Askar 131F Flat-Field Refractor
Askar 131F Flat-Field Refractor
Large refractor aperture and photo-ready optics come together in this offering! Pushing Askar's F-Series even further, this telescope brings you big 5" refractive optics and the series' signature internally corrected images and great performance. Reach out with ease and realize more resolving power, with the Askar 131F Flat-Field Refractor!
Large optics, internal field-flattening, and smart design meet for an astrophotography option that makes reaching for more easy. The Askar 131F Flat-Field Refractor has a 131 mm aperture with an f/7.5 focal ratio, for a 983 mm focal length. This longer reach makes for a great platform for honing in on medium to smaller targets, or capturing features of larger ones in more detail. This features a quadruplet optical design, containing one ED element, which internally flattens the images through this telescope for superb results without additional correctors or meticulous backspacing. Ensuring you can confidently bring these views to even the stoutest imaging trains, the telescope comes equipped with a large 3" rack & pinion dual-speed focuser, which additionally is designed to easily accommodate common electronic filters for modern convenience and precision. This stellar optical train is supported with visual & imaging filters packed-in the box and three Synta-style mount points for accessories, for a fantastic 5" astrophotography refractor value!
Askar 131F Flat-Field Refractor At a Glance
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Learn More About the Askar 131F!
From optics, to hardware, to included accessories, Askar has tailored the 131F to be an excellent and accessible telescope for your astronomy explorations! To learn more, read on below!
131 mm f/7.5 Quad APO Optics
The Askar 131F Flat-Field
Refractor features a large 131 mm aperture f/7.5 design, providing 983 mm of
focal length. This longer magnification is great for a range of medium to
smaller targets, such as the Pinwheel Galaxy, Bode's Galaxy, or Pleiades.
The quadruplet optics provides a flat-field 44 mm image without the need for
any additional flatteners or reducers, allowing you to capture this
telescope's sparkling images with cameras up to full-frame in size without
meticulous spacing! This four element design, featuring an ED element,
provides not just distortion-free views, but also well color-corrected and
sharp images for rich contrast and fine detail.
Photographic and Visual Adapters Included
The Askar
131F accommodates both observers out of the box! Pre-installed on the 131F
is an 1.25" adapter, which can be used with a user supplied diagonal for
observations, or the nosepiece of a camera for a simple, yet effective,
imaging train. If you want to build a more complex imaging train or thread
your camera in place, remove the 1.25" adapter and attach the stack of
photographic adapters. This terminates in the common M48 by default, with
M54 and M78 available for larger accessories and cameras by simply removing
rings from the stack.
3" Rack & Pinion, EAF-Ready Focuser
To support
even the most demanding builds, the Askar 131F Flat-Field Refractor comes
equipped with a large 3" focuser. This is outfitted with a dual-speed, rack
and pinion mechanism, giving you both precision and robust equipment holding
strength. This focuser also comes ready for most bracket-style electronic
auto-focusers, allowing you to add your favorite EAF and unlock micro-step
precision and automated convenience!
0.74X Dedicated Reducer (Sold Separately)
Looking to
push the 131F's optics? Askar has you covered, with a
dedicated 0.74x Reducer for 131F! This brings the 131F's focal ratio down to f/5.6, collecting the same
amount of information as the stock f/7.5 in less time. The faster focal
ratio also provides a wider field of view, bringing the focal length to a
medium reach of 727 mm. The triplet design maintains the 131F's full-frame
coverage rating and provides excellent correction, for a boost in speed that
still provides incredible results.
Please Note: Adding the reducer to the Askar 131F will remove the
forgiving backfocus functionality. Backfocus with the reducer installed is
the industry standard 55 mm.
What's in the Box?
Included with the Askar 131F is a
suite of hardware and accessories to get your rig off the ground on day one!
For mounting your telescope, a set of rings and 300 mm V-style dovetail bar
are included. For a convenient carry solution and accessory mounting, a top
handle complete with a full-length Synta-dovetail slot has also been
included. For even more accessory mounting solutions, two finder shoes come
with the scope. To connect your camera and imaging equipment, the Askar 131F
Flat-Field Refractor also comes with an 1.25" visual connection and a stack
of photographic adapters.
Frequently Asked Questions
Why not pick a reflector for a large aperture telescope?
Reflector telescope designs lend themselves well to scaling, leading to
a wide variety of options covering a large range of needs and price points.
However, these require periodic re-alignment (a process called collimation),
especially after transport, and can introduce additional balance concerns with
designs like the Newtonian which places observing/imaging equipment off to one
side. Refractors on the other hand generally do not need adjustment by the
user and have most of the mass on-axis, making them great for users looking
for a 'set up and go' type of system.
What is backfocus? Why would someone want a system that doesn't require
it?
A simple imaging setup consists of a telescope, which can be a
refractor or reflector, and a corrective element that 'fixes' the distortions
from the optics so that stars will be sharp and round from corner to corner.
The area that this corrected image covers is known as the image circle, which
then informs how big of a camera sensor one can use. However, this corrected
image circle is projected a very specific distance away from the corrective
optic. Being on either side of this distance will result in sub-optimal
correction and performance. This specific distance is what is being referred
to by backfocus. Some optical designs however, factor the correction into the
internal design, and in doing so relax the very particular spacing
requirement. There is still a distance that things come to best correction,
however you now have the focuser range to move your build to that point,
instead of having to manually set it with spacers.
What is the benefit of more complex refractor designs?
To correct for the color fringing inherent to glass elements, multiple
elements are needed. At minimum, two elements can do a good job of correcting
for distortions, however three elements are needed to fully correct for red,
green, and blue. Additional elements can then be used to correct for
distortions, either internally or in the form of a separate corrective
field-flattener. Glass type plays a part in this as well, which is where
'extra low dispersion'(ED) and 'super low dispersion' (SD) glass come in,
pushing the performance of an optical design with their superior properties.
Astronomy Hub: Your one-stop-shop for Astronomy Knowledge!
Our Gear Experts have compiled a wealth of information to help expand your astronomy knowledge! Below you’ll find links to articles, videos and "how-to" guides. Just one more reason that our Astronomy Hub is a one-stop-shop for all your astronomy and astrophotography needs!
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