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Post Info TOPIC: Jessops TAC 360 70 Refractor


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RE: Jessops TAC 360 70 Refractor

Moon through 70mm Short Tube Refractor Telescope

A short video of the moon taken with a short tube 70mm aperture refractor telescope with a 400mm focal length.



Posts: 131433

Jessops TAC 360 70 Refractor

Objective 70mm
Focal length 360 (f5)
20 and 9mm 0.965" Huygen eyepieces
90 degree diagonal
3X Barlow and 1.5X erecting lenses.
Finder *
Table top tripod


These small richfield refractors can be purchased secondhand for less than £25.
For the price this achromatic telescope is excellent value; however there are some aspects which degrade the performance.
The tiny tripod is very flimsy (but usefully light for hiking), and cannot be elevated beyond 45 degrees! (Thankfully, the bottom of the scope has a standard camera tripod thread fitting).

A design fault is the black Diagonal holder fitting ring on the silvered plastic drawtube. The fitting is too shallow, which allows the diagonal to swing and not be securely fixed at 90 degrees. Luckily the black holder fitting can be unscrewed from the drawtube and a suitable shim inserted to stop any movement of the diagonal. Alternatively the opening of holder ring can be filed wider to allow the use of a 1.25" diagonal.

The focuser is also quite loose, but acceptable, with only a bit of play in its movement in observational usage (a few felt shims inserted around the drawtube will cure any looseness, or rattling when shaken). There are no improvements to be made inside the scope though; the insides are blackened (apart from some shiny screw fittings) and baffled. And the coated optics are of very good quality.

A good wide-angle eyepiece will be better than the (cheap) eyepieces included.
The 90 degree diagonal is very cheap and loose fitting (masking tape around the barrel should make for a snugger fit; but if the budget allows, it should be replaced).

It should be said that the Huyghen eyepieces supplied, although cheap, are reasonable and give clear planetary images; however, an old binocular eyepiece or Keller design will give nicer wide field views.

The star are crisp and the bands on Jupiter are easily visible. There is, of course, slight violet fringes on bright or high contrast objects.  The Great Red Spot is just beyond the scopes abilities, though a very dark and clear sky and filters may reveal the feature. The Galilean moons, Saturn's ring, crescent of Venus, the trapezium, and attack ships on fire off the shoulder of Orion can all be discerned, as well as most of the Messier objects.  

So, a possible upgrade could be to replace the diagonal with a 0.965" to 1.25" diagonal and then have the luxury of using Plossls.
A further improvement would be to purchase a light yellow filter to counter the chromatic aberrations inherent to fast refractors.

* One last point is that even for a rich field refractor a finder is useful.
The finder on this scope is unfortunately a bit too small, and has an aperture stop (to improve the image quality). 
A small tip is to remove the aperture block;  the front end can be twisted off, and the aperture block slipped out to use the whole area of the single glass objective. The image will be brighter, though not as sharp. 

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