focal length multiplication

[Arnie1]

Can anyone confirm something....I'm a little confused here.

On a 20D or any digi SLR that doesn't have a full size chip I understand that lens focal length is x1.6.

But will this also multiply the f number of the lens by 1.6?

e.g my 17-40 F4 is infact giving me more like F5?

[PacAce]

No, the aperture is not affected by the 35mm equivalent factor.

[Al Nakib]

TCs (teleconverters) increase focal length and increase the aperature value (becomes smaller), focal length multipliers do not ;)

[wilflee]

On a 20D or any digi SLR that doesn't have a full size chip I understand that lens focal length is x1.6.
That statement isn't exactly correct.

The focal length isn't multiplied by 1.6x.

Instead, the area of the light sensor in these cameras is 1.6x smaller than the area of a 35mm full-frame camera.

In other words, a 50mm lens on a 20D will provide the same magnification, perspective, relative size of objects at various distances from the film plane and depth of field as it does on a full frame 35mm camera. The only difference is the field of view shrunk by 1.6x. So, the field of view is appx the same as an 80mm lens. But everything else is like 50mm. Therefore, the max aperture does not change.

Picture, if you will, a slide projector projecting an image on a wall. Now, mount a screen on the wall that's 1.6x smaller than the original size of the projected image. That's what you lose with the 20D's smaller light sensor.

[tim]

You can ignore the crop factor, and unless you have many years experience with 35mm film cameras, I suggest you do. It doesn't change anything to do with F stops, shutter speeds, or anything else, you just see a smaller area through your viewfinder.

[JaertX]

That statement isn't exactly correct.

The focal length isn't multiplied by 1.6x.

Instead, the area of the light sensor in these cameras is 1.6x smaller than the area of a 35mm full-frame camera.

In other words, a 50mm lens on a 20D will provide the same magnification, perspective, relative size of objects at various distances from the film plane and depth of field as it does on a full frame 35mm camera. The only difference is the field of view shrunk by 1.6x. So, the field of view is appx the same as an 80mm lens. But everything else is like 50mm. Therefore, the max aperture does not change.

Picture, if you will, a slide projector projecting an image on a wall. Now, mount a screen on the wall that's 1.6x smaller than the original size of the projected image. That's what you lose with the 20D's smaller light sensor.

carefull...all was correct except the dof. It does change with smaller sensors...I was corrected on this point a while back myself.

[ron chappel]

The f number doesn't change because it's based on an absolute measure of light ,not a measure based on area
I hope that's not confusing

[Arnie1]

OK, thanks guys.

But! Will there be any difference in the DOP as comapred to using a full size chip?

[Andy_T]

But! Will there be any difference in the DOP as comapred to using a full size chip?

YES ... but it will be negligible, compared to the very large difference in DOF you get from using a small-sensor digicam.

There were some very technical discussions some time ago, but you might not learn very much from looking them up unless you want to take a very analytical approach here:wink:

Best regards,
Andy

[Sailare]

Think of it as "In Camera Cropping" instead of magnification since there is none.

If you have a Canon film camera and say a 20D both with 50mm lens attached and look through the viewfinder (the lens) the objects in both are exactly the same size (no magnification) but the 20D frame is smaller (cropped)

This cropping which generally seems to be viewed as a negative is actually a benefit in a lot of cases. A lens that gets a bad or mediocre review on a full 35 frame can actually be very good on a digital. Lens in general have more problems at the edges and the digital camera is cropping off that section. Just about all lens review, except the newer "made for digital" types are rated on full frame film cameras and its never mentioned. Give it some thought when you are considering that next lens.

[tucked]

You can ignore the crop factor, and unless you have many years experience with 35mm film cameras, I suggest you do. It doesn't change anything to do with F stops, shutter speeds, or anything else, you just see a smaller area through your viewfinder.

First of all... THANK YOU Tim. You don't know how many of your posts here have helped me. You take the time to answer everything. (Many others here too, but everywhere I look, tim has an answer). I totally agree here. I have never used a slr before my d-reb. As far as I care, my 85mm f/1.8 is 85mm. That is how I compare it to my 18-55mm. 30 mm more reach... not 85 x 1.6 - 55 x 1.6 = ??? I understand if you have 35mm equip or equip w/o without the 1.6 crop factor also, you need to understand how your lenses will behave differently on each body. just my $.02.