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my first astrophoto- any tips?


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Just thought I would post this , 8x 15-second untracked exposures through a cheap 28-80mm zoom lens, stacked, pre-processed, and post-processed in Siril. I am aware that this lens is not really suitable for the application, hence the bloated stars, but does anyone have any tips on how to use Siril to make stars more round? Also, can anyone explain or find a tutorial for the photometric colour calibration function, maybe I'm stupid but I just cant figure it out, it just displays error notices. :dontknow:

looks like I might catch the astrophotography bug, in which case I will have to sell some gear and cut my visual budget. . .:crybaby2:

M31.jpg

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38 minutes ago, Astronomist said:

 

Just thought I would post this , 8x 15-second untracked exposures through a cheap 28-80mm zoom lens, stacked, pre-processed, and post-processed in Siril. I am aware that this lens is not really suitable for the application, hence the bloated stars, but does anyone have any tips on how to use Siril to make stars more round? Also, can anyone explain or find a tutorial for the photometric colour calibration function, maybe I'm stupid but I just cant figure it out, it just displays error notices. :dontknow:

looks like I might catch the astrophotography bug, in which case I will have to sell some gear and cut my visual budget. . .:crybaby2:

 

M31.jpg

You could try stopping down the lens to try and curb the aberrations of your stars, but not much to do about them after they have already been captured. You could also crop a bit inwards to hide the worst effected edges of course, but short of that an aberrated star is an aberrated star.(BlurXterminator, an AI tool just released, which may fix this but its a more advanced topic requiring PixInsight to work).

For Photometric Colour Calibration you need to know a few things. Below a screenshot to illustrate a few things.

Capture-pcc.JPG.91b9afd23f484a20c9bc57d33540a580.JPG

In the search bar you can search the object of your image and it will fill in the Right Ascension and Declination coordinates correctly. You need to have this object be near the center of the image which i think your M31 is not, at least not close enough since its a very wide field image. You may need to manually input the coordinates or choose a star close to the center of the image as the reference (you need to browse Stellarium and find out an HD-something-something number of a star and search that for example). You also need to know the focal length and the pixel size used for capturing. The stated focal lengths and pixel sizes are rarely exact and these values need to be pretty close, so try a bit under and over the focal length you thought you captured at, so for example maybe try 70, 75, 85, 90 and see if those work. Note that if you have resized the image before doing this step these variables have changed and you need to change pixel size/focal length accordingly.

Here with this image you may run into a problem, Siril PCC expects a telescope sized image and may not work for very wide fields where it has trouble picking up stars used for the calibration. So it may be possible that it will just not work for your image. If you get an error that it didn't work, try with another Photometric Star Catalogue, if still doesn't work then maybe it just wont work for this image.

You might want to try more with this lens before investing into more gear. What you have here is basically a snapshot, a very short peek into what the skies will give you, try gathering at least a few hours on some target and work with that. You may be surprised how much you can get out of a cheap lens if you accept the limitations in sharpness/stop down the lens and accept the limitations that come with that.

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16 minutes ago, ONIKKINEN said:

may not work for very wide fields where it has trouble picking up stars used for the calibration

ok that would make sense, the error notice said something along the lines of not being able to identify star patterns. for the pixel size and focal length I used the image metadata, and for the coordinates I typed M31 into the search bar. I'll try using the RA/DEC of one of the bright stars in the middle and see if that helps though.

thanks

 

 

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