Focussing with Astro imaging cameras

[sshenke]

Hello, I would appreciate some advice on this matter please. Since buying the HEQ5 Pro Skywatcher mount ( with skywatcher 130PDS ), the world of deep sky astronomy has opened up to me and I am very excited to actually capture some of the DSO's recently, but the issue is with focussing. I am using a Sony A200 DSLR, which doesnt have live view. I have used a Bahtinov mask as well, but again the image seen through the view finder is too dim to adjust the focus. I have tried taking a few test images and then to download onto PC/ mobile phone and then to get an idea of the focus by zooming into the image. I still cant see the diffraction spikes properly to get the image into sharp focus.  Hence I am thinking of other options such as moving onto buying a dedicated astronomy camera in the ZWO range. My question is, will using the astronomy camera help me achieve a sharp focus? Will I be able to use the Bahtinov mask with the ZWO camera and see the live image on a PC to adjust the focus? Sorry if it seems a silly question, but would appreciate any advice, as this has been a vexing problem for me. Thanks in advance.

[Astrosharkey]

Yep with no issues and as you will have to use a capture program most have focus assistants built in as well.

[sshenke]

Oh.. brilliant. Thank you very much. Much happier now..😀

[carastro]

I presume you have tried seeing focus with Bahtinov on the laptop itself.  

But the answer to your question regarding focussing with a CMOS camera and laptop should be much easier, especially if you are using a Mono camera,   Take slightly longer looping exposures and if you can use binning while focussing it makes download quicker.

Carole 

[Owmuchonomy]

Doesn’t the Sony software have a live view function? If so you can just do it via the laptop. That’s how I do it when using my Canon DSLR.

[sshenke]

Thanks. I am not sure if there is a PC software for sony A200, but I am going to have a look online.

[sshenke]

17 minutes ago, carastro said:

I presume you have tried seeing focus with Bahtinov on the laptop itself.  

But the answer to your question regarding focussing with a CMOS camera and laptop should be much easier, especially if you are using a Mono camera,   Take slightly longer looping exposures and if you can use binning while focussing it makes download quicker.

Carole 

Thank you. will definitely try that.  I have seen a few websites discussing the pros and cons of mono and colour cameras. The main message that sticks in my head is that the light gathering efficiency and noise reduction is better with mono's, am I right? Another silly question, most of the DSO images I have seen, have these dazzling colours which is what makes them attractive. Wouldnt that detail be lost if imaged using mono camera?

[carastro]

A Mono camera needs to use filters (which makes it more expensive) to produce colour.  But the sensitivity is better with a mono camera.

Carole 

Edited May 26, 2019 by carastro

[sshenke]

Ok, thanks. Will go for a mono camera then.

[tomato]

If you want to get into DSO imaging I strongly recommend you get a copy of this:

https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

[Datalord]

9 hours ago, sshenke said:

Ok, thanks. Will go for a mono camera then.

While everything said is correct and that I have moved from one-shot color CMOS to a mono CCD, the CMOS with a one shot color has a ton of advantages I sometimes miss. Not least that processing them is SO much easier.

[AngryDonkey]

39 minutes ago, Datalord said:

Not least that processing them is SO much easier.

I think that really depends on what you are trying to achieve. For a quick and 'reasonably good' result that might be true but if you have time to spend and some experience in processing it is most likely the other way round i.e. the mono images will be easier to process because you have the option to process luminance and RGB channels separately which gives you more control and options. In other words I found it quite hard to get a 'really good' image from my OSC camera and it seems much easier with my mono cam.

[carastro]

OSC is OK if you have the right bayer matrix but I got totally messed up with my OSC and the bayer matrix, tried all sorts of combos and in the end gave it up as a bad job.  The colour results from it (when I could get it to process properly) were not as good as I could get with the mono camera which I found far more straight forward.  Plus of course you can do narrowband.

Carole 

[Datalord]

6 hours ago, AngryDonkey said:

For a quick and 'reasonably good' result that might be true but if you have time to spend and some experience in processing it is most likely the other way round i.e. the mono images will be easier to process because you have the option to process luminance and RGB channels separately which gives you more control and options.

I don't think it is all that different tbh. Yes, there are a few extra places you can tweak things, but whether that makes much of a difference in the end is debatable. I will concur that my images have become much better after going mono, but I attribute that more to learning processing than to the root data.

3 hours ago, carastro said:

OSC is OK if you have the right bayer matrix but I got totally messed up with my OSC and the bayer matrix, tried all sorts of combos and in the end gave it up as a bad job.  The colour results from it (when I could get it to process properly) were not as good as I could get with the mono camera which I found far more straight forward.  Plus of course you can do narrowband.

I had a few misfires as well, but once you get the bayer down, it is smooth sailing. And you can actually do narrowband, it just takes longer to get the same signal. 

 

 

I'm also taking into account that the OP is very new to the hobby. Jumping straight into mono and filters and wheels and whatnot is probably not the optimal path to dipping toes into it. And I often yearn for the simpler workflow.

[carastro]

I had forgotten about those multi NB filters for OSC cameras never having used one. But as you say it does take longer.

Carole