Re-focusing a Vivitar/Kiron 28 f2

[harrysue]

I unscrewed the front element and was able to clean the oily aperture blades with solvent. They work well now. However, I did not realize I should have marked the position of the front element, so the lens was pretty soft, no let's say it was awful, at far focus. LOL, it took me months before I figured this out. I almost threw it away.

I have readjusted by trial and error. I see that I screwed it in too deep and turning it out slightly makes it better. My method is to take some shots at near/far with my Olympus M43 camera and look at them on my PC. I'd like to have the best alignment before I lock it in with thread lock.

What's a good way to do this using a camera? Maybe focus at infinity and adjust the front element while looking at the image? Well, that seems obvious, but I thought I might ask

[themoleman342]

So the front element was actually not screwed all the way in to begin with? Was it "locked" in place originally with a glue of some sort?

[harrysue]

I gripped it with tools to break it loose. It may have been fully seated, as it has three copper washers, and they wouldn't need any if they use thread lock.

However, it seem logical that some adjustment is needed. I'm getting better results with it backed out from fully tight,

Maybe the best way to do this is without the washers as the piece is easily adjusted. Then mark it and re-assemble.

[harrysue]

I took out the washers. I can bring it in way deep now. Hmm. What I find is that I can spin the element a turn or two or more and I can see no difference in my EVF, even with 14X mag. However, infinity focus as marked on the lens is an indicated 7 feet, so I need to try a better made adapter and more experimentation.

[themoleman342]

Usually adjustments are done at infinity but who knows, by adjusting element spacing you may be losing sharpness nearing the mfd. And you're actually moving just the front element too, not the front block? Nothing rattles if it's screwed out a little?

I'd say set up something where you can test both infinity and a few other distances before committing. Sounds like a trial and error process to me. Hopefully someone else can offer a better answer.

[harrysue]

Here's what it looks like. The front piece can go in 4 turns w/o washers, and 2,5 turns with them. It seems a little bit sharper at 40 yards backed off 1/4 turn.



However, overall performance of this lens is a disappointment. Heard many good things about the Kiron 28 F2, and while this is a rebranded Vivitar, I thought it would match those praises.

[themoleman342]

Ah, OK. You are moving the entire front block, not just the element. That's what I thought.

Are there three screws in the area between the focusing ring and internal barrel? If you loosen those screws you may be able to freely turn the focus ring and adjust the infinity stop. I have not worked specifically on the 2/28 but many lenses are constructed this way. I think it was a provision to "dial-in" things after everything was put together.

[harrysue]

The "front block" does move with respect to the lens behind the iris, and the whole assembly shifts with the focus ring. Maybe it's placebo effect, but far focus looks sharper with the block adjusted out a 1/4 turn, although I suspect spacing was set with the washers. I believe it was originally locked with two set screws as I see holes in the threaded area, but no screws. That's where I will leave it.

As far as results, I guess I have bloom/flare wide open, not unusual with digital sensors that made everything look soft. Stopped down to f8, I'm now happy with the resolution at infinity.

Thanks for the suggestions, I set the barrel to read closer to infinity at infinity focus too.