Simple question regarding EF-s lens on crop

[Invertalon]

Hey everyone,

I am still relatively new to the dSLR and had a question regarding EF-s lenses and the crop factors of lenses.

My XSI has a 1.6x crop factor, so to find my true focal length I would multiple my lens by 1.6... Such as my EF 70-300mm IS, which turns into 112-480mm.

But with EF-s lenses, such as my EF-s 17-85mm IS, would the focal length be 17-85, or 27-136mm? Confused since the EF-s lenses are made for crop-style SLR's.

Appreciate the help!

[bjyoder]

Focal length is focal length is focal length. Period. It does not change if the lens is meant for a point and shoot, a crop D-SLR, a FF D-SLR, or even a medium format camera. The Field of View is the only thing that changes, based on the camera format.

So, in reality, your 70-300 IS is still 70-300mm focal length, but has the same Field of View as a 112-480mm focal length on a FF camera.

Check out the link in my sig (on page 2) for a longer explanation by me, or check the lens forum for a different way of explaining.

[Invertalon]

Ahh yes... I knew that and should of just elaborated more clearly. Does the Field of View take on the crop factor if it is a EF-s lens? Or will only the EF lenses do so?

[bizzum]

Ahh yes... I knew that and should of just elaborated more clearly. Does the Field of View take on the crop factor if it is a EF-s lens? Or will only the EF lenses do so?

They both take on the crop factor. The FOV on an EFs lens of a given length would be exactly the same as an EF lens of the same length. ie. The FOV of the EFs 17-55 on the 17 end would be the same as the EF 17-40L at the 17 end.

[Invertalon]

Alright, thanks!

I need to look into the purpose of the EF-s lenses... But ill search that, thanks!

[SkipD]

Hey everyone,

I am still relatively new to the dSLR and had a question regarding EF-s lenses and the crop factors of lenses.

My XSI has a 1.6x crop factor, so to find my true focal length I would multiple my lens by 1.6... Such as my EF 70-300mm IS, which turns into 112-480mm.

But with EF-s lenses, such as my EF-s 17-85mm IS, would the focal length be 17-85, or 27-136mm? Confused since the EF-s lenses are made for crop-style SLR's.

Ahh yes... I knew that and should of just elaborated more clearly. Does the Field of View take on the crop factor if it is a EF-s lens? Or will only the EF lenses do so?Any lenses that you can mount to your camera, set to the same focal length, will provide the same field (angle) of view.

The EF-S lens family has a different design criteria which is intended to make short focal length lenses less expensive to design and build. There are two basic design factors that set EF-S lenses apart from Canon EF lenses.

The first difference is that the EF-S lens' rear element is allowed to extend further into the mirror box, getting the rear element closer to the sensor than is allowed for EF lenses.

The second difference is that the EF-S lens projects a narrower cone of light onto the sensor than an EF lens would. This is because APS-C lenses have a smaller sensor than cameras which the EF family of lenses was designed for (such as 35mm film cameras).

The "true" focal length of any lens is what's printed on it. There are no lens manufacturers that I am aware of who print "equivalent" focal lengths on any of their lenses.

[Invertalon]

Thanks for all the info, really appreciate the help!

[PFDarkside]

EF-S lenses are designed for the smaller sensor. The focal length is the same, but since it's designed for a crop sensor, the image circle is smaller than an EF lens' image circle.

Take an EF 24-70mm and an EF-S 17-55mm lens. Set them both to 35mm and you'll get the same field of view on your crop sensor camera. (If you could mount them both on a full frame camera, set to the same focal length, you'll get the same field of view, but the 17-55mm will vignette heavily, as it's designed for the crop sensor)

[RDKirk]

Ahh yes... I knew that and should of just elaborated more clearly. Does the Field of View take on the crop factor if it is a EF-s lens? Or will only the EF lenses do so?

You only have an APS-C camera, right? If so, your field of view is what it is. The focal length is what it is and your field of view is what you see in the viewfinder. There is no crop factor for you to consider if that's the only format you own.

The thing to know is the "normal" focal length for your camera, which is about 28mm. Everything else is either shorter than normal (wide angle) or longer than normal (telephoto). If you ever need to make a comparison between your format and any other, you only need to know the factor from the normal focal length for that format.

For instance, the "normal" focal length for the 60x45mm format is 70 or 80mm. If you see a photograph taken with a 180mm lens in 60x45mm format, you know that lens was about twice its normal focal length. That would compare to a lens approximately twice your normal focal length, around 60mm.

The normal focal length for the 24x36mm focal length is about 50mm. If you see a photograph taken with a 24mm lens on the 24x36mm format, you know that is about half its normal focal length. That would compare to a lens approximately half your normal focal length, about 14mm.

[SkipD]

Hey everyone,

I am still relatively new to the dSLR and had a question regarding EF-s lenses and the crop factors of lenses.

My XSI has a 1.6x crop factor, so to find my true focal length I would multiple my lens by 1.6... Such as my EF 70-300mm IS, which turns into 112-480mm.

But with EF-s lenses, such as my EF-s 17-85mm IS, would the focal length be 17-85, or 27-136mm? Confused since the EF-s lenses are made for crop-style SLR's.Just out of curiosity, do you know where acquired the information you've posted here? I just had the idea that it would be interesting to try to figure out how new photographers get so radically confused regarding the APS-C format cameras and the so-called "crop factor".

Many new photographers seem to believe that focal length of an EF lens actually changes when the lens is mounted on an APS-C format camera. Is the misinformation coming from the salespeople selling the cameras? Is it coming from other relatively uninformed photographers? I'd really like to know.

Thanks.

[Chrazer]

Could it come from the way they sell P&S cameras and talk about the zoom factor, like my boss is so proud of her nikon P90 with it's 24X optical zoom. I can see that this thinking can lead to believing that focal length is a ratio and not a physical property. Like length or weight.

[RDKirk]

Just out of curiosity, do you know where acquired the information you've posted here? I just had the idea that it would be interesting to try to figure out how new photographers get so radically confused regarding the APS-C format cameras and the so-called "crop factor".

It's in the manufacturers' marketing documents.

[SkipD]

It's in the manufacturers' marketing documents.The stuff about multiplying a focal length to get a "true" focal length surely is not in the manufacturer's marketing documents. There's also nothing there that would tell anyone that EF-S lens focal lengths are any different from EF focal lengths. :rolleyes:

[nemo man]

gawd... if you want to prove this...

get a lens, any non-telephoto lens, stick it on a table (minus the camera) near a white wall and point the front to a bright window. The room needs to be low-light. The image of the window and outside will be projected onto the wall upside down (don't worry) after you move the lens forward/back a bit to get it in focus. Stick a business card against the wall. Image projected onto business card. Measure from front lens glass to the business card. That is the focal length. Cut business card in half (to simulate a crop factor sensor) Hey! what do you know, the image is still in focus... ergo... the focal length is the same. But, the field of view is changed as the image will overspill the half card.

Measuring the focal length doesn't work with some telephoto lens as they are compressed internally to keep the physical lengh of the body short. But any basic lens will do. This is one that you can try at home.

[20droger]

As i've said before, there is nothing in photography that has caused more misunderstanding, confusion, and downright error than the term "crop factor."

"Crop factor" is a marketing term, and has absolutely nothing to do with how a camera takes pictures. A camera takes the pictures it takes. It does not take pictures equivalent to those taken by another camera.

A case in point. Presume a Canon SX10 IS p&s camera (good camera!). This camera has a 1/2.3" sensor with a 4:3 aspect ratio and a 5-100mm lens (35mm equivalent 28-560mm). Published data.

First, this camera cannot take a picture equivalent to one taken by a 35mm camera because the aspect ratio is different (4:3 versus 3:2). But we'll ignore that.

The sensor on this camera has a diagonal of approximately 7.7mm. Compare this with a 35mm camera, which has a film diagonal of 43.3mm. This camera has a "crop factor" of 5.6.

With crop factor of 5.6, setting this camera's lens to 8.9mm should produce an image that is equivalent to one take with a 35mm camera with a 50mm "normal" lens.

It does not!

It produces an image whose angle of view is equivalent to that of the 35mm camera, but everything else about the image is different!

The biggest single difference (but not the only difference) is the depth of field. The depth of field is that of an 8.9mm lens, which is nowhere near that of a 50mm lens. The bokeh of the SX10 image is virtually non-existent. That alone, prevents the SX10 from producing an image equivalent to that of a 35mm camera.

There's a reason why studio photographers rarely (if ever) use SX10s for portraiture.

The images captured by an SX10 with its 5-100mm lens are not, and can never be, equivalent to the images captured by a 35mm camera with a 28-560mm lens. Period. Only the angles of view can be equivalent.

And we won't even get into image quality (as if the lens of the SX10 could compete with the EF 500mm f/4L IS USM, or the sensor of the SX10 could compete with that of the EOS-1Ds Mark III for resolution and noise)!

While not as extreme, the same concepts apply to the APS-C cameras versus the FF digital cameras. The difference in sensor size causes a difference is angle of view. Nothing else.

Now, unless a person is using the same lens on cameras with different sensor sizes, what possible difference can it make what a camera's "crop factor" is? If you have only one camera, you get the images a given lens captures on that camera. Period. You do not get the images that lens may capture on a different camera.

God, I hate "crop factor"!!!

[JeffreyG]

I need to look into the purpose of the EF-s lenses... But ill search that, thanks!

Most of the EF-S lenses occupy a position for 1.6X body shooters that otherwise would not exist and which would be very expensive in EF mount.

For example, many FF shooters like to have an ultra wide angle lens like the EF 17-40L. This needs a lens in the 10-20mm range, which would be very difficult to make if it had to cover the full FF sensor (which all EF lenses must do). So we get the EF-S 10-22 to serve as the 1.6X shooters UWA zoom.

The EF-S 17-85 IS is the 1.6X version of the EF 28-135.

The EF-S 17-55 is the 1.6X version of the EF 28-70/2.8L

The EF-S 18-55 is the 1.6X version of the EF 28-90 1:4-5.6

[silverstar189]

just to clarify then, a 17-85 on a 1.6x body will have the same field of view as a 28-135 on a full frame body?

[jacuff]

The "true" focal length of any lens is what's printed on it. There are no lens manufacturers that I am aware of who print "equivalent" focal lengths on any of their lenses.

I have a Casio EX-F1 that has... "12x OPTICAL ZOOM 36 - 432mm 35mm EQUIV." printed on the lens. ;)

[SkipD]

just to clarify then, a 17-85 on a 1.6x body will have the same field of view as a 28-135 on a full frame body?Not precisely, but close.

If the ratio of the formats is exactly 1.6 (which it is not and can vary a little from camera model to camera model), the 35mm equivalent of the 17-85 (on an APS-C camera) would be 27.2-136.

[silverstar189]

Not precisely, but close.

If the ratio of the formats is exactly 1.6 (which it is not and can vary a little from camera model to camera model), the 35mm equivalent of the 17-85 (on an APS-C camera) would be 27.2-136.

thanks! if i'm using a 17mm ef-s lens on a 1.6 crop at the moment though, what focal length would give me the same 17mm field of view on the 1.6, on a 1.3 and a full frame body? i think i'm being a bit dim today.....

[D Thompson]

thanks! if i'm using a 17mm ef-s lens on a 1.6 crop at the moment though, what focal length would give me the same 17mm field of view on the 1.6, on a 1.3 and a full frame body? i think i'm being a bit dim today.....
17mm on 1.6 = 27.2
21mm on 1.3 = 27.3
28mm on FF = 28

[jacuff]

17mm on 1.6 = 27.2
21mm on 1.3 = 27.3
28mm on FF = 28

The question asked if he was using a 17mm EF-S on a 1.6x crop, so the answer should be

To get really similar angle of views:
17mm on an APS-C
20.9 mm on an APS-H
27.2mm on a Full frame

It always comes down to symantics. Because 17mm = 17mm no matter how you slice and dice it.

[D Thompson]

The question asked if he was using a 17mm EF-S on a 1.6x crop, so the answer should be

To get really similar angle of views:
17mm on an APS-C
20.9 mm on an APS-H
27.2mm on a Full frame
Excuse me for being a fraction off in my answer :rolleyes:.

[jacuff]

Excuse me for being a fraction off in my answer :rolleyes:.LOL. I said it comes down to symantics, here is what I mean..

17mm on 1.6 = 27.2
21mm on 1.3 = 27.3
28mm on FF = 28

17mm on 1.6 = 17mm
21mm on 1.3 = 21mm
28mm on FF = 28mm

Focal length doesn't change. Really it's the format that changes. To normalize things, we talk about equivalent angle of views, but even then that's sort of a misnomer.

[silverstar189]

thanks for answering that for me, i've been trying to get my head round it all day :-p
edit: just so i know, how did you work that one out?

[D Thompson]

Focal length doesn't change. Really it's the format that changes. To normalize things, we talk about equivalent angle of views, but even then that's sort of a misnomer.
Agree. My answer was the equivalent/whatever which was the question. 17 is 17 is 17.;)
thanks for answering that for me, i've been trying to get my head round it all day :-p
edit: just so i know, how did you work that one out?
Simple math.
a * b = c (17 * 1.6 = 27.2)
c / a = b (27.2 / 17 = 1.6)
c / b = a (27.2 / 1.6 = 21)

[SkipD]

17mm on 1.6 = 27.2
21mm on 1.3 = 27.3
28mm on FF = 28

Agree. My answer was the equivalent/whatever which was the question. 17 is 17 is 17.;)

Simple math.
a * b = c (17 * 1.6 = 27.2)
c / a = b (27.2 / 17 = 1.6)
c / b = a (27.2 / 1.6 = 21)In both posts, you were trying to provide the "35mm equivalent" focal lengths, but that was NOT what the question was about.

The question was....

thanks! if i'm using a 17mm ef-s lens on a 1.6 crop at the moment though, what focal length would give me the same 17mm field of view on the 1.6, on a 1.3 and a full frame body? i think i'm being a bit dim today.....

The answer is:

ANY 17mm focal length lens used on the APS-C camera provides the same field of view. It does not matter whether the lens is an EF-S design or an EF design. 17mm is 17mm is 17mm.

Thus, here are the equivalent focal length lenses that will provide the same field of view as an EF-S lens set to 17mm on an APS-C format camera:

-------Camera format:-----------Focal Length:
APS-C (the so-called "1.6 crop") - 17mm
APS-H (the so-called "1.3 crop") - 20.9mm
35mm (the so-called "Full Frame") - 27.2mm


To Dennis: The question was asking what focal lengths mounted to each of the three format cameras would provide the same field of view on each of the cameras with the reference being 17mm on an APS-C format camera. Your answers were wrong in a couple of ways. First, you didn't answer the question. Secondly, when referring to "35mm equivalent" focal lengths, you really need to state that categorically. The focal length of any lens, on any camera, is the focal length marked on the lens.