From: Martin Brown on
On Apr 16, 4:59 pm, David Dyer-Bennet <d...(a)dd-b.net> wrote:
> Martin Brown wrote:
> > On Apr 13, 6:11 pm, David Dyer-Bennet <d...(a)dd-b.net> wrote:
> >> Is any company offering removal of the Bayer filter from a Nikon-mount
> >> DSLR? Particularly the D40? (I suspect it may not be feasible due to
> >> the stacking order and how the microlenses, AA, IR cut, and Bayer are
> >> combined, and other issues, and I haven't been able to Google up much,
> >> but I thought asking might still turn something up.) I'm interested in
> >> a high-sensitivity B&W camera for low-light situations.
>
> > Would you not be better off with a faster IS lens?
>
> Maybe, but I'm *already* using 24/2, 58/1.2, 85/1.8, and 135/2 lenses.
> The 85 could be a stop faster or some such, and I could add a 28/1.4 or
> 30/1.4 for various amounts of money (and the 30/1.4 is on the wishlist
> currently). I'm reasonably close to the limits in that direction already.
>
> IS wouldn't help much; I'm currently limited largely by *subject*
> motion. IS would simplify my shooting some, letting me use my current
> shutter speeds in a wider range of positions (not so much need for
> leaning against things!). But all the IS lenses I'm familiar with are a
> stop or two *slower* than what I'm currently using.

OK. How about a lateral thinking solution then - from low light
wildlife photography.

Using a camera with the IR filter removed and then buy a very high
quality infrared lowpass filter for your flashgun and no-one will ever
see the flash. Something like Schott RG820 ought to be enough, maybe
RG850 would be better. Then you can freeze motion reliably and there
is no visible flash to startle the subjects and with flash you can
have some half decent depth of field.

You might even be able to get away with a crude IR pass plastic filter
like unexposed slide film for a quick trial.

Regards,
Martin Brown

From: David Dyer-Bennet on
Martin Brown wrote:
> On Apr 16, 4:59 pm, David Dyer-Bennet <d...(a)dd-b.net> wrote:
>> Martin Brown wrote:
>>> On Apr 13, 6:11 pm, David Dyer-Bennet <d...(a)dd-b.net> wrote:
>>>> Is any company offering removal of the Bayer filter from a Nikon-mount
>>>> DSLR? Particularly the D40? (I suspect it may not be feasible due to
>>>> the stacking order and how the microlenses, AA, IR cut, and Bayer are
>>>> combined, and other issues, and I haven't been able to Google up much,
>>>> but I thought asking might still turn something up.) I'm interested in
>>>> a high-sensitivity B&W camera for low-light situations.
>>> Would you not be better off with a faster IS lens?
>> Maybe, but I'm *already* using 24/2, 58/1.2, 85/1.8, and 135/2 lenses.
>> The 85 could be a stop faster or some such, and I could add a 28/1.4 or
>> 30/1.4 for various amounts of money (and the 30/1.4 is on the wishlist
>> currently). I'm reasonably close to the limits in that direction already.
>>
>> IS wouldn't help much; I'm currently limited largely by *subject*
>> motion. IS would simplify my shooting some, letting me use my current
>> shutter speeds in a wider range of positions (not so much need for
>> leaning against things!). But all the IS lenses I'm familiar with are a
>> stop or two *slower* than what I'm currently using.
>
> OK. How about a lateral thinking solution then - from low light
> wildlife photography.
>
> Using a camera with the IR filter removed and then buy a very high
> quality infrared lowpass filter for your flashgun and no-one will ever
> see the flash. Something like Schott RG820 ought to be enough, maybe
> RG850 would be better. Then you can freeze motion reliably and there
> is no visible flash to startle the subjects and with flash you can
> have some half decent depth of field.

Those terms are unknown to Google. Wow! Are those flash models, or
filter designators?

Yes, something like that might be a usable solution. It doesn't give
the ambience of the event as well, which is a drawback, but not a fatal
one.

> You might even be able to get away with a crude IR pass plastic filter
> like unexposed slide film for a quick trial.

Do the converted cameras have a visible-blocking filter in place
internally? If not I'd need one externally, which would blank out the
viewfinder.
From: ASAAR on
On Tue, 17 Apr 2007 10:45:39 -0500, David Dyer-Bennet wrote:

>> Using a camera with the IR filter removed and then buy a very high
>> quality infrared lowpass filter for your flashgun and no-one will ever
>> see the flash. Something like Schott RG820 ought to be enough, maybe
>> RG850 would be better. Then you can freeze motion reliably and there
>> is no visible flash to startle the subjects and with flash you can
>> have some half decent depth of field.
>
> Those terms are unknown to Google. Wow! Are those flash models, or
> filter designators?

Filters, apparently. Maybe RG820 was a typo, because that
produced hits for electronic components, sprinklers and other
things. But searching for RG850 got many hits for filters and only
one for a sprinkler, at least on the first page. :) A sampling:

> RG715, RG9, RG780, RG830, RG850 Filters, optical transmission
> Here you will find the transmission curve of the Schott RG715,
> RG9, RG780, RG830, RG850 Filters.
> www.pgo-online.com/intl/katalog/curves/optical_glassfilters/RG715_RG9_RG780_RG830_850.html - 7k - Cached - Similar pages

> KAYA PF Hoya RM RM90 RM100 Shott RG RG780 RG830 RG850
> RG1000 1050 ...
> KAYA PF Hoya RM RM90 RM100 Shott RG RG780 RG830 RG850
> RG1000 1050 1060 nm Kodak 87 87A 87B 87C Tiffen Dia Diameter
> 27 30 30.5 37 43 46 49 50 52 58 mm Step ...
> www.kaya-optics.com/products/applications.shtml - 14k - Cached - Similar pages

> RG850 Printable Data Sheet
> Optical Filter Components Resource. back to rg850 optical transmission
> curve and data page.
> www.optical-filters.com/rg850-printable.html - 4k - Cached - Similar pages

> Schott RG850 Glass Transmission Filter Data | Optical-Filters.com
> home optical filters schott filters schott RG glass schott RG850 ...
> Schott RG850 Glass Filter Data [ print this data ] ...
> optical-filters.com/rg850.html - 7k - Supplemental Result - Cached - Similar pages

From: Ilya Zakharevich on
[A complimentary Cc of this posting was sent to
David Dyer-Bennet
<dd-b(a)dd-b.net>], who wrote in article <462456e1$0$272$8046368a(a)newsreader.iphouse.net>:
> >> But removing the IR filters probably remains undesirable (for a
> >> low-visible-light camera) because lenses don't focus IR and the visible
> >> spectrum close enough together to really want both at once; you really
> >> have to choose one or the other.
> >
> > Not necessarily: For low-light work under incandescent or candlelight or the
> > like, the incident spectrum will be heavily tilted to red and IR, and I'd
> > think that red and IR wouldn't be as bad for focus discrepancy as IR would
> > be in landscape work. But even in landscape work, one is often stopped way
> > down, so it might not be that much of a problem.
>
> Hmmm, yes, true, red will predominate pretty heavily, and IR will very
> likely focus closer to red than to blue with pretty much any lens.

Irrelevant. With any half-decent lens, red and blue will focus at the
same plane. :-( ;-)

Hope this helps,
Ilya
From: Ilya Zakharevich on
[A complimentary Cc of this posting was sent to
Roger N. Clark (change username to rnclark)
<username(a)qwest.net>], who wrote in article <46243DEE.1020803(a)qwest.net>:
> So for current cameras, 8x or 3 stops is about what we can
> hope for by removing the Bayer and IR filters in current
> digital cameras, and another stop increase with higher QE
> detectors.

This is in accordance to what I was claiming about 2 years ago, when
my calculations have shown that digital cameras (of that time) worked
at about 5-10% "throughput QE". However, these calculations where
based on (flawed) data Roger put on his website; my current estimates
of the same number are closer to 14%.

Which means that no amount of tinkering can bring a gain above about 3
stops. (In particular, the Bayer filter itself eats about 1.5stops of
the signal.)

Hope this helps,
Ilya