Kson Ke’sil Skysweeper 150mm 750mm f/5 (OTA) (O Variant)

Original price was: $1,699.95.Current price is: $1,399.95.

The Kson Ke’sil Star Seeker is an f/5 classic air spaced, crown and flint doublet achromat refractor with a huge 150mm aperture with key differences that keep it in a class of its own.

Only 1 left in stock (can be backordered)


Astro Dog and Kson have been in partnership since 2019 and are excited to announce a limited production run of an Astro Dog exclusive premium scope, the Kson Keʹsil 150 Skysweeper A 150mm (5 inch) f/5 widefield large aperture achromat refractor.  Just for the pure pleasure of visual observing alone, this is a great instrument with incredible value.

The Keʹsil1 is one of the largest air-spaced large-area achromatic refractors designed for large field observation with exceptionally high resolution bright images.

The Keʹsil1 is one of the largest air-spaced large-area achromatic refractors designed for large field observation with exceptionally high resolution bright images.

  • Objective Lens Diameter of 150mm – Genuine 150mm effective aperture.
  • User Collimatable Lens Cell (New!)
  • Achromatic refractor lens configuration – Hand figured, fully multicoated lenses. Every lens cell is checked for collimation and artificial star tested for quality assurance.
  • Upgraded to K9/ZF2* Glass (New!)  (*ZF2 glass allows better astigmatism handling and is a more expensive)
  • Telescope Focal Length: 750mm (f/5) – Ultra wide field specialist scope
  • Resolution : Rayleigh; .92, Dawes; .77
  • Sturdy 2″ dual-speed crayford style focuser with compression ring – Allows direct SLR Camera Connection.  Accepts 2″ eyepieces and accessories and also helps prevent vignetting when using widefield eyepieces or imaging with large sensor cameras.
  • Quick release bracket on scope.
  • High strength cradle ring assembly and vixen plate made from extruded aluminium for extra strength are included as standard
  • Includes practical adjustment / carrying handle
  • Flat black internal baffling blackened tube to reduce internal reflections
  • OTA tube weight is 8000gr
  • Color: White  (Note that the image shows black one).
  • Dew Shield: Fully Retractable / Extendable
  • 80mm Removable aperture cap – This unusual feature allows the aperture  can be stopped down to f/9.4 allowing for higher power planetary, lunar or solar work (New!)

INCLUDED IN THE ‘O‘ Variant – Almost $900 worth of accessories!

    • Solar Filter : Included – Special 80mm glass coated solar filter, screws into dew cap
    • Handy Nylon Case


Several variants are available to choose from

Kson Ke’sil (O) $1699.95 150mm 750mm f/5 Widefield Specialist (O) OTA Only

Inclusions: Includes Full Padded Case, Solar Filter

Kson Ke’sil (V) $2195.95 150mm 750mm f/5 Widefield Specialist, comes with over $ (V) Visual

Inclusions: Includes Handy Nylon Case, 2″ 90 Degree Star Diagonal /w compression ring, 2″ 495nm filter plus a 2″ Wratten 56, Kson 8×50 Astrometric Finder, 2″ Kson 32mm Eyepiece and a 1.25″/2″ Dual Use Eyepiece Case

Kson Ke’sil (AP) $1899.95 150mm 750mm f/5 Widefield Specialist (AP) Astrophotography

Inclusions: Includes Handy Nylon Case and Special 2″ Corrector/Flattener*

  • The Special Flattener may be added to the ‘V’ or ‘O’ variants for $200 extra.  Flattener applies semi-ED properties to the scope.


Use the Ke’sil with your choice of Mount.  For visual, we recommend a Saxon EQ3 w/Steel Tripod (adequate), a Kson EQ3 (slightly better) with a second counterweight, a EQ5 (good) or a HEQ5 or EQ6 Pro if your looking at automating. 

Is it hard to transport?

No, it’s extremely compact and easy to transport despite it’s significant aperture, largely due to the retractable dew shield.

What eyepieces are best?

The Ke’sil (V) includes a good quality 2″ 32mm eyepiece giving x23 [the 25mm (x30), 18mm (x42) in the series are also available].  It is very comfortable to view through regardless of experience level and provide amazing clarity and light transmission.  You may however, wish to add extra eyepieces.  You can consult our eyepiece advisor for some strategies for selecting eyepieces, but note the eyepiece sets below which we especially recommend.

The Kson Orthoscopic set is also a great pick and is recommended by Kson.  (LE 4.5, LE 7.5, LE 10.5, 16.8mm and 24mm)

Typical Use

The Kson Keʹsil allows for impressive observations.  It truly excels at open star clusters.  Observing with the supplied eyepieces is ideal, or you can use a variety of clever eyepiece sets to bring the most out of this exceptional refractor.   Nebulae, galaxies  and open and globular clusters are also spectacular and are another speciality of the scope and it will generate memorable, terrific, high contrast images of a variety of deep sky objects.

Chromatic Abberation is relevant when you need higher magnifications of more than 25x per inch aperture (especially when observing planets) and it is more disturbing on brighter objects.  As such, with this type of refractor, we would advise avoiding high powered eyepieces.  Be aware that concern about false color can be overrated – it depends on what your doing and your sensitivity.  The special aperture cap on the Ke’sil, it can drastically reduce CA.  It changes the character of the telescope entirely, allowing you to get some good high powered views that would not normally be possible.

We’ve bundled the Ke’sil ‘V‘ (visual) with some superb filters that are well suited to this type of speciality scope and greatly expand the flexibility of objects that can be enjoyed with it.  Try lunar views with the cap for stunning resolution, or give the 495nm filter a go!  A green filter can also cut the spectrum being viewed and sharpen up the view offered through an achromat and let you do more with the Ke’sil.

Deep Sky Performance

It’s deep sky performance, is, as you would expect, impressive.  Chromatic abberations are a non-factor when viewing less than 5th magnitude objects.  Try giving it a shot at the rich Sagittarius and Scorpius star concentrations and the bright diffuse nebulae in that area of the sky for some truly delightful viewing pleasure.  Use without a filter.  1As many nebula’s have emissions at 486nm, 496nm and 501nm, avoid the 495nm filter, and try Wratten #8, or #3.


Of course, we all wish we had 10k to spend on a 150mm APO – but we don’t.  The Ke’sil is capable of astrophotography, with its diffraction limited optics, baffling, precision focuser it has potential, with the obvious issue that it is an achromat.  Let’s discuss what can be done about that.

The Ke’sil has the option of something no other 150mm Acromat we are aware of – the ‘P’ pack includes a special corrector/flattener.  Notice the significant improvement on colour fringing when it is used.  We can’t wait to see what you guys manage to do with it!

Here are some techniques / ideas some suggest if your use is imaging to improve results even further.  There is enough for you to do that it’s very unlikely you will be dissapointed.

  • Make sure you get the ‘P’ version.  The corrector/flattener is exceptional, especially when combined with narrowband filtering
  • As above, but try the supplied 495nm filter in the ‘P’ package.
  • Monochrome imaging – Use a mono camera and a single Ha filter.  It’s special.  Jon Rista is a huge fan of this approach.
  • Post processing – Try affinity (photoshop alternative) and use the “filters”, “colors” then “chromatic aberration” and “defringe” as needed.
  • Try narrowband imaging using just the RGB line filters (use 1.25″ for micro 4/3 size sensors, 2″ filters for everything else), without using the L.  For the B, put on the aperture mask (changing the scope to a f/9.3), or add a wratten #3, #8 or the 495nm.  We recommend a ZWO ASI183MM Monochrome camera or similar but you can get great results with many other cameras.

Explanations for narrowband imaging

Notes on Atypical use

As a specialised 150mm wide field achromat, the Ke’sil produces some colour fringing.  It is designed from the ground up as a deep sky skyweeper and is not designed for the observation of the moon, planetary bodies, or bright objects.  However – the Ke’sil’s special aperture cap (changing the f/ratio to f/9.3), and its range of filters produce near miracles.

Venus – necessitates use of a w56 filter and the cap.  Venus will have has a monochrome green appearance, but you can get a sharp disc.

Saturn – The W56 will be needed, and you should be able to enjoy the equatorial bands, the ring shadow and you may get the cassini division.  With the cap, the the image improves, but you won’t be able to take it much further than 150x.

Lunar – Try 50x, use the w56.  It will turn the moon green, and you will enjoy impressive definition.

Double Star observations – With the w56 filter, the Ke’sil will produce tightly defined, very sharp but monochromatic results, without it, resolved but colourful and messy.

Use with image-intensifiers – You can try this with a H-Alpha setup at about 50x for some impressive viewing.

Our Subjective Comparisons

How does the Kson Ke’sil compare with the older Celestron Omni XLT 150r?

Apart from the aperture, the Ke’sil is very a different scope. The Ke-sil was designed from the ground up to support a 2″ diagonal – with all that that entails, and also features a high grade, heavy duty 2″ dual speed focuser which was missing from the Omni – and does all that just weighing 800 grams more than the XLT 150R.   The Ke’sil V offers amazing accessories right out of the box – a great 32mm 2″ eyepiece as well as three specialised, quality filters (the 495nm, the rare wratten #3, and the Wratten 56) to help you get the most out of the viewing experience and take an already incredible view to the next level, while the The XLT only ever came with a single 25mm eyepiece.  The Ke’sil comes with an adjustment carry handle build into the cradle system.  This makes it much easier to use, and whereas the XLT had a fixed dewshield, the Ke’sil’s can be collapsed for easy transport.  The finder options on the Kson are also completely different, with a bright 8×50 illuminated reticle finder or a 30mm red dot.

How does the Kson Ke’sil compare with the Explore Scientific AR152?

The Ke’sil has a wider field of view at f/5 and allows rich field views that simply are not possible with the AR152. If your going to get a low-power richfield achromat – we think go all the way.  The 750mm length vs 988mm is not trivial when it comes to setting it up – 750mm is different from setting up one that’s almost a quarter longer – not to mention the weight.  The Ke’sil has the option of changing the f/ratio completely by removing the cap, allowing entirely new viewing possibilities which we think is a better approach than compromising what a 150mm refractor is supposed to do best. The Kson also offers a very high quality stock 2″ focuser as standard– and its unlikely you will want to change it out. The AR152 offers NO eyepieces, no filters. At f/5, the imaging, the Ke’sil is also faster allowing you to pull in exposures faster.  The finder too, though 8×50 benefits from Kson’s clever slider which lets you move it further up or back the scope depending on where you want it, meaning it’s more likely to be exactly where you want it.  It also comes in a whopping 2700 grams lighter than the AR152 and is far more compact and easy to handle thanks to a collapsible dewshield.  Among those who have tried it, many prefer the Kes’il’s crystal clear metal finderscope with its intuitive adjustment system over the AR152’s focuser with its plastic adjustment screws.

How does the Kson Ke’sil compare with the Skywatcher Startravel 150 OTA?

The Startravel and the Kes’il have some things in common, 150mm lens, f/5 with a multi-coated objective lens, but it mostly ends there.  The Kes’il comes supplied with not two, but three, and not 1.25″ but 2″ eyepieces allowing for a wider field of view and a greater range of magnifications.  The 8×50 finderscope is adjustable, and features an astrometric illuminated view, not a feature of the Startravel.  The focuser is one of the most crucial differences.  At f/5, the 1:10 crayford fine focuser will make a big difference – many have found switching out the Startravel’s focuser necessary to get it performing the way they want (about $300 extra).  The Ke’sil comes supplied with some of the best filters to handle the Chroma on this type of refractor pushing it right up there in performance.  The Kes’il offers fantastic value for money in comparison.

PRE ORDER TERMS AND AVAILABILITY – Accepting orders now for for the next batch due March ’23.  You can select ‘layby’ on checkout, and put $200 down as a non-refundable deposit to secure yours.  8 weeks before the ETA, you pay the balance off over 4 equal payments over 8 weeks (4 equal payments every 2 weeks).  Of course, you can pay in full now if you wish.

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Additional information

Weight 12 kg
Dimensions 79 × 26 × 30 cm