Askar 71F Quadruplet Flatfield APO Imaging Refractor OTA

The Askar 71F is an OTA with an aperture of 71mm, a focal length of 490mm, and a native focal ratio of F6.9. 

The Askar 71F adopts a quadruplet air-spaced APO lens design, including one piece of ED glass， which can effectively reduce chromatic aberration. The Askar 71F supports 44mm full-frame imaging with great performance of the surrounding star points.

The Askar 71F is a self-flattened design that allows users to avoid calculating the back focus and buying additional flattener, after attaching the imaging accessories, users can directly use it for shooting after the OTA is in focus. This further reduces the cost and improves the pleasure of shooting.

With practicality and versatility in mind, the Askar 71F's weight and size are effectively controlled, making it easy to carry and use. The Askar 71F OTA weighs only 2.5kg and the gross weight is 3kg (including the tube rings and dovetail plate).

The Askar 71F is versatile in its use, allowing for both visual observation and astrophotography. For users' convenience, we've also included three observation accessories standard for the 71F: an 8mm eyepiece, a 20mm eyepiece, and a 1.25-inch 45° erecting prism.

The 8mm eyepiece has a magnification of 60x and the 20mm eyepiece has a magnification of 25x. The Askar 71F can be used with different eyepieces depending on the target, and both eyepieces are ideal for viewing birds and landscapes.

Both eyepieces have a 1.25-inch barrel and a rubberized top for a soft and comfortable user experience.

The 1.25-inch 45° erecting prism provides correct left-to-right and down-to-up image views, making users easy for you to observing without the hassle of seeing images reversed up, down, left, and right.

The Askar 71F also comes standard with a photographic extension tube, which includes M48*0.75&M54*0.75 adapters, it also contains a built-in 2-inch filter thread for easy shooting connections. No matter whether connecting a traditional DSLR camera or a professional astronomical camera, it is very convenient to use. When users go out, they can directly connect the shooting accessories to record the beautiful view at any time.

The mechanical design of the Askar 71F itself adheres to Askar's consistent philosophy of taking into account the user's habits and minimizing the user's invisible costs.

The dew shield of the Askar 71F is a retractable design, further shortening the overall length and increasing portability. The entire lens tube of Askar 71F is crafted using high-quality CNC machining. All the inner of the Askar 71F's dew shield is covered with matting paint to effectively reduce stray light reflections. The overall blue and white color scheme makes the telescope look more refined.

On the handle bar of Askar 71F, it designs a finder base slot. Besides, there are two finder bases on both sides of the focuser, which not only eliminates the need for disassembling when changing the position of the finder scope but also provides additional mounting positions for other astronomical accessories.

In terms of the focuser, the Askar 71F is equipped with a dual-speed R&P 2.4-inch rigid focuser, which has a 1:10 fine adjustment and a 360° scale field rotator at the rear end for precise angle adjustment.

The Askar 71F's dovetail plate is a 230mm standard Vixen dovetail plate, which slotted 1/4 screw holes as well as 3/8 screw holes for direct tripod attachment.

As an affordable and high-quality versatile self-flattened OTA, we look forward to the Askar 71F accompanying you to discover more beautiful!

Specifications

Product Size Diagram

71F Connection Diagram

Locking Screw Position Diagram

EAF (optional) Installation

Optical Path Diagram

Spot Diagram

Some items that are showing as in stock are in stock at our holding warehouses, not at the shop. To double check the stock levels at the shop, please contact us on 01909774369 or sales@rothervalleyoptics.co.uk.

The delivery times for most items is 1 - 2 days but again, please double check stock levels on important orders before placing an order via the website.

The delivery costs for courier next day are for mainland UK only. If you live in the Scottish Highlands/Islands, Channel Islands or Northern Ireland, then a shipping surchage will apply. please contact us for prices. Smaller items can still go 1st class via Royal Mail.

Please note that if you are wanting to take advantage of our Saturday and Sunday timed services or next day pre 12 or pre 10:30 services, you MUST check that the stock is here at the shop before placing orders. Also, orders using the Saturday and Sunday services must be placed before 1pm the previous working day. Also, please remember to check that the stock is here at the shop before placing orders. If the stock is not at the shop, we won't be able to ship on any of the timed services. 

Please note International customers will need to contact us for a shipping price prior to ordering via the website. We don't ship all items internationally. It is at our discretion what we ship outside of the UK. This all depends on the size and weight of the items. Please get in touch with us for any postage costs. Please note we do NOT ship telescopes or heavy items outside of the UK. This is due to massive postage costs and problems regarding returns.

If you have any questions regarding stock levels or delivery, please get in touch.

Zygo Interferometer Testing For ED Refractor Telescopes!

We are extremely pleased to announce our Zygo Interferometer is now installed and ready for use! Our experienced staff can test refractor lenses up to 120mm aperture and provide a comprehensive 2 page report showing the optical quality and Strehl ratio, plus much more information. We are using the very latest Zygo MX software to provide a more detailed report compared to other standard reports.

The interferometer is essentially a measuring instrument. Within the interferometer is a calibrated laser that is pointed through the optical test surface, then onto a high quality reference sphere, then back through the test subject then to an internal camera which gives us the measurement on the screen. From this, we can adjust the position of the test optic and the reference sphere to obtain a perfectly calibrated system. The more central the laser to the test optic and then on return, the better and more accurate reading and measurement we can take. This takes a lot of adjustment to get the best results from the optical surface. Once the measurement has been taken, we are provided with a series of results that show the optical quality of the surface plus other information. Continue reading for an explanation of the individual values and you can also see a test report that was done on one of our RVO Horizon 60 OTAs. 

We are offering certain telescopes with a Zygo test at an extra cost. Mainly ED doublets and triplets. All available telescopes with a Zygo test report are listed here. Just select Zygo Test Report from the drop down box at the top of the listing and we will test the optics in house and provide a full 2 page report with your scope. This will show you the optical quality of your telescope optics. We can also offer this service on your refractor telescope. Please get in touch for more details about this. 

At Rother Valley Optics, one thing we pride ourselves on is customer service and quality of our equipment. When we test your telescope, we will ensure that it is of the highest quality otherwise, we will reject the scope under our strict quality control and test another model for your peace of mind. One of the main values to look at when testing a refractor is the Strehl ratio. The higher this number, the higher quality lens you have. At Rother Valley Optics, we will guarantee the highest possible Strehl ratio for your telescope.  We will aim to provide 0.95 Strehl or higher on Takahashi, RVO Horizon, William Optics and many more! Generally, the higher the Strehl ratio, the lower the Astigmatism and Coma meaning a better image quality from your instrument. 

Other measurements such as the PV and RMS are important too. With these measurements, the lower the number the better as it shows less curvature on the lens. The flatter an optical lens, the better it will perform. The PV rating (Peak To Valley) is a measurement from the highest point (Peak) to the lowest point (Valley). From this we get the RMS (Root, Mean, Square). This is a similar figure to the PV and measured exactly the same way. The RMS is basically an average height difference from the PV so again, the lower the better. As you can see form the example below, we measured an RMS of just 0.027 wave which is a very good value.

We also measure the Power with our systems which is essentially the error from the reference sphere to the test optic. The reference sphere we use on our system is a very high quality sphere so the closer to zero the Power, the less error between the 2 elements thus ensuring a higher quality optical surface. 

You will also see some more values such as Astigmatism and Coma. Again, these are measured by the interferometer when we take measurements of the optical surface after adjustment. These are values which ideally would be at 0 but as our test optics are all curved lenses, there will always be astigmatism and coma present. The lower the number, the less of these aberations you will effectively see but with most refractors, you can buy field flatteners which will compensate for the coma anyway. The astigmatisms value is explaining the error between the symmetrical curvature of the lens. Basically, no lens will be perfectly symmetrical, the lower the astigmatism, the more symmetrical the lens surface is. 

Once the Zygo test report has been completed, the optical alignment is thoroughly tested and tuned to ensure they are spot on before they leave us. 

All available telescopes are on the website at the link below and ones we've tested already that are available straight away are also listed.

https://www.rothervalleyoptics.co.uk/zygo-tested-refractors.html

Here is an example of the test what we provide. This was a test on one of our Horizon 60 ED OTA's.

For any questions about this amazing new service, please either call 01909774369 or email sales@rothervalleyoptics.co.uk.

Are you interested in this product but would like to speak to someone with some more information? Simply fill in the form below and we will get back to you as soon as we can!

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