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03-30-2010, 10:27 AM   #1
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help me assess the IQ of my Bigma

In an earlier thread about "replacing my Bigma", I wondered if the IQ of my Bigma was up to snuff. Is my copy a good one? Does it need adjustment?

So, I took some test shots from my Bigma for critical observers to help me decide. Let's hope I provided good test conditions....

Camera: Bigma, without filters and with lens shade, attached to a K20D. The lens was securely attached to an arca-swiss style plate, which was securely mounted on an Acratech GV2 ballhead/clamp, on top of an Amvona carbon fiber tripod. I also took some shots with the GV2 in gimbal position. The tripod was placed on a flat, hard surface out of the (light) wind. The camera was set at aperture priority, pattern metering, SR off, RAW (DNG) format, AdobeRGB, Auto White Balance with very slight shift off of center, Central Autofocus point, color +1, Contrast +1, Sharpness +1. Shutter was activated by remote control. For manual focusing, I first focused by eye (my glasses give me at least 20/20 vision) and then made sure the camera indicated “in-focus” as well.

Subject and conditions: The subject was a decorative object on a heavy iron mesh table on an outside patio surrounded on three sides by walls. Camera-to-subject distance approximately 12-15 feet. Camera pointed slightly downward toward object. These mid-afternoon shots were in bright sunshine with slight tree cover overhead.

Shots: I took several series of shots, varying f stop, ISO, and manual vs. auto focus. Each series contains 5 shots taken (approximately) at 50mm, 200mm, 400mm, 450mm, and 500mm.

Series 1: f8, ISO 100, auto focus
Series 2: f8, ISO 100, manual focus
Series 3: f16, ISO 100, auto focus
Series 4: f16, ISO 100, manual focus
Series 5: f22, ISO 100, auto focus
Series 6: f22, ISO 100, manual focus
Series 7: f22, ISO 400, auto focus (ballhead in gimbal position)
Series 8: f22, ISO 400 manual focus (ballhead in gimbal position)
Series 9: f22, ISO 100, auto focus (ballhead in gimbal position)
Series 10: f22, ISO 100, auto focus (ballhead in gimbal position)

I will open these in ACR within CS3 with no post-processing. Which shots would it be helpful for you to see? And what kinds of crops? Or are these other shots that I should take as well?

Any help appreciated.

03-30-2010, 12:43 PM   #2
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QuoteOriginally posted by sholtzma Quote
In an earlier thread about "replacing my Bigma", I wondered if the IQ of my Bigma was up to snuff. Is my copy a good one? Does it need adjustment?

So, I took some test shots from my Bigma for critical observers to help me decide. Let's hope I provided good test conditions....

Camera: Bigma, without filters and with lens shade, attached to a K20D. The lens was securely attached to an arca-swiss style plate, which was securely mounted on an Acratech GV2 ballhead/clamp, on top of an Amvona carbon fiber tripod. I also took some shots with the GV2 in gimbal position. The tripod was placed on a flat, hard surface out of the (light) wind. The camera was set at aperture priority, pattern metering, SR off, RAW (DNG) format, AdobeRGB, Auto White Balance with very slight shift off of center, Central Autofocus point, color +1, Contrast +1, Sharpness +1. Shutter was activated by remote control. For manual focusing, I first focused by eye (my glasses give me at least 20/20 vision) and then made sure the camera indicated “in-focus” as well.

Subject and conditions: The subject was a decorative object on a heavy iron mesh table on an outside patio surrounded on three sides by walls. Camera-to-subject distance approximately 12-15 feet. Camera pointed slightly downward toward object. These mid-afternoon shots were in bright sunshine with slight tree cover overhead.

Shots: I took several series of shots, varying f stop, ISO, and manual vs. auto focus. Each series contains 5 shots taken (approximately) at 50mm, 200mm, 400mm, 450mm, and 500mm.

Series 1: f8, ISO 100, auto focus
Series 2: f8, ISO 100, manual focus
Series 3: f16, ISO 100, auto focus
Series 4: f16, ISO 100, manual focus
Series 5: f22, ISO 100, auto focus
Series 6: f22, ISO 100, manual focus
Series 7: f22, ISO 400, auto focus (ballhead in gimbal position)
Series 8: f22, ISO 400 manual focus (ballhead in gimbal position)
Series 9: f22, ISO 100, auto focus (ballhead in gimbal position)
Series 10: f22, ISO 100, auto focus (ballhead in gimbal position)

I will open these in ACR within CS3 with no post-processing. Which shots would it be helpful for you to see? And what kinds of crops? Or are these other shots that I should take as well?

Any help appreciated.
I would say (remembering the other thread), that you should simply post the three sharpest shots at f/8. The smaller apertures are not very meaningful, as basically any lens of a comparable fl will give very similar results at f/16 or f/22, which is already showing softening by diffraction.

Ben
03-31-2010, 08:15 PM   #3
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Okay, here are the three shots from the 400-500mm range, at f8, cropped to the focus point (both autofocus and manual focus) and enlarged to 100%:

The first shot shows the subject at 50mm and the red circle encompasses the focus point. The next shot is at 400mm, manual focus. The third shot is 500mm, auto focus. And the fourth shot is 500mm, manual focus.
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04-01-2010, 03:36 AM   #4
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QuoteOriginally posted by sholtzma Quote
Okay, here are the three shots from the 400-500mm range, at f8, cropped to the focus point (both autofocus and manual focus) and enlarged to 100%:

The first shot shows the subject at 50mm and the red circle encompasses the focus point. The next shot is at 400mm, manual focus. The third shot is 500mm, auto focus. And the fourth shot is 500mm, manual focus.
The AF shot at 500mm doesn't look bad. When comparing the fine crack lines, it looks definitely a bit sharper, than the manual focus image and en par with the 400mm image.

Ben

04-01-2010, 07:17 AM   #5
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Should I then conclude that there is nothing wrong with this lens, that in terms of sheer IQ power it is fine for its kind?
04-01-2010, 08:07 AM   #6
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QuoteOriginally posted by sholtzma Quote
Should I then conclude that there is nothing wrong with this lens, that in terms of sheer IQ power it is fine for its kind?
I did not write that in my last post, because it is so hard to evaluate. See, at this comparetively short distance f/8 might offer such a shallow DOF, that some parts of the rounded flower pot are already slightly OOF. Ofcourse I think, that a good prime lens of that focal length will give you a sharper image. But then, the question is, whether the Bigma's quality is good enough for the kind of thing you do with the final image.

The images look to me, as whether they will stay up to some considerable sharpening and thus I guess could be printed up to and slightly above DIN A4 easily. If that is an application, which would be meeting your expectations, than the lens is good enough. If you want DIN A2 prints, I guess, you are in for a really good 500mm prime lens.

Ben
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