Celestron 24mm Ultima Edge

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Re: Celestron 24mm Ultima Edge

#21

Post by LDW47 »


Don Pensack wrote: Mon Feb 20, 2023 11:26 pm Yes, but a 1.4 spacing is too close at low power.
Example: 1250mm focal length:
30mm = 42x.
24mm = 52x
17.5mm = 71x.
The 30 to 17.5mm jump is only 29x, which is a small jump in magnification any way you look at it.
If the focal length is shorter, that jump is even smaller and makes even less sense.

And a 1.4x spacing is too much at high power.
300 becomes 420x, and most people would say a 120x jump is a bit too large when you might be bumping up against seeing.

So, though the 1.4x rule is followed by Pentax XW and Baader Morpheus in the focal lengths sequences, it doesn't always work.
Yet observers don't mind using 10-12-15 power binos to gain an advantage over their bare eyes but 10-20x jumps in eps is not enough to give that bit of gain in your view ? Right ? PS: Lets not get into costs vs the benefit !
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Re: Celestron 24mm Ultima Edge

#22

Post by LDW47 »


Bigzmey wrote: Tue Feb 21, 2023 8:37 pm There's more than one way to catch a rabbit (don't like the cat's version :D) and as you mentioned it is all about "noticeable difference in appearance change". For my scopes and targets stepping from 24mm to 18mm makes perfect sense, for you it may not. It just seems odd to me that you are discouraging OP to get 24mm based on "it is too small of a step".
Well, Well said ! Exactly the point ! The additional cost, many times, doesn't even factor in.
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Re: Celestron 24mm Ultima Edge

#23

Post by LDW47 »


LDW47 wrote: Tue Feb 21, 2023 10:06 pm
Don Pensack wrote: Mon Feb 20, 2023 11:26 pm Yes, but a 1.4 spacing is too close at low power.
Example: 1250mm focal length:
30mm = 42x.
24mm = 52x
17.5mm = 71x.
The 30 to 17.5mm jump is only 29x, which is a small jump in magnification any way you look at it.
If the focal length is shorter, that jump is even smaller and makes even less sense.

And a 1.4x spacing is too much at high power.
300 becomes 420x, and most people would say a 120x jump is a bit too large when you might be bumping up against seeing.

So, though the 1.4x rule is followed by Pentax XW and Baader Morpheus in the focal lengths sequences, it doesn't always work.
Yet observers don't mind using 10-12-15 power binos to gain an advantage over their bare eyes but 10-20x jumps in eps is not enough to give that bit of gain in your view ? Right ? PS: Lets not get into costs vs the benefit !
Yet some binoers have every size bino under the sun ie 7x, 10x, 12x, 15x, etc.,etc. ...... to increase that view just a little bit.
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Re: Celestron 24mm Ultima Edge

#24

Post by John Baars »


Interesting discussion.

I've never really cared about any formulas by which eyepieces can be chosen. I used to have plenty of them to choose from. Nowadays with a Leica ASPH zoom in between, it makes quite a difference in the amount of eyepieces I have with me.

Following these stories, I got busy doing the math anyway. I carefully selected the focal points of the eyepieces that I actually use. In other words, what I actually observe with during longer telescope time. So not the intermediate sizes with which you look at most for a minute or so.

The results were not surprising. As the focal length of the telescope increases, the intermediate steps become smaller. So on average 1.4X for a 2000 mm focal length to 1.8X- 1.9X for a 500 mm focal length. And somewhere around 1.7X for a 900 mm focal length.

From the very lowest possible magnification and a short focal length, even 2.5X as a succeeding step does not seem excessive. When asking 30 mm, 24 mm or 18 mm, everything depends on focal length, observer taste and whether the exit pupil does not exceed the eye pupil.
Refractors in frequency of use : *SW Evostar 120ED F/7.5 (all round ), * Vixen 102ED F/9 (vintage), both on Vixen GPDX.
GrabnGo on Alt/AZ : *SW Startravel 102 F/5 refractor( widefield, Sun, push-to), *OMC140 Maksutov F/14.3 ( planets).
Most used Eyepieces: *Panoptic 24, *Morpheus 14, *Leica ASPH zoom, *Zeiss barlow, *Pentax XO5.
Commonly used bino's : *Jena 10X50 , * Canon 10X30 IS, *Swarovski Habicht 7X42, * Celestron 15X70, *Kasai 2.3X40
Rijswijk Public Observatory: * Astro-Physics Starfire 130 f/8, * 6 inch Newton, * C9.25, * Meade 14 inch LX600 ACF, *Lunt.
Amateur astronomer since 1970.
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Re: Celestron 24mm Ultima Edge

#25

Post by Don Pensack »


Bigzmey wrote: Tue Feb 21, 2023 8:37 pm There's more than one way to catch a rabbit (don't like the cat's version :D) and as you mentioned it is all about "noticeable difference in appearance change". For my scopes and targets stepping from 24mm to 18mm makes perfect sense, for you it may not. It just seems odd to me that you are discouraging OP to get 24mm based on "it is too small of a step".
And looking at the scopes the OP lists, I would bet that not one has a focal length longer than 1000mm.
Even using 1200mm, the difference between a 24mm and 18mm would be considered small(only 16.7x).
And 30mm to 24mm is only a 10x change.
Yes, I regard that as too small to make such a small change.
Astronomer since 1963
Currently using a 12.5" dob and a 4" apo refractor
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Re: Celestron 24mm Ultima Edge

#26

Post by Bigzmey »


Don Pensack wrote: Wed Feb 22, 2023 8:39 pm
Bigzmey wrote: Tue Feb 21, 2023 8:37 pm There's more than one way to catch a rabbit (don't like the cat's version :D) and as you mentioned it is all about "noticeable difference in appearance change". For my scopes and targets stepping from 24mm to 18mm makes perfect sense, for you it may not. It just seems odd to me that you are discouraging OP to get 24mm based on "it is too small of a step".
And looking at the scopes the OP lists, I would bet that not one has a focal length longer than 1000mm.
Even using 1200mm, the difference between a 24mm and 18mm would be considered small(only 16.7x).
And 30mm to 24mm is only a 10x change.
Yes, I regard that as too small to make such a small change.
Coming back to binoculars. They are fast scopes, typically F5. So 10x50 binos would have 250mm FL. Stepping up just by 5x to 15x power is considerable in terms what you can resolve. So, we have a scope with short FL were small in absolute terms difference of 5x makes big impact. So, larger difference of 16.7x in longer FL would not? Just don't see any logic in that.

I agree though that 30mm to 24mm is a small step, because it is only by 1.25x factor. The same step of 10x in binos from 10x to 20x would make a huge change, hence factor of 2x.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
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Re: Celestron 24mm Ultima Edge

#27

Post by Don Pensack »


If we are talking how a deep sky object appears to the eye in the scope, the "noticeable difference in appearance change" that I advocate for is not going to be 10x or 20x, and 30x is *barely* in the category.

I've had 31 scopes and many of them were 80-100mm sizes. And I've spent 60 years with over 360 different eyepieces looking at DSOs.
If we take a small scope, like a 4" refractor, and slowly increase the magnification from its lowest power, perhaps with a zoom eyepiece, at what point does the next magnification up provide a larger image with more details and better resolution
and a noticeably darker background sky?

In a typical scope, I would say a 100% increase from its lowest power.

The magnifications in between become a kind of "flyover zone", because, even when zooming, the view is just not significantly different.
Yes, a 50% increase does show the object a bit larger, but it doesn't answer the need for a significantly different view.
If the low power isn't enough, you want the next power up to be a very different, and much larger view.

And that is because, with most small scopes, low power will be in the 15-30x range.
If your scope is a 20" and low power is 100x, then, obviously, a doubling of that power is probably too large a jump.
And that much of a jump, percentage-wise, cannot be extended to higher powers because it quickly becomes too large a jump.

Take M57.
It's total size is larger than we see. Most of us see a view about 1.5'. It's oval, not round and we are heavily rounding off the say it's that size, but go with the argument.
At 30x, its apparent size is 45'. Great vision can see its shape, but not its ringlike character. We need the image to be at least 1° and preferably 2° in apparent size to begin to see it as a ring.
Would a 40% increase in size to 1° be a significantly different view? Would a 100% increase in diameter to 1.75° be better?
In this case, the next significant difference in appearance would be probably an increase to an apparent size of 3°, or an increase in magnification of 4x, or 120x.
So, for a small object, the low power eyepiece to the next noticeable change is likely to be significantly more than 100%.

So the object, as well as the scope's true field of view, and the scope's aperture, will determine the next magnification up.
But, whether you look at it from the standpoint of image size, exit pupil difference, or light grasp, keeping with the idea of a significant difference, where deep sky objects are concerned,
means a jump of at least 30x, and, in the case of tiny objects, a lot more.

In my 4", I start at 24x. That finds the object. Some large objects are OK at that magnification. I have eyepieces that produce 24x, 32x, 41x, 51x, 57x, 65x, 79x, etc.
I recently noted that almost every time I jump from low power it's to at least 65x. The eyepieces in between are in the "fly over zone" because they simply don't provide a significant difference in the view.

Beginners don't start with a box full of eyepieces, so how can we advise a starter set that won't break the bank, yet provide adequate spreads between magnifications?
One way, I think, is to advocate for a low power to next magnification jump of double the lowest magnification.
There will be plenty of time to buy an eyepiece in between, if desired, farther down the road.
But I'd be willing to bet that, for most observers, a desire for an eyepiece in between may never appear. And if it does, that in between one will become the de facto new lowest power.
Astronomer since 1963
Currently using a 12.5" dob and a 4" apo refractor
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Re: Celestron 24mm Ultima Edge

#28

Post by LDW47 »


As usual and as with other astro sites this has mushroomed in to a lot more than my simple question about my acquiring that ep. The post / issue was not pointed towards beginers, ep sets etc. But thats okay I guess although the captioned eyepiece seems to have disappeared in the fray !
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