Widening my approach

[seanhoxx]

Interesting stuff guys, Peek you make some really good, nicely explained points on the science and behavior of light, feel free to continue to share that info! Has anyone attempted to get Sony involved in this for some input?

[Peekayoh]

......... My curiosity is whether the "crop factor" of the APS-C sized sensor is simply a matter of a reduction in the field of view or whether it also has an effect on the DOF. Hence the experiment. After all, if we knew the answer for sure, then I wouldn't be out today experimenting!!

But we do know the answer. The crop sensor is responsible for the changed DOF because we need to use a smaller CoC to achieve the greater enlargement required to ensure a 250micron CoC on the 8 x12 image.

It's clear that my explanation lacked the clarity needed to put over an admittedly difficult to grasp concept. I apologise

50mm on A900 f8 at 10 ft DOF =6.28feet FOV= 7.2 feet
50mm on A700 f8 at 10 ft DOF =3.98feet FOV= 4.8 feet
If you now change the lens to a 33.5mm on the A700 to get the same FOV of 7.2feet DOF=10.54feet (deeper approximately by the crop factor).
On a P&S (crop factor >2 )the DOF is practically infinite.

[DWessel]

But we do know the answer. The crop sensor is responsible for the changed DOF because we need to use a smaller CoC to achieve the greater enlargement required to ensure a 250micron CoC on the 8 x12 image.

It's clear that my explanation lacked the clarity needed to put over an admittedly difficult to grasp concept. I apologise

50mm on A900 f8 at 10 ft DOF =6.28feet FOV= 7.2 feet
50mm on A700 f8 at 10 ft DOF =3.98feet FOV= 4.8 feet
If you now change the lens to a 33.5mm on the A700 to get the same FOV of 7.2feet DOF=10.54feet (deeper approximately by the crop factor).
On a P&S (crop factor <1 )the DOF is practically infinite.

Your explanation makes sense and sounds logical. At the same time, some of those responding to this discussion are convinced that the change from FF mode to APS-C mode on the a900 is no different than cropping the FF image in PS. That presumption would appear to be incorrect, because, following your explanation, a shot taken at FF is going to have a both a larger DOF and FOV compared to the same shot taken in APS-C mode.

[Peekayoh]

Yes, it was me that said it...

Oh Boy! Are you guys getting your knickers in a twist or what.
If you take a pic with an A900 camera and crop it in Photoshop, the DOF won't change.
That's all the crop mode does on camera. Ergo the DOF is the same.

Remember what I have since said about the relationship with CoC and enlargement determining the DOF.
When the A900 crops an A700 sized portion out of its FF sensor the two FOV's become the same (4.8 feet in the last example), they both need the same factor of enlargement to become an 8x12 print, ergo DOFs are identical.

This assumes that the second pic is taken with an A700 using the same lens, aperture and distance to focal plane.

[Peekayoh]

BTW I had to go back and edit the P&S Crop factor to On a P&S (crop factor >2 )the DOF is practically infinite.
Brain fade.
Well, this is all pretty confusing!

[DonSchap]

Darin ... can you take and subsequently post the shot(s)? LOL

[DWessel]

Here's an idea with the 50mm set at f/2.8, not f/1.4 ... which may be too shallow to adequately determine a difference.

These numbers allow seeing a real change in image. Use a tape measure and shoot along it, placing items (colored blocks)
at the specified "N/C" extreme (Close/Far) distances. You should clearly see a change, if it does change.

10-feet

A900 . . . . Lens . . . . . Aperture . . . . DOF Width . , , Close . . . . . Far

Crop . . . . 50mm . . . . . f/2.8 . . . . . . . 1.36 ft . . . . . 9.36 ft . . . 10.7 ft

N/C . . . . .50mm . . . . . f/2.8 . . . . . . . 2.06 ft . . . . . 9 ft . . . . . 11 ft



20 –feet

A900 . . . . Lens . . . . . Aperture . . . . DOF Width . , , Close . . . . . Far

Crop . . . . 50mm . . . . . f/2.8 . . . . . . . 5.6 ft . . . . . 17.6 ft . . . . 23.2 ft

N/C . . . . .50mm . . . . . f/2.8 . . . . . . . 8.6 ft . . . . . 16.6 ft . . . . 25.2 ft

.
.
N/C = Not crop (normal mode)

Attachment 46727

Here's the results of the test.
All shot with the A900 w/ Sony 50mm f/1.4 lens set in Aperature priority mode at f/2.8 spot focus on the center point object (the LEMON not Orange).
The clamps are set at 5' intervals from the center point.


10ft, Full Frame Mode


10ft, APS-C Mode


20ft, Full Frame Mode


20ft, APS-C Mode

Now, in the above set of images, I saved each for web in PS at 800wX533h. The original FF images were 6048X4032. The original APS-C images were 3984X2656.

[DWessel]

This is the first set I took at 10ft and 20ft, using the yellow golf ball as center focal point. Same setings of A900 w/ 50mm f/1.4 lens using Aperature priority mode at f/2.8.

In this set, I saved for web using 15% size of original.


10ft, Full Frame


10ft, APS-C Mode


20ft, Full Frame


20ft, APS-C Mode

Now, I don't know if it's my ancient laptop (2 years old with not the sharpest of screens), but there is definite pixelation in the APS-C images as compared to the FF images. This may be the only time I use the APS-C mode.

[dr4gon]

Hard to tell without the original size. 10ft would be enough of a test to use, but from what I can tell it looks identical.

[seanhoxx]

o.K. first of all, does the center focus item the orange look like a yellow lemon or is it my monitor? I first rolled through the images going where the hell is the orange!