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

[Visual Amco]

Hey,

Good job! I am a afraid of ruining my kowa bell and howell with this. I would like to check the sharpness mod. But how do you know it is at it sharpest point?(do you mount it onto a camera and turn it until it the most sharp on camera?) Or is there a good trick for this? Also do you need to remove the brass tabs before turning? (I did not get that part, a howto video would be awesome )

Cheers

[Hans Punk]

It's ok to be afraid!...it is a mod that is probably not worth attempting for most anyway.

I would not recommend anyone to mess with or dismantle ANY lens unless they were very sure how to put it back together - or had a lens in such a bad condition there would be little to lose if it all went wrong. Like I said in opening post, I had a Kowa that I could afford to mess with...so I had nothing to lose. 

As for the sharpening/alignment tweaks, yes - it is best to unscrew/remove all brass tabs first, freehand focus front Kowa assembly at an object at infinity focus whilst at maximum zoom on evf or monitor...tweak rotation until sharpest image is reached, then look at the screw holes left by the removed brass tabs, if they are not perfectly central to the new position you have set, it indicates that re-seating the tabs into the new position would increase sharpness.

From my limited experience, 3 Kowa B&H's out of the 4 that I've owned have benefited from this modification, so it's completely possible a few owners out there already have a perfectly aligned lens.

[Hans Punk]

Here is a quick example shot to help explain how much minimum focus can be squeezed from just shortening the brass tabs.

Seems like I underestimated the normal minimum focus distance of regular Kowa B&H. Modification basically allows a foot closer to be obtained (not a massive amount but the visual jump is impressive). Modded min focus is 2 feet 8 inches which is around the close focus distance that a Tokina +0.4 will give you on an unmodified Kowa. But the cool thing is that if you add Tokina on the modified Kowa, you get exactly 2 feet minimum focus (from front optic). 

 

[enny]

I think its worth doing this going from 5 ft to 3 ft i am just below 3 ft my self. and its not a big complex modification bras are still there alignment is still there its just you cut the bras shorter and you gain more. I wanted to get tokina go get down to 2 to 3 ft. But i now have no really need for tokina now and save 600$

[ken]

I am pretty sure, closer focus distance would make less ratio in my experience until I got a D.O. 16F ana lens.

D.O. lens actually is a shortened lens from Sankor/Singer/Eiki 16F.  Make the the 2x lens become about 1.6x when focus in minimum distance.  So the D.O. lens can focus to closer less than 1m.   But it is lack of infinity ability.  I just add a negative lens in front to let it is able to focus to infinity. And the advantage is that it can take wider lens, basically as wide as 16H.

[Hans Punk]

[enny]

so what is this is actually does kowa b&h goes 2x squeeze to 1.55 when trying to focus or it stays 2x even with modification  or is this for kowa 16 h so basically does kowa always stays at 2x from 3ft to infinity and in between Thanks

[Hans Punk]

All Anamorphic squeeze ratios are the measurement of image compression at infinity. The closer an object is in focus, the less the compression will appear at that object of focus. When people sometimes say 'my 2x is more like a 1.75x or my 1.75x is more like a 1.5x' - they are mostly noticing that at medium/close compositions, most lenses do not resolve the full compression value on that plane...because infinity is not usually the focal plane (unless shooting landscapes). 

Above picture was to demonstrate that the difference in modifying the lens results in no perceivable drop in squeeze ratio from the 'standard' Kowa optics. 

You can easily see the apparent squeeze value change throughout focal range in the video below (the breathing effect). Most modern cinema anamorphics have minimal breathing artefacts as a purpose refinement, therefore more consistent FOV and compression values throughout focus range, but what we are primarily talking about projection anamorphics that are usually trying to handle weird and wonderful taking lenses and imaging areas that were never intended for their design, so a variation in apparent squeeze ratio at varying distances is inevitable on a few of these 2x lens types.

[Hans Punk]

Here is a quick example shot to help explain how much minimum focus can be squeezed from just shortening the brass tabs.

Seems like I underestimated the normal minimum focus distance of regular Kowa B&H. Modification basically allows a foot closer to be obtained (not a massive amount but the visual jump is impressive). Modded min focus is 2 feet 8 inches which is around the close focus distance that a Tokina +0.4 will give you on an unmodified Kowa. But the cool thing is that if you add Tokina on the modified Kowa, you get exactly 2 feet minimum focus (from front optic). 

 

 

Oooops, deleted my own pic from previous post so reposting here:

[Visual Amco]

By cutting the brass tabs do you mean Saw with a metalsaw? Or how should I do such a thing?

Thanks!

[Hans Punk]

By cutting the brass tabs do you mean Saw with a metalsaw? Or how should I do such a thing?

Thanks!

You can make a clean cut by carefully cutting with a metal handsaw/ hacksaw, or like I did...use some needle nose pliers and snap it off! Then used a file to clean up the edge that was sheared off. 

 

Remember that when re-assembling the body, the numbered focus marks will no longer be accurate - as you would have offset that scale by allowing slightly more travel to the helicoid. But since these lenses are dual focus anyway - that is not a great loss, since focusing is mostly achieved by eyeballing the image. 

 

[Bioskop.Inc]

This all looks awesome, but i'm happy to stay as it is - its seems to be less hassle to bung a diopter on the front.

However, I do have a question:

My Kowa for B&H turns beyond the 5ft mark by a little less than the distance between the 6 & 5ft markings, is this normal?

I've never really questioned this & you can focus lower than 5ft, just above 4ft. I've had the lens for over 4yrs now & it was in mint condition when i bought it (got the box, the lens caps, but no leather bag). I was just wondering if anyone elses does this or is mine just a freak of nature.

[Hans Punk]

Yes - I totally agree. This modification shaves a foot off  minimum focus distance, which is very nice but not earth shattering. Only worth doing if you can't afford a Tokina, and if your kowa is not a pristine copy and could do with a disassembly for fungus removal/ cleaning and re-lube anyway (like my example).

I kind of don't want to encourage people to hack apart perfectly good lenses, unless the potential gain is worth the potential loss. These lenses in particular are beautiful and should be preserved as is.

Fortunately I'm keeping my other Kowa B&H pristine (in its bag/box/caps) - I paid 60 quid for last year  

Yes - It's normal for a Kowa B&H to go off the min focus scale...to around what would be the 4 foot mark. (i measured my 'factory' Kowa to be 3' 8" minimum focus distance) -The shortening of the brass tabs allow that 'retraction' travel to increase slightly to give 2' 8" minimum focus distance. Add a Tokina +0.4 into that mix and min focus is exactly 2 feet.

[liamlumiere]

My Kowa focuses past infinity, does that mean previous owner has modified it or attempted to modify it and would that affect sharpness?

[Bioskop.Inc]

no that's normal too

[Hans Punk]

Yep - normal

 

 

[mdominic20]

Here's some tips, based on my experience with the sharpness tweak:

I'm not sure if this is the case with every lens, but with mine, it was possible to adjust the sharpness without even removing the brass tabs.

Just by loosening all 6 screws, but leaving the tabs in place, it created enough rotational play in the front optic for me to fine-tune the sharpness. This is because the holes in the brass tabs are ever so slightly bigger than the screws, so you have a little room for rotation.  For me it was just enough. 

Once you find the sweet spot, simply re-tighten the screws.  No glue needed.  Be careful that the act of re-tightneing the screws doesn't nudge the optic. This took me a little while to get right.  Once everything is tight, check the image again to make sure it's still sharp.

As Tito says in his video, it's easiest to judge the sharpness using a long lens at (or near) infinity, and stopped down to 4 or 5.6.  In my case,  I could never get a sharp image with the Kowa and taking lens at infinity.  I had to focus both lenses slightly less than infinity to get a super sharp image. 

This is very important, especially if you are using a single-focus solution.  Don't blindly trust the infinity marks on your Kowa or your taking lens.  You might be able to get a MUCH sharper image by adjusting them slightly under infinity.  I'm sure this will vary from lens to lens.

Hopefully this helps!

 

[PowersFilms]

Hey Everyone,

I've discovered a new method that is far safer than adding super glue to the metal tabs.

If you remove the three metal tabs, and slowly increase the diameter of the holes in each tab by using a drill, you now have extra rotation. This extra "play" or rotation in the front lens element, will allow you to better calibrate "infinity" focus.

My method: I started with a 1/8" drill bit and held the metal tab with a pair of pliers. With the drill in reverse, I started to bore a hole. After a few seconds, I switched the drill into forward mode and held on tight with the pliers until the hole was widened. Then, I repeated the same steps, but with a larger drill bit (a 9/64ths bit).

After drilling, make sure to file both sides to remove any sharp edges.

By using this method, you aren't introducing super glue into the equation and you can adjust the amount of play by filing the sides of the brass tab as well.

Let me know if anyone would be interested in watching a tutorial of this method. If enough people are into this, I may consider making a video similar in style to my other videos. Check out this video I made for repairing the viewfinder on a Sony FS7 camera:

 

[dr5chrome]

Hello - I was curious if this technique works for other scopes..? Sankor? ISCO? Thanks.  dw

[Henchman]

On 3/28/2021 at 12:50 AM, dr5chrome said:

Hello - I was curious if this technique works for other scopes..? Sankor? ISCO? Thanks.  dw

Yes, it does.