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Filter in front of .85 reducer/Flattener predictions?

Chris M48

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My setup: SW Evostar120ED on EQ5 Pro, SW .85 Reducer/Flattener, ZWO Duo band filter 1.25”, ZWOasi294mc cooled camera.

Filter is 6.6mm in front of sensor, Reducer is 55mm in front of sensor.

LP is not too bad here but Moon is overhead.

what should I look for to assess how badly the filter has affected the image?

I will try and find a subject as far from the moons influence as possible.

I tried to place the filter between the scope and the reducer but had reflections and generally poor results.

It would be really handy if it works but I’m expecting it not to.

Any advice will be very welcome.

Clear skies and stay safe.




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 You should have a 1.25" filter adaptor which screws into the 11mm spacer on the front of the camera. This places the filter as close as it can be to the sensor, avoiding vignetting, reducing the chances of reflections and allowing the whole sensor to be used to capture the image.

I've not used the ZWO Duo Band filter, I have the L-eXtreme which I use with my ASI 294MC Pro, but you'll need to use it on emission nebula, which mostly have Ha & Oiii, like the Heart, Rosette & California. They don't work well on planetary nebula and galaxies but they do allow you to take longer exposures during the full Moon period, which is what I bought the L-eXtreme for. ;) 


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Thanks Martin.

Exactly what I did but the moon and the mist proved too strong for decent results. Even so looks promising enough for better conditions. I can wait.

Thanks for your assist.

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One other thing with using this type of filter with ASI294MC; if you find you're having issues getting the flats to calibrate correctly then use a gain of 200 and offset of 30 and they should calibrate correctly. ;)


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