Meade 152ED/APO Collmination

Hi,

I just got my Meade 152ED back from Meade. They actually turned it around very quickly. It was sent in to have the lens cell updated and a lens alignment or collimation.

I was out with it last Friday night under very good skies and I was disappointed in the images. Using different eyepieces I could see a smear or a flare at the top of most objects (Saturn, Jupiter, Jupiter's moons). Thinking back I did not try a different 2" diagonal. It would be nice if that were the problem, but I do not think that was it.

Saturn's rings where not very clear but the bottom of Saturn was very clear and sharp. I did not do a star test. I just took a quick look at the moon, Jupiter, M42, and Saturn.

I was hoping someone could point me to any information on aligning a Meade ED series lens. I am going to give the scope another chance or two before I start tweaking, but I would like to read up on the theory of adjusting the lens cell.

Don Durbin

My hunch is that the 152ED's objective is a smidge (or would that be a *smudge*?) misaligned -- the objective's axis is tilted with respect to the scope's mechanical axis. Net result is coma (and some astigmatism). You can verify this with a high-magnification star test and/or by viewing the extra-focal patterns (fresnel rings) on either side of best focus. When the objective is tilted with respect to the optical axis, you'll see non-centric fresnel rings -- an off-kilter bull's-eye pattern, similar to figure D in the .pdf which Bob noted. Even a millimeter can skew things and show that smear or flare you're seeing.

If/when you make adjustments, do so "straight through" -- without a star diagonal in place. And if you end up going solo, I recommend using simple sketches to record the progress of the focal and fresnel patterns -- before 1st tweak, after 1st tweak, after 2nd tweak, etc. Nothing fancy -- a circle on paper where you can note positions/orientations of the brightest/best "point" of focus -- similar to a clock face.

Although the process can be tedious, correcting misalignment is pretty-much straightforward. You do have one big/huge advantage -- the adjustable cell simplifies the process *very* much.

Best wishes and luck.
-Dan

http://groups.yahoo.com/group/meade_refractors
These guys have an alignment manual for the Meade ED/APO