Aperture Comparison between Fixed lens & DSLR

[dimitrz]

Note sure wether this is the right forum - anyway here goes

Hi Gang,

Just found the answer to something I was searching for a long time , it’s a very interesting and useful information so being the nice guy I am, I thought I’ll share it with you guys just incase someone else ever requests the same.

I was looking for the comparison aperture value between a SLR & Fixed lens camera like my Sony DSC H2.

(Note : The values are approximate & may change based on camera specification.)

Wulf - as clarified by the discussion below, this chart explains why point and shoot cameras can't easily play with the blurred background effects enjoyed by DSLR owners. f/2.8 is f/2.8 - a big hole letting in lots of light -but other factors also come into play

Fixed Lens / DSLR (sorry the table formating is not holding)

f/2.8 = f/11

f/4 = f/16

f/5.6 = f/22

f/8 = f/32

f/11 = f/64 (yes a whooping f/64 which no DSLR can beat :-) ) That reflects into awesome DOF ability


Note : Everything which has a Up has a Down and that in this case sadly is the largest aperture which is only as big as f/11 :-( , That translates into a serious handicap for low DOF photography (read less blurring of background at large aperture )


Cheers and feel free to add, comment & provide feedback on the topic.



Dimitrz

[vandergus]

Guess you'll have to take up landscape photography to take advantage of that enormous DOF

[Taallyn]

That large of DoF is very useful in macro photography.

[sk66]

Ok, I'm a little confused. How can f2.8 = f11? I do understand f-stop, basically the number= the number of times that size opening could fit into the overall lens opening. i.e. f11 means the opening at that setting is 1/11th of the total possible, it would fit into the maximum opening 11 times. (larger f-stop number= smaller opening= greater DOF)
But that raises it's own question for me....Isn't the f-stop then a particular percentage of ONLY that particular lens or similar lenses? The answer is obviously yes, so then you can not directly compare f-stop between lenses unless they are VERY similar. That's something of a revelation for me....and I've been taking photo's for decades.....
Guess I'm just not too into the technicalities of photography...(that's odd for me, I'm pretty anal)

[Taallyn]

It is due to the size difference between the compact camera and a frame of 35mm film. Because the imaging area is a different size, the effective aperture and focal lengths are different. To get them to a common number for comparison, you convert the smaller frame's values up to the 35mm equivalent using the "crop factor". The same goes for DSLRs, although the conversion ratio is quite a bit closer. Cropped DSLR sensors have a slightly greater DoF than full frame 35mm film/sensors. Most users can't tell the difference though in the DoF.

[geotography]

Okay, I want to ask, and I mean this sincerely, why should we care about that particular technical point relative to making go photographic compositions? I don't mean DOF and such...that's hugely important...but why do we care about the differences. One knows and continues to learn what his or her camera can do.

[Taallyn]

It is important for owners of point and shoot cameras to understand why their cameras don't give the "nice, creamy backgrounds" at their camera's f/2.8. The reason is that their camera's f/2.8 is equal to a different aperture for a full frame 35mm camera. Thus, their DoF will be quite a bit larger at any given aperture.

There have been a couple of questions about this in the past week or so.

[geotography]

Taallyn posted:

It is important for owners of point and shoot cameras to understand why their cameras don't give the "nice, creamy backgrounds" at their camera's f/2.8. The reason is that their camera's f/2.8 is equal to a different aperture for a full frame 35mm camera. Thus, their DoF will be quite a bit larger at any given aperture.

Craig,

Thanks for articulating that so well. I'm there. , Geo

[vandergus]

Ok, I'm a little confused. How can f2.8 = f11? I do understand f-stop, basically the number= the number of times that size opening could fit into the overall lens opening. i.e. f11 means the opening at that setting is 1/11th of the total possible, it would fit into the maximum opening 11 times. (larger f-stop number= smaller opening= greater DOF)
But that raises it's own question for me....Isn't the f-stop then a particular percentage of ONLY that particular lens or similar lenses? The answer is obviously yes, so then you can not directly compare f-stop between lenses unless they are VERY similar. That's something of a revelation for me....and I've been taking photo's for decades.....
Guess I'm just not too into the technicalities of photography...(that's odd for me, I'm pretty anal)

The f number is the ratio of the focal length to the diameter of the opening that the light enters through. For example, a 50mm lense at f2 has an opening 25mm across.

To be perfectly clear, there is no difference in f-stop number between different formats (sensor sizes) when it comes to how much light the medium is exposed to. F2 is f2 when it comes to exposure. The 35mm equivalent that dimitrz is referring to is the equivalent depth of field. The depth of field is not a function of just the aperture but also of focal length. The dependence on focal length, typically much smaller in a digicam, to have such a large depth of field.

[wulf]

This is a very useful chart. I've made a small edit to the first post to include vandergus's clarification but think it will be very useful for a number of discussions that have come up recently.

Wulf