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Speed up your lens?


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145 replies to this topic

#141 Erik Lund

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Posted 21 February 2013 - 16:35

:) great plan!

#142 brianc1959

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Posted 23 February 2013 - 05:51

A "flying dutchman from India" reports that SB can be used in UV below 340nm. :)


Not a chance!

365nm and up, maybe, but no way should it transmit anything below 340nm. The issue here is that I had to use a dense flint glass (S-TIH1 from Ohara) to correct chromatic aberrations, and this glass simply doesn't transmit below 360nm. That said, I would be very curious to see a UV transmission plot of the SB to see what it actually does. The coatings are another issue, since they are optimized for the visible spectrum only, and I don't actually know how they perform in the UV.

Also, there will be plenty of focus shift (i.e., chromatic aberration - not spherical aberration) in the UV band, so having a live-view camera will be either handy or essential, depending on your skills. I calculate about 150 microns of focus shift at 365nm compared to the visible.

At the other end of the spectrum, the Speed Booster is actually pretty well corrected in the near-IR out to ~1000nm. I haven't thoroughly checked for IR ghost issues yet, but so far have not heard any troublesome field reports.

#143 brianc1959

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Posted 23 February 2013 - 06:10

I'm eagerly waiting for this as F=>m43 SB is the exact prescription I need. Let's see what the famous Coastal Optics APO f/4 can do with an SB kicking its rear end.


I haven't tested the 60/4 on the m4/3 Speed Booster yet. However, with the NEX version of the SB it gives the best performance of any lens that I have, especially out to the corners.

According to my MTF calculations in the visible, on m4/3 the 60/4 will be slightly sharper in the center when it becomes a 42mm f/2.8 lens. Off-axis, the 42mm f/2.8 converted version will either be very similar to the "original" 60mm, or else slightly sharper, depending on exactly where in the m4/3 field you are. The bottom line is that in the visible band it will be very good.

Unfortunately, the UV excellence that the 60/4 gives is largely taken away by the SB. The situation in the IR should be much better, however. See my post to Akira about this.

#144 nfoto

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Posted 23 February 2013 - 08:31

That source may have been misquoted as my source only claimed UV response in the upper UV-A range. However, as much of the biological response is seen already here, the Coastal + SB still is an exciting prospect to explore.

Only wish the maker, Metabones, would "speed up" (sic) the delivery of their m4/3 models.
Bjørn

#145 Akira

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Posted 23 February 2013 - 10:49

Brian, thanks for the details!

As Bjørn noted, I've misunderstood the comment of the "flying dutchman". He said he found no useful transmission at 340nm.

Edited by Akira, 23 February 2013 - 11:09 .

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#146 brianc1959

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Posted 23 February 2013 - 14:07

Only wish the maker, Metabones, would "speed up" (sic) the delivery of their m4/3 models.


I'm also anxious for this, since I generally prefer m4/3 to Sony NEX. However, I can assure you that the people at Metabones are hard at work on it!




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