I would imagine 5 years to become proficent in astropohotography

[JBW]

This shot is all about practicing the craft. Getting a good focus. Converting to black and white. Keeping the stars roundish.

Sony Alpha a58 ~ Tamron 90mm 272E ~ ISO 6400 ~ shutter speed 4s. ~ F/4.5 ~ 124 color frames, 60 darks, 50 bias. Stacked in DSS

[george013]

This shot is all about practicing the craft. Getting a good focus. Converting to black and white. Keeping the stars roundish.

Sony Alpha a58 ~ Tamron 90mm 272E ~ ISO 6400 ~ shutter speed 4s. ~ F/4.5 ~ 124 color frames, 60 darks, 50 bias. Stacked in DSS

Looks good. But I don't understand it.

George

[Shadowman]

Nice capture.

[JBW]

Looks good. But I don't understand it.

George

Let me attempt to explain. Astrophotography is often called the most complex photography. Getting a sharp focus is hard in DSLR AP because between my camera and the stars is the atmosphere which nicely distorts things. The second prtoblem is the constant movement of the heavens. Without constant tracking you must live to the rule of 500. Take your focal length and divide it into 500. The answer is the number of seconds you can continuously shoot before you start seeing star trails.

Colors are incredibly faint. Many are shades of red which most DSLRs' cut off.

Because the light is so dim stacking is used to bring out detail. The more you shoot the more you see. Darks cut out noise as do bias.

Within this shot there are at least 25,000 separate stars and at least one galaxy.

Tonight if the clouds cooperate I'll try to get a good shot of the Andromeda galaxy. it will require as many color frames as I can get (200 to 400) 50 dark and another 50 bias. Then after a quick tweak in Capture 1 I will move everything into Deep Sky Stacker and after 2 to 4 hours I will have one nicely stacked shot to put back into Capture 1 to do a whole bunch more pp.
Brian

[george013]

Let me attempt to explain. Astrophotography is often called the most complex photography. Getting a sharp focus is hard in DSLR AP because between my camera and the stars is the atmosphere which nicely distorts things. The second prtoblem is the constant movement of the heavens. Without constant tracking you must live to the rule of 500. Take your focal length and divide it into 500. The answer is the number of seconds you can continuously shoot before you start seeing star trails.

Colors are incredibly faint. Many are shades of red which most DSLRs' cut off.

Because the light is so dim stacking is used to bring out detail. The more you shoot the more you see. Darks cut out noise as do bias.

Within this shot there are at least 25,000 separate stars and at least one galaxy.

Tonight if the clouds cooperate I'll try to get a good shot of the Andromeda galaxy. it will require as many color frames as I can get (200 to 400) 50 dark and another 50 bias. Then after a quick tweak in Capture 1 I will move everything into Deep Sky Stacker and after 2 to 4 hours I will have one nicely stacked shot to put back into Capture 1 to do a whole bunch more pp.
Brian

Taking 200 to 400 pictures of 4s is taking minimal 800 to 1600 seconds. Deep Sky Stacker is adjusting them?
What do you mean "124 color frames, 60 darks, 50 bias"

George

[MrB]

This sort of procedure doesn't appeal to me, Brian, but just curious - in the clear image of post #1 is there an object or group that non-astros might have heard of?

Cheers.
Philip

[JBW]

Taking 200 to 400 pictures of 4s is taking minimal 800 to 1600 seconds. Deep Sky Stacker is adjusting them?
What do you mean "124 color frames, 60 darks, 50 bias"

George

color frames are your everyday shots. Darks are when you put the lens cap on and shoot give or take 50 shots at the same settings and temperature as your colour shots. Bias shots are with the lens cap on and your shutter speed cranked up as fast as it will go.

Yup DSS lines them up and does all sorts of magical stuff I can't even begin to explain.

[JBW]

This sort of procedure doesn't appeal to me, Brian, but just curious - in the clear image of post #1 is there an object or group that non-astros might have heard of?

Cheers.
Philip

Nope. Just a tiny bit of the immense universe. But I did just post a SOOC of the Andromeda galaxy. Hopefully tomorrow I'll be able to process it and then post to show the difference.

[george013]

color frames are your everyday shots. Darks are when you put the lens cap on and shoot give or take 50 shots at the same settings and temperature as your colour shots. Bias shots are with the lens cap on and your shutter speed cranked up as fast as it will go.

Yup DSS lines them up and does all sorts of magical stuff I can't even begin to explain.

A dark for the noise reduction. But why 50. And what are the bias shots for?

I'm asking for I just made my first startrail picture on my holiday in Sardinia. Clear sky and no close neighbors.

George

[JBW]

A dark for the noise reduction. But why 50. And what are the bias shots for?

I'm asking for I just made my first startrail picture on my holiday in Sardinia. Clear sky and no close neighbors.

George

You have made two mistakes George. (1) you think I understand what I'm doing (2) you forget I'm the least technical person in this club.

But here's the info you were curious about with a link to help you sort things out.

'The Bias frames are very short exposures made with no light reaching the sensor. With a DSLR, they are taken at the fastest possible shutter speed and lowest possible ISO, with the body, lens or telescope capped. There purpose is to remove the read noise that is present and roughly the same in every frame. You should take a large number of Bias frames (~50), and DSS will average them to create a master Bias frame, which it will subtract from every other frame used in the image processing. You don't need to take new Bias frames very often, just once or twice a year, because the read noise doesn't change much over the life of a DSLR. The Bias frames also contain the "Offset" signal, an elevated baseline added to every image by the camera electronics. With my Canon 350D, the Offset signal is 255 counts out of a maximum range of 4,096 counts (12-bits). So subtracting the Bias frame from every other shot removes the Offset signal as well as the read noise. Dark frames are made at the same exposure time and ISO as the subject light frames, but with no light reaching the sensor. They should also be made at approximately the same temperature as the light frames. Normally they are interspersed in the imaging session, or taken at the end of the imaging session. Their purpose is to remove the thermal noise from the light frames. Normally you want between 10 and 20 dark frames during each imaging session, and if you use multiple exposure time or ISO values for the light frames during a session, you must acquire sets of dark frames to match the exposure and ISO of each set of light frames. The master Bias frame is subtracted from each of the dark frames before they are combined to create a master dark frame. Flat frames are short exposures made through the imaging optics with the camera pointed at an evenly illuminated field. They record uneven field illumination due to vignetting caused by the optics and due to partial obstructions in the light path such as dust particles on the sensor, and they are use d to remove that uneven field illumination from the light frames. Flat frames can be taken by pointing the camera at the twilight sky, by covering the aperture with a smooth, translucent, light colored material such as a t-shirt, or by covering the aperture with a specially constructed "light box", and making 15 to 20 exposures in Av mode. They must be taken with the camera in exactly the same orientation relative to the telescope as used for the light frames, so they are usually taken at the beginning or end of each imaging session. ISO isn't critical but most people use the same ISO as used for the light frames. The master offset frame is subtracted from each flat frame, and then the flat frames are averaged to make a master flat frame. The master flat frame is divided into each of the light frames, after the master Bias and master Dark frames have been subtracted from the light frames. Applying the Offset, Flat and Dark frames to the subject frames is called calibration. A few months ago I made a photo documentary of the calibration process on my PBase site, and you can find it here: http://www.pbase.com/dtreed/how_its_doneexternal link Click on the images to read the descriptions. Don'
http://photography-on-the.net/forum/...d.php?t=876394

But please do keep asking me questions because it helps kme to sort things out too.

[george013]

I always make mistakes.


I do understand now. I'll read that link later. Interesting.
You don't need that much dark frames. If you download Dead Pixel Tester you can see where they're used for.
I just looked at my star trail pictures and found that when I move the left slider to the right a little I get a much better result. I think I do the same as your dark frames.

George

[JBW]

I always make mistakes.


I do understand now. I'll read that link later. Interesting.
You don't need that much dark frames. If you download Dead Pixel Tester you can see where they're used for.
I just looked at my star trail pictures and found that when I move the left slider to the right a little I get a much better result. I think I do the same as your dark frames.

George

One of the first rules of pp in astro photography is that it's all about what works for you. There are many excellent AP who don't use dark frames.

[Manfred M]

Brian - I suspect there must be an explanation somewhere, but it strikes me that the bias frames and the dark field shot are effectively capturing a portion of the same data. The bias shot will capture base circuitry noise. In addition to this the darkfield shot will capture the same base data PLUS the effects of noise generated by heating the camera circuitry (including the sensor)and the additional noise introduced from this component of the operation of the camera over a specific period of time.

I understand the dark field subtraction, but the bias images sound like one is compensating for the same problem twice which would in fact decrease image quality.

[JBW]

Brian - I suspect there must be an explanation somewhere, but it strikes me that the bias frames and the dark field shot are effectively capturing a portion of the same data. The bias shot will capture base circuitry noise. In addition to this the darkfield shot will capture the same base data PLUS the effects of noise generated by heating the camera circuitry (including the sensor)and the additional noise introduced from this component of the operation of the camera over a specific period of time.

I understand the dark field subtraction, but the bias images sound like one is compensating for the same problem twice which would in fact decrease image quality.

Manfred as you well know I'm no wiz kid. I do know that AP is counter intuitive and seriously complex. My shots look better when I use both. But i have seen some serious eye candy where neither were used.

[Wavelength]

Good one

[James G]

I think that the darkframe,as opposed to the bias frame, enables noise reduction linked to temperature. As the camera warms during shooting, the noise ' forum's changes. My dark frames are taken using the same exposure times as the normal exposures.

[steveg4iwr]

This shot is all about practicing the craft. Getting a good focus. Converting to black and white. Keeping the stars roundish.

Sony Alpha a58 ~ Tamron 90mm 272E ~ ISO 6400 ~ shutter speed 4s. ~ F/4.5 ~ 124 color frames, 60 darks, 50 bias. Stacked in DSS

If you become competent in 5 years you can then progress to becoming good. I have been involved on photography of various disciplines for about 50 years and would say I’m competent. There are some fantastic imagers out there that I will never be as I don’t have that final bit of skill/imagination to give me that edge. Good luck and I hope you make your 5 year goal.


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[JBW]

If you become competent in 5 years you can then progress to becoming good. I have been involved on photography of various disciplines for about 50 years and would say I’m competent. There are some fantastic imagers out there that I will never be as I don’t have that final bit of skill/imagination to give me that edge. Good luck and I hope you make your 5 year goal.


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This is one of those marvelous obsessions where the journey is more fun than the arrival.