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04-16-2009, 09:43 PM   #1
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New to SLR with questions on lenses.

New here so I appreciate some education on different Pentax lenses from anyone knowledgeable and patient. If someone can post a link where its already explained, I'll quietly go away and read.

I'll use different 50mm f1.4 lenses as examples on a K20D body to ask my dumb questions.
  • Auto Focus (F and FA)
How does the A setting work? What is the difference between if I set the aperture ring to f2.8 vs. setting the aperture ring to A and then choosing f2.8 using the thumb wheel in Av mode?
  • Manual K-Mount (K and M)
K and M lenses. When I pop one on, rotate the aperture ring to f2.8, focus and press the AE-L or the green button, what is the camera showing me in the Viewfinder? What will the camera do if I just release the shutter? What exactly is stopping-down and who's doing it? And why?
  • A lenses
And what's with these lenses? Are they like a bridge between the K and M, and the Auto Focus? How do they work compared to the manual lenses, and also when compared to the F and FA lenses when used in A setting?
  • Screwmount lenses
How does the camera meter through these lenses without opening the blades? How does it work in Av mode as some members were discussing it?

Thanks all.


Last edited by warp; 04-16-2009 at 09:45 PM. Reason: list
04-16-2009, 10:10 PM   #2
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Edit: I just changed details on FA and F, turned out you can indeed use the aperture ring + green button, M lens style.

IINM

For all lenses with aperture ring (maybe except screwmount?), you need to turn on "permit lenses with aperture ring" on the menu.

F and FA:
Using the aperture ring only: works like M lens
Using the A setting, you set the aperture on the body just like a DA lens.

K and M (on K100d, K20D maybe different)
Put aperture ring to 2.8, pressing green buton will set the shutter speed to what the camera reads as correct exposure.
On K100D Green button is the AE-L. AFAIK you can program the AE-L to do other things in manual mode on K20D.
Stop-down metering is exactly that, pressing the green button after putting the aperture to the desired position. You have to do it because the digital mounts are crippled and can't do "open(?)" metering without pressing green button.

A lenses:
They're the same as F and FA lenses but without autofocus.

Screwmount:
K20D can't meter these guys without the aperture blades closing down (this is called "manual" on the lens). Usually people use Av mode instead of M to reduce one step. With M mode you can still press the green button after the blades close down. In some situations this can be useful but I personally almost always use Av when I use screwmounts.

AFAIK some screwmounts are manual only, some auto only, many M42s and most takumars have both options.

Last edited by Andi Lo; 04-17-2009 at 04:38 AM.
04-16-2009, 10:41 PM   #3
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Rather than trying to answer your questions one by one, I'm going to refer you to my Pictorial Guide to Using Manual Lenses on the DPReview forum. It's written for the K100D Super but the same principles apply to all the Pentax cameras. Have a look at it and if you still have questions I'd be happy to contribute what I can.

The only thing I'll add right now is that K and M lenses work identically aperture-wise, as do A lenses if you DON'T have their aperture ring in the "A" position.

A and FA lenses work identically to DA lenses (aperture-wise) assuming you DO have the aperture ring in the "A" position.
04-17-2009, 02:03 AM   #4
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with manual focus lenses you will also find modifying the camera and putting a split prism focus screen in is pretty much necessary (with my eyes anyway) to get proper focus.

04-17-2009, 12:29 PM   #5
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QuoteOriginally posted by warp Quote
New here so I appreciate some education on different Pentax lenses from anyone knowledgeable and patient. If someone can post a link where its already explained, I'll quietly go away and read.

I'll use different 50mm f1.4 lenses as examples on a K20D body to ask my dumb questions.
  • Auto Focus (F and FA)
How does the A setting work? What is the difference between if I set the aperture ring to f2.8 vs. setting the aperture ring to A and then choosing f2.8 using the thumb wheel in Av mode?
Using the aperture ring setting can work in M mode and is sort of the same as using the A position and setting the aperture with the thumbwheel. There are only certain rare instances where it is ever useful. The camera really wants to be able to control the aperture electronically. When it can, you get an aperture readout in the viewfinder and top LCD, multi-segment metering, aperture information recorded in the data attached to the image, P-TTL flash, all modes working, thumbwheel control of aperture, all half and third stop settings and probably other stuff (maybe better SR?. The aperture ring is useful to override P-TTL flash, with macro accessories and older film bodies.

QuoteQuote:
  • Manual K-Mount (K and M)
K and M lenses. When I pop one on, rotate the aperture ring to f2.8, focus and press the AE-L or the green button, what is the camera showing me in the Viewfinder? What will the camera do if I just release the shutter? What exactly is stopping-down and who's doing it? And why?
You will see "F--" on the displays with these lenses. In all modes except M, the camera will ignore your aperture ring setting and use the maximum aperture the lens has, f1.4 in your example. In M mode, pressing the green button makes the camera move the lens's aperture to the setting on the aperture ring (called stopping down), meter the light and set the shutter speed to an appropriate value. The lens is stopped down again when you press the shutter and take the photo.

QuoteQuote:
  • Screwmount lenses
How does the camera meter through these lenses without opening the blades? How does it work in Av mode as some members were discussing it?
The camera has no ability to control the aperture on these lenses. Therefore, you can set the lens to allow the aperture ring to fully control the aperture setting. We take advantage of its normal behavior with a K or M lens - shooting wide open in modes like Av. Sometimes it's useful to use different techniques depending on the lens and your purpose. Screw mount lenses can allow more flexibility than a basic K-mount lens.
04-17-2009, 09:07 PM   #6
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QuoteOriginally posted by Sean Nelson Quote
Rather than trying to answer your questions one by one, I'm going to refer you to my Pictorial Guide to Using Manual Lenses on the DPReview forum. It's written for the K100D Super but the same principles apply to all the Pentax cameras. Have a look at it and if you still have questions I'd be happy to contribute what I can.

The only thing I'll add right now is that K and M lenses work identically aperture-wise, as do A lenses if you DON'T have their aperture ring in the "A" position.

A and FA lenses work identically to DA lenses (aperture-wise) assuming you DO have the aperture ring in the "A" position.
Thank you, the article on dpreview is excellent, although a lot to chew on, for a beginner like me.
04-17-2009, 09:10 PM   #7
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QuoteOriginally posted by Just1MoreDave Quote
Using the aperture ring setting can work in M mode and is sort of the same as using the A position and setting the aperture with the thumbwheel. There are only certain rare instances where it is ever useful. The camera really wants to be able to control the aperture electronically. When it can, you get an aperture readout in the viewfinder and top LCD, multi-segment metering, aperture information recorded in the data attached to the image, P-TTL flash, all modes working, thumbwheel control of aperture, all half and third stop settings and probably other stuff (maybe better SR?. The aperture ring is useful to override P-TTL flash, with macro accessories and older film bodies.



You will see "F--" on the displays with these lenses. In all modes except M, the camera will ignore your aperture ring setting and use the maximum aperture the lens has, f1.4 in your example. In M mode, pressing the green button makes the camera move the lens's aperture to the setting on the aperture ring (called stopping down), meter the light and set the shutter speed to an appropriate value. The lens is stopped down again when you press the shutter and take the photo.



The camera has no ability to control the aperture on these lenses. Therefore, you can set the lens to allow the aperture ring to fully control the aperture setting. We take advantage of its normal behavior with a K or M lens - shooting wide open in modes like Av. Sometimes it's useful to use different techniques depending on the lens and your purpose. Screw mount lenses can allow more flexibility than a basic K-mount lens.
Thank you for the precise answers. The one about the screwmount still blew by me but guess I will cross that bridge when I get there.
04-17-2009, 09:20 PM   #8
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Screw mount lenses have no aperture coupling to the K mount (bayonet) body. Therefore, if you have a manual lens or you put a Super Takumar into Manual mode with the M/A switch, as you move the aperture control, the aperture follows along. With the K mount, the aperture stays wide open until you press the button to meter, hold over the depth of field on the power switch, or take an exposure in M mode.

In my opinion, the ideal M42 lens would be the models I used from 1961 to 1976 - preset lenses. These lenses have two aperture rings. One is click stopped like all the other aperture rings, but does not do anything. The other ring will move only between the aperture you set and the widest (smallest numerical) aperture. As it moves, the aperture closes and opens. If, for example you have the original normal lens, Takumar 55mm f/2.2, and you set your click stop ring to f/11, you can use the second ring to quickly move between f/2.2 for focusing and f/11 for taking the picture without looking at the aperture ring. It sounds harder than it is. I also had a Takumar 135mm f/3.5 preset lens, and took school sports with it. One finger of my left hand was always on the second aperture ring, the rest of it controlling the focus. Flick open, focus, flick closed, snap, wind while flicking open ... you get the picture.

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