17-50 f2.0 vs 24-70 f2.8 - DPChallenge Forums

05/17/2012 08:56:51 AM · #1

Would a 17-50 EF-S 2.0 deliver more light than a 24-70mm f2.8 Fullframe???

05/17/2012 09:03:44 AM · #2

well since you cant use a 17-50 EF-S on a fullframe, is your question would the 17-50/2.0 provide more light on a crop than a 24-70/2.8 on a fullframe?

05/17/2012 09:04:59 AM · #3

Originally posted by mike_311:

well since you cant use a 17-50 EF-S on a fullframe, is your question would the 17-50/2.0 provide more light on a crop than a 24-70/2.8 on a fullframe?

Yes! That's exactly the question

05/17/2012 09:12:41 AM · #4

good question, tricky question, i'm going to say the 2.0 will provide more light to each pixel, possibly not the sensor as a whole.

someone else should chime in with their thoughts.

05/17/2012 09:15:44 AM · #5

Also! The elements on an ef-s 17-50 f2.0 may be similar in size or slightly bigger than a ef 24-70 f2.8 for a full frame.

05/17/2012 11:39:26 AM · #6

bump :)

Canon RF 24-70mm f/2.8 L IS

05/17/2012 11:55:20 AM · #7

based solely only the amount of light projected onto the sensor, the 2.8 will deliver more light.

a FF sensor has 2.06x the total area of an APS-C and the F2 lens will deliver only 1.4X the amount of light over an f2.8.

kirbic

Canon EOS R5

05/17/2012 12:30:07 PM · #8

Well, unless y'all are aware of a product announcement that I am not (very possible) I'm pretty sure a 17-50/2.0 is a hypothetical. But hypothetically then, an f/2.0 lens is f/2, no matter what camera it is mounted on, and will always be a stop faster than an f/2.8 lens.
It's true that the image circle projected by the hypothetical 17-50/2.0 is smaller, but the "f/2.0" in the designation takes this into account. Look at it this way. The EF-S equivalent of any EF lens will need a 1.6x shorter focal length, and can have smaller optical components, while still maintaining the same maximum aperture. This is because the image circle needed is smaller; the design takes into account the smaller image circle, and the max aperture reflects this.
One interesting possibility is the idea of a "negative teleconverter" that would reduce the image circle of an EF lens to EF-S size. This focal length reducer would in effect make an EF-24-70/2.8 lens into an EF-S 15-44/2.0 lens. There is currently a patent (US Patent 5,499,069) that I believe is issued to Kodak that covers this type of "wide converter." It expires in 2014. Unfortunately, it may be that such a wide converter would need to be matched to a specific lens and so not usable for a range of lenses.

Edit for typo

Message edited by author 2012-05-17 12:31:30.

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Canon

05/17/2012 01:12:39 PM · #9

Originally posted by kirbic:

Yay for correct knowledge!!!! yes, any lens transmits the same amount of light at a given f stop.. that is why we use them as a measure... a 24-105 and a 50mm f1.2 both transmit the same amount of light at 50mm @f 5.6, and have the same depth of field.. they will have differing sharpness, bokeh, ect, but they will meter the same.. when you put an ef lens on a crop camera, you are only using the center of the field of view.. the light that does not hit the sensor is wasted..

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Canon

05/17/2012 01:17:59 PM · #10

Originally posted by mike_311:

f2 is a whole stop faster than f2.8.. therefore it is 2x the light..

05/17/2012 01:30:52 PM · #11

Originally posted by apercep:

f2 is a whole stop faster than f2.8.. therefore it is 2x the light..

pardon my ignorance, but isn't it fractional?

ie f2 is 1/2 and f2.8 is 1/2.8?

if so, how is a 2.8 twice the light as a 2.0?

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Canon

05/17/2012 02:01:37 PM · #12

Originally posted by mike_311:

Originally posted by apercep:

f2 is a whole stop faster than f2.8.. therefore it is 2x the light..

pardon my ignorance, but isn't it fractional?

ie f2 is 1/2 and f2.8 is 1/2.8?

if so, how is a 2.8 twice the light as a 2.0?

well, it is a fraction of the diameter of a circle. the actual amount of light is a fraction of a square root..

for example: a 50mm lens.. @ f2.0 = an actual aperture of 25 mm. the area of the aperture is 491 sq.mm
a 50mm lens.. @ f2.8 = an actual aperture of 17.8mm. the area of the aperture is 250 sq.mm
which is approximately half the area, and half the light..

05/17/2012 02:26:26 PM · #13

Where am I going with this? Speculation on matching the "manufacturing cost" of say an ef-24-70, to produce a faster ef-s zoom. I'm assuming size would be a major stumbling block in creating a full frame 24-70mm 2.0

I actually see a patent for a Canon 55-110 f2.0.

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Canon

05/17/2012 02:31:31 PM · #14

if you look at the micro 4/3 stuff, there are some 2.0 zooms.. your speculation is plausible.. and so is your assumption about FF 2.0 zooms.. just as an example of what aperture size can do to overall lens size just compare the 300 f4l to the 300 f2.8l..

Message edited by author 2012-05-17 14:35:24.

Art Roflmao

Canon EOS-6D Mark II

Canon EF 24-105mm f/4.0L IS

05/17/2012 02:59:53 PM · #15

Originally posted by mike_311:

someone else should chime in with their thoughts.

Eeeeek! MATH! *runs*