what controls the f stop the lens or the camera

[jann1033]

i was just reading another thread and noticed a blurry picture i had shot was at 80mm at f5.6...it was an interior shot..i tried ( as per someone's suggestion ) today to see if the f stop would go to 3.5 like it's supposed to at 80mm and it did( outside bright sunlight) but i can never get it to do that ( like when i took that picture, it should have moved past 5.6 since it was at the full zoom of 80 but literally the first time i have ever seen it at 3.5 was today) .it won't go larger than 5.6, it's not that it goes there but blinks, the dial literally won't bring it up, stays on 5.6,..so what would cause that..the camera or the lens? i've tried it on av, tv, manual and program...the lens is a rechipped sigma 28-80mm f 3.5-5.6

is something up with the camera or the lens?

 

[OCSurfCity]

Assuming it is a Canon camera, the camera's body contains the exposure meter that tells the lens which aperture to set for the optimum exposure. Of course, you can manually set the aperture if you want better depth of field too.

Or, you can always use the exposure compensation to increase (+) or decrease (-) the camera's suggested exposure.

 

[JR6ooo4]

the camera controls the setting but the lens tells the camera what settings are available. Your lens says "I don't go that low" "You need to spend more money for that!"

when you zoom out, as apposed to wide, the f stop goes up. Zoom full wide to see the lowest f numbers, enableing a faster shutter.

(disclaimer) if I am remembering correctly
Mikeeee


now that I reread your post I am confused as well. the numbers on the front of the lens are the minimum Av. So what is the max?

What mode was the camera. It may have not allowed the AV to be raised if the camera cannot expose properly with the Av variable.

 

[Charade]

i was just reading another thread and noticed a blurry picture i had shot was at 80mm at f5.6...it was an interior shot..i tried ( as per someone's suggestion ) today to see if the f stop would go to 3.5 like it's supposed to at 80mm and it did( outside bright sunlight) but i can never get it to do that ( like when i took that picture, it should have moved past 5.6 since it was at the full zoom of 80 but literally the first time i have ever seen it at 3.5 was today) .it won't go larger than 5.6, it's not that it goes there but blinks, the dial literally won't bring it up, stays on 5.6,..so what would cause that..the camera or the lens? i've tried it on av, tv, manual and program...the lens is a rechipped sigma 28-80mm f 3.5-5.6

is something up with the camera or the lens?

The reason the image was blurry is probably because of one of two things. The photographer doesn't have steady hands (or needed a tripod) or the subject moved a little during the exposure because the shutter was too slow to stop the motion. The cure for that is more light, a steadier hand or support or a stationary subject.

The aperture is in the lens but controlled by the camera. It's an adjustable hole that lets more or less light into the camera's sensor depending whether it's closed down (higher F stops and greater depth of field) or opened up (lower F stops and shallower (or shorter) depth of field).

Most all consumer grade zoom lens like your 28-80 have what they call a variable aperture. This means that when the lens is set to 28 it has a wider (more open hole and lower F stop) aperture. And when it's at 80, it the opposite. In between those zoom settings the aperture is most likely something between F3.5 and F5.6.

You camera may have several auto modes like full automatic where the camera sets both the shutter and aperture based on the light in scene your shooting.

In shutter priority, you set the shutter and the camera will automatically set the aperture to get the correct exposure. If possible. If you set a shutter that's too slow or too fast, the lens may not have an aperture setting that will produce a correct exposure.

The aperture priority mode is just like the shutter priority mode but just the opposite. You set the aperture, the camera sets the shutter (again, if possible) to get the correct exposure.

TV mode is meant for taking pictures of a TV screen. It sets the shutter to 1/60 sec to avoid capturing the black bars (you can't see them) that TVs use to make a TV work.

Manual is just that. You set both shutter and aperture to get the correct exposure (using your camera's meter or an external light meter).

 

[ndelaware]

Jann as I was trying to explain in a reply to a different post of yours, the lens can only be set to F/3.5 when the zoom is at 28mm. At 80mm the lowest f/stop you can set it to is f/5.6. This is determined by the lens and not the camera. You have a Sigma 28-80mm f/3.5-5.6. Try to remember the low numbers go together and the high numbers go together, i.e. 28mm = f/3.5, 80mm = f/5.6. These are the lowest possible f/stops at the different zoom settings. The only way you can set the f/stop to f/3.5 with this lens/camera combination is to set the zoom to its widest point which is 28mm.

 

[Geoff_M]

Keep in mind that an f-stop represents the amount of light that can pass through the lens and on to the film/sensor. A lens' maximum aperature is determined by the lens design, size of the lens elements, and the quality of glass. With regard to zoom lenses, there are two types: constant aperature (the maximum aperature remains constant throughout the zoom range) and variable aperature (the lens gets "darker" as you zoom from wide to telephoto). This also only has to do with the "maximum" aperature (when the lens iris is wide open). You can still stop the lens down further from the maximum. Constant aperature zooms are move complex to make, and therefore are more expensive. They are mostly found in the "pro" category of lenses. Variable aperature lenses are cheaper to make and almost all "consumer" grade lenses are now variable aperature.

As to your lens: when it's set to 28mm the lens is at f3.5 "wide open" and when it's moved to 80mm the lens becomes f5.6 "wide open". That's a light fall off of 1 1/3 stops (f3.5 to f5.6)... that's a reduction of over 50%! To see this actually happen, set the camera to 28mm and point it at a white wall, without removing your eye from the finder, zoom it to 80mm... Notice how the scene darkens in the finder as you zoom in.

The bottom line is that it's impossible to make your lens go above f5.6 when it's set at 80mm.

 

[PoohJen]

the camera controls the setting but the lens tells the camera what settings are available. Your lens says "I don't go that low" "You need to spend more money for that!"

I may not understand all these fancy schmancy answers, but at least I get the humor!!!

 

[PoohJen]

TV mode is meant for taking pictures of a TV screen. It sets the shutter to 1/60 sec to avoid capturing the black bars (you can't see them) that TVs use to make a TV work.

HUH??? I thought TVs worked by magic. The TV on the XT, I understand, is a semiautomatic mode that lets you set the shutter speed, and the camera sets the aperture automatically. My book also recommends the TV setting for use in low light

 

[ndelaware]

You would be right Jen!!!

 

[Charade]

HUH??? I thought TVs worked by magic. The TV on the XT, I understand, is a semiautomatic mode that lets you set the shutter speed, and the camera sets the aperture automatically. My book also recommends the TV setting for use in low light

On most cameras I've seen with a TV mode is used for just what I said it was. That doesn't mean it can't be used for other things.

Why call it TV mode if it's not meant to take picture of a TV screen?

 

[Charade]

Well now. It appears that Canon calls their shutter priority mode "Tv" and aperture mode "Av". Doesn't make sense to me since I'm used to seeing TV mode used differently

My camera (a D70) calls them "S" and "A". So does my Olympus.

 

[ndelaware]

On a Canon camera "Tv" stands for "Time value".

 

[Charade]

On a Canon camera "Tv" stands for "Time value".

Thats just dumb. The rest of the photograpy world calls it shutter.

 

[Sonno]

Your lens says "I don't go that low" "You need to spend more money for that!"

Hehe... that sounded... dirty...

 

[ndelaware]

Thats just dumb. The rest of the photograpy world calls it shutter.

Well, it's confusing as hell when you are new to the Canon line.

 

[Anewman]

Thats just dumb. The rest of the photograpy world calls it shutter.

Who cares what the other 25% call it????



Just kidding, I imagine "shutter" was too big to be put on the little dial.

 

[ndelaware]

 

[JR6ooo4]

Hehe... that sounded... dirty...

It translates into many professions...

 

[spoon2003]

I often wondered what the f.x-x.x number on the lens meant (I was on the right track) but this thread confirms it. Thank you all.

It took me days to remember Tv = shutter priority. I actually had an index card in my camera bag to remind me as I was new to the whole DSLR world dealing with shutter and aperture speed.

Sue

 

[Kelly Grannell]

Thats just dumb. The rest of the photograpy world calls it shutter.

Dumb as it may be, 60% of dSLR out there uses Tv for "Shutter Priority"

(inside joke)