cheapest Camera that will do depth of field
- Thread starter easyrider
- Start date
Can I just check something regarding dof? Maybe I'm misunderstanding the confusion.
Assuming a focal distance of 3m, should a DX with 50mm @1.8 produce the same DoF as a FX with 75mm @ 1.8? Focal length, focal distance and aperture are identical are they not?
Only they don't.
Assuming a focal distance of 3m, should a DX with 50mm @1.8 produce the same DoF as a FX with 75mm @ 1.8? Focal length, focal distance and aperture are identical are they not?
Only they don't.
DX at f1.8 produces the same DOF as FX at f2.8.
So then, the simple premise that I've always heard attributed to this entire debate that the same effective focal length, focal distance and aperture will result in a shallower DoF on FX than DX is correct?
The only way to match the DOF of a FX w/ 24-70 2.8 on DX would be a 16-46.7mm f1.8, which doesn't exist.
The only way to match the DOF of a FX w/ 24-70 2.8 on DX would be a 16-46.7mm f1.8, which doesn't exist.
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Did you not read any of D.P.'s posts above ?!?!
Of course, I just wanted to clarify my interpretation of it.
Effective focal length is something that people talk about a lot, I've not heard effective apertures nearly as much and I never evne considered that to get the same DoF on DX I'd need a wider aperture.
What I thought was the case is indeed the case, so I'm satisfied.
Effective focal length is something that people talk about a lot, I've not heard effective apertures nearly as much and I never evne considered that to get the same DoF on DX I'd need a wider aperture.
What I thought was the case is indeed the case, so I'm satisfied.
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Here's an example of full-frame vs micro-four-thirds sensor sizes which should help those confused: http://www.mu-43.com/showthread.php?t=25093
I too, agree that D.P. throws confusion at newcomers with his method of explanation, whilst simply saying a larger sensor will allow for shallower dof at identical apertures and framing, is sufficient (for people wanting to quickly understand).
I too, agree that D.P. throws confusion at newcomers with his method of explanation, whilst simply saying a larger sensor will allow for shallower dof at identical apertures and framing, is sufficient (for people wanting to quickly understand).
Wrong, see above.
Only by changing th focal length of distance to subject will there be a change in DoF.
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No. The focal length has changed from 50mm to 75mm, therefore the DoF has decreased.
If you kept the same lens then you would get the same DoF but the subject would be smaller.
Any camera, the longer the focal length of the lens the shallower the DoF, irrespective of changes on sensor size.
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Columbo is wrong here, see my long post above.
At the same focal length, same aperture and same focus distance you get the same DoF but a different framing. If you change either of these 3 properties you will change the DoF. So changing the focal length from 46mm to 70mm will change the DoF. If you used the 24-70mm on the DX camera and stood the same 3.0m away as you suggest then the DoF would be identical but the image would look different. Simples
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No, you see people like Colombo have already got confused and got it wrong due to talk of effect aperture differences. My explanation is much simpler and would help DBT85 correctly understand what is happenings when the focal length of the lens changes.
yes, the field of view will be correct, and since you changed the focal length the DoF will change.
If you put a 35mm on a DX camera and a 35mm on an FX camera and you stood still the DoF will be the same, but the FX camera will have a much wider field of view and so the subject will be smaller within the frame. You may or may not want that. The fact that the field of view is wider is a great bonus for landscape and architecture photography for example.
Now since the fiueld of view is wider on FX, if you want to get the subject the same size, e.g.a person, then you will have to change something. you will either need to get closer, or use a longer lens - the 50mm as you pointed out. Doing either will reduce the DoF
Perspective is another complex matter which many people don't get or simply don't realize.
you can experiment with your camera and a zoom lens. E.g. if you have an 18-55 (or 18-105mm etc) then stand far away from something and zoom the lens all the way in to the 55mm (or 105mm) and set your aperture to f/8. Take a photo and then change your lens to 18mm. Start walking closer and closer and checking the subject in the viewfinder, once the subject is the same size take a photo and compare.
Although the subject is the same size the background will be very different.
I know everything else you are saying, I'm trying to wrap my head around your explanation for the dof which until now I've been quite happy not thinking about.
You say a 35mm on a DX and FX would be the same dof (not FOV) , but the calculator on Dofmaster.com disagrees.
It says that for 50mm, at 1.8 with a focal distance of 3m, the DX will have dof of 25.3cm, while the FX will be 38cm.
As do all the other calculators. Is that not contrary to
?
As I said in the D750 thread, I don't want to sound like a git, I just need to understand things, and your words and the dof calcs not lining up is confusing me over something that really doesn't matter, since I'll only shoot both DX and FX at the same time for a few hours to see for myself when my D750 arrives.
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The first thing to note is that with those numbers (and what all the DoF calculators all say), the smaller sensor actually has the smaller DoF. For most people that is quite a surprise because they have all been told that bigger sensors have a shallow DoF but the DoF calculators clearly show otherwise! Some people would swear you are living if you say that!
The DoF calculators take into account the circle of confusion. This is a much more complex concept and relates to the pixel density of the sensor, the final print size, viewing distance, lens optical characteristics also how good your vision is. The DoF calculators make some educated guess at what threshold one would deem sharp and at what would be soft- the DoF is the distance between the near and far sharpness limits. But these limits are not black and white and also depend on how big you view the final image. Furthermore, as the distance increases or the focal length increase the importance of the circle of confusion becomes less important.
Ultimately it is complexity you can do without. When you view the image image at the same size and below the circle of confusion limit of the smaller sensor, DoF is not strongly proportional to sensor size (and if it is the theory actually states the smaller sensor has the smaller DoF) and everything I said holds true. The reason I say to ignore the circle of confusion is it only has a small part to play and is dwarfed by other erros. For example, that f/1.8 lens might actually be closer to f/1.9, and those 50mm might really be 47mm (and 44mm when focused closely). The manuf a true round down/up to the nearest common unit that makes their lens sound better.
The true math behind DoF and circle of confusion is quite daunting, what I presented is a summary that is physically correct simplification that is more intuitive.
http://en.m.wikipedia.org/wiki/Depth_of_field
http://en.m.wikipedia.org/wiki/Circle_of_confusion
What a larger sensor is allowing you to do is capture more detail which can be enlarged to a bigger size (or conversely, if you enlarged the image size by a constant factor of 100 the bigger sensor will enlarge to a bigger size). If you display the image bigger then what you perceive to be sharp is reduced, and that reduced the apparent DoF, so the smaller sensor seems to yield a shallow DoF, contrasty to what some would lead you to believe.
Confused? Well, you know sometimes you have a photo that looks sharp on the LCD screen but when you zoom in on your monitor at home it looks soft, that is related to circle of confusion. If you enlarge the image enough then you see different sharpness or softness. Bigger sensors allow capturing more detail that be viewed bigger. If you view it bigger then the visual DoF changes.
Another analogy is when you have a shallow DoF photo where the background is all blurred. If you view a small thumbnail of the photo the background looks sharp.
In the real world the circle of confusion just isn't important unless you print as large as you can possibly can (and in which case, smaller sensors have a smaller DoF), ergo the difference in sensor size again doesn't affect the DoF directly, but indirectly and in a way that you might not expect.
In summary, a larger sensor has a wider field of view for a given lens, can capture more detail, is better in low light, and can make it easier to capture a shallower depth of focus by letting you get closer or use longer lenses. The take home message is a bigger sensor makes it easier to capture a shallower DoF, for the most part it doesn't do that directly (and in reality actually increases DoF under constant conditions). It is quite obvious to me that a larger sensor captures a wider field of view and when making adjustments for that you change the DoF. The circle of confusion can be ignored and thus any differences in the sensor it self ignored. If you are determined to believe the sensor makes a difference then the truth is the smaller sensors have a smaller a DoF.
The DoF calculators take into account the circle of confusion. This is a much more complex concept and relates to the pixel density of the sensor, the final print size, viewing distance, lens optical characteristics also how good your vision is. The DoF calculators make some educated guess at what threshold one would deem sharp and at what would be soft- the DoF is the distance between the near and far sharpness limits. But these limits are not black and white and also depend on how big you view the final image. Furthermore, as the distance increases or the focal length increase the importance of the circle of confusion becomes less important.
Ultimately it is complexity you can do without. When you view the image image at the same size and below the circle of confusion limit of the smaller sensor, DoF is not strongly proportional to sensor size (and if it is the theory actually states the smaller sensor has the smaller DoF) and everything I said holds true. The reason I say to ignore the circle of confusion is it only has a small part to play and is dwarfed by other erros. For example, that f/1.8 lens might actually be closer to f/1.9, and those 50mm might really be 47mm (and 44mm when focused closely). The manuf a true round down/up to the nearest common unit that makes their lens sound better.
The true math behind DoF and circle of confusion is quite daunting, what I presented is a summary that is physically correct simplification that is more intuitive.
http://en.m.wikipedia.org/wiki/Depth_of_field
http://en.m.wikipedia.org/wiki/Circle_of_confusion
What a larger sensor is allowing you to do is capture more detail which can be enlarged to a bigger size (or conversely, if you enlarged the image size by a constant factor of 100 the bigger sensor will enlarge to a bigger size). If you display the image bigger then what you perceive to be sharp is reduced, and that reduced the apparent DoF, so the smaller sensor seems to yield a shallow DoF, contrasty to what some would lead you to believe.
Confused? Well, you know sometimes you have a photo that looks sharp on the LCD screen but when you zoom in on your monitor at home it looks soft, that is related to circle of confusion. If you enlarge the image enough then you see different sharpness or softness. Bigger sensors allow capturing more detail that be viewed bigger. If you view it bigger then the visual DoF changes.
Another analogy is when you have a shallow DoF photo where the background is all blurred. If you view a small thumbnail of the photo the background looks sharp.
In the real world the circle of confusion just isn't important unless you print as large as you can possibly can (and in which case, smaller sensors have a smaller DoF), ergo the difference in sensor size again doesn't affect the DoF directly, but indirectly and in a way that you might not expect.
In summary, a larger sensor has a wider field of view for a given lens, can capture more detail, is better in low light, and can make it easier to capture a shallower depth of focus by letting you get closer or use longer lenses. The take home message is a bigger sensor makes it easier to capture a shallower DoF, for the most part it doesn't do that directly (and in reality actually increases DoF under constant conditions). It is quite obvious to me that a larger sensor captures a wider field of view and when making adjustments for that you change the DoF. The circle of confusion can be ignored and thus any differences in the sensor it self ignored. If you are determined to believe the sensor makes a difference then the truth is the smaller sensors have a smaller a DoF.
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Easy and accurate aren't always the same thing lol