Can I use an observing filter for imaging?

[Tom62e]

Hi all,

 

Just curious if I could use the Celestron OIII filter 93624 for imaging?  I originally bought it for visual use but the website does not  mention if it can or cannot be used for imaging.  

 

Also, can I take separate subs with different filters the way you do with Mono imaging but using a colored camera?

 

In other words, I'm looking to use my ASI294MC-PRO (color) to take 15 subs with an OIII filter, then 15 subs with a SII filter, and then 15 with a H-alpha filter.  Then combine them in processing the way you would with mono imaging.  Would that work?

Thanks 

 

[vlaiv]

41 minutes ago, Tom62e said:

Just curious if I could use the Celestron OIII filter 93624 for imaging?  I originally bought it for visual use but the website does not  mention if it can or cannot be used for imaging.  

In principle you can, but there could be a few issues.

First is that camera is sensitive in broader range than eye. Maybe filter was designed to filter out visible light in all but OIII wavelengths - but does not prevent IR light from passing. Eye won't be able to see that - but camera will. In order to fix this - you can combine such OIII filter with UV/IR cut filter if you find that it passes out of band light.

Second issue that can happen is nasty reflections. Again - visually these don't cause any issues but with long exposure and other glass elements in optical path (like sensor cover window or some sort of corrector / flattener) - you can get nasty reflections around bright stars.

Even some photo filters suffer from this.

Best thing to do would be to try it and see if it works well.

44 minutes ago, Tom62e said:

Also, can I take separate subs with different filters the way you do with Mono imaging but using a colored camera?

Yes you can

45 minutes ago, Tom62e said:

In other words, I'm looking to use my ASI294MC-PRO (color) to take 15 subs with an OIII filter, then 15 subs with a SII filter, and then 15 with a H-alpha filter.  Then combine them in processing the way you would with mono imaging.  Would that work?

It will work - but it won't be as sensitive as mono camera and will require special processing.

Ha and SII wavelengths are in deep red and only red channel will pick up these with sufficient sensitivity - that means only 1/4 of pixels will pick those wavelengths up. If you image with such filter - best way to extract Ha or SII data would be to do super pixel mode and then extract red channel only as mono for both Ha filter and SII filter (separate sessions of course - producing two mono images).

For OIII - you need to consult QE graph as both blue and green capture that wavelength.

If this QE graph published by ZWO is to be believed - G is much more sensitive than blue at 500nm - so I'd go with green because of that and the fact that there is 1/2 of pixels in that color (meaning double that of blue and red). Again - method would be the same - use super pixel mode debayer, then stack and extract G channel as OIII mono.

 

[Tom62e]

I understand.  I think I'll stick with a tri-band filter designed for OSC cameras.  Thanks guys!

[vlaiv]

2 minutes ago, Tom62e said:

I understand.  I think I'll stick with a tri-band filter designed for OSC cameras.  Thanks guys!

Just be careful - multi band filter when used with OSC camera simply can't distinguish SII and Ha.

Tri-band is usually Ha, Hb and OIII

Even if you have SII and Ha (like in quad band) - those two wavelengths will be joined together in red channel without possibility of splitting them.

Btw - such filters are good way of producing bi-color images - as you shoot multiple channels at once instead of one by one and that saves you time (you can image for couple of hours with multi band filter instead of one hour each channel), but problem is that it is inherently only "bi color" regardless if it is duo, tri or quad band. That is because of already mentioned Ha / SII issue and also because Ha and Hb signal are linked together - you can't have Hydrogen beta line without having Hydrogen alpha line (opposite can happen if Hydrogen gas is not excited enough to cause Hb transition - only Ha). This means that you'll get same signal distribution for Ha and Hb (as it is produced by same gas).

[Tom62e]

Got it. Thank you. Sounds like eventually I'll be moving to mono imaging with a FW.