Smart Astronomy 2" 90° Dielectric Diagonal

4.0 Smart Astronomy (Galaxy optics) 2" Dielectric Diagonal.

Tough Dielectric coatings. Optically very good with an attractive,durable design and finish. Good ergonomics.

Price may be high now compared to others?

I became a fan of William Optics products after buying their Crayford focuser to use on my 6" Mak. I mention this because this diagonal appears to be the same(and has the same specs)as the W.O. 2" dielectric diagonal without the massive price tag. A reputable UK dealer is currently selling the W.O. version for 159 pounds, or over $300! The SmartAstronomy 'clone' cost me somewhat less.

Although it's an interesting question, without the necessary testing equipment it's not possible to say if this diagonal is effectively the same as the W.O. one, but is there any readily perceivable difference? Since the 14oz Aluminum body is identical in every way the solid, ergonomically correct, 'quality' feel of this diagonal can be taken as read and this impression remained when I began to use it.

There isn't any noticeable light loss because the dielectric coating is essentially a perfect reflector and more importantly the mirrors accuracy does seem to leave those photons where they're meant to be instead of smearing them into halos around bright objects or generally brightening the sky background. Fine detail on the moon and planets is left intact,although I had a nasty surprise when I took the diagonal from a warm room straight into the cold and tried to use it immediately. There was quite an active weather system going in that Aluminum housing, but it quickly died down as everything reached ambient temperature. Something that can't be avoided is the change in focus position that using any diagonal causes and just using primary mirror movement to focus is s l o w, so for SCT's and Maks an add on Crayford is preferable, although a low profile 2-1/4" adapter instead of the somewhat chunky one supplied would have helped.

So for me at least this diagonal does what it's supposed to do at a price that's a little easier to justify.

Since buying it about eight months ago the price of $120 has become less of an advantage as a W.O. 'original' can be had in the states for maybe another $25 with, I expect, a higher re-sale value. Also SmartAstronomy now offers other very attractive diagonals at prices that are very competitive with this one. It's good to have the choice though.