NickTrop
Veteran
So you think a f1.45 lens wouldn't be sold as an f1.4 lens? [...] They can't rely on a manufacturer's statement that the lens is f1.4 to mean anything.
Fortunately, for still photography, with the latitude available in film and digital sensors, a few percent fudge factor on the largest aperture doesn't matter.
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/