Lever in lens / Using extender lens with Sony A-Mount or Sigma zoom

[ExitAisle]

Given the dearth of affordable long lenses for my A77ii, I bought a Sigma 170-500. It sorta autofocuses at the low end zoom and not so well at the high end. Nonetheless in my quest to get closeups of birds, I bought a cheap 2x extender teleconverter (Jessop MC 2X MX/AF). It seems to work on manual focus but it's REALLY HARD to get a clear focus. As I examined my lenses, including the one that does work just fine (Sony 18-135), I notice a little lever inside the lenses (photos attached). Do you have any idea the function of this lever? The one on the extender seems unfastened, giving no resistance and moving back and forth easily when detached. Could this lever affect the AF?

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[thebeardedgroundsman]

Hi, the lever in the lens controls the aperture of the lens and is sprung loaded so the iris closes when not activated - (to help stop dust getting onto the more vital elements of the lens, especially when changing lenses - I think)

The extender has a similar lever to transfer the setting from the camera to the lens, but does not need to be sprung loaded (it only has fixed magnifying lens and no moving elements), so it feels unfastened but that is how it's designed and is not a problem.

Someone else can give you better knowledge about autofocus and long lenses - I think it's something to do with lower contrast which some AF systems use as their means of telling if the image is in focus.

[XKAES]

What does "REALLY HARD" mean here?  Does that mean the focusing ring PHYSICALLY is difficult to turn?  Or do you mean the image in the viewfinder does not seem sharp?  Or do you mean something completely different?

Edited June 24, 2021 by XKAES

[michelb]

Depending on the maximum aperture of your lens, when using a 2X teleconverter your max aperture is multiplied by 2 so a F 5.6 max aperture lens becomes an F 11 lens and any working aperture smaller than F8 is likely going to be a struggle for the AF system of any camera that were designed to work up to about F 8. Anything smaller and most of the time the body won't even find focus and at those aperture settings, the viewfinder gets so dark it will always be a struggle to find correct focus.

 

Edited June 25, 2021 by michelb

[pscocoa]

Recently I had been struggling with Auto Focus on a Tamron 150-600 mm lens which was traced to the aperture lever on the lens having detached. It was an easy fix (in my case) for someone who knew how.

Edited June 25, 2021 by pscocoa