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08-16-2011, 06:39 PM   #1
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Questions about using M42 lenses - focus and metering

I just got my first Pentax...the K20D. Seems like a nice camera.

I also learned from Rio to remove the spring from the infinity adapter...and then, I learned the hard way

Anyway, I have a few questions regarding focus and metering when using M42 lenses, or manual lenses for that matter:
Got a question or two.

1. Focus: Should I set the focus point to the middle focus point and recompose. I don't really do that on my other cameras, but I'm not sure if that is how you are supposed to do that with manual lenses.

2. Metering: Does it matter what kind of metering I select? Center, multi, point....

3. Metering again: Got to get used to how it meters. Need to develop a feel for when I need Exposure Compensation. Can't tell yet how well it meters in various situations, but it does seem a bit quirky.

4. The shutter sounds a bit noisy. Hopefully this is nothing to be concerned about.

5. Using Flash: The metering is completely different when I engage the flash in M mode using the green key and A mode. M seemed almost not to care that the flash was engaged when I pressed the green button, and the metering didn't change whether the flash was up or down. In A mode though, it seemed to take the flash into consideration.

Thanks for any feedback.

Steve

08-16-2011, 07:14 PM   #2
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Hello... just giving my 2 cents...

For question 1... I like setting my focus to center and it works well for me.
2. any will do, never had problems. It depends on the situation
3. In tricky multi zone lighting is when I select the spot
4. It is the funny part of K20D... I get folks asking if it is broken all the time.
5. ...sorry not much a flash user.
08-16-2011, 08:39 PM   #3
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to answer your questions

1) I use center focus point always, unless there is a real need to set it to something else. I read somewhere that some cameras only allow center spot with old lenses, not sure this is either accurate or applies

2) only spot or center weighted work, multi segment needs KA lenses or, someone will srely advise sticking bits of tinfoil under the lens.

3) I have a K10D, same basic body as K20 just different sensor, metering is , well, lets just say "interesting" with old lenses. I have seen a couple of different issues, one is some M42 lenses have a permenant offset of a couple of stops, I think because they don't touch the pind or are painted black so they don't short any, and there is a really non uniform way that the camera meters with non A lenses. I think the camera compensates when it knows the open aperture, but below F4 you will tend to progressively under expose, between F5.6 and F11-16 you will over expose progressively by up to 2 stops, and above F16 it starts falling back, so that by F32 it is +1 stop. I have posted these results in a graph, do a search.

4) K10D is really loud too, don;t worry its normal

5) flash. either learn manual flash calculations, get a flash with "auto mode and use it, or get an *istD because it can do TTL metering with any lens you stick on it. P-TTL needs the aperture contacts of an A lens- sorry
08-16-2011, 08:45 PM   #4
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I would suggest using AV mode for M42 lenses, and then learn the exposure compensation you need at different apertures. On my K10D, I need to give + exposure compensation at wider apertures than F4, and minus compensation above F4... once you learn it, it becomes second nature to you...

08-16-2011, 10:05 PM   #5
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Good advice above. Here's my take:

I cheat. I leave metering and focusing at spot or center-weighted. I shoot, then I chimp and delete and adjust and re-shoot, and fix in PP as needed. I may depend on CIF if I have the aperture open enough (f/8 or wider); or I may zone-focus, or actually measure the distance. When I get the right exposure, I may lock-down the shutter and aperture and just shoot with the same light awhile. That's how I learned to do this stuff, on an ancient folder (German 1934 Kodak Retina I, the very first 135 camera) with auto nothing.

Metering can be fun. I don't rely on systems, just on chimping, and some old tricks: If I can't meter a subject well, I read off something of similar tone|brightness, which may be my skin or sleeve or the ground around me. Or I'll spot-read off the darkest point and brightest point in a scene, then average the readings for the exposure. On non-A-type manual lenses like M42's, I may leave the mode dial on my K20D at TAv, which is right next to M. Being in any Auto mode defaults to Av, and there I'm just one click away from M and the Green button.

Yes, M is Manual and ignores the flash. My lazy trick: Go to X mode (which defaults to 1/180 sec), and shoot and chimp and delete and adjust the aperture and re-shoot. And for fun, play with the flash syncs (slow-speed and trailing curtain). But learn to judge distances and flash requirements. As with EV adjustments, pretty soon it all becomes second nature.
08-17-2011, 05:21 AM   #6
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Really helpful, but particularly interesting from what I am hearing is that the exp. compensation varies with aperture, so I better take enough images to get a handle on that.

Thanks
08-17-2011, 07:13 AM   #7
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QuoteOriginally posted by Spodeworld Quote
I just got my first Pentax...the K20D. Seems like a nice camera.

I also learned from Rio to remove the spring from the infinity adapter...and then, I learned the hard way

Anyway, I have a few questions regarding focus and metering when using M42 lenses, or manual lenses for that matter:
Got a question or two.

1. Focus: Should I set the focus point to the middle focus point and recompose. I don't really do that on my other cameras, but I'm not sure if that is how you are supposed to do that with manual lenses.
If you're using MF (manual focus) option on your camera, it will (I believe) default to center focus...
QuoteQuote:
2. Metering: Does it matter what kind of metering I select? Center, multi, point....

3. Metering again: Got to get used to how it meters. Need to develop a feel for when I need Exposure Compensation. Can't tell yet how well it meters in various situations, but it does seem a bit quirky.
I use center 100% of the time and if the circumstances calls for it, spot meter. But the only way to describe metering on the K20 regarding m42 lenses, consistently inconsistent. You said it best, one must get to know each lens/camera and it's tendencies. I know, on my K20 or K10, compensation is almost always needed; outdoors usually -comp and indoors +comp. They also do have a weird way of metering when stopped down, as other have indicated. There are no fast rules here, as exposure compensation changes with ISO as well

The base of m42 lenses are usually too small to touch the contacts around the camera mount, this is what cause a lot of the inconsistent metering, if you search PF about using "foil" paper with m42's, it'll be interesting reading...
QuoteQuote:
4. The shutter sounds a bit noisy. Hopefully this is nothing to be concerned about.
More of a "thud" on the K10 v. that "springy" sound on the K20... your presence will not be missed at any event...
QuoteQuote:
5. Using Flash: The metering is completely different when I engage the flash in M mode using the green key and A mode. M seemed almost not to care that the flash was engaged when I pressed the green button, and the metering didn't change whether the flash was up or down. In A mode though, it seemed to take the flash into consideration.

Thanks for any feedback.

Steve
I believe flash operation will be 100% manual. Like the old days of knowing the Guide Number on your flash, @ISO100 and distance to subject.

But in the end, it's all fun; just like hacking around on the golf course all day, and then finally, on that long par 4 #15, hitting that sweet spot on your driver, watching your shot rise majestically, hanging in the air for what seems like forever and landing right where you aimed... then you can't wait till the next shot (golf or otherwise)

Have a good time! (if this post is a bit loopy, my dog got me up at 5:00am!!!)
08-17-2011, 09:24 AM   #8
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QuoteOriginally posted by Spodeworld Quote
Really helpful, but particularly interesting from what I am hearing is that the exp. compensation varies with aperture, so I better take enough images to get a handle on that.

Thanks
There is the real beauty of a digital SLR. Unless it is that one split second once in a lifetime shot, there is no need to keep what you don't like and you can immediately reshoot. A couple things to keep in mind. Once you have your exposure set in a given location, there is usually little need to change it. If you get a handle on how shutter speed, aperture, and ISO all play together, there isn't anything you won't be able to do (unless the camera actually limits you).

I use spot metering and center point for the focus. If you are in manual focus however there is no reason you cannot use other parts of the viewfinder instead. The Flash, with an M/K or M42 lenses will always fire at full output regardless of what mode you are in. The camera has no way of knowing what your aperture setting is with those lenses and therefore, cannot calculate flash output. I simple solution is an inexpensive shoe mount flash that has Auto settings. With one, you can set your ISO and Aperture and the flash will deliver a reasonable exposure.



08-17-2011, 09:41 AM   #9
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QuoteOriginally posted by JeffJS Quote
There is the real beauty of a digital SLR. Unless it is that one split second once in a lifetime shot, there is no need to keep what you don't like and you can immediately reshoot. A couple things to keep in mind. Once you have your exposure set in a given location, there is usually little need to change it. If you get a handle on how shutter speed, aperture, and ISO all play together, there isn't anything you won't be able to do (unless the camera actually limits you).
Indeed. I've mentioned elsewhere about locking-in an exposure once I know it's right for the situation. An example: Shooting 'scapes in the Red Rock country around Sedona AZ, with red-brown hills, dark-green foliage, blue skies, white puffy clouds. Shooting with auto-exposure gives wildy differing results depending on precisely where the lens points. Instead, I find the right exposure in M mode via Green button (and chimping and adjusting), then stay there and shoot away. And chimp and delete and adjust and reshoot, and fix in PP as needed. T'ain't no big thang.
08-17-2011, 10:04 AM   #10
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if you are really serious about using M42 lenses or any legacy Manual aperture lenses (non KA mount) then you might want to consider swapping the focusing screen out of the K20 for the one supplied with the *istD.

My K10D meters infinitely better with the *istD screen than the K10D screed (same as K20D btw)

see the graph below. each change of 40 greyscale (vertical axis) is 1 stop exposure error.

by putting the *istD screen in a K10D I was able to reproduce the *istD exposure behavior on the K10D.

08-17-2011, 11:17 AM   #11
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QuoteOriginally posted by RioRico Quote
Indeed. I've mentioned elsewhere about locking-in an exposure once I know it's right for the situation. An example: Shooting 'scapes in the Red Rock country around Sedona AZ, with red-brown hills, dark-green foliage, blue skies, white puffy clouds. Shooting with auto-exposure gives wildy differing results depending on precisely where the lens points. Instead, I find the right exposure in M mode via Green button (and chimping and adjusting), then stay there and shoot away. And chimp and delete and adjust and reshoot, and fix in PP as needed. T'ain't no big thang.
Last time I was in Sedona was with my Olympus OM-1nMD with a 50mm f1.4..



This is a scan from a print because the negatives are long gone from that trip. At the time, I didn't have my own handle on 'exposure' and the match stick meter of the camera was it (didn't really understand exposure compensation and the like). I really wish I had known better at the time because I don't see myself getting back there anytime soon. That's why I tend to get on people about learning the basics, even with our fancy new fangled machines. The above was taken summer 1996 IIRC.

08-17-2011, 11:52 AM   #12
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Lots to get a handle on here.

Yes, I will be doing lots of chimping for some time to come. But, it already is a bit of a practice. I know to trust the histogram over the image on the LCD.

Also, I believe someone here said the with the aluminum foil trick you can improve the auto exposure metering. Is that really correct? I thought it was only to enable CIF.

And, the focus screen issue is a blank page to me. I'll have to look into what that is about and what it means and entails to swap one out.

Thanks!

Last edited by Spodeworld; 08-17-2011 at 01:26 PM.
08-17-2011, 01:35 PM   #13
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QuoteOriginally posted by Spodeworld Quote
Also, I believe someone here said the with the aluminum foil trick you can improve the auto exposure metering. Is that really correct?
No, it is not true. The problem is with stop-down metering and how it is implemented on your K20D and other older bodies (the problem has been corrected on the current model line). No amount of foil will allow true open-aperture metering with non-A contact lenses since those lenses do not provide for aperture control from the body and the K20D lacks the coupler to detect the current aperture set on the lens due to its having the so-called "crippled" mount.

So it goes like this: Meter, chimp, adjust, repeat...

Sorry

As for using the *istD screen, Lowell swears by this solution and it may very well work as described. Lowell, do you retain proper metering with A-contact lenses?

Steve

Last edited by stevebrot; 08-17-2011 at 01:42 PM.
08-17-2011, 01:46 PM   #14
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"Crippled mount" I've heard that term...looks like I've got a lot of catching up to do

Thanks for your help.
08-17-2011, 04:02 PM   #15
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QuoteOriginally posted by stevebrot Quote
As for using the *istD screen, Lowell swears by this solution and it may very well work as described. Lowell, do you retain proper metering with A-contact lenses?

Steve
Oddly enough, no, I never thought to

at the time there was a rather heated debate about the cause of the metering error, and some anicdotal comments about the *istD and DS screen (it is the same) working better, as did some split screens. I had already carried oout a lengthy discussion with pentax about the metering difference, and had the *istD and K10D metering plotted out with my K50/1.4. I had also noted that with a teleconverter, my sigma 70-200F2.8 metered with a constant exposure error on the K10D, but not on the *istD.

I don't know what causeed me to try the screen, other than the anicdoptal comment, but I replicated the *istD performance almost perfectly (as you can see) and the K10D test was done over a year after the *istD test.

Since the K10D has an issue with tele converters, and with not knowing the true lens aperture, I simply assumed, perhaps wrongly, that what ever error correction they did, would be incorrrectly applied to A lenses, but at least the error would be constant, (since all metering is open aperture) and that it would be predictable lens to lens as a function of maximum aperture
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