Hello friends,
Back with a topic that never seems to never really get resolved!
I am trying to gauge the better choice between the following FCD1 triplet and these similarly priced FPL53 doublets:
a) Explorer Scientific ED 102mm F/7 FCD1 Triplet (currently retailing for around £900), vs
b) Any of the Kunming ED 102 F/7 FPL53 Doublet variants (such as the Altair Starwave 102ED-R FPL53 or the TS-Optics Doublet SD Apo 102) (all also currently retailing for around £900)
All other factors aside (such as price, cool down time, quality of the focuser, included accessories etc.), which has the superior optics for viewing and photo use – the ES FCD1 Triplet or the Kunming FPL53 Doublet? Has anyone here on SGL had the opportunity to directly A/B test them side-by-side? And if so, do you have any photographic evidence you could share? I’ve searched the forums as well as Astrobin, but have never found a satisfactory answer to this, and due to COVID (as well as the unfortunate lack of an adequate returns policy from many retailers), I am unable to test these out in the flesh. I’m a numbers guy, so looking for solid evidence or any data that can prove the superiority of one over the other. Any specialists in optics out there that care to chime in? The closest I’ve come to an answer is in this link that someone on the forums posted:
https://www.telescope-optics.net/polychromatic_psf.htm
The charts in this document seem to suggest the triplet is the better option, but I know there are a lot of variables including build quality / QC etc that come into play, hence why I am asking about these specific scopes as opposed to triplets and doublets in general.
Some background: Like many, I’m in the market for an affordable (<£1,000) semi-APO refractor for some casual observing. I plan to use this primarily for visual use (save for the odd shot of the moon taken from my smartphone with a suitable adapter) – mostly lunar and planetary viewing to be specific, from my balcony in (light polluted) central London. I already have a larger, rather heavy SCT on an EQ mount gathering dust in the basement, and I’m looking to simply my rig by switching over to a relatively light 4-inch refractor on a solid AZ mount. This size was chosen for being small / easily manoeuvrable, allowing adequate magnification for my needs (I have achieved a crisp 250x on similar sized ED scopes with good seeing), as well as for having the maximum aperture that I can afford at this time (i.e. that the Mrs will allow).
As far as the mount is concerned, I’ll be using it with the TS Optics AZ5 (Skytee 2 clone) on vibration pads, with upgraded ADM saddles and a heavy-duty Skywatcher 1.75” steel tripod (borrowed from my EQ mount), on which it will be mounted weight-balanced with the top slot for the Telrad. The scope will be used with my Nagler 3-6mm and Pentax 8-24mm zoom eyepieces.
I should mention that I briefly owned a cheap Celestron refractor that I bought on impulse, wrongly believing that I could improve it by using a quality diagonal and eyepieces. Unfortunately, the CA was unbearable (the purple fringe was wide enough to severely compromise planetary viewing) and expensive eyepieces made no discernible improvement, forcing me to return it. Lesson learned: your rig is only as good as the weakest link in the optical chain. Apologies for the long post, but I’m trying to avoid the usual, “I haven’t tried them both, but they both seem like great scopes…” type responses.
All the best,
Al