BST EP for Skywatcher 130P to Replace 10mm?

[Nomad Z]

If I had a Skywatcher 130P and wanted to upgrade the supplied 10mm with a BST EP, which of the 8mm or 12mm would be the best in terms of getting a noticeably improved viewing experience? 

This would be for a glasses wearer, not me. My scope (MAK127) has a longer focal length, so I"m wondering whether the 8mm would be better than it is through mine (for which I would choose the 12mm). 

[rwilkey]

Hi NomadZ, both eyepieces will give equally good views and I would recommend the 12mm, which will also work well in the Mak.  The 12mm covers that great middle ground of star clusters, globs and planetary nebulae. 

[Nomad Z]

It’s not for use with the MAK, only the 130P. (It’s for a mate who has the 130P - I already have 8, 12, 18 & 25mm for my MAK.)

[rwilkey]

Hi Nomad, then it all depends what the persons targets might be, if you know?

[Nomad Z]

He’s talked about planets a fair bit.

[Ricochet]

The Starguiders might be a bit tight on eye relief for a glasses wearer. Has your friend tried yours to see if they work ok with his glasses? If they are ok then for planets with an f5 scope I would suggest starting with the 5mm and the 8mm with a 2x barlow (so effectively a 4mm). If the eye relief on the Starguiders is too tight then the Celestron Xcel LX range have a touch more eye relief. 

[wookie1965]

The 12mm Starguider has 16mm of eye relief have to see if that is enough for a spectacle wearer.

[Nomad Z]

On FLO, the eye relief is given as 16mm for both (and the Celestrons are getting a bit pricey).

Given the focal length of scope, I think I'm leaning towards the 8mm BST.

EDIT. Or even the 5mm, or is that pushing it with a Barlow on the 130P?

 

[Ricochet]

1 hour ago, Nomad Z said:

On FLO, the eye relief is given as 16mm for both (and the Celestrons are getting a bit pricey).

Huh, I could have sworn it used to be 18mm. ? 

1 hour ago, Nomad Z said:

EDIT. Or even the 5mm, or is that pushing it with a Barlow on the 130P?

I suspect so. I think the optimum will probably be 4-5mm without a barlow.

[Alan64]

The 130P, 130mm f/5 Newtonian, has a focal-length of 650mm.  That's a bit short, and with the telescope designed for low to medium powers, but certainly capable of the higher and highest of powers.  50x per roughly 25.4mm of aperture is 250x.  I'd say to shoot for 175x, if the telescope is well collimated beforehand.  Let your friend know about the importance of collimation, especially at f/5, if they do not already.  As you go up in power, the optical-system of the telescope has to work harder, therefore the collimation should be as near-perfect as possible.  The BST 8mm(81x) with a 2x barlow would realise a power of 163x.  I'd suggest this barlow with the BST 8mm...

https://www.firstlightoptics.com/barlows/baader-classic-q-225x-barlow.html

...and for 181x with the 8mm.  However, it is not known if the user requires greater than 16mm of eye-relief.  We'd want him to see the entire field-of-view whilst wearing his glasses.  I think 20mm is the maximum eye-relief among eyepieces.

Are you able to have him test your 8mm with his telescope?

 

[Mr Spock]

I'd think an 8mm + Barlow is the maximum you should use on a 130mm. The scope has good quality optics, but, as an illustrious colleague once said, "you canna change the laws of physics"; a 130mm is always going to be limited by its size and trying for too high a magnification will give disappointing results.

[Nomad Z]

Yes, I tend to agree that the 8mm is about right. 

It's for a leaving present for a workmate (and astronomy buddy), and needed to be sorted out rather quickly (and no opportunity to test for eye relief, but he manages with the existing kit). An 8mm has been ordered.

Thanks all.