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Marc I didn’t get a chance to test the FSQ-85 last night. Before starting the image sequence I noticed the outer covering for the power cable going to the ZWO ASI6200 camera was torn and needed to be replaced. I didn’t want to risk possibly frying the camera if the actual wires running inside were also damaged. I replaced the cable today, but now the clouds have moved in 🤦♂️. I will test the retracted dew shield theory as it relates to the inverse Lighthouse effect as soon as I get clear skies again. Bob |
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As a follow up to my earlier post on the possibility of the fully extended Dew shield on the FSQ-85 causing the inverse Lighthouse effect : I finally got out during the break in the clouds to try out the FSQ – 85 and the new .73X reducer with the dew shield only extended about an inch versus fully extended. I imaged 2118 the Witch Head nebula using two minute exposures and included Rigel in the frame. I also imaged comet Ponds-Brooks that is now low in the western sky for us here in Northern Nevada. I only managed to get four 2 minute light frames of the comet before it went below my preset photography cut off of 20° horizon. Looking at the results I don’t see any inverse Lighthouse effect on the stars surrounding the comet image., but those stars are not that bright. Looking at the Witch head finished stacked image in Pixinsight the inverse Lighthouse effect is still there on Rigel and a few of the brighter stars- even with the shield only extended approximate 1 inch. But it does not appear as extensive on the lesser magnitude stars as it did when I imaged the Witch a few months ago with Rigel in the field of view. Since my telescope is in a domed observatory and I don’t have a huge amount of light pollution in my neighborhood I personally plan on extending the dew shield only halfway in the future. I do have a dew heater on the scope just behind the front front objective lens assembly. Sorry this is not a more precise scientific analysis. I can only conclude that the dew shield being fully extended does make somewhat of a difference as far as the Inverse lighthouse effect on the brightest stars. Bob |
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| You may be able to reduce this effect by using an aperture mask. It will slow your scope down a little bit, but should improve these artifacts and give all your stars a more crisp edge reducing the slight flaring. I did this a while back when I used a WO scope that produced the iron cross shape stars. |
