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02-10-2009, 02:32 PM   #1
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"Auto" lenses?

Hi,

I'm looking to add to my manual-focus prime collection (doubling it from 1 to 2). Some of the off brands I'm looking at (Vivitar, Sears, maybe others) call themselves "auto," but they don't have an A setting for the aperture. Can anyone tell me if these will or will not work on my K10D in aperture priority mode?

As an aside, does anyone have any experience with Sears brand (28mm, I'm looking at) lenses. I'm wondering what brand they are beneath the Sears name.

Thanks in advance.
Vinny

02-10-2009, 02:36 PM   #2
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Unless there's an 'A' setting on the aperute ring, you will only be able to use them in M mode with stop-down metering. However, you can use Av so long as you're using the lens wide open (at its largest aperture).

The 'Auto" refers to the fact that the camera will stop the lens down automatically when you take the shot. It used to be that you had to stop lenses down manually before taking a shot.
02-10-2009, 03:38 PM   #3
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That is correct, though with one extra twist:

AUTO M42, screw, mount lenses refer to the aperture pin being available in the mount, for automatic operation with screw mount cameras. Unless the lens has an A/M switch, these are a pain to use with K mount adapters - essentially you have to block the aperture pin down, and use them in manual mode in that way.

However, many M42 Auto lenses do have that switch. It helps to have a photo, or to ask the seller.

On the K mount side, the A on the aperture scale, and the presence of the K-A contacts in the mount, are key.
02-10-2009, 04:05 PM   #4
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Last things first:

Most Sears lenses are re-branded Ricoh Rikenon. Ricoh did not make their own optics and speculation on the actual maker runs from Tomioka to Chinon and others. The primes have a generally good reputation and some are excellent performers. One should be aware though, that some k-bayonet mount versions may have the infamous "Ricoh pin" If there is a "P" on the aperture ring, beware! The lens could jam onto the mount of a Pentax AF body.

As for lens jargon:
  • "Auto" on a lens always means auto-aperture. The lens is wide open to focus, stops down just prior to the shutter opening, and reopens just after the shutter closes.
  • Auto-focus (AF) means just that
  • Auto exposure is a body feature
  • "A" setting or "A" aperture ring means that the lens supports aperture setting through the camera body. This is indicated by a position on the aperture ring with a prominent "A" marking. When the ring is at the "A" mark, the body sets the aperture. When it is on any other position, the aperture is controlled at the lens by the ring.
  • "A" contacts (see "A" setting above)

Steve


Last edited by stevebrot; 02-10-2009 at 05:17 PM.
02-10-2009, 04:29 PM   #5
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QuoteOriginally posted by Miserere Quote
Unless there's an 'A' setting on the aperute ring, you will only be able to use them in M mode with stop-down metering.
As I understand it, "stop-down metering" means there is no auto-diaphragm, and you have to meter from the lens being stopped down. This is opposed to metering from wide open and having the camera stop down upon pressing the shutter via the auto-diaphragm lever.

If my understanding is right, I believe you're wrong, Miserere. As long as the lens has an auto-diaphragm lever (many of the M series and third party lenses do) you won't have to do stop down metering. That makes for a much brighter viewfinder when the iris is set smaller than wide open.

I can't speak to the K10D, because I don't have one, but if the green button behind the shutter works like the one on the K200D and the K20D, here's a little trick while shooting in Manual mode (I never tried it in other modes). Go into the menu, set the green button to adjust shutter speed for correct exposure when pressed. As long as the lens has an auto-diaphragm lever (which many lenses older than the A-series have) the camera will grab that lever, stop it down, set the shutter for correct exposure, then release the lever again. Now you're correctly exposed and ready to shoot. I used to do this all the time on a K200D and K20D with a K mount Takumar Bayonet that had no A setting on the aperture ring.

I should mention auto-diaphragm is the same as auto-aperture, and Steve's remarks are very informative to that end.
02-10-2009, 04:50 PM   #6
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Bruce, what you're referring to with the M/K lenses is still considered stop-down metering:

Stop-down metering is a somewhat different subject than auto aperture. With 'A' or newer lenses, you can use "open aperture metering", where the light reading is taken with the lens wide open, and the body can 'predict' what will happen when the lens is stopped down at shooting time. With M, K, or M42 the aperture has to be closed, and the light reading is actually taken with the aperture stopped down.

Auto aperture instead means that at the moment the picture is taken, the aperture is closed to the preset value. This works fine with M and K lenses--but not with M42 where you need to stop the lens down yourself.

The K10D green button behaves exactly like the one on the K20D and K200D. On the other single-e-dial bodies, AE-L serves the same purpose. Optical DoF preview also functions to stop down the lens based on the aperture ring preset.

Hope this helps.
02-10-2009, 05:41 PM   #7
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Stop down metering & auto aperture/diaphragm are different though related, like Andrew says.

Just to be clear: when open-aperture metering is not available in a camera/lens combo, then the photographer must stop down the lens to measure light and set the aperture / shutter speed combo. After that, if auto-aperture is available, the lens can be open for focus and composition, and the body will stop it down for exposure.

If auto aperture is not available, then the lens must be used in pre-set mode, where you stop the lens down before exposure, as the camera cannot do so.

These things get confusing as 'manual' aperture means several different things these days depending on context.

All Pentax K mount lenses are auto aperture on Pentax cameras. Pentax M42 mount lenses with the adaptor are 'pre set' aperture lenses on K mount cameras. This takes care of the actual exposure.

The exposure measurement variations get baroque when all combinations are considered. But on a dSLR, M lenses need to be manually -stop down- metered. A lenses do not, and can use all the exposure automation modes.

(Pre-set lenses, i.e. M42's adapted to K mount, can be metered manually or in 'pre set' aperture priority mode - since you have to stop the lens down by hand, effectively the camera measures the light at that aperture as well - so Av is viable. This isn't so with the M K mount lenses, as they shoot wide open. Thus the need to manually stop down meter with them.)
02-10-2009, 06:00 PM   #8
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Yeah, all this is interesting. As I said, I have one manual lens, a 50mm 1.4 M. With the green button, I think of it as a sort of 2-step auto-aperture setup.

I'm really trying to decide if I want to spring for a 28mm lens with an "A" setting for a little quicker operation. The 28 that I'll be buying (whether A or M) will be on my camera a lot in family-gathering / event situations. I'd like to be as quick on my feet as I can. But, given reasonably consistent lighting, do I need it? Better to go for the best glass I can find instead? Honestly, I'm trying to get by as cheaply as I can for now, with a plan of stepping up to something a little faster when I have a little money--f2 28, maybe, or even an Sigma 30 1.4. So my choice right now feels like this: a beat-up A, or a nice M.


Last edited by unkabin; 02-10-2009 at 06:06 PM.
02-10-2009, 06:12 PM   #9
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According to Photozone, the Sigma 30 1.4 has horrendous border performance. The Pentax FA35 f2 is my favorite lens. Excellent images across the frame from wide open with very good bokeh.

Thanks to everyone for setting me straight on stop-down metering.

I love that little green button.
02-10-2009, 06:48 PM   #10
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Yes, the little green button. In conjunction with legacy lenses, the biggest reason I switched to Pentax (and am sooo happy with the brand!).

The 35 is outta my league right now. I have heard mixed reviews of the 30. It's just that it's fast and affordable. I'll probably end up seeking out a manual-focus 28 2. I think I would have a lot of fun with one.
02-10-2009, 10:29 PM   #11
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QuoteOriginally posted by unkabin Quote
...I'm really trying to decide if I want to spring for a 28mm lens with an "A" setting for a little quicker operation. The 28 that I'll be buying (whether A or M) will be on my camera a lot in family-gathering / event situations. I'd like to be as quick on my feet as I can. But, given reasonably consistent lighting, do I need it? Better to go for the best glass I can find instead? ...
I have learned to live without it for great glasss or a reasonable price, but it is nice to have. For some focal lengths, the A or A-equivalent versions carry a big premium - example, 135mm. At 28mm, you can find some decent Vivitars with an A position, though there are many different models and manufacturers. The A position "turns on" so many camera features, so it's not just a bit of convenience.
05-25-2009, 12:01 PM   #12
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If you don't mind my jumping in and asking a question.....

I just got a K1000 which came with a Takomar 50mm lens that is a 42mm screw mount. The body came with a K mount/screw mount adapter. The lens has the manual/auto feature. I noticed that in manual I can see the effect of F stop changes. My question is in auto, I don't (won't) see the effect of the F stop changes....consequently, how do I know how it's going to be stopped? Do I focus in auto and then to to manual to preview the exposure? Sorry if this is so simplistic but I'm still learning.
05-25-2009, 01:19 PM   #13
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QuoteOriginally posted by Unshriven Quote
If you don't mind my jumping in and asking a question.....
No problem, we're all friendly here...

QuoteQuote:
I just got a K1000 which came with a Takomar 50mm lens that is a 42mm screw mount. The body came with a K mount/screw mount adapter. The lens has the manual/auto feature.
Have a look at the back of the lens. There tyou'll see a little pin, say 4mm long. With the lens on its side and aperture scale up (as it would be when attached to a camera) you'll see that the pin is at the bottom.

In Auto setting on the lens you'll find that if you turn the aperture ring (to say f/16) the diaphragm will remain open, but it will stop down when you push the pin. When the lens is in Man mode the diaphragm will stop down as you turn the aperture ring.

Now look into the camera without a lens attached. With an M42 mount camera you would see a metal lever at the bottom of the mount that pushes the pin when the shutter button is pressed. On a K mount lens you'll see that there is no such lever.

QuoteQuote:
....consequently, how do I know how it's going to be stopped?
In Auto the lens will not be stopped down with a K mount camera because there is no lever to push the pin mentioned above.

QuoteQuote:
Do I focus in auto and then to to manual to preview the exposure? Sorry if this is so simplistic but I'm still learning.
Yes, that is the usual way to do it. The Auto setting is only useful to open the diaphragm wide for focussing, and once you have the focus, switch to Man and measure the exposure (the green button) and then take the picture.

Richard
05-25-2009, 02:02 PM   #14
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Thanks, that being said....if I use this lens with my Spotmatic F and the lens on auto, how will I know how the Aperture will be stopped?
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