2mm Exit Pupil for DSO = Perfection?

[Stu]

10 minutes ago, Stardaze said:

 

I didn't think so, but thought you guys new something I didn't for a moment there 😀

You haven’t met Louis have you?

[Louis D]

1 hour ago, Stu said:

You haven’t met Louis have you?

What a great likeness. 😁

As far as exit pupil goes and wasting light, who cares?  I can use the 40mm on my 127 Mak as well to keep down the exit pupil.

When viewing large, bright open clusters in an f/6 Dob, getting the whole thing into a single view is more important to me than worrying about a few photons crashing into my iris instead of my retina.  When I was showing my daughters and their boyfriends the Pleiades and Collinder 70 over Christmas through my 40mm SWAs (Meade 5000 SWA and Pentax XW in two different ~f/6 scopes), none of them said "Oh my God, stop wasting photons with too large an exit pupil!  Replace those eyepieces with your 30mm ES-82 and APM UFF eyepieces immediately".  They just reveled in the sight of those magnificent clusters.

[John]

I used to have a 40mm Aero ED - very nice eyepiece. I just didn't find it effective for me though because the background sky was just too bright with it. The 31mm Nagler is better in this respect but even that suffers a little so the 21mm Ethos and more recently the 17mm ES / 92 and the 13mm Ethos are my most used DSO eyepieces with my F/5.3 12 inch dob.

The 31mm Nagler works better with my F/6.5 102mm refractor where the exit pupil is under 5mm.

Well that's what I've found anyway

YMMV as they say  

[niallk]

I built my EP set for my 15" dob around a 10E - approx 200x and 2mm exit pupil.  Next 2 EPs were 17mm and 6mm.  Tbh, I change EP based on the target... often higher mag for planetary nebs, and lower mag for greater tfov for larger objects.  But the 10mm / 200x / 2mm exit pupil is a favourite, and does get a lot of use!

[Stardaze]

2 hours ago, niallk said:

I built my EP set for my 15" dob around a 10E - approx 200x and 2mm exit pupil.  Next 2 EPs were 17mm and 6mm.  Tbh, I change EP based on the target... often higher mag for planetary nebs, and lower mag for greater tfov for larger objects.  But the 10mm / 200x / 2mm exit pupil is a favourite, and does get a lot of use!

And did you end up buying the intermediate FL’s in the end, too? So 8mm/13mm. I guess the 13mm is my base too which gives 197x.

[niallk]

Just now, Stardaze said:

And did you end up buying the intermediate FL’s in the end, too? So 8mm/13mm. I guess the 13mm is my base too which gives 197x.

So the base is 17-10-6.  Each of these EPs is excellent, imho.  I added the N31T5 for greatest tfov within an ~upper limit for exit pupil.  Then rather indulgently I added an 8mm... but it is handy to have finer step sizes at higher power.  I don't feel any need for a 21 or 13.

The 6 is great on small planetary nebs, and also for the likes of planets at 330x.  I will really only go observing planets when conditions look good enough for the 8 or 6 mm - I always check the jetstream forecast.  I don't bother if the conditions aren't up to it.

I have a 2x PM, for additionally high power options.  I only use it on the 10/8/6 ... this keeps the weight spread in the focusser reasonable too for balance.

[Stardaze]

1 hour ago, niallk said:

So the base is 17-10-6.  Each of these EPs is excellent, imho.  I added the N31T5 for greatest tfov within an ~upper limit for exit pupil.  Then rather indulgently I added an 8mm... but it is handy to have finer step sizes at higher power.  I don't feel any need for a 21 or 13.

The 6 is great on small planetary nebs, and also for the likes of planets at 330x.  I will really only go observing planets when conditions look good enough for the 8 or 6 mm - I always check the jetstream forecast.  I don't bother if the conditions aren't up to it.

I have a 2x PM, for additionally high power options.  I only use it on the 10/8/6 ... this keeps the weight spread in the focusser reasonable too for balance.

A PM could reduce mine by a couple if I were to replace the 5mm with one. A 10 and 7 would mate well for those planetary high mags. I’m not too bothered about a 3.5mm so I’ll stick to the plan. If I can find a good secondhand E13 later in the year I’ll be futureproofed, which is part of the plan. 

Edited May 9, 2021 by Stardaze

[Don Pensack]

On 07/05/2021 at 11:29, Stardaze said:

 

Well, I'm pretty committed now as the 8mm and 6.7mm have sold..

So my idea of a lineup would be:

30        41x.        6mm ep

20        64x.        4mm 

13         98x.       2.6mm

10        127x.       2mm

7          181x.       1.4mm

5.         254x.      1mm

3.5.      363x.      0.7mm

Looks great from an exit pupil perspective but there are some large jumps from 7mm down. I agree that a 3.5 wouldn't be used much and so bottom of the shopping list for sure. It's a massive jump as Don highlights from the 5mm but it does provide a 32x magnification? Even 5mm to 7mm is a large jump.

@Louis DI've never thought of a 40mm as being of use really as it gives an 8mm exit pupil but magnification of 32x? Obviously some of that light will be wasted but is the FOV with a filter possibly still worth it? 

 

Look at the magnification jumps you have:

23x (how do you even see the difference?), 34x, 29x, 54x, 73x, 109x.

If you observe in a place with excellent seeing, I might be able to see the high magnification jumps.  After all, most high mag. objects are quite small.

But having the low power eyepieces be that close together means it is unlikely you will use them in sequence.

I'd bet you either run from 30 to 13 to 7 much of the time or from 20 to 10 to 7.  Having two ranges isn't such a bad idea if your seeing is highly variable.

But your range could have been different, like a 25-26mm, 12.5-13mm, 8-9mm, 6-6.5mm, 5mm, 4mm and have been more evenly spaced.

There is never a wrong answer if you are happy with what you have, but in my experience you never feel the need for an eyepiece in between if the jumps are not too large,

and never feel you have too many eyepieces if the jumps are not too small, and that is up to your own determination.

 

[Stardaze]

9 minutes ago, Don Pensack said:

Look at the magnification jumps you have:

23x (how do you even see the difference?), 34x, 29x, 54x, 73x, 109x.

If you observe in a place with excellent seeing, I might be able to see the high magnification jumps.  After all, most high mag. objects are quite small.

But having the low power eyepieces be that close together means it is unlikely you will use them in sequence.

I'd bet you either run from 30 to 13 to 7 much of the time or from 20 to 10 to 7.  Having two ranges isn't such a bad idea if your seeing is highly variable.

But your range could have been different, like a 25-26mm, 12.5-13mm, 8-9mm, 6-6.5mm, 5mm, 4mm and have been more evenly spaced.

There is never a wrong answer if you are happy with what you have, but in my experience you never feel the need for an eyepiece in between if the jumps are not too large,

and never feel you have too many eyepieces if the jumps are not too small, and that is up to your own determination.

 

Thanks Don. I am wondering whether 20/10/7 might be the natural selection. It’s the 10mm that I haven’t used yet. Maybe the 10mm needs to be 100 deg on that basis? 

[Stardaze]

I think a lot depends on the 10mm or 13mm decision. If I go with the 1.41 calculation then, 20-14-10-7 are the steps. Will 20 to 10 be too much of a jump, is the question (64x to 127x so a doubling) ? 10mm provides the 2mm exit pupil. I will definitely add a 30 later on. I like the 100 degree view of my 13 and so of 10mm were to be the most used medium mag EP, I'd be better off cashing in the 13 and going Ethos on the 10mm.... I'll sleep on that some more...

Edited May 9, 2021 by Stardaze

[Mr Spock]

Back when I had a 250mm f4.8 (and again in the future when the new one arrives), my most used eyepiece was a 13mm LVW - x92. I found this just right for most objects. If I needed to go a bit deeper, I'd switch to the 8mm LVW - x150. I wouldn't want a 10mm in there, it would be wasted.

[Stardaze]

1 minute ago, Mr Spock said:

Back when I had a 250mm f4.8 (and again in the future when the new one arrives), my most used eyepiece was a 13mm LVW - x92. I found this just right for most objects. If I needed to go a bit deeper, I'd switch to the 8mm LVW - x150. I wouldn't want a 10mm in there, it would be wasted.

My most used is definitely the 13mm too, but I always found the jump to 8mm quite a lot. Tricky to know without trying I guess.

[Littleguy80]

Just now, Stardaze said:

I think a lot depends on the 10mm or 13mm decision. If I go with the 1.41 calculation then, 20-14-10-7 are the steps. Will 20 to 10 be too much of a jump, is the question (64x to 127x) ? 10mm gives the 2mm exit pupil. I will definitely add a 30 later on. I like the 100 degree view of my 13 and so of 10mm were to be the most used medium mag EP, I'd be better off cashing in the 13 and going Ethos on the 10mm.... I'll sleep on that some more...

When I had all APM 100 degree eyepieces (200/13/9), I spent most of the time bypassing the 13 and going straight to the 9. Odd targets, like M33, seemed to like the 13mm. I also recall using the 13mm as a middle step when hunting down some comets. I now go 20 to 12.5 most the time and less frequently onto the 10. Part of the reason is the Noblex gives much better contrast than the APM 13. The extra mag of the Delos can help on some targets. I do go back on forth on whether the 10 is too close to the 12.5 but I think the Delos 8mm is too much of a jump. I also tend to start with the 10mm for Lunar/Planetary and work my way up from there. My instinct for you would be to go for a 10mm and see if you feel like you’re missing something in between. Another option is the APM 12.5mm 84 degree. It seems to have built a good reputation. 

[Stardaze]

4 minutes ago, Littleguy80 said:

When I had all APM 100 degree eyepieces (200/13/9), I spent most of the time bypassing the 13 and going straight to the 9. Odd targets, like M33, seemed to like the 13mm. I also recall using the 13mm as a middle step when hunting down some comets. I now go 20 to 12.5 most the time and less frequently onto the 10. Part of the reason is the Noblex gives much better contrast than the APM 13. The extra mag of the Delos can help on some targets. I do go back on forth on whether the 10 is too close to the 12.5 but I think the Delos 8mm is too much of a jump. I also tend to start with the 10mm for Lunar/Planetary and work my way up from there. My instinct for you would be to go for a 10mm and see if you feel like you’re missing something in between. Another option is the APM 12.5mm 84 degree. It seems to have built a good reputation. 

My question to you Neil would be: if your 10mm Delos had the 100 degrees, would that negate the 13/12.5mm? I like the idea of 'less is more' in many ways. I'd rather spend that bit more on the core 3 that I use most. 100 degree fields have negated lots of EP's in-between I've felt.

Edited May 9, 2021 by Stardaze

[Xilman]

I don't know about you guys but I find magnifications > x200 or so essentially unusable with a Dob. The speed at which objects traverse the field of view (not to mention having to focus during that short interval) and the difficulty finding them again afterwards makes calculations based on exit pupil rather academic.

Perhaps it's just old age and incompetence but I restrict myself to x150 or lower.

Only if you have a decent drive should you start worrying about diffraction-limited magnification or excessively small exit pupils. Again, IMO.

 

[Stu]

1 minute ago, Xilman said:

I don't know about you guys but I find magnifications > x200 or so essentially unusable with a Dob. The speed at which objects traverse the field of view (not to mention having to focus during that short interval) and the difficulty finding them again afterwards makes calculations based on exit pupil rather academic.

Perhaps it's just old age and incompetence but I restrict myself to x150 or lower.

Only if you have a decent drive should you start worrying about diffraction-limited magnification or excessively small exit pupils. Again, IMO.

 

What eyepieces are you using to get to the x200? One benefit of the 100 degree afov eyepieces is significantly more time in between nudges compared with, say a Plossl or 68 degree.

Alternatively, do as I do and get an EQ platform. I use up to x360 with my tall and spindly 8” f8 quite easily with the target remaining centred for long periods.

[Xilman]

1 minute ago, Stu said:

What eyepieces are you using to get to the x200? One benefit of the 100 degree afov eyepieces is significantly more time in between nudges compared with, say a Plossl or 68 degree.

Alternatively, do as I do and get an EQ platform. I use up to x360 with my tall and spindly 8” f8 quite easily with the target remaining centred for long periods.

I don't, as I said. I restrict myself to about x100.

I was commenting on figures presented earlier in the thread where figure > x250 were bandied around, as were sub-5mm focal lengths.

That said, back in the late 80's when I had a 18" Dob, a 10mm EP would give me over x200. Wasn't very useful so I stuck to (IIRC, it's been a long time) a 20mm, a 30mm and 2x Barlow for the odd occasions I thought high power would be useful. Only have a Skywatcher 250 now so the issue isn't as important.

Good point about an EQ platform. I'd like to find one which doesn't cost more than the scope. For me DIY means damage-it-yourself so making one isn't an option.

 

[Stardaze]

1 minute ago, Xilman said:

I don't, as I said. I restrict myself to about x100.

I was commenting on figures presented earlier in the thread where figure > x250 were bandied around, as were sub-5mm focal lengths.

That said, back in the late 80's when I had a 18" Dob, a 10mm EP would give me over x200. Wasn't very useful so I stuck to (IIRC, it's been a long time) a 20mm, a 30mm and 2x Barlow for the odd occasions I thought high power would be useful. Only have a Skywatcher 250 now so the issue isn't as important.

Good point about an EQ platform. I'd like to find one which doesn't cost more than the scope. For me DIY means damage-it-yourself so making one isn't an option.

 

You do have a valid point. The 5mm at 254x was initially a little problematic, but notably the typical target have been planets and so providing the 9x50 was well centred, I haven’t suffered too much. Going over 300x sounds ‘interesting’ however..

[Littleguy80]

14 minutes ago, Stardaze said:

My question to you Neil would be: if your 10mm Delos had the 100 degrees, would that negate the 13/12.5mm? I like the idea of 'less is more' in many ways. I'd rather spend that bit more on the core 3 that I use most. 100 degree fields have negated lots of EP's in-between I've felt.

Mmmm that’s a tricky one. The first two 100 degree eyepieces I got was the 20mm and 9mm. For awhile, I wondered if I needed the 13mm at all. In the end, I got the 13mm as there were occasions when it was useful. At the moment, despite the 12.5mm and 10mm being too close on paper, I find what have works well for me. 

Maybe the answer is the Nikon Nav HW 12.5mm. I think that comes with a focal extender so you can use it as a 10mm too. They’re supposed to be tier performers. Pricey but if it’s two eyepieces in one….

[Littleguy80]

21 minutes ago, Xilman said:

I don't know about you guys but I find magnifications > x200 or so essentially unusable with a Dob. The speed at which objects traverse the field of view (not to mention having to focus during that short interval) and the difficulty finding them again afterwards makes calculations based on exit pupil rather academic.

Perhaps it's just old age and incompetence but I restrict myself to x150 or lower.

Only if you have a decent drive should you start worrying about diffraction-limited magnification or excessively small exit pupils. Again, IMO.

 

I’m a little crazy in this respect. I use a Vixen HR 3.4mm in my manual dob (350x mag and 0.12 degree TFOV). You have to work for it but I’m quite well practiced now. I was able to see Neptune’s moon Triton with this combo. I only had orthos for high power eyepieces when I first got my dob so I had no choice but to get used to that. I guess a lot depends on the quality of the mount you’re using too. 

[Xilman]

1 minute ago, Littleguy80 said:

I’m a little crazy in this respect. I use a Vixen HR 3.4mm in my manual dob (350x mag and 0.12 degree TFOV). You have to work for it but I’m quite well practiced now. I was able to see Neptune’s moon Triton with this combo. I only had orthos for high power eyepieces when I first got my dob so I had no choice but to get used to that. I guess a lot depends on the quality of the mount you’re using too. 

You're a better man than I, Gunga Din. Definitely old-age and incompetence, especially the latter...

[Stardaze]

13 minutes ago, Littleguy80 said:

Mmmm that’s a tricky one. The first two 100 degree eyepieces I got was the 20mm and 9mm. For awhile, I wondered if I needed the 13mm at all. In the end, I got the 13mm as there were occasions when it was useful. At the moment, despite the 12.5mm and 10mm being too close on paper, I find what have works well for me. 

Maybe the answer is the Nikon Nav HW 12.5mm. I think that comes with a focal extender so you can use it as a 10mm too. They’re supposed to be tier performers. Pricey but if it’s two eyepieces in one….

I’m thinking now, that if I can pick up a 10mm Ethos, I’ll spend some time with it alongside the APM 13. I don’t want to ship the the 13, just in case. Maybe that could be the answer. At least if I pick one up at the right money, I won’t lose out too much either way.

[Littleguy80]

7 minutes ago, Xilman said:

You're a better man than I, Gunga Din. Definitely old-age and incompetence, especially the latter...

Haha nothing but practice. Rest assured that I am also capable of impressive levels of incompetence  

[Stu]

30 minutes ago, Xilman said:

I don't, as I said. I restrict myself to about x100.

I was commenting on figures presented earlier in the thread where figure > x250 were bandied around, as were sub-5mm focal lengths.

That said, back in the late 80's when I had a 18" Dob, a 10mm EP would give me over x200. Wasn't very useful so I stuck to (IIRC, it's been a long time) a 20mm, a 30mm and 2x Barlow for the odd occasions I thought high power would be useful. Only have a Skywatcher 250 now so the issue isn't as important.

Good point about an EQ platform. I'd like to find one which doesn't cost more than the scope. For me DIY means damage-it-yourself so making one isn't an option.

 

I’m guessing eyepieces back then had narrow apparent fields of view, so perhaps it’s worth revisiting now that wider fields are available? Although not everything is about magnification, there are times when higher power than x100 can really help.

[Pixies]

1 hour ago, Littleguy80 said:

I’m a little crazy in this respect. I use a Vixen HR 3.4mm in my manual dob (350x mag and 0.12 degree TFOV). You have to work for it but I’m quite well practiced now. I was able to see Neptune’s moon Triton with this combo. I only had orthos for high power eyepieces when I first got my dob so I had no choice but to get used to that. I guess a lot depends on the quality of the mount you’re using too. 

Occasionally I've been using a 4mm ortho in an F6 8" (x300 magnification). It's not very often the seeing is good enough - but I've found it useful when trying to split something very tight.

I must admit, it's not relaxing.