max aperture?

[andrew_chen3]

If I understand correctly, the mechanism that controls aperture is

inside the camera body (the metal plates that overlap each other).

Since this is so, why do lenses have a max aperture. Couldn't you

just choose to make the aperture hole bigger manually with the

camera, rather than be limited to only certain f-stops.

[bacsa]

it seems, that you do not understand it correctly.

<p>

The mechanism that controls the aperture is in the lens. The <i>shutter</i> is in the camera body(in most cases).

<p>

The "maximum aperture" is the maximum ratio between the focal length and the diameter of the lens at a certain point(i.e. the diameter of the "hole"). That's why "maximum aperture" corresponds to minimum f-number. Now you cannot make a hole bigger than the lens itself, can you? Cheers!

[andrew_chen3]

okay so the actual parts that create the aperture (the plates that slide over each other) are in the lens, right?

[mark_bouquet1]

It's difficult to engineer a lens with a very fast aperture that yields a fine image quality too. I suppose that manufacturers could open the aperture just a bit more in some lens designs, as you're proposing. But the image quality would be an embarrasment to their hard earned reputations for making fine lenses.

[bacsa]

Right. And the hole between them cannot be larger than the max. inner diameter of the lens... They are used to stop DOWN the lens to smaller apertures. The max aperture is defined by the lens' inner diameter, when these little blades are fully open.

[andrew_chen3]

thanks for the info. I have a feeling that the lens companies tend to purposely not make their lens more versatile and have a wider range of apertures. If they did they would be competing against their own lenses. It is better to make ton of different lenses with different apertures and qualities so that you end up having to buy many of them in order to take good pictures in different settings. Albeit, the sharpness and image quality would probably suffer if they tried to create larger diameter lenses and ones with a wider range of focal lengths, but even if they did find a way to do it and keep a high level of optical quality, they would probably hesitate to market it. Everyone would end up buying just those few good versatile lens and forget about the other $1000-5000 lenses that the company also wants to sell.

[minh_thai]

Andrew <p>

 

It is not necessary strictly a business decision to restrict the max aperture. When the aperture is openned up a lot of bad things happens:<br>

1. Bigger lens elements needed: increased size and weight, also much tougher demand on the glass manufacturing process,<br>

2. Chromatic aberation increases, look at the Sony 828. CA can be resolved by having a design with a lot of elements, again complexity, quality control, size, weight, and cost,<br>

3. Geographical distortion increases at close focus range.<p>

 

I'm sure others will come up with more issues... M

[minh_thai]

Andrew <p>

 

It is not necessary strickly a business decision to restrict the max aperture. When the aperture is openned up a lot of bad things happens:<br>

1. Bigger lens elements needed: increased size and weight, also much tougher demand on the glass manufacturing process,<br>

2. Chromatic aberation increases, look at the Sony 828. CA can be resolved by having a design with a lot of elements, again complexity, quality control, size, weight, and cost,<br>

3. Geographical distortion increases at close focus range.<p>

 

I'm sure others will come up with more issues... M

[stephen_w.]

You've postedg some VERY basic questions, recently. May I suggest a class at the YMCA, or at least a trip to the library and/or bookstore?

[Matthew Currie]

"I have a feeling that the lens companies tend to purposely not make their lens more versatile and have a wider range of apertures. If they did they would be competing against their own lenses."

 

Most lens manufacturers do offer many different aperture choices, so they do in a sense compete. But if you think it's just a marketing decision, take a look sometime at, for example, one of the fast (F 2.8) long zoom lenses from Nikon. They are HUGE! Heavy too. To get that kind of speed requires a truly prodigious amount of glass. Even if by some miracle it became possible to manufacture and buy such a lens at a price comparable to a slower zoom, and even if the very informative postings above with regard to comparative optical quality were false, there would still be an argument for the existence of both on the grounds of ergonomics alone.

[charles_stobbs2]

Also the thicker the stackup of glass in front of the film, the less difference (contrast) there is between the lightest and darkest parts of an image.