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Hi Everyone

Is it possible to image the Horsehead Nebula using a Lunt LS60 THa (With a ZWO 294MC Pro) if the Blocking Diagonal is removed?

Just a thought......

Thanks

Hi,

I don't see why not... It might be quite small as you will get a fairly widefield view of about 2 by 1.5 degrees (see https://astronomy.tools/calculators/field_of_view/). I presume that the blocking filter in the diagonal is the only filter in the LS60THa, meaning it is a normal telescope with that removed?

cheers,

Robin

Hello,

If the Ha etalon stays in place then you will have the following ...

here 3 images (with my Lunt 50 mm filter) and a spectrometer:
- Sun spectrum (centred to the Ha line)
- Sun spectrum after placing the Lunt 50 etalon in front of the spectrometer (without blocking filter, the image a little bit overexposed)
- Sun spectrum after placing the blocking filter before the camera (so with etalon filter)
If you can use the telescope without any filter, then it will be like other telescope.
If you dismount the blocking filter, but you have still the etalon filter ... then you will have the middle image.
So not only the Ha line, but all other wavelength over the full spectrum.

I have not an image with the blocking filter alone ... but it will be similar as the Ha narrow band filter.

Regards,
Jean-Francois

Jean-Francois wrote: Tue Apr 23, 2024 4:59 pm Hello,

If the Ha etalon stays in place then you will have the following ...

here 3 images (with my Lunt 50 mm filter) and a spectrometer:
- Sun spectrum (centred to the Ha line)
- Sun spectrum after placing the Lunt 50 etalon in front of the spectrometer (without blocking filter, the image a little bit overexposed)
- Sun spectrum after placing the blocking filter before the camera (so with etalon filter)

Sun_Ha_blocking-filter.jpg

If you can use the telescope without any filter, then it will be like other telescope.
If you dismount the blocking filter, but you have still the etalon filter ... then you will have the middle image.
So not only the Ha line, but all other wavelength over the full spectrum.

I have not an image with the blocking filter alone ... but it will be similar as the Ha narrow band filter.

Regards,
Jean-Francois

Thank you for the detailed and comprehensive explanation, However...........Will I be able to see on my screen the Horsehead Nebula? (I figure it would need processing after to bring out detail?) or would I get an Image the same as the ones you posted (Lines) - Thanks Carl.

Hello Carl,

The first question is ... is the Horsehead an emission nebula or a reflective nebula ?

Other question ... can you dismount the etalon filter ?

If the etalon is fixed ... then you will have the light at the Ha wavelength, but in addition thousand of other lines.
The contrast will be very few improved.

In the case that the Horsehead is an emission nebula, then it is better to use a dedicated Ha (and/or OIII) photographic filter (Baader, Lumicon, ...).
In the case it is a reflective nebula, then you will have no improvement using the telescope with the Ha etalon without the blocking filter.
You will have no other potential emission lines. You will have some blocking of the background sky illumination (pollution), but only for the narrow emission lines (and only if not by chance on one peak of the etalon transmission). The diffuse illumination from the LED will be not blocked.
In addition, you will need to have a much longer exposure time (10 to 20x more).

So the last question is ... how long can you expose ? ... So yes, you will see something, but it will take more as with the right filter.
The image will have lower contrast as with traditional Ha imaging filter.

Jean-Francois

Carlgreen
IN case you are still wondering about your scope use.
The Lunt 60 THA is the "special " model designed to work as a solar scope and as a normal night time scope.
To use as a Night time scope you will need to remove the Etalon (Red section of the scope) and the blocking filter.
The Etalon is designed to be be easily removed.
If you look on the Lunt site they have a youtube video showing how to use the scope for nighttime visual or imaging.
You can then use with your ZWO 294MC Pro camera .
Take care