Infrared NEX3 cannot achieve infinity focus

Started Feb 8, 2014 | Discussions
jmseight Junior Member • Posts: 43
Infrared NEX3 cannot achieve infinity focus

Hi,

I converted an NEX-3 by removing the hot mirror, and did not replace it with anything else.  I can get infinity focus with the 18-55 kit lens.

But when I tried it with an adaptor on old manual Nikon lenses, which had infinity focus before removing the hot mirror, I could not get infinity focus.

I think removing the hot mirror, which has a refractive index > 1, would have the effect of moving the focal plan further back.  So infinity focus should never be a problem.  So I found that not being able to achieve infinity focus with old MF lens with adapter strange.

Has anyone tried this?

Thanks,

James

 jmseight's gear list:jmseight's gear list
Panasonic Lumix DMC-FZ70 Nikon D50 Nikon D60 Sony Alpha NEX-5 Sony Alpha NEX-3 +6 more
Sony Alpha NEX-3
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john-photoguy Regular Member • Posts: 470
Re: Infrared NEX3 cannot achieve infinity focus

I had my NEX3 converted to full range (IR + visible + UV) essentially just removing the hot filter.  I had it done professionally and it works GREAT!  Infinity focus with all kinds of legacy lenses, and retains full function with the Sony Glass and the hot filter on the lens.

I had done a conversion on a D70 back years ago, and didn't like it.  I just couldn't get it clean enough when I put it back together, so this time I paid to have it done.  Much better results

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Let just all take more photographs!

 john-photoguy's gear list:john-photoguy's gear list
Nikon D200 Nikon D5000 Nikon D300S Sony Alpha NEX-3 Sony a7 +19 more
PeteGanzel
PeteGanzel Senior Member • Posts: 1,417
Re: Infrared NEX3 cannot achieve infinity focus

James:

So you have no glass in front of the sensor?

I used a coated Marumi protective filter that has almost the same thickness as the filter pack of the NEX 3 and 5.

http://www.pbase.com/pganzel/inside_the_nex_5

Doesn't a piece of glass extend the rear focus distance about 1/3 the thickness of the glass?

So yes, I can imagine that if you were at the exact limit of infinity focus with a manual lens (and not focused "past" infinity normally), the lens would be short of infinity focus without the filter pack. The AF lenses may be able to accommodate the minor difference.

Pete

http://www.pbase.com/pganzel

OpticsEngineer Veteran Member • Posts: 7,009
Re: Infrared NEX3 cannot achieve infinity focus

"doesn't a piece of glass extend the rear focus distance about 1/3 the thickness of the glass?"

that is correct

Thanks for the link to the NEX5 internal pictures.  It is always amazing to see how much Sony can pack into such a small volume.

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OP jmseight Junior Member • Posts: 43
Must Remove Sensor Shim

I realized that I did not take our the 3 shims for the sensor.

I took the NEX3 apart again and took out the shim.  Now I get infinity focus with IR and almost infinity focus visible.

Thanks,

James

 jmseight's gear list:jmseight's gear list
Panasonic Lumix DMC-FZ70 Nikon D50 Nikon D60 Sony Alpha NEX-5 Sony Alpha NEX-3 +6 more
OP jmseight Junior Member • Posts: 43
Re: Must Remove Sensor Shim

jmseight wrote:

I realized that I did not take our the 3 shims for the sensor.

I took the NEX3 apart again and took out the shim. Now I get infinity focus with IR and almost infinity focus visible.

Thanks,

James

I looked it up and the glass actually decreases the optical path, so the focus is further back.  Removing the glass increased the optical path, so the focus is moved forward.  At the infinity focus, the lens is the shortest, but without the glass the focus should more forward, or even shorter.  So infinity focus is gone.

I found that out of the 3 shims I removed, 2 are 0.35mm 1 is 0.30mm.  So the focal plane may be a little tilted.  0.3mm is a little short of the the right amount to remove, since the amount of sensor shift forward should be around 1.2 * (1-1.5)/1.5 = 0.4mm [found on the internet]

James

 jmseight's gear list:jmseight's gear list
Panasonic Lumix DMC-FZ70 Nikon D50 Nikon D60 Sony Alpha NEX-5 Sony Alpha NEX-3 +6 more
OGroot New Member • Posts: 2
Re: Must Remove Sensor Shim

Hi,
Thanks all for your insights on achieving proper infinity focus on the IR Nex series. I'm about to convert one myself too, but cannot find anything about the shims that you're referring to, could you elaborate ( even though this thread is unused for a few years now..)
thanks,
Olivier

alxgom New Member • Posts: 1
Re: Must Remove Sensor Shim

I'm thinking of buying a nex3 for cheap and converting it myself, so i would also like to know about the shims.

Thanks.

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