Tricky. Tricky.

Not really better compared to the Sigma SPORT 60-600 mm ƒ 4.5-6.3 lens. That is mainly because the Olympus OM-1 with its smaller sensor, results into a very grainy liveview - which makes it utmost difficult to focus exactly. I wasn't able to set the focus exactly - so it was slightly off. Sure i used Topaz AI sharpening - but the details where slightly less compered to the when i used the Sigma SPORT 60-600 mm lens.

The image above at 1000mm with all the AI sharpening, is visually OK, but in detail when zoomed in - it is not.

I will of course test it on the moon, when it is clear - because the contrast of the moon surface was very ,very weak. Therefore it was almost impossible to focus manually with the Olympus OM-1. Even with the Canon EOS R6 and the Sigma SPORT 60-600 mm lens, it would been extremely difficult to set the exact focus.

Also because that the lenses (both of them) are in the aperture range of ƒ6.3 at the 500-600mm focal length. Both cameras have difficulties to find the exact focus, and the live-view gets very grainy.

From an amateur perspective

I find it all very exciting. It looks nice in my Diary - like a moon going close. It ain't perfect. It ain't super-duper lenses, not are those bright in aperture.... but the moon looks like a moon, despite the high, relative dense cirrus clouds which lowered the contrast of the moon surface considerably. (As I am writing this, the moon is already gone, as the clouds have taken over).

But... I am pretty happy for what it is !

Other options ?

You can always aim at better lenses. For example the older Canon EF 400 mm ƒ 5.6 L - which second hand, gives a good value for the money, at the same time has a good optical quality. Especially when you additionally add some AI sharpening, then the lens goes on steroids. If you put it onto a Olympus or Panasonic M4/3 type of camera, you get 800 mm. The lens can be had for around 500 € and upwards.

Another option would be the Canon EF 100-400mm ƒ 4.5-5.6 L IS II lens - which is of very high quality - but the second hand price is of course higher, too. By the way - that one can also be used successfully on the mediumformat Fujifilm GFX camera with adapter (when you take off the black plastic on the back / at the mount the vignetting goes away in the extreme corners). And of course, you can use it on an Olympus OM-1 or Canon EOS R type of camera, too, with an appropriate adapter.

Not bad, eh ?

Nevertheless - I wouldn't use or buy the Russian Maksutov 3M-6A 500/6.3 lens, if i didn't already have it.

So, there is that.

Another option: TTArtisan 500mm ƒ 6.3
fullframe lens ( E / Z / RF / L / EF / GFX / X / F)

For 369 $ there is the new TTartisan, 500mm f 6.3 lens with manual focus. It appears that it renders sharp once you stop it down to ƒ8 and ƒ11, even in the corners. For that little money, it is a serious (and probably better option compared to the old Russian Russian Maksutov 3M-6A 500/6.3 from the 60s and 70s)

I would probably still favor the Canon EF 400/5.6 L lens second hand.

Unstable / unsettled air...

Is perhaps the biggest threat to really sharp images with super telephoto lenses. And boy, it really becomes visible when you enlarge the LCD screen with a 500mm lens... how much the air "flimmers". This of course reduces sharpness of any tele lens, no matter quality level - in the fine details.

So. There is that.