An ISO Quality question

In article ,
Brian Baird wrote:
In article ,
says...
The lens is capable of going down to a 3X magnification ratio,
but the closest that I can get at present is a 2/3X magnification ratio
because of the exposure situation.

I really need to modify the power pack to reduce the flash power
enough for those closer shots.

ND filter?

I've considered that, but it is an uncommon diameter (IIRC,
38.7mm or something close), and it would have to go into the middle of
the stack because the most powerful lens of the set has only the male
threads, as it is designed to always be the greatest distance from the
prime lens. All combinations which are documented for the lens have one
or two close-up lenses from the kit on the front of the prime lens,
never three.

I think that simply adding a switch to the power supply to allow
reducing the capacitance supplying the flashlamp power to produce about a
two stop reduction would work nicely. And, IIRC, there is physical room
for such a modification.

I have read that there was a special cord to go from the power
supply to the lens to allow operation at higher ASAs, but I have never
found such a cord, and no information on how to construct one. I would
guess (since there is no capacitance at the flash head) that it would
consist of a resistor in series with the high voltage lead, and a
smaller capacitor closer to the flash head.

And, since I have only the AC powered supply, I might be better
off to design and build a battery powered one which works from normal
batteries -- ideally NiMH rechargeable ones, or perhaps even the same
LiON ones used by the camera itself. Certainly if I were to find the
original battery power supply for it, I would be stuck purchasing 350V
batteries (or are they 277V ones? In any case, rare and expensive in
today's market. :-)

Enjoy,
DoN.
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In article , wrote:
In message ,
(DoN. Nichols) wrote:

Not a consideration on the Cannon, but my Nikon D70 has a
minimum ISO of 200, and this prevents me from shooting at the highest
magnification range of the old 200mm Medical Nikkor (with the built-in
ring flash). It does the exposure calculation based on an ISO (actually
marked as ASA) setting ring, and a magnification ratio ring, resulting
in setting of the aperture ring.

Have you tried shooting with the manual flash for 100 when the camera
was set to 200?

I did while shooting jpegs, and there were blown highlights.

That might not be a problem at all, if you're shooting RAW. 100% matte
reflectance would probably not clip; only specular highlights, which
should be subdued by the ring, anyway (and which would generally even
out the lighting, in your favor).

Hmm ... it is worth a try. But I think that I would prefer
getting the right amount of light to start with.

Thanks,
DoN.

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In article ,
Cockpit Colin wrote:

"Al Dykes" wrote in message
...

Is there *any* reason to use 100 if 200 has imperceptably more noise
and one stop faster shutter speed is apt to result in a sharper
picture ?

I did a few portrait tests at ISO 100 to 1600 on my Canon 350D. Between ISO
100 and 200 the difference was minimal - but still detectable. In the end I
decided that if I was to take a portrait that was going to be enlarged and
hung on the wall, then it would have to be @ ISO 100.

I'm having trouble finding a compromise between ISO and shutter speed to
freeze a moving scene - being a picky/fussy ******* I'm going to invest in a
faster lens to get around the problem (present lens has max aperture of 5.6
@ 55mm).

Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
You might look for the same -- or perhaps the 50mm f1.8 would serve as
well for you. (The above are Nikon lenses, and I see that you have a
Cannon, so you will have to see what is available to fit your camera.

Does your local camera store stock used lenses? Do they have
reasonable prices?

Good Luck,
DoN.

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In article ,
David J Taylor wrote:
- well size 40,000 electrons (white)
- 12-bit digitisation, step size 10 electrons

Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12 = 4.88
electrons. At 25 electrons or more, shot-noise exceeds quantisation noise.


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could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency

In message ,
(DoN. Nichols) wrote:

In article , wrote:
In message ,
(DoN. Nichols) wrote:

Not a consideration on the Cannon, but my Nikon D70 has a
minimum ISO of 200, and this prevents me from shooting at the highest
magnification range of the old 200mm Medical Nikkor (with the built-in
ring flash). It does the exposure calculation based on an ISO (actually
marked as ASA) setting ring, and a magnification ratio ring, resulting
in setting of the aperture ring.

Have you tried shooting with the manual flash for 100 when the camera
was set to 200?

I did while shooting jpegs, and there were blown highlights.

That might not be a problem at all, if you're shooting RAW. 100% matte
reflectance would probably not clip; only specular highlights, which
should be subdued by the ring, anyway (and which would generally even
out the lighting, in your favor).

Hmm ... it is worth a try. But I think that I would prefer
getting the right amount of light to start with.

I consider the ISO numbers on the camera to be pretty arbitrary. My
first DSLR, the Canon 10D, had a reputation for blowing out JPEGs unless
the contrast parameter was set to -2, or you used negative exposure
compensation. Upon further investigation, I found out that the camera
was actually metering for ISO 64, when it was set to ISO 100. I also
found out that I could use an external incident meter, or spot-meter on
a grey card, and expose for ISO 40, and no white that was purely matte
would blow out.

IOW, the minimum of ISO 200 on your camera might only be for big
headroom, and may actually work as ISO 100 like slide film. Try it, but
you must do it in RAW. With RAW, even if you blow one channel out, if
it is a white highlight or specular highlight from the light source,
some converters will treat areas where one or two color channels are
clipped as greyscale. The D70, like the 20D and 10D, are most sensitive
to green, and least sensitive to red, so the red channel often contains
extra greyscale highlight detail.
--


John P Sheehy

"DoN. Nichols" wrote in message
...

Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
You might look for the same -- or perhaps the 50mm f1.8 would serve as
well for you. (The above are Nikon lenses, and I see that you have a
Cannon, so you will have to see what is available to fit your camera.

I've decided to get the 100mm F1.2 L series lens - 50mm has proven to be too
short for me, in addition to the other limitations

Does your local camera store stock used lenses? Do they have
reasonable prices?

Local stores don't have anything - it's all online auction sites for me. In
any case, I prefer to buy new - it's just the "picky/*******" bit in me
coming out again!

In message coh.net,
(Philip Homburg) wrote:

In article ,
David J Taylor wrote:
- well size 40,000 electrons (white)
- 12-bit digitisation, step size 10 electrons

Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12 = 4.88
electrons. At 25 electrons or more, shot-noise exceeds quantisation noise.

Arithmetically, perhaps, but things are more complex in the realm of
human perception. Noise doesn't really hide detail as much as the
arithmetic would suggest.

The kinds of things that you seem to be taking into consideration are
the kinds of things that determine the usefulness of single pixels as
accurate measurement devices, not necessarily the usefulness of arrays
of such pixels as "imaging" devices, especially in light of the brain's
abilities in the area of pattern recognition and rejection.
--


John P Sheehy

In article ,
Cockpit Colin wrote:

"DoN. Nichols" wrote in message
...

Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
You might look for the same -- or perhaps the 50mm f1.8 would serve as
well for you. (The above are Nikon lenses, and I see that you have a
Cannon, so you will have to see what is available to fit your camera.

I've decided to get the 100mm F1.2 L series lens - 50mm has proven to be too
short for me, in addition to the other limitations

Does your local camera store stock used lenses? Do they have
reasonable prices?

Local stores don't have anything - it's all online auction sites for me. In
any case, I prefer to buy new - it's just the "picky/*******" bit in me
coming out again!


ebay.


--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

In article , wrote:
In message ,
(DoN. Nichols) wrote:

In article , wrote:

[ ... Medical Nikkor with D70 & ISO 200 minimum snipped ... ]

Have you tried shooting with the manual flash for 100 when the camera
was set to 200?

I did while shooting jpegs, and there were blown highlights.

That might not be a problem at all, if you're shooting RAW. 100% matte
reflectance would probably not clip; only specular highlights, which
should be subdued by the ring, anyway (and which would generally even
out the lighting, in your favor).

Hmm ... it is worth a try. But I think that I would prefer
getting the right amount of light to start with.

I consider the ISO numbers on the camera to be pretty arbitrary. My
first DSLR, the Canon 10D, had a reputation for blowing out JPEGs unless
the contrast parameter was set to -2, or you used negative exposure
compensation. Upon further investigation, I found out that the camera
was actually metering for ISO 64, when it was set to ISO 100. I also
found out that I could use an external incident meter, or spot-meter on
a grey card, and expose for ISO 40, and no white that was purely matte
would blow out.

O.K. Note that the chart which comes with the lens suggest that
for 2:1 reproduction ratio, a maximum ASA (now ISO) of 50 is suggested
for color, and 25 for B&W. (This is an old lens system, of course.)
The chart is incomplete, but it looks like it will require an ASA of 25
(or perhaps 32) with the full 3:1 ratio, so I may have to cut the
illumination anyway. I can't see pushing it that far down.

IOW, the minimum of ISO 200 on your camera might only be for big
headroom, and may actually work as ISO 100 like slide film. Try it, but
you must do it in RAW. With RAW, even if you blow one channel out, if
it is a white highlight or specular highlight from the light source,
some converters will treat areas where one or two color channels are
clipped as greyscale. The D70, like the 20D and 10D, are most sensitive
to green, and least sensitive to red, so the red channel often contains
extra greyscale highlight detail.

Well ... we'll see what experimentation with RAW shows. But I
suspect that I'll still have to perform an capacitor-ectomy to get to
the maximum close-up with the built in ring flash.

Thanks,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Philip Homburg wrote:
In article ,
David J Taylor

wrote:
- well size 40,000 electrons (white)
- 12-bit digitisation, step size 10 electrons

Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12
= 4.88
electrons. At 25 electrons or more, shot-noise exceeds quantisation
noise.

Yes, in the lighter areas of the picture 12 bits is enough, agreed. But
where you see the quantisation noise is in the dark shadow regions.
Remember that the eye's response isn't linear, but more like log.

David