m42 adapter modification

Hi all,

It seems all the adapter design is a copy of one another.
what bugs me is the thigtness issue when mount-unmounting them. So, I make comparison between 2 adapters and standard min.af mount.

Here is crude schematics


Overall lens mount plate (flange) diameter (not lens tube) of km(17-35,35-70) and tamron 90 is 62mm; both adapters is 64mm. Maybe this 2mm diameter differences designed to facilitate extraction by grabbing, or old design based on minolta slr, don't know for sure.

Notice the blue box in above schem. (which min.af lenses don't have). That part is 1mm outermost diameter of the adapter, the thickness (height) at (A) is actually not level with flange on camera, hence the protrusion.

Ignore B, it's the highest thickness in C which important, must not exceed 1mm, but I can't meassured it with my cheap plastic caliper.

In my adapter copies, thickness at A (blue box, 1mm outermost part) is varied between 1,3 to 1,5mm. When mounted on camera, due to the thickness, this part is 'enveloping' camera flange. The problem is, it's also pressing and make friction with camera body surface just outside the mount; maybe also affect infinity focus on some adapter. I hope there is no other side effect to lens mount precision.

I think that part is unnecessary, or part of bad design. Too bad I don't have right tools to level out or cut that part :(

Anybody willing to try modifying their adapter?
Please share your obsevation... especially adapter thickness at C and A (blue box, 1mm outermost part)

update...

Obviously one of my adapter is too thick along C, so lens attached to it can't achieve infinity focus. I have reduce the thickness of that adapter, sanding the adapter surface at the side facing the lens.

It's ugly but works, now lens attached to it can focus at infinity.

BobJanesSE2 wrote: The measurements of my adapter are as follows ... : A: 1.55 - 1.59mm B: 1.94 - 1.97mm

Similar like my HongKong adapter, for comparison, my unmodified old Hama is around 1,3mm at A and 1,85-1,9mm at B.
For HK adapter I'm reducing the thickness at A and B. For Hama only at A.
Now both adapter measurement at A is around 1mm and 1,8-1,9mm at B.

BobJanesSE2 wrote: This gives a depth of C (measured where it meets A)of between 1.06 and 1.1mm.

According to mount register data at http://www.a1.nl/phomepag/markerink/mounts.htm thickness of m42 to min.af adapter (at this point) must not exceed 1mm. I don't know the tolerance treshold, but it's better be slightly thinner than thicker.

BobJanesSE2 wrote: The overall depth of my adapter (measured from the front plate to the back of the bayonet is 5.9mm I've not tested this adapter with M42 glass to see if it will focus to infinity.

My unmod.hama and mod.HK is 5,75mm.

Thanks for your input Bob.       

BobJanesSE2 wrote: So the next question is - what would be the best way of taking 0.19mm off the face of the adapter? Bob

this is what i've done:

-'hack' inclined:
sanding down adapter face, using flatened sandpaper on level surface, adapter on top of sandpaper with gentle equally pressured rotating movement, also rotate the adapter orientation every 30 stroke or so.

-'socially' inclined:
i've 'persuade' the adapter maker to redesign the adapter using my measurement :D he's already working on it, but still have to wait for the new version though.

it's obvious that i aim for cheap solution :)     

hmmm...

under 1 hour, i go slowly and hesitant at first :)
it includes several cycle of sanding, washing, and test, as i don't really know how far i should go; can't relly on my cheap plastic caliper :)

i just comparing pics on computer at 100%, and repeat as necessary. HK adapter is quite soft & i've done it at lunch hour :D

and don't forget to rotate the adapter on your grip periodicaly, as our finger don't give equal pressure.

should be easy for you (and you have reliable caliper) :)

will do,
already ask him about it, will report here when it's available and pass the test.

thanks Kiklop,
i'm sure it would be a very good support. i've quoted your post and forwarded it to him. i'm sure producing / modificating it can be done -cheap- in HK.