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01-29-2008, 09:43 PM   #1
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Question aout the aperture stops.

I recently received my parent's old Pentax camera and attached lens for a Beginning Photography class I'm taking.

The camera model is the Pentax SF1, and the lens is a (reading off the side) SMC Pentax-F Zoom 1:3.5-4.5 28-80mm.

Now, I've figured out most of the workings, but the one thing I can't figure out are the actual aperture stops. Every manual I've looked at lists the stops on the lens type (not exact model) differently, and none match mine.

The f-stops listed on the side of the lens are: A, 22, 16, 11, 8, 5.6, and 3.5.
And I know that there are more than this because it has more "clicks" than numbers listed, as well as the fact that this is what the manual tells me.

But can anyone tell me what each actual stop is??

01-29-2008, 10:18 PM   #2
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I'm not exactly sure what you specifically want to know but I'll give it a shot...

Normal f-stops are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22. Each letting in half as much light as the previous and increasing the depth of field. So this is pretty much what you have except I guess they skipped 4 because it was close to 3.5. At f/3.5 your lens is wide open letting in the most amount of light and and the shallowest depth of field.

P.S. My girl friend is from Arcata.
01-30-2008, 01:09 AM   #3
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Your lens most likely has clicks for every 1/3 or 1/2 stops. Count how many clicks there are between two numerical values. If there is 1 click then the click spacing is 1/2 stops, if 2 then 1/3 stops.
01-30-2008, 04:06 AM   #4
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Lukas and Procyon have given you most of the relevant aperture information on your 28-80mm zoom, Deo. I can think of just one more thing to keep in mind: the variable aperture of this zoom means that the widest aperture, f/3.5, will be available in the wider-angle range of the zoom, and then the widest aperture will begin narrowing down until it is f/4.5 near the telephoto end of its zoom range.

You would have to get fairly deep into the technical literature to know exactly what maximum aperture you have available at particular intermediate focal lengths, but the difference from wide to tele is about 2/3 of a stop in all.

01-30-2008, 06:49 AM   #5
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QuoteOriginally posted by DeoLupin Quote
I recently received my parent's old Pentax camera and attached lens for a Beginning Photography class I'm taking.

The camera model is the Pentax SF1, and the lens is a (reading off the side) SMC Pentax-F Zoom 1:3.5-4.5 28-80mm.

Now, I've figured out most of the workings, but the one thing I can't figure out are the actual aperture stops. Every manual I've looked at lists the stops on the lens type (not exact model) differently, and none match mine.

The f-stops listed on the side of the lens are: A, 22, 16, 11, 8, 5.6, and 3.5.
And I know that there are more than this because it has more "clicks" than numbers listed, as well as the fact that this is what the manual tells me.

But can anyone tell me what each actual stop is??
As others have quoted, there will be increments in 1/2 stops with the clicks.

Also note that the markings on the lens are at the shortest focal length, at the longest focal length, the lens is F4.5 to F32. that is why the lens marking is 1:3.5-4.5. F3.5 corresponds to 28 mm and f4.5 to 80mm.

In your class, I assume you will be shooting in Manual mode, as that is usually how they will teach the course. You can do this in possibly 2 ways. I am not familiar with the SF-1 so what I suggest may not be correct.

You should have a manual mode that allows you to set apature through the camera body. On my PZ-1 it is a thumb wheel, If you do, you should use this, because the camera will know the true apature of the lens as you zoom and it is feeding this to the camera all the time through the lens contacts.

If you have to control apature using the ring. you will need to think about what you are doing a little. and remember that if you are using an external light meter (for example) that the apature will change from the markings by 1/2 stop at 50mm and 1 stop at 80 mm
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