Askar FMA230 230mm f/5.5 Triplet APO Astrograph With Reducer

Since the FMA135 and FMA180 have hit the market, we receive numerous positive feedback.
It’s really an encouragement for us to further introduce our FMA230 astrograph, hoping to offer more choices for our customers.

The FMA230 has a compound lens system. The front objective lens comprises three lenses and the posterior reducer is composed of four lenses and thus it’s sometimes dubbed as a “three at the front and four at the rear” system. The aperture size of the objective lens is 50mm and the original focal length is 275mm thus we’ve got a relatively fast focal ratio of f/5.5. The objective lens contains two ED glasses which are adapted to cure chromatic aberrations.

One can barely find an equal counterpart in the market as designing a three-element apochromatic objective lens in astrograph with such size demands more on craftsmanship and processing technique. We made it because we consistently cling to the belief that we have to deliver a better imaging result to our customers. The FMA230 can solely function as a lens to observe the ground scenery or stars in the sky, or as a telescope for direct-focus photography. You should just fine-tune the helical focuser to perfectly focus without adding extra optical devices.

The four-element reducer is a 0.84×optical device which can change the the FMA230 into a 50mm-aperture astrograph with a focal length of 230mm and a focal ratio of f/4.6. The reducer is designed specially for sophisticated astrophotography, which plays an essential role in improving the image quality generally across the whole field of view. And it pays special attention to the stars at the edge of the image. The pictures will be greatly enhanced and detailed under the help of this dedicated reducer even the imaging equipment you use is a rather professional full-frame ordinary or astronomy camera.

FMA230 is equipped with useful standard accessories.

The pair of tube rings are artistically pierced. Its stalks are lengthened which means that the tube rings provide more room for the devices, like a camera, that are attached to the FMA230, so they won’t collide with the dovetail plate under the astrograph.

The FMA230 comes with a Vixen-style dovetail plate. Screw the tube-ring-wrapped astrograph onto the dovetail plate and then directly slide the assembly into the slot on top of an equatorial mount. The slot at the center of the dovetail plate is carved for the attachment to a tripod. It’s quite convenient and helpful especially when you carry out some ground imaging or observation.

In order to solve the awkwardness of carrying around your astrograph when you engage in field astrophotography, the FMA230 is designed with a pretty-looking and utility handle. The detachable handle is installed on the top side of the tube ring. The handle is not just literally a handle, the dovetail slot carved out of the handle can also be a base for the attachment of finders, guiders or ASIAIRs that have a corresponding dovetail foot. So you have more room to integrate as many accessories as possible. Besides, the handle is carved with 45°Arca-swiss style slots at the sides, so an upside-down handle can be directly slid into a corresponding Arca-swiss clamp on a camera tripod.

The lightweight and compact FMA230 is a new sibling from the Askar FMA- family, it will definitely bring your observing and imaging experience to a whole new level!

Aperture：50mm
Focal length：275mm
230mm（with the reducer）
Focal ratio：f/5.5
f/4.6（with the reducer）
Objective lens：Triplet air-spaced APO with two ED glasses
Septuplet full-frame astrograph（including the reducer）
Length：248mm（imaging with the reducer）
221mm（observing without a diagonal）
Weight：1045g
Rear-end adapter type：M48×0.75（for imaging）
2" socket（for observation）
Package items：an FMA230 astrograph, a pair of tube rings,
a Vixen-style dovetail plate, a manual, 2" adapter

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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