NGC6960 limited data

[Miguel1983]

Hi,

a few months back i took a shot at this subject, but afterwards there seemed to be a defect on my camera,  thursday we had somewhat clear weather but unfortunatly also a working-evening, so with limited time i took some shots at the Witches Broom.

I ended up with 17 5min subs and took 8 darks, yesterday after work i took 75 flats from my laptop screen.

Images were taken with the ED80 + 0.85 corrector + Canon 750Da and the STC Duo Narrowband filter, i removed the filter for the flat frames as they came out red, could be wrong from my part, but i thought they would not be usefull (correct me if i'm wrong)

 

[david_taurus83]

Hi Miguel

 

That looks really good. That STC filter does a good job. Regarding the flats, you should not remove anything from the image train. Even if everything was spotless clean and you didn't change focus, removing the filter will effectively change the focal distance slightly as glass adds back focus. The colour of the flats doesn't matter as they are only used to subtract optical artefacts like vignetting in the corners and dust artefacts. Your image has come out well though.

[Miguel1983]

On ‎15‎/‎12‎/‎2018 at 09:16, david_taurus83 said:

Hi Miguel

 

That looks really good. That STC filter does a good job. Regarding the flats, you should not remove anything from the image train. Even if everything was spotless clean and you didn't change focus, removing the filter will effectively change the focal distance slightly as glass adds back focus. The colour of the flats doesn't matter as they are only used to subtract optical artefacts like vignetting in the corners and dust artefacts. Your image has come out well though.

Hi David,

thanks for the advice, will do in the future !

In my case the focus does not change with or without filter in terms of distance from the telescope objective to the camera sensor (2" filter is mounted on a nosepiece so the filter doesn't ad its thickness ) , but i guess the lightpath probably changes slightly when the filter is or isn't in place. 

I have noticed a tiny difference in focus between different filters, so there's definitely something happening to the lightpath.

 

 

[wimvb]

32 minutes ago, Miguel1983 said:

Hi David,

thanks for the advice, will do in the future !

In my case the focus does not change with or without filter in terms of distance from the telescope objective to the camera sensor (2" filter is mounted on a nosepiece so the filter doesn't ad its thickness ) , but i guess the lightpath probably changes slightly when the filter is or isn't in place. 

I have noticed a tiny difference in focus between different filters, so there's definitely something happening to the lightpath.

 

 

Light travels slower in glass than in air (by an amount equal to the refractive index). This has the same effect as an increased lightpath (refractive index x physical thickness). But what's more important, filters change vignetting and can add dust bunnies (when close to the sensor).

The image turned out very nice, imo.

[newbie alert]

Great image, thanks for sharing.. regarding removal of the filter I was told whatever you use for your lights should remain in the flats..say you had a bunnie on the filter then done some flats without it then it wouldn't calibrate out as it's not there on the flat..see what I mean?

[Miguel1983]

11 hours ago, newbie alert said:

Great image, thanks for sharing.. regarding removal of the filter I was told whatever you use for your lights should remain in the flats..say you had a bunnie on the filter then done some flats without it then it wouldn't calibrate out as it's not there on the flat..see what I mean?

You're right, and that is how i know it to, but that duo narrowband filter gave a verry red flat frame, so i tought it would be worse, my mistake so it seems.