How many light frames and which lens?

[Happysnapper79]

Hello all, I am sorry if this is a daft question but how many images is a good starting point when stacking? I have done a fair bit of Milky Way imaging but I now want to have a go at deep space stuff.

Further to the how many frames question which lens would be best, I have a 10-20 lens that I use for Nightscapes but I see lots of people shooting at 200mm, I have a 70-200 f2.8, would this be the better option?

Thanks in advance

John

[Dr_Ju_ju]

in simple terms, the more the merrier, some will be unusable due to cloud etc., so take lots, I usually go for 50+ ....

and then darks, bias, lights...

As for what you'll see on your camera, have a look at this site http://www.12dstring.me.uk/fov.htm. Just enter your camera, which lens your going use and a target..

[Stub Mandrel]

As a beginner myself it's an interesting lesson to learn that doubling the number of frames doubles the quality, so 32 frames are six times better than one, but to be seven times as good you need 64 - the returns get less the more you do, although you can load the dice by deleting poor frames. I seem to be getting results with 40-60 frames that encourage me to keep going. I need to start experimenting with longer exposures, so I suspect it will be longer exposures and perhaps fewer frames .

A classic target for a lens of that sort of length is the North America Nebula, but you could also do M31.

[MattJenko]

The more time you have in terms of total exposure the better, as you gather more and more photons and get a better and better representation of the target as opposed to random noise. In terms of stacking, there are different stacking algorithms to do with removing noise and artefacts, like plane and satellite trails and most of these work best with more than 8 exposures. (There are some stacking processes, like drizzle, which work best with over 30!). So rather than give you an "it depends" answer, I would suggest that at least 8 exposures on any particular target for any particular exposure time gives you the best chance of getting decent stacking, but obviously more is better. Longer exposure times are needed for non stellar DSOs, as you actually don't need long exposure times for stars - if you do, you saturate out the colour.

As for which lens, you are talking about completely different focal lengths here. A 10-20 will give you big old milky way widefields, whereas a 200mm lens is going to show a significantly smaller part of the sky across the sensor. A zoom lens tends to be of a lesser quality than fixed length lenses because of all the extra bits needed for the zoom, but if you have one, give it a go, so if I were you I would use the 10-20 at around 12mm for nice big milky way shots (and meteor captures/timelapse etc) and then  use your 70-200 at around 150-200 for closeups of some of the larger nebula and smaller constellation regions.

[D4N]

At 200mm you will need to be tracking or you will get star trails on anything but really short exposures, do you have a tracking mount?

At least with the zoom lens you can centre your target at 70mm then increase the focal length to 200.

/Dan

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[MarsG76]

another thing to point out is lens distortion with lenses like 10-20mm. There will always be some pin cushioning effect and at wide fields like this, all wide angle lenses suffer from it to some point, unless some equatorial tracking is utilized, there will be a double radial blur effect as the software stars the stars. Telephoto don't seem to have such a big problem with it, hence why maybe a lot of people use 50mm and longer lenses.

Maybe that's just the way nebulosity stacks but when using a tripod and occasionally just recentering the Milky Way, later I always ended up with major radial blur vortexes at the edges, needing me to crop it out. Equatorail tracking always solved that issue since the lens distortion was stacked at the same place on the same star.

[happy-kat]

Do you have any prime lenses?

[Happysnapper79]

Many thanks for all the info and replies.

Sadly at this moment I don't have a tracking mount so I guess it will be a trade off between exposure time and focal length. I do have two primes, a 35mm and a 50mm both are f1.8 and had never really considered using these to be honest.

With regards for numbers of images I think I will go with the more the merrier option, can set my camera up to snap away for a set number of exposures so it will just click away till told to stop.

[happy-kat]

The 35mm is the one I would try first over all the others and then the 50mm.

[D4N]

I'd definitely go for those until you get a tracking mount.

If you can't afford one you could always make one, it isn't too difficult for such short focal lengths.

/Dan

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[happy-kat]

Hand made diy ones are called barn door mounts. Or scotch mounts.

[Owmuchonomy]

Just a note on zoom lenses. If you get zoom creep during a long session it will not be a happy ending! Use primes if you can.