The Sun Now
Saxon 70mm f/7 Achromatic Refractor
Submitted: Thursday, 22nd March 2007 by Chris Lewis
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Saxon 70mm f/7 Achromatic Refractor. Model Number 705 - AZ3. An 'entry' level astronomical telescope
I always think it is important to review the more 'entry' level telescopes available. Hence this brief review of an entry level 70mm refractor - the 'Saxon' 70mm F/7 refractor with the full height AZ-3 mount, it comes with 3x 1.25 in. eyepieces, 45 degree diagonal ['for 'correct' day time viewing] and a small 'finder' telescope. 'Skywatcher' produces a similar telescope.
I thought it more interesting to compare it with a similar entry level refractor that is available on the market so potential buyers can make a more informed decision.
About a year ago I bought a 'Scopetronix' 80mm F/4 'short tube' refractor second hand as a 'Grap and Go' scope. This is a 'clone' of the many popular 80mm refractors for sale that are produced in China and are sold primarily via the internet. The Scopetronix had 'coated' only [light blue] lens and no internal baffles. It has a rear plastic focus holder. It is approx. 38cm long.
About a month ago I bought the above mentioned Saxon 70mm. I was keen to buy a small and portable 'quick look' telescope but was also keen to acquire the mount it came with - an 'AZ-3' - a basic 'Alt- azimuth' mount that has slow motion controls that moves up / down and sideways. This is opposed to the more expensive and complex 'equatorial' mount.
I intended to use the mount for other telescopes that I have, however, the more I used the telescope itself the more I became impressed with its optical abilities. The Saxon is a Chinese 'Synta' product - the Scopteronix is not. Synta also make telescopes for Celestron, Skywatcher and Konus.
The Saxon has 'Multi coated' lens [deeper blue] and internal baffling. It is important to note that good lens coatings [and internal baffling] help reduce internal reflections and C.A. [Chromatic Aberrations - or 'false color' - mainly reds and blues] and therefore improve overall image quality. The 'best' lens coatings are 'Fully Multi Coated' lens followed by 'Multi coating' lens and lastly 'Coated' lens.
The Saxon 70mm has a basic rack and pinion focus unit that is relatively smooth with little 'play'. The focus holder is plastic. The three supplied eyepieces are a 25mm 'Superwide', a 10mm 'Super' and a SR 4mm to give set magnifications of 20X, 50X, and 125x. [They are not Plossls] .The 45 degree diagonal as noted gives 'correct' day time viewing. The Finder and holder was small and made of entirely plastic and mounted to the tube via 2 screws. The length of the tube is 50cm. The tube weighs 1.25 kgs. The total weight of the telescope is 8 kgs. This would be considered 'light' weight which makes very portable. Portability is a very important part of buying and using a telescope.
The Saxon is considered a 'short tube' refractor however is really lies in-between the genuine 'short tube' telescopes at F/4 [ Wide field ] and the long tube varieties at F/10. The larger [80mm +] long tube refractor telescopes are often called 'Planetary' scopes as they can achieve higher powers which the Planets require, but at a much reduced field of view (FOV). The longer the focal length of a refractor also generally means less C.A.
At 70mm this Saxon would be considered too small to be a planetary scope. However having a moderate focal length it is a good compromise between providing low power 'wide field' views yet still be able to achieve reasonably high magnifications to give some detail on the brighter planets and also provide good lunar views.
The Optical Tube Assembly (OTA) is held to the mount via 2x tube ring holders which are easy to remove. Other telescopes could be fitted to the mount as long as the correct diameter tube ring holders are acquired. I have mounted my 4 inch Orion ED100 Apochromatic [long tube] on this mount for quick looks. This size telescope would be the limit for this mount as balance started to become an issue. My 3 inch Orion ED80 [shortish tube] is very suitable.
I quickly stopped using the supplied eyepieces and started to use better quality eyepieces that I already have. The supplied eyepieces gave inferior images [although the 25 mm Superwide was 'acceptable'], They also gave narrow field of view images. Color fringing was also noted on the 2 higher power eyepieces especially with the very inferior SR 4mm.
A quick star test shows good collimation. [When the telescope is focused 'in and out of focus' on a bright star concentric rings appear in the enlarging star image [Airy disc]. It is better to use high magnifications for this ie.100x +. The 'rings' should appear all be equal. Star testing should be done on a clear and steady night].
Saturn is an interesting view at present. With the Saxon 70mm I could get up to 150x [ 500mm divided by Meade 6.7 mm Ultra wide and Televue Barlow lens 2x ]. Saturn at this high magnification was well defined with little color. The image was becoming dim which is to be expected in a 70mm refractor at high magnification. Subtle shading could be seen on the planets surface and the gap between the rings were clearly defined.
150x in a 70mm achromatic is actually very good. The maxim for maximum magnification is 'multiple the aperture in millimeters by 2x hence 70 mm x 2 equals 140x. It is also to be noted that viewing conditions were very 'steady'.
I must stress however that astronomical observations are not about 'high' magnifications. It is more about light gathering. 'Low' power views give bright and clear images. As the power increases images become dimmer, less defined and increasingly difficult to keep 'centered' in the eyepiece. Atmospheric conditions play a large part in how high the telescope can magnify on a particular night.
The Scopetronix scope would only manage a maximum magnification of 80x. C.A. became intolerable and double images started to form.
Venus is a difficulty object to view at the best of times being close to the Sun. Both scopes displayed similar vague small planetary discs. There was noticeable less false color with the Saxon.
The Moon was clearer and sharper in the Saxon. Small craters at 100x were visible in the Saxon that were not seen in the Scopetronix telescope - at this magnification the Scopetronix was difficult to focus properly and again false color hindered the view. The moon in this telescope excels as 'high' magnifications are achievable -120x + while still maintaining sharpness.
The image is not too dim due to the overall brightness of the moon.
Orion's Nebulae looked better in the Saxon at low power -25x [ Celestron Plossl] - stars were more pinpoint and stars displayed more contrast. Nebulosity was clearer also in the Saxon.
The stars in the Pleiades at low magnification appear sharp and clear with a black background in the Saxon.
The Saxon was very mildly dimmer overall but clearly made up for it in sharper and virtually color free viewing.
Daytime viewing up to approx 50x the view was similar in the two scopes. The Scopetronix being slightly brighter, however when viewing tress / power lines - slight purple fringing could be seen in the Scopetronix telescope which detracted from the view.
There is a minor issue concerning the mount itself in that the slow motion for altitude can reach only 45 degrees towards Zenith [from the horizontal]. This can be remedied somewhat by slightly loosening the large locking nut so that coarse manual adjustments for objects higher then 45 degrees can be made. You then can use the slow motion control to fine center on a object. This is workable but mildly frustrating. The Mount itself was very solid and relatively vibration free. It is important to note that a telescope is as only good as its mount.
For Astronomical use the 705-AZ3-3 Saxon 70mm F/7 is a good entry level achromatic refractor that is supplied with a easy to use solid mount. It was clearly superior to the 80mm F/4 clone refractor that I compared it to. For general day time / general low power viewing the Saxon was also more acceptable - which is primarily related to the lack of false color.
- If you are looking for a relatively inexpensive robust entry telescope I would recommend the Saxon 70mm F/7 refractor. It also comes with a useful AZ-3 mount that can be used for other scopes at a later date. The Saxon 70mm AZ-3 is light weight and very portable - remember the best telescope is the one you use the most.
- The better build quality, longer focal length, superior baffling and multi coatings of the Saxon resulted in sharp and relatively color free images. These images were superior to the inexpensive 80mm F/4 'clone' refractor.
- Terrestrially both telescopes were equal until about 50x however with increasing magnification the Saxon won again - as CA again became intolerable on the Scopetronix.
Some modifications could be made to improve the Saxon telescope immediately: [Placed in decreasing importance].
- Acquiring some superior eyepieces.The supplied ones gave relatively poor images. The smallest eyepiece, the SR 4mm, was almost unusable. Most any Plossl from a reputable astronomical dealer would be better then the supplied eyepieces. I would suggest getting 3x Plossl say a 6 mm, 10 mm and 25 mm to give 83x, 50x and 25x. A x2 Barlow could then be added to double those available magnifications. The 6mm Plossl may be difficult for some to view easily as it has a small exit pupil - a more expensive option would be a low power 'wide angle' eyepiece that are available on the market.
- Replacing the fairly useless 5x24mm finder. It was to small to be of any major use and false color was a major problem. A red dot finder would be more useable.
[At low power however [20x] a finder in a scope this size is almost redundant].
- Replacing the 45 degree diagonal with a higher quality 90 degree diagonal. My GSO 90 degree diagonal gave mildly less CA on bright objects. I personal prefer the 90 degree version also for viewing comfort.
It is regrettable that whilst the telescope itself is of 'good' quality the accessories supplied are inferior - noticeably the eyepieces and the finder. This is done [presumably] as a cost cutting exercise.This unfortunately reduces the full potential of the telescope itself. One could question the cost benefit of buying a telescope where you have to 'replace' the 'accessories'. The writer believes that if buy some quality eyepieces from the start these will last you many years and they will be able to be used in a variety of telescopes in the future.
- There are some amateur astronomers who say that you cannot really see much with a telescope under 4 inches [100mm]. Obviously this is a very subjective comment. Telescopes between 70 and 100mm can give rewarding views and with such telescopes you do have to learn to 'see' - a skill that is important and one that will help you observe no matter what size telescope you acquire in the future.
- It is recommended that a 70mm refractor telescope is a 'minimum' aperture. It gives 36% more light gathering ability then a 60 mm version. The 70 F/7 Saxon is recommended over any 'departmental high power 525 x 60 mm refractor'. These come with 'wobbly' mounts and give very inferior images.
- Alternative astronomical telescopes such as a 114mm Newtonian reflector are also available as 'entry level' telescopes. These telescopes come primarily on a equatorial mount. Reflector telescopes have greater light gathering ability - however they are more 'fragile' and require more maintenance to keep the mirrors aligned.
- Again avoid 'departmental' reflectors with 'built in barlow lens' - these double the focal length. These have 'spherical' mirrors and give inferior images. Parabolic mirrors are superior. A 114mm reflector would be considered a minimum for astronomical use. A 150mm reflector on a 'Dobsonian' mount [easy to use] is an excellent alternative telescope.
- The writer suggests observing with as many telescopes as possible and then making an informed decision. A precision well made 'entry level' telescope will bring years of viewing pleasure.
I have no association with the above mentioned manufactures.
Review by Chris Lewis. Discuss this review on the IceInSpace Forum.