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Following on from 70mm "Shootout", Part 1: Daylight... Well, this is going to be a whole lot shorter . Sky wasn't brilliant, but it at least permitted comparisons. A reminder: LE = Lunt Engineering 16x70 HA = Helios Apollo 15x70 S2 = Helios Stellar II 15x70 Strath = Strathspey 15x70 Dark space visible between members of δ Cep (40 arsec, mags +4.1, +6.1): LE: starts to deteriorate at 80%, still visible at 90% of FoV HA: starts to deteriorate at 50%, still visible at 75% of FoV S2: starts to deteriorate at 40%, still visible at 50% of FoV Strath: starts to deteriorate at 25%, still visible at: 30% of FoV Faintest star seen NGC 1981: LE: +9.7 HA: +9.6 S2: +9.3 Strath: +8.9 Trapezium stars seen: LE: 3 (fleeting) HA: 2 S2: 2 (fleeting) Strath: not split. Impression of M42: LE: Clear and detailed HA: Slightly less crisp than LE S2: Similar to HA, but not quite as bright Strath: Comparatively washed out. Jupiter-Io, 28 arcsec separation: Could resolve Io in LE, not in others (washed out by planet glare) Glare from Moon just outside edge of field: LE: None HA: Perceptible S2: Obtrusive Strath: Very obtrusive Colour rendition: LE: "vibrant" HA: good - colours of μ,ζ,λ,δ Cephei easily distinguished S2: as HA Strath: Washed out, ζ and δ look very similar Chromatic aberrration: LE: V. good on axis, noticeable but not obtrusive on Venus and lunar off-axis, none on first magnitude stars (but colour of Betelgeuse seemed to change slightly towards the edge of field). Very sensitive to correct eye positioning! HA: Good on axis, noticeable on Venus and the lunar limb even slightly off-axis, noticeable on first magnitude stars near the edge of the field of view. S2: as HA Strath: Halos on 1st mag stars on axis. Noticeable off axis. Contrast: LE > HA > S2 > Strath The LE did not "feel" brighter than the HA, but it was the increased contrast that enabled slightly fainter stars to be seen. It is also probably what made M42 seem so much crisper. Verdicts on the "new" ones: LE: Really nice binocular. Lighter and crisper than the HA. I got one. S2. Mixed bag. Probably the least expensive "true" 70mm around, but optical quality (especially contrast and control of stray light) not as good as the Pentax 20x60, which is the same price at TBS. Full reviews on both of these now posted on my Reviews Page.
One of the other subsections here had the owner of a 70x700mm Bresser refractor grumbling about the views he got with his telescope. This prompted me to get my 70mm out on 28 Dec and have a look through it. I should explain that this is a vintage Ross terrestrial telescope, originally sold by Charles Frank as an astronomical telescope with an equatorial mount. I didn't get the mount and surveyor-style tripod, as the son of the late owner wanted a lot for them compared with the scope. The mount looked like it needed a rebuild anyway. That was probably a mistake as I later spent nearly £200 providing an adequate mount for a very long telescope weighing around 5Kg. It has a 33mm dia (note that figure) Huygenian eyepiece and an erector lens set. This eyepiece slides out (one can feel the air pressure sucking it back in) and can be replaced by a 31.7mm dia astro eyepiece wedged in with a bit of card. With the erector set left in place the effective focal length is ridiculously long (over 3 metres), and even a 25mm astro eyepiece gives a high magnification. Many decades ago, a 3" brass refractor was what amateur astronomers aspired to. So how does it perform? On a previous outing I could see Airy disks with it. On the recent outing I got, with poor seeing, Venus as a half-disc with some yellow aberration at the bottom, Mars as a clean reddish disc, both close doubles of epsilon1 and epsilon2 Lyrae resolved, Gamma Ari well split, and Beta Cyg split easily and and looking good. Under these conditions a much bigger telescope would not have done strikingly better (as I proved a few nights later with my 200p trained on Mars and Venus). My Mak would not do much better with the original eyepieces. It's a shame that newbies may not get the chance to see what a 70mm aperture can do before they are urged to get a big aperture scope regardless of mounting type. Unfortunately some of the 70x700 mm refractors on offer will be made to be cheap rather than delivering maximum performance. How much would one have to pay today for a 70mm f10 'frac to guarantee premium performance? Rather a lot, I suspect, but the mounting can be lighter. Of course, a larger aperture scores on nebulae, galaxies and star clusters, where it makes a big difference to the spectacle.
Hi, I'm looking at getting a short focal length, wide field scope to add to my equipment list if possible. Uses will mainly be wide field visual, some EAA, and a gentle 'dip the toe' into imaging. There seems to be a wealth of choice currently, especially offered from TS and Altair. Ideally looking at the 60 to 70mm offerings from Altair but would consider others. Many thanks for reading,