Does an f/1.4 lens at f/5.6 let in more light than an f/4 lens at f/5.6?

[sfogel2]

Hi, all...

Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?

Thanks

[William W]

No.

[george013]

Hi, all...

Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?

Thanks

Exactly the same.

George

[William W]

Maybe it was a trick question . . .

If we want to get pedantic and technical: then my answer is "no idea unless we have accurate data concerning the T-Stops of the two lenses in question."

The T-Stop is a measure of the light exiting the end of the lens. This can be quite important in Cinematography, but less so in Still Photography, though T-Stops are used for some forensic Still Photography applications.

The T-Stop (typically) may vary less than one third of a Stop when compared to the F-Stop of any one particular lens.

T-Stops can vary 'considerably' (maybe two thirds of a stop) between lenses of the same Focal Length.

WW

[Manfred M]

The f-stop number is nothing than the ratio of the lenses focal length divided by the entrance pupil, so the amount of light of any 100mm for the same f-stop will, in theory, be the same. The reason I say this is that other factors like the effectiveness of the lens coatings, the number of lens elements, etc. can make a minor difference in the actual light transition. If you ever see a cine lens, these don't use f-stops, but rather use "t" numbers where the "t" stands for transmission. This is a more accurate way of gauging how much light the lens actually lets in.

The reason for buying a "fast lens" is that it lets more light in when it is wide open, so one can shoot at a lower shutter speed or ISO level. Also, a lens with a wider aperture (smaller number) setting will give you a shallower depth of field than one with a narrower maximum aperture (larger number).

[Dave Humphries]

Welcome to the CiC forums sfogel2.

I do not disagree with anything written above and it may be pedantic of me to mention this but ....

Also, a lens with a wider aperture (smaller number) setting will give you a shallower depth of field than one with a narrower maximum aperture (larger number).

Again, to be crystal clear - the narrower DoF is also only when those wider apertures are actually being used - e.g. set between f /1.4 and f/4 for the 'example' lenses you gave. So yes, you can pay a lot of money for apertures your style of photography may rarely use - arguably it may be money 'wasted' if your long term aspirations are limited.


Could you do us a favour please?
Could you click Settings (right at the top),
then Edit Profile (on left)
and put your first name in the Real Name field
and where you are (roughly) in the Location field,
then click the Save Changes button below and to right,
this helps everyone give you more personal and relevant answers - thanks in advance.

Cheers,
Dave

[rpcrowe]

Hi, all...

Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?

Thanks

No and yes... No when the lenses are stopped down to the shooting aperture (f/5.6) but, yes at the focusing aperture f/1.4 or f/4). That is why there is often a difference in focusing between faster lenses and slower lenses. As an example, many cameras cannot auto focus with lenses slower than f/5.6 or f/8 aperture, This often comes into consideration with longer lenses or longer zoom lenses which have a maximum f/5.6 aperture and are being used with a 1.4x or 1.5x teleconverter which loses one stop converting an f/5.6 lens to f/8; or when being used with a 2x converter which costs two stops; converting the f/5.6 lens to f/11...

"T" stops were mentioned above. The "T" stop differs from the f/stop as explained: Calculations for f/stops are a ratio between the usable aperture and the focal length; while the "T' stop is an actual measurement of the light being transmitted by the lens. Note f/stops are designated using "f/" while T-stops are designated by "T-"

Also as mentioned the "T" stop system was developed for cinematography so that one lens of a "T" stop set would transmit EXACTLY the same amount of light as the other lenses in that set. That way the various shots from that set of lenses could be inter-cut without any great difference in the density of the image.

"T" stop lens sets were extremely expensive. As an example:
https://www.bhphotovideo.com/bnh/con...EG&sku=1199499


Of course there are several additional differences besides being a T-stop system that make these lenses super expensive..