Photography Explained Podcast – What Is Crop Factor? Hi and a very warm welcome to Episode 161 of the Photography Explained podcast. I’m your host Rick, and in each episode, I will try to explain one photographic thing to you in plain English, in less than 27 minutes (ish), without the irrelevant details. I’m a professionally qualified photographer based in England with a lifetime of photographic experience which I share with you in my podcast.
Here is the answery bit
Crop factor is the number that is used to calculate the effective focal length when taking a photo with a cropped sensor camera or a micro four thirds camera.
A full-frame camera has a crop factor of 1 in theory, a cropped sensor camera has a crop factor of 1.5 – 1.6 and a micro four thirds camera has a crop factor of 2.
The crop factor converts the focal length stated on the lens to the effective focal length, for example
- 50mm on a full-frame camera is 50mm.
- 50mm on a cropped sensor camera is effectively 75-80mm.
- 50mm on a micro four thirds camera is effectively 100mm.
Basically, crop factors relate to the different sizes of digital camera sensors. The term crop factor is very important in photography, we really do need to understand this. This is about the physical size of the sensor, and how this affects the focal length selected and the effective focal length that you get.
OK – that was the answery bit.
You can listen to the episode here
Or carry on reading – up to you.
Now a very brief history lesson. Don’t worry, I need to do this ok?
Back in the film days, the most popular cameras were 35mm cameras. I am talking most popular for pro photographers and anyone else with any level of interest in photography. Sure there were other camera systems, but 35mm was the most popular.
A 35mm camera has a film negative which is 36mm wide and 24mm high. The 35mm bit is actually the physical height of the negative including the sprocket holes that were used to secure the film in place and wind it on.
A full frame camera has a sensor which is 36mm wide and 24mm high. The same as a 35mm camera film negative.
Missing out a massive part of the evolution from film cameras to digital cameras, this makes sense as 35mm was an established format and size. And another massive oversimplification, remove the film chamber, add in a digital sensor and voila, you have a digital camera! Not quite I know but you get the point.
And the term full frame camera, well the full frame bit anyway, also goes back to film days, and I am not going to go into that now. This will not help us.
Now the why question is an interesting one that I am going to look into and cover in a future episode, but I guess it was easier to use an existing established ecosystem such as 35mm than start from scratch.
So we start with full-frame cameras, with a full frame sensor, and from these cropped sensor and micro four thirds cameras have evolved.
What is a full-frame camera?
A full-frame camera has a sensor which is 36x24mm. This is a full-frame sensor. Oh sorry, here it does not matter if it is a mirrorless camera or a DSLR camera – the same applies. But there is no 35mm anywhere now ok so we can forget about that.
And the bit that I missed from the script is this – you can get full frame and cropped sensor mirrorless and dlsr cameras, but micro four thirds cameras are mirrorless. You cannot get a micro four thirds dlsr camera.
What is a cropped sensor camera?
A cropped sensor camera has a sensor which is smaller than a full-frame camera sensor. The crop factor relates to the relative difference in the sensor sizes.
For example, the Canon EOS R100 is a cropped sensor camera (OK Canon call it APS-C) with a 1.6 crop factor, The sensor is 22.3 x 14.9mm. Multiply 22.3 x 1.6 and you get 35.68. And do the same with 14.9 and you get 23.84.
That’s near enough.
The crop factors vary slightly with different manufacturers, and the sensor sizes do not all exactly scale to 36×24, but they are all pretty close, and they are similar enough to be considered together.
What is a micro four thirds camera?
A micro four thirds camera has a sensor which is smaller than a full-frame camera, and also smaller than a cropped sensor camera. A micro four thirds camera has a crop factor of 2. The Olympus EM5 Mk 2 has a sensor which is 17.3 x 13.0mm. Time this by 2 and you get erm 34.6 x 26.
Again, not an exact scale up but apply the crop factor of 2 to relate back to full-frame.
What are the most common crop factors?
1.5 and 1.6 ish for cropped sensor cameras and 2 for micro four thirds cameras.
What does this mean for focal lengths?
- 50mm on a full-frame camera is 50mm.
- 50mm on a cropped sensor camera is effectively 75-80mm.
- 50mm on a micro four thirds camera is effectively 100mm.
What do I mean by effective focal length?
A 50 mm lens is a standard lens. This is similar to how we see the world. 50mm gives us the same view that we see with our own eyes.
50mm on a cropped sensor camera is actually an effective focal length of 75-80mm, which is not the same. And on a micro four thirds camera 50mm gives you an effective focal length of 100mm.
So while the lens might say 50mm, that only applies when using a full-frame camera. The effective focal length is the one that you actually get when you multiply the focal length by the crop factor.
But, the actual focal length of the lens does not change. The focal length of a lens is separate from the sensor size. Yes folks, that 50mm lens for a micro four thirds camera is optically 50mm. It is when you put it on the camera that the crop factor kicks in. I am pretty sure that this is correct.
So what?
To get the equivalent field of view that a 50mm focal length gives you on a full-frame camera you have to divide the focal length by the crop factor.
- For a cropped sensor camera to get the same field of view you need to use a focal length of 31-33mm.
- For a micro four thirds camera to get the same field of view you need to use a focal length of 25mm.
The crop factor has a direct impact on the focal length of a lens.
Wide-angle lenses have focal lengths less than 50mm on a full-frame camera, but you can have a focal length on a cropped sensor camera of 38mm which is an effective focal length of 60mm, which is not wide angle.
And the 38mm on a micro four thirds camera has an effective focal length of 76mm, which is definitely not a wide angle.
So what is a standard lens on full-frame can actually be a telephoto lens on a cropped sensor camera.
Confused by all of this?
Don’t be. You just have to remember to apply the crop factor to the focal length that you are using. Remember that and everything should be fine.
Why all these different formats?
Sensors are expensive things. If you make a camera with a smaller sensor size this is cheaper than a larger sensor, and the camera body and indeed the lenses can be made smaller. This means that cropped sensor and micro four thirds cameras are generally smaller, lighter and cheaper than full frame equivalents. But in very general terms, the larger the camera sensor the higher the image quality. In general terms that is.
Yes, larger sensors are better than smaller sensors. Or are they? Not necessarily One for another time. I have added that to my list.
But there are lots of different cameras out there serving everyone’s needs which has to be a good thing.
Let’s recap on focal lengths and crop factors.
Standard view
- 50mm on a full-frame camera.
- 31-33mm on a cropped sensor camera.
- 25mm on a micro four thirds camera
Wide angle
I tend to think of anything less than 40mm as wide angle.
- Which on a cropped sensor camera is anything less than 25 – 26.
- And on micro four thirds camera is anything less than 20mm.
Wide-angle focal lengths give you a wider field of view.
Telephoto
I tend to think of anything greater than 60mm as telephoto.
- Which on a cropped sensor camera is anything greater than 37.5-40mm.
- And on micro four thirds camera is anything greater than 30mm.
Telephoto focal lengths give you a narrower field of view.
What do standard, wide angle and telephoto mean?
Check out these episodes where I covered each in turn.
Wide Angle Lenses Explained In Plain English In Less Than 10 Minutes
Telephoto Lenses Explained In Plain English In Less Than 10 Minutes
But different sensor sizes have different crop factors which give different effective focal lengths.
What about other camera formats?
I have not covered medium format cameras, and how they relate, as they are viewed separately. And large format is even more remote. And there are other formats out there but the main ones are full frame, cropped sensor and micro four thirds. But if you want me to cover another camera format just let me know and I will shoehorn this into a future episode. There used to be loads of different compact cameras but I think these are on the decline now with the rise of the camera phone.
No, full-frame, cropped sensor and micro four thirds covers the majority of consumer cameras.
Are larger sensor cameras better than smaller sensor cameras?
In theory yes, but it is not that simple. If only. And can you tell the difference? Well, this is definitely one for another episode. Added to my list. But you can take great photos with small sensors, and rubbish photos with massive sensors. Let’s not forget that!
Why would I buy a camera with a smaller sensor?
They can be smaller, lighter and cheaper. And you can also use the crop factor to your advantage. if you have a 300mm lens on a full-frame camera that is what you have. But put that 300mm focal length lens on a micro four thirds camera and you have an effective focal length of a whopping 600mm. Yes, the first use of the word whopping on my podcast!
That is massive. The 600mm not the use of the word whopping of course.
There are certain types of photographers who will benefit from this, such as sports photographers, wildlife photographers, bird photographers, and anyone who is taking photos of things a long way off.
And what about APS-C?
Cropped sensor cameras are often referred to as APS-C cameras. I hate this term, in my head, APS-C means something else so I stick with cropped sensor camera. You will also find a cropped sensor camera can be called a crop sensor camera by some people.
Does crop factor affect the aperture?
No, it does not.
Does crop factor affect the depth of field?
I will cover depth of field in the next episode, so I will leave that one for now. Phew dodged one there!
Does crop factor affect the shutter speed?
No, it does not.
The talky bit
The one question I have is this. Why, when cropped sensor and micro four thirds cameras were being developed, did they not apply the crop factor to the focal lengths there and then? What it’s the point of saying that a camera lens has a focal length of 50mm when it actually isn’t? That is the one thing that I don’t get. Maybe one of the camera manufacturers can let me know. That would be nice.
The reason is that the focal length of the lens is just that – it is not related to the sensor size. This is why we refer to the effective focal length (or equivalent focal length) which is the one that you get after applying the crop factor.
I don’t know, it does all get rather complicated, doesn’t it? Surely there is an easier way?
Other than that, this is just something that you need to be very aware of as the three different types of cameras, full-frame, cropped sensor and micro four thirds have different-sized camera sensors. And this difference applies to everything else, making them separate, and not interchangeable camera systems.
If you start off with micro four thirds, the only way to change to full-frame is to change absolutely everything. And if you start with full-frame but want to change to micro four thirds the same applies.
And the same applies to cropped sensor cameras, although there is the odd bit of interchangeability with full-frame but I would ignore that as it is so limited.
Treat the three as separate camera systems and you won’t be far off. Full frame is one camera system, cropped sensor is another, and micro four thirds another.
And every time you look at a lens apply the crop factor as that is what you are actually getting.
Right – talky bit over. That was a short one which was nice.
What if I use a phone and not a camera?
Well, it doesn’t really apply. I think that phones and cameras are so different we do not need to worry about this.
What if I use a film camera?
What you have is what you have. And it is probably 35mm so all nice and easy. If you have another format of film camera let me know.
What do I do?
I use a full-frame digital camera and I also use a micro four thirds camera. And I don’t worry from one to the other – I really don’t think about it. This is probably because I tend to take photos with the widest focal length available to me, and I work with what I have.
On my full frame Canon 6D with my go-to 17-40mm lens, this is 17mm. With my Olympus EM5 and go-to 12-40mm lens, this is 24mm, going to an effective focal length of 80mm. So the 12-40mm lens on a micro four thirds camera has an effective focal length of 24-80mm.
I don’t overthink this – when I am taking photos with my Canon 6D I use what I see to get my compositions, and simply do the same with my Olympus EM5. I know what the limitations are with both the full frame and the cropped sensor camera. I don’t ever think about the different sizes of image sensors, each one is its own thing.
I use the Canon 6D with the 17-40mm lens for my photos of buildings, I need the full 17mm for the work that I do. I don’t use the Olympus camera for this, to do so I would need the rather splendid 7-14mm lens, which would give me an effective focal length of 14-28mm.
But I am fine using the EM5 for my travel photography.
This is what I do.
Some thoughts from the last episode
Episode 160 – What Is Auto Exposure Bracketing (AEB)?
One question that came out of that episode, from Jeremy in Ohio, was this. And thanks very much for the question Jeremy, great to hear from you. Here is the question
“What good free software is out there that will blend your AEB photos into one photo?”.
Well, I use Lightroom, which costs me less than a tenner a month. But free software? I don’t know, I don’t use any. I sent Jeremy a couple of links but if you have used some free software to merge together bracketed photos just let me know and I can share this will the other listeners.
Next episode
Depth of field is what I have on my list, so depth of field it is then! My Guide To Understanding Depth Of Field In Photography.
Ask me a question
If you have a question you would like me to answer just head over to the podcast website – photographyexplainedpodcast.com/start where you can find out what to do. Or just say hi. It would be lovely to hear from you.
And it would save me from having to come up with a question!
And a shout out to Joanne in Illinois who emailed with a question – thanks for getting in touch Joanne, great to hear from you.
You don’t have to ask me a question for a podcast episode, you can just ask me a question and I will get back to you, and it might get made into a new episode. But I will give you a shout-out.
That’s all
This episode was brought to you by, for a change, a cheese and pickle sandwich and salt and vinegar crisps washed down with a nice cold Diet Pepsi before I settled down in my homemade, acoustically cushioned, recording emporium. Today’s acoustic treatment is, well nothing. I am in my new recording emporium, yes we have successfully relocated so I am now recording my podcast in a new space which is excellent.
OK, it wasn’t a cheese and pickle sandwich, check out the episode to find out what it was!
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 27 ish minutes of your valuable time. I think this episode will be about 27 minutes long after I have edited out the mistakes and other bad stuff.
Take care, stay safe
Cheers from me Rick
OK – that was the podcast episode.
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Thank you
Thanks for listening to my podcast (if you did) and reading this blog post (which I assume you have done as you are reading this).
Cheers from me Rick
