Help please - which 2" eyepiece?

[Andymarrison]

Hello everyone! I'm just starting out and last night managed to get a few hours of clear skies for the first time with my CPC 800 and Baader Hyperion 24mm from FLO. Saw some amazing sights and in particular loved the globular clusters M3 and M13, and galaxies M81 and M82. However I'm now lusting after some more magnification, particularly so that I can see some more detail in the two lovely clusters. Which eyepiece would you recommend next? I've got a budget of about £100, and should mention that the skies near me are quite light polluted, so I guess I don't want too much magnification, right? Thanks for your advice!

[rwilkey]

If the Baader Hyperion works well in your scope and you like the views I would suggest the 8mm Baader Hyperion, I have both and they are very comfortable ep's to use.

[Andymarrison]

Thanks Robin - I certainly did enjoy the Hyperion, so I probably will go with the 8mm you suggest. I'm a bit confused by something on the Baader information sheet for these EPs, which says that removing the forward 1.25in reducing lens group (which I have to do to expose the 2" barrel to fit into my 2" star diagonal) results in a longer focal length and wider FoV. So when I remove the 1.25in barrel, have I still got a 24mm eyepiece, or actually one with a longer focal length than the quoted one?

[John]

I don't think it works with the 24mm as it does not have a lens set within the 1.25" barrel as the other Hyperions do. Removing that part with the other Hyperions gives something around a 22mm I think but it's not a terribly good quality eyepiece, or so I've seen reported.

[faulksy]

as said cant do it with the 24mm all the others you can i have the 21mm remove the front part of elements gives me something like a 24mm and find the views great on and off axis, you can also add fine tunning rings which alter the focal lenth cost about a tenner each you simply screw these on and increase your power to suit very good

[Andymarrison]

Thanks for the advice - just dug out the 1.25" barrel section and indeed it has no lens group on the 24mm. So if I go for an 8mm, for example, and take off the 1.25" section, will I end up with a 2" eyepiece that doen't perform quite as well as with the 1.25" bit left on? Not so worried about the small increase in focal length, but would be worried about losing quality.

[rwilkey]

Hi Andy, the posts above are quite right, remove the front lens group on the 8mm and you have a wider field and decrease the focal length. You can increase it by adding the Fine Tuning Rings (FTR's), which makes the Hyperions very flexible, for example you can alter the 8mm to become a 6mm (with the 14mm FTR) or to become a 5mm (with the 28mm FTR) see table here: http://www.firstlightoptics.com/baader-planetarium/baader-hyperion-finetuning-ring.html

[Andymarrison]

Sorry to be a bit of a dummy here......so if I buy an 8mm Baader and decide to use it as a 2" eyepiece then I have to remove the 1.25" reducing group and end up with an eyepiece with a focal length greater than 8mm and therefore with lower magnification than the 250x I might have expected based on 2000mm divided by the advertised 8mm? Thanks for all the help here guys - as you can see I'm new to this stuff!

[John]

I think you get something like a 22mm when you remove the lower lens group. It's not a very good 22mm but it might be OK with your F/10 scope. It will give you around 90x magnification.

[Andymarrison]

Thanks very much John - any idea how I find out what the 8mm Baader eyepiece would turn into if I removed the lower 1.25in section?

[John]

Thanks very much John - any idea how I find out what the 8mm Baader eyepiece would turn into if I removed the lower 1.25in section?

That was the question I thought I was answering with my previous post

As far as I know, when you remove the bottom lens set, all the 1.25" Hyperions, apart from the 24mm, become a 22mm-ish eyepiece.

[Andymarrison]

Sorry John - took a while to sink in that this was the case with the entire range i.e that this happens with all of the Hyperions.

[John]

Sorry John - took a while to sink in that this was the case with the entire range i.e that this happens with all of the Hyperions.

When I borrowed a set for testing I came to the conclusion that the top sections of all, except the 24mm, had the same optics in and it was the bottom group that delivered the different magnifications. If I'm right they are not the only eyepiece design to work that way - I guess it's an efficient way to design / manufacture them.

[Andymarrison]

I think I get it now. Because I only have one eyepiece, namely the 24mm Hyperion with no lens group in the 1.25" barrel, I had just assumed that to use the Hyperion eyepieces in a 2" star diagonal, I would remove the low er section (which of course has no effect in the case of my 24mm). However, it seems that with anything other than the 24mm I should be dropping the entire assembly into the 2" dagonal (with 1.25" lower section and its lens group still attached). Sorry for all the dumb questions.

[John]

... However, it seems that with anything other than the 24mm I should be dropping the entire assembly into the 2" dagonal (with 1.25" lower section and its lens group still attached)....

I think you would find that the lower section would contact the mirror in the diagonal if you do that. It's certainly worth checking the clearance - a replacement 2" diagonal would cost as much as a Hyperion

When I was using the Hyperions I stuck to using them in 1.25" mode - even when they were used with a 2" diagonal.

[Andymarrison]

Thanks John - I'll follow your advice and use in 1.25 mode.

[rwilkey]

Hi, I tend to use them with the 1.25" nosepiece attached, less fidley to be honest.

[rwilkey]

Removing the first lens group on the 8mm, would probably turn the ep into a 10mm, the average addition seems to be 2mm, so if you use it as a 2" ep then this will give you 200x instead of 250x in an f/10 scope.