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a question about apreture
I have a question. I have been getting to know my camera and learning about things such as apreture and fstop. Now when ever I see examples of f-stops Although we see 1.8 and 3.5 in lense f-stops, you dont see it on any apreture example and calculators..

Does anyone know why this is. Are these no diff than what is above or below what is actually show. Please advise if these make a diff in range of light..

Thnx..

Comments (12)

If you are serious about the equipment you already have in this thread:.

Http://forums.dpreview.com/...forums/read.asp?forum=1014&message=26724383.

There is nothing wrong with the ambitions, but I think you are ahead of yourself in hardware, and need to spend some time learning the basics. I don't know what your time frame is, but some courses at the local community college or a decent photography institute will really help you get a solid foundation..

Best regards,Doughttp://pbase.com/dougj.

Http://thescambaiter.comFighting scammers WW for fun & justice..

Comment #1

F is lens focal length divided by aperture diameter. When you narrow the aperture you let less light through, but (key point) the amount of light you let through is set by the area of the aperture, and area is pi x [radius (= half the diameter) squared]. So, an fstop of 2 does NOT mean twice as much light as an f stop of 4, it means 4 times as much..

Now, an f stop of 1 means, eg, for a 50mm focal length lens, a 50mm aperture. But, (!) 1.4 squared is 2, and 2 squared is 4, and 2.8 squared is eight, and 4 squared is 16 and so on. So the traditional "whole f stops" - 1.4, 2, 2.8, 4, 5.6 and so on - are just the values of [focal length divided by aperture diameter] that correspond to halving the area and halving the light that is let through..

Every time the area is reduced by half = one f stop higher, the light is reduced by half, and to keep exposure constant, the exposure time has to be doubled. In the old days, before in-camera metering, it was very handy to know that one f-stop up or down meant halving or doubling the shutter speed. There are still manual lenses! People who use them still need to know that one f stop corresponds to halving or doubling the shutter speed. Most people do not use this fact..

So you are right that for most lenses there is no longer any compelling reason to have the "f" ring set up so that it has stops - clicks at fixed intervals - or to design lenses so that maximum aperture corresponds to one of the traditional whole or half stops, or to design thumb wheels so that aperture changes in jumps rather than continuously...

Comment #2

ItzBitz wrote:.

I have a question. I have been getting to know my camera and learningabout things such as apreture and fstop. Now when ever I see examplesof f-stops Although we see 1.8 and 3.5 in lense f-stops, you dont seeit on any apreture example and calculators..

For many practical purposes the effect is almost the same as the closest standard f-number value. So 1.8 is close to 2 and 3.5 is close to 4, and you could look for these figures if using some sort of exposure calculator..

Does anyone know why this is. Are these no diff than what is above orbelow what is actually show. Please advise if these make a diff inrange of light..

The question of why - there are many compromises and trade-offs in lens design. For example, size, weight and of course cost all increase as the lens is designed with a wider aperture. So instead of making the maximum aperture fit neatly into the standard scale, there are many other things to consider by the lens designer and manufacturer..

Does it make a difference in terms of brightness and exposure setting? Yes, but not a huge amount..

Say for example you were taking pictures in dim light and wanted to reduce blur by using the fastest possible shutter speed. If the shutter speed is 1/30 second at f/4, it would be 1/40 sec. at f/3.5. And very similar with the change from f/2 to f/1.8. Not a huge difference, but it might give a better resulting picture.Hope this helps,Peter..

Comment #3

Thnx for the info I did finally find one..

I just help with me planning my shots..

And for the other comment. I have a lot of eq but this has nothing to do with the question at hand. I am in and have taken some classes done some shotting and do more each day..

Thnx..

Comment #4

Sorry... something doesn't gel here..

You claim you're a beginner, and you own these cameras:.

Canon Rebel XtiCanon EOS 30DCanon EOS 40DCanon EOS 5DSony Alpha A100k.

..... and yet you're asking a question like this about apertures?.

I don't think so!..

Comment #5

Just in case you don't think your original question has been answered....

F1.2, 1.8, f3.5, f4.5, f6.3 are some fairly common non-standard apertures, and these numbers were, until recently, most often encountered engraved on the front of lenes, indicating the maximum aperture..

They are determined usingthe math thatyou've already been told..

Once a lens designer / manufacturer calculates the maximum aperture, the "names" for the other apertures, and the notches for setting them, etc. are based on a conventional scale of f1.4, f2, f2.8, f4, f5.6, f8....

With more electronics in cameras, you can now set interdediate f stops, between the ones int e conventional list. Depending ont he camera, they may be half stop differences, ior 1/3 stop differences..

My Canon says f4 (conventional) and then f4.5 and f5 before it gets to the next conventional stop, which is f5.6.

F6.3, f7.1, f13, and lots more are "new" f stops, which you can set on some but not all cameras, and read on some, but not all, light meters. I got a new meter yesterday and set the meter so that it will read in 1/3 stops, but out of the box, it jumped from 2 to 2.8 to 4 to 5.6....

BAK..

Comment #6

That's what the green square mode is for. You can drive an expensive sports car without knowing what an "overhead cam" actually is, or why you might want more than one..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #7

You really ought to start out at the community college. The classes where I'm at meet once a week for 4 hours which is easy to work around. You might find something similar in your area. I think this would be the quickest and most cost effective way to get up to speed. Investing in education would have far more impact than purchases of any additional equipment...

Comment #8

Ed, I suggest you read the thread posted in the pro digital forum. I think the OP will need more than the green zone to get to reach his objectives. He has a fairly aggressive plan that covers a few styles..

Best regards,Doughttp://pbase.com/dougj.

Http://thescambaiter.comFighting scammers WW for fun & justice..

Comment #9

BAK wrote:.

- - - Snip! Snip! Snip! - - -.

F6.3, f7.1, f13, and lots more are "new" f stops, which you can seton some but not all cameras, and read on some, but not all, lightmeters..

Hi,.

Just a point: if these are "new" then how come I've them on my 1930's camera's lenses? And on my 1940's light meter?.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Regards, David..

Comment #10

Doug, if you use the threaded view, you'd see I was replying to the guy who was dubious about big-equipment-list vs limited-aperture-knowledge. As to whether the OP really was using Green Square, or how he got to this point without understanding the trivia of aperture theory and history, I would have no idea of course. Which is all this is... most calculators don't have 1/3stop because most cameras never did either..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #11

There are two ways light hits the image sensor of your camera one is the shutter and the other is the f/stop you sellect. These numbers are marked on the lens. If there are two sets of numbers they refer to how fast the lens is. Or how much light gathering power the lens has. One import thing to remember is if you open up your lens from one stop to another you are letting in twice as much light and if you close up your lens then you are halfing the amount of light. The more light gathering you lens has the faster it is and the more expensive the lens is.

If you do not know this term then go to google and look it up...

Comment #12

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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