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Teaching an old dog new tricks from 35mm to CCD/CMOS

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#1 lee38367

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Posted 19 January 2021 - 11:23 PM

Good evening folks,

Bear with me as this is my first post on CN after months of reading and acquiring equipment.

So to lay some foundations here... I'm an old film guy that got out of the hobby long ago. In my heyday it was gas hypered Fuji 800 and hand guiding 90 min exposures. My goodness it has come a long way !!!

The equipment I have picked up from you folks so far are a CPC 1100, Heavy Duty Wedge, Celestron 80mm guide scope and I just picked up an AT102ED to replace the 80mm to use as double duty guide/imaging. Various eyepieces and visual accessories.

My camera is a Cannon T3i non modded, and a ZWO ASI290MC Guide/Planetary imager. I have rear cell F6.3, OIII and Broadband. 

Of course being and old film guy, so far all I have accomplished is a few experiments with Orion by simply varying exposure times and rudimentary stacking a few frames. I see a ton of post talking about Flats, Darks, Lights and assuming these are frames to somehow integrate into a "stacked" image. I've tried to use some software packages mentioned in here to not much avail... I just cant seem to understand some of the features, but that's another post another day... Right now, I'm tryin to find what I would call a basic primer on Darks, Flats, and the frames needed to integrate into a picture, and their purpose.

I've searched through the forums till my eyes are sore and read a lot of conversation talking about taking them, but cant seem to find that perfect explanation of them... 

Can ya'll help explain or point me to a thread that goes over them in detail?

 

Many Thanks and Clear Skies,
 
Lee

 

 


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#2 aleigh

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Posted 19 January 2021 - 11:48 PM

Not exactly what you asked, but I found "The Deep-sky Imaging Primer" by Charles Bracket to be well worth the $25.


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#3 Dave_L

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Posted 19 January 2021 - 11:53 PM

Hi Lee,

 

If you are running that ZWO, do you have it connected to a laptop, and what software are you using to acquire and tweak images? SharpCap seems to be one of the popular choices. It will acquire and "stack" images and allow you to play with exposure, white balance and all those fun adjustments. And then save the stacked images as a JPG (or whatever) so you can share with friends or post here on CN! Clear skies! 


Edited by Dave_L, 19 January 2021 - 11:54 PM.

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#4 SnowWolf

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Posted 20 January 2021 - 12:05 AM

 

 

I've searched through the forums till my eyes are sore and read a lot of conversation talking about taking them, but cant seem to find that perfect explanation of them... 

Can ya'll help explain or point me to a thread that goes over them in detail?

 

Many Thanks and Clear Skies,
 
Lee

 

 

A brief guide:

 

https://practicalast...bration-frames/


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#5 lee38367

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Posted 20 January 2021 - 12:08 AM

Hi Lee,

 

If you are running that ZWO, do you have it connected to a laptop, and what software are you using to acquire and tweak images? SharpCap seems to be one of the popular choices. It will acquire and "stack" images and allow you to play with exposure, white balance and all those fun adjustments. And then save the stacked images as a JPG (or whatever) so you can share with friends or post here on CN! Clear skies! 

So far I've only used the ZWO to snap a few planetary images, it was my understanding it wasnt well suited for DSO's. I use my T3i for DSO's and so far have played with SharpCap, still very much learning that package, but was more interested in getting the "data" taken and how Darks, Flats, Lights, etc... come into play. We havent had many good nights for viewing and the setup is a beast to move in and out until i can cobble together an observatory to keep it in.



#6 clint.ivy

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Posted 20 January 2021 - 12:08 AM

Hey Lee,

Here’s a quick primer on calibration frames (as they are collectively known) that’s decent: https://nightskypix....bration-frames/

 

Bias Frames: suppress read out noise (electronic noise caused by camera reading the sensor data)

Dark Frames: suppress the sensor thermal noise from your light frames

Dark Flat Frames: suppress the sensor thermal noise from your flats

Flat Frames: suppress vignetting (or other constant light uniformity issues) and dust in the image train from your lights

 

IMHO, getting your flats properly exposed is the biggest challenge and can cause the most problems when they’re not right. (Don’t misunderstand, getting any of your calibration frames ‘wrong’ leads to problems but for me flats have been the biggest issue)

 

 

Clear Skies!


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#7 lee38367

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Posted 20 January 2021 - 12:13 AM

If they had a "love" button instead of a like... you'd get it !!!! That was one of the best explanations of purpose and "how to" I've run across... Thanks so much !!!



#8 lee38367

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Posted 20 January 2021 - 12:18 AM

Hey Lee,

Here’s a quick primer on calibration frames (as they are collectively known) that’s decent: https://nightskypix....bration-frames/

 

Bias Frames: suppress read out noise (electronic noise caused by camera reading the sensor data)

Dark Frames: suppress the sensor thermal noise from your light frames

Dark Flat Frames: suppress the sensor thermal noise from your flats

Flat Frames: suppress vignetting (or other constant light uniformity issues) and dust in the image train from your lights

 

IMHO, getting your flats properly exposed is the biggest challenge and can cause the most problems when they’re not right. (Don’t misunderstand, getting any of your calibration frames ‘wrong’ leads to problems but for me flats have been the biggest issue)

 

 

Clear Skies!

Excellent article as well... why in heck couldn't i find these in all my searching... smh.


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#9 clint.ivy

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Posted 20 January 2021 - 12:38 AM

Excellent article as well... why in heck couldn't i find these in all my searching... smh.

Ha! Like any craft you have to learn the inside lingo to get anywhere (I wish there was a lexicon somewhere). If you’re like me then you were searching for ‘dark frames’ or ‘dark master’ of ‘flat frame’, etc and the results there are not great. Searches for ‘astrophotography’ and ‘calibration frames’ or their variants seem to be much more fruitful.

 

If you’re guiding (it sounds like you might be) some of the guiding software will give you recommendations on settings for your flats (or so I’ve read I’m not at the guiding level yet)


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#10 bobzeq25

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Posted 20 January 2021 - 01:01 AM

 

Good evening folks,

Bear with me as this is my first post on CN after months of reading and acquiring equipment.

So to lay some foundations here... I'm an old film guy that got out of the hobby long ago. In my heyday it was gas hypered Fuji 800 and hand guiding 90 min exposures. My goodness it has come a long way !!!

The equipment I have picked up from you folks so far are a CPC 1100, Heavy Duty Wedge, Celestron 80mm guide scope and I just picked up an AT102ED to replace the 80mm to use as double duty guide/imaging. Various eyepieces and visual accessories.

My camera is a Cannon T3i non modded, and a ZWO ASI290MC Guide/Planetary imager. I have rear cell F6.3, OIII and Broadband. 

Of course being and old film guy, so far all I have accomplished is a few experiments with Orion by simply varying exposure times and rudimentary stacking a few frames. I see a ton of post talking about Flats, Darks, Lights and assuming these are frames to somehow integrate into a "stacked" image. I've tried to use some software packages mentioned in here to not much avail... I just cant seem to understand some of the features, but that's another post another day... Right now, I'm tryin to find what I would call a basic primer on Darks, Flats, and the frames needed to integrate into a picture, and their purpose.

I've searched through the forums till my eyes are sore and read a lot of conversation talking about taking them, but cant seem to find that perfect explanation of them... 

Can ya'll help explain or point me to a thread that goes over them in detail?

 

Many Thanks and Clear Skies,
 
Lee

 

 

Sure.  Simplified, but "good enough" for now.

 

Digital cameras add an offset to every frame to stop noise from driving the signal negative.  Bias frames are shot at the shortest possible exposure, with the optics covered, to capture just the offset signal, so you can subtract it out.

 

Dark frames are shot at the same exposure as the lights, but with the optics covered.  They capture the thermal noise of the camera, also to be subtracted out.

 

Flats are more complex.  You take an image of an evenly lit surface.  That captures dust on the sensor, and optical vignetting.  And some other more minor, but important camera imperfections.

 

For complicated reasons, you divide by flats, not subtract.  And you must correct for the offset (bias) in the flats, or they don't work well. Math.

 

I _strongly_ recommend Astro Pixel Processor to you for calibrating your frames with bias, flats, darks; stacking, and processing.  It does things in a logical, easy to understand fashion.  It will actually help you learn.  The "free" alternatives are inferior, and not free in terms of your time, frustration level, and image quality.

 

Do not omit the calibration frames even when you're just starting out.  The minor point is that they'll improve your images.  The major one is that, wihout them, you're very likely to learn bad habits in processing.  Processing is hard enough without having to unlearn bad habits.  <smile>

 

This book is extremely helpful.  There's far more to learn than you can get from short posts here.  CN is good for specific questions, the book is _far_ better for building your essential knowledge base.

 

https://www.amazon.c.../dp/0999470906/

 

This works better than film.  In some ways it's not as tricky to do, but it's _way_ more complicated.

 

Lights are just the actual images of your target.  The key thing to know is that quality is completely dependent on your "total imaging time".  How to break that into subexposures is a complicated topic, but, provided you're close, it's not very important.  Rule of thumb.  One hour minimum, two is better, four good.  What makes this work is gathering a lot of data, and processing it intensively.

 

Welcome to the hobby.  The bad news is that it's _really_ complicated.  The good news is that you will never, ever, run out of new things to learn.  Part of the charm for many of us.  I have an extensive bookshelf.


Edited by bobzeq25, 20 January 2021 - 01:10 AM.

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#11 Benschop

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Posted 20 January 2021 - 01:40 AM

One more for you to browse that explains calibration...

http://www.astrosurf.../howto-ccd5.htm


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