Digital & F?

[IncompletePete]

When you pop an extender onto a lens, you lose atleast one F stop. So when you put a lens onto a digital body your zoom increases, but does this affect the F stop? :?

[Rayz]

No. F stop remains the same, unless you want to change it in aperture priority mode or manual mode.

As a matter of fact, it doesn't really increase your zoom. It just crops the image giving the impression that the zoom has increased. You would get the same effect cropping a full frame 35mm image on your monitor.

(I assume you're referring to the 1.6 multiplier effect of cameras like the 10D).

[IncompletePete]

No. F stop remains the same, unless you want to change it in aperture priority mode or manual mode.

As a matter of fact, it doesn't really increase your zoom. It just crops the image giving the impression that the zoom has increased. You would get the same effect cropping a full frame 35mm image on your monitor.

(I assume you're referring to the 1.6 multiplier effect of cameras like the 10D).

Cool, that's ok then.

Don't need to think about it just yet, getting an EOS 1N for now 'n a 20D this December :D

[slin100]

While exposure is unaffected by 1.6x cropping factor, DOF is affected due to the greater magnification required to achieve the final output image. This article (http://www.photo.net/learn/optics/dofdigital/index.html) gives you the lowdown.

[Rayz]

Here's an extract from that article you refer to:-

If you use the same lens on a EOS 10D and a 35mm film body and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL

[Jesper]

Here's an extract from that article you refer to:-

If you use the same lens on a EOS 10D and a 35mm film body and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL


That's right. If you take a photo with the 10D and a 35mm film camera from the same point with the same lens, and you cut off the edges of the 35mm photo, it will look *exactly* the same (same DOF, same perspective etc.) as the 10D photo.

However, suppose you take a photo with a film camera and the 10D with the same lens, but you change your position because you want to fill the frame the same way. If you do that, with the 10D you'd need to go further away from your subject to get the same field of view as with film. If you do that, it's as if you're using a longer focal length and the DOF will change.

[slin100]

Here's an extract from that article you refer to:-

If you use the same lens on a EOS 10D and a 35mm film body and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL

Yes, that is true, but that's not a useful fact. People generally use the entire frame of their respective camera's format; people don't crop 35mm film. They compare pictures taken with the same field of view. This implies using a different lens on each camera (e.g. a 50mm on a 10D and a 80mm on a 35mm film camera) to compensate for the different in sensor size on the digicam. Yes, this implies shooting from a different distance, which means the DOF will change. Therefore, the useful extract from that article is this:

For an equivalent field of view, the EOS 10D has at least 1.6x MORE depth of field that a 35mm film camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format need a lens with 1.6x the focal length to give the same view).
If you want to insist on using the same lens on both cameras, then this excerpt applies:

If you use the same lens on an EOS 10D and a 35mm film body, then shoot from different distances so that the view is the same, the 10D image will have 1.6x MORE DOF then the film image
This are a lot of misconceptions about how DOF is affected by sensor size, and the assertion that DOF is the same is only true for a special case. The article I referenced goes into the details quite well without too much math.

[Rayz]

However, suppose you take a photo with a film camera and the 10D with the same lens, but you change your position because you want to fill the frame the same way. If you do that, with the 10D you'd need to go further away from your subject to get the same field of view as with film. If you do that, it's as if you're using a longer focal length and the DOF will change.

Okay! I see what you're getting at. Yes, DoF will change if you change the distance between yourself and the subject. But this applies to any lens on any camera. I think the significant point here, considering the 1.6 factor of the 10D, is for exact equivalence of lens, FoV and DoF, everything has to be multiplied by 1.6.

For example, a 50mm lens at F4 on the 10D will be equivalent to an 80mm lens on full frame 35mm at f6.4 (from the same position). Agreed?

[Muffin Princess]

Woah! Although I perfectly understand everything that's been said in this thread, it all seems a bit complicated! LoL! Who invented digital anyway? It makes things ever so confusing! :P

*NOTE* This is a joke, I am not putting digital down, I rely on digital cameras to earn my living!

Does anyone else hate it when people refer to them as "digicams"? It drives my colleague round the bend!

[Jesper]

Woah! Although I perfectly understand everything that's been said in this thread, it all seems a bit complicated! LoL! Who invented digital anyway? It makes things ever so confusing! :P

*NOTE* This is a joke, I am not putting digital down, I rely on digital cameras to earn my living!

Does anyone else hate it when people refer to them as "digicams"? It drives my colleague round the bend!
It's not complicated at all, all the fuss about the crop factor only exists because people insist on comparing cameras with APS-sized sensors with 35mm film cameras. I thought the word "digicam" was a synonym for compact, point-and-shoot digital cameras (as opposed to DSLRs).

For example, a 50mm lens at F4 on the 10D will be equivalent to an 80mm lens on full frame 35mm at f6.4 (from the same position). Agreed?
Hmmm, I don't know if that's exactly true, could be, but I've never worked out the mathematics.... Here is a nice DOF calculator, in which you can specify your camera type, focal length, aperture, and distance to subject and it will tell you which area will be sharp:

http://dfleming.ameranet.com/dofjs.html

[Jesper]

Woah! Although I perfectly understand everything that's been said in this thread, it all seems a bit complicated! LoL! Who invented digital anyway? It makes things ever so confusing! :P

*NOTE* This is a joke, I am not putting digital down, I rely on digital cameras to earn my living!

Does anyone else hate it when people refer to them as "digicams"? It drives my colleague round the bend!
It's not complicated at all, all the fuss about the crop factor only exists because people insist on comparing cameras with APS-sized sensors with 35mm film cameras. I thought the word "digicam" was a synonym for compact, point-and-shoot digital cameras (as opposed to DSLRs).

For example, a 50mm lens at F4 on the 10D will be equivalent to an 80mm lens on full frame 35mm at f6.4 (from the same position). Agreed?
Hmmm, I don't know if that's exactly true, could be, but I've never worked out the mathematics.... Here is a nice DOF calculator, in which you can specify your camera type, focal length, aperture, and distance to subject and it will tell you which area will be sharp:

http://dfleming.ameranet.com/dofjs.html

Note, there is also a link on the bottom of that page to the equations used, so you can understand the mathematics behind it if you want....

[Jesper]

Hey, what's wrong with this post, I don't see the Edit button on my own post ???

[Rayz]

Jesper,
There's no Canon 10D format on that DoF calculator. APS film is bigger. However, using the basic formula for calculating hyperfocal distance, H = f squared / nC, the maths seems reliable provided you also increase C (circle of confusion) by a factor of 1.6. Since the larger format needs to be enlarged less, the CoC for acceptable sharpness can be greater, thus

50^/4x0.03 = 80^/6.4x0.048 = 20.83 metres

[Jesper]

Jesper, There's no Canon 10D format on that DoF calculator.
Are you sure you looked at the thing? There is a listbox with the text "Film format, digital camera, or custom circle of confusion" to the left side of it. You can choose "Canon 10D" there. ???

[Rayz]

I looked at the thing, but not long enough :D . It seems they have film based cameras in order of format size and digital cameras in alphabetical order. That threw me because my mind was in logical mode :D .

Anyway, the DoF Calculator conforms with the basic equation I've used to determine Hyperfocal Distance, with very minor discrepancies.

However, in my example I used a larger CoC than would be recommended for an 8x12 print viewed from about 10" away. But the principle is the same, ie. multiply everything by 1.6; the focal length, the f stop number and the CoC diameter ..... for same size prints of equal sharpness. (That's going up from the 10D to the 1Ds. Going the other way you would of course divide everything by 1.6 :D ).