Fast lens??????

[Philnz]

I hear a lot of talk about fast lens. IE f1.4 is a fast lens.I understand that at f1.4 it would let more light in to the camera therefore let you use a faster shutter speed. However if you shut it down to say f11 how can it let in any more light than a f2.8 or f4.5 lens at the same f11 setting. Am i missing something here?

 

[Don Kuykendall_RIP]

You are not missing anything. People want fast lenses for three reasons.
1. They want very narrow depth of field.
2. They shoot in very low light.
3. They like to brag that that have the fastest lens on the block.

 

[aroy]

. A fast lense gets more light wide open, so it is generally faster in AF.
. Many fast lenses are sharper and more even across the field when stopped down. For example a F1.2 lense (or an F1.4 for that matter), may be much better at F4 than an F2.8 lense. So at times fast lenses are preferred even if you stop them.
. Some fast lenses are designed for low light shooting. Here the "comma" reduction plays an important role. Comma is when a point of light (or say a candle) does not appear as a point but as a point with a tail. The "Noctulux" series are such lenses. In contrast he Nikon 50mm F1.2 is not a low light lense as it has a lot of comma, but at F1.2 it has tremendous bokeh, and beyond F2.8 it is better than most Nikon 50mm lenses.
. Some lenses are designed to perform best at full aperture (most get better as you stop them down). The Zeiss 135mm F2 APO is one such lense. You gain very little in sharpness as you stop it down.

In short in today's scenario a fast lense will focus faster, have a shallow DOF and may be sharper stopped down compared to slower lenses.

 

[Horoscope Fish]

I hear a lot of talk about fast lens. IE f1.4 is a fast lens.I understand that at f1.4 it would let more light in to the camera therefore let you use a faster shutter speed. However if you shut it down to say f11 how can it let in any more light than a f2.8 or f4.5 lens at the same f11 setting. Am i missing something here?

The speed of a particular lens is a reference to its maximum aperture; nothing more.

...

 

[Philnz]

Thanks for the replys that is just what I thougth.

 

[fotojack]

Everything that aroy said, Fish said in 15 words. Both are absolutely correct.

 

[STM]

I hear a lot of talk about fast lens. IE f1.4 is a fast lens.I understand that at f1.4 it would let more light in to the camera therefore let you use a faster shutter speed. However if you shut it down to say f11 how can it let in any more light than a f2.8 or f4.5 lens at the same f11 setting. Am i missing something here?

The "f stop" of a lens is a ratio of the focal length of the lens to the diameter of the opening created by the aperture blades. Unlike the focal length, which is usually measured in mm, the f/stop does not have any units of measure. However, a 50mm lens at f/8 will allow the same amount of light (in lumens) to the film or sensor as would a 600mm lens at f/ 8.

 

[gqtuazon]

I hear a lot of talk about fast lens. IE f1.4 is a fast lens.I understand that at f1.4 it would let more light in to the camera therefore let you use a faster shutter speed. However if you shut it down to say f11 how can it let in any more light than a f2.8 or f4.5 lens at the same f11 setting. Am i missing something here?

I have compared an 85mm f1.8 and an 85mm f1.4 lens before. F11 is something that I do not use except on specific application and it defeats the purpose of buying that lens and not use it to get some artsy-fartsy creativity and to lower iso levels.

However, if both lenses were used with the same camera, mounted on a tripod, shooting at F1.8 aperture, 1/160th, auto ISO, the significance can be measured at higher Iso level. The 85mm f1.8 lens gave me a ISO 4000 and the f1.4 lens only recorded around ISO 2,800 if my memory is correct.

Is that enough justification for you? That is all up to the individual photographer. I do prefer the creamier bokeh that the f1.4 produces but it might not be a worthy investment if you do not use it a lot. a studio type photographer might not need a faster lens if he shoots at f8.


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[Philnz]

I have compared an 85mm f1.8 and an 85mm f1.4 lens before. F11 is something that I do not use except on specific application and it defeats the purpose of buying that lens and not use it to get some artsy-fartsy creativity and to lower iso levels.

However, if both lenses were used with the same camera, mounted on a tripod, shooting at F1.8 aperture, 1/160th, auto ISO, the significance can be measured at higher Iso level. The 85mm f1.8 lens gave me a ISO 4000 and the f1.4 lens only recorded around ISO 2,800 if my memory is correct.

Is that enough justification for you? That is all up to the individual photographer. I do prefer the creamier bokeh that the f1.4 produces but it might not be a worthy investment if you do not use it a lot. a studio type photographer might not need a faster lens if he shoots at f8.


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So someone (me) that just takes Snap Shots most of the time does not really need to worry to much about f stops Unless you are after short DOF, when you can step the ISO up to 6400 and still get acceptable photos.

 

[aroy]

So someone (me) that just takes Snap Shots most of the time does not really need to worry to much about f stops Unless you are after short DOF, when you can step the ISO up to 6400 and still get acceptable photos.

Not many cameras have low noise at ISO 6400. High ISO in my opinion is for those situations where nothing else will work. For normal lower end bodies, ISO 800 is about the limit for clean images (in my D3300 it is ISO 200, beyond that you can see the noise).

Most of the camera bodies also struggle with AF on "slow" lenses, and beyond a point will not AF. That is one of the reasons for having a fast super telephoto; like 300mm F2.8 and 400mm F2.8; they acquire and track autofocus very fast. So you buy them even though most of your shots will be at F4 or more.

Of course if you shoot predominantly in low light, fast action and require a lot of DOF, then High ISO is your only recourse, and you can use slow lenses.

 

[PaulPosition]

So someone (me) that just takes Snap Shots most of the time does not really need to worry to much about f stops Unless you are after short DOF, when you can step the ISO up to 6400 and still get acceptable photos.

Just to be clear : short DOF comes with wide aperture (low f-number). You'll usually crank the ISO when you need bigger DOF thus higher f-number, thus less light getting through).

 

[gqtuazon]

So someone (me) that just takes Snap Shots most of the time does not really need to worry to much about f stops Unless you are after short DOF, when you can step the ISO up to 6400 and still get acceptable photos.

Phil - yes. For those who are not so critical with other factors, and as long as you are happy with the results then it is all good.


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