blue in center of FOV

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MicroBob
Posts: 3154
Joined: Sun Dec 25, 2016 9:11 am
Location: Northern Germany

Re: blue in center of FOV

#31 Post by MicroBob » Mon Feb 11, 2019 7:38 am

Hi together,
perhaps this bit of information can help: The first generation of the Tamron 90mm 1:2,5 Macro lenses had a blue spot problem when used on a DSLR. Reason was the completely flat rear element that didn't work well together with the flat sensor. The problem became only visible when the aperture was closed beyond 8.

Bob

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75RR
Posts: 8207
Joined: Sun Oct 12, 2014 2:34 am
Location: Estepona, Spain

Re: blue in center of FOV

#32 Post by 75RR » Mon Feb 11, 2019 12:12 pm

The first generation of the Tamron 90mm 1:2,5 Macro lenses had a blue spot problem when used on a DSLR. Reason was the completely flat rear element that didn't work well together with the flat sensor. The problem became only visible when the aperture was closed beyond 8.
That is a very good point.

With an afocal setup the lens should be focused at infinity (real infinity - not what the dial says*) and the aperture wide open.

*Place camera on a tripod - focus carefully on the farthest object you can see clearly on the horizon and then tape the lens so that it can't move.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: blue in center of FOV

#33 Post by MichaelG. » Mon Feb 11, 2019 12:54 pm

MicroBob wrote:Hi together,
perhaps this bit of information can help: The first generation of the Tamron 90mm 1:2,5 Macro lenses had a blue spot problem when used on a DSLR. Reason was the completely flat rear element ...
That's optically similar [albeit not identical] to the Pentax problem that I mentioned here:
viewtopic.php?f=9&t=7027&hilit=pentax+filter

In the Pentax case, the reflection was bounced between the rear of a flat filter and the flat face of a lens element. ... so they produced a 'watchglass shaped' filter.

MichaelG.
Too many 'projects'

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