[bm75]

Hi all.
I've already brought a M 20mm f/4 in perfect conditions. I've taken some photos during a mountan trip with my k-5 and results were strange.. .There's a light blue dominance in the pictures. I tought it could be really high UV radiation in mountain (altitude not higher than 1950mt) or WB ( I controlled it: was ok on auto and "natural"
no custom settings, no digital filters) and I had to shoot compensating -0,3 -0,5 ev .The same pictures taken with DA 17-70 are much better , but settings are the same.
Had anyone noticed the same behaviour of the lens? I'll be grateful for any suggestion.
Best Regards.
Matteo

[luftfluss]

Yup, same thing with the non-SMC Tak 55/1.8 I used to have. Just a quick tweak of WB in post-processing makes everything all right!

[wtlwdwgn]

If the lens has any visible yellowing that might account for the extra blue light hitting the sensor. Just my $0.02.

[Na Horuk]

Do you have a filter or lens hood mounted? A filter could cause problems. And a lack of a hood can cause flare and ghosting.
Do you shoot jpeg or raw? If jpeg, jpeg mode and WB can be the problem. Pentax already has slightly cool colours in the modern DSLRs, I think, so it would potentate any lens characteristics.
I think your best bet is to use "natural" jpeg mode, the WB best for your scene (daylight, shade, etc.). And if you shoot raw, you can tweak WB in post. This doesnt solve the problem, but it does deal with it.

Does the lens have haze or fungus? You probably already checked this, though. What about image quality overall? Any optical problems?
Other thing you can try is dismounting the lens and leave it in the sun, have UV rays go through a little. Just make sure it doesnt focus on something flammable lol

Edit: Oh, and I just remembered a thread on some ultra wide lenses from the film era.. I remember some had a cast or an odd purple vignetting, because the angle of incidence of those ultra wides was okay for film, but doesnt jive well with digital sensors. Not sure if this applies to Pentax gear.. and if this were the case, it would probably be mentioned in the lens review database or the sample photo gallery.

[wombat2go]

I have seen that on the Pentax K-01 here on AWB with some Pentax -M lenses. It has been mentioned on a thread on PF too.

I do not see the problem with the Pentax ist-ds

To fix the K-01 error, I use Raw+, then I can pull the color temperature by about +200K to get close to a gray balance.

[narual]

Why wait til post? If you're shooting with just that lens, set up a grey card, snap a shot of it, use it to set the camera white balance, and go from there.

[wombat2go]

set up a grey card, snap a shot of it, use it to set the camera white balance,

Yes I tried that, result was similar to AWB. I think I put test photos on another thread recently. I should try some more -M lenses.

[bm75]

Thanks all for the suggestions.
I have never seen it before with other K or M or A lenses I use (perhaps only Takumar 35 m42 Mount on the magenta side but I supposed it to be due to old coatings). Without UV filter the situation is really worse and pictures have a lack of contrast - they look "washed" and I have problems with metering ( I noticed a huge overexposure) so I think I might buy a better UV filter ( I used HOYA HMC UV(C) in both M 20 and DA 17-70 ) for these situations (the place was sunny and lots of UV reflections on rocks, no terrain absorbing UV) . I will follow your suggestions on WB custom settings .
The lens has good sharpness , also compared with DA 17-70 and has not so many CA , except for a kind of blue fringing . It's worth the price I paid for that!!!
Thank you all very much.
Best regards.
Matteo

[Na Horuk]

I suggest you always use the lens hood.
If you want to use a filter, you can maybe even find a UV filter that is a little orange, to combat the blue. But I think using a custom WB is a more elegant solution, if you have the time to set it up.

[bm75]

I suggest you always use the lens hood.
If you want to use a filter, you can maybe even find a UV filter that is a little orange, to combat the blue. But I think using a custom WB is a more elegant solution, if you have the time to set it up.

I totally agree with you. I Always use the lens hood. I haven't got the original hood for the M20 so I used a square type adapted one, probably not so efficient. Lately I tought it would be better using a circular polarizer but I had to move forward and had to pack the camera in the bag. I will try with different WB settings to find out a good solution with warmer tones that are more similar to my likes. The lens is ok, no fungus or other problems. It's a real pleasure to use and in different situation it captures more natural tones. Many thanks for your suggestion. Matteo

[narual]

There's always the Xrite color checker passport. That will ensure that colors match.
x-rite Colorchecker Passport reviews - Pentax Camera Accessory Review Database
X-Rite ColorChecker Passport ? X-Rite Photo ? X-Rite Passport

But also,

If the lens has any visible yellowing that might account for the extra blue light hitting the sensor. Just my $0.02.

-- did you check for yellowing? Though a quick check of a list shows the takumar 20mm as susceptible, not the M-20. Radioactive lenses - Camerapedia

[wtlwdwgn]

Although filters are not supposed to have an effect on digital sensors, I use Skylight filters which were designed to control the Kodachrome blue skies which were unnaturally dark blue. Worth a try.

[narual]

Although filters are not supposed to have an effect on digital sensors, I use Skylight filters which were designed to control the Kodachrome blue skies which were unnaturally dark blue. Worth a try.

Straight UV filters shouldn't have much effect.

A skylight filter isn't *just* a UV filter. Skylights have a magenta tint.

Haze filters are also common UV substitutes - those have a yellowish tint.

[jsherman999]

Hi all.
I've already brought a M 20mm f/4 in perfect conditions. I've taken some photos during a mountan trip with my k-5 and results were strange.. .There's a light blue dominance in the pictures. I tought it could be really high UV radiation in mountain (altitude not higher than 1950mt) or WB ( I controlled it: was ok on auto and "natural"
no custom settings, no digital filters) and I had to shoot compensating -0,3 -0,5 ev .The same pictures taken with DA 17-70 are much better , but settings are the same.
Had anyone noticed the same behaviour of the lens? I'll be grateful for any suggestion.
Best Regards.
Matteo

The M 20 f4 can shoot a little cool. It's something that's so easy to tweak in post that it doesn't matter much, though. I loved that lens' blues

[bm75]

The lens has no signs of yellowing , not the coating not the internal lenses. Perhaps the problem was focused on the place and scene where I took the picture. I Will try WB custom setting changing K degrees , let's see what will happen!! Pictures taken with K 55 -my beloved one- in similar conditions but different place are beautiful without problems, but the lens is not UWA designed.
I sometimes used skylight filters on film but i still no more have them because I loved BW and usually took pictures with delta or Tmax film with stronger filters that are still part of my gear. If I'm not wrong there were two different types of Skylight filters, not so?
I'm really happy...here in PF there's a lot of shared different experiences. People, you're Great!!

---------- Post added 10-24-14 at 06:44 PM ----------

The M 20 f4 can shoot a little cool. It's something that's so easy to tweak in post that it doesn't matter much, though. I loved that lens' blues

I agree. The lens is capable of really good colour rendering. I had problems in a particolar situation I didn't realized why so I'm trying to understand how to avoid problems or fix them. I admit I prefer not too much PP, I'm convinced a good work is done from the biginning. Your photos are a beautiful exemple of what the old M 20 is capable of. Thanks!