Photography: 14mm vs 20mm or 24mm
My Case for a New Lens
I’ve been photographing with a 14mm lens for the last two years. It is a cheap lens that lacks auto-focus, the Rokinon 14mm f/2.8 lens. And, for the last two years I have loved this lens: I’ve used it for weddings, for architectural photography, portraits, and of course for Landscape Astrophotogoraphy. For the quality of photos this lens delivers, it’s a no brainer. But I’ve been having some reservations with the lens.
For one, I’m starting to think 14mm is too wide because the distortion is a lot to handle. This makes portraits really awkward, as you can’t get too close because facial features start to get out of whack and you can’t get too far away otherwise the subject is really small. Secondly, since there’s no auto-focus it makes things really difficult during weddings and general events since you can’t tell people to “hold that position” while you focus a 114º image in a viewfinder the size of a thumbnail. It’s not easy.
It’s a bit different with landscape astrophotography. I’m shooting the landscape with the stars, so my subject is very far away which helps in eliminating a lot of the distortion effects. Often times I just go out whenever I have time and photograph the night sky, and even if I plan a shot I arrive an hour or so early, so I have all the time in the world to focus my shot. But, that said, I think this lens is too wide for landscape astrophotography as well.
On the corners of my photos, the stars turn into streaks. This particular issue hasn’t affected any prints I’ve had made of my photos but it’s something I am seriously at ends with. For those experienced with lens terminology, it doesn’t look like coma. See below.
For the sake of disclosure, I’m considering these three lenses in the Sigma ART lineup. The Sigma 14mm ART DG HSM, the Sigma 20mm ART DG HSM, and the Sigma 24mm ART DG HSM for Canon DSLRs.
The Case For
I am incredibly comfortable with 14mm. Almost every landscape astro shot I’ve ever taken has been on a 14mm. I know what will be include in the frame and how to make the scene look as natural as possible. I’ll be able to take wide angle photos and crop in if I need to, emulating a 20mm and the 24mm lenses.
The Case Against
The distortion. It’s entirely possible better lenses won’t have this distortion, and I should definitely rent a lens before I buy it. However, it’s also an expensive lens. This lens will be purpose bought for landscape astronomy in mind and thus, I’ll be buying as fast of lens as I can get, which is the Sigma ART 14mm f/1.8, which comes with a $1,500 price tag.
It’s also really wide. Look at the Milky Way photo at the bottom of the post. While it’s a phenomenal photo, it can definitely be better. By tightening the crop so the Milky Way ends at the edge of the frame rather than dissappearing into the night sky, our galaxy would feel more prominent. At least at my latitude, 14mm maybe too wide.
The Case For
Pulling in the frame will cut off the Milky Way at around the edge of the frame, which is where it seems to blend in with the night sky. Ending the frame where the Milky Way is still such a visible subject would be perfect for astronomy landscapes. I’m again looking at the Sigma ART lens which offers a f/1.4 aperture. So, it’s faster than the 14mm. I feel like this lens is the sweet spot in the focal range line up.
The Case Against
The 500 Rule.This rule dictates how many seconds the shutter can be open before the stars start to visibly trail in the image. For a Full Frame camera, start with 500 and divide by the focal length of the lens. So, a 20mm lens can take, at most, a 25 second photo. I like to try and shoot under that by a few seconds, so let’s go with 20s, which is the next shutter selection on my camera. But, if I were to base decisions entirey off this rule I’d always want to consider wider lenses, such as an 12 or even an 8mm. Which, would put me into fisheye territory.
The Case For
I have a 24mm lens with an aperture of f/4.0. I love it and have taken a few landscape astronomy shots with it. It’s another lens I’m pretty comfortable with.
The Case Against
It’s pretty tight. It’s not a 35mm or a 50mm but 24 can be pretty restrictive in terms of frame. A 24mm lens can only photograph a 20 second photo, but since I like to shoot under that time limit, I’d select 15s.
These two shots are taken withthe same exact camera and subject position, just with a 24mm lens then a 14mm lens. Both shots are taken with the aperture as fast as it’ll go, with a shutter at 30s, and an ISO of 3200.
The key differences between these photos is the space left above Orion’s Belt. In the 24mm, it’s in the upper third while in the 14mm, it’s easily in the middle third. Here’s a side by side with the originals included.
There are two drastic changes here. One, the amount of light entering the lens is significantly reduced. This because of the aperture. Remeber that the 24mm’s aperture only opens to an f/4.0 while the 14mm’s aperture opens to an f/2.8. Since both photos were captured at ISO3200 and with a shutter of 30 seconds, we can see the direct impact aperture has. Couple that with shutter speed, the 14mm lens makes a really good case for itself. I didn’t cover the Rule of 500s with this lens above, but I’d be able to keep the shutter open for 35 seconds before trails appeared. But, I’d realisitcally shoot for 30 or even 25 seconds. Also, another bonus of more light is a lower ISO. I’d be able to shoot at ISO 1600 or even 800 if I shot wide open.
Two, it’s a pretty drastic field of view reduction, infact the 14mm captures roughly 302.25% more of the scene than the 24mm lens. Part of me would really hate losing all that space. (Aha, get it?) It’s a tough decision and why I feel like 20mm would be a great compromise. Then of course, there’s cost.
The 20mm and 24mm are about $900, while the 14mm is almost twice that. The 20mm and 24mm are both f/1.4 while the 14mm is f/1.8. Since light plays a large part of the photo, it’s worth considering the f/1.4. The difference in light we saw in the two original comparison photos is a full stop. But, the difference in light between the 1.4 and 1.8 isn’t as dramatic.
A quick lesson before I continue: A Full Stop is 1.4x from the last stop. So, if we start at an f/1.0, the next full stop is 1.4, then 1.4 times 1.4 is ~2.0. Multiply that by 1.4x and we get 2.8, and again we get ~4.0.
So, in that regard, the 14mm 1.8 lens is almost a full stop faster than my current 14mm f/2.8 and a full two stop faster than the 24mm I currently own. But, there’s another reason to buy a fast lens other than the aperture. Lenses do actually have an aperture sweet spot, meaning where they take an optimal photo with minimal vignetting and incredible detail sharpness. This range is usually a full stop down from wide open. So, if I were to get the 14mm f/1.8, I’d probably still be shooting at f/2.8, maybe a tad faster like f/2.0 or f/2.4. The only reason I don’t stop down my current 14mm, is that I don’t want to shoot at f/4.0.
24mm is probably out. Because, if there are any lens distortions it’d be hard to crop them out. On the 20mm and 14mm lenses, I would have some wiggle room to crop down and avoid the corners.
Below is an image I originally took at 14mm but have cropped to fit a 20mm and a 24mm frame. I had to guess on the 20mm frame but I used the data from the 14mm-vs-24mm photo above to accurately crop the 24mm frame. These may not look all that different because I went ahead and reframed each shot so that it was still interesting. Otherwise the 24mm would have had too much space in the corner with my friend and not enough Milky Way.
24mm is way too narrow for my desired application of this lens. While it would be a great lens to have, there are better lenses out there for other purposes. That’s not say I’ve gotten awesome landscape astronomy photos with this focal length, this lens just won’t adequely capture the scale of the Milky Way in the landscape.
The 20mm, from my guessed framing, seems like an entirely plausible contender. Especially with the fast f/1.4 aperture. I’d rather just frame the shot in camera and not lose any megapixels when I crop down the 14mm lens. I’m going to have to rent this lens to further aide my decision. It’s also $50 more than the 24mm lens.
The 14mm is still my favorite. I really enjoy the idea of a f/1.8 aperture but at a $700 premium over the 20mm. Like the 20mm, it’s a lens I should rent before making a decision.
I’ll keep you guys updated :)