Friday, 11 March 2016

Bigger is better!

There's no field where the above statement is more true than in astronomy. No matter how you cut it or for how long we discuss about image quality, contrast and light-pollutes skies, there simply is no substitute for aperture. In the 35 years that I've been an astronomy enthusiast I've had the privilege of owning or using just about every type of telescope you can imagine, even some very exotic ones like a 25cm f/20 Schiefspiegler built by the extravagant German artist Anton Kutter. But every single time that I've had the opportunity to compare two different instruments of equal build quality, the bigger one always won the contest. So over the years my hunger for more became an unstoppable craving. The desire to see ever better and to penetrate ever deeper into the depths of our universe in order to satisfy my humble curiosity kept throbbing in my chest. I just couldn't help it. I got overwhelmed by an extremely virulent disease we astronomists call "aperture fever". It basically means that you can't stop buying new, and especially bigger, telescopes. Once you're under its spell, there's hardly any cure and the only thing you can do is to give in. So after my very first scope, a small 60mm Vixen refractor which I've held and pushed to the limits for almost 20 years (!), I bought a 20cm (8") Celestron Schmidt-Cassegrain (or more commonly called "SCT"). The 8" SCT was everybody's dream telescope in the 1980's but at the time only accessible to a lucky few, so you can imagine how happy I felt when I realised that I could finally afford one! Only to find out... that over time things had changed a little and that the 8" SCT was no longer the mightiest kid on the block. 

In the 1960's an American amateur astronomer called John Dobson built his first telescope out of plywood, formica, closet flanges and other bits and bobs. Its design was incredibly simple: a classic Newtonian reflector on a home-built mount which allowed you to move the telescope to the left or right and up or down. No complex equatorial mount with gearboxes and motor drive. No aluminium tripods and counterweights. It just looked like a giant soap drum on a wooden crate. But oh boy did it perform! The enormous advantage of the simplified version of old Newton's design was that you got a lot of all-important telescope aperture for very little money. Many amateurs even started grinding their own mirrors with surprising results and by the end of the 1980's a 20cm (8") mirror had become small compared to what many astronomers managed to build in their own garage. It didn't take long before the so-called Dobsonian telescope was commercialised and these days the names of Obsession, Starmaster, Webster and Lukehurst resound stronger in the astronomy world than the classical telescope manufacturing brands such as Meade, Celestron and the like. Moreover, the home-grinded optics of the Dobsonians are usually far superior to those of the large-batch factory telescopes and are probably only exceeded in quality by Nasa.

When I eventually put my 8" SCT next to a friend's completely home-built 35cm (14") Dobsonian, I was in for a shock. Not only did it blow my classic telescope to smithereens optically speaking, my friend had actually paid a lot less for his telescope than I had done for mine! So my SCT quickly ended up for sale because I wanted to see at least as much as what I had seen through that 14". So I got a 14,5" second hand. A wonderful telescope made completely out of carbon fibre, which made it extremely light and incredibly easy to transport to a dark site. But still my hunger wasn't satifsied so two years later I built my own 18" Dobsonian: the notorious PeterDob. But then I ran into another problem. After having spent the first 30 years of my astronomy existence peering through telescopes with one single eye, I got sick and tired of it. I tried to use an eyepatch so I didn't have to squeeze the eye I didn't use all the time, but that didn't help. The ideal solution appeared to be a so-called binoviewer: a set of prisms that split the single light beam of the telescope in two so you can watch with both eyes. Unfortunately, these binoviewers come with a price and I'm not just talking (a lot of) money here. In the end a binoviewer doesn't just split the light beam but also loses a lot of it in the process. Considering that for astronomical observing you need every photon you can get, this was very bad news indeed. On top of that, binoviewers are long and in order to get them to focus you need to attach a corrector lens in front of it which squeezes out even more light and comes with an unwanted extra magnification. Eventually I've owned or tried just about every binoviewer on the market, from the cheap chinese over the top-notch Baaders and Denkmeiers up to the enormous 2" Siebert beast. None of them, however, were able to show me as much as with single-eyed viewing and this was yet another disappointment. 

Now, I've come at a point in my life where I want to buy the telescope of my dreams, an instrument that will keep me happy for the rest of my life and which will not be a compromise of any kind. Of course there are limits and budget isn't the most important one. You can want the biggest telescope in the universe but what good is it if you can't get it in or out of your garage? Worse still, what use is an incredibly big telescope when you're living in a city centre and need to get way out of town to find a decent sky for observing? So in the end, my dream telescope is still a compromise but one that will be difficult to surpass: a 457mm (18") BINO-Dobson! Yes! You've read it correctly! I've ordered a telescope that's essentially two 18" Dobsonians tied together so you can watch with one eye in each! No more nasty binoviewer hassle, increased magnification, light loss and... it comes with another incredible advantage over monocular telescopes with a much bigger mirror: a binoscope delivers the same optical performance as a telescope with 1,4 times its diameter (so my 18" bino will be at least equal to a 25" mono), but you can still use rather low magnifications. I already explained that telescopes have a minimum magnification and that this increases with its aperture. For example, with a 25" mono you can forget looking at the entire Orion Nebula in the same field of view. With my 18" bino on the other hand, this is still perfectly possible. But there is more. Watching with two eyes seriously increases contrast. That's because it's unlikely that a weak but "true" light signal is being discarded by both eyes as "false" at the same time. The result is a darker background and much more contrast on faint objects. According to scientists, a binoscope therefore performs like a telescope even 1,8 times its diameter here! For my 18" that would mean the performance of a 32" without the latter's enormous size, weight, unearthly minimum magnification and having to stand on a ten-foot ladder. 

Critics of this rather new kind of telescopes say that they're incredibly difficult to adjust because the alignment of both tubes must be absolutely perfect. This is true, but nowadays the build quality and technical solutions more than take care of that. Some also argue that a binoscope is exuberantly expensive. That... turned out to be false! Actually I'm paying a lot less now than if I had ordered a classic 25" Dobsonian from a quality manufacturer, let alone a 32". 

Currently, after having waited for almost a year, my dream telescope is almost finished. I can't thank the builder, Mr. Otte, enough for his excellent craftsmanship and patience and hope that it'll arrive at my door soon. There's still a lot of testing to be done but now I'm sure that I've found the perfect telescope for me. And then... I'll keep posting hundreds of sketches here so you can have part of the fun as well. And shouldn't that be enough to satisfy you, Italy isn't all that far away...

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