Confusion about my f/stop #s. Why do they look different on my camera than books?

[JenniferB]

Hi!

I'm very confused about the F-stop numbers on my Pentax K100D.

I know what they do. I know where to find them on the LCD and how to change them (turn the e dial) but the numbers appear as whole numbers. There aren't in the form "f/1.6" (mine doesn't even go that low. the lowest number I can turn to is 4). Why are they different looking on my camera?

In AV mode, the order is 5.6, 6.7, 8.0, 9.5, 11, 13, 16, 19, 22,....38.

Am I doing something wrong? Are these shown as the way the would be shown if they were halved or doubled, or whatever?

Can someone point me in the direction of an article that may explain this in very newbie terms?

Thanks! jennifer

[OsmosisStudios]

Aperture is written as a fraction. When you see things like f/1.8 or f/8 or things like that, it's a fraction. As such, the smaller the number, the larger the opening is. Cameras often dont have the space or the need for the f/ bit, and just make to with the number. That's fine.

Now, most lenses have a "maximum" aperture, or maximum opening. This is usually in the lens code.

Example: my Nikon 18-70mm f/3.5-5.6 ED. This means the lens goes from 18 to 70mm of focal length and has maxium apertures of 3.5 and 5.6 at those lengths. So, if Im at 18mm (wideangle) i can open it up to 3.5, but as I extend the lens, it drops to 4, then 4.5, then 5, then 5.6. This is just because of physics.

Most standard zoom lenses have a 3.5-5.6 or similar range, and they cant go below that. You can also get "fast" lenses, that go down to 2.8. Then you get into prime lenses, which dont zoom at all, but offer apertures of 1.8, 1.4, 1.2 and even smaller. These lenses are fixed length, and will go from 1.8 to 22 or 36 or whatever the highest number is.

I dont know the K100D at all, so I cant tell you how to fix it, but I hope I explained the aperture system well enough. if you have any questions, please let me know.

[Mr Guy]

I've got a K110D which is close enough to the same camera, and his explanation is spot on.

The aperture numbers are, as explained, limited by the design of the lens. Smaller numbers are wider openings. On less expensive zoom lens, as you zoom out, the less wide it's capable of opening up, so you can't go as low.

When you see "5.6" then your aperture is set to "f/5.6" as described by books. You aren't doing anything wrong at all, that's just the limit of the lens you have. Since you have a Pentax, you don't have the option of buying a super cheap 50mm like the $100 Canon prime that's very popular, however, you CAN get a manual focus SMC Pentax 50mm f/1.7 that is a GREAT little lens, but takes a bit more effort to use, and can be found used for less than $50.

Basically, the lower numbers buy you the ability to take pictures in lower ambient light without adding lights. The kit lens performs "ok" in those conditions, but a more expensive "faster" lens will allow you lower aperture numbers, thus wider aperture, thus better performance in lower light.

[vandergus]

Your camera is just saving space on the display. It leaves off the "f/" because it doesn't change from value to value. No point in wasting valuable screen real estate for information that never changes. You just have to put "f/" in front of whatever your camera is displaying to make it match your book.

It will do the same thing with shutter speeds. If the camera is set to a shutter speed of 1/1000th sec it will display '1000'. Same reason, it's just trying to cram as much info onto a small screen as possible. To distiguish between 2 sec and 1/2 sec the camera uses a quotation mark. So 1/2 sec will be displayed as '2' and 2 sec will be displayed as ' 2" '. Wow, all those quotes look confusing.

[kencaleno]

Hi jennifer, The sequence of numbers you have written is in half-stops-some cameras have 1/3 stops which number like this:

3.5;4.0;4.5;5.0;5.6;6.3;7.1;8.0;9;10;11;13;14;16;1 8;20;22;25;29;32;36;40;45; Ken

[JenniferB]

Thank you, thank you, thank you! I just wanted to make sure I wasn't crazy and that it was ok to not have the "f/" or have the shutter speeds in fraction form, for that matter.

You guys are so smart and generous with your knowledge!!! I'm gonna like it here!
Jennifer

[(CMC)]

Originally Posted by JenniferB

Thank you, thank you, thank you! I just wanted to make sure I wasn't crazy and that it was ok to not have the "f/" or have the shutter speeds in fraction form, for that matter.

You guys are so smart and generous with your knowledge!!! I'm gonna like it here!
Jennifer

I'm glad you asked your question. It helped me figger out the shutter speed readouts on my camera.