Refractor objective.

I have a Meade 178ED Apo refractor. Not a bad scope until one considers the price paid for it new: from the viewpoint the thing is a piece of junk. I have been stewing over this for the three years since I bought it. A thought came to me: What if I could buy a first class objective all set in a lens cell, that could be mounted inside my 178ED tube (after removing the cells from the Meade, of course--not sure what I would do with them after, though... could make a great magnifying glass for starting campfires I suppose).
I would like to hear from ppl about this idea. Anybody know where I could buy an objective of Astrophysics or TMB quality for this purpose... ?

Hi,

Go to the TMB website and click on "products". TMB sells APO lenses with cells. Be prepared for the sticker shock though. Your fix will not be cheap. BTW, keep me in mind if you decide to sell the Meade lens. I would love to experiment with it.

http://www.tmboptical.com/

Keith

I think you'd be better off fixing or selling the Meade scope.
There is a wide range of stuff that could be done to improve the
Meade optically -- lens cell modifications, re-spacing the lens,
corrective lenses. Some experienced people speak very highly of
these scopes, though perhaps the quality is uneven.

As regards an AP or TMB -- most of the cost will be in the
optics. Be better to just get the entire scope.

A few years back right here on Astromart, I was able to pick up a "slightly scratched" FS128 Takahashi fluorite objective for a very reasonable price. I was just about to order the tube and focuser from Texas Nautical, but later found myself in the possesion of Chinese made 127mm f8 OTA. A little turning on the lathe to get the extra 1mm on the lense cell and I was in business. I now have a simple looking 5" OTA, that gives knock you socks off views.

Re-building a refractor can be lots of fun, provided the lenses are available !! Another possibility is getting a nice 7" achromat lens in the size you need installed in your lens cell. There is a fellow I am working with now in China who is making an 8" f6 lense for me. The first one I received had a small chip in it, so I am waiting to get the replacement second lense and cannot give any optical qualifications yet. I believe they also make 7" lenses as well. Another more distant possibility is to get these folks to do a 7" f9 ED doublet which although costing (much?) more, may give a much better visual image than the Achromat, but may have the same centering/spacing/collimation problems of the Meade.

A true 7" apo triplet lens will be a thing of awe both in perfomance and price !

It is my understanding that the Meade lenes were very sensitive to misalignment. You may be suffering from that if you have color issues.
What exactly is the problem with the optics?

Lawrence:

Here's my understanding having followed this story various times here:

1. These scopes, particularly this one are well known to have alignment problems. I would contact Meade directly, explain your situation including any difficulties with the vendor and ask them to take care of it. They are well aware of the problems and I believe have redesigned the cell which they should supply, whether it is in warranty or not...

2. As others have said, if you are going to buy a new objective, you might as well buy the whole scope.

3. Our mentor Roland Christen can explain what the difficulties are with this objective cell... If he pops in, it would be most instructive...

jon

Your scope is no different than the rest of the Meade ED178s. The cell design allows the lenses to shift. The newer ones, or the older ones that have been modified, have lateral screws that act on the center ring that affect the relative TILT of the two elements. If there are lateral adjustment screws (not the front end push-pull screws) the lens can be adjusted and the scope will perform superbly. If you send it back to Meade and they adjust it it will leave their factory in perfect adjustment but will get knocked out of adjustment the first time the box is bumped. I notice you have posted on the Meade Refractors Group. They have details on how to deal with your problem in their files section. With a couple of allen wrenches and an hour's worth of trial and error you will have a 7 inch kick-ass refractor.