It was such a great (5.00 a.m.) morning here in the Lower Blue Mountains I decided to use my my near 40 year old 4" Unitron Alt/Az refractor to view the Moon and Jupiter which were favourably placed in the sky. The Unitron was my first telescope bought new back in either 1969 or 1970 for the princely sum of $299. These f15 scopes are brilliant performers however the old Unitron 0.965" eyepieces whilst very sharp have poor eye relief and small field of views.
I tried out a number of 1.25" EP's including Tak 3.6mm, 5mm, 7.5mm, 12.5mm, Baader Hyperion 24mm and an Ethos 13mm. The Taks were superb as expected showing no CA and were sharp right to the edge of the fields. The Hyperion surprised me as it was sharp right to the edge of the field which isn't the case with my Tak TOA-130 and SKY-90. It seems that long focal length scopes are kinder than the recent crop of faster ones. I wasn't prepared for the views through the Ethos however, the Moon and Jupiter at 115X were simply stunning. The contrast in the bands on Jupiter were every bit as sharp as my Taks and the moons were pinpoint sharp. One of the moons this morning was very close the the planet and I'll have to do some research to find out which one. Viewing the moon with earthshine at 115X I estimate the field of view was around 3/4 of a degree so there was plenty of room to spare to take it all in.
One of my other surprises was that I normally wear glasses as I suffer from astigmatism in the order of 2.00 diopters in both eyes. For some unknown reason there was no need to wear them with the scope/EP combinations. I think it all has to do with the size of the exit pupil as astigmatism isn't a factor around the 1mm mark.
Another aspect of the setup is the diagonal. I used a 1.25" Unitron prism diagonal from my 6" Unitron (circa 1960) and it performed flawlessly. No streaking, ghosting etc. of any kind and from an uncoated prism!
I am sure that many amateur astronomers (mainly younger ones) have not seen what a superb achromat can do. The Unitron excels in splitting double stars, one example being Antares. To view Antares small green companion is no mean feat especially as it is so bright in comparison. The airy discs of Antares are so clearly defined that you have to be patient in detecting the companion between the diffraction rings. Alpha Crucis is another example, although easy to separate, the stars are two perfectly even blue pinpoint spheres with both airy discs interacting.
I have attached some pics of the Unitron and hope this small contribution to the forum will be of interest.
They are very pretty scopes steve ..Its quite an eye opener as to what our american brothers are prepared to pay for one of these smallish refractors with all the bells and whistles .
Wow, that brings back memories! I never had one but a bloke I used to know did. Those where the days when long f-ratios were still appreciated. You've got me thinking about some of the old scopes I knew like the ubiquitous 60mm Unitron refractor or the original C-8s.
For what it's worth I've got a couple of old Unitron eyepieces. The 40mm Kellner was basically retired years ago but I still like the 20mm Erfle. I've got better eyepieces in that size now but it is just so comfortable to use I still enjoy it.
