Kowa B&H Close Focus Mod & other 'Tweaks'

[Hans Punk]

Kowa B&H Close Focus Mod & other 'Tweaks'

 

Recently I picked up a very cheap Kowa B&H that needed a lot of internal cleaning and a fresh re-lube. Since it was my 'Spare' Kowa, I have a chance to illustrate/share my findings on some simple modifications that I discovered a couple of years ago on another lens. Since I already have a 'Standard' Kowa to compare with, it should prove easier to illustrate the difference in performance before & after modifying such a lens.

These principles will work on many lenses of this type that share a similar construction.

Following these steps are at your own risk.

 

The modifications allow:

* Minimum focus to be reduced from 5 feet down to 3 feet.

* Reduction/elimination of 'Veiling Flare/ Barrel Glow' that is common with Kowa lens types.

* Overall sharpness improvement.

 

Close Focus:

To achieve closer focus from the 5 foot factory standard is pretty easy.The focus mechanism transport is done by a helicoid pushing/pulling the front element that is seated within a tube, guided by brass tabs/stoppers within slots in the housing.These brass tabs/stoppers ensure that the linear travel is straight and true (ensuring correct alignment with rear optic). By cutting these tabs to be shorter, the travel of the front optic assembly is allowed to seat closer to the body - allowing closer distance between front and rear optic.

This allows an increase in optic proximity to be achieved. This modification effectively allows the focus ring to turn to it's maximum close focus position, and not restricted by factory limits.

 

 

 

 

Veiling Flare/ Barrel Glow - Reduction:

 

A common artefact of Kowa lenses in bright light situations seems to be a strong Veiling glare. It is similar to a strong vignette of light that happens when the front optic is hit with off-axis light. Although this can be a desirable artefact, often it is too overpowering to the image when purposely flashing the lens to pop a flare for effect.

A simple solution I found is to blacken the edge of the front optic - this is the edge that gets hit by light and pools the image with a 'Barrel glow'.

Taking a fine tipped marker pen does the job well (without needing to disassemble lens) - even better would be black paint and a fine brush and a steady hand if you wanted to eliminate glow completely. I personally tried the marker pen method, as you can carefully remove or thin the ink with a tiny amount of lighter fluid on a brush - creating a reduction/dulling effect, rather than remove the glow effect completely. At least it is good to know how to minimize the glow effect, especially when shooting in bright sunlight without a mattebox and you don't want everything to be washed out all the time.

 

 

Overall Sharpness Improvement:

This came from a few year back when playing on another Kowa lens and is the nicest find I've discovered so far (about most projection anamorphic lenses). I found that when removing the brass tabs that are used for alignment, you can separate the front and rear optic assembly for cleaning etc.

But If you do not re-install the tabs into the pre-set positions (using the screw holes aligned in the factory) - you can often tweak the alignment and fine focus to be even sharper.

 

As a pure guess, I can only presume that back in the day when most of these lenses were made the tolerances for alignment were only considered for image projection, rather than image acquisition (iscorama/bolex types an exception) I found that by freehand rotating the front optic assembly (when attached to camera) - It is possible to achieve more finite sharpness from the alignment. Using high magnification on my camera and additional magnification on my EVF + focus peaking at a reference at infinity - it was possible to rotate the front element assembly to what is probably fractions of a millimetre from the factory alignment, then glue the brass tabs into a very slightly new position. Glue works well, as it does not require additional holes to be drilled to re-seat the brass tabs, or forever alter the lens. The glue does not bear any load of consequence, mealy seats the tabs to prevent rotation.

The lens can be easily returned to its original alignment by dissolving the glue with solvent and returning the tabs to factory position. I’ve found that the very slightest tweak to factory alignment in 3 out of the 4 of these Kowa lens types I've owned, improves the sharpness noticeably.

 

[Bold]

Awesome stuff man!  Kudos for doing all this research and sharing your findings!

[Zak Forsman]

looks like i have a new project!

[Bold]

Lens-cyclopedia has been updated with a reference to this thread 

[mjamerson]

awesome will have to try this

[ken]

IMO, for closer focusing, it is not much useful.  The ratio would drop too (might down to 1.6x), also difficult to get sharp image.  Using dioptre is better. 

[Hans Punk]

Actual close focus mod brings minimum focus to 2 feet 8 inches (I was being a bit conservative before). With added Tokina +0.4 it comes down to 2 feet. Not having a problem with sharpness at minimum focus at all, just under 3 feet minimum focus without diopter is better (for me). Not having to add additional optics to the pathway for closer focus can only be a good thing.

The stretch ratio is always going to be 2x at infinity, giving plenty of defocus separation from foreground at minimum focus - even if it is not resolving full compression value up close.

[Bold]

Veiling Flare/ Barrel Glow - Reduction:

A simple solution I found is to blacken the edge of the front optic - this is the edge that gets hit by light and pools the image with a 'Barrel glow'.

Removing the front element to paint target areas on the front housing is a great solution for other anamorphics too (my B&H 16mm projection lens has barrel glow issue also).  Good ol' Testors flat black and an accurate, good quality brush. Though if your anamorphic's front element has painted sides as part of the manufacture process, you run the risk of the paint flaking off by removing it. 

[Hans Punk]

The nice thing is that you can blacken the edge on this Kowa type without having to open the lens at all. The edge is accessible from the front as is.

Other lenses can be treated the same way, but some may require disassembly first to get access to the optic edge...be very sure to check how to reassemble properly before attempting though. 

[buggz]

Wow! 
Very impressive work!
I am not so certain I could perform this type work for the focusing mod.
Question on the blakening the edge of the lens:
You are darkening the lens itself mounted?  Not on the outside edge of the lens?

 

[Hans Punk]

The blackening is applied to the front optic outside edge, without having to remove or unscrew it. The optic is concave, so it catches light from off-axis (not just front) - this is what causes the heavy glow/ veiling flare.

To apply blackening, carefully apply black marker pen or matte black paint with a fine brush to the frosted optic edge only.

 

 

[Tito Ferradans]

I'm definitely doing this edge blackening on the next few days! Great thread, these DIY things are awesome and I miss them more in our community. Thanks for sharing, James! 

[bzpop]

thank you Hans!

Thank you so much!

[liamlumiere]

Is it simple enough to dismantle and reassemble, any guides out there?

I'd like to have a go at making mine sharper. I've tested the B&H against the Moller 32/2x and it's notably less sharp. I'm sure it should/could be sharper.

Cheers!

[Hans Punk]

Is it simple enough to dismantle and reassemble, any guides out there?

I'd like to have a go at making mine sharper. I've tested the B&H against the Moller 32/2x and it's notably less sharp. I'm sure it should/could be sharper.

Cheers!

I made a video a while back about how to disassemble the Kowa to fit inside the FM lens which shows disassembly.

https://vimeo.com/115331343

In the video you can see how to access the brass tabs. I'd recommend unscrewing and removing the tabs first, then play with rotating the front assembly by hand to see if you can gain any sharpness. It only takes a very tiny amount of rotation to obtain maximum sharpness, people may find that the tabs were already in the correct position on their lenses. Out of the four Kowa B&H's I have owned, all but one of them needed a slight adjustment to get to maximum sharpness. If you want to add closer focus, cut the 3 tabs shorter and fix into its new alignment position, as explained in the opening post.

Ps: Before opening the lens up, it is worth doing a visual check of alignment, using the horizontal flare from the lens.

Level your camera on a tripod in a dark room and align the lens using a light source to flare the lens. Pan the camera left and right to check That you see all the horizontal line streaks in the flare are perfectly parallel to each other. If any of the line\streak look off axis, the lens won't be aligned as well as it could be and the lens might be worth adjusting.

 

[enny]

Hans cutting the brass will it throw lens out of alignment? and focus will be from 5 to 2ft? and it still stay 2x?

 

PS what screws drivers are you using  in the video

 

thanks

[enny]

Hi guys my MOD was fail why? because I found out that i don't have as much space to play with as OP i can actually slide razor blade in my space and not have any play . And there are 3 bras tabs on my 2 identical as original post and one longer (pic below) and it is the longer one that is actually preventing the from element to go further back for close up. My kowa will give me sharp close up at 3 ft 44 inch. Thinking if i should do this MOD at all or just go with diopters

I made a video a while back about how to disassemble the Kowa to fit inside the FM lens which shows disassembly.

https://vimeo.com/115331343

In the video you can see how to access the brass tabs. I'd recommend unscrewing and removing the tabs first, then play with rotating the front assembly by hand to see if you can gain any sharpness. It only takes a very tiny amount of rotation to obtain maximum sharpness, people may find that the tabs were already in the correct position on their lenses. Out of the four Kowa B&H's I have owned, all but one of them needed a slight adjustment to get to maximum sharpness. If you want to add closer focus, cut the 3 tabs shorter and fix into its new alignment position, as explained in the opening post.

Ps: Before opening the lens up, it is worth doing a visual check of alignment, using the horizontal flare from the lens.

Level your camera on a tripod in a dark room and align the lens using a light source to flare the lens. Pan the camera left and right to check That you see all the horizontal line streaks in the flare are perfectly parallel to each other. If any of the line\streak look off axis, the lens won't be aligned as well as it could be and the lens might be worth adjusting.

 

did you cut both brass tabs?

[Hans Punk]

Originally I cut all 3 tabs to get close focus to its maximum, but still using one of the original screw holes (instead of two) to re-attach tabs. This is to simply allow maximum travel of lens. Yes the longer tab controls the distance limit, but that can be cut down along with the other two tabs to get a new distance.

Best thing to do is unscrew the tabs and remove them to have a play with manually setting minimum focus and alignment (before committing to any cutting). If you push the two optics as close together as possible, you'll see that without the tabs in place, a new position is possible. By cutting /shortening the tabs and re-installing them again, you will have kept alignment as before, but increased minimum focus.

unscrewing all tabs and repositioning by hand is a good way to test if the new minimum focus distance is worth shortening the tabs for you, if not - simply screw tabs back on.

 

[enny]

Originally I cut all 3 tabs to get close focus to its maximum, but still using one of the original screw holes (instead of two) to re-attach tabs. This is to simply allow maximum travel of lens. Yes the longer tab controls the distance limit, but that can be cut down along with the other two tabs to get a new distance.

Best thing to do is unscrew the tabs and remove them to have a play with manually setting minimum focus and alignment (before committing to any cutting). If you push the two optics as close together as possible, you'll see that without the tabs in place, a new position is possible. By cutting /shortening the tabs and re-installing them again, you will have kept alignment as before, but increased minimum focus.

unscrewing all tabs and repositioning by hand is a good way to test if the new minimum focus distance is worth shortening the tabs for you, if not - simply screw tabs back on.

 

I cut down all 3 tabs and have 3 ft focus which is awesome. Question is there a special way to screw back the main part one with numbers and infinity sign on it it took me long time to get it to rotate properly. I was trying to align infinity sign to white line that is on main body and then screw it back on but then it would rotate all the way backward in the opposite direction then 5 ft number to the white line then screw it back on but then it would rotate until 9 ft and stop. I got it to work finally but just wondering.

What is your thought of shewing down the metal  part of main lens thinking it will even go down further for even closer focus spinning it from infinity to to infinity symbol  or would eternal lens touch or rub against one another

 

[Hans Punk]

lining up the distance markers takes a bit of time to get right, like you say it is a case of finding the correct starting point on the helicoid to end up hitting the hard stop at infinity mark. Obviously with a new minimum focus travel - the minimum marker won't line up. On the factory standard throw, the minimum focus hard stop goes just beyond the 5 foot marker anyway. Shortening the tabs simply squeezes out more travel for minimum focus.

I don't think cutting the body is a wise idea IMO, as getting a clean cut on that helicoid (without ruining the the start points) would be very difficult. You would also run out of helicoid throw to get the lens to infinity I expect.

Note: If you ever wanted to return the lens to factory min-max focus throw, simply altinate one or two of the cut tabs 180 degrees - allowing the uncut half of the tab to hit minimum stop again.