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05-26-2012, 07:15 AM   #1
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Aperture Question

I am a rank amateur and I have what may appear to be a dumb question. The answer though will help me determine the answers to a few other questions...

On my soon to be delivered K-5 one of the lenses has a F3.5-5.6...

My question is generally about photography fundamentals more than any specific lens...

I have seen some lenses that have apertures from 1.4....some with 1.7...some with 2.4 and so on and so forth...assuming focal length is standard really what would be the 'big difference' between a 1.4 and 1.7 and 2.4 or so on and so forth?

What can you do with a 1.4 that you can't do with a 1.7 or 2.4 or whatever...

In other words I don't have that aperture range covered (yet) so I would like to know or have a little discussion about it...

05-26-2012, 07:32 AM   #2
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This is a good start...

Aperture - Wikipedia, the free encyclopedia

Understand what is Aperture in photographic basic
05-26-2012, 08:22 AM   #3
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Larger aperture= smaller depth of field, allows more light to enter the lens, which makes it a faster lens.

You may want to pick up an old film-era photography book from your library or a thrift shop to understand aperture. The older the book, the better.
05-26-2012, 08:38 AM   #4
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Boris... thanks... that second link was a little more what I was after...

Really though what I would like to see is some pictures side by side showing the differences between 1.2 1.4 1.7 and so forth so I can get a visual feel of things...

Right now 3.5 is the smallest (or biggest) I got...and I am wanting possibly to expand out and get another lens (or two) because it will give me more leeway on the bokeh side of things...The question is more along the lines of 'the devil is in the details'...

05-26-2012, 08:43 AM   #5
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QuoteOriginally posted by Julie Quote
Larger aperture= smaller depth of field, allows more light to enter the lens, which makes it a faster lens.

You may want to pick up an old film-era photography book from your library or a thrift shop to understand aperture. The older the book, the better.
I have been reading books on photography for the last 18 months and recently ordered my first dslr... (K-5)....

Please don't misunderstand my question as in 'what the heck is aperture'... I know what it is...

I am wondering more on a fine scale and possibly seeing examples side by side of capabilities before blowing even MORE money...

I have a 1.8 in mind and I also have a 2.4 in mind...but if I go with the manual lenses I can even go down to 1.2 and so forth.

I am hoping to get to some more in depth talk on finer points of difference than sheerly 'here is what aperture is'...
05-26-2012, 08:44 AM   #6
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Mostly it boils down to this:
1. With a large-aperture (F/smaller number) you can shoot in lower light, since every 1.4x increase in number means one stop less light or two times less light (f/2 is one stop darker than f/1.4, the math is 1.4*1.4~2).
2. Larger-aperture lenses produce a smaller in-focus area, which blurs the background. This effect also depends on sensor size. If the sensor is larger, the depth-of-field is smaller.
3. Since 99% of lenses get sharper as you stop down (close the aperture), you can usually get a sharper image with a faster lens stopped down to equivalent apertures (a 1.8 lens will produce sharper images than a 3.5 lens with both stopped down to f/4.

Edit: Whoops, beaten by a lot of people

Find reviews of fast lenses that include full-size pictures at different apertures, or
http://www.flickr.com/photos/reidsphotography/sets/72157611278405754/

Last edited by Giklab; 05-26-2012 at 08:50 AM.
05-26-2012, 08:49 AM   #7
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QuoteOriginally posted by alamo5000 Quote
I have been reading books on photography for the last 18 months and recently ordered my first dslr... (K-5)....

Please don't misunderstand my question as in 'what the heck is aperture'... I know what it is...

I am wondering more on a fine scale and possibly seeing examples side by side of capabilities before blowing even MORE money...

I have a 1.8 in mind and I also have a 2.4 in mind...but if I go with the manual lenses I can even go down to 1.2 and so forth.

I am hoping to get to some more in depth talk on finer points of difference than sheerly 'here is what aperture is'...
In this set I compared several different 50mm lenses. The A50/1.7, M50/1.7, A50/2, Sigma A 50/2.8 macro, Sears 50/1.7, and Super Tak 50/1.4.

It's not perfect, the tripod moved when I was changing lenses.
05-26-2012, 08:51 AM   #8
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Yes, grab some books. But here's an overview.

An f-stop is a ratio, the ratio of a lens' focal length to the diameter of an aperture. With a 50mm lens, f/2 means the aperture is 1/2 the focal length or 25mm; f/4 is 1/4 of 50mm or 12.5mm; etc. We don't care about the size itself but we do care about the ratio because its easy to calculate exposures based on f-stop and shutter speed. Note that just as 1/2 is a bigger number than 1/4, so f/2 is a wider-diameter hole than f/4 on the same lens.

The size of the aperture hole (the f-stop) has two main effects: 1) it controls the amount of light reaching the frame (film or sensor), and 2) it controls the sharpness of an image and the range of sharpness. This latter is called DOF (depth of field) -- the range of distances from a lens where the image is acceptably sharp. A lens with a wide (large) aperture lets in lots of light but has very thin DOF. An extreme example: shooting a portrait with an 85/1.5 (85mm f/1.5) lens, we might get the end of the subject's nose sharp while everything else is OOF (out-of-focus).

Thin DOF is good when we want to isolate a subject from their surroundings, like for a street portrait. Thick DOF is good when we want an entire scene to be sharp, as with many landscapes. A *fast* lens (with a wide aperture) allows great DOF control. A *slow* lens (with a tight aperture) may be sharper overall but allows less subject isolation.

My fastest lens is a SMC (K) 50/1.2 (50mm f/1.2). I use it when I want great DOF control -- and it also renders images beautifully, being one of the greatest lenses ever made. My slowest lens is a Loreo Perspective Control 35/11 (35mm) which only has aperture settings for f/11 and f/22. I use it for certain architectural-type shoots where I want great sharpness and control over foreshortening.

Lens speed also relates to exposure and action. A fast lens allows a higher shutter speed so faster action can be captured. Say I'm comparing my Industar-50/3.5 and the K50/1.2. There is a 3 f-stop difference between those lenses. So wide-open, a shot with the Industar that needs 1/25 second for a good exposure, can be shot with the K50 at 1/200 second. We use fast lenses to stop action, and slow lenses to either blur or ignore action.

There's lots more, but this should get you started. Have fun!


EDIT: So you already know this? Well, hush my mouth...

Ok, so just go for the f/1.2 lens. You can do stuff with it that slower lenses just can't. It's as simple as that.

05-26-2012, 08:51 AM   #9
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Start at 1 and then start doubling: 1, 2, 4, 8, 16, 32
Now do the same, starting at 1.4: 1.4, 2.8, 5.6, 11, 22

Put them together and you've got your basic aperture, or f-stop, series: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32

These numbers are ratios: the focal length of the lens divided by the width of the hole that the light comes through. Smaller f-stop, bigger hole. You may notice that each number in the series is the previous one multiplied by the square root of two. This because if you multiply the diameter of the hole by 1.4, the area doubles, resulting in double the light hitting the sensor.

You can get the same doubling of light by doubling the time that the shutter is open. But then you hit a snag: either your shaking hands or the motion of your subject will result in your photo being blurred and unpleasing.

So basically, a lower f-stop will let you get faster shutter speeds, and hence sharper pictures, in worse light. Consider your kit lens at 50mm focal length. It will have an f-stop of 5.6. Now consider an F1.4 50mm prime. At F1.4 it will be four stops (count 'em) better than the kit, which means that it will let in sixteen times as much light for the same shutter speed, or, alternatively, you can reduce your shutter speed by a factor of 16 to get the same exposure. This basically means that you can get decent shots in certain circumstances, such as a dimly lit interior, that you couldn't with your F5.6 kit lens.

As for numbers like 1.7 and 2.4, they simply indicate an in-between value: F1.7 is fifty percent better than F2 but fifty percent worse than F1.4.

Partly related to the f-number is your depth of field (DOF) or the distance in front of and behind your subject that is in sharp focus. The bigger the absolute size of the hole (so not the f-number itself) the smaller the depth of field at a given distance. This allows you to get the pleasing result of your subject being in focus with all the other stuff in the frame blurred, something that you will struggle to achieve with a compact digital camera. Too little DOF is not good, however: you don't want one of your subject's eyes in sharp focus while the other is blurred.

Finally, if you're wondering why it's the ratio of the aperture to focal length that's important for exposure rather than its absolute size, it's because at longer focal lengths the light has to travel further. If you recall, light drops off proportionally to the square of the distance that it travels. This means that a 50mm lens with a 25mm aperture (F2) will give exactly the same exposure as a 100mm lens with a 50mm aperture: the larger aperture may let in four times more light, but the longer focal length diminishes it by the same amount.
05-26-2012, 08:54 AM   #10
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You might like this link as well.
Understanding Camera Lenses

and here is a list with more things you might want to look into too.
http://www.cambridgeincolour.com/tutorials.htm
05-26-2012, 08:54 AM   #11
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QuoteOriginally posted by Giklab Quote
Mostly it boils down to this:
1. With a large-aperture (F/smaller number) you can shoot in lower light, since every 1.4x increase in number means one stop less light or two times less light (f/2 is one stop darker than f/1.4, the math is 1.4*1.4~2).
2. Larger-aperture lenses produce a smaller in-focus area, which blurs the background. This effect also depends on sensor size. If the sensor is larger, the depth-of-field is smaller.
3. Since 99% of lenses get sharper as you stop down (close the aperture), you can usually get a sharper image with a faster lens stopped down to equivalent apertures (a 1.8 lens will produce sharper images than a 3.5 lens with both stopped down to f/4.
I have a K5 in en route to my house so that's the camera its going to be on...

Will a 1.4 aperture produce a sharper image than a 1.8 aperture? Is there a point to where things become counter productive in this area?

What about a 1.2 aperture? I am considering going into the market for a 1.? aperture lens (one of the old manual ones) but thus far I am not sure what to get exactly.

I want my ability for creative control... but I am essentially trying to figure out what to shop for? If it essentially won't make 'that much difference' in visual distinction then having a 1.2 and 1.4 won't really matter so much... but I am wondering 'where' the differences really start to become apparent....a 1.8 vs a 3.5 is going to be totally different...but amongst the 1.? range is there going to be substantial differences in visual quality and effect?

IE comparing a 1.2 to a 1.4 to a 1.8 etc...
05-26-2012, 09:00 AM   #12
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We've been jump-posting, so I edited my post in the time the discussion went on.Check the link for practical effect.

As to your question, a 1.4 lens might be sharper (might!) than a 1.8 lens AT 1.8. Of course, there are exceptions.

For practical use, just start at 1 and then start multiplying by 1.4. You won't see much difference between 1.7, 1.8 and 2, but you will see the difference between 1.8 and 2.4 for example.
05-26-2012, 09:04 AM   #13
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Another in addition question... to the sheer aperture... I am new to pentax (and dslr photography)... but I also need a little lesson in the lenses that will work on a K5....I see all these different brands...I see names, names, and more names of brands and I don't know the differences.. bayonet mount, M, A, screw mount and so on and so forth so...

I am not sure which ones are good and which ones are cheap russian knock offs...most of the manual lenses were made about the time I was born (or most likely before)....

A, M, K, Screw...arrgggg...

I am trying to narrow my search here for a lens with a nice aperture....pentax is coming out with one (on their website) that has a 1.8 aperture...but I am not sure if that's the one I want or not. I might just say what the heck and get it anyway once its in stock....but I don't know where to begin with the variety of manual lenses of this range...do I need an adapter, don't I need one? Can it meter? Will it not meter? How can I know all these things before I just go start buying stuff off ebay?
05-26-2012, 09:09 AM   #14
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QuoteOriginally posted by alamo5000 Quote
Will a 1.4 aperture produce a sharper image than a 1.8 aperture? Is there a point to where things become counter productive in this area?
A good f/1.4 will be very sharp wide-open, but ONLY in a very narrow range, so the image overall will seem softer than the same or another lens at f/1.8 or slower. But an f/1.4 lens stopped-down to f/1.8 may be as sharp or sharper than a wide-open f/1.8 lens. Also keep in mind that they're designed differently. My M50/1.7 indeed has better flatfield sharpness @f/1.7 than my FA50/1.4 @f/1.4. But the f/1.4 isolates a subject better wide-open, and they're equally sharp by f/2.

QuoteQuote:
What about a 1.2 aperture? I am considering going into the market for a 1.? aperture lens (one of the old manual ones) but thus far I am not sure what to get exactly.
The K50/1.2 is just one of the greatest lenses ever. So is the A50/1.2 but it costs twice as much for the convenience of aperture automation. Remember, we don't use fast-fast lenses for edge-to-edge flatfield sharpness (get a slow macro lens for that). We use them to grab images that other lenses just can't.

QuoteQuote:
I want my ability for creative control... but I am essentially trying to figure out what to shop for? If it essentially won't make 'that much difference' in visual distinction then having a 1.2 and 1.4 won't really matter so much... but I am wondering 'where' the differences really start to become apparent....a 1.8 vs a 3.5 is going to be totally different...but amongst the 1.? range is there going to be substantial differences in visual quality and effect?
The faster the lens, the greater the control.

I use dozens of different Fifties ranging from f/1.2 to f/5.6. Each has their purposes. If I had to lose all but one, I'd keep the K50/1.2.

Last edited by RioRico; 05-26-2012 at 09:24 AM.
05-26-2012, 09:16 AM   #15
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QuoteOriginally posted by alamo5000 Quote
A, M, K, Screw...arrgggg...
Somebody here will provide a link to a reference on lens mounts. Here are the basics:

* 39mm screwmount: could be Leica-compatible LTM, or Zenit-compatible M39, or enlarger-lens L39. M39s can be used on Pentax SLRs but avoid these for now.
* M42 screwmount: most Takumars and many many other lenses. An adapter is required. We'll tell you all about adapter pretty soon now.
* M-mount (also K series, marked only as SMC): only mechanical aperture control. You must be in Manual mode to use these. Cheap and fun.
* A-mount: has contacts on the lens base for electric aperture control. Easy to use and more expensive generally.
* AF-mount: these are F- and FA- and DA-series. The DAs are for dSLRs and will vignette on FF film cams. The others work just fine on dSLRs too.

Again, there's much more. This is a start.
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