Infinity Focus - Does it really matter?

Started Mar 4, 2014 | Discussions thread
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Rich O Regular Member • Posts: 421
Infinity Focus - Does it really matter?

Being trying to get my RJ FD->NEX Focal reducer adjusted for infinity focus.

Have been experiencing a few issues and have a few questions

When mounting my Canon FD 50mm 1.4 SSC the rear lens element was colliding with the reducer. The focus ring was in fact not moving past the 5m mark. Moved the lens group of the reducer closer to the sensor just enough to clear the lens set to infinity.

Been trying the Star test for infinity focus. and I think it is now hitting infinity somewhere between the 5m and 10m mark.

Am I doing this correctly?

Here is what I've been trying. Set the camera S mode, set the shutter to 1/100 to avoid camera shake, set the aperture to f/1.4, crank the ISO to 12800. Look for bright star in the sky.

At the infinity mark the star is an white circular orb, dial the focus back a few degrees until the star become a point.

The when the orb becomes a point its at between the 5m and the 10m mark.

As you can see this is quite far from the infinity mark on the lens.

Can someone please post what the star should look like at infinity for reference?

Another question: Should infinity be at the start of the infinity symbol (Position 1) or in the middle of the symbol (Position 2)

I think since I can't move the reducer element further away since it will collide with the lens. I need to shim my adapter to move slightly further away.

Any recommendations on how to do that?

And before I go thru all this trouble, Does it really matter that it doesn't line up exactly? If I can go beyond infinity that should be OK. Correct?

I'm guessing that the distance scales will be off no matter what since the focal reducer doesn't eliminate all of the crop factor.

Another question. I have a Tamron SP 35-80mm (01A) it is supposed to be a parfocal zoom. I should be able to zoom to 80mm, focus zoom back to 35mm and still be in focus. That is not happening on a simple adapter. Is it because infinity focus is off or because of the crop factor?

If I do happen to get the focal reducer adjust for infinity. I should be able to use the lens as a parfocal zoom or will the not matter because of the crop factor still present even with the focal reducer?

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