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Hi guys, Yesterday I was not able to focus. There were relatively strong northern winds but nothing I haven't seen before, and the telescope was well protected (no shake at all). I used the exact same equipment (178MM + VMC 110L) that I had used the night before yesterday, but things simply looked too fuzzy. When measuring with the Ekos Focus module, the best possible HFR was around 2.2 (usual value: 0.9 - 1.1) and when using a Bahtinov mask I could see the pattern having perfect symmetry except all spikes were fuzzy. I thought the VMC was throwing a fit (perhaps it somehow became uncollimated) so I tried with my small 30/360 apo and the result was the same: the stars never stopped being fuzzy balls, at "sharpest" focus they were simply smaller fuzzy balls. I also excluded the camera or the filter or the reducer having an issue by trying with another camera and all kinds of filters (or no filters) in front. And I was able to focus closer than infinity, I picked a street lamp about 200m away and focusing was so sharp you could see the scratches on its pole. So I am reasonably confident it wasn't my equipment. My question is: is this a known thing? As far as I could tell the sky was very clear, stars were not twinkling, I could see quite a lot of asterisms with the naked eye and PHD on the small guiderscope was also recording fairly good SNR (in the 30s and 40s while 18-25 is more typical). Also this morning I was able to see the moon in the Western horizon with quite a lot of detail, until about 11 am actually. But my imaging telescope(s) just couldn't deliver anything better than fuzzy balls or fuzzy Bahtinov diffraction patterns. Any ideas? Thanks, D. |
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Did you have any Dew on your optics that’ll make that happen every time. Chris CS |
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Nope. It was a very dry night. And I did check for dew (and dust). You are right that dew would make that happen but it wasn't. Tonight (right now in fact) I can focus. The only difference is the northern winds are not as strong. |
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| What exposure time were you using for focusing? It might have just been bad seeing. |
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| Are you in a location subject to that recent Saharan dust storm by any chance? |
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Hi, My usual exposure for focusing is 1-2 seconds (depends on the brightness of the star in hand). For imaging it is 120-180 seconds. Both were fuzzy. But not shaky at all. It did look like serious dew except there wasn't any dew. I am in Greece. Saharan duststorms are not very rare and are real showstoppers. I'd say at least two weeks per year in total. But they are brought by southern winds. Northern winds usually mean super clear skies. I remember reading somewhere that seeing can be bad because of conditions in the upper atmosphere even though things seem pretty good to the naked eye. But I can't find the link. |
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You are the victim of what I call really fast seeing. This is high altitude stuff. Was the jet stream overhead?. I have see for instance the disc and rings of Saturn dissolve and enlarge to twice the diameter or worse. If you look at an out of focus bright star outside focus you'll be able to see via a Scherin effect what's happening up there . Beer is useful at this point. Don't forget to wave your hand in front of the objective to see a graphic example of heat currents. PJM |
