Canon APS-C 1.6 multiplier.

[YosemitePaul]

Perhaps a silly question.

I've an EOS 7D with a 10-22mm lens.
As this is an EF-S lens does this mean it is actually 10mm or is it; using the 1.6 multiplier equivalent to 16mm?

I ask, as I've also just bought a 5D MkII and was contemplating a WA lens, perhaps the 16-35mm (if I can find one at a good price).

What I'm asking is basically, will the focal length be the same, or is the 10mm actually wider.

Thanks,

Paul.

 

[pete.rush]

Perhaps a silly question.

I've an EOS 7D with a 10-22mm lens.
As this is an EF-S lens does this mean it is actually 10mm or is it; using the 1.6 multiplier equivalent to 16mm?

I ask, as I've also just bought a 5D MkII and was contemplating a WA lens, perhaps the 16-35mm (if I can find one at a good price).

What I'm asking is basically, will the focal length be the same, or is the 10mm actually wider.

Thanks,

Paul.

You still have to apply the crop factor to the lens, so its equivalent to a 16-35mm lens on a full frame sensor. Its all to do with the angles of light and size of the sensor.

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

The "S" in EF-S stands for "short back focus", which means that the rear element of the lens is closer to the image sensor than on regular 35 mm SLR cameras.

 

[hunnymonster]

The focal length doesn't actually change - it's always a 10mm lens (in your example) but due to the change in the sensor size it gives the same field of view as a lens 1.6x longer would on a full frame. So the 16mm lens on the 5DII would (should) give the same FOV as 10mm on the 7D.

 

[iPhoto]

Perhaps a silly question.

I've an EOS 7D with a 10-22mm lens.
As this is an EF-S lens does this mean it is actually 10mm or is it; using the 1.6 multiplier equivalent to 16mm?

I ask, as I've also just bought a 5D MkII and was contemplating a WA lens, perhaps the 16-35mm (if I can find one at a good price).

What I'm asking is basically, will the focal length be the same, or is the 10mm actually wider.

Thanks,

Paul.

Hi Paul,

Forget the 10-22 for a moment because that as you know is an EFs lens and will only fit on your crop body. Take something like the EF50mm. Put it on your 7D and its equivalent to the field of view of an 80mm (50 x 1.6 =80) on a 35mm film camera. Put the same lens on your Full Frame 5D and its equivalent to a 50mm field of view on a 35mm film camera. The lens however in both cases still has 50mm written on the outside. The same applies to EFs lenses like the 10-22. When its on your 7D it has a field of view equal to a 16-35 would have on a 35mm film camera (or on your 5D if it would fit.

So if you want the same field of view from a lens on your 5D2 to that you got from the 10-22 on your 7D you need to get an EF lens in the 16-35 range.

Clear as mud ?

Mark

 

[BeeJayEff]

The lens however in both cases still has 50mm written on the outside.

And as I understand it, has the same DoF, regardless of sensor size. Correct ?

 

[arad85]

And as I understand it, has the same DoF, regardless of sensor size. Correct ?

Don't go there DoF is ONLY apparent when you render the image and it depends how big you render the image (and consequently how much bigger you are making it to the sensor) taht determines DoF. Sensor size DOES come into it accordingly, but it's really difficult to describe without sitting down in front of someone with a piece of paper and pen....

 

[Phil V]

Can open - worms everywhere!

Seriously, for your sanity, always insert the term 'field of view'. Focal length is a constant.

Loads of people never get the focal length issue because in the digital age, everyone including the manufacturers uses the term 'focal length multiplier', which is short hand and overly simplistic. And in the long run causes more problems because of this.

 

[HoppyUK]

Perhaps a silly question.

I've an EOS 7D with a 10-22mm lens.
As this is an EF-S lens does this mean it is actually 10mm or is it; using the 1.6 multiplier equivalent to 16mm?

I ask, as I've also just bought a 5D MkII and was contemplating a WA lens, perhaps the 16-35mm (if I can find one at a good price).

What I'm asking is basically, will the focal length be the same, or is the 10mm actually wider.

Thanks,

Paul.

Put it this way, if you take a shot with the 7D and 10-22 lens at 10mm, and then from the same position with the 5D2 and 16-35 lens at 16mm, the two images will be framed identically. Same at 22mm and 35mm respectively, and all focal lengths inbetween pro-rata.

While the focal lengths are as marked, the 7D has a smaller sensor that records less of the image - as if it was 'cropped' from the midddle of the 5D2 frame. The difference is a linear factor of 1.6x, which in area terms is 1.6 squared, ie 2.56x. Basically the 7D's sensor is a bit under half the area of the 5D2.

Correspondingly, at a given f/number, the 7D image will have greater depth of field, to the tune of a fraction over one stop. Using the crop factor again, multiply the f/number by 1.6x, eg f/5.6 on the 7D would deliver the same DoF as f/9 on the 5D2.

 

[YosemitePaul]

WOW,

Thanks folks, through the answers, 'I can see clearly' now.

It is what I perhaps thought that in effect 10mm on the 7d equates to 16mm on the 5d.

Now, do I try and save and find a 16-35 or buy the cheaper 17-40.

Dilemma time.

Thanks again.

 

[HoppyUK]

WOW,

Thanks folks, through the answers, 'I can see clearly' now.

It is what I perhaps thought that in effect 10mm on the 7d equates to 16mm on the 5d.

Now, do I try and save and find a 16-35 or buy the cheaper 17-40.

Dilemma time.

Thanks again.

Glad you've got it

You have to want/need f/2.8 very badly to get the 16-35. 17-40 is a great lens (and takes more sensibly sized 77mm filters ).

 

[woof woof]

Sensor size DOES come into it accordingly, but it's really difficult to describe without sitting down in front of someone with a piece of paper and pen....

Personally I find that taking pictures is much better than resorting to pen and paper which is IMVHO where people get bogged down on this issue. Anyone with two cameras with different sensor sizes and lenses that'll fit both should be able to sort FoV AND DoF questions out in just a few minutes, without the need for any trees to die

 

[arad85]

Personally I find that taking pictures is much better than resorting to pen and paper which is IMVHO where people get bogged down on this issue.

No they don't

Anyone with two cameras with different sensor sizes and lenses that'll fit both should be able to sort FoV AND DoF questions out in just a few minutes, without the need for any trees to die

Yes, you can do the same experiment on a computer screen. Hence the word RENDER in my original post. I've done the experiment. The maths and theory work - you don't even need different images to do it either - just display the same image at different sizes and the DoF changes