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Just a noob question i've been thinking about for awhile.

I understand the principle of Aperture in Lenses, but can someone please answer this scenario:

Two simlar lenses where the main difference is Maximum Aperture, will they both let through the same amount of light at the same aperture?

e.g. Will the 50mm1.4 let in the same or more light than a 50mm1.8 at the same aperture, say f/4?

Cheers
- beej

If you had two 50mm lenses ( f1.4 and f1.8 ) and set the aperture to f4 with the same iso and same subject, then your exposure time should be the same.

Thanks.

But then why the fascination with such lenses where you'll rarely use them wide-open due to such shallow DOF?

Theoretically they can be a great aid in low-light situations, but there will a negative effect on your images where only a thin plane in focus.

Beej, I fully agree with you regarding the use of fast lenses in low light - you're compromising depth of field just for 'getting the shot'.

The differences in your example transcends beyond mere maximum aperture values. There is substantial difference between the 1.4 and 1.8 50mm primes in build quality. I guess that's where your extra dollars go.

People do use them wide open, the depth of field will get shallower the closer you move towards the subject. So if you are far away them DOF wont be too shallow.

The F1.4 gives you the option to shoot at f1.4 the f1.8 doesn't. Sometime you need that option.

Another advantage of the 1.4 is that when used on a more recent Nikon cameras such as the D70 (where you must set lenses with aperture rings to its maximum aperture before mounting it on the camera, e.g. 50mm f/1.4 at 1.4), is that it helps focussing in low-light.

Bigger aperture = more opening for light to shine onto focus sensors = quicker to lock focus.

The camera will try to acquire focus when you press the shutter halfway (or using the AE/AF button, if you set it to AF-on) at the lens' maximum aperture (1.4), and only stop down to the selected aperture (e.g. f/4) when you press the shutter all the way down.

beej wrote:e.g. Will the 50mm1.4 let in the same or more light than a 50mm1.8 at the same aperture, say f/4?

Good question, Beej.

F4 is F4 is F4.

So yes, they will let the same anount of light through. I'm sure someone will post the formula for this.

TheK wrote:.....where you must set lenses with aperture rings to its maximum aperture before mounting it on the camera, e.g. 50mm f/1.4 at 1.4....

Are you sure this is correct? I've never done this. Why is it necessary. I thought the cpu enabled connections told the D70 all it needed to control the lens fully.

stubbsy wrote:

TheK wrote:.....where you must set lenses with aperture rings to its maximum aperture before mounting it on the camera, e.g. 50mm f/1.4 at 1.4....

Are you sure this is correct? I've never done this. Why is it necessary. I thought the cpu enabled connections told the D70 all it needed to control the lens fully.

Yeah I have never done this either

W00DY wrote:

stubbsy wrote:

TheK wrote:.....where you must set lenses with aperture rings to its maximum aperture before mounting it on the camera, e.g. 50mm f/1.4 at 1.4....

Are you sure this is correct? I've never done this. Why is it necessary. I thought the cpu enabled connections told the D70 all it needed to control the lens fully.

Yeah I have never done this either

Maybe we're talking about different things here, but I have to do it on my 50mm 1.4 and on my 70-300mm otherwise you get the dreaded FEE error... They have to be manually set to the widest aperture (and have a little locking switch to keep them there)...

leek wrote:
Maybe we're talking about different things here, but I have to do it on my 50mm 1.4 and on my 70-300mm otherwise you get the dreaded FEE error... They have to be manually set to the widest aperture (and have a little locking switch to keep them there)...

Thinking about it maybe the lens I use (70 - 300) is always in the locked position anyway. So yeah your probably right.

I have just no t noticed it before.

W00DY

On a lense with an aperture ring the aperture must be set at the minimum eg-f22 on a consumer Nikon camera otherwise you'll get and FEE error.

Leek and The K are correct. Maybe the reason Woody and Stubbsy haven't done it is because you guys don't have 50 1.4s. One correction though is that you actually set the lens at its smallest aperture possible (largest number), but as TheK says, it stay wide open till you depress the shutter button. The 50 1.4 is an older design than the newer AFS and G lens you two are used to using. Most of the AF lenses are like this.

Glen wrote:Leek and The K are correct. Maybe the reason Woody and Stubbsy haven't done it is because you guys don't have 50 1.4s. One correction though is that you actually set the lens at its smallest aperture possible (largest number), but as TheK says, it stay wide open till you depress the shutter button. The 50 1.4 is an older design than the newer AFS and G lens you two are used to using. Most of the AF lenses are like this.

Thanks Glen. So the 50/1.4 is old school - maybe I shouldn't get one since I have more to remember

Glen wrote:Leek and The K are correct. Maybe the reason Woody and Stubbsy haven't done it is because you guys don't have 50 1.4s. One correction though is that you actually set the lens at its smallest aperture possible (largest number), but as TheK says, it stay wide open till you depress the shutter button. The 50 1.4 is an older design than the newer AFS and G lens you two are used to using. Most of the AF lenses are like this.

Ahh I thought they were referring to the G lens also.

Cheers,

W00DY

Thanks Glen. So the 50/1.4 is old school - maybe I shouldn't get one since I have more to remember

Peter,
That's the way of the 50/1.4 and no other Nikon 50mm is G lens and most of the prime has two rings AP and Focus ring. Once you set it to the minimum and that's, never go back.

Peter, Birddy put it right, set it once and never touch again, then just use like a G series, plus it can also be used on bodies which don't support G series lenses. They need lenses which work on basic film cameras as well. Not so much old school rather no need for a redesign as there is not much you would want extra on this lens such as AFS or G

Peter,
Go for the Noct or the Repro 85/1.0

W00DY wrote:Ahh I thought they were referring to the G lens also.

The G series (includes the Kit lens) lenses have no aperture ring. They are effectively always stopped down to their minimum aperture, and thus there's no need (nor is there any way that you can) set this from the lens.

Glen wrote:...One correction though is that you actually set the lens at its smallest aperture possible (largest number), ...

Thanks for the correction, Glen. I got things mixed up.