Short eye relief challenge

[Paz]

I have used long eyebrelief eyepieces exclusively for years (SLVs, Delos, and long focal length Naglers and plossls), but recently I was mulling over getting a pair of 8mm eyepieces for binoviewing and thought I didn't need glasses to fix astigmatism as I'd be using them with a lot of barlow and so have small enough exit pupils for astigmatism not to matter.

There isn't an 8mm SLV and I didn't want the weight (or cost) of a pair of 8mm Delos so I went for a pair of 8mm Vixen NPLs.

I tried them out and to be honest I found them really distracting to use, my eye sockets and eyelashes touching the eyepieces constantly if I was to get the field stop correctly positioned in view.

I think I am going to struggle to get used to such short eye relief, and these are nowhere near the shortest eye relief one can get!

[globular]

Might be worth trying a couple of Ursa Major FMC Flatfield Eyepiece 7.5mm.  £39 each from FLO.  At 16mm eye relief they should be a lot more comfortable to use than the NPLs.

https://www.firstlightoptics.com/ursa-major-eyepieces/ursa-major-fmc-flatfield-eyepiece-75mm.html

[John]

NPL's are plossls. Plossls and orthos have eye relief that is around 75% of their focal length. 

Luckily for us today there are plenty of designs that offer much longer eye relief but there are usually additional glass lens elements involved in achieving that, so additional weight.

I have a 4mm HD ortho which has eye relief of 2.7mm I believe. I do use it very occasionally but never for long to be honest. Optically it's excellent but I soon get tired of trying to hold that tiny exit pupil while tracking and the AFoV is just 40 degrees. 

Even the Nagler 4mm-2mm zoom seems comfy after using the 4mm ortho !

 

 

Edited May 3 by John

[Paz]

1 hour ago, John said:

NPL's are plossls. Plossls and orthos have eye relief that is around 75% of their focal length. 

Luckily for us today there are plenty of designs that offer much longer eye relief but there are usually additional glass lens elements involved in achieving that, so additional weight.

I have a 4mm HD ortho which has eye relief of 2.7mm I believe. I do use it very occasionally but never for long to be honest. Optically it's excellent but I soon get tired of trying to hold that tiny exit pupil while tracking and the AFoV is just 40 degrees. 

Even the Nagler 4mm-2mm zoom seems comfy after using the 4mm ortho !

I guess those 8mm NPLs will be about 6mm eye relief, I feel a bit queasy even thinking about 2.7mm eye relief! 

[Ags]

2.7 mm is all eye and no relief!

[NGC 1502]

BST Starguider do an 8mm. I have used one and found it excellent, especially considering the price.

[John]

The odd thing is that you don't hear any complaints about eye relief from owners of Zeiss ZAO ortho, TMB Supermonocentric or Pentax XO eyepieces, which are very tight in the shorter focal lengths. Presumably the optical performance of these legends is so good that the effort required to use them is worthwhile 🙂

[stormioV]

I use 8mm BST Starguiders in Binoviewer and for me they are great, no problems with merging or eye relief and they are very comfortable, observing with these is effortless.

[Don Pensack]

4 hours ago, John said:

The odd thing is that you don't hear any complaints about eye relief from owners of Zeiss ZAO ortho, TMB Supermonocentric or Pentax XO eyepieces, which are very tight in the shorter focal lengths. Presumably the optical performance of these legends is so good that the effort required to use them is worthwhile 🙂

They are used only for planets or close double stars, so the eye is held back far enough the field size is reduced.

Only recommended in scopes that track.

[John]

5 hours ago, Don Pensack said:

They are used only for planets or close double stars, so the eye is held back far enough the field size is reduced.

Only recommended in scopes that track.

I had the TMB Supermoncentric 5mm for a while. Superb high power eyepiece but with a ~30 degree AFoV and around 3.5mm of eye relief, challenging to use with my undriven scopes. The University Optics HD 5mm ortho that I also had at that time was as good under moderate to normal skies but the TMB SM showed just a little more under better skies, which means around 15% of the time.

These days I'm happy to sacrifice a little in performance for comfort 🙄

 

Edited May 4 by John

[NGC 1502]

3 hours ago, John said:

These days I'm happy to sacrifice a little in performance for comfort 🙄

 

 

Comfort is a very important point, more especially as you get older, also convenience is a big factor.

If your scope is easy to set up, comfortable in use, your eyepieces are not challenging to get a good view then you’re much more likely to take advantage of any clear skies.

 

[Louis D]

Do you already have a Barlow element somewhere in the optical train with your BV?  I find the SVBONY 68° Ultra Wide Angle to be very comfortable with eyeglasses.  With the optical element of the Meade 140 2x Barlow screwed into the nosepiece of my Arcturus BV, I get a 3x result.  Thus, the eyepieces operate at 20/3 = 6.7mm.

 

[Mr Spock]

I have a 4mm Circle-T ortho. Surprisingly easy to use (for me) though these days I use my 4mm TOE as that has a wider fov and even wider still the 4mm Nirvana.

If you want 8mm the 7mm Nirvana actually measures 8mm  Lovely sharp eyepiece and every bit as good as an SLV.

[Highburymark]

The wider eye lens on the XO makes it more comfortable than a similar plossl or ortho, even though the eye relief is under 3mm. I almost never see the field stop when I’m using it, just hang back a little and use it mostly on a tracking mount as Don suggests. The TOEs (and I presume the HRs?) are obviously more comfortable though, with 10mm eye relief. 
I think it makes real sense at these higher powers to keep at least one specialist planetary eyepiece along with a widefield or two. The two options complement each other perfectly, and allow you to go deeper when conditions permit. 

[Paz]

3 hours ago, Louis D said:

Do you already have a Barlow element somewhere in the optical train with your BV?  I find the SVBONY 68° Ultra Wide Angle to be very comfortable with eyeglasses.  With the optical element of the Meade 140 2x Barlow screwed into the nosepiece of my Arcturus BV, I get a 3x result.  Thus, the eyepieces operate at 20/3 = 6.7mm.

 

I would use an 8mm pair with either a 2.6x gpc with refractors or a 1.7x gpc with the VX14. It would only be used where I'm using my 10mm SLVs and feel the conditions would allow more, which isn't often but it can happen, particularly with the VX14. With that scope 8mm eyepieces would get me to 340x but still giving a 1mm exit pupil!

[Paz]

On 04/05/2024 at 08:25, NGC 1502 said:

BST Starguider do an 8mm. I have used one and found it excellent, especially considering the price.

21 hours ago, stormioV said:

I use 8mm BST Starguiders in Binoviewer and for me they are great, no problems with merging or eye relief and they are very comfortable, observing with these is effortless.

Thanks you thusbhas reminded me that I have one of these lying around that I got years ago to fill this gap in the SLVs when I was only observing cyclops, I had forgotten about it. It has been languishing in a box as I couldn't cope with having one eyepiece different to the rest (pathetic I know).

I can get another one of these to make a pair.

[Louis D]

2 hours ago, Paz said:

I would use an 8mm pair with either a 2.6x gpc with refractors or a 1.7x gpc with the VX14. It would only be used where I'm using my 10mm SLVs and feel the conditions would allow more, which isn't often but it can happen, particularly with the VX14. With that scope 8mm eyepieces would get me to 340x but still giving a 1mm exit pupil!

Are you sure about that exit pupil size?  I looked up the VX14, and it is claimed to be an f/4.6, making your exit pupil 8/2.6/4.6 = 0.67mm.  That is doable for me with BVs, but not in monovision due to my prodigious floaters.  1mm is doable for me in monovision.  It's sort of like a cliff-edge just beyond 1mm with my floaters.

[Paz]

43 minutes ago, Louis D said:

Are you sure about that exit pupil size?  I looked up the VX14, and it is claimed to be an f/4.6, making your exit pupil 8/2.6/4.6 = 0.67mm.  That is doable for me with BVs, but not in monovision due to my prodigious floaters.  1mm is doable for me in monovision.  It's sort of like a cliff-edge just beyond 1mm with my floaters.

I only have a 1.7x gpc to use with the VX14, the 2.6x gpc I only use in refractors.

I'm the same re floaters, at smaller exiit pupils binoviewers are fine but cyclops gets a bit murky.

[globular]

My 1.7x gpc actually measures more like 1.4x.  If it's the same for you then you're probably getting 8/1.4/4.6 ≈ 1.25mm exit pupil.

[Paz]

I got another 8mm BST in the end and having tried it with my other one in the binoviewer all is well, without glasses on I can hover just off the eyepieces which is what I prefer and still see both field stops and merge the image.