SolarChat!

christian viladrich wrote: ↑Wed Mar 20, 2019 6:55 pm Mark : not yet ;-)

You tease

christian viladrich wrote: ↑Wed Mar 20, 2019 6:55 pm Bart, the idea of removing the coating of the secondary, or of having an MCM-like coating on the secondary, is not a good idea. This is because the secondary mirror support would get all the heat load. There would be no mechanical problem. This is just you will have the equivalent of a 40 Watts heater (for a 200 mm aperture) just in front the focus. The seeing would be awfull.
On the other hand, having a 200 mm primary mirror coated by MCM (Ha + CaK) would be OK. The only issue is to gather a group of four 200 mm mirrors to fill the coating chamber.
Unfortunatly for my 300 mm telescope, 250 mm is the max possible size for MCM coating chamber

Mark : not yet ;-)

Hi Christian, thanks, I understand what you mean. But does the same problem not occur when you mount the Baader Blue just before the secondary?
Hmm. So now I have to find three more people who want to build a 20cm CaK / H-alpha Newton. (-;
I read somewhere that MCM can go up to 250mm, that is the reason the mirror I will be making this winter will be a 250mm f/6. But the idea of 4 20cm mirrors is very interesting.
Good luck with the experiment!
Bart.

Hi Bart
The blue Astronomik filter transmits about 20% of incident energy and reflects the other 80%.
So, for a 300 mm diameter, it means 20% x 100 W = 20 W going to the secondary.
The secondary reflects 90% of energy. It means that 20 x 0.9 = 1.8 W heats the secondary mirror support. This is not a big deal.

If you are interested, I can get you in touch with other people for a CaK/Ha coating. Drop me a personal message.
Christian

A nice spot in the last couple of days, but no time to image. So tonight, while watching soccer (Netherlands vs Germany), tweaked the Newton a bit.
- Changed the little allen screws (to collimate the secondary) for simple M4 screws. Why on earth do they use these small screws in the first place?
- From a plastic milk carton I cut two small discs that rest on the secondary mirror holder. The central screw of the secondary hold them in place, the M4 screws don't touch the aluminium anymore, but the plastic discs. This way the collimation is much more accurate.
- Tweaked the focuser a bit so now it does not operate so stiff anymore.
- Wrapped the scope in radiator foil. Did that a long time ago with my Intes for night time use, now this one also looks like a silver tube.

Earlier today I made a drawing for a Serrurier Truss version in wood. Really simple. 4 22x22 bars, some 9 mm triplex and 4 mm aircraft plywood. But first try this version.
So. The scope is ready, the sun is bald and we lost in the last minute or so.

[Edit] Ken corrected me, and he was right. The drawing I made was not a Serrurier Truss, but an open truss design, less complicated than the Serrurier Truss version.

First light yesterday! Terrible seeing, did not use the SSM because I just wanted to try everything out quickly. The original focuser is even more terrible than I thought, so changed it for a 2 inch focuser that I had bought for a future project. That was a major improvement.
Single stack CaK PST#1, used the 2 inch filter tube of the Lunt BF. Don't know if I used a single Baader K-line, it is all about administration....
Anyhow: gain 94, gamma neutral, 6,9ms. Stacked 50 images. That is a bit low, but with 100 and 150 images the result was worse. So a lot of noise, and a lot of improvement possible. Now waiting for a day with better seeing.

Sun_142754_310319_Gain=94(off)_Exposure=6.9ms_Gamma=100(off)41646 by bart moors, on Flickr

First light is always exciting!!
Well done for getting reasonable result.
Onwards and upwards.

The first light CaK looks good Bart...well done!!!

Brian

Seems to be working well Bart!

Thanks guys!
Hoping to find out the potential with better seeing and curious how big the negative effect of the original tube will be.

The first light seems promising, Bart. However looking at the full res image I see lot of noise, I think you should try stacking more images in better seeing conditions or to use a weak focal reducer to gain brightness. By placing a common 0.5x eyepiece reducer very close to the sensor, for example, it would work around 0.8x and should allow to reach focus even in your newtonian. This would require some adaption but it should be feasible.

Anyway I have found that my solar newtonian is most useful for imaging in the K-line with the Baader filter and in the G-line with the Andover filter, in these domains high resolution work is really possible when seeing cooperates.

I agree with what you say Raf: a lot of noise. Will keep experimenting!

Really cool Bart, I look forward to seeing how this progresses.

Any thoughts on transmission with that CaK filter? I'm curious how this would perform for high resolution CaK imaging in terms of keeping a high transmission compared to a 6" achromatic refractor with an ERF?

Very best,

You start off with about 4% of the light, so that is the big disadvantage for the stripped Newton compared to a 6 inch refractor with a Tri-Band Erf. If I were you I would go for a 150mm Newton, don't strip the mirror, but install the Tri-Band Erf on the front.

bart1805 wrote: ↑Wed Apr 03, 2019 9:27 pm You start off with about 4% of the light, so that is the big disadvantage for the stripped Newton compared to a 6 inch refractor with a Tri-Band Erf. If I were you I would go for a 150mm Newton, don't strip the mirror, but install the Tri-Band Erf on the front.

That's what I was wondering in general. I would imagine this is a great way to go for g-band imaging. I wondered if it would have enough transmission for something more narrowband. But as you pointed out, 4% transmission means likely not, at least, unless we're able to image with smaller pixels and a faster focal-ratio to match at a good sampling for the pixels.

I was curious for the sake of an 8 inch parabolic newt.

Very best,

Not sure whether this is relevant information : uncoated primary mirrors (4% reflection) are quite appropriated for G-band (FWHM = 2nm) and K-line (FHWM 8 to 10 nm) imaging.
However, for Ca K imaging (< 0.3 nm FWHM), the exposure time becomes too long.

Was not satisfied with the collimation of the telescope. This evening I used this little toy:
https://www.teleskop-express.de/shop/pr ... copes.html
So when weather and time allows I can compare the Newton with the 100 mm.

20190506_234342_resized by bart moors, on Flickr

I look forward to your next tests Bart, I'm always interested in CaK reports!

I've been looking at longer focal-ratio reflectors lately and think one may just find its way into my kit. My SCT is bad at these short wavelengths.

Looks like your mirror behaves nicely with 393nm!

Very best,

Was looking for a aluminised 150mm f/8 mirror but found for very little money another complete Skywatcher 150mm f/8. The light blue tube. The very good news is that it has a retrofit GSO 2 inch 1:10 focuser. The bad news is that the cell of the primary can't be collimated really easy.
So in the category "don't try this at home", and don't ever use it visually here is another approach to the CaK quest. Thanks to very large toothpicks and Duct tape (and a bit of MacGyver) here is the way I can mount a 2 inch Baader Blue CCD before the secondary.

20190519_233324_resized by bart moors, on Flickr

Hah, that works Bart!

Are you doing that as an alternative to dealuminizing the primary?

Very best,

MalVeauX wrote: ↑Tue May 21, 2019 7:52 pm Hah, that works Bart!

Are you doing that as an alternative to dealuminizing the primary?

Very best,

Hi Marty, yes that is correct. Exposure time has to be shorter than I am able to reach wit the de-aluminised version. Christian calculated that this would be the case, but off course I had to try it myself.....

bart1805 wrote: ↑Tue May 21, 2019 8:33 pm

MalVeauX wrote: ↑Tue May 21, 2019 7:52 pm Hah, that works Bart!

Are you doing that as an alternative to dealuminizing the primary?

Very best,

Hi Marty, yes that is correct. Exposure time has to be shorter than I am able to reach wit the de-aluminised version. Christian calculated that this would be the case, but off course I had to try it myself.....

I understand, I had asked earlier for that reason too, to be able to do 393nm & 430nm at large scale without the need of a big costly D-ERF and without using broad transmission grinders like ND3.8 solar film. At 430nm, you can definitely do it and have plenty of transmission. But 393nm, well, the filters that are narrow enough to do that down to 2.4A or less grind transmission significantly so it soaks up all the transmission at large scale.

I currently am testing a 200mm F6 quartz mirror using a D-ERF in front of it. Transmission is very high with the D-ERF. The low transmission bits in the train are generally always the narrowband filters themselves. My transmission in my 430nm train is so high that I have to use a ND1.8 filter just to grind it down enough to not saturate the sensor at the shortest exposure of 0.032ms. Need to better collimate it and then hopefully a new spot will show up soon to test it.

For long wavelength, dealuminized mirrors are fantastic for high resolution. The tricky part are these pesky short wavelengths!

Very best,

Hi All...

This was likely covered before, but the de-aluminized mirror seems to work well with G-band filters, but is there sufficient light to utilize an Ha filter (PST/Quark/Quantum)?

Also, if the de-aluminized mirror does not provide enough light for CaK filters, could the mirror me partially aluminized to provide sufficient light...say 10%, or the required level? My thought is coating 'pie' shaped sections of the mirror...narrow slivers..enough to increase the refection to reach the desired amount of reflection. You might get enough light to collimate on a bright star as well? Partial coating would keep the parabolic shape and reflected light cone should be the same as a full mirror, just less intense?

Crazy idea maybe, but if you could boost the light for CaK and add a filter ahead of the secondary to attenuate the intensity for other bands it could make a versatile instrument.

Brian

Hi Brian

no, based on my experience there is no enough light for imaging in H alpha with a deluminized mirror. However the field is not completely dark, at least with my Quark, may be something can be done at low resolution but in my opinion is not worth the effort.

I have no experience with Lunt CaK modules however with a Quark Calcium (H) imaging is possible, I did it many times. The problem with a newtonian is the sun heat entering the tube which causes much turbulence, the tube should be open to minimize this effect whichever solution is adopted for the optics.

Christian wrote something here about the effectiveness of placing a filter ahead of the secondary.

Yes, with a Quark CaH it is possible. It is less narrow than a Lunt CaK module or a PST#1 filter.
Brian: MCM can apply coatings to a mirror so it reflects just H-alpha and CaK.

Hello Bart,
I like your filter support system :-)
I have made no progress on my side since I was busy on other things. I've got to get into this in June.
BTW, did you observe any temperature issue with the filter ?
Best regards
Christian

christian viladrich wrote: ↑Wed May 22, 2019 6:51 pm Hello Bart,
I like your filter support system :-)
I have made no progress on my side since I was busy on other things. I've got to get into this in June.
BTW, did you observe any temperature issue with the filter ?
Best regards
Christian

Hi Christian,
No heat issues at all at the moment. But it is still standing on my desk. (-;
Hope to be able to test it soon, will let you know the results.
CS! Bart.