A question about f stops

High,

I use ps cameras, so the following question of a friend of mine who uses a A300 I just couldn't answer. Could you? I'm sure, you are dealing with reflex every day.

His lens (sony 18-70mm) states an aperture range from 3.5 to 5.6, but the camera offers the possibility of even f32 on the narrow side. Is it the camera with a software filter that simulates further blade reduction? Or is the lens just advising about the minimum range?

Sorry for just a stupid question, but I couldn't tell.

Kindos regardos,

Miguel

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Moving as smooth as possible on a thin skin of ice protecting me from myself

It is not a constant aperture design of length, in other words the fully open aperture with that lens varies with focal length - It is F/3.5 at 18mm and F/5.6 at 70mm. The lens can be stopped down much further of course.
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David

Miguel Furlock said:

His lens (sony 18-70mm) states an aperture range from 3.5 to 5.6, but
the camera offers the possibility of even f32 on the narrow side. Is
it the camera with a software filter that simulates further blade
reduction? Or is the lens just advising about the minimum range?

Click to expand...

It means that with that lens.... if he's shooting at 18mm then he can use 3.5 however at some point of zooming in the lens will force him to use an FStop of 5.6 and smaller. This is why I hate shifting aperture lenses.. they force you to change your exposure. No the camera doesn't simulate the blades stopping down.. the lens actually stops down to F32.

Example. Let's say that you're shooting something inside where its dark and you decide... that you're going to "try" and use 3.5.. Your lens is at the widest end (18mm) but you decide that you need to zoom in more. Well . . . your lens will automatically force you to use 5.6 which lets in less light. If you're not using flash then you're forced to lower your shutter speed to compensate for the light loss or bump your ISO sensitivity. It is for this reason that I try to buy only constant aperture lenses. My only shifting Aperture lens is my sigma 10 - 20 but I never use it below F8 so it doesn't matter.. and when I do use it I have a tripod and enough light.

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Ivan
Stop by my neck of the woods sometime
http://www.ivanwatkins.com/blog

It's advertising the wide open range. The kit lens (18-70mm f3.5-f5.6) offers wide open apertures as follows:

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20-23mm@f4
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30-33mm@f5
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So, over most of the zoom range, it's f5.6. It can be stopped down in the A, P or M modes using the dials - all done by the camera as purchased. The completely stopped down aperture also varies by zoom (focal length) when completely stopped down (from f22 to f36).

However, the auto focus always works at the maximum lens opening (f3.5 - f5.6)

For more information on this lens see:

http://www.dyxum.com/lenses/detail.asp?IDLens=312

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AEH
http://aehass.zenfolio.com/
Question: What do you do all week?
Answer: Mon to Fri. Nothing, Sat & Sun I rest!

Thank you very much for your answers. This is then the same performance as on PS cams. I just didn't want to make an error, as maybe there could have been another extra done by digital reflex cams, that I would have ignored.

Great, you too do a great job at this forum.

Kind regards,

Miguel

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Moving as smooth as possible on a thin skin of ice protecting me from myself