Zoom or Prime?
This is one of those never-ending discussions in photography.
Purists love prime lenses, considering the zoom as the tool of choice for amateur and lazy photographers. One of their favorite sayings is “you zoom with your feet, not with your lens”.
But why are prime lenses considered to be superior to zoom ones, and in what sense? And what about astrophotography?
In this article, we will try to put a bit of order in this matter.
What Is A Prime Lens
A prime lens is a lens with a fixed focal length.
Notable examples of prime lenses are the 50mm prime lenses, the so called nifty fifties, the 135 mm, and 300mm lenses.
The Canon 50 f/1.8 STM is one of the best budget prime, useful in many situations.
While lacking focal length adjustment, prime lenses are often much faster than zoom, and for this they are a favorite among portrait and studio photographers.
This is because fast lenses have wide apertures capable, among the rest, of collecting a lot of light per unit of time.
What Is A Zoom Lens
Zoom lenses, as opposed to prime ones, are photographic lenses for which the focal length can be adjusted within a specific range.
Every camera and lens maker has a complete and comprehensive offer of zoom lenses, from Pro graded to affordable kit lenses.
As a matter of fact, these days zoom lenses are much more popular than prime ones. Their popularity is the result of the combination of good image quality and flexibility.
Framing and composition are made easier by altering the focal length of the lens and travel zoom lenses, such as the Sigma 18-200 f/3.5-6.3, are kind of “one fits all” lenses for travel.
Most bridge and compact cameras offer a superzoom lens. With its impressive 24-3000mm zoom lens, the Nikon Coolpix P1000 can let you photograph breathtaking landscapes by day as well as letting you enjoy lunar and planetary astrophotography by night.
The Difference Between Prime Vs Zoom Lenses
The obvious and more striking difference between prime and zoom lenses is focal length.
With prime lenses, you have to pick only one focal length per lens, and if you go down this road, you will soon find yourself buying several lenses: a 35mm for street shots, the versatile 50mm nifty fifty, and maybe a 135mm (or longer) lens for portraiture.
And maybe something really short for landscape photography.
From this it is clear that prime lenses appeal more to professional photographers working in a specific field, rather than the average, all-rounder, amateur photographer.
Zoom lenses are much more flexible, and one could photograph pretty much everything with a single travel zoom, covering from landscapes to portraiture and wildlife.
And even the Moon!
Here is where things get subtle and where prime lenses get their edge over (most) zoom lenses.
To be clear, here I’m not using the term “aperture” to indicate the diameter of the front element, like is usually done for a telescope. In photography, aperture is the diameter of the wide-open diaphragm inside the lens.
Zoom lenses, particularly the affordable ones, have a variable maximum aperture. The wide-angle end of the zoom has the widest aperture, while at the telephoto end the aperture maximum aperture is reduced.
Usually, the telephoto end of the lens can be quite slow, at f/5.6 or worse.
Prime lenses, instead, are often fast, with an aperture of f/2 or better. This is of course great news for indoor photography and for taking moody portraits in natural life.
Perhaps more importantly, for a given sensor size fast lenses have a shallow depth of field when used wide open.
Portrait photographers in particular, exploit this as a nice way to separate their model from the background, thanks to the so-called bokeh (less poetically known as blurred background).
Sharpness and Image Quality
As a rule of thumb, It is often said prime lenses are sharper than zoom and offer better image quality, and this is probably still true today.
The fact is that there is less glass for the light to pass through to reach the sensor in prime lenses with respect to the zoom ones.
And every time the light passes through a lens, all sorts of aberration and degradation can happen.
Most zoom lenses, except for the high-quality ones, are known to be somehow softer at their telephoto end than at the wide-angle end, and it is advisable to use them not at their maximum focal length.
Size And Weight
Personally, I don’t think it is possible to come up with a general rule for which is heavier or bulkier: a prime or a zoom.
The Samyang 135 f/2, arguably one of the best lenses for astrophotography and (possibly) portraiture, weighs 815gm and has a front element diameter of 77mm.
For comparison, the Canon 55-250 f/4-5.6 weighs 390gr and has a front element of 58mm in diameter. And It is shorter too!
Again, it is difficult to come up with a clear trend for pricing.
In general, since things like autofocus and image stabilization are common to both types of lenses, what makes zoom lenses more expensive than prime ones of similar quality is the greater complexity of the optical scheme and number of lenses involved in zoom lenses.
Shooting Astrophotography – Prime Or Zoom Lenses
When it comes to astrophotography, which one is better: prime or zoom lenses?
Astrophotography is all about collecting the most of the available light, and for this reason prime lenses are to be preferred.
We already saw prime lenses offer wider aperture and have less glass the light has to pass through. More aperture means more light, and less glass means “better” light.
This is the reason why telescopes and refractors for astrophotography are prime lenses.
But this does not mean astrophotography is not possible with zoom lenses: if you have a look at astrobin, for instance, you will see plenty of wonderful images taken with zoom lenses.
Benefits of using a Prime lens
High-end prime lenses have many positives over comparable zoom lenses when it comes to astrophotography.
- Fast aperture, to collect more light.
- A long prime telephoto lens like the Olympus M.Zuiko 300 f/4, combines relatively long reach and fast aperture.
- High optical quality for a sharp image.
- Well corrected optics makes them usable also wide open.
- You are stuck with a single field of view: you may need to carry more lenses if you want to image different things during the night.
Benefits of using a Zoom lens
Zoom lenses win hands down over prime ones for flexibility, and this is again, the stronger plus in choosing a zoom lens for astrophotography.
My Sony RX10 (together with the more recent versions II and III) bridge sports an outstandingly good, fast 24-200 f/2.8 travel zoom lens. With one piece of gear, I can take wide shots of the Milky Way one moment, and close in on Andromeda Galaxy the moment after.
- You can choose the best field of view for your intended target.
- You can photograph a starry landscape, a star field, or a deep sky object close up with the same lens: great to keep at a minimum the amount of the gear you need to carry around.
- Zoom lens make finding your target easier: start zoomed out to locate the target and then zoom on it for the final composition.
- Focus can change with the focal length: if you change the zoom level, you have to refocus.
- Zoom can suffer from creeping in under their own weight: this will cause the focal length, field of view, and focus to change during your imaging session. Some zoom has a locking mechanism, else tape down the zoom ring.
- Budget zoom lens have variable aperture, and the telephoto end is the slowest one: this can limit the amount of light you can collect per unit of time.
- Image quality is not consistent with the zoom level, and often the image is softer at the telephoto end.
- Zoom lenses may be heavier than prime ones, making them less suitable for using with star trackers.
What Should I Use For Astrophotography?
If you are just starting out, use what you have. Before worrying about lenses and cameras, you should consider improving in the tripod area and to get at least a star tracker, if not a full-grown astronomic equatorial mount.
When you feel you have grasped the basic principles and techniques in astrophotography, you can start thinking about improving image quality with better lenses or even dedicated refractors.
What to take depends on what you need: if you are into different photographic genres, like sport, portraiture, and astro, a zoom lens like the Canon 70-200 f/2.8 L or Olympus Zuiko 40-150 f/2.8 PRO are certainly a good choice.
If you are looking for something to use only for astro, a long telephoto lens is probably the best choice, after a dedicated refractor.
But not everyone has a long telephoto lens at home, and good ones are expensive. If you really want to try one but have a low budget, there is good news for you.
Prime lenses were like the best possible lenses for film photography. We now call them “legacy lenses”, and many are available in the second-hand market for a fraction of their original cost.
With the notable exception for collectible models.
Well kept legacy lenses age well and can be a bargain if you are looking for something affordable to bite into deep-sky astrophotography.
Of course technology in glass and lens design has improved during the years, and legacy lenses may suffer more from coma and chromatic aberration and you may need to use them stepped down by 1 or 2 stops.
Sometimes though, a lens will simply not work, so do your research, particularly if you are shopping for a vintage lens.
If you want to know more about the use of legacy lenses in astrophotography, have a look at this post I wrote on my personal blog.
Common Questions About Zoom And Prime Lenses
Here some of the most frequently asked questions about prime VS zoom lenses.
Are Prime Lenses Better Than Zoom?
In photography, I’m afraid very few questions have an absolute, clear cut answer. Are prime lenses better than zoom? Yes they are, for some things. Well maybe not. I mean, it depends 🙂
A better question would be, “Are prime lenses better than zoom for portraiture?” Yes, they are. “Are prime lenses better than zoom ones for travel photography?” All considered, probably not.
Prime lenses may have better optical performances than zoom, but they are less flexible. It’s up to you to look at what you like to photograph and how, and decide what you value more.
What Are Zoom Lenses Good For?
Zoom are perfect lenses for all those situations where you may want to change quickly (or often) your composition and field of view. And for when you don’t know what you will find.
High-end zoom lenses are great for stage, music, sport, and travel photography. Depending on their reach, it is a great choice for wildlife photography too.
Again, ease of use and flexibility is the key.
Can Prime Lens Zoom?
With prime lenses you zoom with your feet: too close? Walk away. Too far? Go closer.
Sometimes this is not possible because of some sort of barrier: if you are a stage photographer at a classical concert, you may find yourself working in a very restricted area.
And if you are trying to zoom with your feet In astrophotography, well, good luck with that 🙂
Which is better: a prime or a zoom? Only you know the answer, as it depends on the type of photography you are in, your budget, if you need to keep your equipment small and light, or you can have two or three lenses to cover different situations.
And as per astrophotography, a prime lens is surely the way to go, if you can sacrifice the comfort of shooting a starry landscape one moment and a galaxy close up the minute after that.