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I have a question for all of you Hyperstar imagers. I noticed that my Celestron Dew Shield is not perfectly round when it is on the end of my C8. Will this effect the roundness of my stars? Thanks, Mike |
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| I have Astrozap's aluminum dew shield, and I really like that a lot. I'm rarely up at dawn, so I don't how I'd take flats without it. |
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Hi Mike: It's unlikely unless it is REALLY out. However, I can highly recommend this: Astrozap Aluminum Dew Shield. I have it on my Edge HD 8 and it is great. Tim. |
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Anything impinging on the light path can cause diffraction effects, leading to odd stars or spikes. But first you will notice vignetting.. I do flats first without the dew shield and then with it. The two set of flats should be identical, and when applied to your image taken with the dew shield should look the same. If that is good, you should have no issue, as the shield is not in your light path. In theory, you can tolerate some vignetting, and just use the appropriate flat with the same configuration, but better safe than sorry. The other option is just to some simple trigonmetry--take 1/2 your max FOV for your setup and camera frame size, and calculate for the length of the shield what your dewshield radius must be as a minimum at the open end. This makes sure you are out of the lightpath, and it doesn't matter if it is not round, just that it flares out enough at the minimum radius. If your dewshield is not flared out with hyperstar, you likely have some vignetting, even if it is round. Rick |
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Damien Cannane:thanks Damien |
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Tim Hutchison:Thanks Tim, I will check it out. |
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Anything impinging on the light path can cause diffraction effects, leading to odd stars or spikes. But first you will notice vignetting.. I do flats first without the dew shield and then with it. The two set of flats should be identical, and when applied to your image taken with the dew shield should look the same. If that is good, you should have no issue, as the shield is not in your light path. In theory, you can tolerate some vignetting, and just use the appropriate flat with the same configuration, but better safe than sorry. The other option is just to some simple trigonmetry--take 1/2 your max FOV for your setup and camera frame size, and calculate for the length of the shield what your dewshield radius must be as a minimum at the open end. This makes sure you are out of the lightpath, and it doesn't matter if it is not round, just that it flares out enough at the minimum radius. If your dewshield is not flared out with hyperstar, you likely have some vignetting, even if it is round.RickThanks so much for your detailed explanation Rick! |
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| I use the flexible dew shield also, particularly to do my flats and have noticed nothing. |
