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03-18-2011, 11:17 AM   #1
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Problem With SMC Pentax M 50mm F4 Macro

I have quite a trouble adjusting with this lens. I just got it today. Please share your experience with me, so I can determine whether the problem is me or the lens.

I have only test it few hours, and it's already nite in here. I use available room light and the viewfinder looks dark, the result pics also until I bump to ISO 800 on my K100D. I got many foggy/blurry/white images at F4, yet the glass seems to be free from haze/fog, even dust or fungus. I tried it's max magnification (1:2?) and then move a bit back, 20-30 cm from the subject, looks the same. When I'm at F8 however it looks sharper, must be because of the fog is no more. The reviews said that this lens is, well, is always sharp at any aperture.

All with 0.10 sec. - ISO 800


F4



F8



F4



F8


So, what Am I missing here? Is this lens is more a 'under the sun' lens? Is it the character of this lens, or just another bad copy that I have to return?

ADDED:
- Shots are taken handheld.
- I use a combination of Fluorescent and bulb lamp in my room.


Last edited by minahasa; 03-18-2011 at 11:58 AM.
03-18-2011, 11:29 AM   #2
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I don't know if there is any wrong with the lens, just want to raise some general points about macro photography:

- The indicated F stop is when the lens focuses at infinity. At close focusing distances, the F stop drops (slower). At 1:2 magnification, the actual F stop is about 1 stop slower than the setting. If you set the lens at F/4, at 1:2, the aperture is actually F/5.6. This is why the viewfinder is dim.

- At close focusing distances, the DOF is very very thin. Focusing thus becomes critical. For macro photography, a tripod is essential. A flash gun and a macro focusing rail are very important.

Also, you stated that shutter speed was 0.10 sec. Are these photos handheld?

Have you tested the camera/lens combination for front/back focus problem?
03-18-2011, 12:15 PM   #3
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QuoteOriginally posted by SOldBear Quote
I don't know if there is any wrong with the lens, just want to raise some general points about macro photography:

- The indicated F stop is when the lens focuses at infinity. At close focusing distances, the F stop drops (slower). At 1:2 magnification, the actual F stop is about 1 stop slower than the setting. If you set the lens at F/4, at 1:2, the aperture is actually F/5.6. This is why the viewfinder is dim.

- At close focusing distances, the DOF is very very thin. Focusing thus becomes critical. For macro photography, a tripod is essential. A flash gun and a macro focusing rail are very important.

Also, you stated that shutter speed was 0.10 sec. Are these photos handheld?

Have you tested the camera/lens combination for front/back focus problem?
Thank You for responding.

Yes, I'm shooting handheld. Since this is only a preliminary test, I'm thinking of it only as a 'quick glance' test. More test hopefully will be done when the sun rises tomorrow, and I'm sure I'll use a tripod. Good sharing there on the nature of the aperture, really appreciate it.

I'm familiar with macros before, but more like a 'pseudo macros'. This is my first 'macro' lens. I understand about the DOF theory, what I found confusing is the 'foggy' results at F4. I have a 50/F1.4, while at wide open it gives relatively brighty images, usually is quite sharp and fog-free from F2 and up.
03-18-2011, 04:31 PM   #4
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This doesn't look like an out of focus or motion blur problem to me, but rather like a problem caused by inconsistent metering compounded by glare from stray fluorescent light. At f/8 the camera seems to have metered more conservatively and has come up with a different white balance that did not result in as much boost for the green and blue channels. I think you might want to try again with AWB turned off and you should use a tripod so that variability from changing angles relative to the light source is taken out of the equation.

03-18-2011, 06:29 PM   #5
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QuoteOriginally posted by Ikarus Quote
This doesn't look like an out of focus or motion blur problem to me, but rather like a problem caused by inconsistent metering compounded by glare from stray fluorescent light. At f/8 the camera seems to have metered more conservatively and has come up with a different white balance that did not result in as much boost for the green and blue channels. I think you might want to try again with AWB turned off and you should use a tripod so that variability from changing angles relative to the light source is taken out of the equation.
That's what I thought. too. I did try to change the source of lighting to one particular light only, but the problem still there. I did not use AWB, I used a few types of presets, and yes the results is different in terms of color tone, but the glare stays, until I used really small aperture.

I have been able to test it this morning, and I think it's more than just the issue of flare involved in here. Take a look at these pics, help me judge:

I'm using daylight preset WB, metering by 'green button', and then adjusting again manually







This lens has problem at infinity focus, or even focusing at closer than infinity. Few shots at wide open, really bad. I tried stepping down the aperture, it helped a bit, but there still is a 'vortex-like' effects on the corner.








I've had trouble adjusting to my M 50 f1.4 before, but this is really-really frustrating.

Last edited by minahasa; 03-18-2011 at 06:37 PM.
03-18-2011, 07:17 PM   #6
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I'm certainly no expert with this lens, but it does seem to me from your photos that something a little wonky is going on...
03-18-2011, 07:40 PM   #7
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Send it back.
03-18-2011, 09:24 PM   #8
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I concur. There is clearly something wrong with this lens.

03-19-2011, 08:28 AM   #9
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I will send it back. I've given this lens a day of testing, yet I'm still getting problems. I'm also not an expert on lenses, but I had a few manuals before and they always gives good results. Just for knowledge sake, does anyone have any explanation for this oddity?
03-19-2011, 10:13 PM   #10
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Looks like it is pretty badly decentered, probably because someone dropped it. See here for an explanation.
03-20-2011, 12:48 AM   #11
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QuoteOriginally posted by minahasa Quote
I will send it back. I've given this lens a day of testing, yet I'm still getting problems. I'm also not an expert on lenses, but I had a few manuals before and they always gives good results. Just for knowledge sake, does anyone have any explanation for this oddity?
You shouldn't be having this much trouble. Even if your methods are poor, you should be able to get good results out of this lens. Here are some taken with one I sold recently here at PF.

Index of /Photos/ForSale/50mmf4macro

My bet is, somebody took it apart and didn't know how to put it back together. Also be sure the aperture is working properly. Lastly, I would assume you know this, M lenses, in any mode other than M, will shoot wide open regardless of how you set the lens.

03-20-2011, 01:14 AM   #12
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I concur: based on the photos I'd say that the lens was once disassembled, but one or more elements were left out or reversed. The 50mm f/4 macro should give very sharp and contrasty results.
03-20-2011, 08:19 AM   #13
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Sending it back tomorrow. The seller informed me that it was once adapted to fit Canon.
03-20-2011, 08:38 AM   #14
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Here is one from mine, tested as soon as I received it, hand held wide open.


03-20-2011, 09:51 AM   #15
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QuoteOriginally posted by minahasa Quote
Sending it back tomorrow. The seller informed me that it was once adapted to fit Canon.
It was sure nice of him to tell you that AFTER you bought it

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