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Lunt CaK B1200 + PST #1 yellow

Posted: Mon Oct 01, 2018 12:02 am
by george9
I was experimenting with a PST #1 yellow filter with my Lunt B1200 CaK. I was testing on a 70mm F/6.8 doublet. I only have an R2 Revolution imager, so no reasonable photos to show. I will try to attach iPhone shots of the R2 monitor.

Lunt with the yellow filter vs. Lunt without:

1. Gain had to be increased from 6dB to 18dB, so it was dimmer.

2. It seemed a little higher contrast between the active region and the rest of the disk, within the limits of the R2.

3. I think is could see more subtle variation within the active region itself.

4. I could not see the H-alpha filament in either one.

5. I could see subtle linear details in both, but perhaps better with the yellow filter but not sure.

6. There was a faint reflection with the yellow filter that I could tilt off axis. It only showed up at higher (e.g., 42 dB gain).

7. Prominences were visible only in the solo Lunt (at about 42 dB).

Some of the difference in contrast, perhaps, could be the change in brightness and the fact that the R2 has discrete gain settings. Maybe the dimmer version just lined up better with the R2's thresholds.

So I probably will not be able to tell much more unless I move up to a real camera and computer.

I may just sell the PST CaK, stick with the Lunt Cak and R2, and put my investment mostly into H-alpha because I am mostly visual.

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Re: Lunt CaK B1200 + PST #1 yellow

Posted: Mon Oct 01, 2018 6:14 pm
by marktownley
This using the filter that is in the end of the gold tube / entrance to the black box George?

Re: Lunt CaK B1200 + PST #1 yellow

Posted: Mon Oct 01, 2018 9:19 pm
by george9
Yes, the first filter after the objective lens. It is thin and yellow and 25mm in diameter. The one after it is mirror-like. Then the black box.

(In case it's not obvious, the image with the 18 above is the one with the yellow filter. And thanks for the advice, Apollo.)


Re: Lunt CaK B1200 + PST #1 yellow

Posted: Sun Nov 11, 2018 9:37 pm
by george9
Some follow up. I finally got a decent chance to compare my Lunt B1200 CaK, the Lunt with the PST yellow filter, and the Lunt with a neutral density Moon filter (just to ensure any improvements weren't due to dimming the image to a better place in the imager's range). First image is Lunt alone, then Lunt+PST, then Lunt+Moon. While the middle one clearly looks best, it looks in these iPhone shots like a mere difference in telescope focus or seeing. I can assure you that I put in a lot of effort to focus for all three, but of course hard to control seeing. But my impression over time swapping back and forth across a lot of different seeing matched these images. There was a real increase in contrast. The Moon filter apparently transmits poorly at 393 so that adds to its challenge.
CaK options.jpg
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Re: Lunt CaK B1200 + PST #1 yellow

Posted: Mon Nov 12, 2018 12:41 pm
by Bob Yoesle
Hi George,

I don't know if you saw these, but here's my recent results using a $350 Chameleon CCD camera. I already knew from a few years ago that double stacking CaK filters provides a contrast improvement. Triple stacking CaK filters is useful for bringing out details near to the solar limb. The super-granulation also seems to my eye to be more apparent.

Left to right, PST, PST/PST, ChromaTech/PST/PST:

Stacking CaK effects.jpg
Stacking CaK effects.jpg (481.17 KiB) Viewed 2734 times

Stacking of course requires longer exposures and better seeing for ultimate detail, but I do think it is advantageous in my system using an ED100 f9.

Re: Lunt CaK B1200 + PST #1 yellow

Posted: Tue Nov 13, 2018 12:41 am
by george9
Thanks, Bob. Yes, you have a similar effect. George

Re: Lunt CaK B1200 + PST #1 yellow

Posted: Tue Nov 13, 2018 6:13 pm
by Valery
TheSkyBurner wrote:
Mon Oct 01, 2018 1:39 am
do not sell it for too cheap, these things are worth no less than your b1200 filter; and the demand for them is insane.

keep in mind it is much larger than the b1200, and supposedly has narrower bandpass. I ask no less than $700 for mine. That is more than fair for how rare these are.

people are saying they are dual or triple cavity filters. That places them in the thousand dollar range by manufacturing standards.
Hi Apollo,

I now quite confused with your two polar statements. This one and here: viewtopic.php?f=9&t=25174

So, where is the truth? Thanks for the clarification.

BTW. Your 2" SkyBander has arrived. Thanks a lot!

BTW2 I planned to use the Skybander in experiments with CaK filters. And I hoped for 1,25" SkyBander. It is difficult to put the 2" one in my
CaK imaging rig. But I will try.