# I was so mistaken!



## sanj (Mar 29, 2014)

I had thought differently earlier...

http://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/


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## Click (Mar 29, 2014)

Very good explanation of the effect of crop factor. Thanks for sharing sanj


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## Mt Spokane Photography (Apr 6, 2014)

Focal length and aperture are lens properties and the lens does not change no matter what body you put it on!

There are a ton of confusing articles that cause confusion because of the terminology used. People will glance at that title and become convinced that its true.

Where the confusion comes in , is that some assume the same lens to subject distance, while some assume the same composition (move the camera further away).

If you move the camera further away to get the same angle of view as FF, then the depth of field is different. If you keep the camera at the same distance, then the angle of view is different.

The focal length and lens aperture never change.


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## Don Haines (Apr 6, 2014)

Mt Spokane Photography said:


> Focal length and aperture are lens properties and the lens does not change no matter what body you put it on!
> 
> There are a ton of confusing articles that cause confusion because of the terminology used. People will glance at that title and become convinced that its true.
> 
> ...


You hear so many complicated explanations, yet the answer is so simple.... A crop sensor samples the central portion of the image, usually at a higher density.... 

It is incredible how many people believe that the optics magically change when you mount the lens on different bodies...


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## sagittariansrock (Apr 6, 2014)

Yeah, crop factor affects field of view, depth of field and handholdability.
The first one I knew before, but the rest I learned here, on the CR forums (thanks, y'all).
Nice video with clear illustrations.


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## sanj (Apr 6, 2014)

Mt Spokane Photography said:


> Focal length and aperture are lens properties and the lens does not change no matter what body you put it on!
> 
> There are a ton of confusing articles that cause confusion because of the terminology used. People will glance at that title and become convinced that its true.
> 
> ...



I though so too. But this guy seems to be proving me wrong.


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## sagittariansrock (Apr 6, 2014)

sanj said:


> Mt Spokane Photography said:
> 
> 
> > Focal length and aperture are lens properties and the lens does not change no matter what body you put it on!
> ...



I don't know if you are being ironic. 

Tony Northrup was clear that crop factor affects field (and angle) of view and depth of field. The person who wrote the PetaPixel article brought in the phrases focal length and aperture, in what my guess is a misguided effort to make it simpler for the lay person to understand. I don't think anyone was actually claiming focal lengths or aperture of a lens changes with the sensor size in the video or article.
I think this video is useful because many people don't know that crop factor also affects the depth of field and the handholdability of a lens. Northrup comments when manufacturers post equivalent focal lengths on their smaller format lenses, they should also include equivalent apertures (regarding FoV and DoF, respectively).


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## yorgasor (Apr 25, 2014)

Ugh, the terminology the guy was using in the video was horrible. If I was new to photography, I would come away from that video completely misguided. When I look at the aperture of a lens, I think primarily how much light it lets in, and know that the effect of a larger aperture gives me a narrower depth of field.

When he tells you that when you compare cameras of different sensor size, he keeps telling you that you also need to multiply the crop factor and the aperture, even calling out manufacturers for not being as honest when selling their crop factor lenses, that the aperture isn't the true value for the lens. The amount of light coming through at f/1.8 is the same for a micro 4/3s as it is for a full frame. He never clarifies that. He makes it sound like aperture and depth of field are the same thing, when they're clearly not.


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## sagittariansrock (Apr 26, 2014)

yorgasor said:


> Ugh, the terminology the guy was using in the video was horrible. If I was new to photography, I would come away from that video completely misguided. When I look at the aperture of a lens, I think primarily how much light it lets in, and know that the effect of a larger aperture gives me a narrower depth of field.


I think that's unfair. New photographers are not familiar with depth of field or circle of confusion as they are with aperture and background blur. He was just using more familiar terms but he did not use them incorrectly. If one listens carefully, he shouldn't be misguided.



yorgasor said:


> When he tells you that when you compare cameras of different sensor size, he keeps telling you that you also "need to multiply the crop factor and the aperture..."


"... because it allows you to compare lenses in terms of background blur." 
That's correct, isn't it?



yorgasor said:


> even calling out manufacturers for not being as honest when selling their crop factor lenses, that the aperture isn't the true value for the lens.


Actually, he said manufacturers multiply ONLY the focal length by the crop factor (to give equivalent FoV) and NOT the aperture (to give equivalent DoF). And he gives an actual illustration from Amazon. He urges them to convert BOTH if convert at all.



yorgasor said:


> The amount of light coming through at f/1.8 is the same for a micro 4/3s as it is for a full frame. He never clarifies that.


The amount of light may be the same (and he doesn't comment on that) but the light gathered by the sensor is different, due to different sensor sizes (and that, he does specifically state).



yorgasor said:


> He makes it sound like aperture and depth of field are the same thing, when they're clearly not.


Actually, he keeps saying multiply aperture by crop factor to get same amount of blur.

I was oblivious of the effect of crop factor on depth of field for a long time until Neuro corrected me. I think this is still a pretty common mistake among beginners. Northrup was trying to correct that without going into technical details of circle of confusion. I am sure there are better ways to explain it, but I think this was a decent effort.


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## climber (Apr 26, 2014)

Ok, I'm a bit confused because don't know what the "circle of confusion" is? Maybe someone could explain in two sentences?

And please correct me if I'm wrong with this:

200 mm, f/2.8 on full frame gives the same DoF as 133 mm, f/2.8 on crop. (i get 133 because 200/1.5 = 133) Let say, I put 70-200 2.8 lens first on FF and then on crop. In both cases aperture is 2.8, only on FF I turn zoom ring to 200 mm and on crop to 133 mm. Is DoF in both cases the same?


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