Your thoughts on eye relief.

[Theninjagecko]

So I only have the celestron 40mm plosl with my Evo 9.25 and a 2x and 3x barlow. both meade I think.  The only EP's I've ever got other than the stock EP's are the ceelstron X-cel when I had my OO 250px.

My question is regarding eye relief, everywhere and everyone seems to state more eye relief the better, But I found it annoying. In my old scopes I had my eye upto the rubber cup and it not only blocked out the surroundings but gave better views. 

with my c9.25 and my 40mm I feel like I'm 2 inches away from the EP almost. Is this down to my SCT ? or the EP ?

Also whats your thoughts on the subject.

Had a lovely couple of hours this evening just getting used to my scope again, fantastic views of the moon. Split rigel easily and also saw the E star in orion. Not bad fir such terrible sky's here and I was out the front with the full force of street light pollution.

[pipnina]

If the EP has an adjustable eyecup... More eye relief is a bonus IMO at least for us glasses wearers. Never used an EP that can show the whole FOV with my glasses on, I looked through an x-cel which is 20mm and that still wasn't enough.

 

[scarp15]

I used to use an 8" SCT and my two favourite eyepieces at the time were an 11mm and 8mm TeleVue plossl with respectively I think 6mm and 5mm eye relief. I had to wedge my eye right into the rubber cup and observe for shortish periods followed by a pause, but they were exceptional eyepieces, particularly on planetary views and the tight eye relief personally was not such a problem.  The most comfortable eyepieces I have used are perhaps a 10mm Delos and with considerable eye relief, a 35mm Panoptic, both oculars also have comfortable eye placement.

[ronin]

I have the BST's and a few others. They appear to have around the 15-18mm eye relief value.

I wear glasses and will often keep them on, but not always.

So the 15-18mm area appears reasonable and in my case adaquate.

The "problem" of a 40mm p[lossl is that the  eye relief is about 28-30mm and usually a plossl has a simple rubber eye cup, so there is nothing at the best position to place your eye. In effect your head/eye has to be held at the right position with little or no point of contact.

The advantage of a 40mm plossl on an SCT is that the focal length they have means you need a long focal length to get a lowish magnification and a widish view.

[Theninjagecko]

I just came across this thread.

 

Seems most 1.25 40mm EP's suffer from the same problem, no so much eye relief but possibly its field of view. Someone said its like looking down a toilet roll, and thats exactly how it is but my eye being about 25-40mm away from the ep.

 

 

[michael.h.f.wilkinson]

Plössl EPs are a scaled design, so the eye relief is a fixed percentage of the focal length (about 75%). This means that a 40mm has a massive 30mm eye relief. That is so long that it becomes uncomfortable. My old 36mm Vixen Plössl had a similar long eye relief. For me, with glasses, 16-20 mm eye relief is optimal. Those without glasses require less, as a rule.

[Theninjagecko]

26 minutes ago, michael.h.f.wilkinson said:

Plössl EPs are a scaled design, so the eye relief is a fixed percentage of the focal length (about 75%). This means that a 40mm has a massive 30mm eye relief. That is so long that it becomes uncomfortable. My old 36mm Vixen Plössl had a similar long eye relief. For me, with glasses, 16-20 mm eye relief is optimal. Those without glasses require less, as a rule.

Learning all the time. Love this place   Why on earth do a 40mm 1.25 ? It seems to make no sense.

[Mak the Night]

With Mak's/SCT's getting a low power with a high enough exit pupil is often more difficult that getting really high powers. I have a 40mm TeleVue Plossl which has a 28mm eye relief and I need an eye guard added to it to effectively use it. I plan on getting a 235mm SCT soon so it will be very useful for low power viewing. On a 102mm Mak it allows me to use a UHC filter for a 32.5x with a 3.14mm exit pupil.

As I don't wear eye glasses I find that I can comfortably tolerate up to a 10mm, although my ideal is around 13mm, which I find just about perfect. As with almost everything in astronomy it is often personal preference and what subjectively suits you as an observer.

The 19mm TV Panoptic and the 16mm Nagler T5 (above) have very similar dimensions and overall weights. The 68° 19mm Panoptic was the first wide angle TeleVue eyepiece I ever bought and it is still a favourite. Its 13mm eye relief seemed just about perfect to me. The Nagler has an 82° FOV and is quite spectacular to view with, but its 10mm eye relief is just about tolerable and can be a bit tiring on long sessions. Fortunately it is light enough to happily sit in a Barlow which will actually extend its eye relief a little.

Many orthoscopics have more generous eye relief than their equivalent focal length Plossls. The Astro-Hutech 18mm (above) has 15.2mm and the 12.5mm has a decent 10.41mm compared to the rather 'squinty' 8mm of the TeleVue 11mm Plossl. I'd much rather 'Barlow-up' a larger eyepiece with a better FOV and eye relief than use a shorter f/l. I can deal with the 40mm TV Plossl. With a large SCT though, any longer focal length than 40mm will possibly enable the obstruction to be seen. TeleVue make a 55mm (2") Plossl which would give your scope a 5.5mm exit pupil. This may enable you to observe objects such as the Horsehead Nebula. It has a 38mm eye relief!

http://www.televue.com/engine/TV3b_page.asp?id=51&Tab=EP_EPL-55.0

[SonnyE]

19 hours ago, Theninjagecko said:

Learning all the time. Love this place   Why on earth do a 40mm 1.25 ? It seems to make no sense.

Well, you can sit back in your easy chair and still see the view?

Ducks... runs....

[John]

When you use a barlow lens, the eye relief is extended which is why they are not mormally used with eyepieces that already have long eye relief such as 40mm plossls.

[Louis D]

Sufficient eye relief is important if you have severe astigmatism and need to wear eyeglasses to get a sharp view at the eyepiece.  It is also important if you have long eyelashes as they will bump up against super short eye relief eyepieces.  This can transfer oil to the eye lens.  It is also important on super humid or super cold nights as eyepieces tend to fog faster the closer your eye gets to them under those conditions.  If those conditions don't exist, then shorter eye relief eyepieces will tend to work better.  If you want a 40mm with shorter eye relief, look into an erfle or konig derived super wide angle design, but you'll need a 2" diagonal and visual back to use it.