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Hi there, I posted my first tracked Astrophotography yesterday https://www.astrobin.com/uk9tl2/ and I want wondering what is needed to get the deep teal blue colour out of the stars in many of the Pleiades images (example https://www.astrobin.com/u3meax/?nc=picks ) . I am currently using a D5200 (no mod), Nikon 70-300mm F4.5-5.6 (shot at 300 f5.6), tracked on a Star Aventurer, Class 5 Bortle, Although I shot 60 frames 60 seconds each about 25 were ruined by cloud, so I left those out. What could I do to improve? More frames, longer exposures, lower aperture (2.8/3.5), better post-processing, less light pollution, light pollution filters? All criticism welcome  |
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Hello Adam, welcome to Astrobin and of the greatest hobbies in the world! I just took a look at your picture and maybe/hopefully I can help you with some things: Your stars look a bit egg-like as if the star adventurer wasn't aligned correctly in 100 % and eventually didn't track as accurate as it usually does. Maybe it was a windy night too, so some frames have these egg-stars and some don't. If you're using Deep Sky Stacker for processing make sure you look at the SCORE of each single frame, the better it is, the better the stars are. You can also choose the best frames assorted by score directly in Deep SkyStacker. Your camera is fine for astrophotography, even unmodified but I would go higher in ISO, 800 or 1600 and not use a zoom lens at f5.6. Try something around 2.8 or a small telescope. I also recommend taking frames longer than 60 seconds, try 120 or 180 sec. The star adventurer should manage lenses up to 200mm focal length without bigger tracking problems. Make sure to take some dark frames, too. As for processing try to strech the image after stacking it using the histogram. Nebulae should become visible then when the night was clear. You can also adjust the colours afterwards. Just some basic hints but hopefully this was helpful for you. Best Jo |
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Adam, Good examples of M45 are very doable with a setup like yours - here is an M45 I took a year ago with a portable tracker (Lightrack II), 5D Mark IV camera and 400mm f/5.6L lens, 41 frames x 90 seconds at ISO 400: https://astrob.in/79bmfm/0/ I agree with much of what Jo says, though some caveats. Longer exposures than 30 seconds would help, but even at 30 seconds, you should get more nebulosity than you are getting. Are you doing any kind of background subtraction to get rid of light pollution? If not, you should be, since a lot of the nebulosity could be hidden behind the light pollution. PixInsight has nice tools for this. I suspect background neutralization might reveal more nebulosity than what your image shows. Light pollution filters work better for emission nebulae than reflection nebulae, since the cut off gets rid of desirable light from the object as well as light pollution; with M45, I've been able to get reasonable nebulosity from sites much brighter than yours without a light pollution filter. Other than that, you have obvious tracking errors, but also some coma, which I suspect is just an attribute of your lens; zoom lenses are worse for this than primes. But that should not affect the nebulosity. Better polar alignment would help, I suspect. |
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| I think there is some neblousity there, and that you need to "stretch" the image. Use curves and/or levels to bring out the dim, blue reflection nebula, while keeping the background dark. |
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Hello Adam,welcome to Astrobin and of the greatest hobbies in the world! It was slightly windy yesterday, I did plant my tripod into the grass to reduce that but it was probably misaligned. As a guide what would you advise as a usable score? I did also select the best 80% of the frames. I was wondering about the ISO actually and I think that 1600 would be a better choice next time. I do have a some frames at 100 seconds but they were all ruined by cloud thats why I chose to shoot at 60 seconds. I think on a clear day I would use a 2-3 minute exposures, it was just I wanted more usable frames so I went with 60 in the end. I did end up with 17 dark frames, I am still very new to all this Bias, Dark and Flat frames. I do have a vague idea but still not familiar just yet. I was think of getting a prime lens for astrophotography. I couldn't decide between the nikon 135mm AI-S f2.8 or the nikon 180mm AF f2.8 , both roughly the same price. Thank you for the tips, and hopefully there will be a good improvement in my coming photos. |
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Adam,Good examples of M45 are very doable with a setup like yours - here is an M45 I took a year ago with a portable tracker (Lightrack II), 5D Mark IV camera and 400mm f/5.6L lens, 41 frames x 90 seconds at ISO 400: https://astrob.in/79bmfm/0/ Not sure what you mean by background subtraction (I used this video pretty much to edit it, excluding the Actions addons). I don't know if I have an issue with polar alignment, when I look through the polar scope I see a star which flickers whether that is me who is moving, I don't know but the star isn't focused either it is sort of a bright white circle rather than a star. Sometimes I see nothing at all. I use a polar alignment App to show where I should put polaris. Not sure what you mean by Coma, I do have a bit of trouble with polar aligning I do admit. |
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Erlend Langsrud: Should I do this by each channel or RGB? |
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Adam Quinn: Hi Adam, the score differs from image to image depending on the total number of stars in the frame and the focal length I think. I would just have a look at the single frame with the highest score and use that as your reference frame. I usually watch some of the lower scores too and see how low I can get, but that's all to your personal preference. Arun mentioned background substraction for processing. That's a good idea and it does a lot for the final result. But be aware that Pixinsight is quite expensive for a beginner (it's definitely worth it though). From my experience you can also get some nice results using only open source processing tools at the beginning, that's what I did for the first years at least and I don't regret it. |
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Adam Quinn:Erlend Langsrud:Should I do this by each channel or RGB? There is no short answer to that question. The color balance is probably not so far off straight from the camera, so dont fool around to much with the colors. The light pollution might add some color (often orange/red) to the background (and indeed the whole image, but most visible where the sky is supposed t be dark). You want to "substract" this light pollution. A simple method is to use "levels". |
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Hi Adam. It’s no small achievement getting your first tracked astro image. And your image is pretty good for a first attempt. As regards feedback, I’d say the following. The Star Adventurer is fine for what it is, but I found it a little fiddly to get it decently aligned. Any errors in alignment will be magnified by longer focal lengths. You were at 300mm ... the Williams Optics Star 71 is around 350mm: the Takahashi FSQ 85 with reducer is around 325mm. The star adventurer may be able to manage this, but I’m guessing your polar alignment would have to be pretty good. So, in short, I’d suggest backing off the f/l quite a bit. A lot of people like the Rokinon 135 which is not especially expensive. I don’t imagine camera lens manufacturers design their products based on their astro performance. A little bit of coma in a portrait or landscape shot is neither here nor there. You have quite significant coma in your image - many of the stars look like little fans, not circles. I get this with my Nikon prime lenses too. It can be reduced by stopping the lens down a bit. The tendency to coma may vary from one ‘sample’ to the next: I have seen images from the well-liked Rokinon that exhibit coma when shot wide open. I’d suggest, therefore, that you try a shorter focal length and consider stopping it down a tad if you get coma. You could try this with your zoom, but primes will generally be a bit ‘faster’ and so may be better in the long run. You should bone up on calibration frames. There isn’t time to give a full description here. I’d recommend buying Steve Richards’ book ‘Making every photon count’. If you’re not calibrating then you’re not maximising what data you have. The subject of Darks with a DSLR is a long (and boring) subject. But you should definitely be shooting bias (very easy to do and reusable - so you could do them now and reprocess your data). And flats are important too, but are trickier. It’s not clear if you had decent conditions. Having to dodge round clouds makes it sound like they were not ideal. And was there moon around? Moon will kill faint nebulosity very quickly. It’s best to conserve your energy for when conditions are a bit more amenable. And you know, of course, that longer integration times will be better. The more frames, the more you reduce noise and the harder you can stretch without it becoming messy. It would be interesting to see what 120 clean 60s frames looked like. The image you linked to had over 3 hours of integration time. You cannot have too much. Hope some of that helps. Steve |
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| Hello AdamI think the first thing you would have to solve is the obvious comma your stars have. I do not have much experience in this type of photography but I suppose you should try with another focus, exposure and opening times, sometimes it is not possible without using concealers.For the rest I subscribe to everything the colleagues have told you and I would also add the approach, since it gives me the feeling that your photography also has some blur, you should use a cheap and easy-to-use Bahtinov mask.And also read a lot and see how others do their job, always compare similar equipment and similar conditions, the photo you refer to other differences has more than three hours of integration.I hope it serves you and sorry for my bad English. |
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Steve Milne: Hi Steve, I have been looking at the Nikon AI-S 135mm F2.8 or the Nikon AF 180mm ED f2.8. I can manage 100mm at f4.5, 135mm f4.8. I have just ordered a Nikon AF 50mm f1.8 which should be interesting. The moon was at 13% luminocity and set around the same time that I started shooting. Hopefully we will have a few clear nights after the plenty of storms the UK has had. It's just a shame that I want to improve so badly but there's little chance to do it, due to the moon, weather, location etc. Thank you for your tips! |
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I have the 50mm 1.8D and the 180mm f/2.8. Both great lenses, but I've not used them for astro. I don't know anything about the 135mm. If you have the 50mm coming then why not play with that for a while? You can improve your polar alignment routine with the Star Adventurer. And you can test out the effect of stopping down the 50mm on coma (if you get any coma wide open that is). There are a number of super widefield targets you could try (although we are heading into galaxy season). I've been where you are - trying to shoot through gaps in clouds and shooting when the moon is about (deluding myself that if I pointed 'away' from the where the moon was in the sky then somehow it wouldn't affect the image). Imaging in the UK is very challenging. And there is some value in familiarising yourself with the equipment. But if you look at top imagers, Olly Penrice, for example, he pretty much shuts down operations when the moon is around. I won't image any LRGB if the moon is up. And when the moon is 70% full I don't even bother with Ha. |
