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Antlia OAG & Filter Drawer Assembly

Antlia OAG & Filter Drawer Assembly
Price:  £272.00(Inc. 20% VAT)

Brand:  Antlia



Generally In Stock, Please Confirm Before Ordering

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

OAG means Off-Axis Guider. Antlia OAG and filter drawer assembly is an innovative accessory that integrates filter drawer and OAG. It allows you to utilize your primary imaging camera and telescope for auto-guiding, without needing a heavy additional guide scope. The OAG uses a small internal pick-off prism as a mirror to reflect part of the incoming light from the telescope to your independent guide camera. Since the off-axis guiding and imaging camera shares the same image train as the main detector, it handles very well with all bending and tilting that may be present in your setup, and you will achieve tracking accuracy greater than you would with a separate guide scope.

Large pick-out prism 12*12mm, which allows the use of a larger guiding sensor and therefore a greater selection of guide stars.
Mono-block (one-piece) design with the OAG body directly connected to the filter drawer.
Comfortably fits APS-C sensor and Full Frame sensor.
The total thickness plus both side adapters are 37.5mm.
It's right for cameras with 17.5mm back focus distance without additional adapters.
The OAG has been CNC machined from a single aluminium block and provides a very rigid platform for guiding.
High-quality helical focuser assembly, a 1.25-inch helical focuser with a generous 10mm of travel allows you will find the optimum focus for your guide star.
The prism height can be adjusted to better illuminate the field of view of your auto guider. The smaller the imaging sensor in your camera the further down the prism can be set without interfering with the sensor.
Dovetail-type threaded adapters are attached to the body with grub screws, so the adapters can be 360° rotated and locked to align with the telescope and camera.
You can rotate the OAG 360° to find a guide star.
A wide variety of adapters is provided to accompany multiple configurations. Antlia OAG includes 7 popular threaded sizes: M42, M48, M54, and M68 male and female for both sides. (no M42 female)
Application is not limited to a specific brand instrument.
Filter sliders of Dia50mm and 50X50mm, adapter rings of B-48125,B-4836,B-4831 and other adapters can be ordered separately.

The Standard Antlia OAG and Filter Drawer Attached to Imaging Setup

The OAG requires a telescope, imaging camera, autoguider, and a mount tracking equatorially with autoguiding capability. Please refer to Schematic diagram 02 to familiarize with the Antlia OAG.

You need to ensure that the distance from the prism to the main camera sensor is exactly equal to the distance from the prism to the guider sensor.

List of Parts included in the Antlia OAG& Filter Drawer set:
1 x Off-Axis Guider Body, 1 x Helical Focuser, 1 x 2-inch (M48*0.75) Filter Slider, 1 x M42-Male Adapter, 1 x M48-Male Adapter, 1 x M48-Female Adapter,1 x M54-Female Adapter, 1 x M54-Male Adapter, 1 x M68-Female Adapter, 1 x M68-Male Adapter, 1 x M42-6mm*1 for 12.5mm BFD, 1 x M42-1.25-27mm

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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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