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Do i need to add a filter after doing a full spectrum Mod to my DLSR?

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#1 bluesilver

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Posted 07 August 2020 - 10:02 PM

Hi,  I have recently just modified my Canon EOS 600D DLSR doing the Astronomik MC clear class modification.

It is just basically completely removing the low-pass fliter 1 completely,

And also removed the IR cut filter completely ( low-pass filter 2 ) and replacing this with the Astronomik MC clear class.

 

The result it that you get a very red tinge if trying to use it in daytime with a lens,  which it is not intended for.

At night taking photos of nebular and the like i get a lot of red, too much red in fact.

 

I attach the camera directly to the scope, a Dobsonian in this case,  so i am not using the camera lens.

 

What i would like to know is,  Should i or is there a filter that i should be using in the T-Ring to get better colour?  as at the moment the images are way too red.

Should i be using something like the Badder Neodymium & IR-Cut Filter,  Or Lumicon oiii filter,  or Lumicon UHC Filter screwed onto the the T-Ring?

 

Any advice or information would be appreciated.

Thanks.


Edited by bluesilver, 07 August 2020 - 10:23 PM.


#2 17.5Dob

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Posted 07 August 2020 - 10:12 PM

Hi,  I have recently just modified my Canon EOS 600D DLSR doing the Astronomik MC clear class modification.

It is just basically completely removing the low-pass fliter 1 completely,

Removing the IR cut filter completely and replacing this with the Astronomik MC clear class.

 

The result it that you get a very red tinge if trying to use it in daytime with a lens,  which it is not intended for.

At night taking photos of nebular and the like i get a lot of red, too much red in fact.

 

I attach the camera directly to the scope, a Dobsonian in this case,  so i am not using the camera lens.

 

What i would like to know is,  Should i or is there a filter that i should be using in the T-Ring to get better colour?  as at the moment the images are way too red.

Should i be using something like the Badder Neodymium & IR-Cut Filter,  Or Lumicon oiii filter,  or Lumicon UHC Filter screwed onto the the T-Ring?

 

Any advice or information would be appreciated.

Thanks.

Nope, nothing you can do about it, that's the normal color you get with a modded cam....An IR cut just eliminates some star boating, it doesn't change the color at all...

(But that's why you mod a camera...............to get the extended reds.....)


Edited by 17.5Dob, 07 August 2020 - 10:15 PM.


#3 bluesilver

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Posted 07 August 2020 - 10:38 PM

Thanks for the reply,  appreciated.

Just seams a tad odd as everything is very red,  Maybe i have gone too far with the mod,   as even the blackness of space has a tinge of red to it,  Basically everything is a shade of red,   not much other colour comes out,  certainly nothing like the images you see on their site,

No yellow in stars or that blue you see,  I thought there must be something i needed to add in a way of another filter.



#4 17.5Dob

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Posted 07 August 2020 - 11:02 PM

Thanks for the reply,  appreciated.

Just seams a tad odd as everything is very red,  Maybe i have gone too far with the mod,   as even the blackness of space has a tinge of red to it,  Basically everything is a shade of red,   not much other colour comes out,  certainly nothing like the images you see on their site,

No yellow in stars or that blue you see,  I thought there must be something i needed to add in a way of another filter.

You need to learn how to process them....

This is with my modded cam....

49325744106_df4541e788_b.jpg



#5 17.5Dob

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Posted 07 August 2020 - 11:06 PM

This is what a stack looks like before processing ( using PI's screen stretch)

49285117576_b3991d9caa_c.jpg

After processing....

49225519481_7c39d590a9_b.jpg


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#6 Jim R

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Posted 07 August 2020 - 11:08 PM

Beautiful images 17.5 bob, can that PI workflow be approximated in PS?  Can you point us in a general direction? Some broad hints?


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#7 bluesilver

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Posted 07 August 2020 - 11:08 PM

Thanks again,  Yes still learning,  haven't got to the processing part yet.

Just did some random single shot exposures last night to see how the modification went.

I was going from what i can see in the cameras screen after i had taken the shot.

My 45 second shots came back very red indeed.



#8 bluesilver

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Posted 07 August 2020 - 11:11 PM

Just seen the reply you posted as i was tying,  yes,  that first one is pretty much exactly what mine come up looking like,

Still trying to find a software to upload my images to show you, The camera i modified didn't come with the cd software.

 

Just out of interest,  what software did you use to process those images if you don't mind me asking?


Edited by bluesilver, 07 August 2020 - 11:12 PM.

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#9 17.5Dob

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Posted 07 August 2020 - 11:20 PM

Just out of interest,  what software did you use to process those images if you don't mind me asking?

PI


Edited by 17.5Dob, 07 August 2020 - 11:20 PM.


#10 bluesilver

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Posted 07 August 2020 - 11:26 PM

Just did a search on PI,  looks like you are using Raspberry Pi ?

I might have to find an alternative to that unfortunately.


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#11 AgilityGuy

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Posted 07 August 2020 - 11:47 PM

I’m curious as to the stage of processing you took the screen shot.  That’s not an unusual background for my images right after stacking and before background neutralization/extraction.  If that’s the stage you’re seeing it just open Screen Transfer Function and unlink the color channels - click the little chain links on the left side.  I also use a full spectrum camera and use a UV/IR cut filter to control star bloat but no other filter is needed.  


Edited by AgilityGuy, 07 August 2020 - 11:48 PM.


#12 grozmaistor

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Posted 08 August 2020 - 01:11 AM

Just did a search on PI, looks like you are using Raspberry Pi ?
I might have to find an alternative to that unfortunately.

PI should be PixInsight and not Raspberry Pi!

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#13 bluesilver

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Posted 08 August 2020 - 01:16 AM

Ah,  sorry,  You can definitely see that i am fairly new to this,  will look that one up.

Thanks.



#14 sharkmelley

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Posted 08 August 2020 - 01:23 AM

If you have done a full spectrum modification then you definitely need to use an IR/UV blocking filter, otherwise 2 things might happen:

  • You end up with star bloat because of near-IR wavelengths that are not properly brought to focus by the optics
  • Star colour is washed out because the near-IR dilutes the colour 

In any case you will need to perform background subtraction and perform a white balance to remove the overall redness.

 

Mark


Edited by sharkmelley, 08 August 2020 - 01:25 AM.


#15 bluesilver

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Posted 08 August 2020 - 01:51 AM

Thanks again for the information,  lots to learn.

So yes i have done the full Spectrum modification.

I currently have a Badder Neodymium & IR-Cut Filter,  Next time i will put this in front of the camera and give it a go.

I am guessing that the Pix Insight program allows you to perform background subtraction and perform a white balance to remove the overall redness?

 

Sorry if i am asking a lot of basic questions here,  but i think i am getting the basic understanding of it.



#16 endlessky

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Posted 08 August 2020 - 04:19 AM

The color cast can be corrected in post-processing.

 

You could also just put back into place one of the two low-pass filters (I don't remember which one, but one of the two will only filter UV and IR). This should make things a little better, but you'll still probably have some color cast that needs to be corrected in post-processing.

 

That said, the main reason for not going completely full spectrum is that, when using lenses, or refractors, not all light wavelengths focus on the same focal plane. This effect is more evident the further into the red (IR and past) and into the blue (UV and before) you go, resulting in bloated stars or purple/magenta halos around them. That's why you want to put back the UV/IR cut low-pass filter or another type of UV/IR cut filter.

 

This, however, shouldn't matter if you only have mirrors in your imaging train (but will as soon as you add a lens - coma corrector, for example, if you use one).

 

PixInsight allows you to subtract the background (with AutomaticBackgroundExtractor, or DynamicBackgroundExtraction) and has plenty of tools to do correct white balance (my favorite is PhotometricColorCalibration).




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