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ZWO V2 7x 36mm EFW - Antlia 3nm SHO and LRGB Filters


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Here is a bit of investigation I have done into the new V2 version of ZWO's 7 position 36mm filter wheel that I recently bought.

I have not used this yet as I have just ordered a set of Antlia 36mm 3nm filters to go with it.


Version 2 of this filter wheel has 8 extra holes drilled into the main body (camera side) and 4 in the cover (scope side). As far as I can work out these holes have been drilled to enable fitting of the tilt adaptor and direct fixing of certain cameras.




These above image shows the 8 holes which are drilled into the main body




The above image shows the 4 holes drilled into the cover.


All good so far. However there is a big problem with these holes. What was previously a light tight enclosure is now peppered with light passing holes! Not good for darks and stray light entering.


I use the supplied threaded T2/T2 adapter to connect the filter wheel to the scope



Conveniently ZWO supply 7 M2.5 x 6 long countersunk head screws. Not sure why just 7 but more of this later.


So take 4 of these screws and screw them into the tapped holes. They do not protrude into the interior at all and are flush with the top of the adapter as they catch on the flange of the adapter. The filter wheel can be attached to the scope and is light tight at least from the scope side.




Image above shows the 4 countersunk head screws plugging the tapped holes.




Image above shows the inside of the cover showing the 4 tapped holes plugged with the screws.


If you are using a ZWO camera as I will be doing you can screw it directly into the main housing. The camera covers the 4 inner most holes. But there are still 4 holes on the camera side that are still open to the elements.


So now can I screw the M2.5 screws into the holes? Big No. The holes marked in red below are clearance holes that are still exposed to the light as seen from inside the filter wheel .The screw heads should be inside and screw into something on the outside. However the body of the camera comes right up to the inner edge of the clearance holes. So no chance of screwing a nut onto the protruding screw. As I said earlier I am not sure why they have supplied 6 (or 7 as in my case) screws as it should really be 8. The camera body blocks the other 4 holes 2 of which are shown below in yellow.





So I now have to resort to using black tape from the outside. Not all black tape is what it should be and still lets light through.

I may have to bung the holes up with something else.


So the bottom line is ZWO have redesigned the filter wheel and completely made a mess of it. I'm sure I will be able to work around this but you don't expect such basic design flaws such as this.

Oh it also had manufacturing swarf inside so I had to vacuum it out but that wasn't really an issue.

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I got some M2.5 x 4mm long counter sunk screws to bung up the red holes from the inside. A smear of CA glue on the underside of the screw heads, applied with a toothpick, are holding them in place. Be very careful if you are doing it on yours (don't have a big blob of superglue but the slightest smear) as the rubber rim of the rotating plate is very close to the holes - you don't want to contaminate the drive mechanism when inserting the screws. I used the ZWO supplied magnetic screwdriver to place them.


If you ever need to take the screws out then the screwdriver will cleanly break the bond.

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  • TerryMcK changed the title to ZWO V2 7x 36mm EFW - Antlia 3nm SHO and LRGB Filters

I finally had some time to fit the new Antlia 36mm HSO and LRGB filters today.

I found them easy to fit and to work out the correct orientation. Antlia show pictures on their website http://www.antliafilter.com/nd.jsp?id=20 using a pen to work out the orientation.




The image above shows no double image and is the face which points skywards (so towards the scope)




The image above shows a double image which has anti reflection coating which should face the sensor/camera. This is typical of all the different brands of filters I have used, ZWO, Baader, IDAS etc.


Some people on the interwebs have found it difficult using the pen method so I tried it by using the ZWO mini screwdriver supplied with the EFW. I held it parallel with the face of the filter and could quite clearly see the double image on one face and none on the other. This worked for all the filters including the Luminance.


ZWO supply some M2 screws and a series of clamping gaskets to hold the filters in place. A little fiddly to fit but after about an hour fitting them whilst wearing surgical gloves the job was done. Vacuuming the filters to remove any dust bunnies or hairs  worked out ok but you don’t need to stress too much about it. Flats will remove them in calibration.


So after having a few icy cold clear nights recently using another rig I now have clouds and will have to wait a while until the weather clears up so I can get first light on the Antlia filters.

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  • 2 weeks later...

Thanks terry, very useful information. I agree reference the ZWO filter wheel design anomalies, I taped over the holes on mine using thick gorilla tape to the outside. ZWO are not alone with this kind of basic error though.

Having switched to mainly QHY camera’s I encountered a design problem with their US filterwheel (7x36mm) when used with their new 268M camera’s. The 268M comes with 12.5mm back space to the sensor when mounted direct to the QHY FW. This I believed was a bonus as it would enabled me to fit my Pegasus rotator into the available back focus spacing (Reducer & flattener), along with the QHY OAG.  Sadly with the camera and OAG mounted direct to the FW there was insufficient inner focus on the OAG to achieve focus, the additional backspace I hoped would allow the rotator fitting was consumed by a requirement to place spacers between the OAG and FW to allow focus of the guide camera to the main camera. The supplied back space crib card indicating how to achieve different back space requirements showed the OAG connected direct to the FW along with the 268M. This arrangement I found would not allow focus of the guide camera.


In summary, the OAG was designed for a OAG/FW connection to a QHY camera with a rotator type connection to the FW (268C and previous cameras). The introduction of the direct FW connection with the 268M shortened the previous sensor back space distance from the OAG prism such that the same distance from the prism to the guide camera was not achievable. I gave up trying to fit the Pegasus rotator and sold it on.


There are many more similar stories I can tell about a lack of awareness of user requirements within the design of Astro equipment that end up costing us users more money for workarounds.

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