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tl;dr Is there a celestial object which has details that can be seen clearly by a 70mm telescope, but no details at all seen by a 50mm telescope of the same make. E.g. "Jupiter has details that can be seen clearly by a 70 which are its stripes, while no details can be seen clearly by a 50".

I was wondering if what my search gathered is correct.

From what I've gathered from forums etc. it seems like despite different opinions (as in other things), if one is looking to see details that can't be seen with the naked eye, not including fuzzy shapes, there are exactly 3 things that can be seen with a cheap telescope clearly:

  1. More details on the moon.
  2. Details on Jupiter.
  3. Details and rings of Saturn.

Nothing more nothing less. (And specifically, no Deep Space Objects at all.)

And the difference between a 50mm one or a 70mm one would only be the size it would look.

Remember we're not talking about seeing a fuzzy shape of nebulae as opposed to a dot in the sky, only things that would look clear, albeit small. And that some detail will be added by the telescope, so just seeing Jupiter's moons as dots as opposed to not seeing them at all, doesn't count. I'm also assuming whatever would be a "logical" magnification with simple eyepieces.

Obviously more will be seen with a 70mm than a 50mm. I'm asking if there is an object which will have details seen clearly by a 70 and no details at all seen clearly by a 50. If you answer yes, please say which object. E.g. A 70 will be able to see clear stripes on Jupiter while a 50 will only see a blob.

If you absolutely need a specific type of telescope, let's look at this one:

50mm - https://www.amazon.com/gp/product/B0000UMLYI/

70mm - https://www.amazon.com/gp/product/B003AM87PU/

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    $\begingroup$ I'm not an expert when it comes to lenses, but you're probably going to need a lot more than 70mm if you want to clearly resolve the surface Jupiter's moons. With 70mm, you should be able to see them, but as points of light - though it sounds like you're looking for better quality than that. It should be sufficient enough to see decent detail on the moon and even make out Saturn's rings, but you would still be looking at a relatively entry-level telescope. $\endgroup$
    – 4NT4R3S
    Feb 26 at 23:22
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    $\begingroup$ All of those are still fairly small. Best advice is to find a club near you and actually look through some scopes members have. $\endgroup$ Feb 26 at 23:46
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    $\begingroup$ Double stars, phase of Venus, open star clusters $\endgroup$
    – JohnHoltz
    Feb 27 at 1:32
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    $\begingroup$ you're mixing "cheap telescopes" and a question about aperture. A cheap 70mm will probably show less than an expensive 50mm. There are many factors to take into account: the objective lenses and their quality, the diagonal's quality, the eyepiece's quality, the viewer's eyes' quality. Also the sky quality at the observing location. Or maybe there's no viewer involved and you're using a camera? Then the quality of the sensor and the cooling of the camera, and the mount being used, all affect the result. $\endgroup$
    – Aaron F
    Feb 27 at 16:35
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    $\begingroup$ @4NT4R3S Thanks. $\endgroup$
    – ispiro
    Feb 27 at 21:18

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If relevant; Comparing binocs 10x50mm vs. SkyMasters 25x70mm, the 70mm gives for example:

  • Much more detail on the Orion Nebula
  • Andromeda slightly more detail of spiral shape vs. smudge
  • Myriad of detail in the Beehive Cluster (Messier 44 or Praesepe) in the Cancer Constellation

..in addition to the ones you mentioned (Mountain tops on the Moon, clear bands on Jupiter and clear gap between rings and planet on Saturn).

And of course, you see hundreds/thousands of more stars at almost any random point in the Milky Way.

But it sort of stops there. Even if the difference is a bit like using a magnifying glass vs. transporting yourself into space.

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    $\begingroup$ Thanks. This is the first response that really addresses the question. As for the many more stars seen, that might be true, and even interesting, but they're still just more dots. Thanks again. $\endgroup$
    – ispiro
    Feb 28 at 20:37
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What an increase in aperture gives is an increase in light-gathering ability.

This results in an increase in brightness and image resolution.

The size of the image does increase as the size of the aperture increases, but that's not as important because image size is selected by the observer, by using eyepieces of different focal lengths.
The important part of the aperture increase is to see more and in more detail.

All telescopes have their limits at which increasing magnification only increases the size of a blurred image. There are the physical limits of the telescope and the limits imposed by the Earth's atmosphere. Increasing the aperture helps increase the level of magnification supportable.

Here are a couple of bad photos which I snapped with my phone through the eyepiece on December 20th, 2020 - during the conjunction of Jupiter and Saturn.
To the eye, the brightness was about that of the first image, and the detail visible was more than that of the second.


(ƒ/1.8 1/14 4.04mm ISO1552 and ƒ/1.8 1/30 4.04mm ISO100)
(right-click and open in new tab to see full-size)

Here's one of the Moon on the same evening: (ƒ/1.8 1/60 4.04mm ISO100)

The telescope is an 80mm aperture refractor with a 560mm focal length. I can't remember which eyepiece was in it, but it was probably a 5mm or thereabouts, resulting in a magnification of 112x.

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    $\begingroup$ I don't understand how this answers the question. $\endgroup$
    – ispiro
    Feb 27 at 19:19
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    $\begingroup$ @ispiro how does it not answer the question "Will there be a difference in what can be seen with a 50mm telescope and a 70 or even 80 mm one?" ? $\endgroup$
    – Aaron F
    Feb 27 at 19:26
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    $\begingroup$ I still don't know if your answer is yes or no. If yes, please tell me which object. Thanks. $\endgroup$
    – ispiro
    Feb 27 at 19:37
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    $\begingroup$ @ispiro the answer is: yes. the object is: all of them. $\endgroup$
    – Aaron F
    Feb 27 at 19:56
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    $\begingroup$ @ispiro "My question is not if there will be a difference between 70 and 50". Your question "Will there be a difference in what can be seen with a 50mm telescope and a 70 or even 80 mm one?" is literally that ¯\_(ツ)_/¯ $\endgroup$
    – Aaron F
    Feb 27 at 21:45
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Double stars are quite sensitive to aperture. The resolving power of a 50mm scope is about 2.2" and a 70mm would be about 1.5", where both stars are about the same magnitude, and assuming good optics and seeing.

Alpha pisces at about 1.7" should be split with a 70mm but not a 50mm telescope. A bit of searching will find other examples, but be careful with your sources as some double star separations can change significantly over relatively short periods.

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