Konica Hexanon AR 28mm F1.8 collimation

[AntonioS]

Hello,

Recently I acquired a Hexanon AR 28mm F1.8 "as is" for almost no cost. The lens was in bad condition, with tons of oil in the aperture blades, and needed a total CLA. Not difficult to do , but I'm struggling with the colimation.

This thing has a floating system and there are two helicoids linked to the front group.

My question to the dear members is if someone here has the service manual for this lens or some sort of useful information about how to properly do the job ?

At the present state I can have infinity focus (sort of) but the image is extremely blurry at F1.8 and I can't believe this is normal.

Cheers,

Antonio

[visualopsins]

Welcome here AntonioS!

Adjusting the focus distance ring, are closer objects in sharp focus wide open? If so, helicals are close but not quite screwed together correctly, or, helical assembly is not screwed into the body correctly, or, both. Keep trying possibilities. I've found the correct assembly typically almost falls into place after many sometimes difficult tries.

If wide open infinity focusing stops just short of being in-focus, the lens adapter could be too thick.

If wide open infinity focusing goes past best infinity focus, well, that is probably a feature not a problem!

[AntonioS]

Hi ! Thanks for the reply !

I'll make some images as soon as possible. It's almost night here and it will be difficult to proceed.

I adjusted the outermost helicoid to the supposed infinity position with that end of course bolt at the very end of the slit, the loosen the 3 slit bolts of the focusing ring assembly and then finding the supposed infinity position an then tightening back the bolts.

I have infinity focus, confirmed by the focus peaking of my Sony A7300. Focus appears to be correct.

What is bugging me is the fact of this lens being so soft at f1.8. I thought that maybe this could be caused by some sort of problem with the helicoids relative adjustments. This is the first time I try to service a lens like this.

[RokkorDoctor]

I can't comment on the Konica specifically, but AFAIK Konica lenses have a good reputation so my guess would be that indeed the float space is incorrect.

I have serviced similar Minolta lenses with floating focus. Minolta's service instructions require the float space cams to be loosened temporarily, and a "tool" (really just a pin with two mounting screws) is then used to temporarily lock the float space in a pre-calibrated position whilst adjusting infinity focus on the focus helicoid.

Your Konica may employ a similar system, but they may equally likely have a different construction/procedure; it very much depends not only on manufacturer but also on each individual model lens.

If you are lucky the Konica service manual mentions the required float space in mm, so you can make your own float space setting tool. If you are unlucky it only mentions the order number for the float space setting tool, in which case it is crucial to measure that space prior to disassembling the helicoid, or you take a float space measurement at infinity focus setting from a known good other lens of the same model.

[stevemark]

[AntonioS]

Hi !

Thank you for the replies. I really appreciate.

Here are two samples. The focus was made using the peaking aid.
The apertures are F1.8 and F5.6.
Something is very wrong.

For the street sign, the distance was about 1 meter. Note that the sharpness at F1.8 is far better at 1m than at infinity.
Puzzling...



#1
https://drive.google.com/file/d/1TPOE70SchsZBNtah3HglE7fOpQQB9QMm/view?usp=drive_link

https://drive.google.com/file/d/1gq15ZN7VemcPfiy_AO9DLbMNK9HKh7Il/view?usp=drive_link

https://drive.google.com/file/d/1CFSkwga4PVXW9IGOeNsKyFmMcPk5k5Hq/view?usp=drive_link

https://drive.google.com/file/d/1BqdR2AfksaFio8GEB_e6keRSzJjo-q37/view?usp=drive_link

[stevemark]

Just for clarification: Are the 3000x2000px images above

1) 100% crops from the 20 MP A5000 images?
2) re-sized to 6 MP from the original 20 MP images?

S

[AntonioS]

Yes they are resizes. I was not confortable to upload 4 24MP images to the forum, they are too big.
I need to figure out how to post images in a better way in this fortum.
Maybe I can upload to my Google Drive or something like and link them.


PS. Edited the previous message and put links to the original images.

[AntonioS]

[BrianSVP]

Often on lenses with floating elements of this vintage, there is a limited number of positions at which the float can be set, corresponding to helical entry points or keyway orientation, depending on the style of mount used for the floating element.

If this is the case with this particular lens, you might be able to get away with disassembling and reassembling the lens and doing trial-and-error tests at each entry point/cam position.

Somewhat tedious, yes, but doesn't require special tools as in the Minoltas.

[AntonioS]

After three days working on it, I ended up with more questions than answers

This lens is a little nightmare to adjust. Maybe I'll put it inside a box and wait until (and if) I have the service manual.

Thanks anyway to everyone.

[AntonioS]

Hi!

Finally, I managed to re-assemble it and set up the floating element, by trial and error all thread entries one by one.
I was lucky enough to find somewhere a single page of the service manual that was a very nice starting point.

The lens is indeed very sharp from F5.6 and up, but rather soft wide open as expected.
The real improvement after adjusting the floating element was the sharpness at closer distances and wider apertures. Probably it's not perfect but it's acceptable.

Thanks everyone !

[tej]

Not sure whether this video that I just found might be helpful:

https://www.youtube.com/watch?v=4KVMuoWnXOo

BTW, I have a 28/1.8 and it is very sharp even wide open (better close than at distance, which I think is typical for this lens), and extremely sharp from f2.8 or so.

[stevemark]