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Askar ColourMagic Duo Band Narrowband Imaging Filter 1.25"

Askar ColourMagic Duo Band Narrowband Imaging Filter 1.25''
Price:  £138.00(Inc. 20% VAT)

Model:  SHS-DB-1.25
Brand:  Askar



Generally In Stock, Please Confirm Before Ordering

2 Year Warranty On All New Items
(Excluding Batteries & Globes)

The Askar ColorMagic Duo-Band filter is a dual or triple bandpass narrowband filter designed for light polluted skies for COLOUR CAMERAS to maximise the output from your imaging time. The naming depends on the point of view. It features two distinct areas of the visible spectrum, so lets call it duo-band, however from an astro imager's point of view it covers the H-alpha, OIII and H-beta emission lines, so we could equally call it a triple band filter. Well, for now lets stick with the name given by the manufacturer. (intro by Zoltan, 365Astronomy)

The Askar Duo-band narrowband, as its name suggests, has two passbands, which is quite different from those single-band narrowband filters thus more economical and efficient because astrophotographers donít need to purchase a filter wheel or a whole narrowband filter set. And imagers donít have to buy a monochrome astronomy camera as the duo-band narrowband filter goes well with ordinary color cameras. So the duo-band filter is an economical admission ticket for astrophotography lovers into the world of narrowband technology and deep-sky object imaging.

The Askar duo-band filter is suitable for imaging emission nebulae, planetary nebulae and supernova remnants. The Askar duo-band filter has an extreme high transmission at a center wavelength of 500.7nm (O III) and 656nm (H-alpha). Narrow bandwidth enables this astroimaging filter to block all the light pollution and other unwanted artificial lights or night glow. So the Askar duo-band filter is an ideal instrument for astro-imaging in heavily light-pollution hit locations and delivers enhanced contrast at darker places.

The Askar duo-band filter is designed for improving the contrast and details of nebulae and supernova remnants. Featuring narrow bandwidth and a greatly high transmission at a center wavelength of 500.7nm and 656nm, the Askar duo-band filter can bring out the highest amount of details of the emission nebulae, planetary nebulae and supernova remnants. Also, the out-of-band blocking ability is rated with OD3 (0.1%) with the blocking range of 200-1100nm. It delivers an excellent signal-to-noise ratio and a sharp cut-off rate to attenuate the disturbance from other wavelengths.

The narrow bandwidth and an effective cut-off rate are important features when choosing a narrowband filter. The Askar duo-band filter has a narrow bandwidth and an extreme transmission of over 90% at 500.7nm and over 80% at 656nm, whilst sufficiently suppressing other off-band wavelengths. So the Askar Duo-Band filter can efficiently reject all the light pollution. You can expect a terrific performance of this duo-band filter in artificially-brighten background sky with your astronomy cameras (like the ZWO ASI series color cameras).

(A note from Zoltan: the transmission curve suggests a very high value of nearly 98% for both parts of the spectrum, that is what we would expect from an Askar quality products ;o), so we asked the supplier to confirm if there was a mistake in the description as originally they stated 90%... They answered that it was just a mistake as the manufacturer's specification is min 95%, but the filters usually have an even higher resultant transmission.)

The production process is strictly controlled and every single Askar duo-band narrowband filter is individually examined and tested to ensure that they can highly satisfy the observing interests and needs of our customers.

Narrow bandwidth, properly designed for astrophotography both in light polluted or dark locations.
Useful for imaging emission nebulae, planetary nebulae and supernova remnants.
High transmission and sharp cut-off can greatly enhance the contrast and bring out the most detailed information for those deep-sky objects.
Designed to sharply cut off the inference of artificial light from sodium vapor or mercury vapor street lights and other unwanted disturbance like sky glow.
The Askar duo-band narrowband filter is not suitable for visual observation and not designed for imaging or observing the Sun.

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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

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.

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


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