Lets Talk DOF Master

I have some questions regarding this utility for the iPhone. I have downloaded it and have been trying to figure it out. It seems no matter what i put it, the DOF master tells me the shot will be in focus.

For the spot where you put in lens im assuming i would put in the upper limit of my lens. Say i have an 18-55 mm kit lens or a 55-250mm lens i would input 55 or 250.

I understand what to do with the f/stop (i think) I just put in the f/stop that im exposing with correct?

Under focus im guessing i put the distance from the camera to the object i want to take a picture of.

As the example if i want to take a picture of something 10ft away it looks like everything 7.3 to 15.7 ft should be in focus correct? Where im confused is that i have never input a value where it tells me the photo distance i am about to take will be out of focus ( i guess that isnt a bad thing).

I have yet to really figure out what the HD button does. Actually i know what it does but i dont understand it. As in the example. If i were to hit the HD button it takes the Hyper focal distance calculated below and sets that as the focus distance then recomputes everything for that distance.

Courtesy of iTunes

Mudhog79 wrote in post #10362411
I have some questions regarding this utility for the iPhone. I have downloaded it and have been trying to figure it out. It seems no matter what i put it, the DOF master tells me the shot will be in focus.

For the spot where you put in lens im assuming i would put in the upper limit of my lens. Say i have an 18-55 mm kit lens or a 55-250mm lens i would input 55 or 250.

I understand what to do with the f/stop (i think) I just put in the f/stop that im exposing with correct?

Under focus im guessing i put the distance from the camera to the object i want to take a picture of.

As the example if i want to take a picture of something 10ft away it looks like everything 7.3 to 15.7 ft should be in focus correct? Where im confused is that i have never input a value where it tells me the photo distance i am about to take will be out of focus ( i guess that isnt a bad thing).

I have yet to really figure out what the HD button does. Actually i know what it does but i dont understand it. As in the example. If i were to hit the HD button it takes the Hyper focal distance calculated below and sets that as the focus distance then recomputes everything for that distance.

Courtesy of iTunes

The lens field is for the focal length you are going to use. Think of your zoom lens as a group of single focal length lenses.

I think the HD button will put the hyperfocal distance into the focus distance field, so you can see what the near and far limits are.

I don't have this app, but there are others like it on the internet.

The calculator assumes you can focus from 0 to infinity--it just works off of a mathematical formula. Real lenses have a finite value that is their minimum focus distance. You'll never get a result from the DOF calculator that tells you that you are out of focus. Any object not within the near and far limits will be out of focus.

Mudhog79 wrote in post #10362411
For the spot where you put in lens im assuming i would put in the upper limit of my lens. Say i have an 18-55 mm kit lens or a 55-250mm lens i would input 55 or 250.

I would think that you put in the focal length of the shot your taking. If it's a 18mm shot, you enter 18mm

Mudhog79 wrote in post #10362411
I understand what to do with the f/stop (i think) I just put in the f/stop that im exposing with correct?

yup

Mudhog79 wrote in post #10362411
Under focus im guessing i put the distance from the camera to the object i want to take a picture of.

yup

Mudhog79 wrote in post #10362411
... Where im confused is that i have never input a value where it tells me the photo distance i am about to take will be out of focus...

I don't understand the question

Basically it always shows the distace I'm at is within the near and far focus range. I would expect at some times to have to move in or back to get into the acceptable range.

gjl711 wrote in post #10362440
I would think that you put in the focal length of the shot your taking. If it's a 18mm shot, you enter 18mm

yup

yup


I don't understand the question

Ok. Well that is a small problem as my lens only has a very few focal numbers. Written on it. I guess I would have to guestimate.

Mudhog79 wrote in post #10362520
Basically it always shows the distace I'm at is within the near and far focus range. I would expect at some times to have to move in or back to get into the acceptable range.

This won't ever happen. DOF calculations require a focus distance and the near and far limits are based on that focus distance. You'll never be able to enter a non-negative number and get what you are describing.

Mudhog79 wrote in post #10362535
Ok. Well that is a small problem as my lens only has a very few focal numbers. Written on it. I guess I would have to guestimate.

Your lenses have an infinite number of focal lengths between 18 and 55 or 55 and 250, depending on which lens you have attached.

DOF calculations are indeed a guess made difficult by zoom lenses which have few FL engraved.

But consider the fact that DOF calculations are as much a guess even for Fixed Focal Length lenses, because the modern AF lens has so few distances marked on the distance scale past 5' . Tell me that you can find 25' precisely (near DOF limit) and 53' (far DOF limit) precisely when focused precisely at 34' and using f/5.6 on a 50mm lens...either visually in the scene or as marked on the lens, NONE of them are well identified!

Thanks to all for the replies...

Mudhog79 wrote in post #10362520
Basically it always shows the distace I'm at is within the near and far focus range. I would expect at some times to have to move in or back to get into the acceptable range.

The distance you're at, or what you are focusing on, will always be in focus. Why would it not? The near and far distances are derived from your initial focusing distance and will always be a range around that number.

So, the range moves around the focusing point, not the other way around. That's why moving in or back will have no effect.

What you focus on should always be in focus. The range just tells you how much in front and behind the focusing point is also in focus.

Ok i understand now. I guess when i was getting confused i was thinking about depth of focus. Like if im really close to something with my 55-250mm say a flower the center may be in focus but the outer part of the flower could be out of focus.

Willie wrote in post #10365688
The distance you're at, or what you are focusing on, will always be in focus. Why would it not? The near and far distances are derived from your initial focusing distance and will always be a range around that number.

So, the range moves around the focusing point, not the other way around. That's why moving in or back will have no effect.

What you focus on should always be in focus. The range just tells you how much in front and behind the focusing point is also in focus.

Mudhog79 wrote in post #10366048
Ok i understand now. I guess when i was getting confused i was thinking about depth of focus. Like if im really close to something with my 55-250mm say a flower the center may be in focus but the outer part of the flower could be out of focus.

That's true -- to see how that works, try plugging in these numbers: lens = 100mm, aperture = f/5.6, distance = 1 ft. You'll see that the depth of field is very, very narrow, just like you imagine for the flower. In fact, if you stop down the aperture to f/16 it will also be very narrow -- about .02 feet from front to rear.