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07-14-2008, 10:24 PM   #1
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50mm Primes

Looking at getting a 50mm prime for my K20D.

I already have the Pentax-M 50mm f1.4. Whilst it is a decent lens I've noticed when taking pictures at night there is a fair bit of purple fringing. Is this normal?

Here's a picture:



Obviously in good lighting the prime I current have is good.


Anyway, Looking at purchasing AF 50mm prime.

Can someone tell me:

Pentax 50mm F2.8 SMC D FA Macro Lens
Pentax 50mm F1.4 FA Lens

Which is the better/sharper of the two? please note I'd like to use it indoors - so speed is important (f1.4 vs 2.8). Macro is a bonus but not that important.

I'm ok with the price difference.

Is there another alternative?

I want this to be my sharpest lens with bokeh!

Thanks in advance,
David

07-14-2008, 10:33 PM   #2
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I just picked up a pentax f 50mm f.17 and it seems sharper than my m version even wide open. These are going for ~100 on ebay -maybe worth checking out. I'm not sure about pf but the bokeh and sharpness are very good.
07-14-2008, 10:57 PM   #3
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If you are hoping to avoid the purple fringing by moving to a different Pentax 50mm, you might be disappointed. The optical design for the non-macro Pentax 50s is been basically the same (for a given maximum aperture) since the Super Takumar lenses of the late 1960's. There have been some improvements in multi-coating technologies since your M 50/1.4 was made, but nothing that would reduce the type of CA that causes purple fringing.

The exif for your example indicates that you were shooting wide-open (AV mode). It may be that the blue haloing in your example is just simply flare. Try stopping down to f/4 in manual mode, turn off shake reduction (another possible cause), and see if that makes a difference.

Steve
07-15-2008, 06:30 AM   #4
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The F50/1.7 is an excellent lens also.

07-15-2008, 06:36 AM   #5
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FA 50mm f/1.4 is the sharpest from (f/1.2 and f/1.7) as quoted by Ben


cheers
07-15-2008, 06:37 AM   #6
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I just got my FA50 1.4 last week, and I have not been able to take any night scenes like this with it yet, but I plan on heading out tonight to get some shots of the local skyline here. I hope to see what it can do, as I already know it is very sharp even at f/1.4. Also, as some have suggested, stopping it down may help with the fringing you are seeing. The last time I took night time landscape photos, I used f/22. This of course requires a tripod, but it keeps the DOF very large, and can help keep the highlights down. I don't think I would go any larger than 4 when shooting scenes like this. Hope this helps. I'll also experiment tonight and post results so you can see the FA50 for yourself
07-15-2008, 08:53 AM   #7
edl
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Here's a night shot with the K10D, FA50/1.4 at F4.5, 30s, ISO100, SR off. RAW conversion, no other PP.

Not nearly as much PF, but then again much less light in this photo too.
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PENTAX K10D  Photo 

Last edited by edl; 07-15-2008 at 09:05 AM.
07-15-2008, 09:04 AM   #8
edl
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I just looked at the OP's photo again - I bet if he turns off SR that should fix his problems. Each light has a wobbly halo around it, but not a clearly defined star. Looks ilke SR was moving the sensor.

Here's another photo where you can see the "star" effect coming off all the lights. I might be wrong, but I think most lights should give this effect at night.

K10D, Sigma 18-50 2.8, RAW + PP



07-15-2008, 11:14 AM   #9
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QuoteOriginally posted by edl Quote
I just looked at the OP's photo again - I bet if he turns off SR that should fix his problems. Each light has a wobbly halo around it, but not a clearly defined star. Looks ilke SR was moving the sensor.

Here's another photo where you can see the "star" effect coming off all the lights. I might be wrong, but I think most lights should give this effect at night.

K10D, Sigma 18-50 2.8, RAW + PP

I think you are right regarding the shake reduction. As for the star effect, some lenses do this and others don't. Some people like it and others...well, you get the idea.

Steve


BTW...very nice shot...very nice car...
07-15-2008, 03:32 PM   #10
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Thanks guys!

I'll try and get some pictures tonight with SR off!
07-15-2008, 10:19 PM   #11
edl
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QuoteOriginally posted by stevebrot Quote
I think you are right regarding the shake reduction. As for the star effect, some lenses do this and others don't. Some people like it and others...well, you get the idea.

Steve


BTW...very nice shot...very nice car...
Thanks for the comments! Perfect location for nighttime car shots, you'll see more from this location in the future. As for the car, it's gone now but was a fun drive.

I like the star effect but it went a bit overboard in the car shot. A polarizer should cut the effect as well, correct?
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