EP advise please

[Ali C]

Hi

I'm a newbie needing a bit of help regarding EP's.

I have a Celestron 127 SLT GoTo mak. I've become a bit lost with focal ratio's and max usable magnification etc etc.

I want to get a reasonable High, Medium and Low power set of EP's that will not break the bank.

Any advice would be very welcome.

thanks

[Tinker1947]

Well how deep is your wallet, there's cheap types or there's better quality,at a price...

[Ali C]

I would think £40 -£60 per EP would be about the limit.

[bigbox]

Hi, BST explorer's are supposed to be very good value for money, £41

www.skysthelimit.org.uk/

They get recommended on SGL all the time...

Regards Ady

[182570]

can recommend BST's have the 15mm and the 5mm pleased with both

[damnut]

Hi Ali,

Another vote for the BST's excellent value for the dosh!

Links below do all the maths for you to work out magnification and field of view, just type in your telescope data and eyepiece, the scripts do the rest.!

N.A.A. Telescope Math Calculator

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

Have fun

Cheers

[Catweazel]

Hi, BST are nice eyepieces. The TMB II are good as well for planetary viewing. Also, I really like my 32mm GSO plossl for wide field views at a modest price

[Ali C]

thanks for all the links, much appreciated.

cheers

Ali

[sticks]

I have the same scope as you and took ages deciding which EPs to get - eventually I settled for 25mm(*60) 15mm(*100) 8mm(*187) BSTs and am very happy with them. It's like having a new scope and the supplied EPs will be staying in their box from now on.... when I have the dosh I will be getting a 12mm(*125) for use instead of the 8mm when the seeing is really poor.

[Ali C]

Hi Sticks

Thanks for that, The BST's get lots of recommendations, so I will go for them.

The 25 mm supplied in the box I am reasonably happy with. Do you think is worth replacing the 25 mm as well ?

Thanks

Ali

[Charon]

I would as the supplied ones are not the best quality.

[Ali C]

Cheers

Am I right in thinking the 10mm will be the highest powered EP I could effectivly use with a 2 x Barlow ? ( 1500mm focal length ) ?

[John]

Cheers

Am I right in thinking the 10mm will be the highest powered EP I could effectivly use with a 2 x Barlow ? ( 1500mm focal length ) ?

That would give you 300x which is too much power for the scope and the usual viewing conditions we have in the UK. 200x is a more realistic maximum much of the time.

[Ali C]

would this be due to LP ?

[John]

would this be due to LP ?

The theoretical max magnification of a scope is usually said to be twice it's diameter in mm or 50x per inch of aperture. Your scope is 127mm / 5" in aperture so that's a max of 254x in theory.

In practice light pollution and atmospheric unsteadiness reduce the useful maximum somewhat further. That reduction can vary depending on the conditions so that sometimes even 150x is too much. On a good night 180x - 220x would be the most that you will find useful I reckon.

The good news is that high magnification is not required for many astro objects. Deep sky objects are best viewed at low to medium magnfications.

[Ali C]

Spot on,

Earlier, I screwed the barlow optic straight onto the 9mm EP and could not focus on Jupiter. Using the 9mm on its own gave a clean view although the FOV is a bit narrow.

I'm looking forward to seeing the difference the BST's will make. Any advise on the range of EP's, I'm thinking of replacing the 25 mm and adding either a 18mm or 15mm and an 8mm.

Thanks

Ali