ZWO EFW 8 Position Electronic Filter Wheel For 1.25" Mounted Or 31mm Unmounted Filters

This electronic filter wheel from ZWO is most likely of of the smallest 8-position filter wheels in the world. It is also extremely lightweight, it weighs 400g only.

Its housing is CNC machined from aircraft grade aluminium alloy.

The stepper motor, that is the heart of any electronic filter wheel, is made by a reliable Japanese company, NPM. You can trust its quality and reliability.

This high quality 8-position filter wheel has been designed mainly for astro photography, especially, but not exclusively for ZWO ASI1600 cameras.

Depending on the focal ratio of your telescope you can use it with standard 1.25" filters in filter cell or you can choose 31mm unmounted filters where a smaller filter would cause vignetting and use of at least 31mm filters is necessary.

As it is ASCOM compatible, therefore it can be used with cameras of other brands as well.

Up to 8 filters can be installed in the numbered compartments that accepts both 1.25" (mounted) and 31mm (unmounted) filters (or semi-mounted 31mm Astronomik filters), and each can be selected for your eyepiece or camera from an imaging software.

ZWO now offers 1.25", 31mm and 36mm LRGB and narrowband deep sky filters as well.

The filter wheel can be attached to your focuser either by the supplied 1.25” nosepiece adaptor or via a T-thread. There is actually a female T-thread on both sides of the filter wheel, but it also comes with a reverse adapter with male T-thread on both sides.

The robustly constructed filter wheel is supplied with a 1.25” nosepiece and a 1.25” eyepiece holder with brass compression ring.

Please note: your focuser will require 20mm of additional inward focusing distance from the normal focus position to compensate for the thickness of the filter wheel.

This filter wheel will be a good addition to the new ASI1600 range of cameras, but especially for the monochrome versions. (please make sure that your telescope otherwise have enough back focus, of course, e.g. Newtonian telescopes would usually have a back focus issue, unless modified or specially designed for astro photograpy...)

LIMITING F-RATIO

The distance between the filter and sensor is around 10mm when you connect the ASI1600 to this EFW, so a 1.25″ filter won’t have vignetting with a scope with up to about f/8-f/9.5 focal ratio (depending on the thickness of the filter) and a 31mm filter won’t have vignetting up to about f/2.8-f/3.2 lens (depending on the thickness of the filter). Please note, these figures are slightly different from ZWO's own calculations and to be checked in practice.

ZWO's new RGBL filters are recommended to use with ASI1600 cameras, as these specially designed filters will offer nearly 1:1:1 RGB color balance.

The full ZWO EFW 8 set includes:

EFW 8-position filter wheel
T2 nosepiece
1.25″ Holder-T2
T2-T2 adapter
USB2.0 Cable
Notes:

1.25″ filter requirement: threads length shorter than 3mm, height without threads less than 7mm

31mm filter requirement: a set of M2 screws and washers needed to fix the filter are included in the package

How to use it?
you just need to plugin the EFW with a USB2.0 cable and install the ASCOM driver from here.

There are ZWO Filter Wheel(1) and ZWO Filter Wheel(2) to select, you can use either one of them.

You can control 2 filter wheels simultaneously from one software.

SPECIFICATIONS

Limiting F-ratio: appr f/3 with 31mm filters and f/8 with 1.25" filters (calculated with ZWO's 2mm thick filters)
Thickness: 20mm
Power consumption: 150 mA at 5 Volts
ASCOM compatible
Positions: 8 x 1.25" or 8 x 31mm glass, unmounted or semi-mounted (like Astronomik)
Weight: 400g

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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