Blackmagic Forum

Hi, I was ramdomly doing tests with my Pocket 4K and original Metabones Canon FD-MFT 0.71x Speedbooster (out of sale for years now, grabbed it on ebay but mint condition), lens attached was a nFD 28mm 2.8; was playing around with Resolve and I noticed the infamous "magenta dot" or "magenta cirle" very much talked about with cheap speedbooster knock-off; but this is Metabones!

I can't remember how stopped down the lens was, maybe f4, but still this was unexpected;

Do you have similar experience with Metabones SB?
Is it strictly related to overall lighting conditions/restriced to some situations?

I've never noticed before but I only made some indoors test with a siemens star target.

Please, feel free to provide any suggestion, here to learn!

Gallery grabs:


Thanks a lot

I have never seen that. Is it possibly a flare as you have bright light coming from top left that is out of frame? Does it show the same when you have an evenly lit sky or a light coloured background?

Any chance one of the glass elements in the SpeedBooster is loose and misaligned?

rick.lang wrote:I have never seen that. Is it possibly a flare as you have bright light coming from top left that is out of frame? Does it show the same when you have an evenly lit sky or a light coloured background?

Any chance one of the glass elements in the SpeedBooster is loose and misaligned?

Hi, thanks for the reply!

I don't think it's a lens flare as while panning the magenta area didn't change but stayed fixed with the roof tiles going left-right out of it

In indoors test clips with normal home lights I can't see it tough; gotta find time to test this with studio lights; maybe it's only related to the outdoors conditions/strong lights?

In the screengrab attached to the original post, the camera is facing exactly East, the Sun is behind me, but not directly as this was a shot form my flat window so it's from indoor facing outside

Metabones lens loose/misaligned: it doesn't seem to be the case, but I couldn't know about misalignement for sure; it was fine until this, also infinity focus seems proper across 4 different FDs I own

In your experience, what are the conditions that cause this chromatic aberration? Are they tied to strong lights/diffuse lighs/outdoor bright conditions?

Thanks for the additional information. It doesn’t seem to be a flare then or the magenta area would move or disappear as you pointed in different directions.

If the focus is fine then the lenses are properly aligned.

The spot doesn’t show with normal light indoors. Is there any chance that there’s a light leak that only is evident under bright light? Sounds ridiculous but you could wrap some dark material to really shade your lens and SpeedBooster and see if it persists outdoors in bright light? If you can’t see the spot when it’s shaded, then remove the dark wrap and look.

Later Metabones models (for other mounts) have felt material around the optical element, which this one doesn't have. Perhaps that's related?

rick.lang wrote:Thanks for the additional information. It doesn’t seem to be a flare then or the magenta area would move or disappear as you pointed in different directions.

If the focus is fine then the lenses are properly aligned.

The spot doesn’t show with normal light indoors. Is there any chance that there’s a light leak that only is evident under bright light? Sounds ridiculous but you could wrap some dark material to really shade your lens and SpeedBooster and see if it persists outdoors in bright light? If you can’t see the spot when it’s shaded, then remove the dark wrap and look.

Hi! Thanks again for answering, I will definitely try this! Meanwhile, before reading this I managed to find a moment to try again, paying more attention this time, and my two cents is that this is evident where there is a bright light outside and i'm shooting from indoors; I have yet to try to see what happens where I'm completely outdoors; I shall also mention that I wasn't using my NiSi NDs + IR-UV Cut filters, nor my matte box, so maybe the full setup would minimize the Chrom.Aberr. almost completely; so this problem may also be a combination of the outdoor-from-indoors and the lens being stopped down to f8/f16 for the sake of this test.

roger.magnusson wrote:Later Metabones models (for other mounts) have felt material around the optical element, which this one doesn't have. Perhaps that's related?

I can confirm that there is no felt inside (I know what you mean, that felt-like material is inside the regular FD-MFT regular adapter from Metabones which I also have. Here's a photo anyway:



I'f you feel like playing around with the braw, for the curiosity of determining the most probable cause of this problem, here it is: https://drive.google.com/file/d/1DK25No ... drive_link

Thank you all for your help!

Good that you like a mystery; best thing when you solve the mystery.

Although your spot may not be related to your aperture and different lenses have different characteristics, generally you should mot use apertures like f/11 and smaller to avoid diffraction; the lenses are often at their sharpest about f/4 or f/5.6 so adding neutral density filtration when available is advisable to shoot at f/5.6 or larger aperture. Worth trying that just in case it is relevant.

Good idea to go outdoors in the sun and shoot in different directions like the hours on a clock with noon being the sun directly in front and 6 pm the sun directly behind you. Shooting outdoors on an overcast day would also be good to see if it’s all good.

I get a flare with a Viltrox EF M1 adapter (adapter without glass) and a Sigma 18-35 right in the center top.

Its from lights that are coming from the above. A lens hood usually fixes this.

VMFXBV wrote:I get a flare with a Viltrox EF M1 adapter (adapter without glass) and a Sigma 18-35 right in the center top.

Its from lights that are coming from the above. A lens hood usually fixes this.

Hi, sorry everybody for the late follow-up.

I managed to make some more tests: a matte box didn't affect the magenta dot, and overall it seem to show up only in this peculiar situation: shooting from inside a house to the outside, exposing for the outside. But the real reason was that the lens was stopped down to f/8 or more cause I didn't have a ND filter handy while doing the tests.

Still have to rule out the problem at f/2-f/4 with the ND in that exact situation, but I expect the magenta dot not to show up

If I manage to do this last test, I'll notify.

Thanks as always for the support!

Cheers

Just a hint if you’re in that situation and the scene has almost no motion, you can cut your exposure by going with a shorter shutter angle. With almost no motion, without any fast movement in the scene, you possibly can shoot with a 45 degree angle and open the iris 2 stops. Try a similar test scene and see if you notice anything different in post playback.

rick.lang wrote:Just a hint if you’re in that situation and the scene has almost no motion, you can cut your exposure by going with a shorter shutter angle. With almost no motion, without any fast movement in the scene, you possibly can shoot with a 45 degree angle and open the iris 2 stops. Try a similar test scene and see if you notice anything different in post playback.

I'll try and report back! Thanks for the suggestion