Old 22-03-2009, 09:25 AM
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Tilt (Michael)
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WO 0.8x focal reducer/flattener - thoughts?

Hi guys,

Sorry, this is not a thread about IF I should buy one ect

Just asking if anyone else uses a WO 0.8x FR/FF to correct curvature, I've been using one lately with an ED80 however some nights it seems to work better than others. Last night I imaged a chunk of the LMC (including NGC 2070), and the edges of the image look a little suss (stretched, elongated stars). Where as other times I have used the WO flattener, I've had a nice flat field in the images. Any one else recieving random results like I am

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Old 22-03-2009, 09:36 AM
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Octane (Humayun)
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Old 22-03-2009, 10:09 AM
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darrellx (Darrell)
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Yes I do. I was just considering a similar post when I read yours. I have a Megrez90 and use the WO 0.8x and generally I am happy with the results I get. But sometimes, like you, the objects around the edges of the shots are stretched and look like there has been some rotation.

I don't know what causes it,or whether I am doing something to make it happen. All I do at the moment is crop the image to remove the offending objects.

You are not alone.

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Old 23-03-2009, 10:12 AM
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Geoff45 (Geoff)
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Just guessing here, but maybe the field is still a little curved. If you get good focus in the centre, the edge will be out, but if you focus somewhere between the centre and edge or if your centre focus is not spot on, you may get a reasonable average focus over the whole field.
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Old 23-03-2009, 05:08 PM
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[1ponders] (Paul)
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Another thing to consider is if there is sag in your camera to scope connections. I have to take care at times to make sure the camera is held squarely in the focuser draw tube, otherwise I do get problems with stars in parts of images.
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Old 23-03-2009, 09:20 PM
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Tilt (Michael)
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These are all very good thoughts.

Yes I suppose I shouldn't be looking for perfection with a $400 ED80 + flattener, I guess its not possible. Interestingly the results I get are varied, so sometimes the edges are fairly ordinary, and sometimes its very good. So the camera being square on the draw tube might certainly be an issue (I know the flattener moves around a bit as I'm locking it into place). I appreciate the comments.

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