Why I bought a (Takahashi) doublet refractor

Buying your first telescope is simple. You either buy a junk scope from a department store and quit the hobby soon thereafter, or you do some research and buy an 8” Dobsonian.

And an 8” Dobsonian I bought at age 11 or 12 after my parents made the mistake of buying me a book on astronomy for Christmas. I remember lugging out that scope, as tall as I was at the time, out to my backyard for more nights than I can count, and being mesmerized by all of the things I could find in the night sky. It provided years of wonderful views, and still works well today, almost 2 decades later, although it could use a re-coating on the mirror (blog post about this forthcoming).

After a 5-year hiatus from astronomy, and after finally getting my license and a car, (and probably after one too many days of covid-induced boredom), I decided to rediscover my passion for astronomy. I re-joining the exec team at the UBC Astronomy Club and purchased a pair of Canon 15x50 image-stabilized binoculars, with the hope that I could take them camping and on road trips with me, portable and easy-to-use as they are.

It wasn’t long before I decided to purchase a new telescope, one that could supplement my 8” Dob with wide-field views and excellent lunar and planetary performance. I also wanted something that was easily portable, quick to set up, and nice to use. All of these requirements point to an apochromatic refractor telescope in the 4-5” aperture range.

I called my local telescope store, Markarian Fine Optics, and spoke to owner Harout (fun fact, he sold me my 8” dob ~16 years prior!). He’s a self-confessed refractor lover, and we had a long chat about the best options that would suit my needs. Initially, I was hoping to buy a triplet refractor, which uses 3 lenses to reduce chromatic aberration, over a doublet, thinking that the triplet would improve visual performance over the doublet, but Harout wisely talked me out of it.

A triplet has several drawbacks over a doublet. The additional lens of a triplet means that it is noticeably heavier than a doublet, requiring a beefier mount, resulting in a package that is generally more painful to set up and move around. More glass, in turn, slows down the cooling time of the telescope; larger triplets could take over an hour to cool, while a doublet might take less than half that time. Triplets are also more sensitive to collimation, as it requires 3 lenses to be in perfect alignment over the 2 lenses of a doublet. Additionally, a doublet will, all else being equal, scatter less light than the triplet, having one fewer glass element; less scatter means improved contrast, especially valuable for critical planetary and lunar observations. Finally, a well-made triplet is substantially more expensive than a well-made doublet.

So, having settled on buying a fine apochromatic doublet, I had to decide which one to buy. I really had two choices; I could buy a cheaper, Taiwanese/Chinese made telescope from Skywatcher/William Optics/Astro-Tech/etc., or I could buy a more expensive Japanese or American made telescope from Televue (optics admittedly are sourced from Taiwan), Astro-Physics (chronically in short supply), Stellarvue, or Takahashi. While the cheaper Taiwanese/Chinese scopes can be a good buy, they tend to have looser quality assurance. The Japanese and American scopes, by contrast, have a reputation for consistently excellent optics and customer service. During my call with Harout, he suggested that I look into the Skywatcher 100ED or 120ED refractors, which typically have excellent optics. He warned, however, that the mechanics of the telescope, especially the focuser, was not adequate, and would struggle with the heavy eyepieces I was planning to use. Replacing the focuser would easily add another ~$300 to the total cost.

The price of the Skywatcher doublets had skyrocketed recently, due to covid-induced cost increases and supply-chain issues. Telescopes were generally in short supply; I suppose astronomy is a good hobby during a pandemic! It was hard for me to stomach the idea of paying a decent chunk of money for the Skywatcher scopes, having noticed that the scopes tend to fall in price rather dramatically on the used market. I’ve also learned that it’s better to buy once/cry once, rather than buy something of lesser quality and inevitably upgrade in the future. Having to upgrade the focuser right off the bat on a brand-new purchase didn’t sit right with me either.

So I decided to get a nicer refractor. First on my list was the Televue NP101is, a 4” Petzval refractor prized for its wide, flat view and great optics. I’ve coveted this refractor since I was a kid, reading about this venerable scope in the Backyard Astronomer’s Guide. In it, the authors noted, “Optics don’t get any better than this” - as high a praise as one could give. This particular model, the NP101is, was optimized for imaging, removing the need to buy expensive field flatteners and reducers. The cost, of course, was high; with the necessary mounting accessories, probably running over $6000.

I chatted with Harout again and asked about the Televue scope. He praised it, saying that it was a good choice, but also mentioned that he had a Takahashi refractor on order, and asked if I’d be interested in that scope. Takahashi, of course, is a legendary telescope maker in Japan, known for pioneering the use of fluorite glass in telescopes. Fluorite is prized for its very low scatter of light and exceptionally low dispersion, improving contrast while simultaneously reducing chromatic aberration. Takahashi’s fluorite doublets are considered the very best doublet refractors available. The particular Takahashi on order was a relatively new model, the FC-100DZ, a 4” fluorite doublet made to improve on the already-excellent performance of the other doublets in the lineup. Of course, the price was high but significantly cheaper than the Televue - and it was going to be available sooner. After reading some glowing reviews of the telescope, the choice was clear. The Takahashi FC-100DZ was going to be mine.

After an agonizingly long wait, caused by delays in the Texas port where the container ship carrying the precious cargo arrived, the telescope was air-shipped to Markarian, where I picked it up the day it arrived. It came triple-boxed and in perfect condition. Harout and I ooo’d and aww’d over it for a while, then took it outside to check the optics. Fantastic, as expected, the sharpest refractor I’ve used, and also one of the nicest looking.

And that’s how my Dob came to have a friend.

The Takahashi’s name is Takurrito.