In theory, there is no limit to magnification.
Yes. Actually this has been my first response to observers who question why I don't push the power more for some objects. Of course, you can increase the magnification to whatever your telescope, eyepiece and Barlow will produce. But the resulting image may look like a wooly smudge and may show you less detail than you could have seen at a much lower magnification.
And as a matter of fact, I have often been the champion of less is more when it comes to magnification for observing planets.
For example, look at some of the best images taken with large reflectors. These scopes are often working with the equivilent of a 2mm to 4mm eyepeice.
But if you attempted to use this much power visually, it would produce a horrible image.
I don't even want to compare photography with visual, except maybe to find out how much I'm able to see without all the fancy AP equipment and computer processing.
The telscope presents all of the detail it is capable of rendering with the magnification reaches about 1.1x per millimeter of aperture. This is when the smallest detail that the scope is capable of resolving is provided with sufficient angular magnification to be resolved at the focal plane. Past this, you can go bigger and bigger, but no new detail is ever presented.
1.1x per mm of aperture would be about 28x per inch, or about 280x in my 10" Dob. I'm not sure if we should take this as a hard and fast rule. In fact, I'm sure it isn't. There are too many factors involved.
For instance, the adaptation level of the eye should be taken into account. If the eye can be kept closer to photopic, more detail can be seen in the image of a planet at a more moderate level of magnification. If the eye is looking at fainter objects and is well dark-adapted, then more magnification will be needed to begin to see structure in the object. I've seen both of these effects for myself many times.
Also, even among bright planets, I've seen a difference in "best" magnification. As a general rule, Saturn and Mars do better at higher magnifications than Jupiter. Many observers have seen this. The reasons are probably both the different types of contrast for these objects and also the different image scales of the objects themselves. Personally, I think Mars does well at higher than 28x per inch, sometimes much higher, particularly when its apparent diameter is less than about 7 arcsec.
The main reason I resist the message that 50X per inch is the right planetary detail is because over the years, I have heard so many people question if their telescopes were defective. They would read these reports about 50x per inch, but when they used their scopes, they were not seeing any new detail.
I would never make the blanket statement that 50x per inch is the "right" magnification for planet detail. Just as I would never have said that 50x per inch is "too much magnification." Experience should tell us that the interaction among equipment, observer, object and atmosphere is much more complicated than that. Rules of thumb are not laws of nature.
They thought their scopes must be defective because the message seemd to be that the more power you use, the more detail you would see.
This, of course, is a newbie attitude. Reality is more nuanced. Unfortunately, I've seen this attitude too often in more experienced observers who should know better.
Factor in seeing, and 300x is the practical limit for most of us on most of the time anyway, but someone should not be surprised at all if they find that going to 50x per inch doesn't result in additional detail.
Of course. On the other hand, this doesn't mean than an experienced observer cannot appreciate what a good instrument can do under the right conditions when observing some objects.