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Eyepieces for 12” f/5 Dob: Any advantage of 40mm over 30 mm?

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#51 faackanders2

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Posted 28 November 2018 - 11:11 PM

Lots of long winded posts around here lol.gif
 
Just get the ES82 30mm, you can’t go wrong with this excellent eyepiece and it’s well matched to your f5 scope.
 
I may buy the ES68 40mm some day but it would be used at f6.5 for a 6,15mm exit pupil.

If you had a 2" 40-41mm 68-70AFOV you may want to use it on ALL your 2" telescopes for the widest TVOV available with those telescopes. Makes a great finder eyepiece for bright objects.

Edited by faackanders2, 29 November 2018 - 12:12 AM.

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#52 astro744

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Posted 29 November 2018 - 12:20 AM

The negative effect of a larger exit pupil are often over-emphasised.  If your goal is maximum field of view then an eyepiece with the maximum field stop diameter is required.  For star hopping a large exit pupil and any loss of effective aperture is irrelavent.

 

I often switch from Telrad to 41mm Panoptic with no need for a finder except for the more barren star fields.  If you're not worried about maximum field and want a slightly darker background then choose the 31mm Nagler for example.


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#53 Jon Isaacs

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Posted 29 November 2018 - 11:41 AM

The negative effect of a larger exit pupil are often over-emphasised.  If your goal is maximum field of view then an eyepiece with the maximum field stop diameter is required.  For star hopping a large exit pupil and any loss of effective aperture is irrelavent.

 

I often switch from Telrad to 41mm Panoptic with no need for a finder except for the more barren star fields.  If you're not worried about maximum field and want a slightly darker background then choose the 31mm Nagler for example.

 

Well... 

 

The 41mm Panoptic provides a 10% wider field than the 31mm Nagler.

 

The 31mm Nagler provides 32% greater magnification than the 41mm Panoptic.  

 

I have both eyepieces and the 31mm Nagler, I consider the 41mm Panoptic as a specialty eyepiece that I might not even use on any given night whereas the 31mm Nagler is out and used frequently used dark sky night.  And my eye dilates to about 7.7-7.8mm so at F/5, I am still using nearly the full aperture of the scope. 

 

I'd say that added 10% field is overrated.  I star hop 100% of the time, the field of view of the 22 inch and the 31mm Nagler is 0.85 degrees, with the 41mm Panoptic it's 0.935 degrees.  That difference is inconsequential, if I can see it and find it in the 41mm, I can find it in the 31mm.

 

But what is not overrated is that added 32% magnification. It makes small objects pop out more easily.  With the 41mm Panoptic, the object maybe in the field of view but it's just not visible. If I can't see it in the 41mm, it still maybe visible in the 31mm.  

 

If I were buying one low power wide field eyepiece for my F/5 scopes and I were choosing between a ~30mm UWA and a ~40mm SWA, there is no doubt in my mind it would be the 30mm UWA.  I just see so much more with it.  That 32% added magnification is a real advantage.

 

Jon 



#54 astro744

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Posted 29 November 2018 - 01:04 PM

I have and use both the 41mm Panoptic and 31mm Nagler and don't doubt the added magnification is a real advantage, same as with 10x over 7x with binoculars.  I use and prefer the Pan though as a finder eyepiece since I can take in the whole field without having to look around more easily than in the Nagler and for star hopping I think this is important.  Having the maximum field possible means I can get those extra field stars that may sometimes be needed to assist in star hopping.

 

The Nagler I prefer when I want that extra power and want to get the feeling of being closer to the view by having to look around a little.  Eyepieces are very personal and depending on the situation I'll choose one over the other.  For a 12" at f5 though the 31mm Nagler makes more sense because you will get a darker sky background and the contrast will be better but I find too that for even better contrast and magnification you need to be around the 4mm exit pupil and now we are talking 21mm Ethos.  I don't have the 21E but do enjoy my 20mm Type 5 Nagler very much.  (Tele Vue did make a 26mm T5 Nagler and this too would be very nice with f5 but it has been discontinued for some time now).

 

If I'm star hopping and only want to see field stars, I'll choose the 41mm Panoptic.  I'll also choose the Panoptic if I have a dark site and want maximum exit pupil for the Veil nebula for example.  If I'm not star hopping and just browsing through Sagittarius for example I'll go the higher power with the 31 or often the 20mm NT5.  It really depends on the telescope, the target, the sky and perhaps the biggest variable is simply how I feel like enjoying the the sky on any given night and sometimes it is with the widest field and lowest power I can get and that just simply looking up without any optical aid.

 



#55 Jon Isaacs

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Posted 29 November 2018 - 02:34 PM

For a 12" at f5 though the 31mm Nagler makes more sense because you will get a darker sky background and the contrast will be better but I find too that for even better contrast and magnification you need to be around the 4mm exit pupil and now we are talking 21mm Ethos.

 

 

To see field stars, I use the magnifying finder.  Beyond that, mostly the 21 mm or the 13mm Ethos's. My two bigger scopes operate at ~F/5 with a Paracorr. If I want a wider, brighter field, I just remove the Paracorr.

 

More field of view that the 41 Pan, more Magnification by 15% and a better fit with the exit pupil.

 

Jon



#56 astro744

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Posted 29 November 2018 - 08:57 PM

...More field of view that the 41 Pan, more Magnification by 15% and a better fit with the exit pupil.

Yes but 41mm Panoptic without Paracorr still has largest true field.  My point is that for use as a finder eyepiece a 41mm Panoptic (with or without Paracorr) is an excellent choice.  An oversized exit pupil is irrelevant (and not really an issue for people with oversized pupils).  The apparent loss of effective aperture is not even noticeable as one is looking at relatively bright stars (that are also on a chart like Uranometria or Sky Atlas to hop by not 12th magnitude ones.  Contrast difference is noticeable as exit pupil increases but again irrelevant for 8, 9 or 10th magnitude stars through a telescope.

 

I just see so often comments about exit pupils being too big as if it was a hard and fast rule.  Not many people though have or want a 41mm Panoptic just for use as a finder but when you have multiple telescopes you find that you also end up with multiple eyepieces and they each behave differently in the different 'scopes.



#57 Jon Isaacs

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Posted 29 November 2018 - 09:56 PM

Yes but 41mm Panoptic without Paracorr still has largest true field.  My point is that for use as a finder eyepiece a 41mm Panoptic (with or without Paracorr) is an excellent choice.  An oversized exit pupil is irrelevant (and not really an issue for people with oversized pupils).  The apparent loss of effective aperture is not even noticeable as one is looking at relatively bright stars (that are also on a chart like Uranometria or Sky Atlas to hop by not 12th magnitude ones.  Contrast difference is noticeable as exit pupil increases but again irrelevant for 8, 9 or 10th magnitude stars through a telescope.

 

I just see so often comments about exit pupils being too big as if it was a hard and fast rule.  Not many people though have or want a 41mm Panoptic just for use as a finder but when you have multiple telescopes you find that you also end up with multiple eyepieces and they each behave differently in the different 'scopes.

 

If all one is doing is looking at bright stars to try to navigate the sky in the main eyepiece, there is no need for an expensive, well corrrected eyepiece like the 41mm Panoptic, eyepieces like the 38mm AgenaAstro 70 degree/Orion Q70. These offer the same true field of view as the 41mm Panoptic.

 

The exit pupil "rule" is applicable if one is actually using the eyepiece to view objects. If one is also trying to see the object of interest, then the slightly smaller field of view of the 31mm Nagler combined with the 32% greater magnification makes it better choice, at least for me. Since I am both using the eyepiece as a "finder" eyepiece to star hop with as well as a "finder eyepiece" to find the object itself, the small added field of view of the 41mm Panoptic over the 31mm Nagler is just not much help.  

 

But we all star hop differently.  I use Sky Safari so I can customize the field to use with my 50mm finder as well as the main eyepiece.  I align the cross hairs of the finder vertically and horizontally and with it's 6.8 degree field of view, I have a lot of stars to work with and by precisely aligning the finder with the star field, I can put the object within a relatively narrow field, the 21mm Ethos provides 0,74 degrees at 134x, only about 21% narrower than the 41mm Panoptic.  The 13mm Ethos provides a 0,45 degrees, about half that of the 46 Pan but at over 3 times the magnification. 

 

For hunting down more difficult objects, the higher magnifications almost always are more effective because the objects are visible whereas very often, they are too small to be see in the 41mm Panoptic.

 

But all this is neither here nor there.  I think we both agree that if one is buying one eyepiece for an F/5 Newtonian, a ~30mm UWA is a better all around choice than a ~40mm SWA...  And yes, if one is not looking for the object itself, and trying to star hop on bright stars, then exit pupil is pretty much irrelevant.  But then just how often is one only using an eyepiece just to star hop and not look for objects, for me, that is not very often.

 

For what it's worth. I bought the 41mm Panoptic specifically to increase the TFoV of the 25 inch F/5 for star hopping.  With the 31mm Nagler and the Paracorr, that provided a 0.67 degree field.  The 41mm Pano added field of view but it was basically a bust for star hopping.  The added field of the 41mm was just not enough to make it worth while. 

 

But in the process I did discover that my eye dilated to something closer to 8mm than to 7mm and there are occasions where I can take advantage of that. 

 

Jon 



#58 faackanders2

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Posted 30 November 2018 - 12:21 AM

If all one is doing is looking at bright stars to try to navigate the sky in the main eyepiece, there is no need for an expensive, well corrrected eyepiece like the 41mm Panoptic, eyepieces like the 38mm AgenaAstro 70 degree/Orion Q70. These offer the same true field of view as the 41mm Panoptic.
 
The exit pupil "rule" is applicable if one is actually using the eyepiece to view objects. If one is also trying to see the object of interest, then the slightly smaller field of view of the 31mm Nagler combined with the 32% greater magnification makes it better choice, at least for me. Since I am both using the eyepiece as a "finder" eyepiece to star hop with as well as a "finder eyepiece" to find the object itself, the small added field of view of the 41mm Panoptic over the 31mm Nagler is just not much help.  
 
But we all star hop differently.  I use Sky Safari so I can customize the field to use with my 50mm finder as well as the main eyepiece.  I align the cross hairs of the finder vertically and horizontally and with it's 6.8 degree field of view, I have a lot of stars to work with and by precisely aligning the finder with the star field, I can put the object within a relatively narrow field, the 21mm Ethos provides 0,74 degrees at 134x, only about 21% narrower than the 41mm Panoptic.  The 13mm Ethos provides a 0,45 degrees, about half that of the 46 Pan but at over 3 times the magnification. 
 
For hunting down more difficult objects, the higher magnifications almost always are more effective because the objects are visible whereas very often, they are too small to be see in the 41mm Panoptic.
 
But all this is neither here nor there.  I think we both agree that if one is buying one eyepiece for an F/5 Newtonian, a ~30mm UWA is a better all around choice than a ~40mm SWA...  And yes, if one is not looking for the object itself, and trying to star hop on bright stars, then exit pupil is pretty much irrelevant.  But then just how often is one only using an eyepiece just to star hop and not look for objects, for me, that is not very often.
 
For what it's worth. I bought the 41mm Panoptic specifically to increase the TFoV of the 25 inch F/5 for star hopping.  With the 31mm Nagler and the Paracorr, that provided a 0.67 degree field.  The 41mm Pano added field of view but it was basically a bust for star hopping.  The added field of the 41mm was just not enough to make it worth while. 
 
But in the process I did discover that my eye dilated to something closer to 8mm than to 7mm and there are occasions where I can take advantage of that. 
 
Jon

I star hop mentally in my head and then use Telrad geometry with it's 3 circles, and tar pattern intersections/tangents/ and just aim where it should be, sometimes I am luck and it is in the view, sometime not and I hunt and search (left-right, up-down), repeat, repeat, repeat. The wider TFOV and AFOV helps with a non tracking dob, although the cost of tracking would be cheaper than alot of relatively expensive eyepieces. I owned the 40mm 70 AFOV as my first 2" finder eyepiece for my 17.5" 44.1 dob (didn't work for my 10.1" f4.5 Coulture Oddesy dob whose original finder only acommodated 1.25"). I later added 30mm 82 AFOV and then 20mm 100 AFOV, and then alot of higher power 100-120 AFOV eyepieces. With the wide views I like looking at multiples objects even if trasitory ones passing by.

#59 astro744

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Posted 30 November 2018 - 04:08 AM

I think you and I have taken over this thread and I apologise to the OP and hope they are getting something out of it.  My first 2" wide field eyepiece was a Celestron 32mm Erfle.  When I first looked through it in my 6" f5.5 I said Wow!  I didn't notice any aberrations because I didn't really know any different at the time. I just had a nice wide field of view that my 22mm (0.965) and 40mm (1.25") Kellners couldn't provide.  About the same time I got a taste of the original Tele Vue 13mm Nagler as well as the 24mm Wide Field and again Wow! But I knew these were outside my budget and I quite liked my 32mm Erfle for the lower power.

 

Many moons later I wanted a Nagler type eyepiece and they were still expensive so I bought a 30mm 1rpd eyepiece which had an 80 deg field.  Well this eyepiece alone got me on the Tele Vue bandwagon and I have never looked back.  In my 6" f5.5 and 10.1" f6.4 the 30mm 1rpd had severe curvature of field so much so that the outer 30-40% was so far out of focus that any faint fuzzy in the area would be invisible and even the fainter field stars became a faint smudge.

 

I then took the plunge and invested in the 41mm Panoptic only because the 31mm Nagler was still expensive.  Some time later I finally bought the 31mm Nagler because I really did want that 82 deg field.  The first time I used quality eyepieces I was delighted to see pure primary mirror coma alone and not astigmatisim or 'seagulls'.  I invested in a Paracorr and whilst I can see the improvement I tend not to use it but the scope I want to try it on is my 10" f4.7 (kids/outreach scope) but I cannot because the Skywatcher focuser has a stop inside the draw tube preventing full insertion of the Paracorr and as a result I cannot reach focus.

 

I have not used the 38mm Q70 or similar so cannot comment on it but I do enjoy seeing sharp field stars from centre to the edge in my Panoptic.  I cannot see the point of a wide field finder eyepiece if only the centre is sharp.  Mind you that is now and back then with my Erfle I couldn't see the difference and just enjoyed the sky.  I still have that Erfle and its reserved for outreach and still gets those Wow comments and I'll keep it just for that.

 

 

 



#60 Jon Isaacs

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Posted 30 November 2018 - 05:24 AM

I have not used the 38mm Q70 or similar so cannot comment on it but I do enjoy seeing sharp field stars from centre to the edge in my Panoptic.  I cannot see the point of a wide field finder eyepiece if only the centre is sharp.  Mind you that is now and back then with my Erfle I couldn't see the difference and just enjoyed the sky.  I still have that Erfle and its reserved for outreach and still gets those Wow comments and I'll keep it just for that.

 

 

Your story is much like mine. I purchased the BW-Optik 30mm 80 degree eyepiece which was the first version of that eyepiece before the factory decided to sell it to anyone rather than just Markus who had initiated the cloning of the Wide Scan 2.  

 

I like sharp stars and use a Paracorr even in my 13.1 inch F/5.5.  However, for the purpose you describe, star hopping with relatively bright stars with the main eyepiece, sharpness is not a factor.  

 

My real point is that if one is buying a low power, wide field eyepiece for a 12 inch F/5. an eyepiece that provides significantly more magnification, allows the scope to operate at full aperture with only a slight loss of field of view  is significantly more useful than an eyepiece that maxes out the TFoV.  10% is just not that big a deal.  With a ~30mm UWA, it's 1.6 degrees, with the a ~40mm SWA it's 1.75 degrees.  Both are plenty.  On the other, when one is using the eyepiece for viewing DSOs, the 30mm will nearly always be significantly more effective.

 

My concern:  If one has an F/5 and needs to choose one low power, wide field eyepiece, a 30mm UWA is a more effective tool than a 40mm SWA.

 

The only reason I discuss my experiences is to illustrate why I am concerned. 

 

Jon



#61 25585

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Posted 30 November 2018 - 07:46 AM

I progressed from a Vixen 32mm Erfle like the one in my little photo, to a 35mm Panoptic. 

 

A 40mm SWA s.5000 and 41 Panoptic are both too heavy. Vixen 42mm LVW is best lower weight 40+ mm IME for F5.




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