Larger sensor just a luxury?

[2WheelPhoto]

High quality full frame sensors can produce better images than high quality crop sensors. If the physics doesn't make that clear just look at the photographs

[TPF Sponsor]

[O|||||||O]

Yep, DX lens just gets rid of all that wasted light, that's why it is smaller. So if the DX lens is made larger, at the size of an FX lens, doesn't it gain back all those wasted light?

So, basically, if you took a DX lens and turned it into a FX lens, would it behave like a FX lens? Is that what you're asking?

I think your question has the answer in it...

No, the size of the DX lens will be the same as FX, only that it covers only the size of a DX sensor.

Are you talking about the physical size of the lens?

The outer dimensions of the lenses could be the same - that doesn't really matter. The size of the image circle is what matters, and that isn't controlled by the physical size of the lens. There are plenty of full-frame lenses that are even smaller than crop sensor lenses.

[EchoingWhisper]

So, basically, if you took a DX lens and turned it into a FX lens, would it behave like a FX lens? Is that what you're asking?

I think your question has the answer in it...

No, the size of the DX lens will be the same as FX, only that it covers only the size of a DX sensor.

Are you talking about the physical size of the lens?

The outer dimensions of the lenses could be the same - that doesn't really matter. The size of the image circle is what matters, and that isn't controlled by the physical size of the lens. There are plenty of full-frame lenses that are even smaller than crop sensor lenses.

No, I don't mean the physical size of the lens. In a few of my previous posts, I've already stated that, so I assumed you guys know what I'm talking about.

[mjhoward]

Kay. I'll not debate anymore. I guess I'm wrong, since you guys are saying that I'm wrong even after understanding what I'm trying to say. But I'm still not clear why am I wrong, cause' my logic don't seem to go with your explanation and no one had explain why my logic is wrong, they just tell me why they're right.

I can see why would would think that, because it does kind of make sense - but it just doesn't work that way... I'm trying to think of a good way to explain it...

If you had a FX lens on a DX body, the image circle is much larger than the sensor. Yes, there is more light coming through it than the DX lens, but that light is just wasted - it isn't doing anything, since it isn't hitting the sensor. The DX lens just gets rid of all that wasted light.

Yep, DX lens just gets rid of all that wasted light, that's why it is smaller. So if the DX lens is made larger, at the size of an FX lens, doesn't it gain back all those wasted light?

If you change the optics of the lens so that it has the same front element but smaller image circle, then you have to change every element in between which means an entirely different lens with a different focal length and different max aperture. I know that it doesnt sound like it would make sense that the focal length of the lens would change if you didnt physically change the length of the lens, but if you take for example the Canon 800mm, it is only about 18" long but it's focal length is 31.5".

[EchoingWhisper]

High quality full frame sensors can produce better images than high quality crop sensors. If the physics doesn't make that clear just look at the photographs

True enough, but more money is spent to make sensors in professional cameras better. Just look at D3x, it's a great example. The D700/D300 is also a good example. The D700 is almost 2 times better than D300 in the low light score, even though a the D700 is supposed to be only 1 time better in the DxOMark low light score than D300. There must be a lot more things going on.

[Balmiesgirl]

I have a d3 and a d300 .... I use the same lenses on both cameras. The d3 (full frame) has much better resolution and better performance in high iso situations. I keep my d300 (dx) because of the extra reach that I get with my lenses. I use my d3 about 90 percent of the time because the quality is sooooo much better.

[EchoingWhisper]

I have a d3 and a d300 .... I use the same lenses on both cameras. The d3 (full frame) has much better resolution and better performance in high iso situations. I keep my d300 (dx) because of the extra reach that I get with my lenses. I use my d3 about 90 percent of the time because the quality is sooooo much better.

Can't doubt it. A professional camera is a professional camera. Much more money are put into it so that it becomes a better product.

[Garbz]

I don't understand where you get the idea that an FX and a DX sensor of the same resolution would result in the same performance. SNR is depicted as a function of photons converted to electrons vs background noise. More photons = better signal = more dynamic range. There's a good reason they sent large 1mpxl sensors to Mars to take photographs, and there's a reason why large sensors in the kilopixel range are used in space telescopes.

Regardless how companies act, and how they bow to demand of marketing departments who dictate "what people want", the simple fact remains more is gained from a larger physical pixels size.

[Kolia]

Weeee, long topic. OP, you have to separate the sensors from the optics (lens) in your mind. The image projected on the back of the camera will be the same regardless of the type of lens for a given setup.

The "fringe" will be missing from the DX lens image but it would overlay perfectly with the image from the FX lens.

The sensors characteristics, resolution sensitivity etc will have their effect over all. But the "source image" will be the same.

[HughGuessWho]

A large sensor gives a different angle of view when using the same lenses and comparing to a crop sensor. This can be a big difference when you're working indoors and want to use something like a 50mm for portrait work, rather than having to use a 35mm and suffer distortion problems (parts of the shot closer to the camera being enlarged). ...

Agreed, however that same logic can be viewed as a deficit in other areas of photography. For example, when shooting birds the effective focal length increase of 150% is a big benefit.

Exactly - which is partly why I love my 7D (along with its fantastic AF).

Although I should point out that the 7D also has a luxury sensor in it, big and expensive if I compared it to a bridge camera.

That settles it. I have been debating about upgrading from my XSi to something better, in the Canon line, of course, and couldnt decide if I should go with the 7D or spend a few bucks more and go up to the 5D Mark II. But if you "love" your 7D.... good enough for me.

[EchoingWhisper]

I realised I'm slightly wrong. The reason larger sensors' lenses are larger is because their focal length is longer compared to smaller sensors at an equivalent focal length. But it is still similar - they are larger - so if we make DX's lenses larger too then it will have the same low light performance.

[LightSpeed]

I realised I'm slightly wrong. The reason larger sensors' lenses are larger is because their focal length is longer compared to smaller sensors at an equivalent focal length. But it is still similar - they are larger - so if we make DX's lenses larger too then it will have the same low light performance.

Some lenses are compatible with both FX and DX.
The difference is on a FX, a 200mm tammy would be 200mm
Put the same lens on a DX and it becomes a 300mm.
Same amount of light going through the lens.

Sensor pixels are measured in microns. For example the Nikon D4 pixel size is 7.3 microns.
A nikon D7000, with a DX sensor, pixels are about 4.7 microns.

How big is a micron? Look at this (.) period.
That's about 615 microns.

[djacobox372]

Longer focal lengths create less dof at the same subject distance, and with full frame u use longer focal lengths to achieve the same composition as aps. A 35mm f1.4 on aps may produce the same exposure and composition as a 50mm f1.4 on full frame, but it will have a wider dof due to the wider focal length. If u use the same lens on both the aps will have less dof due to the fact that you needed to back up 30% to fit the subject in frame.

An extreme example of this is found when you shoot large format film. This photo was taken at f2.5 on 4x5" film:

http://www.flickr.com/photos/espressobuzz/5339594747/

2.5 isnt an extremely large aperture on small format, but it's very large for 4x5, you'd need a f0.75 lens to achieve this on a full frame dslr due to its much smaller sensor area compared to 4x5" film. You get the same effect when going from aps to full frame, just to a lesser degree.

[EchoingWhisper]

Longer focal lengths create less dof at the same subject distance, and with full frame u use longer focal lengths to achieve the same composition as aps. A 35mm f1.4 on aps may produce the same exposure and composition as a 50mm f1.4 on full frame, but it will have a wider dof due to the wider focal length. If u use the same lens on both the aps will have less dof due to the fact that you needed to back up 30% to fit the subject in frame.

An extreme example of this is found when you shoot large format film. This photo was taken at f2.5 on 4x5" film:

4x5 Aero Ektar Polaroid | Flickr - Photo Sharing!

2.5 isnt an extremely large aperture on small format, but it's very large for 4x5, you'd need a f0.75 lens to achieve this on a full frame dslr due to its much smaller sensor area compared to 4x5" film. You get the same effect when going from aps to full frame, just to a lesser degree.

Longer focal length doesn't create less DOF at the same magnification. Larger sensor do seem to use to get less DOF because you could go closer to the subject at the same focal length. But a DX lens at the size of the FX lens but only covering the frame of DX would have similar DOF.

[Kolia]

As said elsewhere, optical physics has nothing to do with the type of sensor.

The conversion factor only applies to the affective FoV captured by each sensor type.