Lunt B1800 CaK diagonal - first light report

As outlined in another thread, I purchased a Lunt B1800 CaK diagonal recently at NEAF. This filter is for observing the Sun at a wavelength of 393nm. FWIW, calcium makes up less than 0.01% of the Sun's mass. The bandpass of the filter is 2.4A, which is significantly wider than most h-alpha filters. The filter, which operates like a diagonal, is designed to operate in refractors with aperture of up to 100mm.

Yesterday evening and this evening, I tried the filter in my William Optics 80mm refractor. The image is slightly dimmer than the view through a PST H-Alpha but much brighter than what can be seen in a PST CaK. The active regions were clearly visible and the granulation-like effect across the disc was barely visible. A dark cloth placed around the head to block stray daylight from entering the observing eye helps significantly.

I also have a TEC140 refractor -> aperture = 140mm. For this scope, I made a simple 100m aperture mask and temporarily taped it over the front of the scope. With this increase in aperture over the 80mm, the granulation-like effect across the disc was easier to see as was detail in the active regions.

I then tried imaging one of the active regions with my DMK camera.
Below is a very simple test image.
No. of frames:500 - Frame Length:1/10th.sec - Quality Setting:90%



Hope this simple report is useful to anyone who may be interested in purchasing one of these units.

Regards,

Michael.

Hi Michael

Is the level of detail any better than a CaK PST, was thinking of modding a CaK PST too, but wont if this is better. also do you need a front ERF??

Thanks

Looks great btw

DG

Dave,

You do not need an ERF for apertures up to 100mm when using this filter.
It has a built-in ERF at the front of the diagonal which reflects the unwanted energy back out the front of the scope.

Above 100mm aperture, an extra ERF is required at the front of the scope. The ERFs that are normally used for H-Alpha observing, are, in general, not suitable for use with this filter as they usually block the Calcium K frequency (393A). Lunt will sell you an ERF for use with this filter if you contact them, but it's very expensive apparently (approx $1k IIRC).

Advantages of this filter over a PST CaK:
* Much brighter image.
* Much better resolution.

Disadvantages:
* More expensive.

Modding a PST CaK is possible, but personally I wouldn't risk such a solution for visual observing. However, for an imaging-only solution, that may be different.
Do you already have a PST CaK?

Michael.

A second test image from this afternoon:



Michael.

Very nice images Michael, some really good detail.
From a visual point of view, how does the detail compare with a h-alpha pst interms of non granulation detail?, cos I have to say the cal-k pst, all I could see was a disk, no detail,

Dave,

This image shown below here taken by Stephen W. Ramsden is a good indication of the level of detail I could see visually today:



I could well be wrong, but I think you will be able to see detail through this filter quite easily.

My own 2 images shown above do not quite bring out the full level of detail which can be seen visually.

Michael.