q@a

[mysteryscribe]

Since there are so many different skill levels here, I thought it might be a good idea to ask a question. Some might learn, some might relearn, some might think of things in a different way.

Since these days photography is about choices more than any other time in history lets see if we know how to make the right choices...

Purely theoretical question since most customers and just plain viewers in general couldn't tell the difference anyway.

Let's say I build a camera (god forbid) And this camera has a dead sharp lens (yeah right). I am shooting against a black background at eight feet so depth of field will play no role in this question.

My camera's lens is sharp at every distance and aperture. The camera can shoot f128 or f1.4... So will there be any difference in the picture at either setting''

Question picture at f128 will be sharper whether it is noticeable or not... true of false..

 

[Unimaxium]

Well, since the lens performs equally well at every aperture, and since DOF is not an issue, then I would say false. I fact, I would think you are more likely to get a sharper image at f1.4 since it lets you use a (much) shorter shutter speed, thus avoiding camera shake or motion blur. It also lets you use a lower ISO, giving you a less grainy image

 

[mysteryscribe]

assume I have a very good tripod shake is not a problem... why can i use a lower iso... why cant i just lengthen the shutter speed and still use a low iso.

 

[Unimaxium]

Ok, assuming you have a good tripod and there is no camera shake, then you can use a low ISO with f128 as well. But there still might be the problem of the subject moving ;-)

Otherwise, I can't think of any way the two apertures would produce a different image...

 

[Unimaxium]

... just thought of something else. With digital cameras there's the issue of long exposure noise. The shorter exposure at f1.4 I think will still produce a better image because CCDs and CMOSes heat up and produce a noisier image during a long exposure. And with film you might have the problem of reciprocity failure (although this can just be adjusted for I assume).

 

[mysteryscribe]

actually this is a learning experience for me as well about digital since digital sensors do not react the same as film. That is why I put it as a theoretical question since I don't really know the answer on digital.

I think I know it on film, but digital reads in macro dots I think. Not sure if the effect would even be the same in theory. It would be an interesting experiment of course practically we cant test it. Someone in some physics lab might be able to test it.

Some of the old film guys should know what I'm talking about..Hertz for sure should.

 

[Jeff Canes]

For personal experience I think the answer is yes with good lens lower f-stop and high shutters work extremely well with digital, including action shots. Also it’s help to deal with dust on the sensor

 

[mysteryscribe]

my problem with big apertures and fast shutter speeds was I couldn't get it focused fast enough on moving objects. Very small depth of feel for those of us with slow hands and manuel cameras. I expect the auto focus might work really well though.

But still doesn't answer the basic question could the aperture size make a difference (even theoretically) in the sharpness of a photograph. Not in the depth of field but in the actual sharpness of the image.

Again im not sure this holds true for digital. even if it exists it is most likely so small that no one would ever notice. But does it matter.

 

[Soocom1]

Mixed bag on this one.

From personal experience: If shooting at a lower ISO with a larger aperture, I normally will expect a sharp image with a ton of saturation. If the opposite, then obviously I get the tack sharp image, but loose some saturation and contrast due to the increased light.

The problem as I see it isn't the type of lens per sie, but more in the lines of the size of the lens both in focal length as well as FOV. The latter will dictate partially the amount of light coming in. The larger physically the lens, then the ratio of the f-number changes dramatically given the FOV.
So the real trick is figuring out that if the 'theoretical' lens is say a 180mm, then how brighter will the image be if say the 'theoretical' lens is 250mm? That aspect is a no brainer, but if you figure you want near eye like resolution, I would err on the side of caution, and go with a lower ISO and increase the latitude.

 

[Unimaxium]

The more I think about this question, the more I think that in a perfect world there would be no difference between f/1.4 and f/128, mostly due to the fact that you have eliminated nearly all of the variables that would affect image quality. In reality, I would say you are likely to get a higher quality image with the smaller aperture as long as you don't go so small that you have to use a long shutter speed or higher ISO (but the former applies only if we're using digital). This is simply because most lenses perform better at smaller apertures. Although... I have heard that some lenses perform suboptimally at both extremes of the aperture spectrum, which would mean that the best aperture to use would be somewhere in the f/8.0 vicinity (someone correct me if I'm wrong about that).

But, back to the point: eliminating the variables of lens build quality, DOF / bokeh, and camera shake / motion blur, the only things that are left are the problem of long exposure noise with digital cameras and reciprocity failure with film. But if we're working in a perfect world, I'd assume that these issues would be taken care of as well, leaving us with no way the image could be different between the two apertures.

 

[mysteryscribe]

okay heres your hint....

why do you have greater depth of field with a small aperture than a wide one?????

Depth of field isnt the issue but the principal is the same...

 

[Jeff Canes]

my problem with big apertures and fast shutter speeds was I couldn't get it focused fast enough on moving objects. Very small depth of feel for those of us with slow hands and manuel cameras. I expect the auto focus might work really well though.

But still doesn't answer the basic question could the aperture size make a difference (even theoretically) in the sharpness of a photograph. Not in the depth of field but in the actual sharpness of the image.

Again im not sure this holds true for digital. even if it exists it is most likely so small that no one would ever notice. But does it matter.

Charily you’re confusing me. At any ISO if you lower the f-stop then the shutter speed need to increase equally to maintain the exposure.

As far as auto focus on moving suspects you need servo mode auto focus that tracks a subject or you need to repeatedly push the focus/fire button to refocus. A big problem with servo mode auto focus in back ground focusing this occur when you lose a moving subject when panning.

 

[mysteryscribe]

This is true what happens when you set your shutter speed so fast that you have no zone of focus. IE 2.8 or 4 ... If that happens your focus on the moving object has to be dead on... I cant get a moving object in focus before it is gone.

I have to focus on a point in the picture and wait for the subject to enter it. That requires some degree of zone focus.

there are a few tricks to help with slower shutter speeds but over all it is always going to be a trade off. However that is why old timers like me love strobe light. No matter what the camera is set on (in a low light situation) the strobe is the shutter speed and it is fast.

In other words you and I are going out in the sunlight to shoot a bike race. You go out with a camera that has auto focus and I go out with an old piece of crap retro thing. Im going to opt for a higher fstop due to the zone focus effect. Then I'm going to pick out a tree and focus on it. When the bikers get even with the tree I'm going to shoot. If they get a few feet past the tree it wont matter.

If your camera auto focuses fast enough it shouldnt matter that the fstop is lower. You can shoot with a more shallow depth of field. In other words i have two variables to worry about and you only really have one. That most likely is an over simplification but it is reasonably accurate I think. Some of the other guys can probably be clearer.

 

[Unimaxium]

I'm confused now. Since when are we talking about moving objects? I thought this question was about the theory of lens optics when photographing a stationary object with a stationary camera.

 

[mysteryscribe]

This may not be absolutely correct so let's hear others comment on it please

but the answer to the basic question on film is yes but nobody could ever tell.

The reason you dont need a lens in a pin hole camera is because of the properties of light. With every lens it focuses the light beans but it still makes a difference how they strike the film.

Think of it like this. light travels in a straight line and is a beam. Let us consider a paper straw since it is the easiest thing to work with. If you stand a straw on its end on a piece of paper it will have a small round footprint on the paper. However if you were to force the straw to lean at a forty-five degree angle it would hitting the paper at an eliptical pattern not a circle. In other words a larger footprint. The smaller the footprint the sharper the picture. The smaller the aperture the straighter the beam hits the film or sensor. Thats what really makes depth of field.

So in theory the smaller the fstop the sharper the picture... that said I have no idea if that is true in digital since the sensor is not like a piece of film. A sensor, I think, is actually a lot of sensors tied together. It reads in dots not straight lines. So I have no idea if this is true with a sensor or not. Im sure someone here knows.

Im not sure i explained it very well some of the ohters can most likely do better. I am also not up on lenses but it is understanding that to a more or lesser degree this holds true with all lenses.

Again I doubt that anyone in the world could tell the difference between a couple of stops. Or maybe even the full bore but I know my still life camera is f90 and it is a lot sharper than it was at f32... AGain it is film and has a retro lens...