Why 1.5x magnification on most DSLRs ?

[Jed]

Actually, you are quite right. There is no reason to stop at 1.6x, you could well go even smaller, hence the beginnings of the 4/3" system pioneered by Olympus and Kodak (and Olympus has long since been using relatively small sensors in its E series DSLRs).

It remains to be seen at which point the disadvantages will outweigh the benefits, but definitely full frame is not the ideal standard.

 

[StreetShooter]

For me, one of the strongest arguments against smaller sensors is the lack of DOF control. The smaller a sensor (and lens system) is, the greater the DOF for any given aperture. While this may be wonderful for landscapes and macros, it's pretty lousy for portraits and sports photography. Jed, as a soccer sports photog, don't you think it's important to have a shallow DOF to isolate your subject?

 

[ckiang]

Originally posted by StreetShooter
For me, one of the strongest arguments against smaller sensors is the lack of DOF control. The smaller a sensor (and lens system) is, the greater the DOF for any given aperture. While this may be wonderful for landscapes and macros, it's pretty lousy for portraits and sports photography. Jed, as a soccer sports photog, don't you think it's important to have a shallow DOF to isolate your subject?

Well, but consumer digicams and DSLRs work differently in terms of sensor size and DoF control!

Regards
CK

 

[StreetShooter]

Yes, this has been discussed in a separate thread, and I was enlightened by Knighthunter.

The DOF achieved depends on the lens system, not just the sensor.

Assuming we stick to the 35mm lens system, but have a smaller sensor area, the apparent DOF (relative to the entire frame) is greater.

 

[ckiang]

Originally posted by StreetShooter
Yes, this has been discussed in a separate thread, and I was enlightened by Knighthunter.

The DOF achieved depends on the lens system, not just the sensor.

Assuming we stick to the 35mm lens system, but have a smaller sensor area, the apparent DOF (relative to the entire frame) is greater.

My current belief is that if you keep subject distance constant, focal length constant and change between say a 10D and 1Ds, the 10D output will have less DoF.

Regards
CK

 

[reflecx]

Originally posted by ckiang
My current belief is that if you keep subject distance constant, focal length constant and change between say a 10D and 1Ds, the 10D output will have less DoF.

You are right, but in the real world, you would try to keep the framing the same for both cameras. You would then have to change either the subject distance or the focal length. In this case, the 10D shot would have more DoF.

 

[reflecx]

Originally posted by Jed
I asked for questions... those aren't questions, those are statements of your beliefs, in which case congratulations and keep thinking that way.

Well, I refuted a point you made. But I see that you have ignored my refutations because my mode of reply didn't fit your expectations.

 

[vkm]

Originally posted by ckiang
My current belief is that if you keep subject distance constant, focal length constant and change between say a 10D and 1Ds, the 10D output will have less DoF.

If you keep subject distance constant and fill frame with the same subject then you've got to use different focal lenses because of different "crop factors" of 10D and 1Ds.

In other words:

* Let say that you are taking head and shoulder portrait with 80mm lens mounted at 1Ds at 3 meter distance from model and the aperture is f/5.6.

* If you switch to the 10D and wish to get the same head and shoulder portrait with the same perspective (from the same 3 meter distance), you ought to put the 50mm lens. Now if you take the picture with that 50mm lens at the same f/5.6 aperture, you'll get greater DoF, as StreetShooter have mentioned!

Theory says that such image taken with 10D and 50mm lens at f/5.6, will have DoF equivalent to the DoF of image taken with 1Ds and 80mm lens at f/9 (5.6 x 1.6 = 9).

 

[nhyone]

Originally posted by Jed
hence the beginnings of the 4/3" system pioneered by Olympus and Kodak

I am beginning to wonder if a fixed sensor size make sense. This is because there is a minimum pixel size of 4-5 um to get a good signal-to-noise ratio. Once we hit it, the only way to get better resolution is to enlarge the sensor size, and what happen to the lenses then?

Smaller sensors also means the diffraction limit is reached at a wider aperture.

As to the benefit of full frame sensor, what do you feel about mounting medium format lenses to your 35mm camera? An overkill, isn't it?

 

[clive]

for the DOF issue, assuming aperture is not a problem, then i guess it will really depend on whether one is more inclined to change focal length or change subject distance

 

[Jed]

Originally posted by StreetShooter
For me, one of the strongest arguments against smaller sensors is the lack of DOF control. The smaller a sensor (and lens system) is, the greater the DOF for any given aperture. While this may be wonderful for landscapes and macros, it's pretty lousy for portraits and sports photography. Jed, as a soccer sports photog, don't you think it's important to have a shallow DOF to isolate your subject?

Yes it is. I'll ignore the issue of whether there is shallower/deeper DOF or not, and assume there is for the moment.

But with a 1.5x sensor, you get more DOF at similar apertures. However, your lenses can also be built faster for the same size, weight and cost. So instead of an 80-200/2.8, you'd get an 80-200/2.0. Which would make up for the deeper DOF at f2.8 by being able to open up to f2.0.

 

[Jed]

Originally posted by reflecx
Well, I refuted a point you made. But I see that you have ignored my refutations because my mode of reply didn't fit your expectations.

No, you decided to express two commonly held misconceptions. And since you didn't ask to be set right, then I won't try to correct you. Like I said, questions please.

 

[Shadus]

Originally posted by reflecx
Let's see...
1. Bigger sensor, keeping pixel count constant = less noise
2. Can shoot wider angles using existing range of wide angle lenses

I implore not to go into flames here. Not to "target" you, but just to mention this for everyone whose following this thread for information,

The 2 quoted reasons here are common misconception. So lets just leave it at that.

Perhaps Jed have time to write essays on the above 2 issues? since they'll take a rather detailed examination to enable newbies to understand why they're misconceptions.

 

[StreetShooter]

Originally posted by Jed
Yes it is. I'll ignore the issue of whether there is shallower/deeper DOF or not, and assume there is for the moment.

But with a 1.5x sensor, you get more DOF at similar apertures. However, your lenses can also be built faster for the same size, weight and cost. So instead of an 80-200/2.8, you'd get an 80-200/2.0. Which would make up for the deeper DOF at f2.8 by being able to open up to f2.0.

Ah, but there would be no 1.5X crop factor any more. A lens built for this sensor (eg 80-200/2.0) would accomodate the entire sensor area into the optical frame. There would be no cropping effect.

In other words, what you're proposing is in effect an entire new system apart from our familiar 35mm one (let's call it the 24mm system), kind of like what they tried to introduce with *cough* APS. You know what happened....

Good idea, but it will be like turning the Titanic around. Can be done, but with much effort and much time, and risking alienating 90% of the photographic community.

 

[nivlekx]

In my opinion, the reason why it is done this way is cos of marketing. Think about it, it is possible to make a full-frame sensor as the 1Ds and DCS-14n has shown, but will our day to day consumers go for it? No, simply because the cost of producing the sensor is high and on top of that they need to have something special to draw the pros onto their top of the line stuff.

Why 1.6 I don't know, perhaps it is the best ratio they can balance cost and also potential users. We have to remember that as a manufacturer, they are not only wooing new customers, but all those existing Canon and Nikon system users. If they have it too high, no one will go for it simply because the existing lenses will not be effective, but at 1.6x, 28mm can still be acheived rather economically. That's why they went on to produce the new ultra wide angles. That is also why Canon and Nikon are not in the 4/3 system, cos it simply doesn't benefit them, in fact they will be investing to bring down their own 35mm empire if they so decide to put money in 4/3.

Coming up with a new system is going to be tough, 35mm has been in use for decades and there are alot of people who use 35mm systems and they cannot be neglected. The manufacturers jolly well know that their life line depends on these very people that have been supporting them all these while. The need to cater to prosumers is extremely important, but there is also a very strong need to distinguish the professional market from the prosumer market. Otherwise why should a pro go for a pro camera?

 

[ckiang]

Originally posted by StreetShooter
Ah, but there would be no 1.5X crop factor any more. A lens built for this sensor (eg 80-200/2.0) would accomodate the entire sensor area into the optical frame. There would be no cropping effect.

In other words, what you're proposing is in effect an entire new system apart from our familiar 35mm one (let's call it the 24mm system), kind of like what they tried to introduce with *cough* APS. You know what happened....

Good idea, but it will be like turning the Titanic around. Can be done, but with much effort and much time, and risking alienating 90% of the photographic community.

APS died not so much for the size, but more for the proprietary-ness of the thing. Proprietary camera, lens, film, even processing, and the last of them is more costly than processing 35mm film.

On a DSLR, things are slightly different. You start off with a sensor that's big enough that noise is not so much of an issue, big enough that you can pretty much use your existing lenses, big enough for a good cost : size ratio, etc. The way things go, 1.5x FLM DSLRs will probably stay at the mid to low end of the market for several years at least.

Lens wise, it makes a lot of sense then to design a set of lenses optimized for the reduced-size sensor. This can be cheaper than the regular 35mm lenses, and this is the solution to the wide angle problem.

Regards
CK

 

[reflecx]

Originally posted by Jed
No, you decided to express two commonly held misconceptions. And since you didn't ask to be set right, then I won't try to correct you. Like I said, questions please.

OK, one clarification question - are you talking about using a new set of lenses specially designed to fix DX sensor? Or using the current crop of 35mm lenses? Or using the best of both worlds?

 

[YSLee]

Originally posted by StreetShooter
Ah, but there would be no 1.5X crop factor any more. A lens built for this sensor (eg 80-200/2.0) would accomodate the entire sensor area into the optical frame. There would be no cropping effect.

Yes there would. Ever notice that 90mm on 4x5 is considered a wide angle, 6x6/6x7 a normal lens, and 35mm a short telephoto? Focal lengths are absolute. By designing a 80-200mm f/2 lens meant for APS size sensors, it'll give a 35mm focal length equivalent of 120-300mm. But it's f/2.0!

Likewise my IXUS' lens system which was specially designed for it has a focal length of 5.4-10.8mm, but it's no superwide!

CK has addressed the points on APS, so I won't go there.

 

[reflecx]

Originally posted by YSLee
Yes there would. Ever notice that 90mm on 4x5 is considered a wide angle, 6x6/6x7 a normal lens, and 35mm a short telephoto? Focal lengths are absolute. By designing a 80-200mm f/2 lens meant for APS size sensors, it'll give a 35mm focal length equivalent of 120-300mm. But it's f/2.0!

Likewise my IXUS' lens system which was specially designed for it has a focal length of 5.4-10.8mm, but it's no superwide!

Errr, I don't think you addressed StreetShooter's point at all. He was talking about crop factor, not focal length multiplier.

 

[ckiang]

Originally posted by reflecx
Errr, I don't think you addressed StreetShooter's point at all. He was talking about crop factor, not focal length multiplier.

While it behaves like a crop, essentially it's not. It's an entirely different system altogether, and cannot be considered "35mm" anymore. This "APS Digital" system has it's own Circle of Confusion and all. This thing inherently magnifies the image by the crop factor - not just changing the FoV.

So, assuming same subject distance and aperture, the following should look different.

1. 10D + 400/2.8 @ f/4
2. Center crop of 1Ds + 400/2.8 @ f/4

Someone with both cameras help to verify this.

Regards
CK