Tal 125 Apolar apochromatic refractor

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Magazine Verdict: 
Tal 125 Apolar apochromatic refractor

Vital Stats

125mm; 5 inches
Focal Length: 
940mm; f/7.5
2-inch Crayford focuser with 1.25-inch star diagonal
6x 30, straight-through
We were impressed with both the colour correction and how crisp the stars were right to the edge of the field of view

Tal’s 125 Apolar apochromatic telescope comes from a rich Russian heritage of optical quality and solid construction, although the design and materials may seem to come from an earlier age – right down to the heavy plywood box the instrument ships in. Yes, it’s weighty, but this colour-corrected refractor will stay aligned through anything but a major earthquake.

The scope comes with a 2-inch Crayford focuser and 1.25-inch adaptor, 1.25-inch star diagonal, 6x30 finderscope and tube rings with a built-in carrying handle, though you will need to supply your own mounting plate. It doesn’t come with eyepieces either. For our tests we used our own 26mm and 9mm eyepieces, plus 2x and 5x Barlows for added magnification.

‘Apolar’ is the Russian way of saying that it’s an apochromat – a refractor that corrects for colour fringing known as chromatic aberration. This looks like a coloured fringe around the edges of bright objects. Some two-element achromat refractors can do this less well, sometimes not bringing all colours to the same focus. The 125 Apolar focuses colours to one point, not by having expensive high-quality glass elements, but by using more normal glass: it has six lens elements instead of the more usual two or three. This gives it a slightly unusual tube shape that flares out towards the objective lens.

The 6x30 optical finderscope has a straight-through view, which is nice and clear – we were able to locate the brighter stars and some deep-sky objects on our observing itinerary. It’s mounted in a ball-and-socket-style gimbal, and although the idea is simple we found a little play in it when we were aligning with the main telescope.

Fine focus 

The Crayford focuser looks quite basic but it was very smooth and could be locked in place with a screw, with a second tensioning screw located on the underside. This is especially useful when fitting a DSLR camera in the focuser for imaging – it prevents the weight of the camera slowly pulling the focuser out of focus if the telescope is pointing at an object high in the sky. With the correct T-ring, it’s also possible to screw a camera directly into the focuser’s 1.25-inch adaptor, which makes setting up for imaging quick and easy. The Apolar 125’s tube rings come with a fixed carry handle, useful for lifting the scope. You’ll need your own mounting plate to sit between the rings and your mount; because the tube rings are a fixed distance apart, check that your mount plate will fit on the rings.

Our field of view tests on the star Vega gave an impressive view with our 26mm eyepiece. The star was sharp across 90 per cent of the view with only slight degradation towards the edge – no disappointment here. When we put in our wide-field 45mm eyepiece, it was nice to see that it still gave views that were sharp across the inner 75 per cent of the field of view.

Touring some other night-sky favourites with the 125 Apolar produced pleasing views. M82, the Cigar Galaxy, had strong mottling across its disc, even when we pushed the magnification. M76, the Little Dumbbell Nebula, had faint lobes despite being a small object and needing high magnification. We decided to check out Iota Cassiopeia, a triple star that has components separated by just 2.5 arcseconds. The system revealed one star with the 26mm eyepiece, but with the 5x Barlow we cleanly split all three stars.

Next, we slotted in our DSLR camera and took multiple images of the Dumbbell Nebula, M27; the Globular Cluster, M5; and the Double Cluster – shown on the previous page. We stacked and processed the images and were impressed both with the colour correction, the amount of detail we could see and how crisp the stars were right to the edge of the field. It is an accomplished piece of imaging equipment.

The Tal 125 Apolar is an enjoyable telescope to use, and it does a great job on a wide variety of subjects both visually and photographically.

Colour corrector

Refractors can suffer from chromatic aberration, when a lens doesn’t focus different coloured light to the same point. The majority of apochromatic telescopes correct for this with high-quality glass in a doublet or triplet system of lenses.

The 125 Apolar uses six lens elements in three sets to achieve the same level of correction. First comes a single biconvex lens (both of its surfaces are convex) at the front end of the tube; then there’s a group made up of a biconvex lens, a biconcave lens and converging-meniscus lens; and finally a group featuring a biconvex lens and biconcave lens.

Our observations bear out how well it corrects colour aberrations. What impressed us was how well colours were corrected at higher magnifications – we could push the magnification to its theoretical limit and still get good results, especially with Jupiter.

It’s a benefit that works just as well with imaging. With our Canon 50D DSLR attached, the imaging field showed sharp stars almost all the way out to the edges.

Focuser - The detail we saw on planets and in deep-sky objects showed that getting a perfect focus was easy. The focuser was smooth, with a generous amount of travel and not too much slack. Screws on the underside allowed it to be tensioned and locked in position when attaching a camera.

Finderscope - The finder is a 6x30 straight-through optical version mounted on a gimbal-style arrangement. This gives flexibility when aligning it with the main tube. It had a clear view and pulled in enough light for us to find most bright deep-sky objects.

Tube rings - The 125 Apolar comes with two tube rings joined together by a useful carry handle. This came in handy when moving the tube, but they might need to be adapted or replaced to connect to a Vixen-style dovetail or other mount plate.

Dew shield - The metal dew shield is fixed to the tube with two metal screws and protected the objective lens effectively from dew. It also cut out stray light, which can degrade the view. It’s easy to take off if you need to get at the objective lens.

Objective lens - The main lens did its job well, producing bright, well-corrected views with an eyepiece and a camera. Multicoatings on the front lens cut the amount of light lost through scattering down to a minimum and dispelled any internal reflections that can occur when viewing bright stars.

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This review first appeared in the April 2011 issue of BBC Sky at Night Magazine.

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