Choosing a new videocam for DS

[cesco]

Hi all,

due to worsening of LP in my observing site and to darkness time shortening for incoming DST, I decided to stop using my Atik 428EX CCD monochromatic camera for DS astrophotography. Under my obs site conditions ever more integration time is required to improve S/N ratio to decrease luminescent background sky, and too much time is required for R G B capture. My idea is to give up with CCD and choose a  CMOS camera, like the ZWO ASI. I wander if its sensitivity is high enough to allow capture of more frames in less time and to permit R G B capture in considerably less time than with CCD cameras. Alternatively, I would change to a polychrome camera.

By now, I need 1 hr capture time for each color channel and to collect about 80 frames for each channel.....quite unfeasible in summer....I would appreciate any suggestion and advice to choose the right CMOS camera.

Thanks everybody,

Francesco

[Elp]

Have you considered imaging narrowband on emission targets? I'm not experienced with CCD as I've been using ZWO or CMOS based cameras since the start and due to my local LP I also struggle with RGB though not impossible. Due to this I primarily image in narrowband on the targets which allow such a workflow, or if using an RGB/OSC camera I use a dual narrow band filter like the L-extreme.

[cesco]

Thank you. Do you mean that I should simply replace my RGB filters (Baader dielectric) with an H-alpha O-III and S-II triplet and.....bingo!? Which kjind of narrowband filters do you use? How long is your usual integration time in each channel and how many frames do you capture? 

I have no idea how the Atik 428EX CCD will respond to those filters, as I don't have an idea how the Dawn software, calibrated on RGB, will process the narrowband triplet frames...I will ask Atik customer service. The same applies to Registax requiring _R, _G, _B extensions to color files.... do you have an idea?

However, I am attracted to the use of narrowbwnd filters more than to changing my videocam: thank you for your suggestion even if I would like to know something more about your experience.

[Anne S]

I have an Atik428 mono. It's fine with Baader narrowband filters but you do need longer exposures. I normally use 15 minute subs. You do need to guide unless you've a very upmarket mount.

I also have a colour ASI533 which only needs 5 minute exposures using  4nm dual narrowband filter. 
 

I can post an example if wanted.

[Elp]

Is there really that much difference in sensitivity between CCD and CMOS? Having not used a CCD I wouldn't know. You can always bin your images after capture to increase your signal though I believe CCDs benefit from less noise because they can hardware bin in camera.

I also use the Baader 6.5/7nm ones and also have the F2 versions for my faster setups. I normally image between 60-120s mainly due to decreasing probability of bad subs, nowadays you can't really image without a quarter also have satellite trails in them even though you can reject when using kappa sigma when stacking. With the standard speed ones I have gone up to 5 minutes, in the end total time is what counts rather than sub lengths, with a CCD you may also have the benefit of less read noise in the stack.

As the data is all mono (in fits file format) I simply stack each session individually with calibration frames, then if I've got multiple sessions of the same bandpass I'll simply register and stack the stacks. I usually align and layer them manually in PS/Gimp afterward and change the work space from greyscale to RGB and set each layer to r, g and b respectively in S, H and O, or H, O, O on those particular suited targets with minimal S2 signal. It's quite simple to do once you've done it once.

As I'm bortle 7 narrowband is usually the main thing I do as clear skies are also usually accompanied by a near full moon, I've imaged Ha and S2 in the same quadrant as the moon, O3 you have to save for when it's not out or near your target.

Regarding time, I usually do at least 2-3 hours per filter and find that's sufficient though my better projects it's more like double to triple per filter, usually I'm imaging at F2 though. The shortest I've done with a 60mm refractor is less than 1 hour per filter and the image still turned out decent though noisy especially the o3 channel.

Edited March 13 by Elp

[cesco]

Thank you.

 

To Anne S

I expected shorter exposition times with narrowband filters….!

And how many 15-min subs?

Of course I was not considering that the total light entering such a narrow passband is quite dim….but this also means that narrowband filters would not shorten my photo sessions, which is strongly annoying especially in DST periods, unless I decide to stay up a whole night….

Guiding is no problem since I always do.

As for the color ASI533/dual narrowband fiklter, the total time goes shorter by 2/3 with respect to three channels, of course, unless you capture several 5-min subs….

 

To Elp

 

Yes, it seems that a strong increase in sensitivity from CCD to CMOS isn’t the issue. One should expect cleaner background sky in the captured images, not a shortening of exposure time, as my seller told me that one hour integration time at least is needed for each H-alpha OIII and SII channel (in agreement wirth your experience)….

 

Worse than all, my beloved subjects, galaxies, are forbidden targets of narrowband filters…..I could only hope to get good images of emission nebulae and similar emission DSOs, surely better quality than galaxies, though with the same timing problems in summer DST as for galaxies.

However, as an added bonus, I can expect fun in including in my setup the novelty of narrowband filters.

[Anne S]

18 minutes ago, cesco said:

Thank you.

 

To Anne S

I expected shorter exposition times with narrowband filters….!

And how many 15-min subs?

Of course I was not considering that the total light entering such a narrow passband is quite dim….but this also means that narrowband filters would not shorten my photo sessions, which is strongly annoying especially in DST periods, unless I decide to stay up a whole night….

Guiding is no problem since I always do.

As for the color ASI533/dual narrowband fiklter, the total time goes shorter by 2/3 with respect to three channels, of course, unless you capture several 5-min subs….

Ideally at least 2 hours per channel, ie 8, but it usually starts raining here! Even with the 533 and ultranarrowband filters I try for as much as I can get. I haven't tried longer than 5 mins with that but I intend to. I've been getting to grips with a new mount but as it's been managing 96 subs over the evening with no bad ones, it can certainly do longer. The rule with ccd and nb is to go as long as possible, whatever possible is! I tend to stick to 15 mins for ccd because of satellites, aeroplanes, Starlink etc. 

At least you can use nb with a moon around. We don't have any astronomical darkness for the 12 nights around the longest day.

Here's one of my images using the duoband filters with the 533. 8 hours data and really easy to process. Hubble palate.

 

 

[cesco]

Great! Really! It makes such DSOs appealing to me in addition to galaxies....I never imaged them, apart from Orion's and the Ring....