Levenhuk Ra R66 ED Doublet Black OTA review

I am the owner of the Levenhuk Ra R66 ED Doublet Black OTA telescope. This is a compact lens telescope that has ED (low dispersion) glass in the lens. The use of low-dispersion glass can significantly reduce the chromaticity of the position in the telescope (colored halo around bright objects) compared to an achromatic telescope on conventional glass (crown/flint). Small ED refractors are usually used as a traveling telescope for photographing deep space objects, but they can be successfully used for visual observations, as well as photographing the Sun (always with protective filters) and the Moon.

I bought my telescope in January 2020 on the second hand in excellent condition, complete with original aluminum case and protective covers. By the information on the Internet, my telescope is at least 2014, and maybe older (from an old series). This review applies to older telescopes. The modern version, which is now on sale in stores, may have slight changes in design and appearance – a thread has been added at the outlet of the visual adapter, the inscriptions have changed slightly, and a few screws have been added to the body.

The kit includes:

• Telescope optical tube
• Cleaning wipe
• Aluminum case
• Protective caps
• User manual and lifetime warranty

There is no information about the brand of glass, but presumably it is S-FPL51.

The case reliably protects the tube during transportation, but when traveling with a telescope, I prefer to use a small backpack.

Some of my measurements:
Telescope length – approximately 310 mm
Telescope length with extended hood – 370 mm
External diameter of the hood – 84 mm
Weight with covers and finder platform – 1864 grams
Light diameter – 66 mm
Focuser travel – 61 mm
Focuser handle diameter – 39 mm (large), 28 mm (small)
Reduction of the small focuser handle – 1:10
The telescope body is made of metal with a glossy surface. The hood is retractable. At the bottom of the telescope there is a metal plate 80 mm long and 40 mm wide with 1/4″ holes for a photo tripod, it also acts as a Vixen format mounting plate for installation on a compatible mount.

The focuser is compatible with eyepieces and accessories with a 1.25″ fit. There is a brass ring on the visual adapter inside. You can unscrew the clamping ring with a screw, underneath it there is an SCT thread (like most Schmidt-Cassegrains – 2″-24). You can buy an adapter from STC to M48, or SCT-2″, or a 2″ diagonal mirror for SCT.

The focuser is dual-speed; for one revolution of the large knob, the small knob makes 10 revolutions. It is also possible to rotate the focuser around the optical axis; to do this, you need to loosen the ribbed ring in the middle part of the tube.

The measured aperture is exactly 66mm. The lens is two-lens, green-coated. The lens frame is metal. The adjustment screws were not found and adjustment is not provided. Inside there is a number of light-protective plastic diaphragms.
To unscrew the lens, you must first unscrew the metal ring on the front of the hood, then slide the hood towards the focuser until it stops, and then you can grab the front of the lens barrel and unscrew it.

Alas, the telescope does not have a platform for the finderscope. At all. Although there is an opinion that at such a focal length a finder is not needed, I do not agree with this. And attaching a platform for a standard finder is a whole quest. On the tube body near the ribbed focuser rotation ring there is one screw, which is intended for installing some kind of non-standard platform under a non-standard finder. As a result, I found a standard Svbony platform for the finder with holes in the center, carefully disassembled the tube (I completely unscrewed the ribbed focuser fixation ring, the tube splits into two halves), unscrewed this single screw, and using another screw with a nut, carefully connected the tube and the platform. Yes, it was also necessary to glue several plastic spacers to the base of the platform with double-sided tape, but the entire structure holds securely.

Impressions of use
The advantages of the telescope include, first of all, its compactness and portability; I regularly take the Levenhuk Ra R66 ED Doublet Black OTA with me when traveling around Russia to various astronomical events (festivals, tours). I will also note the rapid thermal stabilization – in the warm season it is almost always ready for observations.

The telescope does not come with eyepieces, so you must either purchase additional ones or use eyepieces from another telescope. The required focal lengths are from 30 to 3 mm, but my most popular eyepieces were Explore Scientific 24 mm 68 degrees, zoom eyepiece 8-24 mm, Levenhuk Ra 14.5 mm 68 degrees and Levenhuk Ler 3 mm. Later I also started using the Svbony 3-8 mm zoom eyepiece. Also, do not forget to purchase a 1.25-inch diagonal mirror for the telescope; it is not included in the kit.

Main objects for observation: Moon, Sun (required with a protective filter), double stars, bright objects of the Messier catalog. The moon through a telescope is gorgeous – seas, craters, mountain ranges. The planets, of course, are small with such an aperture, but Saturn has a clearly visible disk, ring and satellite Titan, Jupiter has a disk with cloud belts and four satellites, Venus has phases, Mars has darkenings on the disk and a polar cap (during oppositions) . The test on an artificial and a real star showed a clear diffraction pattern with a slight residual chromatism. For lunar-planetary observations, working magnifications are up to 133x (3 mm eyepiece). During visual observations, chromatism is almost invisible. In a dark sky and after dark adaptation of the eyes, you can admire open star clusters and bright nebulae for a long time.

Please note that if you insert a Barlow lens directly into the telescope, you will not be able to focus. An extension tube or diagonal mirror is required (a extension tube is better).

Levenhuk Ra R66 ED Doublet Black OTA can also be used for ground-based observations. Thanks to good light protection and minimal chromatism, the image is contrasty and clear. To obtain a direct image, you will need a wrapping prism (45 or 90 degrees). With a zoom eyepiece, the telescope becomes an excellent spotting scope.

When using Levenhuk Ra R66 ED Doublet Black Aperture Solar Filters, the OTA turns into a wonderful tool for observing and photographing the Sun. It also pairs perfectly with the Lacerta 1.25″ Herschel wedge. Thanks to the focal length of 400 mm, the resulting images are very convenient to compare and combine with images through the Coronado PST H-alpha 40 mm chromospheric telescope, which also has a focal length of 400 mm. For shooting the Sun, I use an astronomical camera QHY5III178m – thanks to the large 1/1.8″ sensor, the sun is placed entirely in the field of view.

The main problem of the Levenhuk Ra R66 ED Doublet Black OTA telescope when photographing deep space objects is the lack of a native field flattener. A field flattener is a lens accessory designed to flatten out the curvature of the lens field, which causes stars at the edges of the frame to appear out of focus in images.

When visually observing and shooting the Moon/planets/Sun, the curvature of the field does not interfere, but when shooting deep space objects on a large matrix (APS-C format), it immediately becomes noticeable. The field flattener is installed between the telescope and the camera, and with a correctly selected backfocus (the distance from the field flattener flange to the matrix), the stars across the field become as clear as in the center of the field of view. Adding to the complexity is the 1.25-inch output of the telescope and the non-standard thread under the visual adapter, since most field flatteners (including third-party ones) have a 2-inch fit. I tested several William Optics 0.8x field flatteners – alas, I was not satisfied with the quality of correction. I also tried a field flattener from TS Optics 1.0x – it didn’t even work to focus.

The solution to the problem was the purchase of an adjustable field flattenerfrom Long Perng 1.0x (Long Perng 2″ Adjustable Field Flattener for apochromats, Long Perng 2″ Adjustable Field Flattener for APO refractors) and an adapter from SCT thread (female) to M48 (male). And then, you need to select the working distance (the distance from the corrector flange to the photodetector), taking test pictures until the stars at the edges of the field of view become clear.

This field flattener is universal – by rotating the ribbed ring of the body, you can adjust the working distance depending on the focal length of the telescope. The scale on the field flattener is the working distance. Larger value means stronger correction of field curvature.

Telescope focal length (mm)	Backfocus (mm)
>1000	55
800-1000	58
600-800	60
480-600	65
400-480	70

We are interested in the lowest value, but it will still be necessary to take test frames and use them to evaluate the quality of field correction.

Before connecting the telescope, field flattener and camera, you need to unscrew the visual adapter from the telescope, as well as the 2-inch skirt of the field flattener. Below are several options for connecting equipment.

Connection with DSLR or mirrorless camera:
Telescope > SCT-M48 adapter > field flattener > M48 ring for camera mount > camera
or
Telescope > adapter SCT-M48 > field flattener > adapter M48-T2 > T2 ring for camera mount > camera

Connection with astronomical camera:
Telescope > SCT-M48 adapter > field flattener > M48-T2 adapter > T2 extension ring > astro camera with T2 interface

How to set up a field flattener ?
It is necessary to wait until it is dark, install the telescope on an equatorial mount with tracking, focus the camera on a bright star and take a test shot, then assessing the sharpness of the stars on the axis and at the edges of the frame. If the stars at the edges are out of focus, rotate the ribbed ring on the field flattener, selecting a different value on the scale (from 55 to 80 mm) and take a test frame again.

I will also add that when using small sensors (1/2″, 1/1.8″), a field straightener may not be required. Also, when using a large sensor (4/3, APS-C), you can cut out only the central part of the frame, where the stars are without distortion, but then the main part of the field will be lost.

In my opinion, for the consumer it should be like this – you buy a telescope, buy a native field flattener for it, an adapter ring T2 or M48 to the camera mount (mirror/mirrorless) or an extension of the required length (for astronomical cameras), connect everything together and… That’s it, we get a ready-made astrograph telescope, clear stars throughout the field and a satisfied consumer. And I, for example, spent several years looking for a suitable field flattener, buying, selling, looking for another, experimenting with working lengths, etc.

Mount selection
There is no mount included with the telescope. The telescope is light (approximately 1.8 kg without accessories), so the choice of mounts is very extensive. I recommend the following mounts for this telescope:
– For ground-based and astronomical observations: Sky-Watcher AZ3, Sky-Watcher Pronto
– For ground-based and astronomical observations, as well as photography of the Moon, planets, and the Sun: Sky-Watcher AZ-GTe, Sky-Watcher AZ-GTi.
– For astronomical observations, as well as shooting the Moon, planets, the Sun and deep space objects: Sky-Watcher EQ3-2 + set of motors, Sky-Watcher EQM-35 PRO SynScan GOTO, Sky-Watcher Star Adventurer GTi, Celestron CG-4 + set of motors, iOptron SkyHunter AZ/EQ.

Summary
Levenhuk Ra R66 ED Doublet Black OTA is a lightweight and compact tube with high-quality optics and mechanics. Suitable for both visual observations (taking into account the size of the aperture) and for shooting the Moon and the Sun. For shooting deep space objects it is conditionally suitable – either with a small sensor, or look for a field straightener and adapter for use on a large APS-C format sensor. The residual chromatism is small, but still there – purple or violet halos may appear around bright stars.

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