Commenting on the Explore Scientific 165mm refractor

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Lady Fraktor Slovakia
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Commenting on the Explore Scientific 165mm refractor

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Post by Lady Fraktor »


If this does not make sense in any area let me know, I am coming up on 5 weeks of 12-14 hour shifts without time off and not exactly sharp at the moment ;)

A conversation came up recently referring to the Explore Scientific 165mm triplet refractor using FPL-53 as the ELD element.

I had made a comment about this telescope in the past on AF.net which seems to be down now and was unable to get the article I posted from Roland Christen about maximum lens diameters when using FPL-53.

Forging ahead, the problem with making lenses from FPL-53 larger than 155mm is that the glass for the widest blanks is on average only 165mm wide.
Due to flowing onto a moving cooling belt the glass is sometimes wider by a couple of millimetres or narrower.
The glass has radiused edges due to the cooling in place and looks like clear water with wind ripples across the top surface and sides which adds to the difficulty of obtaining a piece wide enough to make a 165mm lens. The typical glass thickness is 40mm.
FPL-53 can also be made in strip form for smaller lenses.

That said, CFF Telescopes in Italy, every 2-3 years will make a limited number of 165mm FPL-53 triplets but usually no more than 9 in a run.
That in itself should say how hard it is to get a large enough piece of FPL-53 glass for a lens this size.
They have a constant run of 160mm or 165mm FPL-55 refractors as this glass can be produced up to 300mm wide and it is widely used by the majority of manufacturers making large lensed refractors.

Currently they have 2 lens blanks left so if you are looking for a quality 165mm f/7.9 FPL-53 triplet and have 9 990 Euro (includes VAT 23%) or 8 122 Euro (outside EU countries) it is there for the taking.


The design was originally put forward by Bresser if memory serves me and was originally going to use FPL-52 which when it was being made was wide enough to produce a lens.
Fast forwarding about 10 years and suddenly Explore Scientific have had this telescope setup at various astro shows but not to look through.
There is one review on youtube if you search quite a bit and it is not encouraging.
The owner has an issue with it as an imaging telescope as it is being outdone by his
Stellarvue SVX 130mm.
Another one that is in the wild is a sample that Bresser gifted to Scientific Association Osnabrück "Working Group Astro" in Germany in 2017.
https://www.bresser.de/c/de/astro-news/ ... ppe-astro/
The wording of the article makes it seem that it is still more a Bresser project than an Explore Scientific one.
I have come across no feedback of the performance so far.

So can Explore Scientific make a mass produced 165mm f/7 refractor?
Yes as long as they do not make it using FPL-53, if they insist on using FPL-53 these are going to be few and far between and at the price they are charging for them I cannot see them selling very many either way when there are actual known premium class instruments this size and larger being sold for much less.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, AXJ, AXD
Az/Alt: AYO Digi II/ Argo Navis, Stellarvue M2C/ Argo Navis
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Takahashi prism, TAL, Vixen flip mirror
Eyepieces: Antares to Zeiss
The only culture I have is from yogurt
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