Other: Making Zoom Lenses Parfocal with Metabones Speedbooster...

Nirv

Nirv

Carbonite Member
I was doing some searching to find out how to adjust back focus with the metabones speed booster and the video below came up in a YT search which seems to suggest a commoner garden zoom lens could be made par focal with a deft adjustment on the metabones.

If so what would be the correct method for doing this or is it just trial and error? I'm assuming this would require a zoom lens not to be a crazy varifocal but just off being par focal which my Nikons seem to be.

If this method really does work then buying several metabones Speedbooster for each of my most used zooms would be a lot cheaper than a Cabrio.

Any help gratefully received.

 
The only "method" I'm aware of - is trial and error.... adjusting that tiny screw on the inside of the MB SB and then re-attaching zoom lens to see if it's more or less par focal. Most of my Canon & Sigma's are "just off" as well. Close, but not close enough.
Agree with you... paying for 3 SB's for 3 par focal zooms a lot easier on the coin than dropping $20k for one servo...
 
Or that focusable front element that SLR Magic have made for turning anamorphised lenses into single system focus - that's a very cool gadget.
 
You can't make a lens parfocal. It is it isn't. Many DSLR zooms simply aren't. Others are to a greater or lesser extent. What speedbooster allows you to do is adjust the back focus so that you if you start with a reasonably parfocal lens you can adjust it to the proper BF so it focuses correctly. Once you do that in theory all lenses for that type mounty should be correct - however back focus is delicate and I've always been skeptical whether all say Canon or EF zooms are exactly correct from the factory anyway.
 
Lenilenapi said:
You can't make a lens parfocal. It is it isn't. Many DSLR zooms simply aren't. Others are to a greater or lesser extent. What speedbooster allows you to do is adjust the back focus so that you if you start with a reasonably parfocal lens you can adjust it to the proper BF so it focuses correctly. Once you do that in theory all lenses for that type mounty should be correct - however back focus is delicate and I've always been skeptical whether all say Canon or EF zooms are exactly correct from the factory anyway.
Click to expand...

This isn't true. Adjusting the back focus has a stronger effect at the wide end than it does at the long end - meaning that the change in optimum object distance at the wide end is greater for a given change in back focus. So, when you adjust back focus in a zoom, or equivalently adjust the Speed Booster back and forth, you can make the long and short ends match. What happens in-between is a different matter since it normally depends on the shape of the cam that controls the motion of the compensating group. Really high-end cine zooms use a back focus adjustment to get the end points correct, and then the compensator cam is re-machined as necessary based on optical bench measurements.
 
Your definition of parfocal is wrong. What you are describing doing with the SB is simply adjusting the back focus on the lens. You are much better off shimming the lens and leaving the SB alone so it works correctly with all your lenses.
That is not what parfocal means. Parfocal means that the lens remains in focus throughout the range. Since front and back focus are fairly easily adjustable on both ends the real problem is the lens holding focus in the middle NOT at the wide end.
Very common misuse of the term that leads to serious issues....
 
Brain, & (I assume) Jacek,

Thanks for joining the conversation.

What is the best practice for adjusting a Speedbooster's backfocus? Via a Lens Technician? I'm particularly concerned with a EF-NEX model, & the only EF lens I have with (somewhat) accurate marks is the 45/2.8 TS, which I doubt is the best metric for a DIY attempt. Be great if the Speedbooster was calibrated for use with EF-mount Cine lenses.
 
Last edited:
optitek said:
Your definition of parfocal is wrong. What you are describing doing with the SB is simply adjusting the back focus on the lens. You are much better off shimming the lens and leaving the SB alone so it works correctly with all your lenses.
That is not what parfocal means. Parfocal means that the lens remains in focus throughout the range. Since front and back focus are fairly easily adjustable on both ends the real problem is the lens holding focus in the middle NOT at the wide end.
Very common misuse of the term that leads to serious issues....
Click to expand...

Chill out! I didn't even use the term "parfocal", much less define it. What I did do is describe how you can make the extremes of the zoom range share a common focal plane by either adjusting back focus *or* by adjusting a Speed Booster. This is what the OP was curious about IMO. I also made a very clear distinction between making the extremes share a common focal plane and what happens in-between. I even spelled out how you can fix the in-between region (if necessary), since I've personally been involved in this labor intensive and very expensive process. Fortunately, in practice for moderate zoom range lenses if you fix the end points the in-between region is almost always good enough. Its only when you get to 5-10x zooms or greater that non-linear in-between aparfocality (if I can use that word) tends to be an issue. Most of my experience in correcting the issue was with a 300x zoom, where virtually everything was in-between the extremes! Note that you don't have to resort to re-machining cams if at least one zoom group is independently driven with a motor, but that's a different story.
 
Bern Caughey said:
Brain, & (I assume) Jacek,

Thanks for joining the conversation.

What would be the best way to adjust a Speedbooster's backfocus? Via a Lens Technician? I'm particularly concerned with a EF-NEX model, & the only EF lens I have with (somewhat) accurate marks is the 45/2.8 TS, which I doubt that's the best metric.
Click to expand...

With the right test lens you can easily do an all-purpose adjustment yourself. Most of the Canon EF lenses I'm familiar with don't have a hard stop at infinity, and they also have very inadequate distance marks. However, I'm not familar with the 45/2.8 TS. If you can get your hands on a fairly decent EF-mount fastish wideangle prime with a hard focus stop at infinity (Zeiss ZE perhaps?), then use that as your test lens. Attach it with a Speed Booster to a camera, focus to infinity (a distant building or tower or hillside will do), and adjust the Speed Booster until you get the sharpest image. To adjust the Speed Booster you simply loosen the little setscrew on the side of the bayonet flange that holds it in place, and simply screw it in or out. Re-tighten the setscrew (not too much force) after you're satisfied with the results. A technician could use a collimator to get an accurate infinity object, but this isn't really necessary. If you want to custom-adjust a Speed Booster for a particular zoom lens, try verifying that the zoom lens focuses accurately to infinity at the long end, and then perform any required Speed Booster adjustment at the wide end, and then double-check that you still maintain good focus at the long end. However, its starting to get late, so if any of this is wrong I will deny that I ever wrote it!
 
After a bit of trial and error I successfully made my beloved Nikkor 28-85 parfocal.

I'm now wondering it is possible to shim my novoflex adapter so it is parfocal on that too.
 
Still not getting it

Still not getting it

brianc1959 said:
Chill out! I didn't even use the term "parfocal", much less define it. What I did do is describe how you can make the extremes of the zoom range share a common focal plane by either adjusting back focus *or* by adjusting a Speed Booster. This is what the OP was curious about IMO. I also made a very clear distinction between making the extremes share a common focal plane and what happens in-between. I even spelled out how you can fix the in-between region (if necessary), since I've personally been involved in this labor intensive and very expensive process. Fortunately, in practice for moderate zoom range lenses if you fix the end points the in-between region is almost always good enough. Its only when you get to 5-10x zooms or greater that non-linear in-between aparfocality (if I can use that word) tends to be an issue. Most of my experience in correcting the issue was with a 300x zoom, where virtually everything was in-between the extremes! Note that you don't have to resort to re-machining cams if at least one zoom group is independently driven with a motor, but that's a different story.
Click to expand...
Well, one can't say I did not try ....:undecided
 
Bern Caughey said:
Brain, & (I assume) Jacek,

Thanks for joining the conversation.

What is the best practice for adjusting a Speedbooster's backfocus? Via a Lens Technician? I'm particularly concerned with a EF-NEX model, & the only EF lens I have with (somewhat) accurate marks is the 45/2.8 TS, which I doubt is the best metric for a DIY attempt. Be great if the Speedbooster was calibrated for use with EF-mount Cine lenses.
Click to expand...


You can adjust it yourself using a "gold" zoom lens (a known properly focused lens)
Once you make sure that the lens holds focus on both extremes you can put a speedbooster on it and verify that focus is still maintained on both ends. If the wide end goes out when you zoom out all the way wide (with the sb on it) you need to adjust the SB location by turning it in the adapter.
I fabricated a microscope and am using it with our Optimator test unit to focus extenders and speedboosters. We manufacture the extenders so we needed to have proper test equipment...
 
Nirv said:
After a bit of trial and error I successfully made my beloved Nikkor 28-85 parfocal.

I'm now wondering it is possible to shim my novoflex adapter so it is parfocal on that too.
Click to expand...

As long as you need to add material to the Novoflex then shims will work great. However, if you need to go in the opposite direction by removing material then you may have a tough row to hoe unless Novoflex already installed a shim that you can remove.
 
OR......

OR......

Nirv said:
After a bit of trial and error I successfully made my beloved Nikkor 28-85 parfocal.

I'm now wondering it is possible to shim my novoflex adapter so it is parfocal on that too.
Click to expand...
Here is the deal:
If all your devices are adjusted properly they are inter changeable. Otherwise they are "fixed " for all practical purposes.
Coming from a rental house background I despise anything that is not set to proper standards. Call it professional desease ;-)
Yes you can compensate one error with another but you are eliminating a very important feature- interchangeability.That leads to serious issues on the set.
In the heat of the battle you put the wrong lens with the wrong adapter on a wrong camera and voila!!! s*%tstorm in full force ;-)Happens more than you think from the frantic phone calls I get ;-)
Which brings us to the subject- Novoflex...
If both your camera FD and the lens BF are set correctly all you need to do is mechanically set the height of the adapter to:
Canon to e-mount -26mm +/- .03mm
Nikon to e mount 28.5 +/- .03mm
Done! no guesss work, no trial and error.
always works- guaranteed.
On the other hand, if either your lens or your camera are not correct- anyones guess... and this setup is only good for this lens, this camera, this novoflex combination. Fixed setup. Change one of the three and here we go again- trial and error. you may get lucky and another combo may work for you- but I wouldn't count on it....
Brian- I'm a big fan of your work- speedboosters are dream come true for our industry. I'm sorry if I came off too harsh and hope you did not take it too personally.
 
Thanks but.....

Thanks but.....

optitek said:
Here is the deal:
If all your devices are adjusted properly they are inter changeable. Otherwise they are "fixed " for all practical purposes.
Coming from a rental house background I despise anything that is not set to proper standards. Call it professional desease ;-)
Yes you can compensate one error with another but you are eliminating a very important feature- interchangeability.That leads to serious issues on the set.
In the heat of the battle you put the wrong lens with the wrong adapter on a wrong camera and voila!!! s*%tstorm in full force ;-)Happens more than you think from the frantic phone calls I get ;-)
Click to expand...

1. I'm not as stupid as you think I am.

2. I thought I made it clear in my original message that I'd consider getting a speed booster for each of my most used zoom lenses should the technique work with them? I am not so stupid to think this is a one size fits all fix for all lenses, the SBU would stay on the lens it was adjusted for. I have no intention of spending the many £1000s required to buy a par focal cinema zoom and the SBU back focus 'hack' would seem to be a very cost effective way achieving the same goal.

Cheers

And thanks Brian for the Speedbooster you designed, I cannot imagine being without one and now probably 2 or 3 more!!!
 
Nirv said:
I was doing some searching to find out how to adjust back focus with the metabones speed booster and the video below came up in a YT search which seems to suggest a commoner garden zoom lens could be made par focal with a deft adjustment on the metabones.

If so what would be the correct method for doing this or is it just trial and error? I'm assuming this would require a zoom lens not to be a crazy varifocal but just off being par focal which my Nikons seem to be.

If this method really does work then buying several metabones Speedbooster for each of my most used zooms would be a lot cheaper than a Cabrio.

Any help gratefully received.

Click to expand...

You can't turn a non-parafocal zoom into a parafocal zoom...period. Floating elements are what makes a zoom parafocal.
Most if not all, newer high quality Nikon's are Parafocal, as are Canons. I have 4 Nikon zooms plus an older one and they all hold their focus.
The real issue is your Metabones Speed Booster.
Metabones claims their adapter is made to exacting standards and you shouldnt worry about back focusing. If that were the case, then why is there a back focus adjustment.?
You just HAVE to set the back focus on the Metabones. You have to. But you really should take it and your lenses to a facility with a collimator and a technician who knows their stuff.
When I first got my FS7 and started using my Zeiss primes via the Metabones Speed Booster, I noticed I couldn't get infinity focus. I thought I was going to have to get each lens adjusted. Then I paid closer attention to my zoom focus and found the same thing so I deduced the MB as the culprit. A back focus adjustment made all my lens sharp as a tack.
So, get your Speed Booster adjusted.
If you don't have access to a collimator then I suppose you could do it by eye and trial and error. You need a good focusing chart and patience. There is an almost hidden screw on the back of the MB that will allow the adjustment.
Your problem will solved.
 
Nirv said:
1. I'm not as stupid as you think I am.

2. I thought I made it clear in my original message that I'd consider getting a speed booster for each of my most used zoom lenses should the technique work with them? I am not so stupid to think this is a one size fits all fix for all lenses, the SBU would stay on the lens it was adjusted for. I have no intention of spending the many £1000s required to buy a par focal cinema zoom and the SBU back focus 'hack' would seem to be a very cost effective way achieving the same goal.

Cheers

And thanks Brian for the Speedbooster you designed, I cannot imagine being without one and now probably 2 or 3 more!!!
Click to expand...
You don't need to purchase a multi $$$$ lens - you just need your lenses adjusted. And your camera FD
Even when you get the SB adjusted with the lens- what if you need a longer fl and use the lens without SB?- it won't work anymore if you lens is not adjusted properly.
That's what I'm saying- you lose hat feature. The SB is an adapter and should be used as such- it was designed as interchangeable and if you are not using it that way it is not used correctly. Of course it's your money to waste and your reputation on the line if your gear does not perform- you are absolutely calling the shots. I'm just giving you my professional opinion from 30 years of experience in the field. Take it or leave it- your choice ;-)
 
optitek said:
You don't need to purchase a multi $$$$ lens - you just need your lenses adjusted. And your camera FD
Even when you get the SB adjusted with the lens- what if you need a longer fl and use the lens without SB?- it won't work anymore if you lens is not adjusted properly.
That's what I'm saying- you lose hat feature. The SB is an adapter and should be used as such- it was designed as interchangeable and if you are not using it that way it is not used correctly. Of course it's your money to waste and your reputation on the line if your gear does not perform- you are absolutely calling the shots. I'm just giving you my professional opinion from 30 years of experience in the field. Take it or leave it- your choice ;-)
Click to expand...

I'll leave it thanks.

The back focus on the SBU takes about 20 seconds to change, I have clear datum marks on adapter to return it to its 'normal' and 'parfocal' settings. It couldn't be easier.

LOL at the down voter... Pragmatism wins over dogma.
 
Last edited:
You must log in or register to reply here.
Back
Top