This is a very, very well made refractor particularly suited for solar observing and imaging. The objective was designed by the late Thomas Back and defined to be an “enhanced achromat”. It uses Ohara S-PMH53 and S-LAH51 glasses for optimum color correction. The scope was initially sold under the brand Burgess Optical and later by the German firm Astro-Professional, with minor differences in the OTA. My one belongs to this latter production and I purchased it from an English amateur because as far as I know the Planet Hunter never circulated in Italy.
The scope has a nominal diameter of 80 mm and an effective aperture of 77 mm with 900 mm focal length (f/11.7). The tube is white, well finished, provided of a Taiwanese-made Crayford focuser with 1:10 reduction which is very useful for focusing at high powers and during high resolution imaging.
Compared side-by-side with a TS 80 mm f/7 refractor (FPL-51 doublet) the Planet Hunter showed better diffraction images and, particularly, much less color; actually the PH can be defined more as a semi-apochromatic refractor than an achromat.
The most striking difference between the two can be seen in the near UV that is in calcium imaging, K and H lines. This is the chromosphere in the calcium line as it appears on the screen during imaging with the TS 80ED:
quite blurred indeed, while below is about the same region in the Planet Hunter after processing
which shows reverse granulation and plage network in good detail, of course within the limits of a 80 mm aperture.
The scope is therefore really well corrected from spherical aberration at short wavelengths. Images in the H alpha are also good but not significantly better than in my 150 mm achromat reduced to 104 mm (f/7.2).