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Aperture questions about a SFXn

fiannor
Posted 14/01/2005 - 08:59 Link
Still fairly new to aperture, and confused by my camera. It's an SFXn, right now with an AF sigma 28 - 80 mini zoom II. 3.5 to 5.6 aspherical lens.

I

Here's my question
I know the camera will automatically control the focus, shutterspeed, and aperture, and I understand the first 2, and somewhat the third. If I use the aperture manually, it appears to alter the shutterspeed for me, cause when I manualy move the Aperture ring off "A", the view panel above changes to an "A", and displays shutterspeeds that change as I manually move the aperture settings. Can i expect it to take good pictures if i want to manualy control the aperture and let it handle the Shutter Speed? Also it has an aperture priority mode. So does that mean I can control the Aperture in the centic panel, as well as manualy move the ring? if so I have not yet seen any aperture numbers on the panel.


I have a great little book by John HedgeCoe on 35 mm photography that I got the basics on. And found some sites on aperture, (and there's allot right here from you guys, probably more). And I found a cool web site tonight that lets you change the aperture and shutterspeed to alter the photo there. But if I wanted to look for for some indepth info on Aperture can anyone suggest a book, or anotherweb site?

I know the basics about the small and the large numbers, (versus the corresponding large and small apertures), and I understand the concept of depth of field, based on diameter of aperture and sh speed. But how do you learn to match them up on the spot without ruining alot of film? I have dreaded learning the F-stops untill recently getting back into photography. Along with shutterspeed it kinda feels like a crossword puzzel. Would be nice if there was a photo slide rule. lol

I know in the end my camera will teach me, I just don't want it to be an expensive lesson.
fiannor
Posted 14/01/2005 - 09:09 Link
2 things.

Yes I read my manual, (did learn allot but still need some help).

And sorry about the [b/] bit, i thought it would bold my selection. I know html, but didn't expect it to just do the text.
George Lazarette
Posted 14/01/2005 - 11:29 Link
In program mode, the camera will alter the shutter speed to allow the correct amount of light through the lens for the aperture you have set.

You will notice that if you move up one stop (say from f8 to f11), the camera will compensate by halving the shutter speed.

Each stop represents half the aperture size of the stop below, and therefore half the amount of light that reaches the film. To get back to the correct amount of light, you have to leave the shutter open for longer.

If you want to over-ride the camera's view of the right exposure, then go to manual mode, and set both yourself.

As long as you don't go over the limits (by setting an aperture so small, for instance, that the camera will have to leave the shutter open so long that the picture is blurred) then you can rely on the camera to give the correct exposure (in normal circumstances).

Bear in mind that small apertures (f11, f16, etc) give greater depth of field, and large apertures isolate the subject by putting the background out of focus.

These are just two reasons why you might wish to choose the aperture yourself, rather than let the camera do it for you.

Generally its safe to leave the shutter speed to the camera. If you don't, you risk getting the wrong exposure. However, in some circumstances (eg: strong back-lighting) you may do a better job than the camera. The SZXn does not pretend to compete fully with an intelligent human.
fiannor
Posted 15/01/2005 - 04:02 Link
Hey thanks for the help George.

Speaking of focus depth, in automatic there's a "program depth mode" on my SFXn. I plan to learn the aperture manually but mean time wondered how this mode works. It's suppose to take more in depth focus shots when selected. I use to think it was a double focus, (cause of the sillowette icon of the man and the mountain), and never really understood it before I started reading my manual, (I ordered my copy from England and recieved it a week or two ago, since I had lost or misplaced the original), and reading about focus depth recently made me realize what it was really about.

You have any idea how much difference this mode makes? Can i assume it will alter the aperture enough so that everythings in focus? How do you know, in manual or in automatic. I mean the camera lense doesn't change. Wouldn't it be great if the focus frame indicator enlarged or shrunk to show it was doing something. I know I;m just going to have to shoot allot with it, but wondered how most of the Pentax automatics that have this option fared.
George Lazarette
Posted 15/01/2005 - 10:00 Link
Fiannor,

I've just pointed my old SFX out of the window at a leaden January sky, and tried the three program modes.

Lansdscape mode gave f13.5, normal gave f8, and action gave f3.5.

So there is a marked difference. The camera selected a shutter speed of 1/30 in landscape (with the focal length at 35mm), which seems sensible. A slower speed could give rise to camera shake.

At f13.5 you will get very good depth of field. If you have a prime lens, you will see a depth of field scale just below the focussing scale. This indicates what will be in reasonable focus either side of the subject.

To be frank, the DOF scale on the AF lenses is pretty hard to read. If you have a manual focus lens, it will be much clearer.

On my M 28 2.8, the 10ft mark on the focus ring and the f8 aperture mark are both coloured red. With these settings, and the shutter on auto (as it would be with an ME ), everything is in focus from four feet to infinity. This is the perfect grab shot setting (the classic advice to photojournalists was: "F8, and be there!") .

Similarly, on the 50mm lens, focussing on 33ft (15m) puts everything in focus from 15ft to infinity. Wide-angle lenses have much more apparent depth of field.

Sometimes you should focus on something other than the subject in order to achieve the best focus for the picture as a whole. You might wish to focus behind the subject to throw the foreground more out of focus, or focus nearer if you want the foreground in focus.

The possibilities are legion, and all point to the fact that a serious photographer will always demand that his camera be capable of full manual control; even though he may use part or full automation when circumstances permit.

Incidentally, I regard the SFX as a pretty good camera, especially for beginners. It's extremely simple to use, and very solidly built - better than all later cameras until the *ist D.

G
fiannor
Posted 15/01/2005 - 19:43 Link
Hey George about your info on the, "Lansdscape mode gave f13.5, normal gave f8, and action gave f3.5", you listed above. These are focus numbers right? I get them in my camera in either manual aperture, or automatic indepth mode. I thought they were aperture numbers at first, (which I wished the camera would show me in auto modes). If these are focus numbers, why are they being listed? So you'll know the light availability? Mine changes mostly due to zooming, and the present lense is only a 3.5 to 5.6. It really confused me for a while because there is a 3.5 on my aperture, but i figured it out when it never got above 5.6, and the A goes all the way to 22.
By the way I was playing with my camera in the backyard earlier, and I do see the difference in the in depth mode. I been cussing the lack of winter light the last couple of days, (and my bad hours), and just noticed I had it on in depth mode. No wonder I was getting below 60 on most of the SS readouts. And on manual aperture i do see the shutterspeed changing when i manually use the aperture ring, so when I get enough light to play with i'll try some small diameter in depth focal shots.
Not sure what the DOF scale you said stands for, but I use my focus manually unless quickly shooting people at a party or holidays in well light, usualy indoors, and even then I do it myself allot. Also I get annoyed at the in focus beeping, and usualy shoot in silent. Wish i could turn the arrows off too, but sometimes they are helpfull in low light. Though the focus on my present lens was probably made more for automatic, which is something a guy at the camera store told me when i asked about it, I hope the 50 1.7 wil have a bigger focal span. By this I mean the actual turning distance. It's pretty short on my 28-80 Sigma. But I can work with it.
I have the 50 mm 1.7 on the way, i think that's a prime lens, but don't know if it will list a distance like yours. I haven't looked through one yet.
Why doesn't the camera tell me it's aperture choices when on automatic, like with shutterspeed? I really could have gotten into this easier if it had.
Sorry for all the questions.
George Lazarette
Posted 16/01/2005 - 15:25 Link
Fiannor,

Aperture is always expressed as an "F" number, as in "f3.5". Don't ask me why, but that is the convention. I was referring to apertures, not focussing.

You will soon recognise the numbers. In full, they are: f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22 and f32. Note how every number is double the previous number but one.

You'll never find an f1 lens on an SLR.

DOF stands for "depth of field".

If I were you, I would leave focus on auto at the moment, until you have mastered the relationship between apertures and shutter speeds, and the effect of aperture on DOF.

If you need to focus on something which isn't in the centre of the viewfinder, point the camera at whatever it is, depress the shutter button half-way, which will cause the camera to focus the lens but not to trip the shutter.

Then frame your shot, keeping the button part depressed (which locks the focus), and press harder to take the picture.

You'll get it eventually!

Incidentally, there is nothing clever or professional about using manual focus. All pro cameras are autofocus because most of the time, AF is quicker than focussing manually.

G
fiannor
Posted 17/01/2005 - 02:15 Link
The reason I thought what you had said were originally focal numbers, was because at 8 and above my f stops are only whole numbers. I've never seen a 13.5 aperture listed on the f-stop ring, (but then haven't seen allot of lenses). I know the difference on my camera between aperture and these other numbers I just don't know what the latter are for, or why they appear in all auto modes. On the box my lens came in, it says F3.5 - 5.6, (after the 28 - 80 mm). And when in any program mode, it displays these numbers as the zoom is used, (and the range in between, 3.5 4 4.5 5.6).
It's not aperture, and I played with it and see now that only changing the zoom alters them, the focus doesn't affect them or the aperture ring. Which means their not some kind of focal numbers like I had first guessed.
So their zoom listings, for what? Are they there to tell me the changes in light ? If I zoom in all the way to 80 it ends on 3.5, and if I back off all the way at it's widest setting 28, it's 5.6

What does this show me, and what use is it?
fiannor
Posted 17/01/2005 - 03:14 Link
Hey I know why I thought they were focal numbers. Because there's an F in front of them, (though I know that usualy means f-stop). Ok in my manual it says it's an "F-number/exposure compensation value". Isn't that the kind used for bracketing multible shots? Not something I want to play with yet, but I know my camera has a bracketing option. Maybe that's the use for them.
George Lazarette
Posted 17/01/2005 - 06:29 Link
Your zoom lens has a variable maximum aperture, which is why two numbers are quoted. At the short end of the zoom range, the max aperture is f3.5. At the long end it is f5.6. Somwhere in between, it might be f4.

With F stops, the lower the number, the larger the aperture. F4 lets in twice as much light as f5.6.

Full F stops are the numbers I listed. However, many lenses have indents mid-way between the full stops to give half stops. Some camera/lens combinations use one third stops. F3.5 and f13.5 are half stops.

It's a pity the people who designed lenses didn't come up with a simple linear scale, where a higher number equals a larger aperture. But, they didn't.

Just remember that shutter speeds and apertures are complementary, and each is half or double the previous one. So, if you increase the F number by one stop, and reduce speed by one click on the speed dial, you will still have have the same exposure value (ie: the same amount of light passes thrrough the lens).

I suspect that when you were playing around with your lens, you didn't have much light. Point the lens at a bright light source, with a slower shutter speed, and you'll soon see f11 and f16.

G
Kimbo
Posted 17/01/2005 - 14:18 Link
I always think of F-stops as fractions ie. the bigger the number - the smaller the hole!

Pentax manuals have charts that show graphic representations of the relationship between apertures/focal lengths and depth of field and also how these shift with regard to the program modes.
Die my dear doctor, that's the last thing I shall do!
fiannor
Posted 18/01/2005 - 00:26 Link
Thanks.

I understand aperture sizes, and that the larger apertures are the smaller numbers, and vise versa. But aparently on the SFXn there are no aperture listings on the centic read out panel. I can change them on my f-stop ring manually, but in no mode do they ever appear in the panel on top. Maybe they did in later models, and some of yall have that as an option. But there are no aperture readouts in the panel on mine, unlike the shutterspeed. That's not a nessesity, but would have been nice early on.
fiannor
Posted 31/05/2005 - 13:20 Link
Hey I finaly figured out part of the mystery. I never had looked for the aperture apearing in the readout after I tried to figure it all out over 4 months ago in the above post. But I happened to be looking at the panel with my 50 mm 1.7 just now and low and behold there are aperture listings. On my older 2 lenses, (the 20 80 sig zoom from christmas, and the 20 to 70 sig that came with the SFXn in 89), there never were any. Just the 3.5 - 5.6 numbers that was also listed on the 20 - 80 box, and they only changed when the zoom was moved. But with the dedicated 50 mm on they show up.

So how come they wouldn't on the other 2? Is it because since they are more complicated or multible lensed that it can't track them? Or is it the amount of light bit based on zoom we covered earlier? By investigating this tonight further I realize the latter sig I bought at christmas is "F" only! It's on the box and lense. I don't get it, the guy never told me it wouldn't handle the aperture in auto. That means when not in aperture mode I have been shooting wide open all the time? Good thing have been learning how to do my own pretty much now.
Wait the older 20 - 70 sig zoom is "AF". And it didn't show aperture either. Yet my 50 mm is "FA" and it did. I'm scratching my head here. I can see the lack of an "A" on the later zoom might have meant it wouldn't confer to the centec panel, (display), but why the former, that had one? Don't tell me reversing the letters makes them different? Or was it the former idea of it being a zoom and so couldn't. I think i need a pipe and an assistant named Watson. Well i could have used the 50 mm 4 months ago when I wanted a lense that I could watch and learn from. Ehh thank god for the internet and you guys.

Glad to have some closure on the A reading/not reading on my display. Always seems to be more questions follow answers, but I feel better knowing my 50 mm can show the f-stop. It's cool watching it change when I flip through the modes, and that's still going to be helpfull, even though i am already shooting in mostly in aperture priority.

Thanks guys.
Kimbo
Posted 31/05/2005 - 16:12 Link
Lenses with KA mounts display the aperture setting on the CENTIC panel when the aperture ring is set to A (automatic), when in Program and Auto mode.
It is not necessary to display the aperture in other modes, you would know what it is because you set it yourself.
Your Sigma lenses should also display the chosen aperture when set to A in Program/Auto mode.
My Tamron lenses perform exactly like A series Pentax lenses, the F series zooms however also enable the SXF sub-modes to come into play (automatically selecting depth, standard or action - based on focal length) but the camera cannot determine the focal length of the Tamrons because of the interchangeable mount. I can change from a wide angle, to a zoom, to a telephoto and the camera wouldn't know the difference but you shouldn't have this problem with your Sigmas unless their built in chips are not as sophisticated as the Pentax ones (they may only provide aperture information and not focal length).

I've tried my SFX with Pentax A, F, and FA series lenses as well as the Tamrons with KA mounts and none of them display the aperture setting on the CENTIC when the aperture ring is moved away from A (or AE).
Die my dear doctor, that's the last thing I shall do!
fiannor
Posted 04/06/2005 - 07:22 Link
Your right Kimbo. I guess the dim light I had checked it in had me thinking the aperture numbers in the centec panel weren't changing more than 5.6
And just now i left the lens cap on lol, yea that makes it hard to see the aperture readout! But taking it into a brighter light, or using the light button on it they are infact aperture listings, (though one was 32 i think and my A only goes to 22). But if the sigma was a "F" only, regardless of what the panel says, doesn't that mean it won't do the aperture itself? I thought now I have been shooting all this time on wide open when in auto "A", but if it shows in the panel maybe not. Ok what does the lack of an "A" on a lense then mean?
As for the 3.5 to 5.6 I think i finally know what they mean. Their a listing of the maximum aperture opening possible, based on the availability of light affected by the zoom. Jeez why didn't they just say that on the box. I guess it's like looking through a tunnel, the other end always looks smaller and is going to set the available dimentions aparent, regardless of actuall size. So the farther the outer zooming lens moves away from the inner, (I assume there's 2 in a zoom), it sets the largest apperture possible regardless of the actual aperture function?
Anyway it's not something that really concerns me unless I need a low light zoom, (does it affect telephoto also, cause their set right)?

Another puzzel revealed, (I think). Learning allot from here, but I must be driving yall nuts.

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