zedds Posted December 16, 2012 Share Posted December 16, 2012 Hello all.I`m struggling with flats making any difference with vignetting and removing marks from the mirror or objective lens depending on which scope i use.I thought i was getting it right as when capturing the flats the histogram is always between a third and half way using ZoomBrowser EX.The flats have always shown up, when captured, as blue. Is this right?Here`s an image of one taken last weekend. I`ve also included what PS Camera Raw shows if it`s of any use.Any thoughts? Link to comment Share on other sites More sharing options...
swag72 Posted December 16, 2012 Share Posted December 16, 2012 Not a problem with them being blue - Mine were always blue with the clip in filter - Looks like a vignette showing as well, these look like decent flats, should work fine. I'd perhaps have been inclined to lower the shutter speed a little so that the histogram is a little more to the left - But I'm sure these'll work. Link to comment Share on other sites More sharing options...
Photosbykev Posted December 16, 2012 Share Posted December 16, 2012 The colour doesn't matter as the information needed is the luminosity which is a the greyscale. Link to comment Share on other sites More sharing options...
Ant Posted December 16, 2012 Share Posted December 16, 2012 I would agree that the peaks should be further to the left IMO, apart from that they look ok.If you stretch them do you see the dust bunnies (assuming that you have them)?Ant Link to comment Share on other sites More sharing options...
Cath Posted December 16, 2012 Share Posted December 16, 2012 Still plenty of red and green in the image .. Link to comment Share on other sites More sharing options...
zedds Posted December 16, 2012 Author Share Posted December 16, 2012 Thanks.Actually looking at the flats in ZoomBrowser EX the histogram is between halfway and three quaters across. Not sure why i thought they were between a third and halfway????Here is a screenshot of the capture in ZoonBrowser EX. Does this histogram mean that the flat is too over exposed. Should it be alot more over to the left.Also Ant, the flat is picking up the dust bunnies. I`ve circled them to show after a little levels tweaking.When i run the flats with DSS the dust bunnies and vignetting are still present.And thanks Cath but not sure what those images mean. Link to comment Share on other sites More sharing options...
zedds Posted December 16, 2012 Author Share Posted December 16, 2012 Looking at ZoomBrowser EX the second flat capture i took looks ok histogram wise. Would you say that`s the way to go. Histogram is a good way to the left. Link to comment Share on other sites More sharing options...
kirkster501 Posted December 17, 2012 Share Posted December 17, 2012 I am having same issues Zedds. My flats show same imperfections in optical train- taken immediately after the lights - but the flats are not removing all the imperfections and dust bunnies in DSS and its spoiling my final pictures. I am at a loss as what to do..... Tried different DSS stacking and registering options to no avail.Only thing I can think of is that the iPad method I use is not working to create the proper flats in terms of the light spectrum. But my master flat - created in DSS in the flats directory I use - certainly looks OK and the bunnies and smudges etc seem aligned enough to the lights in terms of the imperfections in the image.is this the same with you Zedds?Lots of beers to anyone who can help me with this. Link to comment Share on other sites More sharing options...
Uranium235 Posted December 17, 2012 Share Posted December 17, 2012 Convert your master flat to mono, job done Link to comment Share on other sites More sharing options...
Cath Posted December 18, 2012 Share Posted December 18, 2012 Their is an anomaly in the blue channel Andy of your flat, no idea if you get the same when taking normal images of the sky, but if it's not present when you take images then I guess your flat won't be doing what you need it to do ..http://www.youtube.com/watch?v=D9MLwUcU99w Link to comment Share on other sites More sharing options...
billhinge Posted December 26, 2012 Share Posted December 26, 2012 Great thread, I got blue flats using a dslr and a Gerd Neumann panel , thought it was just me, useful info, thanks Link to comment Share on other sites More sharing options...
spectre Posted December 26, 2012 Share Posted December 26, 2012 Cath, That is an amazing image. What program is that and is it available? Link to comment Share on other sites More sharing options...
andrewluck Posted December 29, 2012 Share Posted December 29, 2012 AndyCan you upload a flat and a light frame to Dropbox. Both should be unaltered, as they come off the camera.CheersAndrew Link to comment Share on other sites More sharing options...
zedds Posted January 5, 2013 Author Share Posted January 5, 2013 AndyCan you upload a flat and a light frame to Dropbox. Both should be unaltered, as they come off the camera.CheersAndrewSorry for the late reply Andrew.Here are the two links for the unaltered light and flat. Both took at ISO 800.The light is 210 seconds and the flat is 1/40th second.LIGHTFLAT Link to comment Share on other sites More sharing options...
andrewluck Posted January 5, 2013 Share Posted January 5, 2013 Hi AndyHere's a link to the flattened image. As you can see, there's no problem with the flattened image so the issue must be with the processing. What software are you using to do the calibration?All I did to the flat was load it into Maxim DL, convert to a fit and add a header entry to identify it as a flat. Calibrated the image, colour converted it. I've stretched to show the background and saved as a jpeg.Hope this is of some helpAndrew Link to comment Share on other sites More sharing options...
zedds Posted January 5, 2013 Author Share Posted January 5, 2013 Thank you for that Andrew. Shows the flats work.I use Deep Sky Stacker to get my final image.I need to look into my technique (i use the term loosely ) when stacking.Thanks again. Link to comment Share on other sites More sharing options...
andrewluck Posted January 5, 2013 Share Posted January 5, 2013 Another tip here to help ensure the flat calibration is correct:If you're subtracting darks from the light frames then subtract a master bias frame from the flats. Bias frames should be the shortest exposure you can take (with the lens cap on). Aim for at least 40. The more the merrier; they're quick and easy to obtain. Take as many flat frames as you can. Both these points are critical as noise in these calibration frames will be imprinted on every calibrated light frame.Good luck with DSS. I've no experience with that but lots of people here use it.CheersAndrew Link to comment Share on other sites More sharing options...
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