Thinking of going narrow band

[simmo39]

With nights getting v short Im thinking about next season. I have been putting cash aside (Dont tell the wife ) For a new mono camera and filters as I would like to try narrow band imaging. I already have a OSC ccd camera (QHY 10) which I think I have just got the hand of but narrow band is calling!  Im thinking of going down the ZWO asi1600 mm route with a set of 31mm fiters in a 5 shot wheel. (trying to keep weight and cost down so no RGBL ). Now to the real question. Im using a SW 130 PDS as my main scope would this camera set up be ok? and how much vignetting am i going to get? the reason I ask this one is as of yet I have not managed to get any good flats with my QHY ( always seem to come out with a grid pattern) and I would not want to waste to much time with them.

Just as a side note the other thing why I would like to go cmos is the short exposure. 

Any comments please and thanks in advance.

 

Simmo

[vlaiv]

I get quite a bit of vignetting on ASI1600 and 1.25" filters, mounted as close as possible to sensor (filter drawer instead of filter wheel, so even less spacing requirement), even at F/8. I would expect that with 31mm filters you will also get some vignetting at F/5.

130pds + ASI1600 will be a good match. High resolution at 1.21"/pixel but it should work for HEQ5 mount. I image at 1"/pixel on heq5 with 8" scope, so it's doable.

It is quite sensitive camera so I strongly recommend to take flats. In my subs every single dust particle shows as doughnut. Fortunately subs calibrate just fine. Being CMOS sensor, flats are really fast to do, it takes me less than 10 minutes per filter (I do it each session - no permanent setup).

Btw what kind of grid pattern do you get with QHY 10? If it is OSC camera, Bayer pattern is to be expected, but it should work nonetheless - just calibrate your subs normally like mono before debayering (subtract darks ,divide with flats).

[Adam J]

2 hours ago, simmo39 said:

With nights getting v short Im thinking about next season. I have been putting cash aside (Dont tell the wife ) For a new mono camera and filters as I would like to try narrow band imaging. I already have a OSC ccd camera (QHY 10) which I think I have just got the hand of but narrow band is calling!  Im thinking of going down the ZWO asi1600 mm route with a set of 31mm fiters in a 5 shot wheel. (trying to keep weight and cost down so no RGBL ). Now to the real question. Im using a SW 130 PDS as my main scope would this camera set up be ok? and how much vignetting am i going to get? the reason I ask this one is as of yet I have not managed to get any good flats with my QHY ( always seem to come out with a grid pattern) and I would not want to waste to much time with them.

Just as a side note the other thing why I would like to go cmos is the short exposure. 

Any comments please and thanks in advance.

 

Simmo

I am personally using a 130PDS and ASI1600mm pro + 8 position 1.25 inch filter wheel and I can assure you that while you will see a tiny bit of vignetting its not a problem with flats, I would think that 31mm filters would give less but not none. One of the things you have to remember is that the secondary on the 130PDS is a little small and so you will get drop off towards the edge of the image even with 2 inch filters (Unless you replace it with a larger secondary), for this reason and dust bunnies you will always need flats in my opinion. With this setup I was getting 0.8'' RMS guiding last night with my HEQ5 PRO (belt mod), be that in an observatory setup.  

As a side note on ZWO 31mm filters, you will get reflections from the edge of the 31mm filters unless you blacken them. So if you really want 31mm I would go with a different brand or for ZWO 1.25 inch that will work just fine. 

Adam

[simmo39]

1 hour ago, vlaiv said:

I get quite a bit of vignetting on ASI1600 and 1.25" filters, mounted as close as possible to sensor (filter drawer instead of filter wheel, so even less spacing requirement), even at F/8. I would expect that with 31mm filters you will also get some vignetting at F/5.

130pds + ASI1600 will be a good match. High resolution at 1.21"/pixel but it should work for HEQ5 mount. I image at 1"/pixel on heq5 with 8" scope, so it's doable.

It is quite sensitive camera so I strongly recommend to take flats. In my subs every single dust particle shows as doughnut. Fortunately subs calibrate just fine. Being CMOS sensor, flats are really fast to do, it takes me less than 10 minutes per filter (I do it each session - no permanent setup).

Btw what kind of grid pattern do you get with QHY 10? If it is OSC camera, Bayer pattern is to be expected, but it should work nonetheless - just calibrate your subs normally like mono before debayering (subtract darks ,divide with flats).

Thanks Vlaiv, Thanks for the pointers. I will just have to bite the bullet and learn to do flats, as you say they dont take long just need to get settings right. 

One other question you may be able to answer for me. I see a lot written about hi and low gain settings for this camera, with my OSC i just use one setting for all i just change sub lenght to suit. What would be a good starting point and what would be the average sub length?

[Adam J]

1 minute ago, simmo39 said:

Thanks Vlaiv, Thanks for the pointers. I will just have to bite the bullet and learn to do flats, as you say they dont take long just need to get settings right. 

One other question you may be able to answer for me. I see a lot written about hi and low gain settings for this camera, with my OSC i just use one setting for all i just change sub lenght to suit. What would be a good starting point and what would be the average sub length?

I have been using unity gain (139) for now with 240s subs for narrow band, you can go with gain 200 and 60 second subs, but that is lots of subs to process / store.  

[simmo39]

2 minutes ago, Adam J said:

I am personally using a 130PDS and ASI1600mm pro + 8 position 1.25 inch filter wheel and I can assure you that while you will see a tiny bit of vignetting its not a problem with flats, I would think that 31mm filters would give less but not none. One of the things you have to remember is that the secondary on the 130PDS is a little small and so you will get drop off towards the edge of the image even with 2 inch filters (Unless you replace it with a larger secondary), for this reason and dust bunnies you will always need flats in my opinion. With this setup I was getting 0.8'' RMS guiding last night with my HEQ5 PRO, be that in an observatory setup.  

As a side note on ZWO 31mm filters, you will get reflections from the edge of the 31mm filters unless you blacken them. So if you really want 31mm I would go with a different brand or for ZWO 1.25 inch that will work just fine. 

Adam

Hi Adam. Thanks for the reply. 1.25 filters work  thats good news then. I was only plumbing for the 31mm as  from what I have read on other sites is what you need. Think ill go for 1.25 then. andd have to learn to get those stinking flats right LOL.

[Adam J]

1 minute ago, simmo39 said:

Hi Adam. Thanks for the reply. 1.25 filters work  thats good news then. I was only plumbing for the 31mm as  from what I have read on other sites is what you need. Think ill go for 1.25 then. andd have to learn to get those stinking flats right LOL.

No problem, the time to get 31mm is if you think that you will go below F4 now or in the future. But you dont need them with the 130PDS. 

[simmo39]

5 minutes ago, Adam J said:

I have been using unity gain (139) for now with 240s subs for narrow band, you can go with gain 200 and 60 second subs, but that is lots of subs to process / store.  

Yep thats more or less what I have read on other sites. I will try it at unity gain as soon as I get it. what temp are you using? -20 seems to be the main but again have read anything from -10 to -35

[Adam J]

3 minutes ago, simmo39 said:

Yep thats more or less what I have read on other sites. I will try it at unity gain as soon as I get it. what temp are you using? -20 seems to be the main but again have read anything from -10 to -35

I run at -20c, the camera seems capable of reaching -20c in both winter and summer here in the UK. You could go lower than -20c, but to be honest by -20 dark current is no longer the major source of noise anyway so you wont see much if any difference. 

[simmo39]

Just now, Adam J said:

I run at -20c, the camera seems capable of reaching -20c in both winter and summer here in the UK. You could go lower than -20c, but to be honest by -20 dark current is no longer the major source of nose anyway so you wont see much if any difference. 

Thank you Adam, think you have made my mind up for me. All being well by the start of the new season ill be up and at least nearly running. Now how do i sneak the a new camera past the wife?

[vlaiv]

+1 for what Adam said

-20C, unity gain (139), around 4m for narrowband (240s) and 60s for regular (LRGB) imaging would be my choice.

[simmo39]

36 minutes ago, vlaiv said:

+1 for what Adam said

-20C, unity gain (139), around 4m for narrowband (240s) and 60s for regular (LRGB) imaging would be my choice.

Thanks again vlaiv. Looking forward to giving narrow band ago.