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Minolta 5400 Scanner Lens and Laowa 25mm f/2.8 Comparison
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Macrero



Joined: 01 Sep 2011
Posts: 617
Location: Valladolid , Spain

PostPosted: Sat Jan 12, 2019 11:12 am    Post subject: Reply with quote

Pau,

I did more tests I don't keep, and to me, without a diaphragm there is less resolution/detail resolved, worse coverage (as is to be expected) and a pretty awful glare/fogginess.

100% center crops after adjusting levels.

Without diaphragm:

https://images2.imgbox.com/0e/da/vrczffq6_o.jpg

With diaphragm:

https://images2.imgbox.com/a2/1c/KWI8O3Rd_o.jpg

Also, coverage without diaphragm is worse at 2.1X than at 1.25X with diaphragm. At around 1X it is much worse.

But hey, I don't mind taking the lens back to the repair shop and get it with the diaphragm removed again Very Happy When I have some free time I will make a proper comparison.

- Macrero
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Pau
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Joined: 20 Jan 2010
Posts: 4602
Location: Valencia, Spain

PostPosted: Sat Jan 12, 2019 11:57 am    Post subject: Reply with quote

I wouldn't dismount the lens again, the glare shown is enough argument against doing it.

An interesting test will be to shoot the same subject at the same magnification with the stop in its place (I still see higher resolution at the subject in the higher magnification image, although comparing different magnifications is not a fair test)
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Macrero



Joined: 01 Sep 2011
Posts: 617
Location: Valladolid , Spain

PostPosted: Sat Jan 12, 2019 12:31 pm    Post subject: Reply with quote

Will do a test matching the M of the one without diaphragm. That will be a fair comparison.
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Macrero



Joined: 01 Sep 2011
Posts: 617
Location: Valladolid , Spain

PostPosted: Sat Jan 12, 2019 3:33 pm    Post subject: Reply with quote

Here is the test with the lens with the diaphragm re-inserted:

https://images2.imgbox.com/a9/a4/LmzsJbfj_o.jpg

100% crop without diaphragm:

https://images2.imgbox.com/90/4b/K0JBY3qG_o.jpg

100% crop with:

https://images2.imgbox.com/22/0e/eKoivKa1_o.jpg

I think it is pretty clear that designers have done well with putting that tiny ring between elements Razz Wider aperture not necessarily translates to higher resolution. Not to mention the horrible glare and worse coverage.
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Pau
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Location: Valencia, Spain

PostPosted: Sun Jan 13, 2019 2:14 am    Post subject: Reply with quote

Thank you for performing the test.
Now it's clear that the image with the stop has not only more contrast but also more resolution.
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Macrero



Joined: 01 Sep 2011
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Location: Valladolid , Spain

PostPosted: Sun Jan 13, 2019 6:35 am    Post subject: Reply with quote

My pleasure. I was curious to see how removing the diaphragm would affect performance. It was logical to expect a negative impact, although I had the "remote hope" of getting a higher resolution. I had no luck, but hey, at least I tried...
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