Nagler 7 or Nagler 5?

In my scope my Nagler 9 gives 161x. (The scope is an 11 f4.55 SM Dob with Paracorr yeilding an effective focal e length of 62.5 inches). I need something higher for the moon and planets. Seeing is not so good here in Ohio. A Nagler 7 would give 208x, which sounds a bit low -- 250 would be perfect I think -- and a 5 Nagler would give 280. Which should I choose?
Thanks for any advice.
Bill Meyers

I recommend you buy the 7mm Nagler no matter what. With your f/4.5 scope, the 7mm will give you an exit pupil of 1.5mm. You'll find that will give you improved contrast on most dim objects like galaxies and nebula and improve your view of globulars as well. It's my favorite eyepiece on my 4.5 dob. You'll undoubtedly use it more than your 9mm.

There are few reasons to use Naglers for planetary viewing. The only reason to consider them is if your dob is undriven. The object will stay in view longer than if you use a narrow-field eyepiece. However, don't expect too much out of your scope. Best viewing is only in the center of the field anyways. You are not likely to get any better views at high power if the planet doesn't stay centered, no matter what eyepiece you use. If your scope is driven, you can use less expensive, narrower field eyepieces that will do a better job than the 5mm Nagler.

Albert