Are all apertures the same???
Jul 4, 2018 08:53:17 #
More importantly, learn the Exposure Triangle.
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
Jul 4, 2018 08:59:23 #
IBM wrote:
If you keep going like that you are going to run out of commas.Yea you may be right it sounds as you know very little and are asking the wrong questions ,like what is the fstop and what does it do when I change it , and what does a higher or lower shutter speed change your stop out come if your in manual , then there's iso how many years yo
Been with a camera , hang in there you will do ok
Been with a camera , hang in there you will do ok
Jul 4, 2018 08:59:57 #
TonyF
Loc: Bradenton, FL
swartfort wrote:
Thanks for the condescension. The only thing that you KNOW what I don't know is the question I asked. I do KNOW your response was pompous and might be a CLUE why people hesitate to ask questions here. I am sure there are BOOKS on kindness and generosity that you could invest in. Maybe if I join a camera club I could run into someone as KIND as you face to face. To others who try to help. A sincere thank you.
Jul 4, 2018 09:10:01 #
Jul 4, 2018 09:11:31 #
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
Some nice and some not so nice answers, some probably helpful, others sarcastic. I'll take a middle short route, buy the more expensive better fixed f/2.8 or f/4 Zoom lenses and you will not have to worry about this so much. Yes, f/2.8 with a 28mm lens provides the same amount of light as a f/2.8 135mm lens, with in reasonable standards. And at f/4 with the same two lenses the same. Those of you who think T-stops, cinematographers, will make technical arguments about those vs F-stops. F-Stop -- T-Stop, but say if you are using an in-camera meter none of that technical picky-ness means anything.
Jul 4, 2018 09:13:48 #
StanMac wrote:
Yes, that is short and sweet.
Jul 4, 2018 09:15:35 #
StanMac wrote:
Jul 4, 2018 09:24:17 #
Jul 4, 2018 09:36:45 #
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
Theoretically yes, but in practice, no. Different lenses with differing kinds of glass, element counts, group counts, coatings, etc. will transmit different amounts of light at the same marked f/stop.
See, f/8 only means that the hole in the iris diaphragm is equal to the focal length of the lens divided by 8. Zoom lenses adjust the iris as you zoom.
Hollywood solved this problem years ago, by marking their lenses with T/stops. The T means the aperture scale of the lens is calibrated to reflect identical light transmission for every lens. The scale is the same, but accurate from lens to lens. It ought to be, when paying $5000 to $65,000 for a lens!
Jul 4, 2018 09:40:49 #
The f-stop is a ratio of focal length of the lens and the diameter of the aperture. It is a dimensionless number. Is f/11 the same for on lens than another? No. Ex. the aperture diameter on my Scneider-Kreuznach lenses at f/11 is approx. 10.5mm. On my Schneider-Kreuznach f/11 aperture is approx. 13mm. Same f-number, different aperture diameter.
--Bob
--Bob
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
Jul 4, 2018 09:42:22 #
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
In theory, f7.1 from ALL lenses provides the same volume of light to the sensor for the purposes of exposure. As a practical matter, it can vary minutely do to manufacturing tolerances. That is the exact reason why f-stops are a reciprocal number ratio ! ( for light volume/exposure determination)
The thing that most people do NOT realize is that the actual physical ( absolute) size of the f7.1 aperture will vary according to the focal length of the lens - and this affects DOF directly.
..
Jul 4, 2018 09:45:00 #
Jul 4, 2018 09:46:51 #
Slight correction. The f/8 means the focal length of the lens divided by the aperture of the diaphragm equals 8. f-stop=focal length/aperture.
"...paying $5000 to $65000 for a lens" is the reason I'm very happy that the video bug never bit me.
--Bob
"...paying $5000 to $65000 for a lens" is the reason I'm very happy that the video bug never bit me.
--Bob
burkphoto wrote:
Theoretically yes, but in practice, no. Different ... (show quote)
Jul 4, 2018 09:49:56 #
swartfort wrote:
My "common sense" look at this tells me ... (show quote)
F stop would be about the same although due to variance of lens quality there will be minor differences however it is a good generalization however keep in mind that each lens has a different "sweet spot" so while f7 may be the sweet spot for one lens it might be around f5 on a different larger aperture lens.
my 50 mm 1.8 has a sweet spot around 3.5 whereas my 18-55 3.5-56 kit lens is sweetest around f7 or 8.
Jul 4, 2018 10:01:14 #
A clarification:
F-stop is indeed a purely mathematical calulation; the ratio of the lens' focal length to the diameter of the aperture. So f8 is f8 is f8.
However, two lenses set to, say, f4, may in fact provide different amounts of light to the imaging plane due to absorption and reflection of the optical elements of the lenses themselves. So a prime lens (that has relatively few elements) set to f4 will pass more light to the chip than a complex zoom lens (that has multiple elements and groups of lenses internally).
It is for this reason the "T-stop" - which stands for "transmission stop" - was introduced long ago - this is an actual measure of how many photons make it through the lens. T-stops 'came out' for movie camera lenses, which decades ago had far longer zoom ratios than still camera lenses did (since studios could afford those beasts and normal people couldn't). So a lens set to T4 would throw exactly as much light onto the film as any other lens set to T4.
F-stop is indeed a purely mathematical calulation; the ratio of the lens' focal length to the diameter of the aperture. So f8 is f8 is f8.
However, two lenses set to, say, f4, may in fact provide different amounts of light to the imaging plane due to absorption and reflection of the optical elements of the lenses themselves. So a prime lens (that has relatively few elements) set to f4 will pass more light to the chip than a complex zoom lens (that has multiple elements and groups of lenses internally).
It is for this reason the "T-stop" - which stands for "transmission stop" - was introduced long ago - this is an actual measure of how many photons make it through the lens. T-stops 'came out' for movie camera lenses, which decades ago had far longer zoom ratios than still camera lenses did (since studios could afford those beasts and normal people couldn't). So a lens set to T4 would throw exactly as much light onto the film as any other lens set to T4.
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