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Old Dec 12, 2008, 4:01 PM   #1
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I just bought a new a300. It's my first DSLR after shooting with a Sony DCS-F828 for nearly 5 years. I like the a300 so far but it seems I have an issue with shooting in A mode. I can't make the aperture any larger than f5.6 even when I assigned the controller dial to "aperture", the dial only makes the aperture smaller (up to f36) and never larger than f5.6.

It has erratically shifted into f3.5 and f4.5 on it's own but I can't remember the setting I was in that made it do that and what's worse, if I adjust anything while in f3.5 or f4.5 it will pop back into f5.6 and stay there.

I have read the manual 5 times and there is nothing in it that specifically remedies my problem. I have a feeling I'm over looking something. It's been a week and I'm really stumped. I hope there isn't something wrong with this lens already.

Anyone else experience this?

Any suggestions?

-Sean
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Old Dec 12, 2008, 4:29 PM   #2
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Sean Marshall wrote:
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...
It has erratically shifted into f3.5 and f4.5 on it's own but I can't remember the setting I was in that made it do that and what's worse, if I adjust anything while in f3.5 or f4.5 it will pop back into f5.6 and stay there.
...
I strongly suspect that it shifted to the larger aperature (smaller f/number) when you zoom out to the widest angle. If you seem stuck at f/5.6 I am sure that it is because you almost always shoot at the long end of your zoom
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Old Dec 12, 2008, 6:18 PM   #3
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Isn't that cool?!?!

Anyway ...

BillDrew is correct. The kit lens is the Sony SAL-1870 DT 18-70mm f/3.5-5.6 Zoom Lens. It has a focal length that can vary from 18mm to 70mm, but as the focal length changes, so does the maximum aperture. At 18mm, the maximum aperture is f/3.5, but as you zoom in and the focal length gets longer, the maximum aperture decreases until at 70mm the maximum aperture is only f/5.6.

It is quite common for zoom lenses to have maximum apertures that vary with the focal length. In fact, the f-stop is the ratio of the focal length to thepupil diameter of the lens. So, as the focal length of a lens gets longer, if the pupil diameter remains constant, the f-stop gets numerically larger. Zoom lenses that maintain a constant aperture throughout their zoom range are highly prized. I happen to have two. On eis the Tamron 17-50mm f/2.8, and the other is the Minolta 70-210mm f/4.0 'Beercan' of myth and legend.
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