# Gratuitous brain teaser for frac owners

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Here's one for a rainy day or cloudy night. Say you have three nice fracs and a pile of green-lettered eyepieces. You want to store each frac at a different location so as to have kit available at each place (don't ask, just bear with me here). The object of this little puzzle is to determine how to divide the eyepieces over the fracs in order to get the most out of each set. Assume for the purpose of this exercise that the skies are equally dark at each of the locations.

If you're bored already, now is a good time to bail.

Assume the following fracs, all APO doublets, all with 2" focusers:

70mm f/6

85mm f/7

120mm f/7.5

Assume the following eyepieces, all by Televue:

Ethos: 21, 17, 13, 10, 8, 6, 4.7, 3.7

Nagler T5: 31, 26

Panoptic: 41

Nagler T6: 11, 3.5

Nagler Zoom: 3-6, 2-4

Plossl: 25

I did say it was gratuitous...

All pundits welcome.

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I'd split the 21E, 31N, and 41P among the three for widest field views in each.  I'd also split the zooms among two scopes for highest power views.  The 3.7E should go to the remaining scope.  The 4.7E should go to the 2-4 zoom scope.  The 3.5N should go to the 3-6 zoom scope.  From here, I think you can figure out how to sprinkle the rest to fill out each lineup minimizing overlap and creating a good spread of powers.

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What I am especially interested in is any thoughts on which eyepiece goes to which scope, and why.

It's not a problem to solve, just a thought experiment.

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Put all the eyepieces in a case and take them with you when you go to each location.

then you have the best of both worlds, scopes at desired locations, and a smallish case with the eyepieces in.

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2 minutes ago, Astroframer said:

Put all the eyepieces in a case and take them with you when you go to each location.

then you have the best of both worlds, scopes at desired locations, and a smallish case with the eyepieces in.

Thanks for playing! I've yet to find a 'smallish' case that these eyepieces would all fit into...

And carrying them all around would be total overkill, as there is substantial overlap between them.

So just to be clear: this is not a problem I have that needs a solution. I am merely interested in why you would assign each particular eyepiece to which particular scope, given the specific characteristics of each.

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I would put the widest lowest power eyepiece in the 70mm frac and sell the rest....

Alan

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27 minutes ago, Alien 13 said:

I would put the widest lowest power eyepiece in the 70mm frac and sell the rest....

Alan

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34 minutes ago, Alien 13 said:

I would put the widest lowest power eyepiece in the 70mm frac and sell the rest....

Alan

Full marks for the 'gratuitous brain' part... Thanks for playing!

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1 minute ago, iPeace said:

Full marks for the 'gratuitous brain' part... Thanks for playing!

I am a big fan of low power widefield observing  I used to spend hours as a kid with a handheld 80mm ish military scope with x6 magnification and have not looked through anything better since, unfortunately the scope has gone and we no longer have the realy dark skies we had in the 60s.

Alan

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Just now, Alien 13 said:

I am a big fan of low power widefield observing  I used to spend hours as a kid with a handheld 80mm ish military scope with x6 magnification and have not looked through anything better since, unfortunately the scope has gone and we no longer have the realy dark skies we had in the 60s.

Alan

I love that, too. Often spend the whole night with the lowest, widest eyepiece in the f/7 scope. You may be entirely right, this puzzle may be a total no-brainer...

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To split well in 3 sets you're still going to be a bit lacking a bit in mid-power somewhere and seems to be a bit extreme at the high power side with 2 Nagler zooms, the Ethos 3.7 and a Nagler 3.5

However, I'd recommend:

120ED -  Pan 41 and all of the Ethos ( heavyweight set to match the scope  )

85mm f/7 - Nagler 31, Plossl 25, {could use something around 20mm here in place of the Plossl perhaps}, Nagler 11, Nagler 3-6

70mm f/6 - Nagler 26 (assiming that the scope has a 2" focuser!), {again missing something mid-power} , Radian 10, Nagler Zoom 2-4  (get a small case to put it all in for the ultimate grab and go setup)

Sell the Nagler 3.5 to fill missing spaces in mid-power?

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5 minutes ago, Davesellars said:

To split well in 3 sets you're still going to be a bit lacking a bit in mid-power somewhere and seems to be a bit extreme at the high power side with 2 Nagler zooms, the Ethos 3.7 and a Nagler 3.5

However, I'd recommend:

120ED -  Pan 41 and all of the Ethos ( heavyweight set to match the scope  )

85mm f/7 - Nagler 31, Plossl 25, {could use something around 20mm here in place of the Plossl perhaps}, Nagler 11, Nagler 3-6

70mm f/6 - Nagler 26 (assiming that the scope has a 2" focuser!), {again missing something mid-power} , Radian 10, Nagler Zoom 2-4  (get a small case to put it all in for the ultimate grab and go setup)

Sell the Nagler 3.5 to fill missing spaces in mid-power?

Thanks for playing! Interesting move to keep the Ethos together.

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Well the 120ED is an excellent scope with decent aperture for DSOs right up to the faint and small ones.  The small(ish) increments in focal length are reasonably important for detail on DSOs. 13 and 17mm both sides of the optimal 2mm exit pupil.  The 21mm is perfect for finding DSOs in the first place giving sufficient mganification & contrast against the background but the 13 and 17 would be work-horses for the detail.  Obviously 10mm and below for the brighter and smaller DSOs and going on to planetary viewing.   Bung an OIII/UHC filter in the 41mm Panoptic for emission nebulae or drifting around the MW...

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32 minutes ago, Davesellars said:

Well the 120ED is an excellent scope with decent aperture for DSOs right up to the faint and small ones.  The small(ish) increments in focal length are reasonably important for detail on DSOs. 13 and 17mm both sides of the optimal 2mm exit pupil.  The 21mm is perfect for finding DSOs in the first place giving sufficient mganification & contrast against the background but the 13 and 17 would be work-horses for the detail.  Obviously 10mm and below for the brighter and smaller DSOs and going on to planetary viewing.   Bung an OIII/UHC filter in the 41mm Panoptic for emission nebulae or drifting around the MW...

Excellent stuff!

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On 7/31/2016 at 06:09, Davesellars said:

120ED -  Pan 41 and all of the Ethos ( heavyweight set to match the scope  )

I'd split the Ethos into two groups, 21-13-8-4.7 and 17-10-6-3.7.  They're just too close in powers to keep them together.

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I'd park the 2 smaller scopes and use the excellent and flexible SW120ED with the 41 Pan (great widefield neb combo) and the Ethos.

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2 hours ago, jetstream said:

I'd park the 2 smaller scopes and use the excellent and flexible SW120ED with the 41 Pan (great widefield neb combo) and the Ethos.

Thanks for playing! The puzzle as posed says nothing of make or model of scope, of course - and I maintain that this is just a thought experiment to see how we might match eyepieces to scopes in an optimal way.

Your contribution does deserve extra credit for empathy with my actual situation...

...and is, as are the suggestions of others above, practical and well-founded.

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