recommendation for eyepiece between 42mm and 22mm

[janoskiss (Steve H)]

@Kunama (Matt) That's more basic than I imagined. I foolishly assumed it recommended a set of EPs for a given scope. My bad.

[Kunama]

Originally Posted by janoskiss

@Kunama (Matt) That's more basic than I imagined. I foolishly assumed it recommended a set of EPs for a given scope. My bad.

It is actually quite handy for quick comparisons of TFOV, Exit Pupil, and transit times. I doubt there is a program that I would allow to override my bone encased computer in choosing the actual eyepieces. We all have such different wants, tastes and especially eyesights that we still have to make the final decisions ourselves.

I use the:
Research it
Buy it
Try it
Critique it
and
Keep it or Sell it

protocol in my selection......

[janoskiss (Steve H)]

Originally Posted by Kunama

I doubt there is a program that I would allow to override my bone encased computer in choosing the actual eyepieces.

Have no doubt because your bone encased master is the one you're trying to please.

Not to sound like a TeleVue fanboi (which I'm not; they're fine and dandy just mostly don't suit me), but forgetting about the brand, TV have some great sensible advice on their website re EP selection for any scope: linky

[wavelandscott (Scott)]

I concur that reading some of the material written by Al Nagler and posted on the Telrvue website is time well spent.

I do have a mixed eyepiece case with some TV, Pentax and a few others (Denkmeir) regardless, I do agree with the mindset that Al Nagler espouses in terms of number and key considerations to keep in mind.

[Wavytone]

Originally Posted by janoskiss

@Wavytone sorry to be blunt but your advice on EP selection (3 EPs, abc) is terrible. I can't be bothered explaining why (it's late and I'm out of energy) but maybe others can chip in. Or just think about it for a minute.

Well you've motivated me to explain. Having been a visual observer for 40+ years using scopes from f/3.7 to f/18, I well know the temptation to acquire a box full of eyepieces, having owned upwards of a dozen at times, the rationale being to have all bases covered. Which is bullcrap.

1. Some years ago three friends who were very active DSO observers ran an experiment to determine the optimal run for selecting eyepieces to observe smallish DSO's - mainly galaxies and planetary nebulae. They came up with X1 magnification per mm of aperture.

There is also a good basis for this from optometry - this correlates with a magnification such that the resolution of the scope (the Airy disk) on the retina is similar to the spacing of the rods in your retina used for low light vision. When you do the maths for the average eye this does indeed work out very close to a magnification of X1 per mm of aperture.

On bright objects (the planets) where some colour is visible more extreme magnification is desirable - and useful - due to the spacing of the colour-sensors in your retina (cones) being quite different to that of the rods.

2. Then there is a little matter called "seeing". On most nights at average locations seeing is rather better than 1 second of arc. You can figure for yourself what that means in terms of magnification, but again it leads to a very different result for dim objects where you're relying on your rods, vs the bright objects (planets) where colour is visible, and the cones come into play.

3. Most visual observers have a scope that handles a range of magnifications from lowest to highest around 1:4, this is a consequence of using very fast newtonians. Using factors of 2 you can cover that easily in just 3 eyepieces.

Even a range of 1:10 can be accomplished in just 4 or 5 eyepieces easily. But do you really need them all ?

4. I'll say NO. from a purely practical perspective I have no problems switching from a very low power wide field eyepiece (42 or 50mm) to say 13mm or even 8mm in one step.

Presumably you find this a bit hard and want to swap rather more eyepieces.

I don't, and I suggest you take a hard look at those you actually use often. My guess is there are just 3, and the rest don't matter.

[Kunama]

Interesting ideas Wavy, not sure I agree that one only needs to own three eyepieces. I find I usually only use three eyepiece in a session but the focal length and AFOV of those used in each session varies, I tend to look at the conditions and then select the scope I am going to use. Then depending on that choice I select eyepieces that I think will be suitable for that session.

You choices of LVW 42, 13 & 8 for instance would give me:

42mm .... 61x, exit pupil of 7.5mm and a true field of 64 arcmin
13mm ... 196x, exit pupil of 2.33mm and a true field of 19.9 arcmin
8mm ... 319x, exit pupil of 1.45mm and a true field of 12.2 arcmin

If I used your a.b.c. recommendations I would end up with

63x
457x
685x

That would be rather restrictive.

[casstony]

If you look at the OP's signature I don't think there's much point discussing having only 3 eyepieces. Maybe 3 eyepieces per telescope

[Kunama]

Originally Posted by casstony

If you look at the OP's signature I don't think there's much point discussing having only 3 eyepieces. Maybe 3 eyepieces per telescope

Quite true Tony, I think slotting an N31T5 into that lineup would do for a lifetime of observing.


(since when did threads stay on topic..... )

[Camelopardalis (Dunk)]

I like to have options when I'm observing, but IMO there's little to gain between ~20mm and ~40mm with C11, it's just not a huge difference. For a different _experience_ maybe.

I find it's more useful to have options at the lower end of the focal lengths, so you can pick and choose the right tool for the job based on conditions.

[ausastronomer (John Bambury)]

Originally Posted by Wavytone

2. Then there is a little matter called "seeing". On most nights at average locations seeing is rather better than 1 second of arc. You can figure for yourself what that means in terms of magnification

Hi Wavy,

I think you meant to say "worse" than 1 second of arc, not "better" than 1 second of arc.

Cheers,
John B

[jeelan (Jeelan)]

Originally Posted by casstony

If you look at the OP's signature I don't think there's much point discussing having only 3 eyepieces. Maybe 3 eyepieces per telescope

I was going to note that but find the discussion interesting nonetheless so happy to follow along :-)

cheers
Jeelan

[Kunama]

Originally Posted by jeelan

I was going to note that but find the discussion interesting nonetheless so happy to follow along :-)

cheers
Jeelan

That's what I like about these threads, the original question is usually answered in the first couple responses. There follows always an interesting discussion, on related aspects, that is a great learning resource.

Let us know what you decide. For me the 31mm Nagler was an obvious choice as it gave the largest true field without exceeding 82° apparent field. I find the 100° eyepieces annoying as I hate that 'peering around the corner' feel.

[Wavytone]

Originally Posted by Kunama

I hate that 'peering around the corner' feel.

That's a good description of the problem, matt. More is not always better.

[Camelopardalis (Dunk)]

Luddites

[Don Pensack]

The 31mm Nagler will work for glasses as well, making it a logical intermediary between the 42mm and 20mm.
However, it is a bit wider apparent field than the others, so perhaps a 27mm Panooptic, with the same eye relief as the 31 Nagler would be a better choice.
Looking at the field stops might give us a clue:
42mm LVW 46.5mm
27mm Panoptic 30.5mm
20mm XW 24mm
The Panoptic is logically placed by field size.
Does it make sense from the standpoint of magnification on the C11?
42mm--67x
27mm--104x
20mm--140x
Yes, it makes sense there, too.
So the recommendation of the 27mm Panoptic was inspired.

Just one more thing: if you get a 31mm Nagler, the 42mm LVW will get used less and less and less until it just fades away.
I'm just sayin'.............

[janoskiss (Steve H)]

Originally Posted by Don Pensack

Just one more thing: if you get a 31mm Nagler, the 42mm LVW will get used less and less and less until it just fades away.
I'm just sayin'.............

I agree. For sure it's one or the other since they have about the same AFOV. Anything else is polygamy which is illegal in this country and impractical in amateur astronomy.

[ausastronomer (John Bambury)]

Originally Posted by Don Pensack

The 31mm Nagler will work for glasses as well, making it a logical intermediary between the 42mm and 20mm.
However, it is a bit wider apparent field than the others, so perhaps a 27mm Panoptic, with the same eye relief as the 31 Nagler would be a better choice.

I own both the 31mm Nagler and the 27mm Panoptic. They are both very useable with eyeglasses on. Notwithstanding they both have a stated eye relief of about 19mm, I find the 27mm Panoptic to be slightly easier and a little more comfortable to use than the 31mm Nagler with my glasses on, but they are both pretty good in this regard. This is possibly due to the narrower AFOV of the Panoptic and its slightly different shaped eye lens housing and eye guard.

Originally Posted by Don Pensack

Yes, it makes sense there, too.
So the recommendation of the 27mm Panoptic was inspired.

The 27mm Panoptic is an excellent eyepiece and in some circumstances is a better choice than the 31mm Nagler. For instance in my 10"/F5.3 dob it is my low power eyepiece of choice because it doesn't have the size and weight issues of the 31mm Nagler. It's a really nice compact lightweight package. A similar physical size to the 17mm Nagler but way lighter.

Originally Posted by Don Pensack

Just one more thing: if you get a 31mm Nagler, the 42mm LVW will get used less and less and less until it just fades away.
I'm just sayin'.............

I couldn't agree more. You're 100% correct in that statement Don.

Cheers,
John B