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Do I need an IR/UV cut filter for ASI183MC

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This is my set up

HEQ5 pro

William optics ZS61 MK1


ZWO ASI120MM-C guide cam

50mm astro essentials guide scope


I know it's summer but I think I can do better than attached. I've read I should get a filter, is this the case if so is the astronomik L2 UV/IR cut filter 1.25" the right one?




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The Zwo manual just states that the sensor protect window is AR coated only, and doesn't specify a different window for the colour version like some other cameras, so it passes IR and some extended blue. IR will be out of focus when you're focused on visible wavelengths so will lead to some image blurring. Depending on how well colour corrected the scope is, the shorter blue wavelengths may be out of focus to some degree as well causing noticeable blue halos around stars

The UV/IR cut will remove the out of focus IR and the shorter blue wavelengths leading into UV which should improve your image sharpness, and help with any blue halos. The Astromomik UV/IRfilters have three passband widths. L2 is the middle one and is likely similar to other manufactures UV/IR filters. The L3 has a narrower passband which cuts off more off the shorter blue wavelengths as well as the longer red wavelengths so reducing blue halos more.

Your posted image sharpness looks quite reasonable, but there's almost no colour present and it's faily black crushed so it's hard to say what UV/IR filter would suit you best. It's worth getting an UV/IR cut filter anyway if the camera itself doesn't have one, and the L2 should be fine, but whether you'd benefit more from the L3 I can't say from your image. The L1 is for very well colour corrected optics so wouldn't be the best choice for mid-price scopes.


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The ASI183MC appears to have a significant IR response (though the spec does not show the response beyond 700nm) I would recommend using an UV/IR filter.  ZWO offer one for around £25 which I have used successfully with other of their cameras.

Other ZWO cameras come with a fisheye lens, which I have found mainly useful for demonstrating the funny colours you get if you don't fit an IR-cut filter.  You could experiment with aiming your outfit at treetops in daylight.

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Pretty much all zwo cameras I've used have AR windows (check the camera specs on their website) so need a UV/or cut filter or a luminence filter to cut the bloat. I have however noticed the colour isn't as saturated as a result. You can technically shoot the RGB unfiltered, and layer a luminence image (luminence should be the majority of your hours) on top to control the level of colour coming through as well as sharpen the details. The z61 is decently well corrected as it's a small aperture, I have one.

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