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astophotography question

kingcarp

By kingcarp
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robbieince

robbieince

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Light frames are the exposures you take of the night sky target you are after. Let's say you take 5 mins exposures - 300 seconds. These should be focused on the target.

Darks are exposures at the same duration (300 seconds) but with no light entering the optical system -ie the lens cap on. These can even be done with the camera not attached to a scope - as long as it's capped front and back (viewfinders can leak light). Try and make sure the temperature when you take darks is the same or similar to the lights. Focus us irrelevant here.

If you take darks you don't need bias frames. If you take them - these are exposures at the shortest possible duration possible (say 1/4000) but again with no light coming through the optical system ie lens cap on. These are used to scale darks taken at different temperatures and exposure duration - my recommendation don't bother.

Flats are a separate light exposure taken of a uniformly illuminated neutral target. These should be exposed so that the average reading of the target is 1/2 to 2/3 of full brightness whatever this is with your source. Take flat darks at the same exposure duration but with the optical system covered and no light entering. These will usually be quite fast say less than a second so temperature won't be an issue and flat darks won't use too much time. These need to be taken without changing focus from the light exposures.

Try and get at least 10 of the flats, darks and flat darks and as many lights as you can manage.

Regards

Rob

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kingcarp

kingcarp

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thank you so much, i have been trying to get that awnser for ages but you explained it in english, thanks again Rob, im asuming you are into astrophotography, i have another Q if tis ok, would you sugest i use a x2 barlow or just straight fit to telescope, also would you sugest using filters eg uhc or moonfilters, thanks

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Black Knight

Black Knight

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The recommended approach is to fit the camera directly to the focuser, but some focusers (usually newtonian reflectors) don't have enough inward travel to allow you to reach focus. In that instance a barlow may help you reach focus. Some scopes (such as some Skywatcher models), have what they call a "Direct Camera Connection" - which is a fancy way of saying that the 1.25" eyepiece adapter unscrews revealing a thread which a normal T-ring will attach to. That would be much preferred to a barlow.

The main problem using a barlow is that the light reaching the cameras sensor is reduced still further, so you need to capture even more lights than you otherwise would have to.

As far as filters go, I have recently started using a normal light pollution filter attached to the coma corrector I use, and that helps with LP a lot. You will lose some light through the filter, so again, you just need to be aware of that.

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kingcarp

kingcarp

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i have a skywatcher with the t ring thread on the focuser, olny thing i thught was that the direct link alone would not be enough mag to get any detail, also where did you say you put your filter, ive not heard of a coma correcter

thanks

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Black Knight

Black Knight

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i have a skywatcher with the t ring thread on the focuser, olny thing i thught was that the direct link alone would not be enough mag to get any detail, also where did you say you put your filter, ive not heard of a coma correcter

thanks

Coma correctors: First Light Optics - Coma Correctors

I have the Skywatcher one. My 2" LP filter screws into the non-camera end of the CC. As far as magnification goes, that is certainly true for some objects. But others like nebulae may be too big to fit into a DSLR frame anyway.

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