Mohsen Bahremand

7 minutes ago, Alan64 said:

With my solid-tube 150/750, I use 2x and 3x barlows, but with a 12mm eyepiece, and for an effective, simulated 4mm(3x).  Then, the 12mm has the benefit of a larger eye-lens with which to look through.  With a manual mount, I've found that to be nigh to the limit with that telescope(188x).  However, according to the 50x-per-25.4mm "rule", a 150mm aperture can at least approach 300x, so the former is not set in stone.  Personally, I love to ramp up the power with my telescopes.

I've had a 70/900 achromat up to 225x, on Polaris, and the image was clear enough, not bad at all.  

You do want short barlows with a Newtonian, the shorter the better.  My own are fairly short, the one in the middle particularly...

Some, if not many, opine that excessive magnification results in so-called "empty magnification" -- blurry, soft images -- and at times to the point where you might feel that the telescope will explode if you do so.

Per said 50x "rule", my 70.900 achromat should only reach 138x, yet I've had it up to 225x, and meaningfully, satisfactorily.

In short, by all means, shoot for the Moon.   

Thanks a ton

Complete and satisfactory answer!

Hello everyone

I have a Sky-watcher  heritage 150p with 750mm focal length. When i use a 4 mm eyepiece which gives 188x magnification, i can still see the details on moon very clearly without any blurriness. This makes me think that there's still room for using a 2 or 2.5 barlow although it passes the max 300x magnification.

Do you think that it might work?

Can it make any problem with focusing? For instance  should i put them so close to the secondary mirror that it doesn't fit the tube?