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Evan
08-25-2010, 03:35 PM
Yes, the Moon does have subtle colours. They are very difficult to photograph and I have been trying for a while. Last night was ideal since the smoke is finally gone. I had excellent conditions for photographing the Moon. To bring out the colours takes some very careful post processing including image stacking and separating the colours, then recombining just the colours separately from the detail in order to minimize artifacts in the final image. The very bright spots on the Moon are areas that produce strong backscatter. They are minerals that act like retroreflector paint that is used on signs.

http://ixian.ca/pics7/mooncolour.jpg

lynnl
08-25-2010, 03:43 PM
I thought it was all made of cheese! Darn! Learn something new every day.

Nice picture.

Is it just my imagination, or is the Harvest Moon about this time of every year (i.e. August) more prominent and spectacular to view? It has always seemed that way to me.

Evan
08-25-2010, 03:54 PM
It isn't your imagination. The Moon is closer to Earth this time of year during the full moon cycle.

Your Old Dog
08-25-2010, 03:58 PM
Great shot. Nice to hear you got through the threatening fire okay.

Evan
08-25-2010, 04:04 PM
Thanks. The fire isn't out but it is no longer a threat. The weather has shifted and the smoke is going west. I took this shot yesterday. The sun is sneaking under the heavy cloud over the fire and is filtered to orange by the smoke.

http://ixian.ca/pics7/fire20.jpg

I have to go now to get another blood test so I won't be answering more questions 'til evening.

airsmith282
08-25-2010, 04:07 PM
nice pic of the moon looks cool

Carld
08-25-2010, 05:32 PM
September or October is the Harvest Moon depending on which day of the month the full moon falls on, not August. The Harvest Moon is the full moon closest to the fall equinox. The full moons for each month have one or more names each month.

That is a beautiful photo of the full moon. The Moon is my favorite orb after the Earth and Sun of course.

lazlo
08-25-2010, 05:53 PM
Beautiful picture Evan! How many images did you stack?

macona
08-25-2010, 05:54 PM
Basically HDR Astrophotography?

DannyW
08-25-2010, 06:07 PM
Evan,

Do you get your daily APOD fix?

Link. (http://apod.nasa.gov/apod/)

Danny

A.K. Boomer
08-25-2010, 06:52 PM
That's got to be the most beautiful picture of the moon iv ever seen, youv got something to be proud of there and If I took that Id put my name on it too...

way way way cool...

gnm109
08-25-2010, 08:16 PM
Nice work, Evan. Thanks! This is a pleasant way to "moon" us. :D

Hal
08-25-2010, 08:24 PM
Evan

It always enjoyable to see your photos.
I guess you know there are suspose to be two moons on the 27/th.

Hal

Tony Ennis
08-25-2010, 09:09 PM
Very nice!

Evan
08-25-2010, 09:18 PM
If you are referring to the Moon and Jupiter being fairly close together then yes. But, it won't look anything at all like "Two Moons". Jupiter looks like a very bright star while the Moon is the same apparent size in the sky as the Sun. Also, the pair will still be about 5 to ten degrees apart at the closest apparent approach which isn't all that close (depending where you view it from on Earth). To give you an idea of how much 5 degrees is, the Moon subtends almost exactly one half degree. So, Jupiter will be at closest more than 10 moon widths distant.

Black_Moons
08-25-2010, 09:57 PM
Wow, pertty amazing photo of the moon evan, one of the best ones iv seen.

wierdscience
08-25-2010, 10:00 PM
Very nice photo Evan,glad the fires are dying down too.

Mad Scientist
08-26-2010, 11:20 AM
More moon pictures from NASAís files.
These were B/W photos that have had color added or contrast and brightness changed which brings out detail not seen before. Similar to Evanís photo.


http://tblnfilms.com/Theater1.html

http://www.youtube.com/watch?v=5muO2k0XrG8&feature=related

http://www.youtube.com/watch?v=4xLcatTHCSk&feature=related

http://www.youtube.com/watch?v=4xLcatTHCSk&feature=related

http://www.youtube.com/watch?v=MhEI2pvdtpM&feature=related

http://www.youtube.com/watch?v=Amnlc9McTBY&feature=related

http://www.youtube.com/watch?v=Amnlc9McTBY&feature=related

http://www.youtube.com/watch?v=qNZFiWoxgLE&feature=related

http://www.youtube.com/watch?v=kQIl_mzGuhI&feature=related

gnm109
08-26-2010, 11:35 AM
More moon pictures from NASA’s files.
These were B/W photos that have had color added or contrast and brightness changed which brings out detail not seen before. Similar to Evan’s photo.


http://tblnfilms.com/Theater1.html

http://www.youtube.com/watch?v=5muO2k0XrG8&feature=related

http://www.youtube.com/watch?v=4xLcatTHCSk&feature=related

http://www.youtube.com/watch?v=4xLcatTHCSk&feature=related

http://www.youtube.com/watch?v=MhEI2pvdtpM&feature=related

http://www.youtube.com/watch?v=Amnlc9McTBY&feature=related

http://www.youtube.com/watch?v=Amnlc9McTBY&feature=related

http://www.youtube.com/watch?v=qNZFiWoxgLE&feature=related

http://www.youtube.com/watch?v=kQIl_mzGuhI&feature=related


It appears that all of these videos have but one theme. All of our space exploration has been amed at suppressing information discovered during the travels.

I was interested until I heard the name, "Art Bell" ...I used to hear that show from time to time. He had a succession of kooks, wierdos and consipracy theorists to explain how everything has been "suppressed" because the government doesn't want us to know about the "aliens".....

The show is now done with another emcee and it's still the same. ......yawn.

Evan
08-26-2010, 11:50 AM
Art Bell? He is the undisputed and self proclaimed leader of the great mass of feckless, unwashed and intellectually impaired audience that comprise the 20 percent of Americans that believe Elvis is still alive and is being hidden by visiting Aliens. So why did he quit? Was he abducted?

gnm109
08-26-2010, 12:20 PM
Art Bell? He is the undisputed and self proclaimed leader of the great mass of feckless, unwashed and intellectually impaired audience that comprise the 20 percent of Americans that believe Elvis is still alive and is being hidden by visiting Aliens. So why did he quit? Was he abducted?


The way I heard it, Bell ran out of kooks....I can't believe that, however. More recently, He said on his program on one of his last broadcasts that he married a Filipina and she wasn't able to come to the U.S. so he stayed there. This was, he said, part of a conspiracy to keep him out of the U.S. He actually broadcast from there for a while.

The colorization process that you are using so very nicely shows a great more detail. That's nice. Unfortunately, the kooks use it as "proof" that things are withheld and suppressed. Instead of more detail, they see more conspiracy.

Did you notice that in the introduction to the first video above, they listed all of the members of our space crews who had died so "needlessly"? Good lord, do they not know how dangerous rocketry and space exploration can be?

I learned about the dangers of rocket engines while working on a test stand many years ago. We don't need kooks like Bell and his ilk to tell us that people involved in the program died needlessly. There is always danger lurking around machinery.

Personally, I think all of these announcers are smoking something when they broadcast.

dp
08-26-2010, 12:30 PM
Art Bell? He is the undisputed and self proclaimed leader of the great mass of feckless, unwashed and intellectually impaired audience that comprise the 20 percent of Americans that believe Elvis is still alive and is being hidden by visiting Aliens. So why did he quit? Was he abducted?

He's a nutter. He's quit multiple times and keeps crawling back. He's the moron who promoted the "companion" to the comet Hale Bopp using a shopped photo taken by Dr. David Tholen at the U of Hawaii. Tholen demolished the notion by presenting the original photo including background stars, and described the impossibility of that scene being taken by two different people at different places. The only place in the universe that photo can have been taken was from the top of a volcano in Hawaii, and Tholen was driving the telescope at that time.

Too_Many_Tools
08-26-2010, 12:54 PM
The way I heard it, Bell ran out of kooks....I can't believe that, however. More recently, He said on his program on one of his last broadcasts that he married a Filipina and she wasn't able to come to the U.S. so he stayed there. This was, he said, part of a conspiracy to keep him out of the U.S. He actually broadcast from there for a while.

The colorization process that you are using so very nicely shows a great more detail. That's nice. Unfortunately, the kooks use it as "proof" that things are withheld and suppressed. Instead of more detail, they see more conspiracy.

Did you notice that in the introduction to the first video above, they listed all of the members of our space crews who had died so "needlessly"? Good lord, do they not know how dangerous rocketry and space exploration can be?

I learned about the dangers of rocket engines while working on a test stand many years ago. We don't need kooks like Bell and his ilk to tell us that people involved in the program died needlessly. There is always danger lurking around machinery.

Personally, I think all of these announcers are smoking something when they broadcast.

More like their listeners...the broadcasters give what the public wants.

I consider that you can learn a lot about the public by what people watch and listen to.

The immense popularity of "reality tv" in recent years has greatly disappointed me...I would like to think the public is more intelligent the product shows otherwise.

TMT

gnm109
08-26-2010, 01:03 PM
More like their listeners...the broadcasters give what the public wants.

I consider that you can learn a lot about the public by what people watch and listen to.

The immense popularity of "reality tv" in recent years has greatly disappointed me...I would like to think the public is more intelligent the product shows otherwise.

TMT


Invariably, you take the other side. You are blaming the audience for the crap that is on the radio and TV.

Well, if I had anything to do with the programming, there wouldn't be much left to broadcast.

Evan
08-26-2010, 01:45 PM
The colorization process that you are using so very nicely shows a great more detail. That's nice. Unfortunately, the kooks use it as "proof" that things are withheld and suppressed. Instead of more detail, they see more conspiracy.

It isn't colorization. Those are the actual colours enhanced enough to see. I didn't do that much enhancing either.

All I do is take the original colours recorded by the camera and multiply the colour values by the same amount across the image. There is no selective manipulation of any colour and all the colours are present in the image to begin with.

Here is a simple two step manipulation of a single frame. First increase the saturation of the existing colours, then increase the image contrast. The rest of the process is only a matter of improving the resolution by using information from multiple frames to build up a more detailed single frame image.

http://ixian.ca/pics7/mooncolour2.jpg

Mad Scientist
08-26-2010, 04:50 PM
Those are the actual colours enhanced enough to see. I didn't do that much enhancing either.
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I have no doubt that your colors are probably quite close to being correct. But if you can come up with these colors wouldn't you think that NASA should be able to do the same thing? So way do they continue to show us boring b&W pictures or pictures that over or under exposed?

Would not the astronauts have had a close up view of these colors? Yet one astronaut when asked to describe what the moon looked like said "every thing is shades of gray, like plaster of paris."??? He was 60 miles away at the time thus I would think that would have been close enough to describe some color.

Someone here is not telling the truth and I suspect it is NASA.
So what is it that they are trying to hide from us?

Evan
08-26-2010, 06:26 PM
Someone here is not telling the truth and I suspect it is NASA.
So what is it that they are trying to hide from us?


They aren't hiding anything. My colours are intentionally understated but match theirs quite well.

http://apod.nasa.gov/apod/ap060216.html

The human eye is not very sensitive to colour, especially if the colour values are on a bright sunlit surface.

gnm109
08-26-2010, 06:29 PM
They aren't hiding anything. My colours are intentionally understated but match theirs quite well.

http://apod.nasa.gov/apod/ap060216.html

The human eye is not very sensitive to colour, especially if the colour values are on a bright sunlit surface.


I guess we are having a semantic problem. If you are bring out colors that are hidden, is that not colorization?

aostling
08-26-2010, 06:31 PM
It isn't colorization. Those are the actual colours enhanced enough to see.

Your enhanced image shows a definite green component. Not green cheese, I'm sure, but what might account for this?

Evan
08-26-2010, 06:40 PM
I guess we are having a semantic problem. If you are bring out colors that are hidden, is that not colorization?


The colours aren't hidden, just desaturated. The blue is Titanium compounds for instance. I am sure that you can see the difference between steel, aluminum and stainless steel. Those are very weak colour differences yet they all look like a shade of grey.
edit: The usual definition of "colorization" is to add color to an image that is at the discretion of the image manipulator. I don't do that.


Your enhanced image shows a definite green component

Most likely the colour balance setting of the camera. I can use the raw images but it is a little more work. To tell the truth I forgot I was also taking raw as well as jpeg. It will still depend on how the sensor in my camera reacts compared to others.

dp
08-26-2010, 07:02 PM
Here's a tutorial on pulling the colors from lunar photos using Photoshop although the specific tools are common to many image editors.

http://www.atalaia.org/filipe/moon/colorofthemoon.htm

aostling
08-26-2010, 07:05 PM
Most likely the colour balance setting of the camera.

That makes sense. On many cameras you can set the color temperature, e.g 6000 K. I wonder what would be appropriate value for photographing the moon, an object in direct sunlight unattenuated by any atmosphere?

Evan
08-26-2010, 07:15 PM
an image in direct sunlight unattenuated by any atmosphere?


I don't know about you but we have air here. :D

aostling
08-26-2010, 08:20 PM
I don't know about you but we have air here. :D

I was thinking of what colors the Apollo crew might have seen as they approached. To record this you might have to crank up the camera's color temperature as high as you can set it.

[edit] Well, maybe not so high as that. I just checked, and my Olympus E-P2 allows a setting as high as 14,000 K. Direct sunlight on earth has a temperature of about 6,500 K. I don't know what it would be on the moon's surface.

Todd Tolhurst
08-26-2010, 08:30 PM
That makes sense. On many cameras you can set the color temperature, e.g 6000 K. I wonder what would be appropriate value for photographing the moon, an object in direct sunlight unattenuated by any atmosphere?

The moon is illuminated by sunlight. Normal daylight color balance is appropriate.

Todd Tolhurst
08-26-2010, 08:33 PM
I guess we are having a semantic problem. If you are bring out colors that are hidden, is that not colorization?

Colorization is the addition of colors to monochrome images. What Evan has done is to crank up the natural coloration in his moon images. The colors weren't hidden, just very subtle. Evan has intensified them.

dp
08-26-2010, 09:03 PM
I was thinking of what colors the Apollo crew might have seen as they approached. To record this you might have to crank up the camera's color temperature as high as you can set it.

[edit] Well, maybe not so high as that. I just checked, and my Olympus E-P2 allows a setting as high as 14,000 K. Direct sunlight on earth has a temperature of about 6,500 K. I don't know what it would be on the moon's surface.

They said it looks pretty much like we see it from Earth. The colors are very subdued and the luminosity is very high which causes our eyes to stop down, further cloaking the colors. I've held a moon rock in my hand it to looked like beach sand.

jkilroy
08-26-2010, 10:43 PM
Evan, can you give some detail about your setup? ISO, F stop, shutter etc. What kind of lens? I assume the image was bright enough to not need a tracking mount. Nice shot.

Evan
08-26-2010, 11:17 PM
The black body temperature of the Sun is given as 5780K. That isn't the entire story though. The chromaticity of the Sun doesn't follow a black body curve. It has a significant peak at about 500nm which happens to be green but it also has a significant dip at around 400nm which is blue. This produces a spectrum that is shifted toward pink as seen in space.

Things really change when sunlight enters the atmosphere. Oxygen and Nitrogen produce Raleigh scattering which preferentially scatters blue light. This effect can be seen even with very bright high colour temperature light sources such as my "Flashlight-O-Death".

In this image the flashlight is held above the camera and the scattering of blue light is clearly visible.

http://ixian.ca/pics7/flashlight3a.jpg

This has several consequences to the average colour temperature of sunlight as seen on Earth. The Sky is blue because of Raleigh scattering. Anything illuminated by direct sunlight outside has an effective colour temperature of 5780K minus some blue but plus a lot more blue from sunlight that is being scattered from horizon to horizon. The net result on a clear day is an effective colour temperature of about 6500K. If an object is in shadow the the majority of light is reflected from nearby objects PLUS the contribution from all that scattered sunlight from the blue sky. The effective colour temperature in that case is around 10,000K.

When photographing something bright such as the Moon with a telescope there is only the filtering effect of Raleigh scattering. Scattering still takes place in a moonlit sky but it isn't obvious in a very short exposure. Therefore, a short exposure will show a downward shift in colour temperature.

A long exposure is a different matter. Then the Raleigh scattering becomes very apparent. This is a time exposure of Orion at midnight with a full Moon in the sky.

http://metalshopborealis.ca/pics5/orionmoon.jpg

Evan
08-26-2010, 11:23 PM
The setup is 6" f5 mirror with the camera body at prime focus. No lens, no chromatic abberation. ISO 200 and shutter of 1/1600 using Canon 350D on an equatorial mount. Tracking is a requirement because of the image movement during 30 frames in 60 seconds.

aostling
08-27-2010, 12:17 AM
I've held a moon rock in my hand it to looked like beach sand.

In the summer of 1964 I had a summer job at JPL. On a fateful day all interested employees gathered in the auditorium to view the live feed of the images being sent by Ranger 7 as it headed for its planned crash landing on the moon. All previous Rangers had failed, so it was with great joy that we witnessed the success of this spacecraft. Those images were in monochrome.

Where did you get your hands on a moon rock!? Handling that must have been quite an experience.

dp
08-27-2010, 12:26 AM
Where did you get your hands on a moon rock!? Handling that must have been quite an experience.

It was on display at the Griffith Observatory in Los Angeles at a time when I was hand grinding an 8" mirror with the astronomy club. '71 or so. It was inside a protective container, of course, but there in my hands was a piece of the moon.

Evan
08-27-2010, 03:03 AM
I have also touched a piece of the Moon at the Smithsonian. For a while back in the 70s they had an exhibit with a Moon rock embedded in a chunk of what looked like Wood's metal. About 2 sq inches were sticking out. The display was inside an opening that was the centre of a massive solid metal casting in the shape of a inverted horseshoe. There was just enough room to put your hand in the opening and touch the rock from either side.

dp
08-27-2010, 03:33 AM
We need a "green with envy" emoticon :). I came this >< close!

By the way - a funny thing happened to that first 8" mirror. One of my kids toppled it from the 35 gallon barrel I used for the grinding stand and chipped the rear edge, but the final death came when I fell asleep while it was on the pitch lap where it stuck fast. I think I finally threw it away after 10 years of trying to get them apart.

Evan
08-27-2010, 07:03 AM
I snagged an interesting image with my little Canon TX1 yesterday evening.

http://ixian.ca/pics7/lightning.jpg

jkilroy
08-27-2010, 11:22 AM
Thanks Evan, Did you space the images out of 60 seconds for a reason other than vibration? I assume you locked up the mirror?

Evan
08-27-2010, 12:26 PM
I used 2 second spacing to allow the atmosphere time to shift slightly between photos. This presents slightly different information which is what allows the gain of information to take place in the stacking process. The Hubble must use a different technique since it doesn't have any atmospheric refraction. The Hubble is pointed ever so slightly to a different direction between exposures so that light that was falling between pixels in the sensor grid is then captured.

Image stacking has long been used to improve performance even when film was used. Film was limited to two or three images stacked because of the unavoidable density increase from stacking several negatives for printing. Digital has no such limitation since the data is "stacked" mathematically.

The Canon 300D and the 350D have no detectable mirror vibration so I don't bother with locking the mirror.

jkilroy
08-27-2010, 07:33 PM
All SLR type cameras have mirror vibration, that is quite detectable, but I suspect with such fast shutter speeds and time between exposures its not an issue.

Evan
08-27-2010, 08:31 PM
The mirror in the Canon camera is much smaller and lighter than in a 35mm camera. The sensor is 2/3 the size of a 35mm frame so a mirror that fits that aperture is about 1/4 the weight of a standard 35mm SLR.

:nitpick avoidance: The mirror has less area and so can also be made thinner.

DICKEYBIRD
08-27-2010, 09:52 PM
I love this place! :D

aostling
08-27-2010, 10:30 PM
All SLR type cameras have mirror vibration, that is quite detectable

That is generally true. Now Sony has announced a new type of camera, the SLT http://en.wikipedia.org/wiki/Single-lens_translucent_camera. It has a mirror but it doesn't move out of the way, eliminating this source of vibration. The advantage of a Single Lens Translucent camera over SLR and EVF cameras will mainly be in shooting video or burst sequences of fast action while maintaining autofocus between each shot.

http://www.luminous-landscape.com/reviews/cameras/sony-a55-preview.shtml is a rather lengthy review.

Evan
08-27-2010, 10:41 PM
The advantage of a Single Lens Translucent camera over SLR and EVF cameras....

Not to overlook the fact that you will be able to use the viewfinder even while shooting as long as the exposure isn't very long. The brightness may be reduced slightly in video mode but the time that the light path is blocked will no more than the actual exposure time as a percentage of the total time. The effective maximum shutter speed of my TX1 using the CHDK software is a ridiculous 1/33,000 second. That would probably be good enough to take videos of an atomic explosion if the sensor didn't melt.

aostling
08-27-2010, 11:55 PM
The effective maximum shutter speed of my TX1 using the CHDK software is a ridiculous 1/33,000 second. That would probably be good enough to take videos of an atomic explosion if the sensor didn't melt.

I had no idea you could get a shutter speed that fast. I guess you would need a luminous subject, like the sun or a puddle in a welding arc. Have you thought of any non-nuclear subjects you could "freeze" this way?

dp
08-28-2010, 12:02 AM
I'm not sure what the advantage is of a moving mirror in a digital camera. The need in a film camera is driven by the necessity to shield the film at all times but a digital camera has the imaging surface constantly exposed. My Sony has a digital eyepiece as well as a large viewing screen as most do. I actually prefer the eyepiece most of the time as it's easier to see what is in your frame. The display includes all the metadata the full screen previewer has.

Anyway, there's surely a reason for the mirror and I'd definitely like to know what it is. I'm in the buying mood for a new camera! This time a camera that is controllable from my computer, and one that uses standard lens rings - Nikon or threaded, so long as I can swap out lenses.

Evan
08-28-2010, 12:05 AM
It should make it easy to accurately measure very high rpm spindle rotation by using a perforated disc to interrupt the light from a high power LED. The amount of angular movement can be accurately measured for a given shutter speed.

I am also interested in further pursuing the oscillations of falling water droplets to try and acertain why they seem to follow 12 root of two law. This is an area that currently remains unanswered and as far as I can figure out unexplored and perhaps even unknown to researchers in the field.

Evan
08-28-2010, 12:17 AM
Anyway, there's surely a reason for the mirror ...

The rational is to provide the same operating experience as a film camera as well as accomodating the full line of existing lenses from film SLRs. Manual focusing on a digital viewfinder isn't nearly good enough for most demanding applications. All of my astrophotos are manually focused which wouldn't be possible on a digital viewfinder.

dp
08-28-2010, 12:21 AM
You've just jostled one of my adaptive gray cells. I wonder what effort would be involved in converting the digital camera video stream to an audio stream as in your audiolumitron. Seems like a simple job to place a photocell over the screen of a digital camera and see what comes out. You get video and audio in the product.

aostling
08-28-2010, 12:36 AM
Anyway, there's surely a reason for the mirror and I'd definitely like to know what it is.

According to this http://www.dpreview.com/reviews/sonyslta55/ the main purpose of using a pellicle mirror is to allow use of phase-detection autofocus, which is generally more accurate than the contrast-detection autofocus used in non-mirrored cameras. I'm sure it's mostly this, and not the ability to use heritage lenses from film cameras. My Olympus E-P2 can do that -- I have adapters for Leica, M42, and Minolta MD lenses which I regularly mount on the Micro Four Thirds Camera.

Dennis, since you have several good old lenses you might consider (in your announced search for a new camera) one of these: http://www.dpreview.com/reviews/olympusepl1/. The heritage lenses would have to be manually focused, but the M4/3 cameras make this easy with a magnification boost of the screen image.

dp
08-28-2010, 01:09 AM
I was just reading the specs on a Nikon digital which is what all my film bases SLR's are, and damn if they don't have 14 megapixel sensors. That puts them up into the D size drawing range. That's impressive.

I'm not sure a 35mm film lens is a good fit for the very small sensors. A lot of collected light will be wasted as it will be cast off the sensor. But I didn't expect to be able to revive my beloved 105mm portrait lens so easily :). I'm more interested in the possibility of building a new lens farm for the new media, assuming I'm ever able to retire again.

And speaking of digital photography, and no intention to hijack the thread, but is everyone as burned out on HRD photos as I am? I crave natural landscapes!

Evan
08-28-2010, 01:25 AM
I'm sure it's mostly this, and not the ability to use heritage lenses from film cameras

On the contrary, many older lenses do not have autofocus. The only way to focus them is through the lens.

dp
08-28-2010, 01:41 AM
On the contrary, many older lenses do not have autofocus. The only way to focus them is through the lens.

Yep - I don't like autofocus, in fact, since it always seems to focus on something I'm not real interested in. None of my SLR's had AF.

aostling
08-28-2010, 02:03 AM
I'm not sure a 35mm film lens is a good fit for the very small sensors. A lot of collected light will be wasted as it will be cast off the sensor.

That's true, the M4/3 sensor area (225 mm2) and the Canon APS-C sensor area (329 mm2) are both small compared to the 35mm sensor area 864 mm2).

But the 2x crop factor makes some of the lightest Minolta MD telephotos attractive for use on my Olympus E-P2. I also have the 500mm f8 Rokkor-X mirror lens -- this weighs only 21 ounces and provides a 1000mm equivalent field of view. I'm in the process of adapting an after-market tripod collar for it; since it is too cantilevered and vibration prone if supported off the camera tripod socket.

Your Nikkor 105mm f2.5 is one of the few lenses Nikon never needed to change. Its sharpness is legendary.

ldn
08-28-2010, 08:43 AM
I'm not sure what the advantage is of a moving mirror in a digital camera. The need in a film camera is driven by the necessity to shield the film at all times but a digital camera has the imaging surface constantly exposed.

Anyway, there's surely a reason for the mirror and I'd definitely like to know what it is. I'm in the buying mood for a new camera! This time a camera that is controllable from my computer, and one that uses standard lens rings - Nikon or threaded, so long as I can swap out lenses.

Hi DP.

The mirror in an SLR is not intended to shield the film from light. Every SLR and DSLR has a separate shutter located just forward of the film plane that serves that purpose. The mirror is too big and slow to be an accurate shutter, and if you think about it's motion (swinging up and then back down), it would cause the lower portion of the film to have more exposure.

It is always better in a digital camera to use a normal shutter to shield the sensor from light. The sensor gives a better result if there aren't stray charges that have that have to be electrically cleared. You can also make better sensors if you don't have to devote a percentage of the sensor's surface area to the "virtual shutter" function.

The advantage of a moving mirror is that it allows all the light to either reach the viewfinder OR reach the film plane/sensor. Light is precious and should be conserved at all times. A half (or 30%) silvered mirror throws away a lot of light that could otherwise be used to good benefit.

In a camera with half-silvered mirror your expensive f-2.8 lens effectively becomes an f-4 lens.

Also, as Evan mentioned, manual focus requires a real optical image and as much light as you can get.

Those are some reasons why moving mirrors and real mechanical shutters are still desirable.

I understand that some recent DSLR's are hybrids and can do live preview and video with a constantly exposed sensor, but the physics hasn't changed and the same tradeoffs still apply.