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aostling
02-07-2012, 10:38 PM
The Olympus OM-D E-M5 camera (announced today) has a unique feature which will be very useful for any subject requiring long time exposures. As described here http://www.dpreview.com/previews/olympusEM5/ the E-M5 has a Live Time mode. It is a time exposure just like the "T" setting on old film cameras – the exposure starts with one press of the shutter release button and does not terminate until the button is pressed a second time.

Until now a "T" exposure (whether with film or digital) has always been a guessing game: should the exposure for the Milky Way be five minutes, or twenty-five? The OM-D eliminates the guesswork, updating the live view on the rear OLED screen as the exposure progresses. When the exposure finally looks right, you terminate it.

This might be useful for auroras, too.




http://i168.photobucket.com/albums/u183/aostling/Screenshot2012-02-07at103547PM.png

Evan
02-08-2012, 01:16 AM
I doubt that will be useful for astrophotography. Even with a well exposed image not much will show up on the display.

This is about how a raw frame of the Dumbell nebula will look on the camera screen at proper exposure.

http://ixian.ca/pics9/astroraw1.jpg

This is how the same frame looks after downloading, adjusting brightness and exposure and resizing for this screen.

http://ixian.ca/pics9/astroraw2.jpg

Also, any stray light around is a bad thing. It will also gobble a lot of power. I keep the display turned off at all times.

I am curious how it is able to update the image without disturbing the ongoing exposure. That isn't compatible with how present sensors work.

BobL
02-08-2012, 03:19 AM
What would be perhaps more useful is if it were able to write the cummulative image to files, say every 5 seconds for whatever time T was determined to be of value. The one could pick and chose the exposure time (or sections of the image) without having to retake the image multiple times at differet exposures..

lynnl
02-08-2012, 10:49 AM
A couple of nights ago I recorded three weather related programs on the Science Channel: 1) Lightning, 2) Tornadoes, and 3) Floods.

The one on Lightning was really interesting. The photos were absolutely amazing. There were rare shots of lightning that is initiated at the ground and flashed upward. Also this phenomena they called "sprites" that extend upward into the stratosphere from the top of the cumulonimbus anvil. I'd never heard of that before.

One guy down in Fla has made lightning photography his sole purpose in life. He still prefers using film photography over digital.

Another interesting point, that I'd not heard before: Some of the most beautiful lightning activity is over Venezuela's Lake Maricaibo. Due the high methane accumulation in the atmosphere, from decaying vegetation in the lake, and methane from the oil drilling activity on the lake, some spectacular lightning displays take place almost nightly. ...visible for hundreds of miles.

Florida of course is the most active lightning area here in Nth America, but a region of equatoral Africa is far and away the most active in the world. According to that program, there's something like 50 or 60 lightning strikes per sq mile annually in that area.

dp
02-08-2012, 11:59 AM
I am curious how it is able to update the image without disturbing the ongoing exposure. That isn't compatible with how present sensors work.

Internal stacking comes to mind. No reason the camera can't do it as easily as a PC. It would require only three logical layers, and both difference and accumulative stacking are possible.

aostling
02-08-2012, 02:23 PM
The comments of Evan and Dennis are the only ones that I've seen on the blogosphere that have raised the issue of how the Live Time mode is implemented. Now you have got me curious too.

The best review of the OM-D so far is from Kirk Tuck, an Austin pro: http://visualsciencelab.blogspot.com/2012/02/olympus-fans-rejoice-om-d-is-real-and.html#links. He is the first to mention that it can do aspect ratios of 4:3, 3:2, and 16:9 without cropping. And as a Micro Four Thirds camera it can use every old SLR lens you have sitting on your closet shelf.

macona
02-08-2012, 03:35 PM
Another interesting camera for astrophotography is the Pentax K5 and the O-GPS1 adapter. The camera has the sensor mounted to a linear motor system built in to handle image stabilization. The gps module adds a feature where it will use the IS to track stars for long exposures.


http://www.pentaxforums.com/forums/pentax-k-5-forum/167500-k5-o-gps1-astrophotography-pix-experiences-namibia.html

Evan
02-08-2012, 05:55 PM
Internal stacking comes to mind. No reason the camera can't do it as easily as a PC

Six 10 second exposures stacked is nowhere near the same as one 60 second exposure. A long exposure accumulates photons that will not show up in a short exposure no matter how many you stack.

dp
02-08-2012, 08:59 PM
Six 10 second exposures stacked is nowhere near the same as one 60 second exposure. A long exposure accumulates photons that will not show up in a short exposure no matter how many you stack.


Of course - but the OP never mentioned quality, and there's just so many ways you can achieve timed exposure in optical devices that also produce movies.

http://tawbaware.com/imgstack.htm

aostling
02-09-2012, 01:42 AM
I am curious how it is able to update the image without disturbing the ongoing exposure. That isn't compatible with how present sensors work.

Just to be clear: the updating is not continuous, but occurs at discreet intervals during the long time exposure. The number of these updates is apparently set by the user, and there can be a maximum of twenty-five.

(I assume you read this in the dpreview preview, which is all the information that has been published about this feature so far.)

Could the sensor data stream be paused somehow during the live view update, then restarted without losing any prior information?

macona
02-09-2012, 03:36 AM
Sensors don't work like that. Think of each element as a bucket. When you open the shutter the bucket starts filling with light (charge). The longer the exposure the fuller the buckets get. At the end of the exposure the sensor is read out into memory. So the only time there is data coming from the sensor is at the end of the exposure. If you try to read while there is light on the sensor you get a bad image.

So, probably the best bet is the camera takes multiple short exposures and stacks them internally. This does not allow you to take advantage of the full capabilities of the sensor. Also, who knows what else it does to the data when it stacks it.

I don't think the camera would be very good for astrophotography (AP). Another problem is the sensor is a micro four-thirds size. At 16MP that means a real small pixel size which is not your friend with AP. Lastly the sensor is probably CMOS which is still behind CCD's. I would stick with an older Canon. Nikons are known as star eaters due to their aggressive anti-noise.

Evan
02-09-2012, 04:00 PM
Yep. You don't want a pixel less than 5 microns square and bigger is better. My 300D has 8 micron pixels and the 1000 has 5.3 micron IIRC. As they become smaller the pixel begins to approach the wavelength of light, especially red and IR light. One of these days I am going to rip the filter off my 300D.

aostling
05-22-2012, 09:00 PM
This review http://therovingphotographer.com/2012/05/olympus-om-d-e-m5-review-astrophotography/ reports that the Olympus OM-D can autofocus on Venus, or a bright star. I have never owned a camera that could do that.

Evan
05-22-2012, 10:48 PM
I sure would like that. On a related note, I have found out just how valuable it is to have a telescope frame with zero coefficient of expansion with temperature. I designed my six inch telescope with that in mind using a graphite/epoxy frame that exactly counteracted the few aluminum elements in the chassis that resulted in no change in focal length with temperature.

The ten inch mirror is sensitive to changes of even a few thousandths of an inch and with the all aluminum frame it sure would be nice to have auto focus. There is software that will do that in the computer so that is something on my list to check out.

No eclipse pics here. It was cloudy until a few minutes after sunset when it then cleared up completely.

elf
05-22-2012, 11:14 PM
I sure would like that. On a related note, I have found out just how valuable it is to have a telescope frame with zero coefficient of expansion with temperature. I designed my six inch telescope with that in mind using a graphite/epoxy frame that exactly counteracted the few aluminum elements in the chassis that resulted in no change in focal length with temperature.

The ten inch mirror is sensitive to changes of even a few thousandths of an inch and with the all aluminum frame it sure would be nice to have auto focus. There is software that will do that in the computer so that is something on my list to check out.



If you hadn't gone to all that work making sure temperature change didn't change the focus, you could have focused it with no moving parts using a heater and cooler :)