Levenhuk Ra R80 ED Doublet OTA Review
Many novice astronomers are eager to try their hand at astrophotography. In fact, it's no wonder that among beginning astronomers you can meet a lot of people who are engaged in photography on a professional level or who at least have an extensive amateur background. As astronomy experience is not only limited to visual observations, why not try to capture some breathtaking cosmic views? Then, the following question arises: What telescope to choose for astrophotography? You won't need an instrument with large objective lens diameter; telescopes with modest-sized objectives are suitable for our purpose. Keep in mind that refractors are better suited for astrophotography than reflectors. Refracting telescopes have a much wider field of view - an especially important feature in astrophotography. Apochromatic or semi-apochromatic refractors are loved by astrophotographers all over the world for their quality optics made of a special material, which effectively reduces and sometimes even completely eliminates chromatic aberrations. On the other hand, achromatic refractors are designed for visual observations and don't have these special objective lenses. Such telescopes only provide chromaticity compensation for red and green colors, but the blue spectrum is still affected (celestial objects on your pictures will have a very noticeable blue halo). I recently got the chance to test Levenhuk Ra R80 ED Doublet OTA - semi-apochromatic refractor with 80-mm objective lens diameter and 500-mm focal length. "ED Doublet" in the product name tells us that we are dealing with semi-apochromat (ED is for extra-low dispersion); that means the objective lens is made of extra-low dispersion glass. Moreover, the objective lens is multi-coated to assure the maximum light transmission.
To get a more complete picture, refer to the Specifications Table.
|Optical design||apochromatic refractor|
|Optics material||S-FPL53 ED + S-NBM51 glass|
|Optics coating||fully multi-coated|
|Objective lens diameter (aperture), mm||80|
|Focal length, mm||500|
|Resolution threshold, arcseconds||1.45|
|Eyepiece barrel diameter||1.25"|
|Focuser||dual-speed Crayford focuser, 2|
|Tube-mount assembly system||quick-release thumbscrew|
|Optical tube material||metal|
|Optical tube dimensions, in||4x15.4|
|Optical tube weight, lbs||6.6|
The telescope comes with a quality, reliable, good-looking case. This case is very convenient - you can transport the instrument wherever you need to.
The interior of the case is tightly filled with foam. You even may need to apply some effort to pull the telescope out. But that's a good thing because it guarantees that the instrument won't be damaged in case you accidentally drop it to the ground.
I was pleased with the telescope's compact size and light weight. Moreover, the telescope tube is rather short (thanks to its modest focal length). Telescopes with a shorter focal length have a larger field of view - that is exactly what's needed for taking quality panoramic astro photos.
Metal telescope tube is coated with black lacquer and looks quite impressive and stylish.
The objective lens cap is made of metal as well and has a black matte finish. It sits very tight, which is very important - since it's not rare for a cap to slip very easily from a tube, and that increases the risk of scratching fragile optics.
The objective lens is considered the heart of any telescope. The important parameters of the objective lens are printed on its rim. "Fully multi-coated" means that the lens has multiple layers of coating; the coating can be clearly seen as a greenish-purple tint on the glass.
Viewed from different angles the objective lens can slightly change its color.
I would like to clarify the meaning of the term "doublet". Doublet means that the objective lens consists of two lenses. One of these lenses is made of low-dispersion glass that allows obtaining high-quality views with minimum chromatic aberrations.
The telescope has a retractable dew cap that protects the optics from dew and fog. Many telescopes are equipped with dew caps that are not as convenient, as they make instruments less compact.
A front view of the extended dew cap. The inner surface of the dew cap is blackened to absorb reflections. The back of the dew cap.
Inside the tube you can also see diaphragms - they are also designed to "cut off" unwanted reflections of light.
There are a few different ways of attaching the telescope tube to the mount. I use a mounting plate from a camera tripod head for this purpose. I attach it to the telescope's mounting bracket and then install it on the mount.
Let's pay attention to the opposite side of the telescope tube. This ring is used to rotate the focuser. The embossed surface provides for additional comfort of use.
Just loosen the ring and rotate the focuser. Sometimes that is required for picture framing.
This is the place on the focuser where an eyepiece should be installed. The picture shows the focuser with adapter installed. An opening for an eyepiece is covered with a cap.
This telescope model is equipped with 2" focuser. It allows you to use 2" eyepieces as well as 1.25" ones (using the adapter).
The focuser body is covered with a shiny anodized finish. Looks wonderful! Rubberized focuser knobs are smooth, pleasant to the touch and very convenient - they do not slip in your hands. Coarse focus knobs allow for quick sharpness adjustment.
The smaller focuser knobs are used for fine sharpness adjustment. Thus this focuser provides two focusing speeds - that's why it's called "dual-speed focuser". It's a good idea to acquire a telescope equipped with a dual-speed focuser, as fine sharpness adjustment is very important. Using a single-speed focuser, you can waste a lot of time, trying to "catch" the required degree of sharpness.
Loosen the locking screws and remove 2" to 1.25" adapter from the focuser. Inside this adapter you will see a copper ring that securely holds an eyepiece in place and prevents it from falling out when the instrument is inclined.
The 2" focuser hole has similar copper ring inside.
The locking screw on the focuser tube.
Thanks to the scale on the focuser's drawtube, you can easily use various eyepieces with different focal lengths.
I recommend buying a diagonal mirror (or a prism) for more comfortable visual observations and astrophotography. The diagonal mirror diverts light to a 90 degree angle and allows for a more comfortable viewing position. For example, if you point your telescope to the zenith without a diagonal mirror installed, the vertical tube orientation will force you to take an uncomfortable squatting position.
The bottom of the focuser tube. Notice two threaded holes - these holes are used for autofocus motor mounting. It's really difficult to do astrophotography without it.
To install the autofocus motor I used a ruler, angle bar, and ordinary glue. The rotation is transmitted to the focuser knob through the belt.
With this instrument I've performed the Roddier image quality test. The telescope has shown excellent results:
And let's finally talk about astrophotography! The first photo made with a crop camera (without field flattener) shows us a star field.
I made a series of shots 15x30 sec (ISO 1600) using a Canon 50D digital camera. You can see that the matrix plane is not warped relative to the focuser, which is great. You can notice the effect of the residual chromatic aberration, but it is absolutely normal for semi-apochromatic telescopes. You might ask why not buy an apochromatic telescope to achieve even greater image quality and completely eliminate any aberrations. Apochromatic refractors are much more expensive than semi-apochromatic ones. So if you are a beginner and need a telescope to make your first astro shots, a semi-apochromatic telescope will do the job!
Vega Test. 5x3sec, ISO 1600, Canon 50D:
The following images were made in a red light-pollution zone. If you visually observe in the red zone, the observed objects will be very faint and blurred, but it's still possible to shoot great vivid images. Almost any city center is in the red light-pollution zone - that's why astrophotography is so popular among urban residents. By the way, the telescope gains light from bright objects pretty quickly.
Orion Nebula. 15x30sec, ISO 3200, Canon 50D. Processed with Photoshop and Iris.
Pleiades (star cluster). 15x30sec, ISO 3200, Canon 50D. Processed with Photoshop and Iris.
Landscape astrophotography images look very impressive with this instrument.
Visual observation of one of the most amazing natural summer phenomena - night or noctilucent clouds - is very impressive as well. The scientific interest in the phenomenon of noctilucent clouds and their dynamic structures only grows with time. You can even contribute to scientific research by sharing your own photos of night clouds on special websites.
I'm really satisfied with the instrument. It is compact and not heavy. You can easily take it with you on a night-time nature walk. To become familiar with the night sky you can even use a simple camera tripod, which the telescope's compactness and light weight make possible, as I mentioned above. With other heavy large telescope models you will need a specially selected, stable massive mount - therefore you might have some problems carrying all this bulky equipment with you. Besides, due to its small size, Levenhuk Ra R80 ED Doublet OTA cools down very quickly, adapting to the ambient temperature. This is very important - if a telescope isn't fully adapted to the outside temperature, the images will not be sharp and even blurry. This instrument and all materials used are of a very high quality. It is clear that the manufacturer didn't take shortcuts in production, because everything is at the highest level: dual-speed 2" Crayford focuser, retractable dew cap with blackened inner surface, diaphragms inside the tube, quality carrying case included in the package, and no plastic parts. And most importantly - high-quality images due to the use of high-quality ED-glass. You will obtain sharp, clear views even at high magnifications up to 160x. I'm pleased with the quality of visual views, as well as produced astro photos.
Chromatic aberrations are still noticeable, but not critical. Levenhuk Ra R80 ED Doublet OTA is a perfect instrument for visual observations, as well as for first experiments with astrophotography.