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Is there any difference between jpeg and Raw for framing?

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#1 EEBA

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Posted 31 May 2020 - 04:44 AM

Hi, the sky was clear for a few hours and I decided to practice my basic skills for astrophotography. I was advised to put on hold my 8 inch sct and focus in my zenithstar app 73 mm.
I feel confortable with my polar alignment(still waiting for my polemaster). I practiced 2 and 3 star alignment. three star alignment more accurate. Almost always dead center on my grilled dslr screen. I was able to install and focus my zwo 120 mc with my guidescope and phd2. I wasn't able to learn how to use the software because the clouds covered the sky. During alignment time, I went back to M101 , pinwheel galaxy. Taking different lengths exposure, i wasn't able to see it in Raw file. But when i changed to jpeg in only 15 seconds exposure, I was able to see it.
In the past, ot has been a big issue for me to find and center targets.
Is there any difference between JPeg and Raw that I allows me to distinguish the targets?

#2 Tapio

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Posted 31 May 2020 - 05:14 AM

Sure you can use jpg files for framing. Also you can use highest ISO for framing.

Just use raw frames and lower ISO for 'real' imaging.



#3 EEBA

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Posted 31 May 2020 - 03:14 PM

Again, is there any difference when you see the test frame?

#4 Alex McConahay

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Posted 31 May 2020 - 04:49 PM

>>>>>>Again, is there any difference when you see the test frame?

 

What kind of differences are you looking for?

 

A raw and a jpg pointed at the same place in the sky with the same scope and camera will cover the same area. Therefore for checking framing, they are functionally equivalent. 

 

The problem is that the RAW is just that. It is data as seen by the sensor. If you are taking a picture of a dim object (like a night time sky) you will get a very dim picture. In order to separate the dimmest parts (the sky background)  from the less dim parts (the nebulosity and other celestial objects) you have to STRETCH the data. Most imaging acquisition programs allow one to do a screen stretch so that you can see the data in a RAW image. 

 

When you are looking at a JPG from a modern camera, the camera has already done that stretching. It has decided what should be dark, and what should be brighter. It does that stretching and displays it, and ----most important for distinguishing between RAW and JPG----saves it in its stretched form. 

 

SO. if you take a RAW and screenstretch it, you should see the same as you see from calling up a JPG (which had already been stretched by the camera before being saved).

 

If, however, you do not screenstretch the RAW, you will not see much at all. The detail is lost in the dim image. 

 

There are many other functional differences between RAW and JPG, but if your question is which one to use for checking framing on a target, it is immaterial as long as you can stretch the RAW to view it. 

 

P.S. If you can use JPG, do it (for framing). It is probably faster and easier. But functionally, I think there is little difference.

 

Alex


Edited by Alex McConahay, 31 May 2020 - 04:56 PM.

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#5 EEBA

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Posted 31 May 2020 - 05:00 PM

Alex, thank you for the great explanation. You answered my question. I just need to use 1 jpeg to see the target in my screen. (:


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