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Hello fellow AP'ers, Quick'n sweet, being new to APP, is this what we hate as light pollution? Can't be crossing clouds or low flying elephants. BTW, the nebula in the middle is supposed to be the Seagull IC2177 after 1.7 hours integration😢 Also, it seems that both APP and DSS stacking results are about the same. APP takes longer though. Cheers, and thanks for looking. Robert  |
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Hi, How are you doing your flats (exposure time, source of light...)? Also, what camera are you using? |
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Hi @SicIturAdAstra Sorry, yes, you are right. Nikon D5500 Flats with T-shirt, same ISO as lights, histogram at the middle (ends up mostly 1/2000 to 1/4000 sec) No further calibs. Note: I'm a bloody beginner. |
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| @astropical This does not seem like light pollution to me - it is likely a flat-field problem. Your exposure time for the flats is far too fast. The camera has a mechanical shutter that for very quick exposures cannot guarantee a uniform illumination. Check your individual flats, and you should likely see some curtains and stripes that are shutter artifacts. Aim for longer than 1/1000s. I try to aim for 1/100s or more. If you can get it to less than 1/10s even better. But 1/100 is fine. 50% histogram is a very good starting point (which means your light source must be dimmer, to accomodate the longer shutter speeds). ISO - you are correct, same ISO as lights. T-shirt: personally I do not use a t-shirt, but some people do. Shouldn't be your biggest concern, but try to experiment with/without. I shoot twilight flatsl: just point at a place of clear, cloudless and uniformly illuminated sky. I shoot about 20-30 flats, and move the telescope between each exposure all around the sky (trying to make it as uniform as possible). Flats need to be calibrated for them to work properly. That means either bias or flat dark-subtracting. APP will do this automatically, but you must load your biases/flat-darks (or masters) as well. I strongly recommend watching Mabula's video tutorials on the APP website, they are a great learning resource for the software. Bottom line: make longer flats, and make sure you calibrate them. Best regards, Gabriel |
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Hello @Gabriel R. Santos (grsotnas) Shutter artifacts confirmed. Same on the DSS master flat. You are an angel, thanks so much, my young friend 👍 Cheers Robert |
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| @astropical The other images looks good in your gallery, so yes, as Gabriel said it's most likely your flats. When you have good flats, take note of the exposure length and try to do all your flat frames in this ballpark. For exemple, with my dslr, I was taking flats of between 0.5 and 2 seconds. Less exposure time don't work well either on dslr or dedicated astro camera (for different reasons, mechanical shutter is one of them). And with good flat frames or calibration, you will be able to make the maximum of what your image can. I'm sure this Seagull will look good! Bye Thibault |
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glad you figure it out. clear skies |
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I use APP as well. For the Bias (t=1/4000)and the flats (the histgram has to be in the midIe, usually 2,6 - 3 sec) use ISO 200. The darks and the lights are for my DSLR (cano 600D) ISO 800 This gives exellent pictures. Hans |
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Make sure that your flats, bias, darks and lights are shot at the same ISO. That will ensure that you are subtracting out noise from your image and not confusing the processing with extra noise from your camera amplifier. |
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| Indeed, there is the route of calibrating independently your flats and produce a master flat using an ISO value different than your darks and lights. Of course your lights should be calibrated with darks only. I can understand why this can work, but does anybody have done comparisons using the traditional, same ISO calibration route, and producing a master dark at different ISO |
