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this will prob sound stupid to some


brrttpaul e2
3 203 United Kingdom
2 Jun 2013 7:03PM
but why is it that bridge camera,s/compacts can have an aperture at say 4.5 right through its zoom range and dslr,s dont? For example there was a fuji bridge camera with a constant 2.8 aperture right through its zoom range yet a lens of 2.8 on a dslr will cost thousands? Am I missing something here. I was just wondering why

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The essential reason is that SLRs have much larger sensors than bridge or compact cameras with f/2.8 zooms.

For example, the Panasonic Lumix FZ200 has a constant-f/2.8 zoom lens of tremendous range – equivalent to 25-600 mm on a full-frame SLR – but it only manages that feat because its sensor is very small. The sensor is about 6.3 × 4.7 mm (a size called 1/2.3"-type for historic reasons).

By contrast, a full-frame digital SLR has a sensor of roughly 36 × 24 mm. That’s about 30 × larger by area! Because the sensor is so much larger, a 25-600 mm f/2.8 zoom lens would be truly colossal, prohibitively heavy, and priced so high (probably in the hundreds of thousands) that no-one would buy it.

Although APS-C sensors are smaller than full-frame sensors, they’re still very large indeed compared to most compact cameras: somewhere in the region of 10 × larger. Thus there are no high-ratio f/2.8 zoom lenses for them either.

Another way to look at this is to consider that the Panasonic FZ200 has a 25-600 mm-equivalent lens, but its true focal length – which determines the size (and cost, etc.) of the lens – is only 4.5-108 mm. A full-frame lens of the same range would need to be actually 25-600 mm.
2 Jun 2013 8:56PM
Also on the compact camera, the aperture of 2.8 is not a true 2.8 because of the sensor size. It's probabaly in the region of 5.6 - 8.
Nick
2 Jun 2013 9:04PM

Quote:Also on the compact camera, the aperture of 2.8 is not a true 2.8 because of the sensor size. It's probabaly in the region of 5.6 - 8.
Nick


Sorry f2.8 is f2.8. The size of the aperture has nothing to do with sensor size
discreetphoton e2
10 3.5k 20 United Kingdom
2 Jun 2013 9:05PM
I think you might have to explain that one Nick. You've lost me.
brrttpaul e2
3 203 United Kingdom
2 Jun 2013 9:10PM
Thanks very much both for taking the time to explain that to me, so with that in mind is there anything stopping a manufacturer putting a smaller sensor in a dslr specifically aimed at zoom lenses? so that lenses could be smaller and cheaper? with astrophotography they chip the sensor (i think) specifically for astro images, could a smaller sensor be put in a dslr? and then design smaller lenses specifically for that camera/sensor
3 Jun 2013 5:02AM

Quote:Thanks very much both for taking the time to explain that to me, so with that in mind is there anything stopping a manufacturer putting a smaller sensor in a dslr specifically aimed at zoom lenses? so that lenses could be smaller and cheaper? with astrophotography they chip the sensor (i think) specifically for astro images, could a smaller sensor be put in a dslr? and then design smaller lenses specifically for that camera/sensor

That has been done already in a few ways:
1. "Bridge" cameras have non-changeable zoom lens, smaller sensor and remind closely of DSLR ergonomics - see Fujifilm Finepix HS10/20/30/50 family.
2. Amateur DSLRs have sensors smaller than full frame professional ones, but can take their lens.
3. Newly invented micro 4/3 format cameras have sensors half-size ( by sensor diagonal) of full format cameras and can use dedicated smaller size changeable lens, zoom lens included.

Quote:Also on the compact camera, the aperture of 2.8 is not a true 2.8 because of the sensor size. It's probabaly in the region of 5.6 - 8.
Nick
Sorry f2.8 is f2.8. The size of the aperture has nothing to do with sensor size


It is worth mentioning here that aperture can be absolute ( measured as the lens front element diameter) and relative ( measured as relation of this diameter to the lens focal length). Absolute aperture becomes smaller with the same f number as sensors "shrink", but relative aperture is sensor-size independent.
brrttpaul e2
3 203 United Kingdom
3 Jun 2013 5:28AM
thanks very much michael, that all makes sense. much appreciated
Paul Morgan e2
13 16.1k 6 England
3 Jun 2013 5:31AM

Quote:Also on the compact camera, the aperture of 2.8 is not a true 2.8 because of the sensor size. It's probabaly in the region of 5.6 - 8


No a f2.8 is a f2.8, get yourself a light meter Smile


Quote:Newly invented micro 4/3 format cameras have sensors half-size


New, its been around for about 9 years now.

Your not going to find many compacts with a fixed aperture while zooming.
brrttpaul:

Quote:… so with that in mind is there anything stopping a manufacturer putting a smaller sensor in a dslr specifically aimed at zoom lenses? so that lenses could be smaller and cheaper?

There are no insurmountable technical reasons to prevent this, but there are good marketing reasons not to do it. Photographers buy SLRs in large part because they have large sensors, which are useful for providing very low noise when you can afford to give the large sensor plenty of light.

Faster lenses (lower f-number) in and of themselves are not useful. The typical reasons to use a lower f-number are to get a faster shutter speed or shallower depth of field or both. But with a larger sensor you can get a faster shutter speed by increasing the ISO setting, and you can get a shallow depth of field even at a higher f-number.

This is probably what nickthompson was getting at with his comment above. Although f/2.8 is strictly speaking f/2.8, it behaves very differently on an SLR and a compact camera. In fact, the f/2.8 lens of the Panasonic FZ200 is equivalent to about f/16 on a full-frame SLR in its shutter-speed capability (at equal noise) and depth of field.

In other words, a 25-600 mm f/16 lens on a full-frame SLR would give the same pictures as the FZ200 with its tiny sensor and f/2.8 lens.

No f/16 zooms exist for SLRs, even though they would be easy (cheap) to make, because people who buy expensive SLRs expect better image quality than they’d get from a compact or bridge camera, not ‘equivalent’ quality.
3 Jun 2013 9:52AM

Quote:....
No f/16 zooms exist for SLRs, even though they would be easy (cheap) to make, because people who buy expensive SLRs expect better image quality than they’d get from a compact or bridge camera, not ‘equivalent’ quality.


Not true - f/22 zooms are not uncommon with DSLRs, for example Sigma 18-200mm . And the flagship camera of superzooms Panasonic Lumix FZ200 has the smallest aperture of f/8. And this has been done some solid technical, not commercial reasons. f16, and even less would be simply unusable with a superzoom because of diffraction induced blur - which shows up even with f/8.
3 Jun 2013 10:08AM
That Sigma is an f/3.5-6.3 zoom, not an f/22 zoom. When labelling lenses we use the maximum aperture, of course. (But you know this so I’m not sure what you mean by your comment.)

Certainly there are many SLR zoom lenses that can be stopped down to f/16. Almost all of them, in fact.
3 Jun 2013 10:42AM
I see - it was just not too clear what you meant first. Sure, it would be pretty pointless making zoom lens with largest ( most open) aperture of f/16 - and thus throwing away a lot of creative possibilities and flexibility that DSLRs are noted for.

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