EP's, just checking....

[stardad]

I have with my scope (astromaster 130EQMD) three lens's. They are a 20mm, 15mm and a 10mm with a 2x barlow on its way so giving me 20/10mm 15/7.5mm and 10/5mm if I understand things correctly using a Barlow.

As I have a stigmatisium in one eye I understand I will have problems with smaller EP's than say 8mm.

Am I correct or can I go down to say 6mm EP and stop there?

[pvaz]

It all depends on the EP design. There are 6mm EPs with long eye relief which will allow you to use glasses with them. Problem is with the traditional designs (plossls and orthos).

You may want to have a look at the TMB clones, they go for about 40£ a piece.

[great_bear]

As I have a stigmatisium in one eye I understand I will have problems with smaller EP's than say 8mm.

Depends what you are asking.

Do you mean observing without glasses? If so, it's the LONGER length eyepieces that will show up astigmatism more - on short focal lengths it can disappear completely.

If however you're asking what's the shortest focal length eyepiece that can be used WITH glasses, then it depends on the design, and whether you mind not being able to see the whole view or not. For Plossl eyepieces, even a 15mm would be pushing it, and you'd be better barlowing a longer eyepiece or choosing eyepieces such as William Optic SPLs, BST Explorers, Celestron X-Cels, or (if you have the cash!) Tele Vue Radians.

[E621Keith]

You can get Televue dioptix for your astigmatism. I just wear glasses to observe. It does limit my choices of eyepieces to those with long eye relief. TMB planetary and WO SPL will be a good choice. For a bit more cash, TV Radians, Pentax XFs, and Vixen LVWs are even better.

[russ]

I find my astigmatism is non existent in the short focal length eyepieces, anything less than 10mm. So i never wear glasses with eyepieces in this focal range. I often use a 7mm Ortho or 6.3mm Plossl without issue.

But medium to low power i really need to wear my glasses, so a long eye relief design is essential.

I had a TV Nagler 16mm T6 which i just couldn't get on with due to this problem. But looking through a Pentax 14mm XL with the glasses was near perfect.

[SimonR]

The amount of eye relief depends on the design, plossls which are very common don't have a lot of it. I find a 6mm plossl very hard to use even with my glasses off. With my glasses on I find I can use a 9mm orthoscopic which has eye relief of 7.2mm, but it is the 'volcano top' design which is easier to use than a 'rubber top' if you wear glasses.

[stardad]

I don't wear glasses other than for driving when tired. The worst is I have problems with cross lettering so 'E's' come out as 'I' and 'H's' as 'I I's'.

So far I've not had a problem with celestron 20mm and 10mm but having just got a Ommi Plossl and a 2x Barlow (untried as of yet ) I'm wondering if I've made a mistake.

[great_bear]

So far I've not had a problem with celestron 20mm and 10mm

In that case, anything that has an effective focal length less than 20mm (for example a 32mm Plossl with your Barlow becomes effectively a 15mm) will be fine as well.