Askar FRA300 60mm f/5 Petzval Astrograph OTA

Since their inception, Askar FRA series short focal ratio astrograph have been very well received by astronomical amateurs. This year, we launched the FRA300 Pro —— the smallest 60mm F/5 Petzval astrograph with the fastest native focal ratio in the FRA series so farwith a focal length of just 300mm. The star is sharp and delicate.At the center of its field of view, the RMS radius can reach 2um. Even a serious user can also be satisfied when it comes to the shape of stars.It performs excellence with full-frame and supports 44mm imaging,which is a rare astrograph for amateur astronomers.Compared with F/6 or F/7，F/5 can effectively reduce the exposure time,helps you get the same exposure in less time.In addition, the entire OTA is compact, making it the portable choice for field photographers.

FRA300 Pro 's objective lens adopts a quintuplet fully air-spaced structure, including one piece of ED glass,it also adopts a fully-multi-coating to effectively remove stray light.
In particular, the rear group lens adopts the two pieces of far-separated refractive lenses, which improves both the star quality and the aberration correction performance , and has a very good control of full-frame peripheral light reduction.

Thanks to the native Petzval design, the user does not need to calculate the backfocus, as long as the focus is within a certain range is the optimal position.

Mechanically，FRA300 Pro is assembled with high-quality CNC-machined components , wrapped with smooth spray coating and light oxidation process,both beautiful and practical.The tube ring design is equally lightweight and stylish.Despite the increased cost, we want enthusiasts to use the FRA300 Pro that perform well in every way and are considered in every detail.

The focuser is 2.5"rack-and-pinion focuser, which is solid and beautiful.It's designed with dual-speed hand knobs, twin knobs for coarse adjustment and a fine adjustment knob to accurate the focus, equipped with a universal M48X0.75 thread adapter. There are also two separate M54X0.75 and M48X0.75 adapters in the standard kit for easy access to a variety of imaging equipment and accessories. The end is equipped with a 360° rotator, which is convenient for users to rotate at any angle when shooting.

FRA300 Pro also comes standard with a multi-function handle and a 300mm vixen-style dovetail plate, which can be directly connected to various mounts and accessories, the multi-functional handle can also be connected to the universal vixen-style finder base.The 300mm dovetail plate allows the astrograph to maintain balance on the mount.

Specifications:

Aperture size：60mm
Focal length：300mm
Focal ratio：F/5
Objective lens：quintuplet fully air-spaced Petzval APO (including one ED glass)
Image circle：44mm full-frame
Maximum accessory connection (with the focuser fully retreated)：
1. Imaging mode:
71mm (from the base of M42×0.75 male thread)
67mm (from the base of M48×0.75 male thread)
71mm (from the base of M54×0.75 male thread)
Total length：303mm
Net weight：2.26kg
Gross weight：3.12kg
Rear-end thread ：M48*0.75 male thread
Standard package items：a tube ring, a handle, an Askar 300mm Vixen dovetail plate, a M42*0.75 adapters, a warranty，a manual

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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