coolpix 5000 IR testing (step 1)

[Chris Eastwood-2]

Hi

I've just got my Hoya R72 filter and taken a quick test with my coolpix
5000. Results are good, but the camera can clearly benefit from a
conversion because exposure times are LONG. Also there is a noticable
hotspot being created. I'ts subtle in present lighting conditions, but I
wonder if it will get worse in different conditions.

On the topic of hotspots, is this created by the reflection from the
front element onto the IR filter or is it something else.

Thanks
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[Jason Revell]

The 'hot Spots' are due to internal reflections inside the lens.  I
presume the black coating used on the inside of some lenses reflects
some IR back into the lens that produces the 'hotspot'.  

Sometimes the best way to avoid this is to use the lens fully open as
this makes it less obvious as it's more diffused and spread over a
larger area of the image.  As you stop down the hotspots become smaller
and more 'focused' into the centre of the image.

Jason Revell


-----Original Message-----
From: owner-infrared@... [mailto:owner-infrared@...] On Behalf Of
Chris Eastwood
Sent: 20 November 2007 10:02
To: INFRARED@...
Subject: coolpix 5000 IR testing (step 1)

Hi

I've just got my Hoya R72 filter and taken a quick test with my coolpix
5000. Results are good, but the camera can clearly benefit from a
conversion because exposure times are LONG. Also there is a noticable
hotspot being created. I'ts subtle in present lighting conditions, but I

wonder if it will get worse in different conditions.

On the topic of hotspots, is this created by the reflection from the
front element onto the IR filter or is it something else.

Thanks

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[Cameron Shaw]

Hi Jason,
 You are right it does help to reduce the IR 'hot spot', opening the lens,
 however then image not quite as sharp, (digital camera focus calibrated in
visible spectrum)
and problems in bright light or when you need more DOF, I have really had
difficulty with this
using the 750nm filter with a Fuji IS-1, what a disappointment !,
Only real solution is to change lens or if not possible change camera!
It has been suggested that a band pass filter could help,
blocking the longer IR wavelengths that increase the effect.
My question to the group please, has anyone actually tried this?
Thanks, Cameron

-----Original Message-----

Sent: 20 November 2007 10:39
To: infrared
Subject: RE: coolpix 5000 IR testing (step 1)

The 'hot Spots' are due to internal reflections inside the lens.  I
presume the black coating used on the inside of some lenses reflects
some IR back into the lens that produces the 'hotspot'.  

Sometimes the best way to avoid this is to use the lens fully open as
this makes it less obvious as it's more diffused and spread over a
larger area of the image.  As you stop down the hotspots become smaller
and more 'focused' into the centre of the image.

Jason Revell
-----
Chris Eastwood
Sent: 20 November 2007 10:02
To: INFRARED@...
Subject: coolpix 5000 IR testing (step 1)

Hi

I've just got my Hoya R72 filter and taken a quick test with my coolpix
5000. Results are good, but the camera can clearly benefit from a
conversion because exposure times are LONG. Also there is a noticable
hotspot being created. I'ts subtle in present lighting conditions, but I

wonder if it will get worse in different conditions.

On the topic of hotspots, is this created by the reflection from the
front element onto the IR filter or is it something else.

Thanks


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[Stan-42]

> You are right it does help to reduce the IR 'hot spot', opening the lens,
> however then image not quite as sharp, (digital camera focus calibrated in
> visible spectrum)
> and problems in bright light or when you need more DOF, I have really had
> difficulty with this
> using the 750nm filter with a Fuji IS-1, what a disappointment !,
> Only real solution is to change lens or if not possible change camera!
> It has been suggested that a band pass filter could help,
> blocking the longer IR wavelengths that increase the effect.
> My question to the group please, has anyone actually tried this?

To Cameron and the group,

Back in September (Sept 12 posts) we discussed the IR hotspot. At the time I
tested my camera and found the IR hotspot was dependent on two things -
focal length and aperture. On my Sony/Zeiss zoom lens, the spot was
strongest about mid-zoom and the spot was most pronounced at minimum
aperture. It was too diffuse to see at wide apertures.

The IR hotspot was apparent with all IR filters, from a standard red 25A to
deep purple(?) 87C. This includes my special XDP band-pass filter which I
got from LDP, the company that converted my Sony. So there does not seem to
be a way of eliminating this effect; you have to work around it.

I still would love to know from any of the remaining film shooters out there
if this is strictly a consequence of using digital cameras in the IR band.

Stan Patz   NYC

www.PatzImaging.com

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[Jason Revell]

It's not just limited to Digital cameras.  

I was sent some false Colour IR film that had been taken by the
photographers at the Tate Gallery in London some years back for research
work they were doing and it has the exact same hotspot marking on the
roll of film (just pink/red rather than white).

This was proof to me that it was due to internal IR reflections.  The
cure I gave them was to change lenses which worked.  Again this was a
Nikon lens but I know I have read it happening with a few canon lenses
as well.

Jason Revell
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[Cameron Shaw]

Cc: Cameron Shaw
Subject: Re: coolpix 5000 IR testing (step 1)

> You are right it does help to reduce the IR 'hot spot', opening the lens,
> however then image not quite as sharp, (digital camera focus calibrated in
> visible spectrum)
> and problems in bright light or when you need more DOF, I have really had
> difficulty with this
> using the 750nm filter with a Fuji IS-1, what a disappointment !,
> Only real solution is to change lens or if not possible change camera!
> It has been suggested that a band pass filter could help,
> blocking the longer IR wavelengths that increase the effect.
> My question to the group please, has anyone actually tried this?

To Cameron and the group,

Back in September (Sept 12 posts) we discussed the IR hotspot. At the time I

tested my camera and found the IR hotspot was dependent on two things -
focal length and aperture. On my Sony/Zeiss zoom lens, the spot was
strongest about mid-zoom and the spot was most pronounced at minimum
aperture. It was too diffuse to see at wide apertures.

The IR hotspot was apparent with all IR filters, from a standard red 25A to
deep purple(?) 87C. This includes my special XDP band-pass filter which I
got from LDP, the company that converted my Sony. So there does not seem to
be a way of eliminating this effect; you have to work around it.

I still would love to know from any of the remaining film shooters out there

if this is strictly a consequence of using digital cameras in the IR band.

Stan Patz   NYC

www.PatzImaging.com

I still shoot Kodak HIE, never had hot spots.
so Stan, you've given me an idea, that may answer your question.
I have a Nikon fit Sigma F1.4 30mm lens, that does sometimes make IR hotspot
on the Nikon D50
when used for IR, although not designed for full 35mm film area, its for
smaller digital sensor.
It would fit the film camera body. I should make a digital exposure with
hotspot, then swap the lens to the film camera,
to see if spot reproduced on film....
Cameron   UK



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[Stan-42]

> I still shoot Kodak HIE, never had hot spots.
> so Stan, you've given me an idea, that may answer your question.
> I have a Nikon fit Sigma F1.4 30mm lens, that does sometimes make IR
> hotspot
> on the Nikon D50
> when used for IR, although not designed for full 35mm film area, its for
> smaller digital sensor.
> It would fit the film camera body. I should make a digital exposure with
> hotspot, then swap the lens to the film camera,
> to see if spot reproduced on film....

To Cameron and the group,

The simple test I did showed the IR hotspot immediately; I photographed some
white no-seam. On a fixed focal length lens like the Sigma 30mm, you could
get by with one exposure at f16 to see if it makes a spot. Just make sure
you underexpose the film a bit to get gray paper so the spot will be
apparent.

If you wanted to map the formation of the spot, do a series at all the
f-stops and watch the blemish come into "focus". As a bonus, you may find
this "digital" lens makes a nice soft vignette on the full format. My guess
is that it is such a short focal length it will cut off, making dark
corners - like too many filters on the lens. But wide open, it might be a
nice effect.

Stan Patz   NYC

www.PatzImaging.com

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[Keith Davison-2]

> I still would love to know from any of the remaining film shooters out
> there if this is strictly a consequence of using digital cameras in the IR
> band.

I shot HIE mainly with Canon FD lenses 7.5mm fisheye to 500mm mirror,
cut-down 2424 with Pentax 67 lenses from the 35mm fisheye to the 200mm
with x2 teleconverter. I shot HSI with Schneiders, 47XL to 150mm and an
ancient Ektar 210mm. The lenses were usually stopped down to - HIE, f8,
2424 f11, HSI f22, filter was usually 87C.

Never saw the "hotspot" once. The lenses were all primes with fewer
elements than modern zooms, which will have an influence on internal
reflections, as will the semi-symmetrical designs of the LF glass.

I have converted two Sony F717's to full time IR, both exhibited the hotspot
with filters from 88a1/2 to the LDP 1000nm.

I have mentioned before that when I was doing the conversions I had to
remove the CCD, and its surface was extremely reflective to the naked eye,
much more so than the matte white appearance of Kodak film.

My guess is: - strong back reflection from the glassy CCD + AR coatings not
optimised for IR + modern zooms with many elements and exotic glasses =
hotspot.

Keith




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[Wilko Bulte]

Quoting Keith Davison, who wrote on Wed, Nov 21, 2007 at 10:35:43AM -0000 ..

> > I still would love to know from any of the remaining film shooters out
> > there if this is strictly a consequence of using digital cameras in the IR
> > band.
>
> I shot HIE mainly with Canon FD lenses 7.5mm fisheye to 500mm mirror,
> cut-down 2424 with Pentax 67 lenses from the 35mm fisheye to the 200mm
> with x2 teleconverter. I shot HSI with Schneiders, 47XL to 150mm and an
> ancient Ektar 210mm. The lenses were usually stopped down to - HIE, f8,
> 2424 f11, HSI f22, filter was usually 87C.
>
> Never saw the "hotspot" once. The lenses were all primes with fewer
> elements than modern zooms, which will have an influence on internal
> reflections, as will the semi-symmetrical designs of the LF glass.

All these older lenses are metal construction I assume.  Anybody ever
checked if there is a correlation with newer lenses with more plastic
contents and the hotspot phenomenon?


Wilko
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