FlyPenFly
Senior Member
With an LX3, I am able to extract some DOF but the person/object has to be very close to me. The LX3 is capable of f2 at it's wide end though.
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Would the S90 be able to isolate subjects at F2?
- Thread starter tc333
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Sorry, no, that is not true. The smaller sensor will have much less DOF in that case.
1/1.7" sensor, 22mm, f4.8, 10 feet, DOF = 4.35 feet
full-frame sensor, 22mm, f4.8, 10 feet, DOF = 87.5 feet
Cropping reduces DOF at the same final print/display size.
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Lee Jay
(see profile for equipment)
Julian Macoveanu
Active member
Ops clumsy of me, you are right. I have owned a DSLR for 5 years, but I should indeed spell out everything so everybody understands.
What I wanted to say is that for a DSLR the lenses that you buy will have a lot bigger focal length.
yes, so a an actual focal length of 18 when wide, compared to 6 for S90
Wrong, it's 6-20mm which translates to 28-105 in 35mm format, but when you calculated DOF you look at the actual focal length
Wrong again for the same argument as above, Canon sx20IS has still smaller focal length compared to the Nikon kit lens, 5mm at wide compared to 18 .... HUGE difference.
We are all here to learn and need to be open for that. You have not even clicked on my link to see that smaller sensors does indeed give smaller DOF
For the same physical focal length, f-stop, and subject distance, you are quite correct.
But the framing is then very much different since the large sensor has a much larger field-of-view at the same focal length.
If you equalize the field of view by using a longer focal length on the larger sensor, then the larger sensor has a much narrower DOF at the same f-stop and subject distance.
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Lee Jay
(see profile for equipment)
Julian Macoveanu
Active member
Finally somebody that knows that smaller sensors give smaller DOF
Could you please explain this a little more, what does DOF have to do with cropping.
It's why smaller sensors give smaller DOF at the same focal length and f-stop. Cropping while keeping the same final size means more enlargement from the original image on the sensor to the print. More enlargement means more enlargement of the blur circles as well, this less DOF.
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Lee Jay
(see profile for equipment)
Julian Macoveanu
Active member
Thanks, finally a helpful answer. I guess the dpreview DOF calculator should include a FOV setting as well.
I think we just have to face the fact that DOF is a confusing and not-so-intuitive subject.
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Lee Jay
(see profile for equipment)
DOF is larger as
1) you stop down le lens: move from f2 to f22
2) you reduce the real mm lenght of you lense
3) ther greater the focus distance.
Sensor size does not matter in DOF.
The fact that a compact camera has to get 5mm lens to get to 25mm equivalent (35mm) brings about the exceptional DOF that all the compact cameras have.
1) you stop down le lens: move from f2 to f22
2) you reduce the real mm lenght of you lense
3) ther greater the focus distance.
Sensor size does not matter in DOF.
The fact that a compact camera has to get 5mm lens to get to 25mm equivalent (35mm) brings about the exceptional DOF that all the compact cameras have.
It does, as I demonstrated above.
http://forums.dpreview.com/forums/read.asp?forum=1010&message=32945115
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Lee Jay
(see profile for equipment)
Only at the same equivalent focal length and the same actual f-stop.
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Lee Jay
(see profile for equipment)
Julian Macoveanu
Active member
It has been a long discussion over here today about that. My conclusions are as follows:
Keeping focal length, distance do subject, aperture and everything else fixed you should get a smaller DOF with smaller sensors. However, for a bigger sensor you will have to adjust the focal length in order to remain with the same field of view of a smaller sensor. This inevitable increase of focal length will reduce the DOF. This two factors might cancelled out each other so you might end up being right. That would make things easier.
Agree, if you mean exceptionally bad (large). After playing with the DOF calculator here my conclusion is that the actual focal length is indeed the factor that affects most DOF and should be enough to explain the poor DOF of compacts compared to DSLRs
No, I'm not.
With the same focal length, f-stop, and subject distance, a smaller sensor will have less DOF. If you take any image that has some out-of-focus areas and crop that image, the DOF will decrease.
The reason for this is enlargement ratio . More enlargement = larger blur circles = less DOF. So, at the same final size, cropping either by small sensor or by post processing will reduce DOF if the focal length is not changed to maintain constant framing.
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Lee Jay
(see profile for equipment)
Correct.
Nope. Here's why.
When you crop or decrease sensor size, the DOF decreases linearly with decreasing size (SD
So, halve your sensor size and DOF halves. Double your focal length and DOF is not cut in half, but rather to one quarter of its original value (again, SD
By the way, one reason for this quadratic behavior with focal length is that focal length changes two things (the following is only one way to look at this, there are others). First, increasing focal length increases magnification of the image, and that reduces DOF. But since we are holding f-stop constant, it also increases aperture (f-stop=focal length/aperture). DOF also decreases with aperture.
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Lee Jay
(see profile for equipment)
Habemus_Canon
Senior Member
Why are we actually arguing about this? Just from general usage of my 20D and my G10 I can easily say that there is basically no way of isolating a subject with the G10. The 20D has a larger sensor. Of course, there may be "relative focal lengths" and such involved, but when we are taking pictures out there in the real world, a larger sensor delivers less depth of field than a smaller sensor.
Ok, so I did a little test. I took the same shot, once with the G10 and once with the 20D.
I used full zoom on the G10 which is 30.5mm (140mm). ISO 100 and f/5.6
With the 20D I used the 18-200 zoom at roughly 88mm (x1.6 = 140mm). ISO 100 and also f/5.6.
Pictures were not altered in any way except shrunk to 900 pixel width in PS.
First the G10:
And here the 20D:
I used full zoom on the G10 which is 30.5mm (140mm). ISO 100 and f/5.6
With the 20D I used the 18-200 zoom at roughly 88mm (x1.6 = 140mm). ISO 100 and also f/5.6.
Pictures were not altered in any way except shrunk to 900 pixel width in PS.
First the G10:
And here the 20D:
Blurred background (and DOF) is affected first by sensor size, then distance from the subject, and then aperture. S90 has a tiny sensor, which is it's biggest issue. You can likely focus close, but as another poster mentioned, you can't have f/2.0 at the long end of the zoom. Also, it's only 4X zoom.I have never owned a conpact with a fast lens and am curious about this. I have read that compacts have a greater depth of field compared to a DSLR at any given aperture. What i want to know is is it possible to still have some out of focus backgrounds? I have been longing for RAW in a small Canon compact for a good while now.
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Tony
The end result is that outside of macro shots, the S90 will not be better at subject isolation than the SD series. It will, however, permit more light in at f/2.0, meaning you can stay one full ISO level lower (ISO 400 instead of 800, or 200 instead of 400, etc.). It will not help subject isolation or narrow DOF.
Sorry.
after posting this I see michi98 (above) shows this point by example. 'Nuff said.
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