Narrowband Filters

[Anonymous Astronomer]

Hello everyone,

I'm looking to buy some NB filters and wanna make the best decision.

1. Does the size of the filter impacts the quality of the image? (is it a big impact?)

2. I know that lower HBW is best, but... for example: does the difference between 35nm and 7nm is worth the price?

3.Can you recommend some H-alpha, OIII, SII?

Thank you in advance!

Cheers,
Vlad

[tooth_dr]

1 hour ago, Anonymous Astronomer said:

1. Does the size of the filter impacts the quality of the image? (is it a big impact?)

2. I know that lower HBW is best, but... for example: does the difference between 35nm and 7nm is worth the price?

3.Can you recommend some H-alpha, OIII, SII?

1. The size of the filter does impact the image but not in the sense that the 2" is better than the 1.25" version.  It is related to the size of your sensor and the speed of your telescope.  If your sensor is small and the telescope is say F5 or slower, then you can likely just use 1.25" filter - cheaper and no impact on quality. If the sensor is larger or you have a fast telescope then you will need the 2" filters, as the smaller ones will cause excessive vignetting.

2. 35nm would not be suitable for good deep sky imaging, 7nm will give nice contrast and  is what I use.

3. You often get what you pay for with filters, Baader would be decent.  I have some Optolong Ha Oiii Sii filters that I like also, and seem very comparable to Baader.

 

Edited December 16, 2020 by tooth_dr

[Anonymous Astronomer]

1 hour ago, tooth_dr said:

1. The size of the filter does impact the image but not in the sense that the 2" is better than the 1.25" version.  It is related to the size of your sensor and the speed of your telescope.  If your sensor is small and the telescope is say F5 or slower, then you can likely just use 1.25" filter - cheaper and no impact on quality. If the sensor is larger or you have a fast telescope then you will need the 2" filters, as the smaller ones will cause excessive vignetting.

2. 35nm would not be suitable for good deep sky imaging, 7nm will give nice contrast and  is what I use.

3. You often get what you pay for with filters, Baader would be decent.  I have some Optolong Ha Oiii Sii filters that I like also, and seem very comparable to Baader.

 

All of that makes sense. I really appreciate your input.

Thank you,
Vlad

[rickwayne]

Since you're imaging at f/5 or higher, the bandpass is not going to have a big impact on you. Since these are interference filters, they're rather sensitive to the angle of incidence, and faster optics produce a broader light cone whose edges impact at a more acute angle.

I use 7-nm ZWO "new" filters, and I do OK. Baader and Optolong are somewhere between roughly equivalent to a step up, depending on who you talk to. Astrodons and Chromas are the spendy ones. Not sure how where Astronomik fits.

Something I hear over and over again is that OIII filters are particularly prone to bright stars forming halos, so if you want to splurge on one filter, that's the one. Search for "OIII halo bright stars" to find discussions and examples.

You may find that some manufacturers claim that their filters are parfocal, i.e. you don't have to refocus when switching. I wouldn't count on that too completely, critical focus often requires refocus on switch.

[david_taurus83]

If you are using an off axis guider then I'd at least look for filter sets of the same thickness as refocusing between filters could mean your OAG may become too out of focus to detect stars.

Regarding Oiii halos, my first Baader had terrible halos, I got it replaced under warranty and the replacement one didn't have any halos with the same scope and camera. My current Astronomik 6nm Oiii is also halo free.