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Image quality difference on Lagoon/ Trifid

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#1 waso29

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Posted 24 September 2019 - 03:35 AM

I mostly do visual, and slowly trying hand on imaging with mod Nikon D5100 dslr.

 

Why is there a difference in image quality of sub on the Lagoon and Trifid?

I used bahtinov mask to achieve focus.

Used same mod Nikon D5100 camera for both shots.

From same location in Indy corn field.

Minimal process with stock Nikon Capture NX-D software and MS Office Picture Manager.

 

The 1st sub is 3min iso640 at 327mm focal length.

The 2nd sub is 2min iso640 at 255mm focal length.

 

Would image quality thru 300mm prime lens be better or worse?  

Quality thru SpaceCat 51 at 250mm?

Attached Thumbnails

  • DSC_2888_00001 fsq85 em200 @conway v2.jpg

Edited by waso29, 24 September 2019 - 03:43 AM.


#2 waso29

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Posted 24 September 2019 - 03:37 AM

Here's sub from 255mm focal length.

Attached Thumbnails

  • DSC_3226_00001 m008 m020 fs60cb f4.2 em200 @conway.jpg


#3 Tapio

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Posted 24 September 2019 - 03:53 AM

I see some vignetting (or is it fogging ?) in first image, second is clearer.

But if those are single images I think they are pretty good (and if no calibration files were used).



#4 ramdom

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Posted 24 September 2019 - 03:53 AM

Try this out: https://astronomy.to...ccd_suitability

 

Not sure what your pixel size but you can plug that in with your two FLs at the bottom and see what it recommends.  It also depends on seeing. 

 

--Ram



#5 waso29

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Posted 24 September 2019 - 04:33 PM

I see some vignetting (or is it fogging ?) in first image, second is clearer.

But if those are single images I think they are pretty good (and if no calibration files were used).

interesting observation on vignetting.  could be my aggressive contrast adjustment on this sub.

 

yup, no stacking yet.  just looking at individual subs and noticing the stars are tighter in the longer focal length.



#6 waso29

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Posted 24 September 2019 - 04:48 PM

Try this out: https://astronomy.to...ccd_suitability

 

Not sure what your pixel size but you can plug that in with your two FLs at the bottom and see what it recommends.  It also depends on seeing. 

 

--Ram

the D5100 has pixel size 4.78 ┬Ám.

not sure why the stars are tighter for 327mm compared to the slightly shorter 255mm.

the website link says should be the opposite.  didnt think seeing conditions could change so drastically.

 

will uv/ir filter make a difference too?




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