So I was told...

[trod]

Being new to photography, I have done a lot to try and get my mind wrapped around its concepts to include doing a lot of reading. I thought I had the idea on how to ensure I met maximum DoF by setting my camera at a small enough aperture that my cameras CoC would be able to make use of thus keeping the shot in focus; I understand that opening the aperture to like f1.8 would cause a shallow DoF. The other day, a friend from out of town through a wrench into the monkey works when I was shooting the Golden Gate lengthwise when he told me I could set my aperture f3.5 with the proper shutter speed so that there was no need to use the tripod (we were shooting in low light). Obviously this confused me and I hope I have not confused anyone here as well as I hope I have posted to the right area. What I'm looking for is someone who can explain this to me as I feel I may have misunderstood him, or worse yet, all the reading I have done has been a waste of time. If there are any questions you have that can shed light on this, I will gladly try and answer them. Thanks in advance for your time.

[Henry Wilt]

Hello and welcome,

You're part way right, the larger the aperture the greater the DoF will be but that will also be affected by the focal length you are using. Check out "this DoF calculator" to see how the focal length will change it.

[trod]

Yeah, I understand that lower apertures like f1.8 will cause a narrow DoF and that larger ones like f22 will create a deeper DoF due to the CoC as it pertains to the sensor, but my question is that if your lens is already at infinity, can you use any f stop you want coupled with the proper shutter speed which will give you maximum DoF so that there's a less likely or no need to use a tripod?

[Henry Wilt]

OK, I didn't explain that very well before I just put the calculator in there so you could play and see what your DoF would be.

I don't know what camera or lens you are using so I will give you an example using a Canon crop sensor body with an 18-55mm lens.

If your lens is at it's maximum focal length (which is what I assume you mean by "at infinity"), in this case would be 55mm and the object you were focusing on was 100 meters away, at f/3.5 everything from 30.9 meters to infinity would be in focus. If however the object was 1 meter away with the same aperture setting of f/3.5 everything between 0.98 meters to 1.02 meters would be in focus, giving you a DoF of only 4 centimeters.

The same scenario and settings except this time the focal length is set at 18mm. At 100 meters from the object, everything from 4.57 meters to infinity will be in focus whilst at 1 meter from the object, everything between 0.83 meters to 1.26 meters will be in focus giving you a DoF of 43 centimeters.

I hope that explains better what I meant by DoF is affected by focal length.

[DogHeadGod]

I think we are getting a few different ideas confused here...

Firstly, you are correct in saying a smaller aperture will give a greater depth of field. (I.e. More of the image will be in focus)

If you use a small aperture though less light goes into the camera, so you need to use a slower shutter speed to get the right exposure.

If you use a small aperture in low light conditions you need to keep the shutter open for a long time, this leads to blurry pictures because every little move of your hand, even just pressing the shutter button, causes the camera to shake. You would overcome this by using a tripod or some other form of support to hold the camera steady.

Your friend tells you to use a larger aperture because you would be able to use a faster shutter speed. This would let you take the shot without a tripod as camera shake wouldn't show up because the shutter is only open for a tiny fraction of a second.

But using this larger aperture would give you a shallow depth of field. You basically have to choose between the two depending on wether you want big depth of field or to shoot handheld in low light.

Hope this helps. (I'm writing from my phone and it is hard to scroll around to check all my spelling and grammar, so please excuse any mistakes)

DHG

[milosh]

Ok, I believe there are some misunderstandings here.

Originally Posted by Henry Wilt

If your lens is at it's maximum focal length (which is what I assume you mean by "at infinity"), in this case would be 55mm and the object you...

I believe you misunderstood it, lens at infinity usually means that lens is focused at infinity, it has nothing to do with focal length.

Originally Posted by trod

Yeah, I understand that lower apertures like f1.8 will cause a narrow DoF and that larger ones like f22 will create a deeper DoF due to the CoC as it pertains to the sensor, but my question is that if your lens is already at infinity, can you use any f stop you want coupled with the proper shutter speed which will give you maximum DoF so that there's a less likely or no need to use a tripod?

There are three things that affect DoF, aperture being used, lens focal length and distance from camera to subject.
Since your lens is already focused at infinity, the change in aperture will only affect the near limit of DoF (the distance from you to the beginning of "sharp" area), while the far limit of DoF will stay at infinity.

Check it out on http://dofmaster.com/dofjs.html:
For example, if your subject is 100m away and you're shooting at 55mm and f16, the near limit will be at 9m, and far limit at infinity.
If you're shooting the same subject at 55mm and f4, near limit will be at 28.5m and far limit will again be at infinity.

So, yes, your friend was correct, in this case, you can open up your aperture and obtain a faster shutter speed without it affecting your DoF (if you don't have an object in you foreground which you also want to be in focus). One thing might also change, and that is you lens sharpness, every lens has it's so-called sweet spot.

P.S. Please someone correct me if I'm wrong.

[trod]

Thanks for all the replies as they have all helped to clear things up for me. What I'm gathering is that I only had a portion of DoF down and need to do a bit more follow-up to get the rest. Some times I wish I could find someone to tag along with for just thess instances. Thanks again everyone.

[trod]

Sorry, I actually have one last question. After looking more at the calculator, I can see how depending on the distance of your subject that it could push your DoF from a certain point out to infinity. Is there a quick and dirty way to determine when this has happened?

[ravncat]

Yes. There is

And if you combine that with maximum dof from closest focus to infinity you get something called hyperfocal point

you can use tables but they depend on your choice of CoC size.

You can also use lens scales on older lenses many nikkor d type lenses have simple scales new ones don't

Quickest dirtiest is your eyes and dof preview

[trod]

Yeah, i was trying to make sense of the scale on my 28 to 135 lens with no luck. I took a look on line at the older lenses and their scales were easy to follow. I've tried to use the DoF preview but I'm not understanding what I'm supposed to see.