Scope Views Home



Follow @scope_views


Solar Viewing with Peter Drew at the Astronomy Centre

Peter using his H-alpha converted Vixen FL102

We were camping with friends recently, sitting on camp chairs under a starry sky watching a crescent Moon dipping over the estuary and Perseids streak overhead every few seconds, sipping beers and munching crisps. It was all very convivial. My daughter asked Fred – a friend from before school days – what I had been like as a teenager at school. Fred thought for a moment.

“Conventional …” he replied, never one to waste or mince words.

Long summer evenings mean the Moon and bright planets, no deep sky.

He’s probably right. I’m certainly a bit slow to take up new fads, a good example being H-Alpha solar astronomy. It’s true that from May through July up here, the same wonderfully long summer days that let me finish a day on the fells at ten PM also mean that astronomy is effectively cancelled for three months of the year (apart perhaps from the odd look at the Moon or a bright planet). It’s also true that Solar observing is the obvious way to keep the hobby going through Summer. But until now, the only solar observing I’ve done regularly is with the white-light filter on my antique Questar: it’s a good way to see Sunspots, but not really much else.

One problem has always been the cost of a decent H-alpha scope and I hadn’t been all that impressed with a small Coronado I looked through a few years back. But when I got an invite, from well-known amateur astronomer and professional telescope-maker, Peter Drew, to check-out one of his H-alpha conversions I jumped at the chance. I had heard that Peter’s innovative approach makes large-aperture, high performance H-alpha scopes available at budget prices. So I went to the Astronomy Centre – Peter’s long-term project and workplace – with mutual friend Paul Yates, to see if the claims I’d heard were true.

The Astronomy Centre

The centre’s observatory is located on the A681 between Bacup and Todmorden in Lancashire, on the brown-field site of an old clay pipe factory that Peter has been re-developing for thirty years. Whilst the pipe factory has vanished (apart from an old photo in the main observatory building), mill-town era views – a row of cottages set in the midst of a bleak moor, a brick mill chimney held up by rusting steel bands – are round every corner on the drive south from the M65. The observatory benefits from a dark-sky moorland location, with only love-em-or-loathe-em windmill farms for company. Driving out of Bacup on the A681 you can’t miss the place, which has a large dome (and several smaller ones) that are obvious on the left of the road.

The Astronomy Centre has an impressive array of telescopes and Peter is actively adding more. The main observatory has a surprisingly large ‘proper’ metal dome atop a big stone-built drum that reminds of the observatories Ivy League universities were building a century ago. It’s exactly the kind of observatory I dream of in those ‘what if I won the lottery moments’. The basement acts as Peter’s workshop; both it and the sub-basement are sweetshop-stuffed with all manner of telescopes, binoculars and mounts. ‘Aladdin’s Cave’ is a cliché, but if you’re an Astronomer that how it feels.

The main dome currently contains a 16” Meade on a superb professional mount, but could easily take a much larger instrument. I joke with Peter that what that stately dome and massive mount needs is a really big refractor; I’m thinking a 12-16” LZOS APO. “You buy it, we’ll house it.” Peter quips back. If only …

One bonus of having such a large dome is that there is plenty of room for school or public-outreach groups (and of course other equipment). One of Peter’s sidelines has always been camera obscurers and he has installed one in a dark ‘corner’ of the main dome for fun – it projects startlingly vivid scenes from the surroundings onto a circular white table. We all know how the obscurer works, it’s just a big long-focus objective with a right-angle mirror, but the effect in the darkened dome is fascinating because the image has such high resolution which just goes on revealing extreme detail with a table-top magnifier.

The hillside behind the big dome has a number of smaller instruments in aluminium domes fabricated by Peter. These include a second 16” Meade on the original huge fork mount and an eight-inch achromat on a magnificent German equatorial reminiscent of the mount for the Astro-Systems Newtonian I owned in my teens. I mention this similarity to Peter and he reminds me that he used to run Astro Systems with Rob Miller (whom I knew well as a teenager and bought the Newtonian from) back in the ‘70s and ‘80s. Incidentally, Rob himself went on to design and work-on some of the best mounts currently available from the likes of Astro-Physics (including my AP1200) and Paramount.

Other smaller structures around the site are run-off observatories for giant binoculars – another speciality of Peter’s. He is currently working on several more of these secondary instruments to enhance the public outreach experience and in the basement of the main dome he shows me a superbly made pair of 12” Newtonian binoculars ready to deploy.

Peter Drew with custom-built 12” Newtonian binoculars.

All these instruments would make for a superb dark-sky viewing experience I’m sure – something I hope to confirm in due course! For today though, the reason I’m here is to try-out one of Peter’s H-Alpha conversions.

Design and Build

The approach Peter uses is to convert a long-focal length refractor (F10 is ideal) by inserting a broadband filter to reduce the incoming energy across the spectrum, either before or after the objective, and then do all the clever H-alpha filtering in a module at the back that plugs in downstream of the focuser. The H-alpha module is based on the back-end of a Coronado PST with a custom made adapter.

This approach has two huge advantages:

1)      You end up with a large aperture, high-resolution solar telescope for much, much less than Coronado or Lunt would charge.

2)      The converted scope can easily be used for conventional astronomy by removing the blocking filter and the H-alpha module, rationalising costs even further.



PST module attached to the focuser, broadband filter to the objective.

The example I had come to experience was based on a Vixen FL102, which at F9 suffers slight vignetting, but still offers performance at Coronado 90+ levels for a fraction  of the cost. Apparently F10 TAL achromats also work very well as a much cheaper alternative to the Vixen.

In this case, the broadband blocking filter goes over the objective, leaving the OTA unmolested, but Peter also showed me a solution where the filter slots into a port in the OTA – an even quicker and more convenient way of converting between day and night mode. I’d definitely go for the port option if using a cheaper OTA like the TAL (but understandably not for a valuable classic like the FL102).


In Use – Solar Observing

As I said, my previous experiences of H-alpha observing – with a friend’s 40mm Coronado – had been underwhelming, so I was unprepared for the experience of this scope. Admittedly, we were lucky with the seeing, which proved excellent and permitted resolution of fine detail. As it was, the view of the sun, even with a fairly cheap and basic eyepiece, was stunning, mesmerising. Granulation, plages, sunspots and their surrounding active regions, were all evident at very high resolution, but the eye-grabbing features were the filaments on the disk and the prominences on the limb.

One particular filament could be followed above the granulated photosphere, almost in 3D, until it connected with a large prominence hanging over the limb in spectacular arches, festoons and sprays. Over the course of that fine afternoon, we watched that prominence grow, split and subside, parts reconnecting with chromosphere. Later we witnessed a spot of intense brightness appear on the limb nearby,  from which another arching prominence rapidly began to erupt.

Peter recommended using a black hood, like the ones you see attached to old plate cameras, to enhance the contrast. It really worked, to yield detail at a level I had only previously seen in images from the Big Bear Solar Observatory.

Paul using a hood to enhance contrast – it looks a bit strange, but it works!

Overall, I admit that I was astounded: at the shear rate of change of these enormous solar structures and the seething, violent nature of our closest star they revealed; but also with the performance of Peter’s conversion. Comparison with a Coronado PST set up nearby illustrated just how much better the conversion performed, with premium optics, much more light grasp and 3-4x the resolution yielding views in an entirely different league using the same basic H-alpha technology (and potentially costing little more if you convert an existing scope).

Peter with an unconverted PST: the views through the conversion were in another league.



I am a real convert to H-alpha observing at the level offered by Peter Drew’s conversion (though frankly much less so with the basic PST shown above) and hope to own a similar conversion myself one day. Through a high-resolution H-alpha setup, the Sun is a very different animal from the one you see with a white light filter, with constantly changing activity and a mass of fine detail to enthral you through summer days. A conversion is undoubtedly the most economical way to get that really involving level of solar detail.