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Gradients again!


RonC
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Last night I imaged M51 and Binned 2x2 and got a gradient in the LH Corner.

 

large.M51070521150400FinishSmall.jpg.530183004b0273bc13664d9710a8efb1.jpg

 

Then I imaged M13 Binned 1x1 and got no gradients?? 

 

large.M130705211204001x1FinishSmall.jpg.888b2168cd07f6ab239b50383ace9354.jpg

 

Any idea's?? I've asked the question on Altair Astro's FB page as well!

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I assume M51 was almost at the zenith last night when you took the image which means that the camera would be virtually horizontal whereas M13 would have been at an altitude of about 60° so depending on your scope alignment on the mount, the camera is unlikely to be horizontal.  Are there any low altitude light sources (eg the neighbours switching on an upstairs light) that could cause reflections or light leaks with the camera in a particular physical orientation?

 

Nice images by the way, I particularly like M13, the core doesn't seem blown out.

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Clive, you are right about the the horizontal cam but I use a large dew shield to keep out light along with some flocking and having the secondary mirror housing painted black.

I might try the same target on different binning for a check?

Steve the lappy is in the shed 😀.

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No gradients on the Darks as far as I can see...

Taken last thing after the lights last night..

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11 minutes ago, RonC said:

They are all too big to post?

 

Dropbox it ron 

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Ron in Dropbox hover mouse  on the link icon and click on copy link.

 

spacer.png

 

Select "other media" on here and then "insert image from URL."

Paste the URL you copied in Dropbox into the box.

You will see this. but with your own unique image title.

 

spacer.png

 

Change the  "0"  to a 1 and the  "dl"  to raw.

It will then look like this.

 

spacer.png

 

Select insert into post and it will show up on here.

 

 

Edited by Graham
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52 minutes ago, RonC said:

I'm a little confused, the M51 image is ~120Mbyte and when I open it, it appears as 5440 x 3648 pixels (which I believe is the resolution of the 183C and the file size is similar to my 6000 x 4000 TIF images) but the M13 image is ~400Mbyte (and I can't open it as it just crashes my PC!)  But you mention above that the M51 images is 2x2 binned and the M13 images is 1x1 binned so I was expecting the M51 image to be only 2720 x 1824 pixels?

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Interesting Clive 

I tried to open them in Dropbox and only the M51 would open.

Just got an error come up on the M13.

 

Ron scrub my last as this forum will only accept JPEG images from Dropbox ( my biggest issue )

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2 minutes ago, Ibbo said:

We still need the cali frames as well

 

I assume that being a TIF, it's the output of the stacking program (DSS?) so the cal frames are already embedded.

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6 minutes ago, Clive said:

I assume that being a TIF, it's the output of the stacking program (DSS?) so the cal frames are already embedded.

It would be useful to see the raw image ,the flat and the dark and bias if used as the raw fits files uploaded to dropbox so we can then download

 

Are the cali frames being taken in the shut up obs or the camera covered  ?

Edited by Ibbo
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The gradient appears to be very linear, this is a slice through the linear image from bottom left to to top right (scaled to 1/4 size, M51 is the lump in the middle):

 

large.Before.png.b1b586cf35d91cd203f2c0f059e41da2.png

 

This is approximately the same slice after applying the IRIS gradient removal tool:

 

large.After.png.bdfc5c8c4b5b1ec0faade027b717d748.png

 

This is the resulting image after just applying an IRIS ASINH stretch without any other processing:

 

large_m51.jpg.84459c0da64341b36d0c2fddd9815fca.jpg

 

And when was the 1Mbyte file limit introduced?  I had to save this in the poorest quality JPEG format to be able to upload it!

 

 

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OK, so I've binned the resulting image 2 x 2 so I can save it a a better quality and get rid of the compression artifacts:

 

large_m51.jpg.e9fe6a809c8f4cc8ce4644195d2a8fc8.jpg

 

 

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I have downloaded it converted to 16 bit given it a few levels ( run it through grad x, but don't tell Ron) a couple of curves,3 zaps as a layer to increase saturation a denoise  a final levels and a 50% reduction in size Robert is your mothers brother after a 10 min process including trying to do it at 32 bit.

 

The gradient could be your local light polution and it is not that bad in this image.

 

 

spacer.png

Edited by Ibbo
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ron you can choose in dss to save picture to file rather than autosave  ,i use these settings to save as fits for startools as in picture 

large.1309899636_Captureron.PNG.fab71ee7c3dabf42a4cfe87bb7f8b9cd.PNG

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Wow, it's getting a bit technical for me. I do save the images to file as I usually adjust them in DSS before saving.

If it's clear tonight I will pick a 45-55' subject and use 1x1 and 2x2 binning, perhaps 10 of each, good idea??

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15 minutes ago, RonC said:

Wow, it's getting a bit technical for me .

 Me too 😂 

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