Metabones Causing Loss of Image Quality?

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planetofthe8

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Metabones Causing Loss of Image Quality?

PostWed Jan 13, 2021 3:57 pm

Hey guys, at the recommendation of basically the entire internet I got the BMPCC4k/Metabones 0.71x/Sigma 18-35mm f1.8 combo a few months back and something just seems to be off with the image quality. I bought the metabones used, everything else was brand new.

I know this isn’t simply a grading issue because a few months back I rented a Panasonic Leica DG Summilux 12mm f/1.4 ASPH and the footage with that looked fantastic. I also know the Sigma lens is fine because I had it professionally inspected.

I’m wondering if all of my issues stem from the fact that I got the regular metabones 0.71x instead of the one specifically made for the BMPCC4k. Does anyone have any thoughts on this? Would using the regular one instead of the one specifically made for the BMPCC4k have a noticeable effect on image quality?

I was told on another forum that the glass element inside the metabones could be sitting in the wrong position or could be crooked and this could be the source of my problem. If this is the case, is this something that would not be fixed by rotating the element? I ask because I’ve rotated the element already and the image quality remains the same. Any help would be much appreciated.
Last edited by planetofthe8 on Wed Jan 13, 2021 4:37 pm, edited 1 time in total.
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Robert Niessner

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Re: Metabones Causing Loss of Image Quality?

PostWed Jan 13, 2021 4:34 pm

And what exactly would you describe as "loss of image quality"?
Some original sample footage (not a screenshot, not an exported file) would help tremendously to take out the guess work for everyone else because we can't see what you mean.
Saying "Thx for help!" is not a crime.
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planetofthe8

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Re: Metabones Causing Loss of Image Quality?

PostThu Jan 14, 2021 1:29 am

I suppose I would describe it as a lack of sharpness. Nothing ever seems to be totally focused. As I mentioned before I tried rotating the element of the metabones on multiple occasions but if there’s been any improvement at all it would be very minuscule. I’ll post an example as soon as possible but for now I guess that’s the best way to describe it.
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rick.lang

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Re: Metabones Causing Loss of Image Quality?

PostThu Jan 14, 2021 1:48 am

You should have purchased the SpeedBooster specifically marketed for the BMPCC4K. With a lens stopped down a couple of stops, the SpeedBooster you purchased may be acceptable but not wide open. Try that and let us know if the results are better. I hope rotating the element has not compromised your focus.
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planetofthe8

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Re: Metabones Causing Loss of Image Quality?

PostThu Jan 14, 2021 2:22 am

rick.lang wrote:You should have purchased the SpeedBooster specifically marketed for the BMPCC4K. With a lens stopped down a couple of stops, the SpeedBooster you purchased may be acceptable but not wide open. Try that and let us know if the results are better. I hope rotating the element has not compromised your focus.



Can you elaborate a little on how rotating the rear element to the metabones could compromise my focus?
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rick.lang

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Re: Metabones Causing Loss of Image Quality?

PostThu Jan 14, 2021 6:58 pm

I don’t have a SpeedBooster so no experience doing that, but I understood that some users have rotated the rear element on the SpeedBooster to make fine adjustment to the focus. Please correct me if I’m wrong.
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Mark Foster

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Re: Metabones Causing Loss of Image Quality?

PostThu Jan 14, 2021 10:28 pm

planetofthe8 wrote:Can you elaborate a little on how rotating the rear element to the metabones could compromise my focus?


https://www.metabones.com/article/of/in ... oster-only
cMP 5.1 2x3,46/96GB/2x2TB 860pro/4x4TB HGST/SSD7101A 4x2TB 970evoplus/HP1344/BMD4k/Radeon VII
macOS 11.2.3

BMPCC 6k pro (7.3.1)
BMPCC 4k (7.3)+ MB speedbooster ultra 0.71 (3.60)
resolve studio 17.2.1
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JordanWright

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Re: Metabones Causing Loss of Image Quality?

PostFri Jan 15, 2021 12:25 am

Yeah that 'loss of image quality' is the exact reason I sold my Metabones Speedbooster and won't use it again. It's not only the minor effect on sharpness, it made my flares more complex and ugly, introduced distortion and images seemed to have less 'pop'. I could really tell the difference when i did some side by sides tests using some Contax Zeiss lenses. Light sources in frame such as flashlights and the sun is where I saw the most difference,

Note: I tested 3 different copies of Metabones speed booster all had the same effect.

People seem to talk about them like they are a magic solution that is essential on the Pocket 4k but imo there's not point getting high quality lenses if they are sat in front of a bottleneck.

I was close to getting a Smart Adapter from Metabones instead (18-35mm is a great mid range zoom on the 4k sensor) but I thought It more simple to do away with adapters and get the 6k.

Alternatively there are a lot of beautiful micro four thirds lenses to choose from if you don't want to deal with adapters and want a more compact setup. (Voigtlanders would be near the top of my list)

That would be my advice to you but this is just my 2 cents, others seem to be perfectly satisfied using speedboosters!
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robert Hart

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Re: Metabones Causing Loss of Image Quality?

PostFri Jan 15, 2021 9:48 am

EDITED AND CORRECTED.

The Speedbooster appropriate to your camera would have been the best bet. The position of the optical cell in the Speedbooster body has to be absolutely spot-on or the results may be less than desirable.

The sharpness result from the 0.71x optical cell should not be bad but as your small sensor is still seeing through the centre of the lens/speedbooster combination, any softness in the image may be greater than the image yield by the correct Speedbooster for your camera.

Another responder mentions having have tested three separate Speedboosters and had the same poor result. The chances of three different speedboosters having been mismanaged by a previous owner or gone faulty are pretty low.

If it does not work for you then yes, it is probably best to walk away but I would not give up on it so soon. There are a few variables which may interact additively to cause a problem.

The speedbooster optical cell may be incorrectly adjusted. This is highly likely if yours was bought used and adjustment trimmed to a particular camera/lens combination.

Some stills-camera zoom lenses are not and never can be parfocal. They will never hold focus through the full range of the zoom movement.

The lens may no longer be correctly collimated (some call it backfocused) if mount tails have been swapped and maybe shims lost or a bit of grit or swarf gets in between the faces. This may not be the case with your zoom lens. Do you know its history from new?

If you had access to several different speedboosters to test and the result remains poor, then this following comment will be irrelevent.

The optical cell within the 0.71x speedbooster can be inadvertantly reversed and still work but with poor results. I am prompted to this thought by descriptions of speedbooster cells being "rotated". The backfocus is adjusted by screwing the cell in and out of the body of the speedbooster, ie "rotating".

If however "rotating" has been interpreted as "reversing" the orientation of the optical cell within the speedbooster body by unscrewing it out completely then installing it back-to-front, then it is going to work poorly.

If the optical cell is correctly screwed into the speedbooster body, a small serial number printed on the optical cell should be closest to the sensor, not to the lens tail.

To most successfully adjust the optical cell, use the lens on which you know the focus marks to be accurate.

Position your camera so that the focal plane (sensor) is an accurately measured distance from a focus chart or target. There should be a focal plane mark on the camera body somewhere.

Set your lens focus to that measured distance. I use the 1 metre or 1.5 metre marks.

Light the focus chart or target and set your camera shutter speed so that the lens iris has to be wide-open and the lens depth-of-field as shallow as it can be.

If the lens barrel has to be turned for sharp focus and the focus number in the barrel reads higher (closer) than the number you selected as the real distance, you may have to screw the speedbooster optical cell inwards (clockwise). This direction is when you view the speedbooster from the front.

If the focus number is lower, then you may have to screw the optical cell outwards (anti-clockwise)

Screw the optical cell inwards or outwards only in one-quarter turn increments to find the spot where the lens image is in sharp focus at the measured distance between the focus chart or target and the camera focal plane mark.

Use the largest and sharpest screen monitor you can find. A Siemens-style (slices-of-pie) focus chart is the easiest to use. If you only have a resolution bar chart like a Lemac card, then the camera's tendency towards aliasing may be your best friend as sharpfocus will really pop as a colour shimmer. That's all well and good so long as you do not have an anti-aliasing filter installed.

For an alternative focus target, you can use a sharply defined distant outdoors object such as a power pylon with your lens set to infinity focus, your very widest lens such as a 14mm f2.8 with known good focus marks and enough ND filtering selected to force the depth-of-field to its narrowest with a wide-open iris. This is not as easily accurate but doable.

If the backfocus is really off, take care when adjusting, and avoid screwing the optical cell too far rearward or you may contact the IR filter glass in the camera and crack it. The 0.71x optical cell rests furthur forward than in other speedboosters with a more powerful focal reduction so chances of cracking the IR filter are lesser but still possible if it has already been so badly adjusted you don't know which way is what.

With some speedboosters, the optical cell rocks slightly in the speedbooster body when a small lockscrew is tightened after adjustment. this lockscrew pushes on the cell fro the side at the sensor-end and may skew it ever so slightly and throw focus off on one side-edge.

My personal preference after finding correct backfocus is not to use the lockscrew but to add a small dob of water-cleanable white bathroom sealer on the face of the body across onto the thread.

This material can be easily picked away with a sharp pointer like a dart-end or a tiny screwdriver but holds well enough. Do not use silicone bathroom sealer (smelly stuff), threadlocker or any sort of glue which will wick in along the threads and lock the cell in for good.

I will check the method as it happens that I need to readjust the optical cell in the "Big" URSA after cleaning. If necessary I will correct this post. Meanwhile. please heed the good advice of others smarter and more competent than I who respond here.
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rick.lang

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Metabones Causing Loss of Image Quality?

PostFri Jan 15, 2021 5:29 pm

Thanks, Robert. You’re definitely more smarter than I!
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robert Hart

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Re: Metabones Causing Loss of Image Quality?

PostSat Jan 16, 2021 10:35 am

Something just went across the ageing synapses of my geriatric brain.

A question for the originator of this thread.

Have all your tests of the speedbooster/lens combination been outdoors with the lens iris in the f11-f16 zone?
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planetofthe8

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Re: Metabones Causing Loss of Image Quality?

PostMon Jan 18, 2021 9:59 pm

Thanks everyone. I ended up getting the metabones designed for the BMPCC4K. I figured this was a good excuse to get it even if it doesn’t end up being the problem.
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rick.lang

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Re: Metabones Causing Loss of Image Quality?

PostTue Jan 19, 2021 4:29 am

Looking forward to your impressions after you’ve tested the adapter.
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WahWay

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Re: Metabones Causing Loss of Image Quality?

PostThu Feb 04, 2021 8:16 am

JB is not a fan of Speed Booster but not sure he has given a reason why?
Cant say I have experience any adverse effect using Metabones but other cheaper brands of focal reducer softens the image quite a bit.
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dondidnod

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Re: Metabones Causing Loss of Image Quality?

PostThu Feb 04, 2021 6:34 pm

Although I have no Metabones Speed Booster to compare it with, I find that the 7 layers of anti-reflection coatings on an Aputure DEC Lensregain EF to MFT focal reducer increases sharpness compared to a straight, dumb adapter.

This is most noticible on a vintage lens made before multi coatings became standardized.

Re: Pocket 4K and Old Lenses

viewtopic.php?f=2&t=98383&p=546035&hilit=Berkeley+garage#p546035
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John Griffin

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Re: Metabones Causing Loss of Image Quality?

PostThu Feb 04, 2021 7:35 pm

dondidnod wrote:Although I have no Metabones Speed Booster to compare it with, I find that the 7 layers of anti-reflection coatings on an Aputure DEC Lensregain EF to MFT focal reducer increases sharpness compared to a straight, dumb adapter.

This is most noticible on a vintage lens made before multi coatings became standardized.

Re: Pocket 4K and Old Lenses

viewtopic.php?f=2&t=98383&p=546035&hilit=Berkeley+garage#p546035

Multicoating can’t increase sharpness over no glass. What you are seeing is just the increase in resolution from shrinking the image circle.
Last edited by John Griffin on Thu Feb 04, 2021 8:22 pm, edited 1 time in total.
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robert Hart

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Re: Metabones Causing Loss of Image Quality?

PostThu Feb 04, 2021 7:49 pm

While I cannot offer any science relating to increased "apparent" contrast, I found that using the BMPCC speedbooster on a SI2K camera enabled a lower ISO for the same lens iris setting/shutter speed combination which conferred the benefit of more colour saturation.

It is a subjectively more pleasing image, "apparently" sharper but in reality no sharper than the fairly aggressive OPLF filter on the SI2K permitted. All I can say is that for any disadvantages putting a focal reducer into the path may cause, the advantages outweigh them when using full frame stills lenses.

The speedbooster enabled the Nikon stills lenses similar sharpness to the Super16mm lenses. There was a slight tendency towards a blue colour cast with this speedbooster.

EDIT. Well that fixed that. Youtube clips will not work presently.

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