what magnification do i need

[Venus88]

Hi. I have a focal length of 750mm. What magnification do I need to look at jupiter and saturn. I have 10mm and 20mm eye piece. Well they do the job?

[Somnium]

Hi Amy, for planet observing you want to have the highest magnification you can get. 10mm on a 750mm scope will give you 75 times magnification. just off the top of my head you will be able to see the 4 big moons of jupiter and you will notice that saturn has rings but you probably wont be able to see that they are disconnected from the planet (someone can correct me if i am wrong). you will probably need a barlow of power mate to bump up the magnification. what is your set up?

[raymo]

Your 10mm will give 75x mag which is not enough for planetary work.
You need something in the 4, 5, or 6mm range, which would give
187, 150, and 125x respectively.
You will see nice images of Saturn and Jupiter at 75x, but they will
be very small, and hence not very satisfying.
If your scope came with a 2x Barlow lens you could use that with your 10mm eyepiece which would give 150x mag.
raymo

I see Aidan has already told you much of what I said.

[sharptrack2]

I can confirm that a 10mm EP on an f5 newtonian will just show the rings of Saturn, it looked more like a textbook UFO. Jupiter was a little better, some variations could be seen on the planet and the 4 big moons were bright pin points.

The view should be similar. Keeping the planet in the field of view will be a challenge.

[dannat]

a 2x barlow will get the 10mm to 150x, prob a good start