A doublet [ED] for astrophotography?

[TareqPhoto]

Hi all,

 

Is a doublet scope good for astrophotography? And i am only thinking about Ha filter or narrowbanding filters in general and only Lum filter, not RGB filters, and maybe no OSC camera, but let's say we add OSC camera then we use that L/LP filter to kill/reduce halo, but in general, is it great enough to have sharp contrasty images same or similar to a triplet?

 

We know a triplet is better, but it is always about how the triplet treat the light path for the colors or RGB, but is that also applicable with NB filters or Lum filter?

[AstronomyUkraine]

26 minutes ago, TareqPhoto said:

Hi all,

 

Is a doublet scope good for astrophotography? And i am only thinking about Ha filter or narrowbanding filters in general and only Lum filter, not RGB filters, and maybe no OSC camera, but let's say we add OSC camera then we use that L/LP filter to kill/reduce halo, but in general, is it great enough to have sharp contrasty images same or similar to a triplet?

 

We know a triplet is better, but it is always about how the triplet treat the light path for the colors or RGB, but is that also applicable with NB filters or Lum filter?

I have taken many images with my Skywatcher ED doublet. They are fine for narrowband images, as the channels can be aligned in the processing software. With an OSC camera one channel will always be out of sync when using a doublet.

 

Of course there are many types of doublet, some very cheap ones, and the better quality ED ones.

[TareqPhoto]

3 hours ago, AstronomyUkraine said:

I have taken many images with my Skywatcher ED doublet. They are fine for narrowband images, as the channels can be aligned in the processing software. With an OSC camera one channel will always be out of sync when using a doublet.

 

Of course there are many types of doublet, some very cheap ones, and the better quality ED ones.

 

I just mentioned doublet without talking about the optics quality used, so let's say we use FPL-53 or even Fluorite doublet, then what?

I just said Ha and Lum and no RGB, or OSC with more suppression Lum/LP filter to kill UV and little of blue, because it is always about CA we are talking about, there are filters that will be a bit narrowing of Lum than average wider one.

[AstronomyUkraine]

9 minutes ago, TareqPhoto said:

 

I just mentioned doublet without talking about the optics quality used, so let's say we use FPL-53 or even Fluorite doublet, then what?

I just said Ha and Lum and no RGB, or OSC with more suppression Lum/LP filter to kill UV and little of blue, because it is always about CA we are talking about, there are filters that will be a bit narrowing of Lum than average wider one.

Better quality glass will give you more contrast in your images, and sharper details. A doublet is not going to affect luminance data. Even with filters when using an OSC you will get a certain amount of CA when using a doublet, but software can eliminate this quite easily.

[TareqPhoto]

1 minute ago, AstronomyUkraine said:

Better quality glass will give you more contrast in your images, and sharper details. A doublet is not going to affect luminance data. Even with filters when using an OSC you will get a certain amount of CA when using a doublet, but software can eliminate this quite easily.

 

Ok, it sounds i have to struggle and suffer and just keep saving and spend more, i will get a triplet or more optics design and stop worrying about doublet quality/performance.

 

Thank you

[MarkAR]

I think if you go the ED Doublet route a CCD rather than CMOS would be better.

What I can't get my head around is that with a doublet the RGB do not align properly, different focal point. If you use RGB filters then surely each channel will find the right focal point for it's bandwidth and hey would all be in focus. Maybe I'm missing something 🤔

[TareqPhoto]

47 minutes ago, MarkAR said:

I think if you go the ED Doublet route a CCD rather than CMOS would be better.

What I can't get my head around is that with a doublet the RGB do not align properly, different focal point. If you use RGB filters then surely each channel will find the right focal point for it's bandwidth and hey would all be in focus. Maybe I'm missing something 🤔

 

Yes, i know, but this doublet scope will be using with only narrowbanding filter one of the three or Lum which is a sum of RGB anyway, so only Lum filter was my concern with the doublet.

[MarkAR]

Lum will be the tricky one. A lot will depend on the quality of the glass as to how much CA you will get but I think with modern doublets there is very little CA. It can be processed out anyway or at least minimised.

[TareqPhoto]

23 hours ago, MarkAR said:

Lum will be the tricky one. A lot will depend on the quality of the glass as to how much CA you will get but I think with modern doublets there is very little CA. It can be processed out anyway or at least minimised.

 

Yes, i thought about that.