Finally on the TV firm

[Moonshane]

This is a good point Shane. I find particularly that picking out E & F Trapezium needs an eyepiece that is "just right" and that can vary from night to night. Too much or to little power just does not seem to work with those pesky little blighters

very true John. the differences in view must be something to do with the differences in magnitude and the angular separation vs exit pupil I expect. to be honest though I'm starting to nudge toward the cliff top of ignorance.

I have also found that looking at the moon and then turning straight to the Trapezium can sometimes yield the sixth star - again related to size of pupil presumably. We are a bit off topic now I suppose (although this thread has probably covered every possible topic on its long and winding road!). I'm sure Nick won't mind....

[spaceboy]

Makes no odds to me guys. TBH I'm guessing anyone new to the thread may have given up reading by the 3rd page anyway

[CGolder]

I find when i look at the sun and then look at something else i can still see the sun (not through a telescope i would add)

[spaceboy]

LOL

[Adz]

Reading up a lot and what have been said above, I was thinking of re assembling my EP line up.

Get a 13mm ethos, low mag say my current 35mm Pan and then a selection of high mag BGO's.

What do people think?

[Moonshane]

when you say a selection of BGOs, what were you thinking Adz?

I ask because I really like my 6-3mm Nagler zoom and at your scope's focal length this would work well I think giving from 200x - 400x. Used this might be the cost of 4 used BGOs (although that would be 5,6,7,9mm) and with a wider field and better eye relief (ignoring the zoom benefits).

[spaceboy]

The 35 Pan would continue to sit nice as your low power EP. The 3-6 zoom as it is a superb EP but the exit pupil and x400 magnification at 3mm would mean you rarely get to use the full range of the zoom and in comparison I feel the BGO's offer far better images than the Nag anyway. You could use a 5,6,7mm BGO for planetary and save your self a few quid on the cost of a 3-6 zoom. The 13 Etho at x92 would then be a good work horse for most DSO's. The only other thing to consider then is balancing the scope as the Etho, Pan and gravity will love each other while the BGO's not so much so.

[Moonshane]

I don't disagree about how good the BGOs are but the exit pupil is not a major issue especially on doubles. I use my 6-3 zoom on double stars regularly at 350-400x and in my 6" f11 scope. on my scope the exit pupil would be about 0.36mm at 400x (4mm on zoom) vs 0.5mm at 400x (3mm on zoom) on the 8" f6 so I doubt exit pupil would be an issue?

[John]

Do you folks get problems with "floaters" when you use eyepiece / scope combos with a very small exit pupil to view the Moon ?. I know I do - it must be my age

PS: I only raise the topic as it's one of the few that has not been mentioned in this thread yet

[Moonshane]

I do actually but it's usually bearable. Observing the moon is also a good test of whether or not your eyepieces need cleaning!

[CGolder]

The worsed thng happened to me tonight... i fell in love with my ethos lol i didnt really get naglers over panoptics but that 100 degrees is not wasted and the er is perfect too... swttched back to the pan and felt like i was looking in a plossl... oh ****

Sent from my A101IT using Tapatalk

[Stu]

I get problems with floaters when observing jupiter at high mag with a small exit pupil, around 0.6 mm. Not sure there's anything you can do about it, bino viewers are supposed to help but I don't seem to get on with them.

Was going to start another thread on this but as this is now a cover all topics thread I'll ask it here.....

There is alot of emphasis put on exit pupil by forum members when choosing lenses and I wanted to clarify something. Is it better to choose a lens which gives an exit pupil which definitely fits within a normal dark adapted pupil size, or is it potentially better to go for a slightly oversized exit pupil? It seems that with a smaller exit pupil you are effectively wasting some of the area of the retina so that may reduce sensitivity to the very faint objects, or would this end up wasting photons by letting them fall outside the retina? Common wisdom on the forum is keeping below around 6 mm so I suspect I know the answer but am interested to hear views.

Stu

[Moonshane]

Hi Stu

I am pretty sure that there is a 'best' exit pupil depending on what you are observing. E.g. for faint objects you really want to make the most of your pupil/aperture and match the exit pupil to your own pupil size where possible.

For things like planets, lunar detail and double star splitting you are really trying to get more resolution from the object and therefore a smaller exit pupil will be better 'focused' on the central part of the eye (Fovea centralis - Wikipedia, the free encyclopedia) and by definition more magnified which is going to provide more detail/better splitting of stars etc.

This makes logical sense to me anyway but I'd welcome comments from people more qualified than I am!

[John]

I've read that some folks select their eyepiece sets mainly by exit pupil rather than magnification. Also, I believe that certain narrowband filters are more effective used with certain exit pupil ranges.

Personally, it seems to make sense to me to keep my maximum exit pupil around 5mm which, from the data I've seen, seems to be the average max pupil dilation under low light conditions, for a person of my age (51).

[Stu]

Thanks both. Interesting link Shane, will read in full when I have more time but a quick scan seems to explain what you are saying re double stars etc benefitting from small exit pupil.

I guess the thing I don't quite get is that because exit pupil is absolutely related to magnification for a particular scope aperture, for a particular magnification, you just have to live with the exit pupil you get, if that makes sense? Eg I would always choose a high mag ep for double stars so would naturally get a small exit pupil. The only way if varying that is by changing scope aperture and focal length which isn't something you can do easily! I guess ultimately that comes down to long term kit planning!

Stu

[spaceboy]

Get a 13mm ethos,

Heads up U.K. Astronomy Buy & Sell

[spaceboy]

There is alot of emphasis put on exit pupil by forum members when choosing lenses and I wanted to clarify something. Is it better to choose a lens which gives an exit pupil which definitely fits within a normal dark adapted pupil size, or is it potentially better to go for a slightly oversized exit pupil? It seems that with a smaller exit pupil you are effectively wasting some of the area of the retina so that may reduce sensitivity to the very faint objects, or would this end up wasting photons by letting them fall outside the retina? Common wisdom on the forum is keeping below around 6 mm so I suspect I know the answer but am interested to hear views.

Stu

Is not the idea of keeping the exit pupil of the EP in line with the size of a fully dilated retina purely so you don't go wasting your money on an eye piece that will not show you more than what your eye will allow. While this makes perfect sense it didn't stop me from getting and enjoying the views I get from the 31mm Nag. My exits range from 3.4, 6.2, 6.5mm which the latter is no doubt a tad larger that the absolute maximum my eye could reach after an Hr under perfect dark skies. Even so I don't feel it was money wasted as the stars are sharp and well corrected giving me a respectable 2.4' FOV in my 200P.

I also feel given modern eye pieces you have to make a personal choice to whether your eyes are upto the task and if you will be getting your monies worth from an EP. An argument that often plagues the Naglers and Ethos is that due to the key hole view you get looking through an EP's lens that your eye can only see 60' of sky before peripheral vision makes the outer stars appear fuzzy so whats the point in any EP showing more than a 68' FOV. Anyone who has a large FOV EP no matter what the make cannot deny that a degree of looking around the FOV is required to take in the view. This itself raises the common issues you often hear about like...kidney beaning & black outs. This is simply loosing the exiting light cone from poor positioning of the retina due to incorrect ER distance, looking around the FOV or both. Sure you can avoid KB & BO's but looking around the FOV still means that an area of the view will suffer fuzzy/ duller star due to some of the light cone bouncing of the side of your iris. I think there is a degree of flexibility to exit pupil and it's down to the user to determine if the views they are getting is worth it. I'm not saying if your in your 90's you should use EP's giving exit pupils of 8mm, I'm just saying it's what works best for the individual while taking in the considerations that your not using the EP to it's full potential. While the 31mm Nag works perfectly in my frak (3.4mm) I would have kicked myself if I'd let pass the opportunity of seeing 2.0' of sky in my 10" dob (6.5mm exit) because my pupil only dilates to 6mm or that I settled for 60' FOV EP's because I have to look around to see the other 25 degrees in my Nags. I'm sure back in the day when plossls were the main stream offering 40-58' exit pupil played a big part but I'm not so sure today ???

[Stu]

Thanks for the post Nick, very interesting. I think you are basically in line with my thinking which places less emphasis on worrying whether the exit pupil is too big and more on getting the magnification and fov that you are after. I too have a 31t5 and think it is a wonderful ep. I also have a 41mm panoptic which gets less use but that is mainly because under light polluted skies it tends to lack contrast because the sky background is too light. Under lovely dark skies it gives fantastic wide field results.

Interesting discussion anyway, thanks all for your input

Stu

[spaceboy]

Don't get me wrong I'm not saying that Exit pupil isn't an important consideration. On shorter FL EP's it can dull the image so much the views are robbed of any contrast and detail. Then as has been mentioned floaters can be an utter nightmare for some of us. I often look like Alastor 'Mad-Eye' Moody trying to move my floaters out the way. I just don't feel it is so much of an issue when using longer FL EP's. You still get to see a vast expanse of sky it's just no brighter than if you were using a shorter FL and most of the time WFOV ep's require you to look around the FOV anyway.

[Stu]

No, that's fully understood. It's important but has to be balanced with other factors too.

I keep coming back to the thought that in most cases, the magnification would stop you using too small an exit pupil anyway ie yes, it would give a dim image but also it's likely that it would be giving you far too high a magnification anyway so would give poor resolution and the quality wouldn't be there even if the brightness was.

At the other end of the scale, how significant are the losses caused by having a slightly over sized exit pupil, and would it cause any negative effects?

Stu

[MjrTom]

At the other end of the scale, how significant are the losses caused by having a slightly over sized exit pupil, and would it cause any negative effects?

Stu

My thoughts on it would be like that say for instance an 8 inch scope using an eyepiece with an exit pupil of say 8mm if your eye can only open to say 5mm, 3mm of light is not focused into the eye.

Therefore you are infact reducing the maximum brightness by 25% which equates to using a 6 inch scope.

If this is not correct, by all means elaborate

[Stu]

That sounds very logical, and most likely correct. Sure someone who knows will confirm

If you use an exit pupil of 4 mm, and your pupil has dilated to 6 mm say, do you actually lose anything because you are not using all the available receptors in the eye, or because all the photons are hitting your eye is there no loss?

Stu

[spaceboy]

At the other end of the scale, how significant are the losses caused by having a slightly over sized exit pupil, and would it cause any negative effects?

Stu

Exit pupils in extreme cases may cause shadowing of the secondary mirror and so rendering the EP useless. A slightly over sized exit could possibly cause reflections as the light is reflecting of your eye ball and not actually entering through the pupil to the retina but the WFOV would often mean your only looking a large OC or dim Galaxies, so the likely hood of it happening is rare. The main reason for keeping the exit to a suitable aperture is so that your eye is making full use of the light available. Too large and the light is wasted along with £££'s. Again the FOV is limited for the same reason but as I said above you have to look around most EP's these days anyway.

[Stu]

Thanks for very detailed responses, all clear now :-)

Cheers

Stu

[spaceboy]

This was an article in Astronomy now which has a nice picture explaining.