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Defective lens - what's this?
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PostPosted: Thu Dec 07, 2017 6:17 pm    Post subject: Defective lens - what's this? Reply with quote

I bought a lens from ebay: Pentax SMC 85/1.8
It looks like new.
But the images I get are sharp only in the center.
What can this be?



PostPosted: Thu Dec 07, 2017 6:22 pm    Post subject: Reply with quote

Reversed element(s)? Check the optical diagram below
https://www.pentaxforums.com/lensreviews/SMC-Pentax-K-85mm-F1.8-Lens.html


PostPosted: Thu Dec 07, 2017 8:09 pm    Post subject: Reply with quote

It's obviously defective. I would send it back if that would happen to me.


PostPosted: Thu Dec 07, 2017 10:34 pm    Post subject: Reply with quote

that's barely sharp in the middle, there's something wrong with that lens.


PostPosted: Fri Dec 08, 2017 1:35 am    Post subject: Reply with quote

Does it look like it's been apart before? Check for marks on the spanner slots and any screws visible. There should be some traces to indicate if it's been apart before. Obviously it's missing something or something got put back out of place.

But that shouldn't have to be your call. You've received a defective piece of merchandise. Time to send it back.


PostPosted: Fri Dec 08, 2017 7:02 am    Post subject: Reply with quote

That lens has a serious issue, like the spacing is wrong between the cells or between elements, return it and look for another.


PostPosted: Fri Dec 08, 2017 7:38 am    Post subject: Reply with quote

Thanks for your comments.
I cannot see any marks that it has been opened before.
The front barrel feels unfirm though.

I will send it back.


PostPosted: Fri Dec 08, 2017 8:34 am    Post subject: Reply with quote

It should feel solid.
I still want a K 85/1.8 for my collection, it should be a very sharp lens.


PostPosted: Fri Dec 08, 2017 10:10 pm    Post subject: Reply with quote

Sometimes the spanner marks have been painted over to hide them. But with a good eye it can be spotted.


PostPosted: Sat Dec 09, 2017 11:46 am    Post subject: Reply with quote

The last time I saw that in a viewfinder blende8, I'd put one of the elements the wrong way round in an Olympus 50 1.8. I can't remember which of the elements it was unfortunately. I keep wanting to say the rearmost element, but I'm not honestly sure.


PostPosted: Sat Dec 09, 2017 12:46 pm    Post subject: Reply with quote

The Helios 44 is a good example of that, it's nearly impossible to tell which way it goes.