Just a General question

[msmith1]

If I were going to use an EF lens on a camera that takes EF or EF-S lenses (Rebel T7i) you multiply the focal length by 1.6 to get the focal length the sensor sees. Does the EF-S lens that is made for that camera follow the same rule? Mostly just curious.

[Waddizzle]

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@msmith1 wrote:

If I were going to use an EF lens on a camera that takes EF or EF-S lenses (Rebel T7i) you multiply the focal length by 1.6 to get the focal length the sensor sees. Does the EF-S lens that is made for that camera follow the same rule? Mostly just curious.

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Yes.  The only optical difference is the size of the image circle projected onto the image sensor.

[msmith1]

Works for me. Thanks

[FloridaDrafter]

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@msmith1 wrote:

If I were going to use an EF lens on a camera that takes EF or EF-S lenses (Rebel T7i) you multiply the focal length by 1.6 to get the focal length the sensor sees. "Does the EF-S lens that is made for that camera follow the same rule? Mostly just curious."

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From what I understahd, and you will find conflicting informstion on this. Some say the 1.6 factor should be aplied to both EF and EF-S lenses when used on a cropper. Canon has two deffinitions of the "S" in EF-S. Depending on what Canon rep you talk to, it refers to "Small focus circle" or "Short back focus". Either way the image circle is smaller to get more image on, as wadizzle pointed out, the cropper sensor. The image from the EF-S will project a small image circle on the APS-C sensor. I ran across a crop factor for the EF-S lens, but dont recall where. For example, an EF-S 18mm on a crop camera (1.6) will equall a 22mm FOV that you would get on a FF (35mm) sensor. So even though the EF-S was designed for the croppers, it still has a crop factor and different FOV as compared to a FF camera. It's not the 1.6 calc, but there is a factor non the less, I just don't recal (something like 1.3).

To do this, Canon designed the EF-S so that the rear element protrudes farther into the camera body (short back focus), even though the flange is still 42mm, which is why they will not fit a FF body as the mirror will hit the back element of the EF-S. They also designed them to have fewer elements which makes them lighter and they can produce them at a cheaper cost (they are generally plastic). Also, emphasis in design is more to the center of the image circle so with an EF-S lense, you will see some corner darkening. With 3rd party "S" lenses, it is really noticable.

Personally, I don't even consider any of this. We have both types of cameras, and we just don't think about it. We know what the lenses will do and that is what is important. I think too much emphasis is put on this "crop factor" thing. We have an EF 70-300mm f/4-5.6 IS USMnano II that has an LCD readout that shows FF equvilant FOV when on a cropper. My wife uses it on an R6 but bought it for her T7i. She is disabled and need a light rig, both the T7i and R6 with the aforememtioned lens are perfect for her because they are light.

Newton

[rs-eos]

Crop factor is important in order to understand what the field of view will be.  For example, say you're shopping for a standard focal length.  You read that's typically around 50mm, so you decide to invest in a 50mm.  This will give you a standard field of view on full-frame, but short telephoto on an APS-C sensor.

When wanting to go into wide angle, this is why for APS-C, one is better off getting something in the 14 to 18mm range as opposed to 24mm.  Since 24mm will produce field of views of close to 40mm.  Whereas that 14-18 range will be 22-29mm.

The flip-side is also useful at the telephoto end of things.  e.g., I'm now looking at the EOS C70 (approx 1.5 crop) along with either a 24-70mm (gives 105mm equivalent at the tele end), or the 24-105 (gives ~160mm at the tele end).

And, extremely useful when you want to match field of views between equipment with different sensor sizes.

[ebiggs1]

"... extremely useful when you want to match field of views between equipment with different sensor sizes."

I was involved with folks using all sorts photographic medium for over 40 years.  I never heard a medium or large format guy say, "Hmm, wait a minute, let me figure out the crop factor before I select a lens to use." They just don't do it. They know what lens to use.  

[ebiggs1]

"We know what the lenses will do and that is what is important. I think too much emphasis is put on this "crop factor" thing."

Hallelujah!  Crop factor was a joke from the beginning and it remains a joke today.  Know what your lens does on whatever camera body you use it on.

[ebiggs1]

"Does the EF-S lens that is made for that camera follow the same rule?"

The best thing to know is a lens is a lens is a lens.  They do not know what camera body they are attached to.

[msmith1]

Thanks for all the input. As stated, I was just curious. I'll use whatever lens gives me what I'm looking for.

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@ebiggs1 wrote:

"The best thing to know is a lens is a lens is a lens."  

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[FloridaDrafter]

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@msmith1 wrote:

Thanks for all the input. As stated, I was just curious. I'll use whatever lens gives me what I'm looking for.

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@ebiggs1 wrote:

"The best thing to know is a lens is a lens is a lens."  

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And, thanks to you. It's a crazy topic with lots of differing opinions. BTW, curiosity is a good place to start, LOL!