# 29 Jul, 2018 17:24
i know its an hard topic but i saw some decent result of the brightest objects with just few second of exposure on some good but old equipment and a stack of like 10-12frames plus some heavy postprocessing.|
i was wondering if nowadays with a good fullframe and a fast lens like sigma 105mm f1.4, rokinon 135mm f2 or sigma 180mm 2.8 its possible to achieve something good considering the no-budget and the equipment
# 29 Jul, 2018 18:22
Good is a relative term. Why not just try it and decide for yourself it they are "good".|
# 29 Jul, 2018 18:40
|Well i need to buy one of those lens first, i wasnt sure which one could be the best, that 180mm wouldnt need cropping but a 105 f1.4 is clearly faster and brighter, which in my case is really important. so i was asking if anynone had some experience with this case|
# 29 Jul, 2018 19:17
Yes you can do it with those lenses. To correctly expose your shot and minimize trails, use the 500 rule. I actually prefer using a 300 rule. It goes like this:|
Full frame cameras:
300/You lens focal length = The number of seconds you need to expose.
Imagine you use the 105 mm lens, so:
300 / 105 = 2.85, let's round it to 2.5 seconds. That's the time you need to set at your exposure time with that lens.
APSC cameras use a similar formula:
300 / (105 * 1.5) = 1.9 let's round it to 2 seconds.
Hope this helps! 😀
# 29 Jul, 2018 19:40
Thx, so i guess that the 105 should be the choice even if i need to crop the result,|
i mean f1.4 vs f2.8 is a gain of several stops plus longer exposure cause 300/180 = ~1.5 seconds
# 29 Jul, 2018 19:54
|It can be done, but it will be much easier with a fast wide-angle lens. If you already have a camera and a lens, all you need is a dark location and a view to the Milky Way. Take a look at the recent eclipse images; some of them were made with such simple setups.|
# 29 Jul, 2018 20:22
Whatever lens you choose, you will need to stack multiple frames.
Have a look at my great magellanic cloud. It is a stack of 151, 2.5 second exposures with a Rokinon 85 mm lens:
Great Magellanic Cloud
# 29 Jul, 2018 21:36
Die Launische Diva
Yes i know, i already shoot with a wide angle, but i wanted to try some details
this is a good example of the objects i would like to photograph, what was your iso? for 151 frames you manually shooted 15times with continuous shooting function, 10 frames each time? do you think 85mm could be enough instead of 105?
# 30 Jul, 2018 13:56
It really depends on what your goals are. As one other contributor mentioned you can get good results if you use a fast wide angle lens like the Rokinon 14mm for example. If your goal is to target large deep-sky object like the North American nebula, you should look at focal lengths in between 85mm or 135mm. I strongly recommend that find a local camera store where you can rent the lens your interested in before purchasing it. I was able to test some very expensive glass this way and discovered that some of them did not perform as well as I expected. That being said no lens will give great results wide open. My Rokinon 135mm is incredibly sharp with the aperture set at f 2.4 but the corners are soft when used wide open. To then get a good signal to noise ratio, I take several exposures of between 60 and 120 seconds with the help of an IOptron SkyTracker.|
# 30 Jul, 2018 16:25
daomaoDie Launische DivaYes i know, i already shoot with a wide angle, but i wanted to try some details
I used 3200 iso for this shots. I left an intervalometer with the lock position on continuous shooting. The camera did the 151 shots automatically while I was shooting other stuff with a telescope. I estimated the galaxy movement across my sensor, and framed accordingly so when it finishes the last frame, it will still be on screen. I think the 105 mm lens is better. It will take you deeper.
# 30 Jul, 2018 17:10
thx both i saw some reviews of the new sigma 105 f1.4 especially on lenstip and it should be the new best lens in that range so im quite sure going there,|
an intervalometer is also a useful tool to buy for various jobs
3200 iso is well in range of what a good full frame is capable of, you think going for 5000 or 6400 would have bringed more signal to process? im really interested in that
technically you could continue by adjusting the tripod without problems on alignment, right?
# 03 Aug, 2018 12:04
|any more info?|
# 03 Aug, 2018 14:18
Hi! Closing the aperture one or two more steps and increasing the ISO to 5000 or 6400 may have been a better choice, because stars at my edges are elongated. Stacking so many frames reduces noise, so maybe 6400 ISO would've been a good choice, but remember that you will have less dinamic range, and star colors may blow out.|
You are right about the alignment, you could adjust the tripod, and pixinsight or DeepskyStacker will do its job, aligning the frames.
I would definetly suggest that you aim for a sky stacker. There are no limits with those!
# 03 Aug, 2018 15:13
|Here is an alternative. Spend less on the fastest glass getting something a bit slower like f2.8 and use the difference to buy a portable tracker like the iOptron SkyGuidePro. I've recently been playing with one and was pleasantly shocked when I got round stars on 5 minute exposures at 105mm (that was an f4 lens). A couple of nights ago I shot round 2 minute subs with a 65mm lens at 2.8 (I could not go longer because of the evil Orb). I posted that here so you can take a look. Of course, fast glass makes the process easier and is very helpful with things like shooting auroras, but I can beat the total photons captured in a round frame easily with a tracker.|
# 03 Aug, 2018 15:31
I agree with Richard, no lens no matter the price (I've tested quite a few) will give good edge performance wide open. You're always better off stopping it down a couple of f stops and taking longer exposures. If you purchase a good quality manual lens like a Rokinon 85mm you can take the money you saved to purchase a camera tracker.|
The maximum usable ISO setting really depends on the camera. My modified Canon 60d takes great images when set at 1600 but not so much at 3200 which is not the case with newer models. You should also remember that increasing the ISO will reduce the available dynamic range.
# 03 Aug, 2018 17:57
Yes i already have thought about a tracker, but i wanted to start with something easy and fast to use and see if i'm really interested in deepsky photos.|
I already needed a good fast lens in that range (the only close lens i have now is an old nikkor 60mm 2.8 ) for other reasons like landscape etc so ill start making some tries with that, then i will considerthe tracker option
Do you mean that by overexposing you get too much light and colors?
# 04 Aug, 2018 00:05
No. What they are saying, very correctly, is that as you increase your ISO, the dynamic range of your image will shrink. Plug your camera into this page (http://www.photonstophotos.net/Charts/PDR.htm) and you will see the effect. I am using a Sony a7RIII ATM. AT base ISO it's dynamic range is just shy of 12 stops, at ISO1600 8 stops and at ISO3200 (a not too uncommon ISO in AP) it is way down to 6.3 stops. 2^6.3 is just about 79. So, my image will only discriminate between 79 brightness levels. That is another argument for using a tracker. Given the ability to use longer exposures (minutes, not seconds) you can use significantly lower ISOs. Let say with your sensor/lens you get round stars at 20 seconds and ISO 3200. If you can increase your exposure time to 160 seconds, then you have gained 3 powers of two which you can spend on your choice of smaller aperture and lower ISO. So, you could shoot at ISO 400 at the same aperture. That will greatly reduce your noise and increase your dynamic range – in my case to 9.7 stops of DR v.s. 6.3 at ISO3200
# 04 Aug, 2018 10:42
Ahh ok but i dont see why losing brightness levels in such a plain scene should be worse than not exposing correctly and take the max signal out of it even at 6400 iso.|
Like i said i know the tracker gives always the best result but even if i will buy it sooner or later its not an hurry for me
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