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03-05-2010, 04:49 AM   #1
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Wanted: quick glass, solid metal

I've been pondering whether or not to buy new glass. Pondering even whether or not to post my dilemma up here, since in the end I know I have to make up my own mind. But who knows, writing it down and even getting some feedback might help. So here goes...

I have a K20 and since picking up an M 50mm F/1.7 for 35 euros or so this has by far been my favorite lens. I like the shallow depth of field and I like the build quality. However I do find that I'm almost always shooting wide open since I find metering at other apertures too much of a hassle. And, more importantly, shooting at F/1.7, over half of my shots are out of focus. Though I now take this in account and usually grab at least 6 shots of anything important, shifting focus through the range of what looks sharp, I still end up with shots that are great but just slightly (or heavily) out of focus.

So. What I'm pondering is whether or not to buy a fast automatic aperture / automatic focus prime. Something like the FA 50mm 1.4 or 1.7 would be an option but they look plasticky to me. I'm sure their build quality is better than the average kit lens but I don't think they'll feel as good as my M 50. Then I have been considering the 31mm ltd but 900 euros is a lot of money to spend and I'm not sure I myself would even notice the improved image quality, so I'd spend it on having autofocus and auto-aperture.

As far as focal length goes. I'm quite okay with 50mm. Granted, in some situations it's a bit too long, but I think it helps me focus on details and getting more interesting/unusual framings. I'm not sure the more standard (on APS) length of 31mm would suit me better.

And then, I have a cheap-cheap split focus screen. Will buying a better and more expensive focus screen help me increase my focusing accuracy; thus making a lens upgrade even less necessary?

03-05-2010, 05:06 AM   #2
axl
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If 31 is expensive and 50 is good length you should have a look at 43ltd. It's bit slower at f1.9 but great. Used can be picked up for 400EUR +/- new is "bit" more but cheaper than 31.

BR
Peter

PS: your best bet is split prism focusing screen. I have one and I often find myself MF ing both of my ltds when shooting wider than f2.8
03-05-2010, 05:18 AM   #3
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Squib, I echo axl's choice of the 43 mm ltd. It is a great lens. As far a manual focusing goes, I'm going to suggest some focus exercises. Like most exercises they are very boring, but I've used them and they work. They were developed by Godfrey, a regular poster over at DPR (or at least he used to be a regular poster, I haven't been there in a while) Here's the link:
Re: Is a KatzEye required for those using manual focus?: Pentax SLR Talk Forum: Digital Photography Review

NaCl(check them out, they work!)H2O
03-05-2010, 05:27 AM   #4
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I have been thinking about the 43mm but it's hard to find in the Netherlands. I'll try a bit harder, though.

I do have a split prism focusing screen. It just seems that when the image through the split prisms align, the picture still turns out to be out-of-focus. Of course, this could also be due to re-framing, as accurate use of the split-prism requires I point it at something sharp and contrast-y.

Thanks for the link! I'll check it out.

03-05-2010, 05:43 AM   #5
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QuoteOriginally posted by Scrib Quote
However I do find that I'm almost always shooting wide open since I find metering at other apertures too much of a hassle. And, more importantly, shooting at F/1.7, over half of my shots are out of focus.
I am not sure I understand why metering with other apertures seems to be too much of a hasle for you. What's so inconvenient about pushing the "green button"?

More than 80% of my shots I take with fully manual lenses and I don't see the difficulties in working with different apertures. Understandably the hit-rate with a wide open 1.7/50 is not very high. I can't speak from my own experience, but probably it would not be much different with an AF 1.7/50 lens wide open. As others have stated before, you will probably have to practise a lot in different litghting conditions.
03-05-2010, 05:58 AM   #6
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And don't forget that DOF will get shallow at shorter distances and if you shoot wide open. Check e.g. Online Depth of Field Calculator
At 100cm distance and 50mm/1.7, DOF is +1.26cm / - 1.29cm. So if you're camera or subject moves more than that forward or backward, you have a problem.

Also, your split prism might be slightly misaligned. If you have an AF lens, do a manual focus with that and take a picture. Next use AF and take the same picture. Compare the two. Use a tripod (and 2 sec delay on the camera) and a steady subject.
03-05-2010, 06:00 AM   #7
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QuoteOriginally posted by volley Quote
I am not sure I understand why metering with other apertures seems to be too much of a hasle for you. What's so inconvenient about pushing the "green button"?
I'm not sure if this is normal but just pushing the green button doesn't work on my camera. I need to shift the on/off lever to 'live view' (which I have set in my preferences will not enable 'live view' but instead DOF-preview) and simultaneously either press the green button or turn the dial. An awkward combination as it needs two fingers at the top of the camera.

QuoteOriginally posted by volley Quote
Understandably the hit-rate with a wide open 1.7/50 is not very high. I can't speak from my own experience, but probably it would not be much different with an AF 1.7/50 lens wide open.
I've been wondering about the same.
03-05-2010, 07:54 AM   #8
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QuoteOriginally posted by Scrib Quote
I'm not sure if this is normal but just pushing the green button doesn't work on my camera. I need to shift the on/off lever to 'live view' (which I have set in my preferences will not enable 'live view' but instead DOF-preview) and simultaneously either press the green button or turn the dial. An awkward combination as it needs two fingers at the top of the camera.
I have a K200. But I assume that also for the K20 it is possible to change the settings menue to have the correct exposure time selected for any aperture. As far as I know it should be possible for all Pentax DSLR. The procedure you are describing would drive me nuts too

03-05-2010, 08:17 AM   #9
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I have a couple of observations here for anyone caught in the decision to go with older manual focus and or manual aperture lenses.

first of all, the K10D and K20D are known for very poor metering using the standard focusing screen.

I have posted the following before but it is useful to post here also.

I have a *istD, K10D and K7, the K10D I have checked exposure with 3 different screens, the standard screen, the *istD screen, and a jin finance split image screen.

the results below show the change in greyscale histogram when shooting a block wall at all F stops using the green button to set exposure.



Secondly, the reason I have a split image in the K10D is that I have a lot of MF lenses, ~10 K/KA mount and an equal number of M42 lenses. all of them are fast at their respective focal lenghts. It is a waste of time (in my opinion) to consider using fast MF lenses without a split image screen.

As for green button, the default more on the K10D and K7D (I can only assume K20D is the same) is to set shutter speed for the stopped down aperture when pressed, and DOF preview stops the lens down to the preset aperture and shows the meter reading and over / under exposure. Unless you have played somehow with the setup, it should be the same on the K20

With respect to shooting wide open, if that is all you are going to do, just leave the camera in AV mode because that is what it does with non A lenses
03-05-2010, 09:06 AM   #10
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QuoteOriginally posted by Lowell Goudge Quote
As for green button, the default more on the K10D and K7D (I can only assume K20D is the same) is to set shutter speed for the stopped down aperture when pressed, and DOF preview stops the lens down to the preset aperture and shows the meter reading and over / under exposure.
If I understand you correctly, this is indeed how it works for me. Which means that when you select anything other than the widest aperture on a K20, you need to switch to DOF preview AND press the green button to meter for that aperture.

If any K20 owners here have other experiences with this, I'd be interested to know.



Sterretje: thanks for your suggestion & method to test the alignment of the focusing screen, I will indeed try that.

I popped in the 10-euro split prism focusing screen myself. I assumed that if it clicked, it would be properly aligned. I suppose that if it turns out not to be properly aligned, I will need to take it to a shop to have it fixed.

If I can somehow improve my focusing I think I will remain for a good while longer very happy with my M50.
03-05-2010, 10:07 AM   #11
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QuoteOriginally posted by Scrib Quote
...I popped in the 10-euro split prism focusing screen myself. I assumed that if it clicked, it would be properly aligned. I suppose that if it turns out not to be properly aligned, I will need to take it to a shop to have it fixed.
The cheap ones are not always the same thickness as the original screen. Sometimes they need to be shimmed to be at the correct distance from the mirror. You can test this out yourself with the M50/1.7 wide open, focusing on a particular mark on a ruler at close distances and a 45 angle. It's easier than testing AF because with AF you have to make sure the system doesn't focus on anything besides your chosen point.

I had some sticker shock about the price of a Katz-Eye but I popped it in 4 years ago and it works great. The price disappears after the second manual-focus lens that you add to your kit. My only regret is I have to add $110 to the price of a new camera when I'm considering upgrading.
03-05-2010, 10:50 AM   #12
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QuoteOriginally posted by Scrib Quote
If I understand you correctly, this is indeed how it works for me. Which means that when you select anything other than the widest aperture on a K20, you need to switch to DOF preview AND press the green button to meter for that aperture.
I have a K10D and the following applies:

In standard configuration, the green button closes the aperture and the camera does the metering after which the aperture is opened again. That's all there is to it. The DOF preview closes the aperture as well and will display an under/over exposure value in the viewfinder.

See page 95 of the K20D manual; as you seem to have changed some settings in the configuration, it might no longer work like that.
03-06-2010, 05:19 AM   #13
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QuoteOriginally posted by sterretje Quote
In standard configuration, the green button closes the aperture and the camera does the metering after which the aperture is opened again. That's all there is to it.
Well I'll be damned... when I wrote the first few posts here I didn't have my camera on hand but now I do and I just tried and you're right! I was sure I tried this before but apparently I didn't...

I've also been taking MF shots of a ruler at an angle and it appears that what looks like in focus through the viewfinder is in fact just in focus, but the majority of the depth-of-field is behind it.
03-06-2010, 06:26 AM   #14
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The in focus area should be around the focal point that you choose, not only behind. You can use a DOF calculator like Online Depth of Field Calculator to calculate the DOF.
03-08-2010, 07:17 AM   #15
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Read through this for how to adjust back focus with the screen.

Focusing Screen--How to adjust focusing screen--
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