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04/12/2004 07:00:33 PM · #1 |
I have a modest SONY DSC-85 camera, but it let me shoot at F2.0 aperture, very luminous acording in my knoledge, but I'm planning on testing a NIKON D70, a much better cam, but I am surprised: The kit lenses only reach F2.8 and offer a 3x zoom... like mine but darker/slower!?
I am confused... may it be true that my old sony deliver a faster 3x zomm lenses that a Nikon D70 "official" lens kit?
Please someone with more knoledge on lenses could explain it to me? |
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04/12/2004 07:01:41 PM · #2 |
the lens kit is probably way wider.
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04/12/2004 07:49:40 PM · #3 |
There is a relationship between teh sensor size, the lens diameter, and lens assembly length. Someone here propbably has a link to a site that explains all this in great technical detail.
lower f/stop number means more light gets to the sensor. It is a relationship number, not an absolute measurement of the opening. If you look at zoom lenses, they will be advertised/marked as something like '28-200mm f2.8/5.6'. The 2.8 is the measrument at the 28mm, the 5.6 at the 200mm. If yo look at thte 1.4 or 2.0 600 mm lenses (zoom or fixed) for SLR cameras, you will see they are HUGE in diameter, especially compared to the standard 50mm lens.
I hope that helps a little bit.
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04/12/2004 07:59:35 PM · #4 |
The f-number will Dictate the brightness at the sensor, but a larger sensor will have more surface area /pixel to capture light. In effect a larger sensor will have a higher ISO number. This is why with my camera, a Sony F828, I end up taking almost all my photos at an ISO setting of 64 but a 1DS with a full size sensor can run up to an
ISO of well over 1000 and still take good photos. Also with the smaller sensors you have to keep the f-number fairly high or you suffer from diffraction. A large sensor will also need larger glass to keep the f-number low and that can get heavy fast.
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04/12/2004 08:01:30 PM · #5 |
It's true that your Sony has a pretty fast lens. It's much easier to make a fast lens for a cam with a very small sensor. Fast lenses for DSLRs tend to be even faster, e.g. f/1.4 or f/1.8, but are normally primes (single focal length) lenses. Relatively fast (f/2.8) zoom lenses for DSLRs are available, but are very expensive to manufacture.
So it does seem at first blush that your Sony is "faster" than DSLRs in most cases, but remember that DSLRs can produce very low noise images at ISO 800, comparable to what most consumer digicams ccan produce at ISO 200, giving them a two-stop offsetting advantage. Having an f/2.8 lens on a DSLR is like having an f/1.4 lens on a digicam.
DSLRs also have a much shorter depth of focus for the same f number. Very larger apertures are therefore less desirable, unless a very short depth of focus is wanted for artistic reasons.
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04/13/2004 07:46:27 AM · #6 |
Yes, I come to the idea that a bigger sensor need less light to get the same picture, so a sensor with pixel size 4 times (the surface) bigger than mine would need just a F4 to match my F2.0
Making the numbers, D70 has a 374.35 mm2 sensor with 6.31 million pixels, so surface per pixels is 5.821 microns, while DSC-S85 have a 38.19 mm2 (10 times smaller) sensor with 4.1 millions pixels, so a 0.931 microns pixel size... SIX times smaller pixels.
That means that my F2.0 lens is equivalen to a F5.6!!!!!
I read about F2.0 compared to F2.8 or F4 at www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm |
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04/13/2004 08:08:03 AM · #7 |
Originally posted by bitfarmer:
Yes, I come to the idea that a bigger sensor need less light to get the same picture, so a sensor with pixel size 4 times (the surface) bigger than mine would need just a F4 to match my F2.0
Making the numbers, D70 has a 374.35 mm2 sensor with 6.31 million pixels, so surface per pixels is 5.821 microns, while DSC-S85 have a 38.19 mm2 (10 times smaller) sensor with 4.1 millions pixels, so a 0.931 microns pixel size... SIX times smaller pixels.
That means that my F2.0 lens is equivalen to a F5.6!!!!!
I read about F2.0 compared to F2.8 or F4 at //www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm |
I don't think this math is valid.
If you take both camera's at equal ISO and equal aperture and equal shutterspeed, you will get the same exposure (assuming they are properly calibrated and their curve behaviour is equal).
Yes, the bigger sensor gets in more light and this influences noise, but you can't calculate it to an aperture value.
But you can look at it differently :
If I take a picture at ISO 100 with my F707, I get the same amount of noise as the D70 at ISO 400 or even 800. What the D70 lacks in max aperture in the kit lens (F3.6) compared to my Sony's F2.0 is compensated by the availability of higher usable ISO.
(not talking about other pro/con's of both camera's.....) |
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