D7000 +18-55VR lens. Wise choice for a beginner?

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D7000 +18-55VR lens. Wise choice for a beginner?

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Testing123

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Drdobs said:
Yes, I clearly get the fact that when you shoot at 1.8, 2.8 versus a 5.6 or 8 you are going to get a much shallower depth of field. If that's what you're going for, the DX has an advantage as the DX sensor has an even shalloer DOF than the FX sensor.

By what measure does DX have a thinner DoF than FX?

Drdobs said:
However, sometimes you don't always want that razor thin DOF. On his D7000, if he's at 85mm focal length, 8 feet away from his subjetc at F2.8, he is going to have a in focus range of less than half a foot. Most people's heads are more than that so he'll either need to step back significantly - thus changing the composition - or shoot at a higher aperature which - negates the effect of the F2.8 lens.

Look closely at most portraits. 1/2 a foot DoF is a lot! Many many portraits have a much shallower DoF than that, often to the point of the nose being softer than the eye.

Posted 2 years ago #
spraynpray

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Testing123 said:
By what measure does DX have a thinner DoF than FX?

Er, by a negative amount. DoF is deeper the smaller the sensor, not shallower.

Posted 2 years ago #
Drdobs

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spraynpray said:
Er, by a negative amount. DoF is deeper the smaller the sensor, not shallower.

That's what I always thought, however, I have a couple of good DOF calculators on my iPhone and comparing a Nikon D3 (FX) to a Nikon D7000 (DX) I'm getting numbers that show the full frame sensor has more of the image in focus, not less.

As an example...

FX: 85mm - F2.8 - 8ft from subject = 0.44ft in focus
DX: 85mm - F2.8 - 8ft from subject = 0.29ft in focus

I tried other scenerios, it is showing that the FX's advantage, due to the bigger sensor, is that it can get MORE information in focus, not less.

Am I wrong?

Posted 2 years ago #
Testing123

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But of course you don't have the same photo, the same framing, with a FX @ 85mm and 8' subject distance as you do with a DX @ 85mm and 8' subject distance.

Apples to Apples is a FX @ 85mm and 8' subject distance vs a DX @ 56mm and 8' subject distance.

But running with your apples to oranges comparison brings up a good lesson. The other, minor, DoF difference you are seeing is all to do with lightwell size and circle of confusion size and the classic definition of "DoF". I see an afternoonn with Wikipedia in your future. Quick answer is that the FX sensor IN THIS CASE has greater DoF when looking at pixels, while the two cameras have identical DoF when measured as a ratio of picture height. I don't know what your background is, so I'm not sure what sort of analogy to make. Either you understand the physics or you need an analogy.

Since one looks at pictures, not pixels, the DoF is perceptually the same.

Posted 2 years ago #
Drdobs

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I think I'm foggy either way, but I very much appreciate your input here... I should have rephrased that statement to take into consideration the framing of the image to be as nearly identical as possible... When I do so, as your example above, I get the following...

FX: 85mm - F2.8 - 8ft from subect = 0.44ft in focus
DX: 56mm - F2.8 - 8ft from subect = 0.69ft in focus

Bingo.. I was forgetting to take crop ratio into consideration in mm length and there you have it, giving identical framing FX has a more shallow depth of field than does DX.. I suppose that's a key point for people to realize, including our topic starter and his shiny new D7000...

Now this makes me want an FX sensor again.. lol

Jon

Posted 2 years ago #
studio460

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Drdobs said:
Am I wrong?

Yes, you have it backwards. The larger the sensor, the shallower the apparent depth-of-field. The smaller the sensor, the deeper the apparent depth-of-field. That's why point-and-shoots, with their extremely small sensors, tend to shoot with very deep focus, even wide-open.

Posted 2 years ago #
Testing123

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Duh, forgot to mention:

Most all the DoF calculators I have seen run with the "classic" circle of confusion size of 30 microns for 35mm film and FX. They also treat all 1.5 crop sensors as having an acceptable circle of confusion of 20mm. This is overly simplistic. The values are dependent on print size, viewing distance, lightwell size, and AA filter strength. Use them only as a guide.

In a perfect world a DX sensor would be just the middle 1/2 of a FX sensor. It would have the same acceptable circle of confusion, and therefore the numbers would be identical (in your second 85/56 comparison).

In the real world they are not, there is not two sensors out there of different sizes yet the same density and filter characteristics, that I am aware of. Just keep in mind that CoC is not a hard number and use DoF calculators as hints and not rules.

Posted 2 years ago #
NikoDoby

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studio460 said:
Oh, crap! You do? I don't have the rights to publish those images, even though they're mine. I have to remove those!

For future reference let's only post photos as examples that you own the rights to (no blockie faces). Trust me you can get into major trouble for that.

Posted 2 years ago #
studio460

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Testing123 said:
Most all the DoF calculators I have seen run with the "classic" circle of confusion size of 30 microns for 35mm film and FX.

I think you're right--the two DoF iPhone apps I mentioned earlier, I believe, default to a CoC diameter of 0.03mm (30 microns), but you can change that parameter in the app if desired.

NikoDoby said:
For future reference let's only post photos as examples that you own the rights to (no blockie faces). Trust me you can get into major trouble for that.

Copy that. Will do.

Posted 2 years ago #