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School USSR refractors. The path of “perfection”

The author of the article is Alexey Petsyk, an astronomy lover from Moscow.
The material was published on the website star-hunter.ru at the personal request of the author of the article.
All rights to text and illustrations belong to Alexey Petsyk.
The author of the translation into English is Ruslan Ilnitsky
Translator’s note is in italics.

Perfect is the worst enemy of Good Enough!

But if we pick up … a telescope and look at the sky
with an assisted sight, we will see two stars,
three stars, four stars …
Best of all, of course, five stars!

 

Chapter 1

Small school refractor

Small School Refractor (MShR) RTM-60 - modifications

Small School Refractor (MShR) RTM-60 – modifications

After completing work on the history of the School meniscus telescopes of the USSR, somehow it turned out by itself that I was interested in school refractors of which in the USSR, as everyone knows, 2 types were produced – Large Small school refractor (Bol’shoy Shkol’nyy Refraktor  – BShR) and Small School Refractor (Malyy Shkol’nyy Refraktor – MShR).
It would seem that there is not much to collect here – well, there are two – but this turned out to be true only at first glance. Having dealt with the topic more closely, I found out that the MShR was produced in at least 6 modifications (and the BShR – probably more, until I counted seven), and the development did not go as expected “from simple to complex”, but for some reason the other way around, with what something with an increasing degree of simplification. This article is devoted to the description of the history of the release and “improvement” of the MShR.
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SVBONY SV171 Zoom Eyepiece 8mm-24mm review

I received an SVBONY SV171 Zoom Eyepiece 8mm-24mm (SKU: W9131A). for testing. The zoom eyepiece is very convenient for quickly selecting the optimal magnification, or for cases when you need to quickly change the magnification without having to change eyepieces. The focal length in the zoom eyepiece is changed by rotating the body. Along with the focal length, the angular field of view of the eyepiece also changes.

Declared characteristics:

Focal Length  8-24 mm
Eye Relief 18-19.5 mm
Apparent Field of View 38°-56°
Barrel Size 1.25″
Lens Structure  7-Elements/4-Groups
Filter Threads Standard 1.25″(M28.5 x 0.6)
Coatings Fully Multi-Coated
Blackened Lens Edges Yes
Barrel Safety Recess Yes
Eyecups Twist-Up, metal

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The Explore Scientific 52 ° eyepiece line went on sale in mid-2018. It is represented by eyepieces with a focal length of 3, 4,5, 6,5, 10, 15, 20, 25, 30 and 40 mm.
In my opinion, the greatest interest for observing the planets and the moon is represented by the values of 3 mm, 4,5 mm and 6,5 mm – they are made according to the “negative doublet + Plossl” scheme.

Explore Scientific LER 52 ° 6,5 mm, 1.25 “(AR) eyepiece came to my test.

Explore Scientific LER 52° 6,5 mm, 1,25

Explore Scientific LER 52° 6,5 mm, 1,25″ (AR)

Specs
Item Number: EPWP5265–01
Type: parfocal
Coatings: EMD (Enhanced Multi-Layer Deposition) on all lens-to-air surfaces
Lens elements/ groups: 6 Elements in 3 Groups; Edge Blackened
Field of view: 52° (measured – 51,2°)
Focal length:  6,5 mm
Eye relief: 15,9 mm (measured – 16 ±1 mm)
Field Stop Diameter: 5,9 mm
Barrel Size/Type: 1.25″ O.D. / Double Taper
Filter Thread Fits Standard 1.25-inch Dia. Thread in Filters (1.125-inches x 42 TPI) (measured thread diameter – 28 mm)
Waterproof O-Ring Sealed Argon Gas Purged; Tested Under 1 Meter of Water for 30 Minutes
Eyecup: Removable Flip-Down Style Soft Silicone Rubber
Materials: Optical Glass; Aluminum; Steel; Silicone Rubber
Length: 103.5mm  (measured – 104 mm)
Width: 43 mm (measured – 43 mm)
Weight: 226,8 grams (measured – with protective covers 227 grams, withot protective covers 220,7 grams)
Markings: Laser Engraved: Focal Length; Series; Serial Number; Brand
Country of origin: China for Explore Scientific (Germany)

The eyepiece comes in a beautiful cardboard box. The kit includes an eyepiece, 2 plastic protective covers and a dustproof bag made of soft fabric. The eyepiece is packed reliably, you can not worry about its safety during shipment.
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