MarcoB
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Posts posted by MarcoB
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I've been testing the GH4 with the Sigma and Speed Booster XL 0.64 for the past couple of weeks and haven't experienced any noticeable change in brightness like you describe. And just to be sure, I just took mine out and did a couple of zooms and see no discernible difference in luminosity. Of course, there will be minor changes in luminosity with any zoom, even those with constant aperture. But to assert that the lens is defective, or to demand that a reviewer is obligated to mention the obvious, is going a bit too far, IMHO.
Hi Jonpais,
thanks for your reply.
Seems that a lot of people has my exact same problem with Sigma 18-35: at the end of focal range (28mm) there is more luminance.
Here are some links:
Sigma 18-35mm acting strange...: Third Party Lens Talk Forum: Digital Photography Review
There is an in depth analysis that confirms that change at 28mm:
(you have to look at "Measurement/Transmission" tab)
Note that the luminance problem is increased by speedbooster and that at the min and max aperture is not relevant. It is obvious at intermediate apertures.
I have done a test, you can download it and watch the defect directly with your eyes (it is discernible): stare at the red couch. Zoom test with Gh4+metabones speedbooster NikonG-Micro 4/3 x0.71+Sigma 18-35, manual focus, aperture ring at 4, 4k, iso 1000. https://drive.google.com/open?id=0B_MiHNwWCmT5WTRtVUtsTDAyMFU
It would be very useful to know if your Sigma has the same defect or not; can you check again trying to zooming in and out not at the maximum or minimum aperture? At 28mm you shoud note a luminance increase (if your sigma has the same defect).
Thank you
Marco
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I really start to think that this is just how this lens is build. Although I found 1-2 people reporting the same 'problem', I've heard more people say that theirs doesn't do this.
I just pointed the lens at me, and looked at the lens opening while turning the zoom ring. When zooming in, the 'hole' naturally becomes larger. A longer focal lenght, needs a bigger aperture opening so that's normal.
But when I get to arround 28mm, the opening seems to 'exponetially' become larger. Because not only does the 'inner ring' shift, but at that focal length the outer aperture also opens further. This is visible at all aperture settings, but moreso at F3.5 and onwards.
I'm pretty sure this is what is causing the extra light to come in starting at +- 28mm.
Now the only question that remains is... Is this normal for this lens? Or is it a 'defect' in mine and I do I receive too few light at focal lenghts under 28mm....
Hi Stab, I have the same problem. I did some research and seems that we are not alone. Sigma 18-35 has a problem, and it is not a little one, it has not a constant aperture if you record a complete zoom in (from 18-35 ) or zoom out you will have a luminance change. Andrew should add this information to his useful Gh4 guide. I bought sigma 18-35 and nobody told me about this problem: not guides, posts, reviews, video reviews.
Sigma 18-35mm is brighter at tele end... Normal?
In: Cameras
Posted
Hi Cinegain, maybe it isn tot much of a biggie, but it is a problem. You cannot zoom in or out. You cannot reframe without checking, but most of all Sigma 18-35 has not constant aperture as advertised.