Image quality of Photar 1:2.5/25 lens

amoebahydra · Post by **amoebahydra** » Thu Feb 21, 2013 4:52 am

I have commensed using the Photar 1:2.5/25 lens for macrophotograhy work. However, I found the result quite disappointing as compared with that of Photar 1:5.6/120; there are quite a bit of chromatic aberration appeared in the high light region.

Do anybody had similar experience in taking photo with this lens? Is this because of my lense is defective?

Harold Gough · Post by **Harold Gough** » Thu Feb 21, 2013 7:46 am

I have yet to use mine. You should tell us the magnification and aperture you used.

Harold

Pau · Post by **Pau** » Thu Feb 21, 2013 9:28 am

Because it affects only the out of focus parts, it only seems to be longitudinal chromatic aberration. It may dissapear when stacking, as stacking software just takes the focused regions of each image.

amoebahydra · Post by **amoebahydra** » Thu Feb 21, 2013 12:04 pm

Thanks guy,

I am using 6X magnifaction and f/4 in taking these picture.

I will try stacking after setting up my macro-stage.

Regards

Patrick

Harold Gough · Post by **Harold Gough** » Thu Feb 21, 2013 12:12 pm

I am wondering if this is the same effect as I get with my camera, and is not lens-related. The brightest highlights sometimes give these coloured, pixelated effects. I think this is more to do with the sensor, at least with my camera.

Harold

amoebahydra · Post by **amoebahydra** » Thu Feb 21, 2013 3:08 pm

I tend to agree with Pau regarding the explanation of lateral chromatic aberration in out of focus area. I was mistaken when I first post in this thread, from the hint of Pau I have a closer look at the first photo reveal that it is not only the brightest part having chromatic aberration, but at the left hand corner of the tear part of the leaf (an off focus area) there are blue/red color fringes even in the dark grey zone.

Patrick

Charles Krebs · Post by **Charles Krebs** » Thu Feb 21, 2013 3:48 pm

Patrick,

I've never used the lens so I don't know. But I would like to see a different example of what is troubling you. What you have posted here looks suspiciously like it could be the result of natural constructive and destructive interference patterns that occur in a thin "film" such as a soap bubble or a fly or mosquito wing. I can't really see any "color" in the highlights on the thicker section, but only in the thin clear edge membrane.

Fredlab · Post by **Fredlab** » Thu Feb 21, 2013 4:27 pm

Hello

Charles Krebs wrote:I've never used the lens so I don't know. But I would like to see a different example of what is troubling you. What you have posted here looks suspiciously like it could be the result of natural constructive and destructive interference patterns that occur in a thin "film" such as a soap bubble or a fly or mosquito wing. I can't really see any "color" in the highlights on the thicker section, but only in the thin clear edge membrane.

+1

An example of CA (Olympus MPlan 20 LWD)

Without CA (Nikon MPlan 20 ELWD)

Another example HERE (Olympus MPlan 10)

Interference pattern

ChrisR · Post by **ChrisR** » Thu Feb 21, 2013 6:12 pm

Fwiw I have the Minolta Rokkor bellows macro lens 25mm f/2.5 which I read (hereabouts) was derived from the Photar. I can't confirm that, nor have I used it a vast amount. I do remember seeing some lateral CA creeping into the corners when off the short end of the quoted magnification. It was happier at higher magnification.
Dr Klaus' site http://www.macrolenses.de/objektive.php gives the
"Leitz Wetzlar Germany" Photar's designed range as 6.3x - 20x
There's an earlier "Ernst Leitz, Wetzlar", (see the pictures - click "Details") one without a range quoted,
and the Rokkor's range as 3.2 - 9.3x.

6.3x is really getting rather high for the aperture (diffraction).

At about 4x on APS-C, there wasn't any problematic CA showing in individual images. It's a nice lens at that mag.
(The difference in quoted ranges may come from decisions based on different intended uses (film formats) so I don't know if this tells us they're different lenses or not).

Whatever - what magnification are you using it at?!

amoebahydra · Post by **amoebahydra** » Fri Feb 22, 2013 5:59 am

Hi Guys and Charles, I had taken a photo of a brass screw which should not have thin film to generate the distructive diffraction pattern. The lateral CA still appears and should rule out the thin film theory.

Magnification of the first photo at full size should be around 7X

Regards

Patrick

ray_parkhurst · Post by **ray_parkhurst** » Fri Feb 22, 2013 11:15 am

I'm seeing the same thing in the in-focus parts of the images as I do sometimes in my coin photography. The guys over on my coin photography groups call it "red and blue sparklies" and it seems to be due to local sensor overload. On coins, this is caused by high amounts of luster being present. Luster is specular reflection off the metal grain structures caused by metal flow, with nearby dark areas where the light is scattered by off-angle reflection. The grains are physically small, and present full-brightness specular reflections to the sensor that are sub-pixel in size. These cause local sensor overload in the R or B sensors, and create what I assume is a similar effect to "false color" in moire patterns.

In my coin photography, the situation is made far worse by my use of Jansjo LED lighting, which has a very small emitter spot size compared with a lot of other sources. There are a few simple solutions:
- diffuse your light source
- reduce your exposure (though you may have to go 2-3 stops to avoid overload)
- add another source to decrease local contrast

amoebahydra · Post by **amoebahydra** » Fri Feb 22, 2013 5:39 pm

Thanks, learn again from fellow member !

Harold Gough · Post by **Harold Gough** » Sat Feb 23, 2013 2:25 am

ray_parkhurst wrote:it seems to be due to local sensor overload.

This is the kind of thing I meant by "I think this is more to do with the sensor, at least with my camera."

Harold

amoebahydra · Post by **amoebahydra** » Sat Feb 23, 2013 5:23 am

Oh I see, I thought previously that you meant camera dependent etc stuff. Thanks again

Patrick

Joseph S. Wisniewski · Sun Feb 24, 2013 10:24 am

Patrick, agreed, there's definitely plenty of longitudinal CA in those later examples, in the largest bright highlights. You can see the reddish borders in the areas in front of the plane of focus, and greenish ones brhind the plane of focus. That agrees with my experience with both the 25/2.5 and 50/2.8 Photar. Again, that's something you only get to see in the large highlights, because in the small highlights, any color aberrations are masked by beautiful, natural color speckles.

Hey people! Don"t be dissing the colored speckles, they're one of my favorite parts of macrophotography. They are, indeed, an interference phenomenon, and being able to see them is a sign you have good optics. You don't just see them where there's thin films, you see them when you have fine scratches that are on the scale of light wavelengths, and your light is highly collimated, like in Rick's examples in the other post.

FOTS - Friend of the speckles.