Just wanted to see if these tripped anyones trigger!?!

[Sonoma]

While out shooting today I took these photos.
The first looks sharp to me, but the second looks like the focus is on the second bag under the forearm. WHY?? In both I focused on the forearm just under the scopes on both rifles. I can't for the life of me understand why the focus would be off on the second. I use just the center focus point and recompose all the time. Any and all comments or suggestions welcome.

Thanks
1.)

2.)

 

[jerryw66]

Lefty? The background is blurred better on #1. Did you change any settings? I like the rifles regardless of the point of focus. I haven't had a decent day to shoot yet this spring, rains nearly every day it seems.

 

[480sparky]

To me, the first one is OOF. It was taken an f/4 : ISO 100 : 1/125, while the second one, taken at f/11 : ISO 400 : 1/100, looks much better.

 

[Sonoma]

Lefty? The background is blurred better on #1. Did you change any settings? I like the rifles regardless of the point of focus. I haven't had a decent day to shoot yet this spring, rains nearly every day it seems.

Yup, I am a lefty. I was changing the aperture just experimenting. This is the first nice day we have had in weeks!!!

To me, the first one is OOF. It was taken an f/4 : ISO 100 : 1/125, while the second one, taken at f/11 : ISO 400 : 1/100, looks much better.

So, how do I keep the entire object(rifle) in focus? Is it even possible? According to the DOF calculator, shooting from 10' @ f11 and 70mm should have given me a little over 2.5' in focus. Shooting straight on from the side seems a little boring!

Thanks

 

[photocist]

is 70mm the focal length of the lens? Did you compensate for the crop factor?

To get more DOF, just increase the f stop.

 

[480sparky]

Lefty? The background is blurred better on #1. Did you change any settings? I like the rifles regardless of the point of focus. I haven't had a decent day to shoot yet this spring, rains nearly every day it seems.

Yup, I am a lefty. I was changing the aperture just experimenting. This is the first nice day we have had in weeks!!!

To me, the first one is OOF. It was taken an f/4 : ISO 100 : 1/125, while the second one, taken at f/11 : ISO 400 : 1/100, looks much better.

So, how do I keep the entire object(rifle) in focus? Is it even possible? According to the DOF calculator, shooting from 10' @ f11 and 70mm should have given me a little over 2.5' in focus. Shooting straight on from the side seems a little boring!

Thanks

At 10', the in-focus field is between 106.5" and 137.5". But that's if you focus at exactly 120" away. That might not be the middle of the rifle.

 

[doubleoh7]

Nice. Here is one of mine -

 

[480sparky]

Nice. Here is one of mine -

A stealth gun?

 

[Sonoma]

is 70mm the focal length of the lens? Did you compensate for the crop factor?

To get more DOF, just increase the f stop.

OK, maybe I am using the calculator wrong. The lens is a 70-200, set at 70mm. When I used the calculator I picked 70mm. Is that incorrect? The calculator compensates automatically for the crop sensor.

http://www.dofmaster.com/dofjs.html

 

[480sparky]

OK, maybe I am using the calculator wrong. The lens is a 70-200, set at 70mm. When I used the calculator I picked 70mm. Is that incorrect? The calculator compensates automatically for the crop sensor.

Online Depth of Field Calculator

70mm is the focal length... it has nothing to do with the sensor size.

Think of it this way... take the shot with a full-frame sensor, then in your computer crop it down to APS-C size. That will not affect the DOF at all.

 

[Helen B]

Think of it this way... take the shot with a full-frame sensor, then in your computer crop it down to APS-C size. That will not affect the DOF at all.

If you enlarge the cropped image back up to the size of the original it will affect DoF (it will decrease), and most DoF comparisons and calculations are based on looking at same-size prints/images. With the same focal length, subject distance and aperture a cropped sensor will have less DoF and field of view than a full-frame sensor. With the same field of view, subject distance and aperture a cropped sensor will have more DoF and shorter focal length than a full-frame sensor.

Best,
Helen

 

[480sparky]

If you enlarge the cropped image back up to the size of the original it will affect DoF (it will decrease), and most DoF comparisons and calculations are based on looking at same-size prints/images. With the same focal length, subject distance and aperture a cropped sensor will have less DoF and field of view than a full-frame sensor. With the same field of view, subject distance and aperture a cropped sensor will have more DoF and shorter focal length than a full-frame sensor.

Best,
Helen

What does the sensor size have to do with DOF, a function of the optics? I could put a 10 cm² sensor behind the 70mm lens, and that wouldn't change the DOF of the image one bit.

 

[Sonoma]

If you enlarge the cropped image back up to the size of the original it will affect DoF (it will decrease), and most DoF comparisons and calculations are based on looking at same-size prints/images. With the same focal length, subject distance and aperture a cropped sensor will have less DoF and field of view than a full-frame sensor. With the same field of view, subject distance and aperture a cropped sensor will have more DoF and shorter focal length than a full-frame sensor.

Best,
Helen

What does the sensor size have to do with DOF, a function of the optics? I could put a 10 cm² sensor behind the 70mm lens, and that wouldn't change the DOF of the image one bit.

I can't say why, but if you go to the "on line calculator" and change from a crop body (T1i is what I have) to a 5D( I think a full frame camera) the DOF does increase considerably..

 

[480sparky]

I can't say why, but if you go to the "on line calculator" and change from a crop body (T1i is what I have) to a 5D( I think a full frame camera) the DOF does increase considerably..

I can't speak for someone else's website or address whatever formula they're using. Maybe the creator is changing the mm from a full-frame to the APS format without saying, "You have a 70mm lens on an APS format camera, so I'm going to use 112mm in my calculations instead."

Or, try this one, which doesn't bother asking for the sensor size.


So would changing from a full-frame DSLR to a 35mm SLR camera somehow magically change the DOF? Suppose I take the lens off the camera altogether.... how will that affect the DOF if there's not even a sensor to record the image?

 

[Helen B]

What does the sensor size have to do with DOF, a function of the optics? I could put a 10 cm² sensor behind the 70mm lens, and that wouldn't change the DOF of the image one bit.

DoF is not just a function of the optics, it also depends on the amount the original image is magnified for viewing. The more the original image is magnified for viewing, the more in focus the original image must be. This is why the largest acceptable circle of confusion (CoC, which is used in DoF calculations) is different for different formats. Calculations aside, the effect is quite noticeable to people who use a variety of formats.

A DoF calculator that does not take CoC into account is inaccurate and effectively useless. The correct DoF calculators do not adjust the focal length to account for different formats, they adjust the CoC. The calculator you give a link to that you say does not ask for the sensor size does ask for CoC - so that is how it takes sensor size into account.

Best,
Helen

PS If you wish to continue this, why not start a separate thread?