EF vs. EF-S Lens On APS-C DSLR

[glen_h]

It's not funny or strange to use something everybody is familiar with as a reference.

What is strange, and causes a lot of confusion, is talk about equivalent focal lengths. People will believe that the focal length itself will vary with sensor size.

We really should find a different way to express the effect of cropping an imaginary reference image to something smaller. Something like, i don't know, crop factor.

 

But not everybody is familiar with it, just 35mm photographers.

 

Now, there are a lot of them, but not everybody.

 

I presume that there are some medium format photographers who never,

or maybe only rarely, use 35mm cameras. They would be familiar

with different numbers.

 

Funny thing. I have an eBay saved search for 127 film, which often

enough comes up with a medium format camera and 127 mm lens.

 

I have never used a camera with a 127mm lens (not counting zoom

lenses that can go to 127mm.)

 

But okay, if you consider a 50mm lens as the normal, then it isn't so hard

to consider ratios. However, the diagonal of a 24x36 frame is closer

to 43mm, so 50mm should not be the default lens.

 

Since 50 is half 100, I can quickly figure out that 135mm is 2.7*50,

and 35mm is 0.7*50, but it would make slightly more sense if 100

was the reference.

 

But many digital camera uses never used a 35mm film camera, and

likely don't find it such as useful reference.

[paddler4]

I agree, "effectove focal length" is a confusing term: it's only the same in one respect, not in others. However, spelling the whole thing out is cumbersome, something like "a 300mm lens on a 1.6 crop factor sensor will give you the same angle of view as a 480mm lens on a FF camera," or "a 300mm lens on a 1.6 crop factor sensor will have the same effect as a 480mm lens on a FF camera in terms of the recorded subject size compared to the frame size".

[q.g._de_bakker]

Considering that Full Frame is also 'a thing' in the digital world, many photographers need not be familiar with film cameras to be familiar with 35 mm format as a reference.

 

Yes, MF and LF photographers also have different references, but still are familiar with 35 mm format too. Shows how this 'equivalent focal length' thing is not needed. Those MF and LF photographers (based on a sample of one, yes) do not calculate equivalent focal lengths using 35 mm format's 50 mm normal lens when selecting lenses to use. You just know your lenses and formats (including their aspect ratios).

But when using different digital options behind those LF and MF cameras, the crop has to be considered.

[Ken Katz]

Having grown up in the 35mm film world and experienced the impact of focal length to field of view, DOF, and perspective from that standard for decades, it is still how I approach lens section for my 2x crop factor M43 cameras. When using a 12mm focal length, I am thinking 24mm FF in terms of how I approach an image, even though I have not picked up an FF camera for over 2 years. I still use 35mm as the standard of how wide is wide, and how long is long, because it is a standard I am most familiar with over decades of use.

 

Perhaps today folks newly introduced to interchangeable lens cameras will think that 26mm (FF Equivalent) is a normal view, and anything wider is a wide angle lens and anything longer is a telephoto, since that is how Apple defines it on their phones.

[paddler4]

It almost doesn't matter whether people have had experience with 35mm/FF cameras. This has become the standard for comparing AOV across sensor sizes. You can use it, for example, to compare FLs for MFT and APS-C, albeit with an extra step.

[glen_h]

(snip)

 

Perhaps today folks newly introduced to interchangeable lens cameras will think that 26mm (FF Equivalent) is a normal view, and anything wider is a wide angle lens and anything longer is a telephoto, since that is how Apple defines it on their phones.

 

It does seem that Apple gives the 35mm equivalent without even saying that they are doing it.

 

And yes it is a 26mm lens, but they do call it wide angle. Then there is also a extra-wide and telephoto lens.

 

Samsung gives the angle of view in degrees, so no confusion.

[rodeo_joe1]

Samsung gives the angle of view in degrees, so no confusion

Would that be horizontal (long-side) AoV, vertical (short-side) AoV, or the lunatic diagonal AoV that lens makers are fond of quoting?

[friskybongo]

Still confused despite all these detailed replies. Let's back to the OP's lighthouse example. Say I have a 200mm EF Canon lens and I place it on both a full frame and then a crop camera and take a picture of the lighthouse. My understanding is that the lighthouse itself will be the same size (not magnified on the crop camera) but the top/bottom and sides of pics taken with the crop camera will simply be "trimmed". If this is correct, why do some folks say they don't need a telephoto lens since the pics taken with say a 100mm EF lens on a crop camera will take images equivalent to a 160mm lens if nothing is magnified?

 

Perhaps I need to reread the entire thread.

[Ken Katz]

If you put a 100mm lens on a Canon crop body camera and compare the image to FF camera with a 160mm lens (or a zoom lens set at around 160mm), both cameras will provide the same field of view.

 

"Perhaps I need to reread the entire thread"

 

Sounds like a wise decision.

[rodeo_joe1]

Leaving aside compact point'n'shoots and phone cameras, where the focal length(s) stated are usually a tissue of lies.

 

The focal length engraved on the lens is the focal length. So if the lettering around the lens says "200 mm" then it's a 200 mm lens whatever the size of camera sensor.

 

All that happens between fixing that same lens to a DX or Full-frame camera is that you get a smaller or bigger crop of the image. The image size stays the same - and you're just capturing a smaller or larger section of it.

 

This might make it clearer. Here's the full image taken with a 135 mm lens:

 

And here's a crop of about 1/20th the width of the frame -

Same lens, same shot. It's just been cropped to an equivalent view of what you'd get with a 2,700 mm lens. But I didn't use a 2,700 mm lens, and I don't think one is even made. I just cropped the 135mm lens image. Nothing else changed except the amount of image used.

 

So when a lens or camera maker states a full-frame or 35mm equivalent focal length, it's as meaningless as that.

 

The lens focal length stays the same, and it's just the amount of image that gets captured that changes.

Perhaps if I draw a little crop-box on the first picture it'll clarify things.

[friskybongo]

If you put a 100mm lens on a Canon crop body camera and compare the image to FF camera with a 160mm lens (or a zoom lens set at around 160mm), both cameras will provide the same field of view.

 

"Perhaps I need to reread the entire thread"

 

Sounds like a wise decision.

[friskybongo]

Ken Katz,

Thanks for replying. An additional question regarding your previous reply to my post:

 

"If you put a 100mm lens on a Canon crop body camera and compare the image to FF camera with a 160mm lens (or a zoom lens set at around 160mm), both cameras will provide the same field of view."

 

So if I put the 100mm EF lens on a Canon FF camera and photographed the lighthouse and then put the same 100mm (not 160mm lens as you mentioned) EF lens on a Canon crop camera and photographed the same lighthouse, I'm thinking that the size of the lighthouse in the center of the frame would be the same from both camera/lens combinations but the image taken with the crop body would simply "trim out" the bottom and sides of the image.

 

Sorry for not understanding this and thanks again for your help.

[JDMvW]

Lens focal length conversions - historical comment and autocritique

is my "autocritique" of my earlier saying that no one worried about this before digital....

[Ken Katz]

Friskybongo

I think I understand your question. If you put a 100mm lens in front of a (i) half frame camera, (ii) full frame 35mm camera, and (iii) medium format camera, and loaded all with Tri-x film, the size of that lighthouse rendered on all 3 pieces of film will be the exact same size. If you print all 3 images so that the larger FF and MF negatives are cropped to provide the same view as the half frame camera, all 3 prints would look identical.

 

With current digital equipment though, different sensors can have different pixel densities. A 100mm lens on a 45mp FF Canon R5 would need to be cropped in post to around 17mp in order to render the same field of view as a Canon APSC camera. Put that same lens on a 32mp Canon R7 and resulting image would have almost double the pixels of the cropped R5 image.

[friskybongo]

JDMvW - thanks for the link to Lens Focal Length Conversions.

 

Ken Katz - thanks again for your explanations.

[q.g._de_bakker]

Lens focal length conversions - historical comment and autocritique

is my "autocritique" of my earlier saying that no one worried about this before digital....

Well...

Almost everyone was using the same format, no matter what brand, so what would there have been to worry about?

Some, however, used multiple formats, and they too needed to learn what focal length on what format was good for.

[paddler4]

So if I put the 100mm EF lens on a Canon FF camera and photographed the lighthouse and then put the same 100mm (not 160mm lens as you mentioned) EF lens on a Canon crop camera and photographed the same lighthouse, I'm thinking that the size of the lighthouse in the center of the frame would be the same from both camera/lens combinations but the image taken with the crop body would simply "trim out" the bottom and sides of the image.

 

Yes. I think the confusion stems from two different metrics, both of which are relevant:

 

1. The physical size of the image cast by a lens of any given focal length. Assuming that the sensor is large enough that the image fits, that size is depends only on the focal length of the lens, not the size of the sensor you put behind it.

 

2. The physical size of the image cast by the lens relative to the frame size. Sensor size does affect this because a smaller sensor has a narrower angle of view and hence a smaller frame size. An image that "fills the frame" on an APS-C camera will not fill the frame on a full-frame camera.

 

The next logical question is "why would you care about #2 if cropping the FF image gets you the same image you would have from the crop-sensor camera?" The answer is in Ken's post: pixel density. While there are exceptions, in general, smaller sensors cram more pixels into a given area; that is, they have a higher pixel density. In that case, the image from the crop sensor camera will have more detail than the cropped image from the FF camera because the crop sensor is placing more pixels on the image of the subject. This may not matter if you are just displaying on a screen or printing small, but it can matter in some cases.

 

This is why I almost always use a crop sensor camera (an old 7D) for chasing bugs rather than my much higher quality FF camera (5D IV). I try to shoot very close to maximum magnification, so the image size on the sensor is the same regardless, but the 7D gives me a lot more pixels.

 

This is what people mean when they say that crop sensor cameras have "more reach".

[glen_h]

Before digital, or close enough to before, there were APS SLRs that could use the same lenses as 35mm.

 

But they might not have been popular enough to make a big deal out of the conversion factor.

 

I don't remember half frame cameras with interchangeable lenses, at least not using the same lens mount.

 

For cameras with a non-removable zoom lens, most people just zoom and not think about focal length.

 

As well as I know the history, before 35mm still cameras, there were 35mm movie cameras with

(half frame sized) 18x24mm image and 25mm lenses. When 35mm still cameras came along,

someone doubled that to 50mm, resulting in the popular 50mm lens.

 

Do (or did) movie camera uses ever use 35mm (still camera) equivalent?

For 16mm or 8mm movie cameras?

[rodeo_joe1]

Pixel density..... This is what people mean when they say that crop sensor cameras have "more reach".

But high megapixel full-frame (24x36mm) sensors are now turning that on its head. For Example: The 60 megapixel FF sensor of a Sony a7r4 has a higher pixel-density than the fairly common 24 Mp APS-C sensors - i.e. 26 megapixels over a 16x24mm frame area.

 

Yes there's a cost penalty versus an APS-C camera, but effectively you have two cameras in one. Full-frame for ultimate IQ and when a shallow depth-of-field is wanted, and an APS frame size when you want more 'reach' and more D-o-F.

[glen_h]

As far as I know, Canon full-frame cameras won't mount EF-S lenses.

 

Nikon models like the D850 will mount DX lenses, and with the right option set,

crop a DX sized image and store that. Two cameras in one, without extra work.

 

I believe you can also set DX mode with an FX lens, or FX mode with DX lens,

if you happen to want to do that.

 

(As far as I know, DX zooms will fill an FX frame at some zoom settings.)

[paddler4]

But high megapixel full-frame (24x36mm) sensors are now turning that on its head. For Example: The 60 megapixel FF sensor of a Sony a7r4 has a higher pixel-density than the fairly common 24 Mp APS-C sensors - i.e. 26 megapixels over a 16x24mm frame area.

 

True, although only for a few camera pairs. For example, it's not true of the Canon R5 and R7. For this reason, I often try to persuade people to think about this in terms of pixel density rather than sensor size, but that's unfortunately more complicated.

 

As far as I know, Canon full-frame cameras won't mount EF-S lenses.

 

That is correct. EF-S lenses are constructed for a shorter flange distance.

[Ken Katz]

A Canon R7 has the pixel density that would require a FF sensor of 85 Mp to match. That plus the cost difference ($1,500 vs $3,900) make it a more practical option for the bird/wildlife photographer on a budget. Fuji's anticipated 40MP camera would need a 90mp FF to match up in terms of reach. Your run of the mill m43 camera has a pixel density equivalent to 80Mp FF and the Panny Gh6 has the pixel density of a 100MP FF camera. That said, folk who want to bring back the highest quality images of things that are far away can always buy (and carry) the needed optics to do the job. The Canon RF 1200mm F8 L is only $20k and remarkably, only weighs 7.4 lb!

[q.g._de_bakker]

Yes. I think the confusion stems from two different metrics, both of which are relevant:

 

1. The physical size of the image cast by a lens of any given focal length. Assuming that the sensor is large enough that the image fits, that size is depends only on the focal length of the lens, not the size of the sensor you put behind it.

 

2. The physical size of the image cast by the lens relative to the frame size. Sensor size does affect this because a smaller sensor has a narrower angle of view and hence a smaller frame size. An image that "fills the frame" on an APS-C camera will not fill the frame on a full-frame camera.

 

The next logical question is "why would you care about #2 if cropping the FF image gets you the same image you would have from the crop-sensor camera?" The answer is in Ken's post: pixel density. While there are exceptions, in general, smaller sensors cram more pixels into a given area; that is, they have a higher pixel density. In that case, the image from the crop sensor camera will have more detail than the cropped image from the FF camera because the crop sensor is placing more pixels on the image of the subject. This may not matter if you are just displaying on a screen or printing small, but it can matter in some cases.

 

This is why I almost always use a crop sensor camera (an old 7D) for chasing bugs rather than my much higher quality FF camera (5D IV). I try to shoot very close to maximum magnification, so the image size on the sensor is the same regardless, but the 7D gives me a lot more pixels.

 

This is what people mean when they say that crop sensor cameras have "more reach".

Not so. All this "more reach" is about is angle of view.

People want long lenses to be able to isolate a part of the scene. A crop adds to what increasing focal lengths achieve. More reach.

That you may get as many pixels on some crop sensors as on some full frame sensors is something else. And mind you: more pixels on a crop sensor may sound nice. But it only is nice if the lens resolves fine enough detail, and noise levels remain acceptable.

[paddler4]

Not so. All this "more reach" is about is angle of view.

People want long lenses to be able to isolate a part of the scene. A crop adds to what increasing focal lengths achieve. More reach.

That you may get as many pixels on some crop sensors as on some full frame sensors is something else.

 

Nothing you wrote actual contradicts what I wrote.

 

Take a hypothetical pair of sensors with identical pixel pitches, one crop and one FF. Take the same shot with the same lens from the same location. Crop the latter to the dimensions of the crop. How are the images different? Not at all. You achieve the identical AOV in the completed image, just by different methods.

 

So why do wildlife photographers often prefer to use crop sensor cameras? Depends on the circumstance, but one reason is often pixel pitch.

[glen_h]

 

(snip)

 

So why do wildlife photographers often prefer to use crop sensor cameras? Depends on the circumstance, but one reason is often pixel pitch.

 

All else equal, the larger sensor will be more sensitive, as it has more area to collect light.

 

But sensor technology evolves, so all might not be equal.

 

You need a longer focal length lens to get the same field of view with a larger sensor.

 

The same f/stop value gives you the same amount of light per sensor area,

but for a longer lens, you need a larger real, physical lens diameter.

 

The lens is now longer, larger around, and a lot heavier.

It is harder to hold and to move around.