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Antlia Pro Ultra Narrowband 3nm OIII Filter - 31mm Unmounted

Antlia Pro Ultra Narrowband 3nm OIII Filter - 31mm Unmounted
Price:  £288.00(Inc. 20% VAT)

Model:  ANT-3.0-OIII-31PRO
Brand:  Antlia



Generally In Stock, Please Confirm Before Ordering

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

ANTLIA PRO Ultra Narrowband 3nm OIII Filter - 31mm Unmounted (glass only)
Now these Antlia filters got even better! 3nm bandwidth instead of 3.5nm!

The out of band blocking specification of the new OIII Pro version is rated to OD5 (0.001%) which delivers an excellent SNR (signal to noise ratio) and effective cut-off rate to minimize interference from other wavelengths. Improved sharp cut-off astrophotography! The 3nm Pro filters are designed to minimize halos around bright stars.

The Antlia OIII 3.0nm filter is suitable for imaging Oxigen III emissions from nebulae, planetary nebulae and supernova remnants.
The 3.0nm bandwidth delivers a high transmission at a center wavelength of 500.7nm. The extreme narrowness in bandwidth enables astro-imaging from heavily light polluted locations and delivers improved contrast at darker sites. The filter effectively suppresses interference from other wavelengths, especially artificial mercury and sodium lamps.
Antlia narrowband filters are designed to bring out the faintest features in nebulosity by reducing the unwanted background frequencies. The narrower the filter, the better. Our OIII filter is designed to deliver 90 % transmission at the 500.7nm line. The out of band blocking specification is rated OD3 (0.1%) which delivers an excellent signal to noise ratio and effective cut off rate to minimize interference from other wavelengths.
A sharp cut off rate is a very important performance index since it is designed to sharply attenuate off-band wavelengths. The result is that the Antlia Ha filter delivers excellent contrast with extremely dark backgrounds whilst delivering a high transmission of the OIII signal. The sharp cut-off also minimizes the effect of halos around bright stars.
In the production process, we use very strict quality control standards. Each filter is individually tested and scanned to ensure that the product meets our high-performance parameters. Our exacting attention to tolerances requires each substrate to have a uniform thickness that achieves no more + -0.05mm deviation from specification.

Application and Performance:
Ultra-narrow 3.0 nm bandwidths, designed for astronomy imaging in both light polluted areas and at dark sites;
Suitable for imaging of OIII emission in nebulae, planetary nebulae and supernova remnants;
With the Ha, SII, OIII set of filters you are able to process your images to achieve the impressive Hubble color palette;
With the Ha and OIII filters these can be used to achieve great narrowband results using the Bi-Color process;
High transmission of typically 90% and sharp cut-off delivers an excellent boost in contrast for OIII emitting objects;
All Antlia Narrowband filters are edge blackened to minimize interference from stray light;
This filter is not suited to deep sky objects that do not contain OIII emissions. It can be used to image OIII regions in galaxies and such images can be combined into LRGB images to better highlight the Ha emitting regions of galaxies.

Technical Data:
Schott optical substrate
1.25”, 2” mounted, 31mm,36mm dia (2mm+/-0.05mm)
50mm dia,50*50mm,65*65mm square (3mm+/-0.05mm)
Surface Quality: 60/40 (Refer to MIL-O-13830)
2 sides fine-optically polished to ensure accurate 1/4 wavefront
30 arcsec parallelism
Center-Wavelength of Antlia OIII 3.0nm filter: 500.7nm
OIII 500.7nm T>90%, 90 % transmission at OIII line at 500.7nm
OD3(0.1%)@ 300-1000nm
Both sides with multi-layer anti-reflection coating
Single / Non-glued substrate

Filter Cell (specifications for cell mounted filters only):
1.25” (M26*0.6),2” (M48*0.75)
Ultra-thin filter cell to minimize vignetting by maximize possible clear aperture
Black Anodized Finish
Non-Fading Laser Engraving

Available Sizes:
Mounted: 1.25” & 2” (2mm thickness)
Unmounted:Dia 31mm,Dia 36mm (2mm thickness)
Unmounted:Dia 50mm (3mm thickness)
Unmounted:50*50mm,65*65 square (3mm thickness)

Not Recommended:
Solar Observing and imaging
Visual observation
Serious eye damage will result if you fail to observe the warning.

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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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Rother Valley Optics Ltd
Rother Valley Optics Ltd