Sigma 18-35mm is brighter at tele end... Normal?

[MarcoB]

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 18-35+ speedbooster Brightness is not constant troughout the focal range [Archive] - BMCuser.com - The Online Community for BlackMagic Camera Users

GH4 Sigma 18-35mm is brighter at 35mm... Normal? [Archive] - DVXuser.com -- The online community for filmmaking

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:

http://www.dxomark.com/Lenses/Sigma/Sigma-18-35mm-F18-DC-HSM-A-Canon-mounted-on-Canon-EOS-700D---Measurements__870

(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

 

[jonpais]

I'll give it a shot over the weekend, and I will also have a look at the links you posted

[Inazuma]

This lens on my Nikon d5500 is registering +2/3 EVs at 28mm compared to the rest of the range. Visually I can also see it becomes brighter in the center of the image at this focal length up to 35mm. This result is somewhat consistent with DXOMark's tests. I am not surprised it's not mentioned much because it's not something most people would realise until someone else told them. Tbh I'm not sure why it's such a big deal to some people here though. 

What's weird is that I just tested my GX7 with Olympus 17mm f1.8 against the Sigma 18-35mm on Nikon d5500 and the nikon combination is a stop brighter with the same settings. What does this mean?

[Cinegain]

That f-stop isn't T-stop?

Personally, I just use what is needed. And hardly will I reframe something and then not check the metering/settings. And I don't do zoom-ins/-outs. So indeed I also feel it isn't much of a biggie.

[jonpais]

That f-stop isn't T-stop?

Personally, I just use what is needed. And hardly will I reframe something and then not check the metering/settings. And I don't do zoom-ins/-outs. So indeed I also feel it isn't much of a biggie.

that's why I haven't noticed anything. but I'll still be sure to check it out over the weekend when I have more time

 

[Fritz Pierre]

That f-stop isn't T-stop?

Personally, I just use what is needed. And hardly will I reframe something and then not check the metering/settings. And I don't do zoom-ins/-outs. So indeed I also feel it isn't much of a biggie.

Agreed...if you want a zoom, move the camera....not the field of view on the lens...maybe this is why it does not come up in forums...very few would zoom during a video clip as you would always see the beginning and end.

[MarcoB]

That f-stop isn't T-stop?

Personally, I just use what is needed. And hardly will I reframe something and then not check the metering/settings. And I don't do zoom-ins/-outs. So indeed I also feel it isn't much of a biggie.

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.