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Grateful for CC on this untracked attempt. I seem to have dark halo-ing around the cluster, & also blue colouring of the cluster stars too. D850 30 x 2 sec lights 20 x darks Stacked in APP & processed in PS. f2.8 @200mm ISO 3200  |
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Hi, I am new to astrophotography too. But what i could say is that your exposure time is too short. I tried the same shot months ago, with my 50mm [email protected] and had much longer exposures. With the 300 rule -> 300/50mm=6s i think i did 4 or 5 seconds, just to be save. You should be able to do 300/20mm=15s i would try 13s, zoom in and go down if you have star trails, do 1s longer if not. Do much more subs, i did 1000 Subs and stacked them. If you want to do some more detailed pictures, get a lens with more focal length. The Canon 50mm f1.8 is very good and not expensiv. Untracked i wouldn´'t go over 100-135mm because of 300 rule. So be able to get 2-3s minimum exposure time. CYA PCase |
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| Apologies. I have edited my post lens 200mm, not 20mm |
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| Are you aligning your subs and if so what method/software are you using? It looks, for what can be seen in the pic, as if there is a significant amount of trailing in the star shapes, plus field rotation (the stars at the bottom are much rounder than the one at the top). Given that stacking a set of 2s images at the pixel scale should give you little to no elongation at all I'm wondering what you did to create the final image. My image https://www.astrobin.com/tdct11/?image_list_page=4&nc=&nce= shows a similar setup but no trailing at all. |
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Andrea. I use Astro Pixel Processor for stacking. Have to admit, still learning to use that too. |
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| Unfortunately I am not familiar with APP. PI and Siril yes but APP no. Yet there must be a method to do an alignment that accounts for arbitrary rotation and even change of scale. |
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| And you got Mars too! But you will need much more exposures to get the wisps of dust between the stars. |
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As I am new to this as well, I want to preface this by saying that this is not a critique, but rather is a great resource i've come across... Below is a great website for trying to figure out exposure times for unguided, short exposure photography - this should help keep the stars from stretching out in to lines. If you are shooting frames over a long period of time (more than a half hour) you may want to adjust your exposure time during your session as well, for example if you start shooting at 8pm at one exposure, at 845 pm the exposure time may need to be adjusted as the earth has moved thereby placing your object in a different position in the sky than when you began. (which you can see by placing different coordinates in the fill-ins the exposure times will change) Also when taking short exposures you need to take a lot of them, as for example when you start adding up 2 second exposures to get to a five minute overall you would need about 150 frames, and a few extra frames on top of that incase you loose any to bad focus, camera shake, or the occasional satellite flying through the frame... At any rate, it's worth experimenting with it to see what works. http://web.archive.org/web/20200220123345/https://www.sahavre.fr/tutoriels/astrophoto/34-regle-npf-temps-de-pose-pour-eviter-le-file-d-etoiles The website is in French but you can use the google translate feature in your browser (assuming you are using chrome) to translate the page to english or any other language. Hope you find this helpful. |
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as others have said your exposures are too short to pick up the dust/nebulosity around the primary stars. you could try going to 6s or up to 15s without trailing. try that with iso1600 and see what happens. Watch your histogram. edit: as far as exposure goes, if you're only doing a single non "hdr" image, meaning one set of subs with the same exposures, you're trying to balance the dynamic range of your sensor. for instance, last night i imaged this for the first time. i did a trial exposure which picked up the nebulosity well, but looking at the stars and histogram it felt a bit hot. i did another trial exposure this time being quite a bit shorter to see what the highlights in the stars looked like vs nebulosity. there was no bloat in the stars but there was no nebulosity. so i chose an exposure between the two but making sure i got the nebulosity showing up. trying to bring that faint nebulosity out in post processing would probably introduce a lot of noise. so its a bit of give and take between your brightest highlights and faintests regions trying to balance which is most important to retain detail in. of course if the dynamic range is too much for your camera then you'd have to have two sets of exposure to retain details in the most important highlights and shadows. as far as color, the primary stars to my eye seem too neon blue. compositionally it seems off balance by including mars way at the bottom at the edge of the frame. it almost feels like an after thought. if wanting to include mars with M45 try including a much wider field of view and that would help balance the composition, at least to my way of thinking. ;). i hope this helps! the good thing with digital is you can just keep trying different settings! ;) I use APP and PS for post processing and find it very intuitive to use. but i do come from a landscape bg and have a good feel of PP. |
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It also appears to me that your processing is a bit too aggressive. Trying to remove all background noise will also remove a lot of signal that is buried in the noise, and that is why others are saying you need longer and many more exposures to improve the signal to noise ratio. But since you are unguided, longer exposures will increase the star trails. You could take the ISO up another notch to keep the exposure down, but that also increases the camera noise. Taking many subs tends to smooth out the background noise, but the longer your camera is running, the hotter the sensor gets which also increases noise and the number of hot pixels. There is a point after which more subs does very little, and although that point varies, taking 50 subs probably won't buy you anything more significant than taking 30 subs. Still, some people are saying that 100 to 200 subs increases the signal to noise ratio enough to tease out some hidden detail. It is still important to take the same number of Darks as Lights at the same exposure. |
