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03-09-2013, 07:54 PM   #31
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QuoteOriginally posted by rhodopsin Quote
Thorium doped glass is well known, however, Gerjan van Osten says, in "The Ultimate Asahi Pentax Screw Mount Guide" (1999), there is thorium in one of the coatings. Since Mr. van Osten had access to Asahi Pentax personnel and documentation, I tend to believe him.
This is news to me. Did he say which lens?


Steve

03-09-2013, 07:56 PM   #32
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QuoteOriginally posted by rubender Quote
Thanks for the samples pics of both lenses. Which one do you like better on your 5D? I knoe that the 8 elements flares more but that's not an issue for me (as long as I can controlled the flare not like the sensor reflection issue I'm having).
I bought my 8-element just a few weeks ago, so I don't have enough time to shoot with it yet.
I read people say sharpness of 8-elem is very good.
But with my high-iso+low shutter speed pictures, I don't see difference in terms of sharpness yet.
In terms of coating, may be S-M-C copies can keep better contrast under bright sunlight.
However, IMO, they flare as much at night.

Last edited by MegaPower; 03-09-2013 at 08:05 PM.
03-09-2013, 07:58 PM   #33
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QuoteOriginally posted by rubender Quote
I believe you are right in the info you wrote but in the pic you posted your mark lenses wrong, the one on top is the 7 element SMC (red mark next to 4 is on the left, says MANUAL and AUTO) and the one below is the 8 elements (red mark on the right side of 4, and says M and A). You're right either way.
lol
Yes, I marked them wrong
08-27-2013, 01:19 AM   #34
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Purple spot

QuoteOriginally posted by rubender Quote
Hello,

I recently bought a Asahi Super Takumar 50mm 1.4 (M42), after doing a lot of research and reading this forum, I decided for the non multicoated version. I'm very happy with the lens bokeh, how is built and how good is for pulling focus, so smooth... I got it from ebay so it's not mint, just a few dust specks that won't affect image quality.

I mainly shoot video, and while doing some test today form my window I realized that the lens (I hope is not my camera sensor) was producing a weird magenta/purple circle right in the middle of the frame. It usually produces one when it flares or pointing to a window or any very bright light source, but in this case I was pointing to the ground. I did the same shot with a 28-70mm Nikon AF-S 2.8 on 50mm and I couldn't see that magenta circle in it. I made a few more test and looks like that is more obvious in video mode than stills, but only happens with the Super Takumar.

Has anyone had a similar issue with this lens? The circle's color si very similar to the reflection's color that the lens make when you look straight through it. I was wondering if it is an internal reflection due to the M42-EOS adapter or something that this lens always does. Or maybe I got a bad copy of the lens, I don't know but is driving me crazy... I realized that is more obvious when shooting f8-f11, f8-f1.4 it's almost imperceptible.

I attached some screenshots of the effect/artifact/aberration/glare (I don't know how to call it). Stils are Super Takumar at f16,11,8,4and 1.4

NOTE: There is a soft focus effect in all the shots because the window I was shooting through had a screen that is in the foreground out of focus, and these are screen shots of video shot at 1/50, I have no complains about the lens sharpness.

Thanks you!
Hi, I just returned from Iceland recently. While traveling there, I had this experience with a purple spot in some shots, that I took with my K7 and S-T 1.4/50 (v.1), just like yours. I think, that besides the rear glas reflection on the sensor, certain humid conditions can be the cause somehow? Because on both occasions the weather changed to rain as it happened and shots before and after are fine. I donŽt think, that a filter on the front of the lens matters, since I get ithe spots both with and without a filter on. On both shots I used a hood.

Here are two samples and copies, where I removed other colors and boosted the reds, blues, purples, magentas.

Regards

Attached Images
View Picture EXIF
PENTAX K-7  Photo 
View Picture EXIF
PENTAX K-7  Photo 
View Picture EXIF
PENTAX K-7  Photo 
View Picture EXIF
PENTAX K-7  Photo 
08-27-2013, 01:32 AM   #35
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..IŽll add, judging from the size of the spot, it could in part derive from the aperture somehow? I think, both shots were taken at f:11

Also, that the spot resembles the shape of the object in the photo and, that this area/angle/light has influence somehow?

Last edited by jt_cph_dk; 08-27-2013 at 03:06 AM.
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