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Favorite Exit Pupil/Magnification/Eyepieces on most Nebulae?

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#1 Procyon

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Posted 20 May 2019 - 09:28 PM

Favorite Exit Pupil/Magnification/Eyepieces on most Nebulae?

 

What's everyone using most of the time on these objects?



#2 rustynpp

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Posted 20 May 2019 - 09:41 PM

A 13mm EP seems to find its way into my diagonal more often than other EPs do. In my 4" refractor it gives me 55x, 1.8* TFOV (100* AFOV), and a 1.9mm exit pupil. 

 

There's a reason 13mm was my first (and currently only) 100* EP.


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#3 BKSo

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Posted 20 May 2019 - 10:50 PM

I mainly use the 40mm onmi Plossl with my sct. That is the longest 1.25” eyepiece I can buy. I am thinking about making a 64mm Dollond.

#4 Ernest_SPB

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Posted 20 May 2019 - 11:55 PM

3 mm exit pupil looks nice for relatively large objects

2 mm exit pupil looks better for small DSO, like galaxies in Virgo cluster, nodes in arms of M101 and M33.

Some bright planetary nebulae and clusters can be observed with exit pupil 1-1.5 mm  

Some extended bright and dark nebulae, like N.America, California likes maximal available TFOV and diameter of exit pupil becomes less important.


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#5 Asbytec

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Posted 21 May 2019 - 12:04 AM

My favorite for "most (DSO) objects" I observe is a range between 1mm and 2mm. That's not set in stone.
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#6 Jon Isaacs

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Posted 21 May 2019 - 04:27 AM

I don't have a favorite exit pupil for "most nebulae." Nebulae are best viewed with specifically tailored exit pupils. 

 

For Barnard's loop, I favor an 8mm exit pupil with a small aperture scope. In general, for large, dim, diffuse nebulae, particularly when using filters, I go with large exit pupils.  The Heart and Soul region I see best with an exit pupil greater than 6mm.  

 

For smaller, bright nebulae like NGC1535, (Cleopatra's eye) or the Saturn nebula, an exit pupil under 1mm is best, if the seeing permits. 

 

M42 is one that shows different aspects at different magnifications, different exit pupils.  

 

Jon


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#7 25585

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Posted 21 May 2019 - 04:40 AM

Depends on the nebula brightess and if a filter is in use. Too many variables... 



#8 Tropobob

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Posted 21 May 2019 - 04:45 AM

For nebula, I often commence with an EP that gives an exit pupil near 3.5mm and customize from there. 


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#9 Roragi

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Posted 21 May 2019 - 04:50 AM

Hi,

 

With my ocular ethos are different configurations for my two scopes and for type of object I leave a sample.

 

Newton 16'' F4.1 1638mm focal lenth

 

Ethos 21  Exil pupil  5mm  Power 90x  Fov 1°  large weak diffuse nebula

Ethos 13  ''      ''       3mm  ''        145x  '' 0,7° Galaxia large weak, open clusters of small size

Ethos 8    ''      ''    1.9mm  ''        235x   0.4°   Bright galaxies that need detail and increase, large planetary.

Ethos 4,7 ''      ''    1.1mm  ''        400x   0.2°  Planetary nebulae and general details only when seeing is good.

 

I usually use 13 and 8mm longer.

 

Roberto.



#10 Procyon

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Posted 21 May 2019 - 07:16 AM

Trying to figure out if I should plug a gap between a 25 ES 100 and a WO 40mm 72 (or is it really 65?).

Should have mentioned in the post no planetary Nebulae, strictly large diffuse Nebulae.

#11 25585

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Posted 21 May 2019 - 07:27 AM

Anyone just go for trying out different eps to see which is best suited for the occasion? I go out to look at stuff, not for a self-inflicted mental arithmatic session. gaah.gif


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#12 russell23

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Posted 21 May 2019 - 07:42 AM

I don't have a favorite exit pupil for "most nebulae." Nebulae are best viewed with specifically tailored exit pupils. 

 

For Barnard's loop, I favor an 8mm exit pupil with a small aperture scope. In general, for large, dim, diffuse nebulae, particularly when using filters, I go with large exit pupils.  The Heart and Soul region I see best with an exit pupil greater than 6mm.  

 

For smaller, bright nebulae like NGC1535, (Cleopatra's eye) or the Saturn nebula, an exit pupil under 1mm is best, if the seeing permits. 

 

M42 is one that shows different aspects at different magnifications, different exit pupils.  

 

Jon

waytogo.gif



#13 Asbytec

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Posted 21 May 2019 - 07:46 AM

Trying to figure out if I should plug a gap between a 25 ES 100 and a WO 40mm 72 (or is it really 65?).

Should have mentioned in the post no planetary Nebulae, strictly large diffuse Nebulae.

So with your C11, the gap is between 2.5mm (112x) and 4mm (69x). For large diffuse nebula, I would not think it's all that important for an intermediate magnification in the low power range. Maybe the gap between 4mm and 7mm, if at all possible. But, you're talking a rather long focal length eyepiece with a slow focal ratio. Not really a wide field scope to begin with, but I guess it can be done. 


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#14 Jon Isaacs

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Posted 21 May 2019 - 09:30 AM

Anyone just go for trying out different eps to see which is best suited for the occasion? I go out to look at stuff, not for a self-inflicted mental arithmatic session. gaah.gif

 

I do roughly calculate in my head the field of view , magnification and exit pupil,  it's something my father taught us as children and has served me well as an adult , it's part of being an engineer/scientist .

 

But that's for comparison purposes and just to know.  The eye is the ultimate judge. 

 

Jon


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#15 Jon Isaacs

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Posted 21 May 2019 - 09:33 AM

So with your C11, the gap is between 2.5mm (112x) and 4mm (69x). For large diffuse nebula, I would not think it's all that important for an intermediate magnification in the low power range. Maybe the gap between 4mm and 7mm, if at all possible. But, you're talking a rather long focal length eyepiece with a slow focal ratio. Not really a wide field scope to begin with, but I guess it can be done. 

 

:waytogo: 

 

For "large" diffuse nebula,  something closer to one's maximum dilated pupil would be useful. 

 

Jon


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#16 Asbytec

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Posted 21 May 2019 - 09:52 AM

Anyone just go for trying out different eps to see which is best suited for the occasion? I go out to look at stuff, not for a self-inflicted mental arithmatic session. gaah.gif


Haha...yea. I do. But, I note which eyepeice(s) gave the best view and find some trends that seem to work in case someone asks.
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#17 jdown

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Posted 21 May 2019 - 10:45 AM

I've the same questions as the OP.  There seem to be 8-10 correct answers to every question posted here on CN, although, as advice, "just use whatever works" is of minimal value.

  I've a Takahashi Mewlon 210 on order, focal ratio f/11.5, selected mostly because it gets high marks for lunar and planetary observing.  However, I'd also like to observe DSOs, includng brighter nebulae, with the 210.  I currently have an APM 24mm Ultra Flat Field EP, AFOV 65 degrees, that I would use for observing M42, the Helix, as well as summer targets like M57, Lagoon, Trifid, Omega, Eagle, possibly the Veil, using either UHC or OIII filters, whichever Dave Knisely recommends..  

    My 24mm EPs would yield an exit pupil diameter of 2.1mm.  An alternative would be TV's 40mm Plossls.  That would bump the exit pupil up to ~3.5mm.  With their 43 degree AFOV, I would only see a slight increase in size of the field - ~33%.

    So, considering I want to observe nebulae using narrow-band filters, would a 3.5mm exit pupil be essential?  A vast improvement over 2.1mm?  Slightly brighter but worth the price?  

   


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#18 MartinPond

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Posted 21 May 2019 - 10:55 AM

Depends on the nebula brightess and if a filter is in use. Too many variables... 

And the objective size., and especially nebula visual size...

   ...like you said...many variables.   1 to 5 mm exit pupil?  or more..


Edited by MartinPond, 21 May 2019 - 10:56 AM.

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#19 Vondragonnoggin

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Posted 21 May 2019 - 11:06 AM

Just use whatever works is a valid answer when the variables are too many to go over in single posts.

 

 

For instance:

 

UHC filter + apparent mag 10 nebula - well, the human eyes natural light amplification is a larger pupil size so if you want to see it brighter, then a larger exit pupil is necessary. If you want to see it closer though, then you compromise in brightness perceived by using more magnification which results in a smaller exit pupil. In this case (and many others) - use whatever works is valid. The same for context viewing. If you want to see as much of a certain nebula as possible but the only way to fit the entire object in the FOV with your particular scope is the use of a low power EP with large exit pupil, then you choose that particular EP.

 

If you want to see more detail, you use a shorter focal length eyepiece and get a dimmer image from smaller exit pupil. If it gets too small, then all of a sudden your filter choice is going to hinder enough light to see details come through, but without the filter, the S/N ratio is going to be too low for the specific spectrum the nebula emits to come through - use whatever works to balance for best view.

 

To get the real what works best you would have to list all available scopes and eyepieces and nebula or at least list all factors tailored for the person that asked the question after knowing the scopes they used and conditions they view in.

 

a 3.5mm exit pupil would be desirable over a 2.1mm exit pupil with a UHC or OIII in use IF it still frames as much of the nebula that you want to see or provides enough increase in image scale to be satisfying and still provides the contrast you desire for satisfying viewing.

 

There isn’t a single answer that solves all. There are some lists of good recommendations based on what the observer used for equipment in the Sky conditions they tested in and that is it. Like David Knisely’s comprehensive list of objects and different filters. It’s a great place to start if you have similar equipment and observing conditions.


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#20 Procyon

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Posted 21 May 2019 - 11:37 AM

I've used a 2.5mm exit pupil, 3.1, 3.2 and a 4mm exit pupil. This from dark sites mostly. I think anywhere from 3 to 4 looked great. Was just wondering if there's a sweet spot and what people are using most of the time on the big popular Nebulae like the Swan or Omega, Eagle, Veil. 



#21 Procyon

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Posted 21 May 2019 - 11:40 AM

 

    So, considering I want to observe nebulae using narrow-band filters, would a 3.5mm exit pupil be essential?  A vast improvement over 2.1mm?  Slightly brighter but worth the price?  

Definitely a 3.5mm exit pupil should be a vast improvement on those targets. 


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#22 Jon Isaacs

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Posted 21 May 2019 - 12:13 PM

There seem to be 8-10 correct answers to every question posted here on CN, although, as advice, "just use whatever works" is of minimal value.

 

 

The underlying advice is that one needs to have a range of eyepieces that covers the range of possible exit pupils.  With your F/11.5, the largest exit pupils are not possible but a 55 mm Plossl will provide a 4.8mm exit pupil which is quite bright. 

 

Once one has the range of possible exit pupils available, then determining the exit pupil that offers the best view of a particular object can be determined by "what does work the best."  The original question here is covers a sufficiently broad class of objects, I would not venture to say I have a favorite or optimal exit pupil. 

 

"So, considering I want to observe nebulae using narrow-band filters, would a 3.5mm exit pupil be essential?  A vast improvement over 2.1mm?  Slightly brighter but worth the price?"

 

 

For me, a 2.1mm exit pupil is rather dim for some of the objects, particularly with filters.  A 3.5mm exit pupil is about 2.8 times brighter than a 2.1 mm exit pupil so I would want to have that available.  The 55mm Plossl would be more than 5 times as bright, if it were me, assuming your scope has a 2 inch focuser, I would want to have that available. 

 

My scopes are fast so large exit pupils are not an issue. And I do use them at times, impart because I have a larger than one might expect dark adapted pupil. 

 

Jon


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#23 Richard Whalen

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Posted 21 May 2019 - 12:31 PM

There is no one answer. Large exit pupils work great in really dark sky locations, not so much in your average rural area with near by towns with light domes, and not at all in the middle of a city.

 

As my location has become brighter I rarely use more than 4mm EP, and more often than not my max is around 3mm EP. Humid night and that drops to 2mm EP.

 

When I go out to NM in the Gila I often use around 7mm EP with great results due to the very dark skies on large extended objects.

 

I find on the vast majority of dso's, a EP between 1mm and 2mm works well.


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#24 jdown

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Posted 21 May 2019 - 03:01 PM

Thanks for all the helpful replies.  I'll add the 40mm TVs to my shopping list.  I have a dark site, Bortle 1-2 skies, where I can study the DSOs - really looking forward to that..  


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#25 Asbytec

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Posted 21 May 2019 - 04:46 PM

 

Once one has the range of possible exit pupils available, then determining the exit pupil that offers the best view of a particular object can be determined by "what does work the best."  The original question here is covers a sufficiently broad class of objects, I would not venture to say I have a favorite or optimal exit pupil. 

 

Having a range, then determining what the best exit pupil is within that range for a given object class, is great advice. In fact, since I know I like 1 to 2mm for small bright galaxies, for example, I'll design my eyepiece set for several stops in that range. Add a few broader stops in the low power range for larger targets, a couple between 1mm to 0.5mm for the moon, planets and small bright planetary nebula, then at least one a bit higher at 0.4mm or 0.3mm for double stars, Mars and other small bright planetary nebulae. YMMV based on your observing preferences and conditions. 

 

I have kind of gotten away from using magnification stops and thinking in terms of exit pupil as it adds a bit of information about surface brightness - which is what I am after. I really do not care what the magnification is, anymore. I don't worry if I have 100x (2mm) and 120x (1.7mm) close together, along with one or two others closer to 1mm, because I know somewhere in that 1 to 2mm range (100x to 200x) I am likely to find a 'productive' magnification for subtle detail in small bright galaxies, as an example. Sometimes a little more magnification at a few tenths of a millimeter less than 1mm turns out to be the best.

 

You just never know until the image begins to show something. Or better said, we begin to make something of the afocal image presented to us because, in the end, it's all about the image on the eye and how well we perceive it. 

 

Edit: As Earnest said above, and others mention, framing a large object can be important. More important than the magnification. It depends on what you're after. 


Edited by Asbytec, 21 May 2019 - 05:51 PM.

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