Taking Flats with the Edge HD 8"

Refractors Acquisition Calibration Deep Sky
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Jerry Gerber avatar
Jerry Gerber avatar
I've found a way to take flats with my Esprit 100 ED refractor that seems to work well.  After achieving good focus using a Tri-Bahtinov mask and locking down the focus lever, I take a photo of the image train and drawtube focusing scale so I can see exactly how far the drawtube has been extended. The next morning I set up everything exactly as it was the night before and take flats using an LED light and t-shirt. 

But with the Edge, I am bit stuck.  There is no focusing mechanism that can be locked down with either the original focuser or with the Starlight Instruments microfocuser that I just bought but haven't installed yet.  There's also no drawtube scale so I can't just take a photo of the focuser to see exactly  where the focuser is. 

Can people who use the Edge 8" share with me how they get their flats?  

Thanks,
Jerry
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Stuart Taylor avatar
Stuart Taylor avatar
You will not get an accurate enough focus position that way. Taking a photo of your focuser will only give you a crude measure. Why do you not just do your flats after you've finished imaging? That is what I do. Flats are typically only a few seconds exposure, so shooting 20 or so at the end of the night is a quick process. After several hours of imaging, taking a few minutes to do flats before packing everything away is very simple.

If you are using a LED light why wait until the next morning anyway? I don't understand. Waiting until the next morning is what you do if you're taking sky flats, but that's not your method
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Steve Solon avatar
Steve Solon avatar
Hi Jerry,
This may sound a bit ridiculous, and I don't know what your setup is, but since flats must be taken at the same focus position, cooling temp, etc., as lights, and assuming your lights are in focus (:happy-3smile, I always take my flats at night by taking an image of a star beforehand, focusing on it, then go right to taking my flats.

I don't know if this answers anything for you - if I understood your query correctly -  but that's my method. My flats library is usually good for 2-4 months, since the telescope is housed in an observatory, so it's well-protected.

- - Steve
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Thomas avatar
Thomas avatar
I have an Edge HD 9.25 and just take them at the end of the night. Leave the scope on the mount and aim it at zenith. Then use the LED panel to take flats. Only adds a few minutes at the end of the night and then I  know everything is in the same location and focus. I've tried taking the scope down and doing flats the next day but it is never in the precise same location or focus. I've even left the camera attached to the scope and it still doesn't work. If you have an LED panel, take them as soon as you finish imaging.
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Cfreerksen avatar
Cfreerksen avatar
When you’re ready to take flats, just focus on some stars and pop the flat panel on and go. I only do flats at the end of acquisitions. Even if it’s several nights or even a month long. My scope stays setup in a shed. So no reason for the dust to move. Never had an issue doing that way. 

Chris
Rodolphe Goldsztejn avatar
Rodolphe Goldsztejn avatar
If you use a good robotic focuser, like the ones from Moonlite, you can record the focuser position for each filter, then use it back to take your flats later on.
That’s how I do that, and it works quite well.
My 2 cents.
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