Visualisations of the camera "crop factor"

StewartR

StewartR

Messages
11,513
Name
Stewart
Edit My Images
Yes
Seeing this thread reminded me of the "crop factor" issue that some people struggle to understand, so I thought it might be helpful to share with you a few visualisations that I made a while ago.

Apologies if this is all obvious: I'm new to TalkPhotography and I haven't yet gauged where most people are on the newbie / clueless / expert scale. Feedback would be very welcome.

Anyway, Visualisation #1 shows a simulation of the view through a lens, and the portion of the picture which is captured by sensors of different sizes. (I've used full frame / 1.3x / 1.6x because I'm a Canon user.) As you can see, crop-factor cameras just capture a smaller portion of the scene than full-frame cameras. Nothing else changes.

16395-1473694190-9e6567c7ff95d764fcd0b450791f3442.jpg


This makes it look like crop-factor cameras give you extra "reach" for free: the scene you'd capture with a 200mm lens on a 1.6x camera such as a Canon 350D/400D or 20D/30D/40D is similar to what you'd get with a 320mm lens on a full-frame camera. But that's not the whole story. Another relevant issue is how many pixels you have to play with.

Next, Visualisation #2 shows what you get if you take the same photo with each camera in the Canon range (except the new 40D and 1Ds Mk III, because I made this a couple of months ago), and enlarge it by the same amount.

16396-1473694204-b78325dc17561c71a96b6cbbe8bab0eb.jpg


This is important for people who shoot things like birds. It shows you that the 400D gives you more pixels-per-duck than any of the other cameras here. (Of course that's not the whole story: the more expensive cameras will give you better quality pixels, and better autofocus, and other goodies.) It's also interesting to see, for example, that if you crop the centre out of a 5D image to reproduce what you'd get with a 30D, you end up with fewer pixels and a smaller image than if you'd used a 30D in the first place.

Finally, Visualisation #3 shows (crudely) what those designed-for-digital lenses do. On the left is the image projected by a "traditional" lens like a Canon EF or a Sigma DG: the image circle is large enough to cover a full-frame sensor or a frame of 35mm film. On the right is the same view through a designed-for-digital lens such as a Canon EF-S or a Sigma DC. It's simply a smaller piece of glass, which is why it's cheaper, and you can see why they only work on crop-factor cameras.

16397-1473694214-8dee0bec13345e1b348c47575607a6bc.jpg


I hope that all made sense and that at least some people found it vaguely helpful. Comments and questions welcome.
 
Last edited:
(y) That is without doubt the most concise and easy to understand explanation of the subject I have ever seen :clap: Looks like you put a lot of effort into that and I'm sure it will clear up the confusion between ff and crop sensors for a lot of people. Thanks for sharing it with us :)
 
Good post So good in fact, it should probably be in Tutorials?

As a bird tog, you've nailed my basic problem perfectly. Unfortunately,(for my wallet) you've also shown a very compelling case in favour of the 1DSMk3, even after substantial cropping, (even though you haven't covered the Mk3. it appears the benefits will be pretty obvious)
 
I think a new TP Poll is needed.......How long before CT cracks and orders a 1DSMKIII?

Before the end of the year? :shrug:

Xmas present to himself? :shrug:

Early in the New Year? :shrug:

:D ;) (y)
 
CT said:
As a bird tog, you've nailed my basic problem perfectly. Unfortunately,(for my wallet) you've also shown a very compelling case in favour of the 1DSMk3, even after substantial cropping, (even though you haven't covered the Mk3. it appears the benefits will be pretty obvious)
Click to expand...
I have good news for your wallet. The 1Ds Mk III doesn't give you as many pixels-per-duck as the 400D and the 40D.

One sq mm of the 1Ds III sensor contains about 24,300 pixels.
One sq mm of the 400D/40D sensor contains about 30,700 pixels.

I'm not a birder but I would say that (amongst Canon DSLRs at least) the ideal birder's camera would currently be the 40D.

I've just saved you £5,000. Do I get a commission? ;)
 
LOL. I need to do some serious testing to see what the actual benefits will be, but I can't realistically see any other direction to take at the moment to get better image quality. The real benefits for me are being able to interpolate up to 50mb for stock library shots, even after heavy cropping. At the moment that's a tough call for me, and a lot of my shots don't reach the bar after upsizing.


I quite like the sound of Option 2 in your poll though. :D
 
StewartR said:
I have good news for your wallet. The 1Ds Mk III doesn't give you as many pixels-per-duck as the 400D and the 40D.

One sq mm of the 1Ds III sensor contains about 24,300 pixels.
One sq mm of the 400D/40D sensor contains about 30,700 pixels.

I'm not a birder but I would say that (amongst Canon DSLRs at least) the ideal birder's camera would currently be the 40D.

I've just saved you £5,000. Do I get a commission? ;)
Click to expand...


That's very interesting , and has confirmed what I suspected might just be the case. (y)
 
Absolutely top post Stewart. I suggest we leave it where it is for a while as it will probably get more views, then move it to Tutorials when it's dropped down the thread list. That's assuming you don't mind?

Really good job mate! (y)
 
Thanks for that well presented and easy to understand presentation of the cameras crop factor. You've made a really good job of it, something that an old timer like me can easily understand:LOL:
 
CT said:
Absolutely top post Stewart. I suggest we leave it where it is for a while as it will probably get more views, then move it to Tutorials when it's dropped down the thread list. That's assuming you don't mind?

Really good job mate! (y)
Click to expand...
Of course I don't mind. Thanks for the kind words.
 
Nice one StewartR, as a p&s photographer who is looking to pick up some tips on here this has been a great help to me, thanks.
 
Brilliant, this is the most understandable way of demonstrating the main factors of digital SLR techology. If only you could copyright ideas you'd be rich.

However, there is only 1 problem - it's based on the Canon system :LOL: what about us Nikon users who don't understand; there are only 2 crop sizes 1 and 1.5 so it should be easier.
 
SimonTALM said:
However, there is only 1 problem - it's based on the Canon system :LOL: what about us Nikon users who don't understand; there are only 2 crop sizes 1 and 1.5 so it should be easier.
Click to expand...
It's based on the Canon system because (a) I have a Canon so I'm more familiar with the Canon range, and (b) until very recently I believe Canon were the only people offering a choice of crop factors on their DSLRs. I might get round to doing a Nikon version some day, if you think Nikon users would be likely to understand it. ;)
 
You must log in or register to reply here.
Back
Top