eyepieces and viewing difficulty

[tramsden]

I have trouble getting a comfortable full field of view with most of my eyepieces. I have to push my eye tight to the cup and if I move slightly the view has obscured areas. It really is quite distracting. Is it something obvious with eyepiece design or is it me.

Tony

[NGC 1502]

Hi Tony, eyepieces with a longer eye relief will help, especially if you wear

glasses. It's not your fault, many eyepieces have short eye relief, more

powerful EPs especially. Longer focal length EPs, with better eye relief

can be used with a barlow to obtain a higher magnification.

Hope this helps, Ed.

[Capricorn]

As Ed says it is a "feature" of the eyepieces.

We mainly seem to use plossls as the everyday workhorse and at the shorter lengths the eye relief is small. There is a formula for it but no idea what.

If the scope you have is also "short" then you need short focal lengths to get magnification. Since eye relief tends to relate to eyepiece focal length then smaller eyepieces = greater magnification but smaller eye relief.

I think, and may well be wrong, that the Wide Angles seem to have more eye relief, so perhaps it could be worth considering a few of them. Depends what you have at present.

I know that Orion ED2's have 20mm eye relief, which is good. Also what I think are copies of the Orions ED's sold by Astronomica have the same.

You need to search out eyepiece's and see what the specification is for eye relief. Some are specified as LER eyepieces.

What scope is it and what eyepieces are you using?

[John]

Plossl eyepieces typically have eye relief of around 80% of their focal length I seem to recall. Orthoscopics are similar.

The TMB Planetary eyepieces that you will see discussed a lot on this forum (because they are good VFM !) all have an eye relief of 16mm (even the really short focal length ones) and large eye lenses both of which make the viewing experience much more comfortable.

[argonaut]

I think that Plossls have .8mm eye relief per mm of focal length and Orthos have .7mm eye relief per mm focal length.

Blacking out and kidney beaning is not usually a problem with Plossls and Orthos.

[Ags]

I have the TS Planetary HR eyepieces which are similar to the TMB EPs - the eye relief is good but not long enough for my glasses. Some nights I find the view comfortable and other nights I seem less steady and the image keeps blacking out. You can get these TMB-type EPs for a little more than a regular plossl so I think they are worth it. I paid £49 for mine from Modern Astronomy.

My most comfortable EP is a 25mm plossl - it must have about 20mm eye relief.

[yeti monster]

The WAs and UWAs that I use give me comfortable eye relief, at the expense of a spot of curvature, especially with UWAs, but as that is at the edge of the FOV, I don't really mind.

[tramsden]

does it matter if its a narrow fov or a wide fov? or is it just dependant more on the manufacturer.

.T

[Chris H]

It's more down to the individual eyepiece design for example Pentax make the XW range which have 20mm of eye relief but they also make the XO orthoscopic's which have very tight eye relief less than 5mm.

[AndyH]

Here's a link to an article explaining about eyepiece design.

Eyepiece - Wikipedia, the free encyclopedia

There's probably better ones out there, but I don't have one to hand.

Andy.

[tramsden]

thanks I'll have a read