Are all apertures the same??? My "common sense" look at this tells me that there is a difference, but numbers are the same so.... I am shooting with a lens with variable aperture...

swartfort Loc: Evansville, IN

My "common sense" look at this tells me that there is a difference, but numbers are the same so....

I am shooting with a lens with variable aperture 4-5.6, but I find the sweet spot of the lens is 7.1 or 8. When I purchase a new lens with a 5.6-6.3 variable aperture, but has significant more reach (and size, lens groups etc.) but I still shoot at 7.1, will my camera's sensor still set the same ISO (I shoot auto ISO)?

Another way to state this... Does a 7.1 aperture setting on a short tele lens allow the same amout of light onto the sensor as a 7.1 aperture setting on a long tele lens?

Thanks

LarryFB Loc: Depends where our RV is parked

swartfort wrote:

My "common sense" look at this tells me ... (show quote)

The simple answer to your question is "YES". But there is more to this question than you are asking. I highly recommend reading "Understanding Exposure,"by Brian Peterson.

IBM

swartfort wrote:

My "common sense" look at this tells me ... (show quote)

I suggest read some books ,is a inch the same on every measure tape or school ruler , does f8 and be there ring a bell , if aperture were not the same we all would be in trouble , you have got to start from the beginning ,it appears you know nothing about how a camera works and don't have a clue what each thing is for , join a camera club and get asking questions , I learned through reading books , the first was the time life books on photography about 14 volumes, on every thing you need to know ,

TriX Loc: Raleigh, NC

swartfort wrote:

My "common sense" look at this tells me ... (show quote)

Not necessarily. f stop is a calculated number, so a given lens at an aperture of f7.1 may or may not have the same light transmission as a different lens at f7.1 (likely not). If you want to accurately compare light transmission, then t stop (often used on cine lenses) is the correct metric.

Bill_de Loc: US

The F/stop is a ratio between the focal length and the physical diameter of the aperture. So, the actual size of an F/7.1 aperture will be different on different focal length lenses. But the good news for us is that they should all let in the same amount of light.

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Steve Perry Loc: Sylvania, Ohio

Bill_de wrote:

The F/stop is a ratio between the focal length and the physical diameter of the aperture. So, the actual size of an F/7.1 aperture will be different on different focal length lenses. But the good news for us is that they should all let in the same amount of light.

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^^This

And you can prove it by looking at any light meter. They don't have different F/stops listed for different lenses. Like Bill says, they F/5.6 lets in the same amount of light from lens to lens. There could technically be a difference due to T-Stops, but that's seldom more than 1/6th of a stop.

IBM

[quote=swartfort]My "common sense" look at this tells me that there is a difference, but numbers are the same so....

I am shooting with a lens with variable aperture 4-5.6, but I find the sweet spot of the lens is 7.1 or 8. When I purchase a new lens with a 5.6-6.3 variable aperture, but has significant more reach (and size, lens groups etc.) but I still shoot at 7.1, will my camera's sensor still set the same ISO (I shoot auto ISO)?

Another way to state this... Does a 7.1 aperture setting on a short tele lens allow the same amout of light onto the sensor as a 7.1 aperture setting on a long tele lens?

Thanks[/quote the aperture is like your eye , and a cats eye ,you notice how wide the get in dim almost dark out , if the cat opened its eye
Looking at the sun and open it's eye it , would be over exposed and just get a big blast of sun light and his eyes holes would shrink ]
If it was dark,his eyes would open like the owel s eyes

swartfort Loc: Evansville, IN

IBM wrote:

I suggest read some books ,is a inch the same on e... (show quote)

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.

IBM

[quote=IBM]

swartfort wrote:

My "common sense" look at this tells me ... (show quote)

There is other factors just be cause it's the same stop doesent mean your going to get more or less light . Your shutter speed for one among others

TriX Loc: Raleigh, NC

Bill_de wrote:

The F/stop is a ratio between the focal length and the physical diameter of the aperture. So, the actual size of an F/7.1 aperture will be different on different focal length lenses. But the good news for us is that they should all let in the same amount of light.

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I dunno. I was comparing a Canon EF 70-200 f2.8L at 200mm wide open with a Canon 135 f2 wide open with a 1.4x extender (which should have been f2.8), and the resulting exposure was different by over 1/2 stop (everything else the same). Maybe the extender wasn’t really exactly 1.4 x in terms of aperture, but >1/2 stop difference? Surprised me.

There’s a reason cine lenses (which have to have the same transmissibility when switching between cameras and lenses on a given scene) are calibrated in tstops (and cost so much)

IBM

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.

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

drmike99 Loc: Fairfield Connecticut

swartfort wrote:

My "common sense" look at this tells me ... (show quote)

As others have said, the simple answer is YES. F stops are mathematical relationships that allow us to get the same light through despite the difference in focal lengths. Don't get hung up on this 4-5.6 or 5.6-6.3 "variable aperture." It isn't really a variable aperture. What varies is the MAXIMUM f stop the lens has at a given focal length. It is a lot cheaper to build a zoom lens that has a higher maximum f stop at the zoom end than it is to build one that maintains the same maximum aperture throughout the zoom range. That's why zooms that give only one maximum f stop are so much more expensive. The variable aperture lenses have, for example, a maximum of f/4.5 at the wide angle end, but only a maximum of f/5.6 at the zoom end.

Marionsho Loc: Kansas

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.

Thank you, swartfort.
"might be a CLUE why people hesitate to ask questions here".....Hits it right on the head.

There always has to be a few that will make the OP look like he must be to lazy to look it up, or to dumb.
Takes all the fun out of the UHH forum.

TriX Loc: Raleigh, NC

IBM wrote:

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

Seemed like a pretty clear (and knowledgeable) question to me...

TriX Loc: Raleigh, NC

drmike99 wrote:

As others have said, the simple answer is YES. F s... (show quote)

I think it actually is a variable aperture. If you look at a variable aperture (or fixed) zoom from the front as you zoom, you can actually see the aperture close down - at least that’s what I see on my variable aperture as well as fixed aperture zoom(s). If I recall correctly, it’s an intentional part of the design, but I’d have to check references to provide the in-depth technical reason (been awhile since I read the explanation) Since f# is a ratio of entrance pupil to FL, some internal aperture change would seem to be necessary, even on fixed aperture zooms, or fstop would always change (linearily) with change in FL.