32mm & 40mm Exits?

[Charic]

The brains aching again, and too many choices? I`m after a 2" 32mm or possibly the 40mm Eyepiece. Its going on the Skyliner  200P f/6 and  I`m thinking price wise on the lines of GSO Superview, TMB Paragon.

But there seems to be many concerns, that the eyepiece exit pupil size, can exceed the input pupil size for your eye, producing less than perfect results, on certain eyepieces depending on age, and therefore I should use a 6mm exit due to my age? does it really matter!

I see it that If you have the full 7mm (the average!) then you have full range, as the MK1 Eyeball is fully automated, and controls its own input requirements, its not fixed, but variable.

No matter what you look at, if its bright, your own eye is going to pinpoint to reduce the light levels, especially  if your  looking at  the Moon without any filtering.  Surely, if you only select a lens with an exit pupil to match your age, which could be smaller still as you get even older,  then is it not possible to miss out on  performance when conditions will allow, because of the self imposed restriction. I`ve had 7x50 binoculars (EP 7.14mm) since 1995 and never once thought that they are any worse now than  before.

That said, Im looking into buying a 30mm or 40mm lens from  either GSO, TMB Paragon, Revelation, Maxvision, and loads of others that I think of.  Should I be worried that the exit pupil on a 42mm is 7mm for my age.  Probably not.  What is of concern is the wide-field edge distortions with some of these lense on the f/6 200P.

So Should I  be overly concerned on the Exit Pupil size , as were all different and see differently, I`m eager to learn more.

And what lenses do you use, or recommend.

keeping the prices to below £70 if possible. GSO Superviews keep entering my mind.

[John]

Personally, I try and keep the exit pupil below 6mm, probably because of my age - I'm 53.

I think all the eyepieces you list will show some astigmatism at F/6 but some much less than others. The Paragon's are out of production now but the Skywatcher Aero ED's contain the same optics and they are pretty good at F/6.

I've tried 3 of the GSO Superviews (same as the Revelations) and found them OK at F/10 but pretty messy (ie: distorted stars) in the outer 30% of the field of view at faster focal ratios. They are cheap though.....

The Aero ED / Paragon's are much better. And, surprise, surprise, they cost more. I've not used a Maxvision so can't comment on those.

On the basis of the above, my recommendation, for what it's worth, would be a 35mm Skywatcher Aero ED. It will show a decent 2 true degrees of sky with the 200mm F/6 and maintain a usable exit pupil of around 5.8mm.

Others will differ no doubt 

Edit: I see I've exceeded your budget. Sorry about that but I'll stick to my recommendation I think. 

[Charic]

Cheers John, more lenses to investigate.

After further study, I now understand why getting the maximum amount of light to the eye is crucial. The larger the exit pupil, the more light and the  brighter the image is to the eye.  If the the exit pupil is larger than the eye pupil, then not all of that light from the exit pupil can enter the eye, and the performance of the telescope will be reduced, or so they say?

Exit pupil varies  according to magnification (telescope fl/ Eyepiece fl ) in use. If insert a 40mm EP, I will get a little over 6mm Exit Pupil.  If then, my eye can only dilate to 5mm then effectively, its me that's reducing the performance of what's available from the telescope, not the actual  performance of the telescope itself. The next person to arrive and view may have an eye pupil of 6mm,   therefore a perfect match for maximum transfer of light for them.

But with my eye pupil at only 5mm (example) this equates  to me  now using a 30mm lens even though a 40mm is fitted,  and a reduction of brightness and clarity to my final image (as seen by my eyes only) due to my own eye pupil unable to take in the full exit pupil beam. For this reason, that is why its often referred to balance and match the exit pupil to your age related eye pupil.

Finally, I may  still go near the extremes, and probably end up with a little more exit pupil than I personally  require, knowing that the next person to view in the group, may have better eyesight than mine, and would still be able to receive the full potential of what's available.

There must be an easier subject hobby  without so many reactions to an action? Lol.

[rwilkey]

I think the exit pupil affects people variously depending on age, I think the older you are, the less bothersome it is.  I often see younger people - 40 years old and less - complain about the affects of exit pupil on thier viewing.  From a personal point of view, my dilation is around 7mm I think when fully dark adapted, which effectively means the exit pupil has little or no affect on me (I am 63).  I think this is pretty good for my age.  What bothers me more is too little an exit pupli (less than 1mm) at high mags.  Having said (rambled) all this, I prefer exit pupils around the 1mm to 6mm range as best for me.

[boyfromlincs]

im 53 and use a 35mm 2 inch ep in my 200p f6 and its fine with 5.8 exit pupil, luckily i had a good mate who leant me one first to try as like you i was worried it wouldnt work..

[bingevader]

Any chance that you can try some to find an optimum for you?

Or measure your pupil size with the drill bit technique? Never knew it existed, not sure how you'd do it at night!

My 32mm PanaView is great in my humble opinion, soft round the edges, but only slightly over budget.

Or blow it completely and get the 40mm Maxvision!

Cheers

[bambuko]

There is a lot of interweb/forum wisdom on this (and many other) subjects.

If you have no choice but to rely on it that that's fine, but you get what you pay for (usually) and bear in mind interweb advice is free

The answer is simple (if possible) - try it and see what you like and if you like it forget what others say!

This subject (like a lot of things when it comes to observing) is very much a matter of personal preferences, as well as dependant on your own health/condition.

So me telling you that I (and old fart) enjoy very much what is not supposed to be possible because of my old age and deteriorating health doesn't prove anything and offers little guidance for you.

I was lucky in having a friend who let me try his 2" eyepiece in my scope (thank you Martin) before I blew my money on SW PanaView (and I love it).

[Rustysplit]

There is a 40mm Aero on ABS at the moment for £89. Nearly in your budget and allowing for the larger exit pupil, a pretty good widefield/finder ep maybe.

Not mine I hasten to add.

[Charic]

Thumbs up for the replies so far......... Ive had a look around the web for some 32mm lenses. I've also become aware that my darkest skies will be about a 60 mile round trip in the car, so not expecting too many of those in a Month, whereas my local darker site is about 10 miles round trip. Due to those facts, and  keeping uniformity of  lens fittings, I`d like to stay with the 1.25"  format and have the  lenses listed below in mind. My 26mm BST~SG is ok, but something a liitle wider is needed for M31. I did have a TV32 on the list, but at about £100,  that's out of my self imposed price threshold. 

GSO  Plossl Eyepiece  - 32mm 1.25"  52° afov

Revelation Astro  Plossl Eyepiece  - 32mm 1.25" 52°afov

Meade Series 4000 Super Plossl Eyepiece  - 32mm 1.25" 52° afov

I`m still open to advice on other 32mm EPs around the same prices, but those listed here are top of the list until proven otherwise?  At Present my only option to try before buy  is to get something from skies_unlimited!  I`m hoping someone has one of these lenses on  their  200P  f/6 to offer some advice on their performance. 

[Charic]

....... Just been messing about with Stellarium and the difference between 26mm and 32mm isn't  as much as I thought it would be, to be honest, And I`m assuming Stellarium depicts the best viewing conditions? I lose a bit of FOV ( AFOV is 60° & 52°) and only about 3 stars are depicted as missing? Jump to a 40mm and difference is noticeable! FOV still smaller than the 26mm but more visible objects. Maybe I should jump ship too and bung in the 2" 40mm. Decisions decisions. 

[Charic]

......The Sky-watcher SP Plossl 32mm looks like  great value for about £30 GBP but the 50° afov is too little compared to the 60° AFOV afforded by my BST`s. I've looked at GSO, TV, Agena, SW Aero, Maxvision, Meade and still unsure as to what to buy next . I've been looking at your signatures to see if there is a favourite, but there  doesn't appear to be one that stands above the rest. I want to keep the price down £50-£80 seems reasonable to me. Its an f/6 reflector (f/5.91) and from a normally light polluted observing site. The BST 25mm doesn't  quite encompass M31, or Pleiades so something in the 32mm range for occasional use is what I'm after. There's just too many decisions. 

However, I may have come to a conclusion,  and now leaning towards the Skywatcher Panaview 32mm. Now where's  the cheapest ?

[cantab]

With an obstructed scope, too large an exit pupil and the secondary shadow becomes visible and can be a touch annoying. I can clearly see it with the 25mm eyepiece, giving a 6.3mm exit pupil, in my Heritage. It's less noticeable, but there if I look for it, with a 5 mm exit pupil. I don't know how much the size of the obstruction affects it, but I'd think twice before getting an EP giving a 6 or 7 mm exit pupil.

[Charic]

Almost decision time. My Skyliner 8" f/6 needs a wide view, this is my final list (I think). Where would you put your money?

32mm Skywatcher PanaView 2" EP 

33mm William Optics SWAN 2" EP 

32mm Sky-Watcher SWA 70° 2" EP 

35mm Skywatcher Aero ED SWA 2" EP

30mm GSO 2" SuperView EP 

[Moonshane]

from my perspective, the issue with larger exit pupils is more about darkness of sky than anything else. if you have any light pollution then the sky is quite washed out with an exit pupilof more than 5mm. this is less of an issue with little or no LP.

M31 is about 2.5 degrees across so you will struggle to get this into your scope although the bulk is not visible with eyes anyway. my own preferred minimum (maximum) field is 1 degree. with that the vast majority of dsos can be easily fitted into the view. this also creates darker background sky so objects appear to have more contrast.

[John]

Of the ones you list, I'd go for the Aero ED. I've owned the 30mm and 40mm and liked those so I don't see why the 35mm would not be pleasing too.

[YKSE]

+1 for Aero ED.

I once had a TS 38mm SWA 70°,which might be clone to some  70° SWA in your list,  the astigmatism in the outer area was just too much to my eyes in f7.5 80ED.

[Charic]

+2 for the Aero's, many thanks,  but I have decided on the 32mm Skywatcher PanaView 2" EP  from SGL-FLO. Just ordered. Now where's my umbrella?

[Special K]

This is an old thread but bang-on topic for my next step into a widefield EP for my ED80. I've been reading up a great deal about Pupil Exit, % of surface brightness, etc, and am really leaning toward the 35mm Aero. There's a limited budget and don't want to exceed ~£130. The 35mm TV Panoptic is the same dimensions and would be heavenly but much too much of a stretch at this point! I'm also in the uncomfortable position of only having a 1.25" UHC filter, so might be facing an expense for a 2" filter due to the new EP and what I want to use it for. I'd stick with 1.25" but there isn't so many to choose from.

My reckonings are:

I'm keen to get some success with larger DSO's (as well as other advantages of the widefield viewing in general) and understand that an EP will capture the surface brightness of an object calculated as the Pupil Exit provided in the EP squared, times 2. Thus a 7mm exit would give nearly 100% light transmission of the object brightness, the same as the human eye. However, as I have moderate light pollution, want a bit more magnification, and am getting older, a 7mm exit is not practical. Apparently, the best focal range for the eye is between 2 and 3mm, or 2.4 specifically. My 17mm Hyperion is close to this optimum which must be why it does so well in the scope. However it only provides 10% surface brightness at 35x. A 35mm EP would give a theoretical 44% surface brightness at 17x and a nice wide 4 degrees of sky. Pupil Exit would be 4.7 which is well under 5, which seems appropriate.

I've looked into the classified ads and external resources and not surprised to see a real shortage of widefield EP's for sale! So it looks like the contenders:

Baader Aspheric 31 or 36mm........I don't like the funnel shaped adaptor for 1.25! Nicely priced, however £122

SW Panaview 32mm....reviews indicate significant astigmatism towards the edge. Cheaper at £79

Televue Plössl 32mm......interesting alternative. I suppose the only downside is the 50 degree AFOV. £110 is a good price for TV quality.

Meade 5000 SWA 34mm.........nearly as much as the TV Panoptic so would just go for that. £288

WO SWAN 33mm.......nice price for £99. Not sure it has as good reviews as the Aero?

Am I missing anything obvious? Hopefully I'm on the right track with the whole surface brightness thinking. If this is correct, then I'm shocked by the low percentages I've been working at! My 5mm will yield just 1% surface brightness, which is too low for the galaxies I've been pointing it at.

[John]

I have moderate light pollution as well and find a 21mm eyepiece more effective than a 31mm on fainter deep sky objects because I get a darker background sky. I've owned 35mm and 40mm eyepieces (even a 50mm once !) but found the sky generally too washed out for them to be of much use in any of my scopes. With my fastest scope, (12" f/5.3) the 31mm eyepiece gives me a 5.8mm exit pupil at 51x and the 21mm a 3.96mm exit pupil at 76x.

I'd have thought your 130mm newtonian would have been the best bet for deep sky objects ? - it gathers a lot more light than the 80mm does.

[rwilkey]

Any chance that you can try some to find an optimum for you?

Or measure your pupil size with the drill bit technique? Never knew it existed, not sure how you'd do it at night!

My 32mm PanaView is great in my humble opinion, soft round the edges, but only slightly over budget.

Or blow it completely and get the 40mm Maxvision!

Cheers

Hi Ben & Charic, the PanaView 32mm ep is a good, tried and tested ep at both f/6 and f/5 and I think you will find it pleasing, views better on axis but should work exceptionally well at f/6 in my opinion.

[bingevader]

Hi Robin, yep, been using mine for a couple of years now and would be hard pressed to replace it unless something came up very cheap second hand.

However, 

Am I missing anything obvious?

Yep! If you're considering the Meade SWA, then have you looked at the Maxvision equivalent?

If 68° is okay, then these have had super reviews and are around £95.

Cheers.

[Special K]

I have moderate light pollution as well and find a 21mm eyepiece more effective than a 31mm on fainter deep sky objects because I get a darker background sky. I've owned 35mm and 40mm eyepieces (even a 50mm once !) but found the sky generally too washed out for them to be of much use in any of my scopes. With my fastest scope, (12" f/5.3) the 31mm eyepiece gives me a 5.8mm exit pupil at 51x and the 21mm a 3.96mm exit pupil at 76x.

I'd have thought your 130mm newtonian would have been the best bet for deep sky objects ? - it gathers a lot more light than the 80mm does.

Thanks John, and think I'm starting to understand the contrast implication: I compared the view in the 28mm to the 17mm tonight and noticed the brighter background in the 28. The 21mm you find more effective wouldn't happen to be the Ethos would it?!