NickTrop
Veteran
Right. The f-stop value IS a measurement for the amount of light that a lens captures in the front end of the I/O process. It is not an estimate. It is an exact calculation that is the same for all lenses that was developed in 1897 iirc. However, the lens is an I/O device. The elements, coatings, surface to glass areas are all parts of the internal process of that I/O process that results in light and information loss when the "processed light" exits the I/O device (lens) through the rear element. A lens is a device that processes light. That process "robs" information carrying light to some degree, which varies from lens to lens.
The light that actually hits the film plane or sensor is the "T-stop value". Yes, it is important in cinematography, which is why cine lenses measure light in more accurate t-stops than f-stops (and cine lenses don't have click stops, etc...)
However, the difference or ratio between t-stop and f-stop is also important to still photographers, I argue, and is overlooked. A lens, like the Sigma Art (and many others) may have a t-stop value of 1.7 on a 1.4 lens. You may look at this value difference and shrug, it's only .3. However, if you calculated this as a percentage, this difference is more substantial as the additional corrective elements in this lens over traditional/classic designs for a 50 results in only 82% of the light captured as INPUT in this lens being transmitted to the sensor/film plane and the balance -- 18%, being lost in the "process", and never making its way to the sensor.
My understanding is this loss affects some frequencies more than others (the blue spectrum) and affects microcontrast but not resolution or detail data. I argue that the loss of microcontrast is what attenuates overall fidelity and attenuates "3D pop" of an image.
A "poppy" lens is, indeed, the lowly Nikon 50/1.4 AF-D, a classic 7 element configuration. This lens has an "at or near" 100% transmission rate according to DXO.
If you want to see examples, search this lens in Flickr (or any other low element count lenses). Another good one is the Nikon 45mm 2.8 pancake, which is a Tessar design -- 3 elements.
Here are a couple examples of the 50/1.4D that I think "pop".
https://www.flickr.com/photos/mecca...Ner-7iJjUm-9akLhD-e3DADC-8WzAdx-8wVxrW-cvgLhy
https://www.flickr.com/photos/teamg...er-7iJjUm-9akLhD-e3DADC-8WzAdx-8wVxrW-cvgLhy/
DominikDUK
Well-known
Nick a small correction the Tessar has 4 elements not 3, also maybe Nikon was honest enough and actually used the T Stop instead of F-Stop. I agree the difference between F and T stop can be quiet substantial. But 7 elements ist not really a low element count lens as far as prime lenses go. For a Zoom lens it would but a 6 to 7 elements prime lens is pretty much the standard. Most of them being a double Gauss variation. 4 Elements is enough to correct most optical faults from a lens design point of view.
Also in cinematography you light for the T-stop you want, the shutterspeed can't be used in the same way as in still photography. You can vary the exposure by changing the angle of the shutter but this has some serious effects on the look of the image.
Also in cinematography you light for the T-stop you want, the shutterspeed can't be used in the same way as in still photography. You can vary the exposure by changing the angle of the shutter but this has some serious effects on the look of the image.
NickTrop
Veteran
I have already addressed this. That's the DXO score. Look it up to verify, be my guest. I say there is probably some light loss but it's minimal and this 1.4 t-stop value is due to rounding. The actual number may be something like 1.44 (or something). The newer G-series has a 1.5 t-stop rating, also excellent, with one more element than its classic D-series counterpart. And this has been measured by a third-party, DXO, not Nikon. And what's to stop Nikon? I suppose they could but it's a standard measurement, and nobody buys a lens (nor seems to care other than me, really) based on differences between f-stop and t-stop values.
davidnewtonguitars
Family Snaps
Nick, thanks for starting this thread, and for defending it in the face of some unfriendly criticism. I can't have an opinion whether your theory is true or false as I understand very little of optics, but like the old saying "I may not be able to define it, but I know it when I see it" applies, and because of this thread, I will know a little more of what I am looking at.
brbo
Well-known
The nuts behind "glass is evil" have done that.
I think you will convert to the church when you see how much "pop" the 6 element lens have over 13 element lens (one picture was slightly altered to have roughly the same center exposure, corner fall-off and fov):
You can't see it? Just as well, not everybody has the eye that is required to see the "slower photons" (I'm not making that up!) and the havoc and flatness they create.
Papercut
Well-known
Brilliant post! That link is simply hilarious reading. ... I wonder if there are any eye exercises that can let me see the slower photons too.
shawn
Veteran
Yes to both. It isn't possible for that lens to have 100% light transmission. Go look at the very best (likely extremely expensive) optical glass Schott mades. That is a single thin layer of glass that isn't doing anything else to the light and it doesn't have 100% light transmission. That thinking some couple of hundred dollar lens with many more elements beats that is absurd. You are looking at one single (wrong) spec and using it to try and confirm your hypothesis. That is the definition of confirmation bias.
100% transmission would mean the glass was invisible, you couldn't see it as no light would be reflecting off it. Clearly that isn't the case.
No, you said multiple times it had 100% light transmission and perfect transmission with no information loss. That isn't possible. The spec you keep repeating is wrong and a loss of brightness doesn't mean what you are implying. Stop down 1 stop and light transmission is cut in half. But almost every lens on the planet will improve optically. Think about that. Stopping down, literally passing less light through a lens from input to output, makes it objectively better in many measurable areas as well as subjectively better in sharpness, contrast and even lighting (vignetting). If reduced light transmission equaled information loss that would not be possible.
The 1.4d has about 91% transmission (for green) and its transmission is uneven across the visible spectrum. It has more color shifts that some other lenses.
I understand wanting to try to quantify this but you are trying to quantify something that is personal preference. That means it is a subjective opinion. If you like the 1.4d fine, it has some characteristic that you prefer. No problem.
Where a problem comes into play is when people try and justify or assume their preference is because some technical aspect of the product might be 'perfect' and then go out and try and prove that without much knowledge about all the other variables at play in the product and their preferences related to it.
If you like the 1.4d great, enjoy it. It isn't because of perfect light transmission.
Shawn
mich rassena
Well-known
The nuts behind "glass is evil" have done that.
I think you will convert to the church when you see how much "pop" the 6 element lens have over 13 element lens (one picture was slightly altered to have roughly the same center exposure, corner fall-off and fov):
...
You can't see it? Just as well, not everybody has the eye that is required to see the "slower photons" (I'm not making that up!) and the havoc and flatness they create.
I feel like there must be a bit of sarcasm in your post, but I'll break down what I saw when looking at the article.
In the right image, the camera is closer to the subject than in the left.
If you compare the image of the two heads cropped, where the article says "And there you have it: rounder cheeks, rounder neck, unstretched." you'll find that in the photo on the left, the head is closer to the camera. So, you get a shallower depth of field. Note the objects in the background. The perspective, the arrangement between objects in the foreground and background should not change if the entrance pupil is in the same spot. You could use an 18mm lens and compare a crop from that photo to one taken with a 600mm lens and they should align perfectly, as long as the camera hasn't moved. So something was done incorrectly. Being closer to the camera makes the head on the left appear larger. Putting the images side by side greatly exaggerates the effect. In fact there are a number of well-known optical illusions which rely on objects being compared this way.
For the curious, take the two images and overlap them in Photoshop and switch off the layer visibility and go back and forth. It should be very clear what is happening.
Also that whole business about stretch to the left. Being closer to a subject exaggerates the difference between objects which are near and far. Even the lips and nose of the sculpture will differ in presentation of they are different distances from the camera. Objects further away from the camera appear flatter. There is a typical portrait distance, which happens to coincide with fitting well with the field of view of a 85mm lens on full frame. Get too close, and the nose bulges out and the ears go away.
But again, overlay the two images, compare them. You'll see the differences are trivial.
It's not the camera or the lens, it's where you stand. It's frustrating to have to use the phrase "not even wrong" to describe this article, but there you are.
michaelwj
----------------
It's rounded, fudged, and pushed as far as it can be to either a) be the "fastest" or b) fit in with full, 1/2 or 1/3 stop accepted values.
No, it's not a measurement, it's an ideal theoretical calculation, as you say above.
The light that actually hits the film plane or sensor is the "T-stop value". Yes, it is important in cinematography, which is why cine lenses measure light in more accurate t-stops than f-stops (and cine lenses don't have click stops, etc...)
The difference between T and F stops is only important if you don't use a TTL meter and only if it is big enough to result in a botched exposure.
Correct!! The loss of transmission through a lens of course effects some frequencies more that others. Frequency = colour, and any reflection is a loss. If you look at your 1.4/50 AF-D you'll see that it's coated in purple and amber I believe. You can see those colours because they are reflected while others are not. Reflected = not transmitted, so if you can see a coating (or any part of the glass) then it doesn't have 100% transmission. The loss is specifically in the colours you see reflected.
So, micro contrast and 3D pop. Depending on your definition if 3D pop, micro contrast has an influence, but also how the contrast changes with respect to the focal plane and a whole host of other things. Contrast, micro and global, is important. But, it has nothing to do with T stop or F stop. Nothing.
Now I see the misconception. Blue light. Blue has a shorter wavelength, so it must feature in micro contrast more than red, whose wavelength is longer. This is incorrect.
pagpow
Well-known
+1 +1 +1
Whenever these conversations pop up, it soon becomes clear that different folks mean different things by "Pop", or 3-D, or plasticity, or roundedness. This is usually clearest when someone does post a photo illustrating what they take "Pop" to be about.
After looking at many of these threads, IMO, the argument goes on because people then argue about causes of different phenomena as though those phenomena were one and the same.
I, too, would love to see a set of photos illustrating these implicit definitions. Not so much because I think that would get us agreeing about the causes, but because we might get closer to agreement on nomenclature.
For example, some people showing a photograph they associate with POP show a photo taken at relatively wide apertures with a background in the distance (out of focus) often taken with a lens exhibiting vignetting.
This is not what I mean when I say 3D which often involve one of several situations: 1) the interwoven above ground roots of a tree, often with no out of focus portion, 2 portraits, 3) large woods, or high cathedral interiors, or 4) both rural and urban landscapes with receding lines.
Clearly the last two owe at least part of the 3D aspect to lighting direction and perspective effects in the subject. Not having seen enough such photos, I am not ready to conclude that ALL 3D impression is a result of lighting and subject characteristics.
Anybody interested in generation a group of photos with the characteristic they illustrate: 3d, POP, dimensionality, roundedness, plasticity, etc?
Corran
Well-known
It's just distortion.
brbo
Well-known
teddy
Jose Morales
Ok folks, there is a difference. If you can't see it - too bad. Go to bed, dream of your Leica, Zeiss or Nikkor and sleep well. If you are using a cheap or average monitor with poor colour you won't appreciate the tonal differences. If you do see the difference, they are very minor. Just go, take photos and create art. The FIFA world cup is on, nukes haven't blown us up yet, tomorrow is another day. I might go and use my CV 21/4 with some Fuji SS 400 on my iiif. This could be nice! ;D
LeicaFoReVer
Addicted to Rangefinders
Can someone explain why nowadays there is increasing number of multi-focal lenses with good wide apertures, such as olympus 12-40 f2.8? Or is it my perception? Has the technology advanced? To my knowledge it was hard to obtain single wide aperture for multi focals in the past. So in defense of the OP's main point here, they are supposed to be inferior to old low element count lenses such as my zeiss 45mm f2 for contax g? (I can hear people saying "inferior in what sense?", I dont know lets say its resolution power).
michaelwj
----------------
In short, yes. Technology has advanced that far. Advances in computer simulations and designs, advances in manufacturing and repeatedly being able to make something to within small tolerances, advances in glass and glass-plastic hybrid element mouldings for highly aspherical elements, and lastly, advances in computation on the raw data in camera to reduce distortions and vignetting and such.
As an example, the lens elements in your phone are so highly aspherical that they would have been impossible to manufacture a decade or so ago, now they cost a few cents. See for example https://images.anandtech.com/doci/6777/Frequencies Presentation.013.png
retinax
Well-known
That (what you linked) is a pretty low element count lens
. In earnest though I wonder when these complex surfaces will show up in lenses for larger sensors. That could indeed mean less elements.Roger Hicks
Veteran
Admittedly I have only skimmed this so far but I see no mention of veiling flare. In the early days of Kodachrome it was not particularly unusual to prefer uncoated lenses, or to omit lens hoods, so that veiling flare (non-image-forming diffuse light) flattened contrast by "filling" the shadows. More light in the shadows = higher film speed, the equivalent of a faster lens.
In the 1930s it was famously the case that fast Leica lenses had higher resolution but less contrast (more lens groups -- not necessarily more lens elements) while Zeiss had more contrast but less resolution; this is why 50 Sonnars are 3-group lenses ( 6 glass/3 group for the f/2 and 7 glass/3 group for the f/1.5: fewer air/glass surfaces). Coating bought a lot more contrast to such lenses as the Xenon (7 glass, 5 group) and its successor the Summarit (7/5 again).
Cheers,
R.
In the 1930s it was famously the case that fast Leica lenses had higher resolution but less contrast (more lens groups -- not necessarily more lens elements) while Zeiss had more contrast but less resolution; this is why 50 Sonnars are 3-group lenses ( 6 glass/3 group for the f/2 and 7 glass/3 group for the f/1.5: fewer air/glass surfaces). Coating bought a lot more contrast to such lenses as the Xenon (7 glass, 5 group) and its successor the Summarit (7/5 again).
Cheers,
R.
LeicaFoReVer
Addicted to Rangefinders
No one also mentions about the content of the glasses (e.g.REE contents) or their quality such as the presence of micro bubbles or not. How does it compare past and modern times glasses? I heard from my father that during second world war, Russia took away a lot of raw zeiss or leica glasses, which were aged to get rid of bubbles, and later used those in their early russian lenses and hence the quality of early Jupiters are better (?). Has anyone heard of that story?
Roger Hicks
Veteran
No, and it's not true anyway. You can't "age" glass to "get rid of bubbles", and the impact of small bubbles on image quality is immeasurably trivial.
Sorry, but not sure about what you mean by REE.
Cheers,
R.
michaelwj
----------------
There are trade-offs with glass composition. We have newer glass types, but on the other hand toxic metals are no longer allowed, so I'm not sure if it's better or worse. In many ways modern lens designers have their hands tied compared to their predecessors.
Already in the early 1900's glass making was well established for those who paid for it, bubbles were not an issue for established lens makers.
Case in point is the Hasselblad SWC. Early models had lead containing glass (up to the CF). The 905SWC (CFi lens) had to eliminate the lead for environmental reasons, so newer glass types were chosen and the lens recomputed to compensate. It's considered to be not as good and indeed the MTF charts tell the same story (see links).