EF vs EF-S interchangeability

[privateaddressf]

I know this has been discussed before, but I have a fairly specific case and I'm still not sure how the discussions apply.  My wife has agreed to photograph a relative's wedding.  She has done some semi-pro photography before but her Sony alpha DSLR has been acting up and she is buying an m50 as a backup.  She needs to buy lenses quickly.  

If she buys an EF 50mm and an ef-s 50mm and takes a picture from the m50 (aps-c) with each lens, in the same place, will the two pictures produced by the camera subtend the same visual angle or will one of them portray a larger apparent visual angle?

We don't have time to experiment with lots of things and do three or four rounds of shipping to get the fovs she needs covered. It would also be nice not to waste money on redundant lenses if EF and EF-S focal ranges behave differently when used on her camera.

[johnrmoyer · Accepted solution]

https://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

This article aims to address the question: how does your digital camera's sensor size influence different types of photography? Your choice of sensor size is analogous to choosing between 35 mm, medium format and large format film cameras — with a few notable differences unique to digital technology. Much confusion often arises on this topic because there are both so many different size options, and so many trade-offs relating to depth of field, image noise, diffraction, cost and size/weight.

Background reading on this topic can be found in the tutorial on digital camera sensors.

[krahe]

The short answer is that on a crop sensor camera like the M50, a longer focal length will yield a narrower FOV than a shorter focal length, regardless of whether the lens was designed for a full frame camera or what the FOV would be on such a camera with the same lens.

[Tronhard · Accepted solution]

Read this: 
As has been said, a 50mm lens is a 50mm lens, no matter the mount: EF or EF-S.  What makes the difference is what the sensor can capture from what the lens projects into the camera.  For a full explanation see:
Equivalence.pdf

[privateaddressf]

Ok, let's see if I've got this now after trying to digest all that.

The fov is a function of two things.  Sensor size, and lens focal length.  Swapping lenses of equal focal length on the same camera always produces the same fov.

Changing sensor sizes with a set focal length (e.g. 50mm on a full frame vs 50mm on an aps-c) changes the captured fov.

The "crop factor" then is really an effect of moving to a different sensor size.  A photographer used to using a 50mm lens for a particular setting with a full frame camera will have to adjust which lens/focal length they use in that setting if they switch to a smaller sensor?

[Tronhard]

That is true as far as it goes.  Certainly a 50mm EF lens has the same focal length as an EF-S lens.  However, on a crop-sensor camera, while the lens has the same Angle of View that is what it projects towards the sensor, the sensor captures a smaller area of that (Field of View), which is equivalent to using a lens of a longer focal length on a FF body - hence the term Equivalence.  To go back to the original post, given a Sony Alpha has approximately the same size as a Canon APS-C camera, so the Fields of View, assuming the same or similar lenses, should be about the same.

[johnrmoyer]

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@privateaddressf wrote:

Ok, let's see if I've got this now after trying to digest all that.

The fov is a function of two things.  Sensor size, and lens focal length.  Swapping lenses of equal focal length on the same camera always produces the same fov.

Changing sensor sizes with a set focal length (e.g. 50mm on a full frame vs 50mm on an aps-c) changes the captured fov.

The "crop factor" then is really an effect of moving to a different sensor size.  A photographer used to using a 50mm lens for a particular setting with a full frame camera will have to adjust which lens/focal length they use in that setting if they switch to a smaller sensor?

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Yes

[ebiggs1]

Beyond the FOV issue, I will suggest she not buy or use a 50mm lens on a cropper for a wedding. I have done more weddings than I can count and the times I used a 50mil could be counted on the fingers of one hand. Its just not a very useful FL. 

I don't believe you mentioned what camera she has or what lenses she has. If she has one of the Rebels with the standard, 18-55mm, kit lens she has what she needs. My main most second lens is the 70-200mm as sometime you just can't get up close to the action. Some of the churches limited me to the very back of the church.  Even beyond that grabbing a shot of the actual ceremony with out being right up in front and personal has its blessings. My goto combo is the ef 24-70mm f2.8L and ef 70-200mm f2.8L. Used more than 90% of the time. A similar combo for a cropper like a Rebel is the mentioned 18-55mm and the ef-s 55-250mm.

Not shot with a 50mm nor was the one below.

The big take away from all this is look through the camera's view finder as no matter what camera you have that is what you will get. If you are unfamiliar with the wedding venue make a visit and check it out. Take a willing stand-in subject with you.

Canon 1DX with ef 24-70mm lens. ISO 200, SS 1/250, f8.

[privateaddressf]

My wife had been shooting with an old Sony alpha 500 but hasn't done much for a while. I managed to convince her not to dabble in the professional world for now because she can't keep from getting the images perfect in Photoshop after the shoot which means her pay per hour wouldn't really be worth her time.

The new camera will be an m50 II.

She's done enough volunteer portraits, weddings as a backup photographer, family shoots, livestock, landscape etc. that she knows what she wants.  At least she knows what she uses on the Sony for different shots, its just a matter of figuring out what lenses will provide the same effects on the Canon.  She was under the impression that lenses made for smaller sensors compensated for the sensor size so the length needed to be adjusted when buying older full frame lenses, but after all the great help here I was able to draw the optics diagrams to help her understand how it works (which of course contradicts all the info she got from online people who don't understand this stuff like you guys do.)

[ebiggs1]

My personal recommendation for her would be the Rebel T8i with the standard kit 17-55mm lens and add the 55-250mm lens. I am not and have never been a fan of the, or any, M series cameras. The sheer amount of Canon lenses and other accessories dwarfs what is available for the M series.

[krahe]

I can't say anything about accessories, but as far as lenses go there are actually far more available for an M series camera if you include those that can be used with an adapter than there are for a T8i.