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05-01-2015, 04:00 AM   #1
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K-50, various small issues/doubts

Hi all.


I'm a proud owner of a Pentax K-50, bought last year and used with a lot of satisfaction up to now. During this year I've found, however, a couple of things I've got doubts about, plus I've bought an M lens a couple days ago and I honestly can't understand what's happening with it! So, after a lot of time lurking here around, I decided to sign-up and voila', three brand new shiny questions for all of you


- Camera exposimeter seems to like to be optimistic. I've tried a lot with the three differents metering mode, but it seems most of the time when exposimeter says "exposition is ok" I still need to use exposure control to add 2/3 stop to get a correctly exposed picture, and often I still get a sligthly dark picture. It's not that a huge problem, but I just wanted to understand I'f I'm missing something.


- Viewfinder seems a bit dark. Well, a lot, actually :-D
Scene is bright, Liveview show a bright scene, Viewfinder is dark, I shoot the picture, get a bright picture. It just seems that the viewfinder loose some light along the way. Again, am I missing something?


- Third problem is funny and really strange...premise: I've bought an old Pentax 5mm F1.7 M, it was cheap, I was curious to try a manual lens, and on the forum everybody says it is one of the best.
So, I've installed it on my K-50, followed the steps to enable it, tried it in "auto" (the camera just choose shutter speed), and was amazed from the quality and the luminosity of the shots; not to be much surprised, actually, as my fastest lens was one of the two in the kit, and at 3.5 it's a lot less light than 1.7


However I did try it in full manual mode, and here is where things goes a bit funny. To summarize in short:
Same scene, same ISO, test done first in Auto ("Aperture priority, Automatic Exposure" is the only available mode other than Manual that the K-50 when using this lens) then in Manual at the same shutter speed choosed by the camera in Auto


Auto, F1.7 1/400
Manual, F1.7 1/400
Gives exactly the same shot (he same light, the same blurred background behind the in-focus subject)


Auto, F22 1/400
Gives the same shot, too


Manual, F22 1/400
Totally black frame


Manual, F22 1/15
Gives same shot in term of light, obviously without blurred background


I can come up with and explanation, here

05-01-2015, 04:13 AM   #2
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QuoteOriginally posted by Drizzt Quote
- Viewfinder seems a bit dark. Well, a lot, actually :-D Scene is bright, Liveview show a bright scene, Viewfinder is dark, I shoot the picture, get a bright picture. It just seems that the viewfinder loose some light along the way. Again, am I missing something?
The viewfinder is a tad darker than live view due to the presence of the focusing screen, but the culprit is probably the maximum aperture of your lens. Something that's F2.8 faster should be plenty bright.

QuoteOriginally posted by Drizzt Quote
- Camera exposimeter seems to like to be optimistic. I've tried a lot with the three differents metering mode, but it seems most of the time when exposimeter says "exposition is ok" I still need to use exposure control to add 2/3 stop to get a correctly exposed picture, and often I still get a sligthly dark picture. It's not that a huge problem, but I just wanted to understand I'f I'm missing something.
Shoot in raw, then you can always tweak the exposure if needed. However, over time I'm sure you'll learn the camera and compensate for its occasional inaccuracies.

QuoteOriginally posted by Drizzt Quote
However I did try it in full manual mode, and here is where things goes a bit funny. To summarize in short: Same scene, same ISO, test done first in Auto ("Aperture priority, Automatic Exposure" is the only available mode other than Manual that the K-50 when using this lens) then in Manual at the same shutter speed choosed by the camera in Auto
You need to be in M mode. Av won't properly set the shutter speed with K-mount lenses (except when shooting wide-open).

Adam
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05-01-2015, 04:38 AM   #3
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Hey, welcome! I'm not quite sure what your questions are. Maybe if you post photos (scaled down to max 800 on long side) with exif data in tact and labelled what settings you used, and which lens. These photos should be done in daylight, with a relatively near subject, hopefully using 2sec timer and a tripod/base.

But on to manual lenses. There are some different types of K-mount lenses. I'll explain quickly:
1) Fully manual, preset. I think the Mitakon K-mount lenses are like this. The mount fits on K-mount without needing an adapter, but they have no coupling, no levers, digital contacts, nothing. You simply use Av mode, focus with the lens wide open, then move the aperture to the number that you want, wait for Av mode to re-meter and set the shutter speed (and ISO, if auto-ISO) and take the shot. When you choose aperture, you immediately see viewfinder darkening, DoF widening.
2) Almost fully manual, but has aperture lever. The M series fits this description, like your M 50mm f1.7 (love that lens, btw). Here, the camera doesn't actually know what the chosen aperture is, because the lens has no digital contacts. But the camera can move the aperture from wide open to the one you selected on the aperture ring. The lens aperture is kept wide open for focusing, and gets stopped down when you press the shutter speed - but only if you have M mode selected. Choosing Auto-ISO or any mode other than M will default to Av. Av mode with manual lenses has the advantage of constantly metering and adjusting shutter speed (and possibly ISO), but it always keeps the aperture wide open, ignoring what you selected. You can use green button to have the camera stop down the lens to your selected aperture and set the shutter speed.
3) A-series. These lenses have no AF, but they have A on the aperture ring (you need to press a little button to select it, but then you just leave it there). Here the camera actually knows the aperture, and you can choose aperture on the camera. These lenses don't have in-camera lens corrections or AF, but they allow P and other modes.
4) Fully automatic. These lenses have lens ID, A-mode, etc.

I hope this sheds some light on what the camera is doing. With the M lens, you need to use M mode if you want the camera to choose any aperture other than wide open. Av mode and Auto-ISO can be used if you want to shoot wide open.

This is why different lenses might or might not darken the viewfinder depending on the choice on the aperture ring. And this is why sometimes the camera will ignore your aperture ring, and other times the aperture ring setting will only show up in the photo, and other times it will show up in the viewfinder.

Live view is a little special, because the camera will try to keep it a certain brightness to help you compose and focus, even if the scene and photo will actually be darker.

Regarding metering, I think with manual lenses, the camera can only use spot metering or center weighted.

Maybe you can refresh your manual lens skills with this tutorial:
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html
05-01-2015, 04:50 AM   #4
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QuoteOriginally posted by Drizzt Quote
Auto, F1.7 1/400
Manual, F1.7 1/400
Gives exactly the same shot (he same light, the same blurred background behind the in-focus subject)


Auto, F22 1/400
Gives the same shot, too


Manual, F22 1/400
Totally black frame


Manual, F22 1/15
Gives same shot in term of light, obviously without blurred background


I can come up with and explanation, here
Welcome to the Forums!
I don't know, did I understand the problem rightly, but... if You shoot with manual lenses in Av-mode, then camera exposures it in fully open mode. Always in fully open - irrespective of the lens aperture You have selected.

05-01-2015, 05:25 AM   #5
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And don't forget to change the aperture on the lens' control the setting on the camera is not controlling the aperture. Use green button to meter.
05-02-2015, 09:21 AM   #6
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QuoteOriginally posted by Aksel Quote
Welcome to the Forums!
I don't know, did I understand the problem rightly, but... if You shoot with manual lenses in Av-mode, then camera exposures it in fully open mode. Always in fully open - irrespective of the lens aperture You have selected.
Thanks, this explain it all :-)
And Na Horuk answer, too :-)
And a friend of mine explaining yesterday evening that a camera has a small lever to keep aperture ring wide even if it has no aperture control on manual lens. I was really puzzled that my K-50 cannot control aperture, still it can control it full open
After having spent half an hour playing with the lens in hand, now everything is much much clear :-)

---------- Post added 05-02-15 at 09:27 AM ----------

QuoteOriginally posted by Adam Quote
The viewfinder is a tad darker than live view due to the presence of the focusing screen, but the culprit is probably the maximum aperture of your lens. Something that's F2.8 faster should be plenty bright.
It's the same same darkness with whatever lens I use. I was thinking something in the line of "maybe there is a small plastic veil on it", but cannot find any. Can live with it, however.




QuoteOriginally posted by Adam Quote
Shoot in raw, then you can always tweak the exposure if needed. However, over time I'm sure you'll learn the camera and compensate for its occasional inaccuracies.
Raw is one of the reason I got a DSLR, so I always use it


It's not "occasional inaccuracies", it's "occasional accuracies". I'll soon open a new thread with a few examples, I'm not a photographer at all, maybe it's just my personal taste. I'd love to understand better what's...uhh...better
05-02-2015, 02:11 PM   #7
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Posts: 65
Hi Drizzt -- If you have highlight correction enabled or auto, and shoot in raw, many photos will appear underexposed in your raw program. This is on purpose to avoid blowing out highlights which can't be recovered otherwise. My K50 does this.

In jpg mode the camera does the correction to make it look exposed correctly while preserving the highlights -- you can compare by using raw+jpg.

If highlight correction is off, then...?
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