Also consider the viewing conditions so like advice above stick to around 200x max. So the 4mm will give a comfortable 162.5x.

A couple of links for you to play with regarding power & field of view :-

N.A.A. Telescope Math Calculator

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

Cheers

[DazC]

Thanks to all of you. I'll have a look at the links and read a bit more about focal length.

Thanks again.