A question about aperature...
Feb 25, 2013 14:58:56 #
F/2.8 is the smaller NUMBER and largest aperture OPENING. F/32 is the larger NUMBER and the smallest aperture OPENING.
I am 100% positive that is what was meant by the previous post.
It is impractical and VERY expensive to make a large range zoom lens that is constant aperture. A 70-200 f/2.8 lens is pretty hefty and expensive. Even a 70-200 f/4 lens is more expensive than the equivalent focal length variable aperture lens. Something like a 70-400 f/2.8 lens would be HUGE and prohibitive in cost for 99.9% of the buying public.
I am 100% positive that is what was meant by the previous post.
It is impractical and VERY expensive to make a large range zoom lens that is constant aperture. A 70-200 f/2.8 lens is pretty hefty and expensive. Even a 70-200 f/4 lens is more expensive than the equivalent focal length variable aperture lens. Something like a 70-400 f/2.8 lens would be HUGE and prohibitive in cost for 99.9% of the buying public.
Feb 25, 2013 16:27:18 #
Feb 25, 2013 18:04:18 #
Feb 25, 2013 19:17:57 #
Hi ladies and gents,newcomer here.Pentax k5.of camra flash
witch one to buy plus any laeds .£200..00 range .Im 71 years old and the wife siad i was to old to start another hobby what dose hall yuo GOOD pepol think .Kind regards to all.PS R L supportee HULL FC
witch one to buy plus any laeds .£200..00 range .Im 71 years old and the wife siad i was to old to start another hobby what dose hall yuo GOOD pepol think .Kind regards to all.PS R L supportee HULL FC
Feb 25, 2013 19:20:29 #
k.melvyn wrote:
Hi ladies and gents,newcomer here.Pentax k5.of camra flash
witch one to buy plus any laeds .£200..00 range .Im 71 years old and the wife siad i was to old to start another hobby what dose hall yuo GOOD pepol think .Kind regards to all.PS R L supportee HULL FC
witch one to buy plus any laeds .£200..00 range .Im 71 years old and the wife siad i was to old to start another hobby what dose hall yuo GOOD pepol think .Kind regards to all.PS R L supportee HULL FC
take care of the witch!
Feb 25, 2013 19:26:34 #
GHK wrote:
There is nothing virtual about the aperture diaphragm in a photographic camera lens. It is physical. It changes diameter by closing or opening blades. If you can see it, it ain't virtual!It's a difficult point, but true telephoto construction means that the optical centre (or nodal point) of the lens is in front of the first lens element, so you 71 mm is only effective at this point and it is necessary to postulate the existence of a virtual diaphragm in thin air. Such a diaphragm would not be constrained in diameter.
GHK
GHK
Feb 25, 2013 19:44:23 #
Feb 25, 2013 21:57:06 #
Feb 25, 2013 22:17:02 #
LoneRangeFinder wrote:
THC
Really? You are okay with this?GHK wrote:
Ummmm, ok.I'm not sure that you've got this right. It's a difficult point, but true telephoto construction means that the optical centre (or nodal point) of the lens is in front of the first lens element, so you 71 mm is only effective at this point and it is necessary to postulate the existence of a virtual diaphragm in thin air. Such a diaphragm would not be constrained in diameter. GHK
THC
Feb 25, 2013 23:01:07 #
Nikonian72 wrote:
LoneRangeFinder wrote:
THC
Really? You are okay with this?GHK wrote:
Ummmm, ok.I'm not sure that you've got this right. It's a difficult point, but true telephoto construction means that the optical centre (or nodal point) of the lens is in front of the first lens element, so you 71 mm is only effective at this point and it is necessary to postulate the existence of a virtual diaphragm in thin air. Such a diaphragm would not be constrained in diameter. GHK
THC
Initials. <Bazinga>
Feb 25, 2013 23:06:32 #
Feb 25, 2013 23:08:37 #
Nikonian72 wrote:
LoneRangeFinder wrote:
I am a bit dense. THC?Initials. <Bazinga>
Ah sorry...Tetrahydrocannabinol (THC) is the active chemical in cannabis and is one of the oldest hallucinogenic drugs known.
Feb 25, 2013 23:12:34 #
LoneRangeFinder wrote:
Now that is funny!Ah sorry...Tetrahydrocannabinol (THC) is the active chemical in cannabis and is one of the oldest hallucinogenic drugs known.
Feb 26, 2013 05:43:43 #
Nikonian72 wrote:
LoneRangeFinder wrote:
Now that is funny!Ah sorry...Tetrahydrocannabinol (THC) is the active chemical in cannabis and is one of the oldest hallucinogenic drugs known.
I'm still trying to postulate the existence of a virtual diaphragm in thin air. Sounds like a guaranteed pregnancy, to me!
Feb 26, 2013 05:52:48 #
GHK[/quote]There is nothing virtual about the aperture diaphragm in a photographic camera lens. It is physical. It changes diameter by closing or opening blades. If you can see it, it ain't virtual![/quote]
Yes; I agree that the physical aperture (which must, obviously, be sited within the body of the lens) is limited in diameter, but the virtual, unconstrained aperture is the one whose dimeter should be used in calculation. I did say that it was a difficult point.
GHK
Yes; I agree that the physical aperture (which must, obviously, be sited within the body of the lens) is limited in diameter, but the virtual, unconstrained aperture is the one whose dimeter should be used in calculation. I did say that it was a difficult point.
GHK
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