Revelation 32mm Kidney Beaning

[chrisdg1968]

Just purchased one of these primarily for low power / wide field in my 150 dob. But find myself bit disappointed in having to get my eye in a very correct position to avoid kidney beaning, wasn’t expecting it....I used to have a gso 32mm with my old 200 dob (same focal length ‘scope) and don’t remember any such issue then?  Any thoughts ?

Chris

 

 

[Ruud]

Kidney beaning or blackout? The first is rare in modern designs.

There's also vignetting.

 

When the eye relief is very big, eye placement becomes a problem. There's no feedback from your eye socket touching the eye cup. As a result your head will float about over the eyepiece. This causes vignetting and blackout.A higher eye cup will help you bring your brow or cheek  in contact with the eyepiece . Sometimes it is just a matter of getting used to an eyepiece.

Vignetting makes you lose the edge of the field. With blackout it is as if a curtain is drawn over the view and the whole view disapperas.

Kidney beaning is very specific. A bean-shaped part between the edge and the centre of the view disappears. See the bean on the Moon above. It is caused by spherical aberration of the exit pupil (which does not effect sharpness, btw).

Edited January 25, 2018 by Ruud

[chrisdg1968]

Thanks for your input Rudd, makes me thing it’s probably vignetting.  The Revelation does not have a very high eyecup so I suppose just need to persevere with getting me eye at right distance.

[Ruud]

Do you sit or stand while observing? If you sit it is easier to keep your head still. I have a hight adjustable stool. The seat screws up and down, like a drum stool. It cost only €20 and made a world of difference.

[chrisdg1968]

I’ve got an ironing stool I use for the dob Ruud.

Edited January 25, 2018 by chrisdg1968

[Ruud]

An ironing stool is fine! 

A bit of practice will have to do the trick then. I think that once you are used to it you will love the spacious eye relief. Happy observing!

[25585]

Bean there (sorry!). At least it's not a TV, which brand has had high cost & profile eps with kb and eye placement issues. 

 

 

[John]

5 minutes ago, 25585 said:

... At least it's not a TV, which brand has had high cost & profile eps with kb and eye placement issues. 

 

 

But they do provide pupil guides with the models that are most sensitive to this.

[25585]

31 minutes ago, John said:

But they do provide pupil guides with the models that are most sensitive to this.

That is true, but such now seems almost an anachronism now, a cheap solution to aid acceptance of a design shortcoming. 

I remember some Radians I had & also trying a friend's T4 Naglers, which all needed pupil guides. Those experiences were, apart from my Panoptic 35, what have disinclined me to buy any more TV, though a 41 Panoptic is one I may get some day, if I can find a Barlow interface first (they have disappeared from the market). 

[John]

1 hour ago, 25585 said:

That is true, but such now seems almost an anachronism now, a cheap solution to aid acceptance of a design shortcoming. 

I remember some Radians I had & also trying a friend's T4 Naglers, which all needed pupil guides. Those experiences were, apart from my Panoptic 35, what have disinclined me to buy any more TV, though a 41 Panoptic is one I may get some day, if I can find a Barlow interface first (they have disappeared from the market). 

I found the Radian's and Nagler T4's quite straightforward to use without needing to use the pupil guide. The 22mm T4 was a lovely eyepiece - my favourite Nagler I think.

I'd steer clear of Tele Vue eyepeices if they don't suit you though. There are other decent options around

 

 

 

 

[Ruud]

The first Naglers (1980s) had spherical aberration of the exit pupil (SAEP). They were also the first commercially available UWAs that were sharp across the entire field.  I still have one: the 4.8 mm.

The smaller the exit pupil, the less problems you have with kidney beaning from SAEP. That's why I only got the 4.8 mm. That's a zero problem eyepiece even at f/5 when its exit pupil is 1.2 mm wide. I've never seen a kidney bean in it, even at daytime.

With larger exit pupils, say 3 mm and larger, kidney beaning did occur in the first Naglers, especially on sunny days when the observer's pupil got narrower.

In spite of their SAEP, the first Naglers were well received. Then already, they were the best around. NaglerT2 addressed the kidney beaning issue, T4 is a small series with long eye relief and very little AMD. A special series. Bulky though, and not everyone was prepared for a combination of ultra wide and long eye relief. The eye relief problem comes from having the eye hover over the eyepiece, missing the exit pupil from time to time. This you can see in the post above. The problem disappears with practice and if you have no control over it, a different eye guard will probably help.

The wide angle issue occurs when you want to scan the entire field of an UWA eyepiece. For that you eye has to move. This is needed because while turning your eye from 41° left via straight forward to 41° right, the pupil changes position, and you need to compensate for that. It must stay on top of the exit pupil.

You can see that here. The centre of the eyeball has to move from left to right as the eye scans from right to left.

That some people need an eye guard for long eye relief eyepieces is not a design fault of the eyepiece. It's a motor control issue of the observer  that can be remedied by an eye guard or practice. That the problem existed for some observers only became apparent after such eyepieces became widespread.

Try before they buy and be prepared that you may have to get used to a new eyepiece. Having to keep your eye still enough and having to move it as well can be a bit tricky, but it can be learned!

Here's the source file for the animation above: glasses and UWA.ggb
To open it and play with the sliders you need to download the free app Geogebra from https://www.geogebra.org

[25585]

@Johnand @Ruudthank you. I would like to try some more to disprove my pessimism. But where & how to try a range. Last time I had a Nagler, I was the only person at my AS with such an expensive ep. Nobody wanted to buy it, too dear even at my nice pre-owned price. ?

Since then as John says, there are other makes, and I have great eps, but the disillusion with TV WA eps has stayed with me, and made me cautious to go over 70 deg AFOV (used to be 50, but then Vixen and Pentax became known to me). Are Delites better on eye ease than Delos?

 

 

[cloudsweeper]

I really like my Rev Superviews - 30 and 42mm - for the WA views they give, esp. in the fast 'scope.  It's just a question of getting used to using them.

For the price, they are perfectly serviceable EPs, unless an observer insists on sharp images right to the edges.

The 42mm is a bit more sensitive to eye positioning, but I did have the 50mm, and that one was tricky to use!

Doug.

[Louis D]

Kidney beaning (SAEP) is pretty much confined to negative/positive designs with poorly matched sections.  The Nagler T1s and Radians both had it.  The 6mm and 9mm Expanse type eyepieces have it, and most of the original Celestron X-Cel eyepieces had it.  A positive-only design can't really produce SAEP.  I'm pretty sure the Revelation to which you refer is positive only and so probably cannot have SAEP.  You're probably just having issues with the long eye relief and large exit pupil as described by others here.  I find sitting and keeping a light touch on the focuser or tube can help steady my alignment with the eyepiece's exit pupil to prevent blackout.

[daslolo]

On 25/01/2018 at 13:40, Ruud said:

Kidney beaning or blackout? The first is rare in modern designs.

Animated diagrams! So nice!

It looks like a result of the eyepiece design, is there a thing I can do besides a longer eyecup to get feedback?  I am getting severe kidney beaning with very wide AFOV eyepice (Meade 607018, 100 Degree, MWA 21MM, 2-Inch).

 

Edited February 14, 2020 by daslolo
trimming the quote

[Ruud]

Oh yes, a longer eyecup giving tactile feedback would certainly help. It would help you keep your eye still in the right position for all light to get in.

A wide pupil also helps. For this reason, eyepieces that have spherical aberration of the exit pupil (SAEP a messy exit pupil like in the kidney bean animation) are generally poor for daytime usage.

The larger the exit pupil, the more of a problem SAEP becomes. I have a short focus eyepiece with SAEP (original Nagler 4.8mm) that never causes kidney beaning because its exit pupil is so small.

[daslolo]

7 hours ago, Ruud said:

Oh yes, a longer eyecup giving tactile feedback would certainly help. It would help you keep your eye still in the right position for all light to get in.

A wide pupil also helps. For this reason, eyepieces that have spherical aberration of the exit pupil (SAEP a messy exit pupil like in the kidney bean animation) are generally poor for daytime usage.

The larger the exit pupil, the more of a problem SAEP becomes. I have a short focus eyepiece with SAEP (original Nagler 4.8mm) that never causes kidney beaning because its exit pupil is so small.

Gotcha and small exit pupil = less light output, right? So if I understand, for someone who wants to observe faint objects, the longer eyecup and wide exit pupil like this beany Meade eyepiece is the best option.

I googled around for 20mm eyecups but didn't find anything. Do you have a source? 

These have the perfect length: https://www.amazon.com/gp/product/B07MJ9GS91/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

[Stu]

2 hours ago, daslolo said:

Gotcha and small exit pupil = less light output, right? So if I understand, for someone who wants to observe faint objects, the longer eyecup and wide exit pupil like this beany Meade eyepiece is the best option.

I googled around for 20mm eyecups but didn't find anything. Do you have a source? 

These have the perfect length: https://www.amazon.com/gp/product/B07MJ9GS91/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

I made eye guard extensions for Celestronn Omni Plossls from hobby foam and insulating tape which works very well. They are adjustable up and down, but actually don't need to be too high to allow you to feel where they are enough to keep you eye positioning correct.

[Louis D]

17 hours ago, daslolo said:

Animated diagrams! So nice!

It looks like a result of the eyepiece design, is there a thing I can do besides a longer eyecup to get feedback?  I am getting severe kidney beaning with very wide AFOV eyepice (Meade 607018, 100 Degree, MWA 21MM, 2-Inch).

 

Definitely SAEP.  I had heard the MWAs were susceptible to it, and this pretty much confirms it.

As long as your eye's iris is fully dilated, you probably won't notice it.  However, this rules out using it in the daytime, for solar observing, lunar observing, at twilight, in a heavily light polluted area, or shortly after leaving a lighted area for a dark observing area.  I also recommend staying back a bit and not trying to take in the full view to the field stop.  I find the 12mm and 17mm Nagler T4s have some SAEP and have learned to deal with them in this manner.  That, and I replaced them with 12mm and 17mm ES-92s which completely lack SAEP. 😄

[daslolo]

16 hours ago, Louis D said:

12mm and 17mm ES-92s which completely lack SAEP. 😄

We are promised clear sky on tuesday, I'll see if my pupils dilate enough.

92 degrees with no beans! that's amazing, and I see priced accordingly 🙈

23 hours ago, Stu said:

I made eye guard extensions for Celestronn Omni Plossls from hobby foam and insulating tape which works very well. They are adjustable up and down, but actually don't need to be too high to allow you to feel where they are enough to keep you eye positioning correct.

 

Is nice, I'll try that with my binos.

My eyes won't line up on this pair of celestron you have, same deal with the linears but the eyes work fine with astromania binos with included 33mm though ... I need to collimate my eyeballs, if only I could fine my M1 screwdriver

[John]

10 hours ago, daslolo said:

We are promised clear sky on tuesday, I'll see if my pupils dilate enough.

92 degrees with no beans! that's amazing, and I see priced accordingly 🙈

 

 

The ES 92's are rather nice but also rather large and heavy !. The 17mm is the heaviest eyepiece that I currently own at 2.87 lbs / 1.3 kg:

 

[daslolo]

7 hours ago, John said:

The ES 92's are rather nice but also rather large and heavy !. The 17mm is the heaviest eyepiece that I currently own at 2.87 lbs / 1.3 kg:

 

11.5# for the 9" OTA, 3# for the eyepiece, 0.5# for the diagonal and 2" tube = 15# with a capacity of 14# on the main, this mount is going to love me 😁

I won't spend $500 on an eyepiece so instead I spent $300 on the 82 degree 18mm version, let's see if I like it

[daslolo]

The ES82 are amazing

No beans, true wide field of view that's not sensitive to eye position, very bright, how do they do it that others don't?!

[daslolo]

On 25/01/2018 at 17:00, John said:

I'd steer clear of Tele Vue eyepeices if they don't suit you though. There are other decent options around

Do you have a list? 

ES82 are uneven in quality.

Edited May 9, 2020 by daslolo
Redundant

[John]

23 hours ago, daslolo said:

Do you have a list? 

ES82 are uneven in quality.

Don Pensack's Eyepiece Buyers Guide may be useful:

https://www.cloudynights.com/topic/700069-2020-eyepieces-buyers-guide/?p=10080606