Astrophotography Canon 17-40mm f4L vs Samyang 24mm f/1.4 how much of a difference would there be?

Question

I made my first timelapse lastnight with a 6D and a Canon 17-40mmL. I made it on the outskirts of a city where the light pollution is pretty bad. I was reasonably surprised with the results. I did not expect to see the milky way.

First Astro Time Lapse

I really enjoyed it and I am now considering a better lens for the job. I know the f/4 on my lens is not great. The Samyang / Rokkinon 24mm f/1.4 seems to be highly rated as the best or one of the best astro lenses available. However, it is quite a lot of money to drop on a lens fit for only this purpose.

How much of an improvement would this lens make over my 17-40mmL, would it be worth the upgrade?

Answer 1

There is a HUGE difference. The 17-40 is good for northern lights, moon-illuminated landscape and such where but it will struggle a bit with noise in other "darker" situations. The Samyang 24mm is very, very fast and quite sharp even wide open if you get a good copy...(BUT NOT VERY WIDE, which is why many night photog specialists usually also have an ultra-wide ~ f2.8 as well)

Here are my personal experiences:

I owned the Canon 17-40mm L and now have the new Canon 16-35 mm L. Both capable lenses and usable at night and I also use the 6D. I recently purchased the Samyang 24mm f1/4 however and I was floored how much light it can suck in. I actually overexposed a number of northern lights shots because they were simply too bright and so I had to shorten exposure and lower ISO significantly which I guess is a good thing but there is a learning curve. The secret is; because of the shorter exposure on the 24mm (stars travel less across the sky), I've ended up shooting a number of panoramas both horizontally and vertically and it seems to work quite well so I am beginning to use this lens at night almost exclusively. Definitely a special purpose lens but there are other uses even if you already have an ultra wide. I found I love the ways this lens draws and it's colour rendering which produces images that have a completely different feel from the Canon lens. The bokeh is also quite amazing and silky smooth which opens up some artistic possibilities close up and for portraits. This was a surprise to me because I didn't expect it to be that good in these situations. This however this brings up a problem because the Canon version is not chipped and therefore there is no focus confirm which for hand-held shooting, up close and portraits if pretty essential for me. I am considering adding on an aftermarket chip. If versatility is important to you you could consider the new, albeit more expensive, Sigma 24 mm f1/4 which does have autofocus.

A vertical panorama taken with the Samyang 24mm f1/4 @ f1.4, 22 seconds

Answer 2

F/1.4 vs, f/4 is three full stops. That means the f/1.4 lens allows eight times the amount of light through the lens than the f/4 lens does! This means you can shoot at lower ISO or for shorter shutter times or both. It means at the same ISO and shutter times, with the f/1.4 lens you can capture night sky objects 1/8 the brightness of what you can capture with an f/4 lens.

With this pair you are also looking at the better image quality typically found when comparing a prime lens to a zoom lens. Less distortion, vignetting, and coma.