Setting up filters in a Solar Herschel wedge?

[900SL]

Hi

 

My TS 1.25"  wedge has arrived, with no instructions..

It has a separate dual lens filter (not annotated) which looks like it is the ND3 and 40nm continuum filter 

There is also a circular polarising filter (labeled)

I assume (dangerous with solar, hence the post):

 

 

ND3/continuum comes after the wedge (seems obvious..)

The circular polariser wont fit double stacked, So I have added it to the barlow thread (see diagram)

For good measure I have retained a L2 UV/IR filter as a backstop in case of any UV/IR off band leakage

Q:

Should the ND3 be placed in front of the Continuum (one is dark and one is silvered and I don't know which is which)

I assume the circular polariser will interact with the ND3 and by rotating the camera I should improve contrast?

Many tanks

 

Edited May 16 by 900SL

[900SL]

Found this thread, same set up so looks good. I'll try both w.ith and without the polariser, with the SC and ND3

 

Edited May 16 by 900SL

[Littleguy80]

Beat me to it. I was going to say I posted some pics over my TS optics wedge showing how the filters are screwed in. 

[Louis D]

With my 1.25" Hercules Herschel wedge, I generally put a Meade UV/IR filter on the front of the wedge.  Being an interference type filter that reflects rather than absorbs rejected energy, it doesn't heat up that I've ever noticed.

The Hercules comes with an integrated ND3 filter below the eyepiece holder.  I don't even know if it can be removed.  After all, why would I want to remove it?

I generally set the variable polarizer it came with to about an ND1 to ND2 level, and attach it to the bottom of the eyepiece.  I can then rotate the eyepiece to darken the image more because the wedge itself partially polarizes the sun's light.

If I use another filter, I stack it ahead of the polarizer so I can swap it more easily to try other filters.

The Hercules even comes with an integrated variable iris, but all it does is decrease the effective aperture, which might be useful for an achromat, but not for an APO.

[Vroobel]

I also have the Hercules 1.25" wedge. I've replaced the original ND3 filter (inside the eyepiece holder) with 1.25" Solar Continuum 10nm. Also, I screwed the 1.25" variable polarizing filter into my ASI 678MC camera nosepiece, because it's much easier to adjust the filter there than if it's elsewhere. 

https://www.astrobin.com/f3sum2/

 

Edited May 16 by Vroobel

[John]

My Lunt 1.25 HW seems to work in the same way as the Hercules one ie: an ND filter fitted at the bottom of the eyepiece drawtube. I use a single polarising filter on the end of the eyepiece and turn the eyepiece to adjust the final brightness of the image. The light coming through a HW is already polarised on one plane so the single polarising filter is all that is needed on the eyepiece.

I'm not keen on green solar observing so I don't use a solar continuum filter. 

 

[900SL]

Thanks all

 

Contrary to the norm, my wedge arrived with blazing sun. So after a frantic assembly of bits, I have my first solar image!

GT71, Baader hyperion barlow, TS wedge and filters, 533MM, 100 FITS files with best 15% stacked. I'm dead chuffed with this for a first-out-of-the-box I-have-no-idea-what-I'm-doing thing. Finding the damn thing took ages, I ended up using a stick on the scope on the top and sides to get it aligned (when the shadow disappeared I was in line)

 

[John]

That looks a nice result 🙂

I only observe through my HW. To find the sun I usually remove the eyepiece and look into the empty HW eyepiece tube moving the scope until the sun illuminates the prism. Popping the eyepiece back in usually finds the sun to be in the field of view.

[900SL]

1 minute ago, John said:

That looks a nice result 🙂

I only observe through my HW. To find the sun I usually remove the eyepiece and look into the empty HW eyepiece tube moving the scope until the sun illuminates the prism. Popping the eyepiece back in usually finds the sun to be in the field of view.

Only problem being this could be a gateway drug into the bottomless pit that is Ha solar 🤑

[John]

22 minutes ago, 900SL said:

Only problem being this could be a gateway drug into the bottomless pit that is Ha solar 🤑

I've owned a couple of Ha scopes but not found them engaging enough to keep. I'm a lightweight dabbler in solar observing - mostly for outreach with my astro society really 🙂

If you get in deep though, the costs can quickly mount up. I'm currently minding a 60mm double stacked Lunt Ha scope for my society which I believe would cost over £5K to replace 😲

[Louis D]

I think I looked through an Ha scope once at an outreach event, but I found the deep, dark red color too difficult to make out any details.  Is that what Ha scopes view like?  For me, I'd probably only use one for imaging rather than visual.

[Stu]

Interestingly Baader recommend the Continuum filter being closer to the scope and then the ND3.0, both on the eyepiece side of the wedge of course. This minimises reflections from the shiny Continuum.

The filter in my Mark II is a 7.5nm and I also have a polariser fitted which can vary brightness by moving the lever on the Wedge. I generally prefer it towards the brighter end of the scale, although sometimes granulation is easier to see with it a bit darker.

[Paz]

My white light setup has changed a lot over time, but currently it is...

Objective

2" uv/ir cut (with kg3 which absorbs any ir that is not reflected)

Wedge

Glass path corrector

Continuum filter

ND3 filter

Polarising filter

Filters are on a nosepoece that I can rotate independently of the wedge and the binoviewers to enable use of the polarising filter.

Binoviewers 

Eyepieces

 

The nd3 filter was previously "fixed" on the wedge but I finally worked out how to detatch it as I also use the wedge sometimes for observing Venus, hence the nd3 is how it is now.

[900SL]

On 16/05/2024 at 21:20, Stu said:

Interestingly Baader recommend the Continuum filter being closer to the scope and then the ND3.0, both on the eyepiece side of the wedge of course. This minimises reflections from the shiny Continuum.

The filter in my Mark II is a 7.5nm and I also have a polariser fitted which can vary brightness by moving the lever on the Wedge. I generally prefer it towards the brighter end of the scale, although sometimes granulation is easier to see with it a bit darker.

Thanks Stu.

 

The TS wedge 'Continuum' filter is fairly wide, I think 40nm from memory.

Would I see any improvement (for imaging) using my 4.5 nm Oiii narrowband filter?  

[Stu]

On 18/05/2024 at 07:08, 900SL said:

Thanks Stu.

 

The TS wedge 'Continuum' filter is fairly wide, I think 40nm from memory.

Would I see any improvement (for imaging) using my 4.5 nm Oiii narrowband filter?  

Worth trying I should think. May be a bit too narrow but I’ve not tried one so don’t know.

[terrain_inconnu]

On 16/05/2024 at 22:07, Paz said:

My white light setup has changed a lot over time, but currently it is...

Objective

2" uv/ir cut (with kg3 which absorbs any ir that is not reflected)

Wedge

Glass path corrector

Continuum filter

ND3 filter

Polarising filter

Filters are on a nosepoece that I can rotate independently of the wedge and the binoviewers to enable use of the polarising filter.

Binoviewers 

Eyepieces

Having seen many set-ups that include a UV/IR filter, I am now considering of adding one myself. I noticed that you are using the UV/IR KG3 filter from Beloptik and placed it in front of the wedge. Does it get hot during a session? If so, does this impact local seeing conditions by creating thermal currents inside the tube? I would have thought that putting it further up the optical train, i.e. after wedge and ND3, would substantially reduce any absorbed heat by the KG3 glass. On the other hand, such a placement might introduce additional reflections between the filter cells. Curious what you and others think about the use of UV/IR cut filters in general and KG3 specifically when doing visual WL (e.g. necessary, just in case, better safe than sorry etc).

Edited June 5 by terrain_inconnu

[Louis D]

I have an older Meade UV/IR cut filter on the front of my Hercules wedge, and I've never noticed it getting hot in my 90mm APO.  Since it reflects energy rather than absorbing it, that's not surprising.  Couple that with a KG3 substrate, and the residual IR being absorbed is probably minimal.  Certainly not enough to heat up.

[900SL]

Earlier today. Lots going on!

 

[900SL]

Close up

 

[terrain_inconnu]

4 hours ago, Louis D said:

I have an older Meade UV/IR cut filter on the front of my Hercules wedge, and I've never noticed it getting hot in my 90mm APO.  Since it reflects energy rather than absorbing it, that's not surprising.  Couple that with a KG3 substrate, and the residual IR being absorbed is probably minimal.  Certainly not enough to heat up.

Given that the reflective coating of the typical UV/IR filter only works up to 1100-1200 nm, everything above that goes through. Below is a picture of the sun's spectrum at low altitude (red part). On an aggregated level the residual IR is not that minimal as one might think, but I do not know if it is enough to heat up the KG3 in front of the wedge or more importantly in case of no KG3 cause any damage to the eye after partially passing through wedge and ND3.

Edited June 5 by terrain_inconnu

[Paz]

9 hours ago, terrain_inconnu said:

Having seen many set-ups that include a UV/IR filter, I am now considering of adding one myself. I noticed that you are using the UV/IR KG3 filter from Beloptik and placed it in front of the wedge. Does it get hot during a session? If so, does this impact local seeing conditions by creating thermal currents inside the tube? I would have thought that putting it further up the optical train, i.e. after wedge and ND3, would substantially reduce any absorbed heat by the KG3 glass. On the other hand, such a placement might introduce additional reflections between the filter cells. Curious what you and others think about the use of UV/IR cut filters in general and KG3 specifically when doing visual WL (e.g. necessary, just in case, better safe than sorry etc).

I have thought about this quite a bit and the first set up I had was a IR/UV filter behind the wedge but the reason in the end for putting a 2" filter at the front is just practical. The more filters I have after the wedge the further out the binoviewers have to go in order to make room for them and then it's more challenging to balance as the binoviewers are further from the glass path corrector which pushes up the magnification. I can't have the glass path corrector after the filters as that would mean running out of in focus or having to add even more spacers totry and get focus, leading back to problems with balance and practicality due to the binoviewer being so far out. In cyclops mode the above does not matter.

I have not had any issues with the kg3 filter overheating but I do think it must be releasing some heat inside the ota and I guess that might cause some tube currents.

Letting the wedge deal with the heat would still mean heat in the wedge potentially percolating back up the ota to some degree, but I guess wedges are designed to handle this sensibly to some degree.

I have thought that in theory a 2" dielectric UV/IR at the front (I.e one without kg3) and then a kg3 filter after the wedge might be ideal as you bounce some IR straight back out and let the rest through, then the wedge takes most of the rest out and the kg3 filter then catches the rest... and the 2" filter n the nose would also stop any heat from the wedge going back up into the ota (and a 2" filter in the nose also stops creepy crawlies venturing into my scope via an open bottomed wedge).

I've got the right bits and pieces to try that configuratuon above but testing for marginal improvements in solar kit even back to back is tough as the seeing constantly changes, hence I have been more guided by practicality than by establishing the best configuration for managing heat and getting potentially better views.

...but now I've said this I'm going to have to try it!

P.s. I never got to the bottom of how much an IR/UV filtering is necessary and I know there is a spectrum of opinion on this (pun intended), but just for myself, I know that when I observe with such a filter I mostly think about what I'm observing, and when I don't use one I mostly worry about whether I should be using one, hence I use one.

[terrain_inconnu]

4 minutes ago, Paz said:

I have thought about this quite a bit and the first set up I had was a IR/UV filter behind the wedge but the reason in the end for putting a 2" filter at the front is just practical. The more filters I have after the wedge the further out the binoviewers have to go in order to make room for them and then it's more challenging to balance as the binoviewers are further from the glass path corrector which pushes up the magnification. I can't have the glass path corrector after the filters as that would mean running out of in focus or having to add even more spacers totry and get focus, leading back to problems with balance and practicality due to the binoviewer being so far out. In cyclops mode the above does not matter.

I have not had any issues with the kg3 filter overheating but I do think it must be releasing some heat inside the ota and I guess that might cause some tube currents.

Letting the wedge deal with the heat would still mean heat in the wedge potentially percolating back up the ota to some degree, but I guess wedges are designed to handle this sensibly to some degree.

I have thought that in theory a 2" dielectric UV/IR at the front (I.e one without kg3) and then a kg3 filter after the wedge might be ideal as you bounce some IR straight back out and let the rest through, then the wedge takes most of the rest out and the kg3 filter then catches the rest... and the 2" filter n the nose would also stop any heat from the wedge going back up into the ota (and a 2" filter in the nose also stops creepy crawlies venturing into my scope via an open bottomed wedge).

I've got the right bits and pieces to try that configuratuon above but testing for marginal improvements in solar kit even back to back is tough as the seeing constantly changes, hence I have been more guided by practicality than by establishing the best configuration for managing heat and getting potentially better views.

...but now I've said this I'm going to have to try it!

P.s. I never got to the bottom of how much an IR/UV filtering is necessary and I know there is a spectrum of opinion on this (pun intended), but just for myself, I know that when I observe with such a filter I mostly think about what I'm observing, and when I don't use one I mostly worry about whether I should be using one, hence I use one.

Great write-up and the last sentence sums it up nicely. Well said.