Improving the D7 (and D7i?)

[ruan]

Hopefully someone will clarify )

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Thanks Rob,
You answer is good enough for me.
Ruan

 

[ruan]

Thank you Bill for the very informative answer
and your effort to do so
Ruan

A hot mirror filter is a filter that blocks IR radiation from the
camera. It is a dichroic, an interference type of filter. That it
is made by depositing a very thin coating of a very precise
thickness on the glass. It is characteristic of such coatings that
radiant energy longer than a given wavelength (in this case some
where in the range of 650nm to 700nm) is reflected and energy with
shorter wave lengths is transmitted (or passed through). This wave
lenght is know as the cut off frequency.

An Infra Red filter is a filter that block visible light and
transmits the IR. They are typically adsorbtion filters though a
few cold mirror filters are available (they would have a much
sharper cut off).

Bill Cook

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Ruan

--
Ruan

 

[PeteGanzel]

Bill:

Well I certainly have been getting an education on IR and Digicams since you started this thread. Do you have a spec sheet for the mirror filter you have? In reading at the website suggested by go2wen at:

http://www.cliffshade.com/dpfwiw/ir.htm

It appears and that CCD sensors are responsive from 700nm to about 1200nm in the IR band. The range from 770 to 1100 cannot be filtered by absorption (normal filters, CCD filters) at all. I'm just curious as to what range of IR your filter reflects, since there it would appear that the near red area is not the only problem.

Thanks, and good luck,

Pete

A hot mirror filter is a filter that blocks IR radiation from the
camera. It is a dichroic, an interference type of filter. That it
is made by depositing a very thin coating of a very precise
thickness on the glass. It is characteristic of such coatings that
radiant energy longer than a given wavelength (in this case some
where in the range of 650nm to 700nm) is reflected and energy with
shorter wave lengths is transmitted (or passed through). This wave
lenght is know as the cut off frequency.

An Infra Red filter is a filter that block visible light and
transmits the IR. They are typically adsorbtion filters though a
few cold mirror filters are available (they would have a much
sharper cut off).

Bill Cook

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Ruan

 

[Mark Pernal]

I've noticed the discoloration with some materials with my D7, and I would like to try using a hot mirror filter. Could someone please suggest a good place to buy one...and what size would you suggest so no vignetting occurs?

Thanks.
--
Mark Pernal
Austin, TX

 

[Bill Cook]

Unfortunately Tiffen did not supply a spec sheet with the filter (you think they would with a filter that has an MSRP of nearly $150 - but they don't). I am trying to get one and have written Tiffen email about the subject.

Please see my "Follow Up" message in this thread.

Bill Cook

Well I certainly have been getting an education on IR and Digicams
since you started this thread. Do you have a spec sheet for the
mirror filter you have? In reading at the website suggested by
go2wen at:

http://www.cliffshade.com/dpfwiw/ir.htm

It appears and that CCD sensors are responsive from 700nm to about
1200nm in the IR band. The range from 770 to 1100 cannot be
filtered by absorption (normal filters, CCD filters) at all. I'm
just curious as to what range of IR your filter reflects, since
there it would appear that the near red area is not the only
problem.

Thanks, and good luck,

Pete

A hot mirror filter is a filter that blocks IR radiation from the
camera. It is a dichroic, an interference type of filter. That it
is made by depositing a very thin coating of a very precise
thickness on the glass. It is characteristic of such coatings that
radiant energy longer than a given wavelength (in this case some
where in the range of 650nm to 700nm) is reflected and energy with
shorter wave lengths is transmitted (or passed through). This wave
lenght is know as the cut off frequency.

An Infra Red filter is a filter that block visible light and
transmits the IR. They are typically adsorbtion filters though a
few cold mirror filters are available (they would have a much
sharper cut off).

Bill Cook

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Ruan

 

[Bill Cook]

Try amazon.com. They had three 67mm ones left at $40 the last I looked. They are closing them out (most pro cameras have them built in now) and when they are gone the MSRP is $150 according to Tiffen.

Bill Cook

I've noticed the discoloration with some materials with my D7, and
I would like to try using a hot mirror filter. Could someone
please suggest a good place to buy one...and what size would you
suggest so no vignetting occurs?

Thanks.
--
Mark Pernal
Austin, TX

 

[Bill Cook]

I took the following pair of pictures this morning (first time we have seen the sun since Wed).





The particulars. Exposure was established at 1/750 at F6.7 using an ExpoDisk and doing an incident light reading and transfering the info to the manual mode of the camera. Both photos were opened in Photoshop 7.0 using the proprietary color profile described in:

http://www.dpreview.com/forums/read.asp?forum=1024&message=2720904

And using the work flow I describe in the same thread. After conversion to sRGB they were resized and saved "For the Web". No further color corrections were made.

The top picture was taken without the hot mirror filter and the bottom one with. The color shift in the black area of the jacket is quite evident to my eyes.

Bill Cook

 

[Frank Magalhaes]

Bill—

I've been lurking here and following this interesting thread. Is it my eye, or is the filtered (lower) shot greener overall? It looks on my monitor like the other chair arm just to the left in the shadow is greenish and the what looks like a white door in the shadow in the background is also greenish. This is not meant as criticism, just further inquiry.
—Frank

I took the following pair of pictures this morning (first time we
have seen the sun since Wed).





The particulars. Exposure was established at 1/750 at F6.7 using an
ExpoDisk and doing an incident light reading and transfering the
info to the manual mode of the camera. Both photos were opened in
Photoshop 7.0 using the proprietary color profile described in:

http://www.dpreview.com/forums/read.asp?forum=1024&message=2720904

And using the work flow I describe in the same thread. After
conversion to sRGB they were resized and saved "For the Web". No
further color corrections were made.

The top picture was taken without the hot mirror filter and the
bottom one with. The color shift in the black area of the jacket is
quite evident to my eyes.

Bill Cook

 

[Bill Cook]

In the absence of the IR contribution there may be a very slight shift to the CYAN side overall. But you may also be looking at the mold that is on my entire back deck and deck furniture. It has been so wet and cloudy here this spring I had to take a quick look at my GPS to make sure I wasn't in London not Rogers, AR.

If I get several sunny days back to back so things dry out a bit it is time to get out the power washer and clean the deck, the furniture and possibly the dog.

Bill Cook

Bill—
I've been lurking here and following this interesting thread. Is it
my eye, or is the filtered (lower) shot greener overall? It looks
on my monitor like the other chair arm just to the left in the
shadow is greenish and the what looks like a white door in the
shadow in the background is also greenish. This is not meant as
criticism, just further inquiry.
—Frank

 

[ruan]

PeteGarizel:

Does that mean that a digicam without a coated Hot Mirror is better for taking IR pictures by using a IR filter. Since a built-in Hot Mirror Filter will reflect off the IR from the normal IR filter.

Ruan

Well I certainly have been getting an education on IR and Digicams
since you started this thread. Do you have a spec sheet for the
mirror filter you have? In reading at the website suggested by
go2wen at:

http://www.cliffshade.com/dpfwiw/ir.htm

It appears and that CCD sensors are responsive from 700nm to about
1200nm in the IR band. The range from 770 to 1100 cannot be
filtered by absorption (normal filters, CCD filters) at all. I'm
just curious as to what range of IR your filter reflects, since
there it would appear that the near red area is not the only
problem.

Thanks, and good luck,

Pete

A hot mirror filter is a filter that blocks IR radiation from the
camera. It is a dichroic, an interference type of filter. That it
is made by depositing a very thin coating of a very precise
thickness on the glass. It is characteristic of such coatings that
radiant energy longer than a given wavelength (in this case some
where in the range of 650nm to 700nm) is reflected and energy with
shorter wave lengths is transmitted (or passed through). This wave
lenght is know as the cut off frequency.

An Infra Red filter is a filter that block visible light and
transmits the IR. They are typically adsorbtion filters though a
few cold mirror filters are available (they would have a much
sharper cut off).

Bill Cook

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Ruan

--
Ruan

 

[Jawed49152]

I just bought the PCT-100 today and saw this while looking through
the manual...

Basically, Minolta discovered the IR problem after it was too late to do anything in the D5/D7 design.

The D7i is supposed to have better IR filtering. Guess Minolta had time to implement the filter. (When I can track down the web page that says this, I'll let y'all know.)

The CCD in the D7 is 8x6mm - a 62mm diameter hot mirror might cost $150 to buy, but there's no way such a small hot mirror placed in front of the CCD would cost $100. The F707 has some kind of IR filtering.

This is why I'm hopeful that Minolta has implemented the filter properly in the D7i.

Jawed

 

[Bill Cook]

Basically, Minolta discovered the IR problem after it was too late
to do anything in the D5/D7 design.

Given that there is at least a 3 year history (more like 5 actually) documenting the problem on the web where were the Minolta engineers, in a cloistered convent? There are a number of plausible explanations but I really don't think that one will fly.

The D7i is supposed to have better IR filtering. Guess Minolta had
time to implement the filter. (When I can track down the web page
that says this, I'll let y'all know.)

When you find the page please let us know. It is to be hoped for but frankly I have my doubts.

The CCD in the D7 is 8x6mm - a 62mm diameter hot mirror might cost
$150 to buy, but there's no way such a small hot mirror placed in
front of the CCD would cost $100. The F707 has some kind of IR
filtering.

Price wise you are right. But retro fitting an internal filter into an existing design is not simple, easy or cheap.

This is why I'm hopeful that Minolta has implemented the filter
properly in the D7i.

Jawed

 

[Mark Pernal]

Thanks....they were all ready out of them, but B&H had plenty.

--
Mark Pernal
Austin, TX

 

[PeteGanzel]

Ruan:

I'm not really sure what portion of the IR band that Bills reflective filter works at. It appears that a reflective filter is the only one that will work in the 770-1100 range though. A DC without IR filtering will be better for IR photography than one with. A normal IR filter (such as a Hoya 72) passes mostly IR and stops most visible by absorption. I think that was your question. Jawed mentioned that the Sony 707 has a moveable IR filter.

To get a visual example of how a reflective filter works, take a halogen bulb that has a built in glass reflector, hold it up to the light with the base toward you. You will see reddish light through the back. Looking at the inside of the reflector (the reflector still facing the light) you will see silver or bluish colors. This is working just the opposite of a IR reflective filter since this reflector is designed to pass IR and reflect visible.

Implimentation of a reflective filter is not easy inside a camera since the reflected radiation has to go somewhere. A flat filter placed at a right angle to the lens axis will just bounce the IR back through all elements of the lens. I think many use a coating on a beam splitter and direct the IR off at a 45. There is a dichroic coating on the outside of many cheap PC cam lenses that is probably for IR reflection.

From the cutaway views of the D-7 I've seen, it's optical path is gloriously unencumbered!

Thanks and good luck,

Pete

Does that mean that a digicam without a coated Hot Mirror is better
for taking IR pictures by using a IR filter. Since a built-in Hot
Mirror Filter will reflect off the IR from the normal IR filter.

Ruan

Well I certainly have been getting an education on IR and Digicams
since you started this thread. Do you have a spec sheet for the
mirror filter you have? In reading at the website suggested by
go2wen at:

http://www.cliffshade.com/dpfwiw/ir.htm

It appears and that CCD sensors are responsive from 700nm to about
1200nm in the IR band. The range from 770 to 1100 cannot be
filtered by absorption (normal filters, CCD filters) at all. I'm
just curious as to what range of IR your filter reflects, since
there it would appear that the near red area is not the only
problem.

Thanks, and good luck,

Pete

A hot mirror filter is a filter that blocks IR radiation from the
camera. It is a dichroic, an interference type of filter. That it
is made by depositing a very thin coating of a very precise
thickness on the glass. It is characteristic of such coatings that
radiant energy longer than a given wavelength (in this case some
where in the range of 650nm to 700nm) is reflected and energy with
shorter wave lengths is transmitted (or passed through). This wave
lenght is know as the cut off frequency.

An Infra Red filter is a filter that block visible light and
transmits the IR. They are typically adsorbtion filters though a
few cold mirror filters are available (they would have a much
sharper cut off).

Bill Cook

I think nobody notice our pleads to know what a "Hot Mirror Filter"
is.
What's the difference between a "Hot Mirror Filter" and a "Infra
Red Filter"?

I hope someone can help.

Ruan

--
Ruan