# DOF and Cropping take 2

Started 10 months ago | Discussions thread
 Like?
 Re: U R Slippery II In reply to awaldram, 10 months ago

awaldram wrote:

Ian Stuart Forsyth wrote:

awaldram wrote:

In your La La world the first image should be over 2 stops under exposed as F2.8 on the Q is f16 on aps-C !

You just proved why it shouldn't be under exposed with your answer here kind of

http://www.dpreview.com/forums/post/53107658

Yep but thats obvious iso 100 = iso 100 on any format , f2.8 = f.28 , 1/180 = 1/180 format is irrelevant there a constant.

So irrelevant of sensor efficiency or size (light density) a camera will have the same exposure solution for the same ISO set.

the Q at F/2.8 1/80 iso 800 needs more gain as it has captured 13 times less total light than K3 at F/2.8 1/80 iso 800 because of the sensor size difference

Not sure what you trying to say. the Q will produce more noise at iso 800 than the k3 because it requires more internal gain to match sensitivity but both will have the same light sensitivity at iso800.

yes

We can reduce the AP on the K3 to F/10 raise the iso 3000 and then it would gather around the same total light as the Q F/2.8 1/80 iso 800

Why would you do this.?

If you required the K3 to have the same DOF as the Q at F2.8

Or think about this if you don't need F10 open it up to F2.8 and shoot the k3 at iso 3200 with a shutter speed 13 times faster and still capture the same total light as the Q F2.8 iso 800 1/80

Or another way to look at it the Q iso 800 = k3 iso 3000

No chance ISo is a standard its calibrated and set on every camera ever made , without it photography would not exist as it does today. Every camera would require custom algorithms for every exposure

Some  sensors photocells collect 10 and other can only collect 2 for that given exposure so each series of  sensor will need a  different gain to meet the iso standard ( kind of like a pre gain)

Q iso800 = k3 iso 800 = 645d iso80 = glass plate camera iso800 = hubble telescope iso800.

As the image I posted proved setting the same aperture , the same shutter and the same iso results in the same exposure across formats.

but different amount of total light collected because of sensor size and different amount of pre gain to bring them up to the iso standard ( think of it this way more total light gathered less pre gain need)

But the Q needs a pre gain 13 times higher to meet that iso standard

this is why the K3@ iso 3200 looks like the Q at iso 800

Not sure what your showing maybe that the k3 noise at 3200 is similar to Q7 @800?

yes same total light same total noise

I could only find the Q7 to compare to the K3

-- hide signature --
-- hide signature --

The Camera is only a tool, photography is deciding how to use it.
The hardest part about capturing wildlife is not the photographing portion; it’s getting them to sign a model release

Ian Stuart Forsyth's gear list:Ian Stuart Forsyth's gear list
Pentax *ist DS Pentax K10D Pentax K20D Pentax K-7 Pentax K-5 +19 more
Complain
Post ()
Keyboard shortcuts: