APO Refractors

I thought that a doublet only used two pieces of glass in the lens, but a triplet uses 3 pieces of glass, each with different properties to correct for color and other aberration's. this is why triplets are so much heavier, due to the massive weight of all the glass used in the lens. is this not correct?

Yes, this is correct. My Takahashi FSQ is a quadruplet (four elements) whereas my AP160 is a triplet (three elements).

Anyway, APO refractors are incredible instruments and I make this statement on the basis of my experience with both an AP160 and Tak FSQ.

By the way, the "ED" refers to extra-low dispersion glass.

I too am looking for an APO or close enough to piggyback on the CGE, for wider field shots, would you recommend the Megrez 90? A Vixen 103 also came into the equation

Steve, I suppose it all depends on wha you want, regarding price, focal length (depending on how good your mount will track) and aperture, the megrez 90 is very popular, but there are some great choices out there today, Vixen, Takahashi, Williams optics to name but a few reputable brands.

Doublet/triplet refers to either 2 or 3 baffles inside the scope to dampen internal reflection, 3 is better

Fintan, I just had a brain fart there :oops: what was I thinking, of course you are right, it's just these damn bright nights

Yours dreaming on.........

Keith..

Woops meant FL 51 methinks! Thanks guys this has been very helpful! Ive been talking to trevor durity and he said that the WO 72mm scope is fantastic. its an APO and it has ED glass. A doublet also. and for 370€ you cant go wrong with its reputation!

However im still undecided about the mount! Well suck it and see i suppose.

If any one has any alternative scopes or setups id love to hear your ideas!

Many thanks again guys!

Yep the 72 is supposed to be quite a bit better than the 66 SD which I have. There was a good review in a recent magazine.

Both are APOs, both are air spaced doublets. I think the 66 uses fpl51 which doesn't give the same correction that fpl53 can + the 72 is a Megrez which is a step up in mechanical quality than the Zenithstar series (the 66 is a zs). That said if you are bang on focus I doubt the glass will make much of a difference.

BTW I believe one of the reasons that triplets are so favourable is that they can give inherently flatter fields straight from the bat - so maybe no need for a flattener? Could be wrong though.

The ED scopes usually have a single ED element so they are not as corrected as true APOs. "True APO" is becoming a bit of a hot debate now though, e.g. my Megrez90 is good but it couldn't compete optically with a Tak or AP of the same aperture methinks

Trev

But the 72 is an APO scope and also has ED glass!

IM getting confused!

Anywho im fairly sold on the megrez 72 and at 370€ its a steal! Now to win the lottery.....

I might have the money saved up soon!

I'm also looking for a (pseudo) APO for my AstroTrac .

Specifically, I'm looking at these:

William Optics Megrez 72mm

William Optics 80mm

Orion EON 72mm ED APO

Apochromatic Refractor 80mm OTA (FPL53 glass)

I'm very tempted to go with the WO 72.

Keep the comments and recommendations coming