Is pro glass faster at same aperture setting?
I had an interesting discussion at a photography meet yesterday. The argument was over whether or not a better lens could be faster (i.e. yield lower shutter speeds) at the same focal length and aperture setting. My understanding has always been that all lenses are the same but that pro lenses typically give you a larger max aperture..

However the counter argument was that by using better quality glass and/or fewer lens elements (when using a prime for example) you should be able to get more light through the optics of a better lens. Since the f number is simply the ratio of pupil diameter and focal length, there should be other factors that affect the total transmission of the optics..

One of the attendees to the meet put this to the test by taking the same picture at f/5 and 50mm and identical shutter speed, once using at nikkor 18-200VR and a second time using a 50mm f/1.4 prime. The resulting images looked the same. Of course that is not really an accurate way of measuring but still an indication that different lenses give the same exposure..

Can anyone shed some light on this dispute?.

Thanks for any input!!..

Comments (17)

F8 is f8 regardless of the lens..

A faster lens will allow the use of a higher shutter speed, but only at the wider apertures..

The greatest of mankind's criminals are those who delude themselves into thinking they have done 'the right thing.'- Rayna Butler..

Comment #1

GodSpeaks wrote:.

F8 is f8 regardless of the lens..

True enough, but all things can be quibbled about.  .

In the old days, before WW II, Kodak marked their lens with T stops instead of F stops. This was a Transmission factor, about how much light actually got transmitted through the lens at each stop. For example, uncoated lens just bounce the light around between the elements, and much is lost or goes back out the front..

But otherwise, it is true that the reason the F stop method is used is because it gives an equalized reading for all types of lenses, wide angle, telephoto, etc...

Comment #2

It's been my experience that some lenses are a little faster or slower than what they are marked, but it's a very small amount..

If you think about it, the notion that there is a wide range of variation between say, f/2.8 lenses, is faulty. If that were the case, the lens that is "faster" at 2.8 would overexpose when an accurate meter is used, and a "slower" lens at 2.8 would tend to underexpose..

I think it's a crock..


Comment #3

Possible. If someone would porduce a lens with absolutely horrible transmission charachteristics.But the reality is that even the cheap lenses use reasonable glass.A member of the rabble in good standing..

Comment #4

Differences between lenses are small (or even negligible). Also where differences exist the manufacturer may change the actual aperture size (effectively making them T-stops rather than f-stops) to ensure consistent transmission between different lenses (as godspeaks says: f/8 is f/8).

Paul - not sure I agree with you - the exposure meter in your camera should be able to compensate for the difference between a 'fast' and a 'slow' f/2.8?.

Thanks for interesting feedback guys - I think I was correct in my argument yesterday but I definitely learned something new anyway!..

Comment #5

Anyone who knows anything at all about the history of photo lens development knows that this whole controversy was argued ad-infinitum in the photographic press many years ago. As lenses became more complex, with many more elements, there was concern that some lenses with more elements would have significantly less light transmission than other simpler lenses. In theory, that is true, and accurate light measurements can prove it. But in practical terms, it makes little difference photographically. For a time, Kodak and others marked some of their lenses in "T" stops rather than "F" stops, but the feature never caught on and was dropped. The advent of automatic exposure systems in cameras made the whole question moot..

Use your cameras to make good pictures and stop splitting technical hairs.Judy.

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Comment #6

GodSpeaks wrote:.

F8 is f8 regardless of the lens..

Yes, but it tells you nothing about how much light is getting through the lens..

Different lenses will meter differently at the same settings....why? Because not all lenses let in the same amount of light...even if they are both at F4...and are 85 MM..


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Comment #7

F4.0 is f4.0 no matter what lens you are talking about. it is a mathematical ratio and that is all. if 2 lenses with same fstop and same number of elements and construction were compared at a given iso then the resulting shutter speed would be the same..

The problem arises when you compare 2 lenses with the same fstop but they have different number of elements or groups, not to mention the type of glass that was used. all glass is not the same. this is when you get into the question of Tstops, which is the actual amount of the light tranmitted through the lens. this can vary between lenses. but how much light(amount are we considering) are we really talking about though? if the answer is coming up to say 1-9% then how could you see a difference between 2 lenses? a 5% difference would still mean that the shutter speeds are the same..

I would think that when you switch to exotic glass materials, like flurite glass elements, you trying get clarity resolution or some other benefit or just plain better image quality...

Comment #8

I lack any "non pro" lenses to conduct this test..

35 L @ F2.816-35 L II @ F2.8.

If you can not see that the prime is brighter...check the histogram...and check your eyes..

Exposure Time = 1/4"F Number = F2.8ISO Speed Ratings = 100Focal Length = 35mm.

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Exposure Time = 1/4"F Number = F2.8ISO Speed Ratings = 100Focal Length = 35mm.

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Comment #9

I've seen f/2 lenses that were f/2 in the middle and f/4 in the corners. And focussed in the middle but....

In general terms the better lenses are f/2 in the middle and in the corners and f/2 is a usable aperture. Meaning it doesn't drop off badly at full aperture. Not all of them are labelled "pro" and a lot of the good ones were labelled "Summicron" and "Zeiss"..

Just my 2d worth..

Regards, David..

Comment #10

Ominous wrote:.

I lack any "non pro" lenses to conduct this test..

35 L @ F2.816-35 L II @ F2.8.

If you can not see that the prime is brighter...check thehistogram...and check your eyes..

Well, my eyes are pretty good but I'm not too proud to check the numbers in Photoshop. It confirmed what I thought, though - that the centres of the two images are the same - within 1%. The difference is that there is *much* more vignetting in the 16-35 image..

Exposure Time = 1/4"F Number = F2.8ISO Speed Ratings = 100Focal Length = 35mm.


Exposure Time = 1/4"F Number = F2.8ISO Speed Ratings = 100Focal Length = 35mm

Comment #11

At the same f- stop all lenses should be the same speed, I am sure there are some which are faster and slower at the same f-stop but the difference is probably very slight. Definately not worth worrying about! I can only get budget lenses and my two fast ones are a 50mm Zuiko 1.4 (100mm on my Olympus) and a Tokina 100 - 300 f4 (200 - 600 on my Olympus)Both pretty fast but very cost effective for their purpose..

If you need fast glass it can be very expensive !!.


Tim Hughes

Comment #12

JudyTee wrote:.

But in practical terms, it makeslittle difference photographically. For a time, Kodak and othersmarked some of their lenses in "T" stops rather than "F" stops, butthe feature never caught on and was dropped..

FWIW, wikipedia claims "modern cinematographic lenses now usually tend to be factory-calibrated in T-stops." at

A little looking around makes it seem obviously true...

Comment #13

If you have two lenses, both marked f/2.8, and you take picture with them at f/2.8, and one produces darker or lighter images than the other, that's a huge problem. Not all of us use internal meters, and many of us shoot in manual. If I changed lenses, I wouldn't want to be thinking about whether I have a "fast" f/2.8 lens, or a slow one...

Comment #14

This is really a topic for Chuxter! (Yoo-hoo!!).

OK, lets say one lens is made of smoky beer-bottle glass and the other is a Canon deluxe "L" lens of the best quality: what then?.

Well, if you use a hand-held meter, I think you will find that your "indicated" exposure will be far too fast (insufficient light), and you will have to do what all photographers have done through the ages, that is: compensate for your equipment..

On the other hand, if you have on-board "through-the lens" metering (in working order), there's no the meter will accomodate for any discrepancy and set your exposure according to the reading it gets from either/any lens you care to use (as is already the case when, for example, you place ND or Polarizing filters in front of your lens)..

Using any "good average quality" lens should produce less of a variation between various lenses than the range of variations already produced by "millions" of other factors in your "exposure train", including idiosyncrasies of shutter and meter, film speed variations between batches, ambient temperature, aperture faults etc already existing in films/sensors, cameras and lenses, even of the same make and model..

That's why "indicated" exposures do not always produce the expected, actual exposure in general...

Comment #15

As seems to be generally agreed, f-stops are a very accurate approximation of a lens' ability to pass light, but the characteristics of any individual lens design can vary that amount. For example, an oldie, the Super-Takumar 50mm f/1.4 lens (M42 screwmount).

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The thorium in this lens has turned quite brown over the last 50 years or so, and it passes considerably less light than my brand new 50/1.8 with both lenses wide open. The theoretical half-stop advantage is lost to the brown "beer bottle" glass. However, as the camera is measuring light through the lens, my metering is still accurate, I just get slower shutter speeds.Nick DavisI love my full frame F4s!Please feel free to critique anything I post. I'm here to learn..

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Comment #16

The performance and transmission of lenses do vary, even at the same aperture and yes f/x IS f/x no matter what else..

So, why?.

1) Precision of manufacturing, particularly of diaphram controllers. Given that the actual aperture diameter of a 24mm lens at f/16 (for example) is 1.5 mm (roughly 1/16th of an inch) any variation in diaphram closing accuracy CAN impact transmission. With anywhere from 5-10 blades closing to create the aperture, any one of them can misalign, (Suggestion: Look through a stopped down lens and see the asymetrical nature of the aperture opening. ) Lubricants, temperature, spilled soft drinks, dust or other problems can affect aperture accuracy at any setting in addition to manufacturing precision..

2) Perception of variation when none exists: F/Stops are continuous and can be set between stops, of course. However, electronic diaphram controllers and LED display readouts are NOT and have fixed ability to display informtion. So, the camera CPU rounds off the displayed setting to within either 0.5 or 0.33 EV of actual depending on how accurate your meter is set to display readings. This displayed reading is not fully accurate, even if the actual aperutre could be accurate..

3) Glass transmission issues. It is true that some glass transmits more light than other compositions. But this is NOT a big issue from most modern manufacturers. Several technologies have evened out the varibles to where the overall volume of light at any aperture is extremely close to it's theoretical f-stop. What is different about different glasses is how they imapacts things like glare, flare, color accuracy and other abberrations. Hence the implementation of low dispersion glass, anomolous dispersion glass, high refraction index elements, aspherical elements and other technical advances to improve performance.

None solves all issues and each has to be used selectively to produce gain and not add expense without benefit. That said, low contrast glass and other shortcuts in manufacturing and design CAN negatively impact image quality..

4) Coatings. About 40 years ago, the concept of "multi coating" began to have a profound impact on flare reduction, color correction, contrast management, saturation and greatly improved the effective transmission of very complex elements. All other things being equal, MC often made results better and was one thechnology that evened out the various transmission issues. However, like most other non standardized features, the exact meaniing of Multi Coating is left to each manufacturer. For some, it is basically a label with little in the way of corrective coatings added to their lenses. Some, have superb coatings that actually add huge benefit at a relatively low cost..

Summary, even the most noted lens makers have some variation (usually of no consequence) in the overall volume of light transmitted at any specific f setting. Most good manufactureres have taken all of the issues into account and the transmission issues are anomolies to specific lenses and not models,. F/X is still f/X because the variation in volume is not significant..

The real issue with lense with the quality of light control within the volume. Color accuracy, flare control, abberration control, contrast control, etc..

I hope this helps.Van..

Comment #17

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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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