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| I'm new here and fairly new to the astrophotography world and loving it! Quick question. I have a cannon DSLR T6 with a rokinon 85MM f/1.4 lens. I took pictures of the M27 nebula, all though everything came out very clear. The nebula is very very small. I hear thatd an easily nebula to take a picture of. Is my DSLR and lens just to small to be able to achieve somewhat detailed pictures of nebulas?? Everything came out clear post process, but the nubula is just tuff to make out , you would have to zoom in but the nubula isn't very detailed. Any help would be amazing , sorry if this is a noob question!! |
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Hi, You can go to this page https://astronomy.tools/calculators/field_of_view/ and see how various targets will look like with your camera and different focal lengths. First select Imaging Mode. If it doesn't have your camera use another Canon crop camera, the result should not differ significantly). Set a custom lens and enter various focal lengths and aperture (aperture is focal length / f-number), finally choose a Messier object and click "add to view". You can add multiple views to compare. The Dumbbell Nebula is about 400 arcseconds across and your equipment gives about 8 arcseconds/pixel resolution (not sure about the exact figure but it should be close to that). So yeah the nebula will be approximately 50 pixels which is tiny. 85mm is good for ultra wide field targets: whole constellations, the band of the milky way, maybe the entire Antares region and the Andromeda galaxy although there won't be much detail. Realistically you need at least 135mm to start doing business with isolated DSOs, I would say 250-300mm is the least that would work with a planetary nebula in particular. Cheers, Dimitris |
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| Thanks so much for that information so helpful!! Would you recommend a good 300mm lens for astrophotography? |
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A 300mm lens will not help, M 27 has a diameter of 960 arc seconds and even with my Boren Simon at F 4 M 27 looks small even with a focus lenght of 1000 mm. What you need is a telescope with a focal lenght of 1200 mm or longer to bring more detail in M 27 and do not forget how smaller the pixel more resolution you are getting. With your 85 mm lens it is ideal to capture nebula in Cygnus or Cassiopeia or the Milky Way under a clear dark sky. You will be amazing what you can see with this lens. Use ISO 800 and also use a light pollution filter, such as a HUTECH IDAS LPV 4, or a OPTOLONG CLS- CCD or better a OPTOLONG L pro, this filter is special for nebula, and if you want H Alha results you can choose the newest filter from OPTOLONG, the L'EXTREME. I know those filters are very expensive but if you want better results a light pollution filter is necessary in a light pollution area. Succes with imaging and show us your results. Have no fear, everyone has to learn to take pictures from the sky and this forum will help you with your problems. Kind regards, Hans Verheijen/ The Netherlands. |
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Hi, I have to agree with Hans. I didn't mean to imply you should get a 300mm lens. I was purely referring to the minimal focal length where a planetary nebula (at least one of the easy ones) will start being visible as something larger than a glorified dot. Moreover, even if you do want to work at 300mm focal length (or anything larger than 200mm for that matter), there are many practical and financial reasons to prefer a refractor and not a general purpose photographic lens. The photographic lens is designed to focus from a few meters to infinity, at different f/ratios and deliver roughly the same image quality all over your sensor. It is therefore heavier and more expensive. The refractor is designed to focus at infinity with a constant f/ratio and be very sharp at the image center where most of the interesting stuff resides. As a result the lens is much more expensive and much heavier than a refractor of comparable focal length, and is not even guaranteed to work as well, since aberrations that are perfectly acceptable and in fact impossible to discern in daytime photography are totally unacceptable in astro. If you want astrophotography with a lens, you generally want to stick to 200mm or lower (135mm is indeed ideal for many targets). And forget about planetary nebulas, except as interesting specks in much larger wide field vistas. If you want large planetary nebulas with details, you need a completely different combination of equipment. Cheers, D. |
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| Thank you for all of this information!! You guys are amazing, I'm definitely more interested in nebulas and DSO, so I'll have to look into a good refractor telescope and I assume I would have to buy a good quality camera that attaches on the telescope and runs to a computer! I'll have to look into how to set all that up exactly. This has all been so helpful! I'll try to look into a decent retractor telescope and camera, if anyone has any recommendations , please let me.kmow! Thanks so much guys! |
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| Very good! |
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Another approach is to use the site referenced above: https://astronomy.tools/calculators/field_of_view/ to find good targets for your existing equipment, some also suggested above. "Rule of 500" suggests that with a 85mm lens your max exposure before star trailing is 500/85 = 6 secs. If you get a 300mm lens that becomes 500/300 = 1.6 secs. Not long enough to collect enough light. So, once you start getting a longer focal length, your most important piece of equipment will be an equatorial mount for tracking to allow for longer exposures. Some say you should spend half your budget on the mount. However with 85mm or shorter focal lengths you can take some beautiful photos of bigger targets from a fixed tripod. Best of luck Max |
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| I actually use a star adventurer pro for tracking and it works absolute wonders. So easy to set up |
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If you want results of planetary Nebula such as M 27 you need a scope with a focal lenght of 1000 mm. A refractor a good one is very expensive, why do you not think to buy a good reflector with a primary mirror of 200 mm at least, The focal reatio must be F 5 or F 6. Orion Optics delivers very good Newtons and it is affordable for you and it is easy to attach a DSLR with a light pollution filter. Guiding can be done with a guiding scope mounted on your Newton. ZWO had a beautiful guiding scope with a llens of 60mm diameter and a focal lenght of 280 mm and the scope is very light in use. You also need a autoguider but there are guiders enough to choose, such as a ZWO ASI mini or a ZWO ASI 120 M and guiding can be done with PHD 2, it is free software and easy to use. The most important thing is of course the mount, You can buy a Skywatcher NEQ 5 or 6 that depends what for scope you have chosen. A NOQ 5 can bear 15 kg and a NEQ 6 can bear 20 kg. Of course there are still better mounts such as the Losmandy G 11 but it is a very expensive mount. I use a G 11 with my Boren Simon Astrograph 250 mm F 2,8 or F 4 with a corrector. I mostly use SBIG cameras they have a self guiding chip and you do not need a autoguider and and a guiding scope. A OAG is also good for using guiding but keep in mind that you have enough back focus of your focusser. A corrector is mostly needed when you are taking images at F 4 or F 2,8, it reduce the back focus mostly to 60 a 65 mm so that a DSLR camera can still use. The back focus of a DSLR camera is mostly 44 mm so that you can place a OAG for guiding the stars. Perhaps you know somebody in your neighbourhood who can help you with your equipment. Or ask it at a good dealer in your country or city. He can help you what you needed for a good equipment. At this forum we can only give you suggestions but you have make the discission by your self. I wish you succes with choose a good scope. |
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I actually use a star adventurer pro for tracking and it works absolute wonders. So easy to set up This is one of the differences when you go to large focal lengths. I think even the 300mm lens is off limits to the StarAdventurer, because of its weight. Above 500mm, even it was somehow able to handle the weight (which it isn't), its tracking errors would be too obvious. Once more, I agree with Hans. Planetary nebulae details need very large magnification so a refractor is prohibitively expensive. You should use either a Newt or a catadioptric (probably a SCT). If you have a large aperture (at least 4 inch), you might even be able to get away without guiding but guiding is probably simpler. But you are aiming for a completely different level compared to what you (or indeed most of us here) are currently doing. Forget quick & easy polar alignment, tiny errors will count. You will discover the atmosphere is much more turbulent (and most nights impossible to work with) than it looks at 85mm. You will need a computer (laptop or single board) on the field: for focusing the telescope, driving the astrocamera and instrumenting a heavy mount with GoTo, it is not trivial at all pointing to a nebula when your field is a tiny circle in the sky about 5 times the nebula's size. You will need guiding and if you don't you will need to process several hundred or even thousands of subs. You will probably need filters, adaptors, a way to power the whole thing... I just wouldn't go from 85mm straight to 1000mm. It takes a lot of experience not only to use the gear correctly but even to know how to select each component and what combinations of components go well together. Perhaps settle for a little less detail initially? A reflector or refractor with 360-600mm focal length (refractor closer to 360, reflector closer to 600) and speed of f/6 to f/4 (reflector closer to f/4), coupled with a CMOS astrocam with a small sensor such as the entirety of ZWO's lineup below the $1000 price range. This will show you the nebula as 200-300 pixels wide and you can probably drizzle your way to twice that in postprocessing. More importantly, it will open up the way for hundreds of DSOs that are equally or more spectacular but slightly less tiny. You will still need a better mount (and tripod!) than the star adventurer plus all the other stuff (computer and so on), including the learning curve. But you will be more likely to produce results and gradually work your way up to more powerful gear and trickier projects. Cheers, D. |
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"Rule of 500" suggests that with a 85mm lens your max exposure before star trailing is 500/85 = 6 secs. If you get a 300mm lens that becomes 500/300 = 1.6 secs. Not long enough to collect enough light. Very good Maxchess! Just a complement, the 500 rule applies to full-frame sensors, if it is a cropped sensor, 300 should be used in the calculation. Clear skies! |
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| thank you for all of this info!!! would this be a good refractor telescope to start out with, since i cant mount my camera on it as well!..i waa thinking about getting the sky watcher evostar 72ED Ds pro OTA , i heard good things about it and it will sit nice on my sky adventure pro mount. any thoughts on that refractor would be amazing thanks guys! |
