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150 mm Solar Newton

Posted: Fri Mar 15, 2019 3:36 pm
by bart1805
Yes, I would like to have a 150mm TOA. But then again: that is a dreamscope! So to move up in aperture for imaging the sun in CaK a Newton seems to be quite ideal. It has been done before, with bigger and smaller mirrors. When you de-aluminise only the primary and not the secondary, the effect can be compared to using a solar wedge. So approximately 4% reaches the filters and camera.

I found a second hand 150mm f/8 Skywatcher, interesting because of its focal length and small secondary. It has a 1,25 inch focuser (that is not so positive) and does not weigh much.
Today I started with stripping the mirror. I followed the same route Douglas described here:
http://solarchatforum.com/viewtopic.php ... ic#p117999

Here is the original mirror:

Image20190315_093632_resized by bart moors, on Flickr

Masking tape around the edges and poured some ferric chloride on it.

Image20190315_112922_resized by bart moors, on Flickr

After about 10 minutes the dissolving started.

Image20190315_120530_resized by bart moors, on Flickr

It took about 2,5 hours to dissolve all the metal. And here is, after cleaning, the now completely naked mirror:

Image20190315_160315_resized by bart moors, on Flickr

Clouds and rain this weekend so enough time to apply a new center marker on the mirror, put everything back together and collimate.

Questions? Feel free! Thanks for reading, Bart.

Re: 150 mm Solar Newton

Posted: Fri Mar 15, 2019 4:04 pm
by MalVeauX
Nice Bart, I've been interested in a solar newt for a while, with respect to white light & calcium, and short wavelength imaging in general at higher resolution without the need for a costly ERF or sophisticated design. Newts can be open and well ventilated and are inexpensive. Other than the weight when you go larger (8", 10" +) they're really a great alternative, albeit, dedicated for the task. I'd love to do a 10" for 430nm, but I can't support the weight on my mount currently.

I look forward to your results!

Very best,

Re: 150 mm Solar Newton

Posted: Fri Mar 15, 2019 4:54 pm
by bart1805
The same here. I am going to start relatively small and see for myself what are the good and bad points. And yes they are cheap. This complete scope will be less than a holder for a medium sized ERF.
If all goes as planned I will be making my own 9 inch f/7 mirror in the last quarter of this year. Looking forward to learning how to do it. And I have time to experiment with this one and try to get an idea how the bigger one should look like.

Re: 150 mm Solar Newton

Posted: Fri Mar 15, 2019 9:41 pm
by MalVeauX
I've looked at the mirror sets you can get for the primary & secondary, nothing else, from Agena Astro and they're inexpensive. I looked at those because while most 10" F4~F5 reflectors are 34~35lbs minimum, most of that weight is the tube (at least at those sizes). The GSO 10" mirror set is like 8~9lbs total. And it's the same mirror in the generic 10" F4/F5 OTAs being sold, so over 20+ lbs for just the OTA tube and accessories. I'm sure the mirror holding cell weighs a bit too. But still. I was thinking of what it would take to build an ultra-light-weight truss. I've seen lots of single truss designs for much bigger scopes using wood and/or aluminum. Could probably shave the weight that way to build an ultra-light-weight 10" F5 (so it's F10 with a 2x). Getting that weight down under 30lbs maybe. That would be a sweet inexpensive entry point to 430nm/Gband imaging that would also be handy for CaK and even 532~540nm.

Very best,

Re: 150 mm Solar Newton

Posted: Sat Mar 16, 2019 9:50 am
by Carbon60
Interesting project, Bart. Good luck with this. At least it gives you something to do whilst it's raining. :D

Stu.

Re: 150 mm Solar Newton

Posted: Sat Mar 16, 2019 3:59 pm
by skyhawk
Unsafe for visual ????

Re: 150 mm Solar Newton

Posted: Sat Mar 16, 2019 5:24 pm
by krakatoa1883
A solar newtonian is a very useful addition to a solar setup. I made my own and I am very happy, It is useful for both WL, K-line and Ca-H without the need of expensive ERFs. Diameters larger than 5 or 6 inch require an open tube and a careful design to avoid internal turbulence.

It is safe also for visual with additional filtering.

Re: 150 mm Solar Newton

Posted: Sat Mar 16, 2019 9:26 pm
by bart1805
krakatoa1883 wrote: Sat Mar 16, 2019 5:24 pm A solar newtonian is a very useful addition to a solar setup. I made my own and I am very happy, It is useful for both WL, K-line and Ca-H without the need of expensive ERFs. Diameters larger than 5 or 6 inch require an open tube and a careful design to avoid internal turbulence.

It is safe also for visual with additional filtering.
Thanks for the link Raf. I saw you left the center marker on the scope when you de-aluminized the primary, that is a good idea! It should be possible to left the center also aluminised, that would make the collimation proces even easier.
Could you please explain this one:
Since the sunspots are high contrast details, the obstruction caused by the secondary mirror is not important as the lens works on the right side of the MTF graph and therefore the "traditional" advantage of the refractor on the reflector is almost missing from the all.
I thought it would be better to work with a secondary as small as possible, if not for the contrast, then to minimise the aperture loss.

Re: 150 mm Solar Newton

Posted: Sat Mar 16, 2019 9:35 pm
by bart1805
@Skyhawk: yes totally unsafe when you use it this way. You could also de-aluminize the secondary and use filters or work the way Raf described. For me it will be a imaging instrument, not a visual one.
@Stu: the rain is (unfortunately) true.... Everything is ready now. Flocked the opposite of the focuser and the focuser tube, collimated the instrument. So waiting for clear skies!
@Marty: don't use a spherical mirror, but a parabolic one. And the faster the scope, the more critical is the quality of the mirror. It is just a whole lot more difficult to make a 10 inch f/5 than a 10 inch f/7. That is the reason "my future mirror" will be 9 inch f/7 or 10 inch f/6,5. A Serrurier Truss concept seems the way to go.

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 6:42 am
by Rusted
How do you deal with the equally strong reflection from the back of the mirror blank?

A wedged blank is possible, but difficult. Rough ground? A conical blank? Obsidian? Black paint wouldn't work.

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 7:14 am
by marktownley
A solar newton is a very good idea.

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 7:52 am
by bart1805
Rusted wrote: Sun Mar 17, 2019 6:42 am How do you deal with the equally strong reflection from the back of the mirror blank?

A wedged blank is possible, but difficult. Rough ground? A conical blank? Obsidian? Black paint wouldn't work.
Hi Rusted, here is more information by Christian Viladrich about the back of the mirror.
http://www.astrosurf.com/viladrich/astr ... /N300.html

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 9:33 am
by krakatoa1883
bart1805 wrote: Sat Mar 16, 2019 9:26 pmI thought it would be better to work with a secondary as small as possible, if not for the contrast, then to minimise the aperture loss.
in general the smaller the secondary obstruction the better the performance for high resolution work. However sunspot umbrae and penumbrae represent black-grey details on a bright white background, much more contasted that typical planetary details. In the MTF graph that represents the performance of the scope in terms of contrast the system works toward the lower-right corner, where it is closer to the contrast curve of an unobstructed telescope. In fact the WL images provided by my solar newt are very similar to those I have from my 100mm ED through the Baader wedge. In calcium light a good filter provides enough contast and the results are similar, I would say even better due to the perfect correction of the newtonian in the UV.

However be prepared to cope with more turbulence, from this point of view the refractor is always better unless the tube of the newtonian is totally open to air. In particular I found calcium imaging with my non-optimized solar newtonian (I kept the original tube) really challenging.

Rusted wrote: Sun Mar 17, 2019 6:42 am How do you deal with the equally strong reflection from the back of the mirror blank?

A wedged blank is possible, but difficult. Rough ground? A conical blank? Obsidian? Black paint wouldn't work.
a rough ground is enough, no problem of unwanted reflections

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 12:17 pm
by Rusted
Thanks. So how does the thick, glass blank behave when constantly bathed in sunlight?
Does it "warm up" above ambient and then need forced cooling?
THis may be the problem rather than passing air currents through the OTA.

You raise some interesting issues with open structures.
Refractors can also be built as open frames. As is my open, folded 180/12 OTA.
I haven't tried this instrument with a Herschel wedge let alone for H-a.
Would it suffer from increased thermal current issues if I simply removed the full aperture foil filter?
I'm just trying to level the playing field here between mirror and lens, solar telescopes.

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 5:11 pm
by bart1805
Thank you Raf.
Will first try it like it is now. Then I will make a simple wooden box 21x21 cm. 3x3 cm bars will function as the trusses. It will be an ultra simple wooden Serrurier Truss telescope. In combination with the SSM I think it will work. In fact, thanks to the SSM, I kind of lost my fear of bigger aperture when imaging the sun.

Re: 150 mm Solar Newton

Posted: Sun Mar 17, 2019 9:38 pm
by krakatoa1883
Rusted wrote: Sun Mar 17, 2019 12:17 pmDoes it "warm up" above ambient and then need forced cooling?
THis may be the problem rather than passing air currents through the OTA.
it depends on the mirror material as explained in the link to Viladrich's newtonian. I never found my mirror hotter than ambient temperature, at least by touching it, but I don't have thermometric mesures.
Rusted wrote: Sun Mar 17, 2019 12:17 pmWould it suffer from increased thermal current issues if I simply removed the full aperture foil filter?
closed tube refractors perform very well with a Herschel wedge, if your scope has an open frame it should behave even better.

Re: 150 mm Solar Newton

Posted: Mon Mar 18, 2019 6:37 am
by Rusted
Thanks for the useful responses.

I could imagine the mirror blank's temperature being easily monitored with a cheap and simple Indoor/Outdoor digital thermometer.
The outdoor sensor on the lead could be taped to the side of the mirror blank but shaded to avoid direct sunlight skewing the readings.
Avoiding local metal parts and placing the Indoor case in the shade is vital for accurate comparison.

Anyone who has tested an uncoated mirror on the Moon will confirm there is still a great deal of light reflected.
One should be very careful about filtering such telescopes since apertures can easily exceed most amateur's refractors.

Re: 150 mm Solar Newton

Posted: Mon Mar 18, 2019 12:30 pm
by krakatoa1883
Rusted wrote: Mon Mar 18, 2019 6:37 amAnyone who has tested an uncoated mirror on the Moon will confirm there is still a great deal of light reflected. One should be very careful about filtering such telescopes since apertures can easily exceed most amateur's refractors.
indeed this is the main advantage of solar reflectors, they makes available large apertures for WL high resolution work at a fraction of the weight and the cost of a refractor of comparable aperture. Mine is perfect for both imaging and visual if additional filtering is applied, larger newtonians should probably be checked for suitability. Btw the filters needed for visual use with my 130mm newtonian (ND3.0 + ND06 + UV/IR cut) are the same that are mounted in the Baader CC wedge for visual observing with my 150mm refractor.

Re: 150 mm Solar Newton

Posted: Mon Mar 18, 2019 5:18 pm
by Rusted
Excellent. Thanks.

Re: 150 mm Solar Newton

Posted: Mon Mar 18, 2019 7:31 pm
by christian viladrich
Hello Bart,
This is an interesting project !
This being said, and for Ca K - H imaging, and considering you have an F/8 mirror, another option would have been to keep the primary mirror coated.
The setup would have been a litlle bit more complex because you have have needed the addition of a subaperture filter just in front of the secondary mirror. A blue Astronomik or Baader filter could do the job for Ca K imaging or G band. The optical quality of these filters is about L/4 P-V.
The issue with the uncoated primary miror and Ca K, is that the level of light is a bit low.
In any case, this is something you can experiment at a later stage of the project. And you are going to have a lot of pleasure with the current configuration.
Cheers
Christian

Re: 150 mm Solar Newton

Posted: Mon Mar 18, 2019 8:10 pm
by bart1805
Thanks Christian. I talked about this project on a Dutch site and there someone suggested the same. But that was also after I had bathed the mirror in the ferric chloride..... It is not an exotic mirror, so someday I will find one to experiment the way you describe here. Mounting it before the secondary would be possible, but maybe making another spider lower in tube to fully use the two inch of the filter is the way to go. The amount of heat will increase a lot when you go bigger than 150mm, would it work (or would you dare it) in a 200 or 250mm telescope?
It will be interesting to see how half a Baader K-line plus one or two of the PST#1 filters will work in this de-aluminised version.
CS! Bart.

Re: 150 mm Solar Newton

Posted: Tue Mar 19, 2019 7:19 pm
by christian viladrich
Hi Bart,
Testing the concept with a 200 mm F/8 mirror (indeed a 300 / F5.5 stopped to 200 mm) is on my to-do list. I think it should be OK.
Before that, I am working on another project related to very narrow band Ca K imaging.

Re: 150 mm Solar Newton

Posted: Tue Mar 19, 2019 8:34 pm
by bart1805
christian viladrich wrote: Tue Mar 19, 2019 7:19 pm Hi Bart,
Testing the concept with a 200 mm F/8 mirror (indeed a 300 / F5.5 stopped to 200 mm) is on my to-do list. I think it should be OK.
Before that, I am working on another project related to very narrow band Ca K imaging.
Interesting! And looking forward to see how you managed to apply the Blue filter before the secondary.
Perhaps it is possible to de-aluminise the secondary and apply a coating that reflects CaK and nothing else. Maybe MCM would be able?

Re: 150 mm Solar Newton

Posted: Tue Mar 19, 2019 8:39 pm
by marktownley
Exciting to hear what you're doing in CaK Christian, are you able to talk more about it?

Re: 150 mm Solar Newton

Posted: Wed Mar 20, 2019 6:55 pm
by christian viladrich
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 ;-)

Re: 150 mm Solar Newton

Posted: Wed Mar 20, 2019 7:12 pm
by marktownley
christian viladrich wrote: Wed Mar 20, 2019 6:55 pm Mark : not yet ;-)
You tease :lol:

Re: 150 mm Solar Newton

Posted: Wed Mar 20, 2019 7:33 pm
by bart1805
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.

Re: 150 mm Solar Newton

Posted: Thu Mar 21, 2019 7:15 pm
by christian viladrich
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

Re: 150 mm Solar Newton

Posted: Sun Mar 24, 2019 10:09 pm
by bart1805
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.

Re: 150 mm Solar Newton

Posted: Mon Apr 01, 2019 9:51 pm
by bart1805
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.

ImageSun_142754_310319_Gain=94(off)_Exposure=6.9ms_Gamma=100(off)41646 by bart moors, on Flickr

Re: 150 mm Solar Newton

Posted: Tue Apr 02, 2019 1:54 am
by Merlin66
First light is always exciting!!
Well done for getting reasonable result.
Onwards and upwards.

Re: 150 mm Solar Newton

Posted: Tue Apr 02, 2019 2:27 am
by MapleRidge
The first light CaK looks good Bart...well done!!!

Brian

Re: 150 mm Solar Newton

Posted: Tue Apr 02, 2019 5:23 am
by marktownley
Seems to be working well Bart!

Re: 150 mm Solar Newton

Posted: Tue Apr 02, 2019 7:00 pm
by bart1805
Thanks guys!
Hoping to find out the potential with better seeing and curious how big the negative effect of the original tube will be.

Re: 150 mm Solar Newton

Posted: Wed Apr 03, 2019 8:00 am
by krakatoa1883
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.

Re: 150 mm Solar Newton

Posted: Wed Apr 03, 2019 7:42 pm
by bart1805
I agree with what you say Raf: a lot of noise. Will keep experimenting!

Re: 150 mm Solar Newton

Posted: Wed Apr 03, 2019 9:11 pm
by MalVeauX
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,

Re: 150 mm Solar Newton

Posted: Wed Apr 03, 2019 9:27 pm
by bart1805
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.

Re: 150 mm Solar Newton

Posted: Wed Apr 03, 2019 9:36 pm
by MalVeauX
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,

Re: 150 mm Solar Newton

Posted: Sat Apr 06, 2019 8:31 am
by christian viladrich
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.

Re: 150 mm Solar Newton

Posted: Mon May 06, 2019 10:20 pm
by bart1805
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.

Image20190506_234342_resized by bart moors, on Flickr

Re: 150 mm Solar Newton

Posted: Mon May 06, 2019 11:23 pm
by MalVeauX
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,

Re: 150 mm Solar Newton

Posted: Tue May 21, 2019 7:28 pm
by bart1805
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.

Image20190519_233324_resized by bart moors, on Flickr

Re: 150 mm Solar Newton

Posted: Tue May 21, 2019 7:52 pm
by MalVeauX
Hah, that works Bart!

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

Very best,

Re: 150 mm Solar Newton

Posted: Tue May 21, 2019 8:33 pm
by bart1805
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.....

Re: 150 mm Solar Newton

Posted: Tue May 21, 2019 9:19 pm
by MalVeauX
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,

Re: 150 mm Solar Newton

Posted: Wed May 22, 2019 1:33 am
by MapleRidge
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

Re: 150 mm Solar Newton

Posted: Wed May 22, 2019 8:48 am
by krakatoa1883
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.

Re: 150 mm Solar Newton

Posted: Wed May 22, 2019 10:38 am
by bart1805
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.

Re: 150 mm Solar Newton

Posted: Wed May 22, 2019 6:51 pm
by christian viladrich
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