DOUBLE STACK LUNT CaK B1800S

[sullij1]

Hello CaK freaks, here we are with a CBSAP exclusive on double stack CaKs.

Mark and Walter have been pursuing the double stack idea to cut the band pass on the CaKs. Mark delivered a fine batch of imagery to demonstrate a cut.

Our own AstroDan dropped me a line asking if I wanted to shoot his B1800s as a double stack to verify mark's results. Of course I agreed. He delivered his diagonal and straight through to run the test with.

I began by trying to simply stack the two devices together. Of course this did not work; there was too much back focus and pre filter in the way to get an image. I tried Barlows and three different scopes of varying focal length and ratios to try and get the thing to work in this configuration. No Go.
This was alluded to by Brian C. (I think).

I had been studying the Lunt cutaway and it was obvious the rear filter assembly of the straight through had to be inserted into a T2 to 2inch visual back. The entire filter assembly on the straight through is held in place by 3 setscrews and is easily removed. Cutaway here:
LS60T-CaKPoster.pdf

This allowed one set of IR and light conditioning filters to be in train and the second 393/2nm to follow. This allowed a proper backfocus for close ups. The full disk was not to be had as there was still too much backfocus. Very close though, somebody mentioned Lunt sells a shorter T2 adapter. With one of those a full disc would be possible (or a 1 inch format chip).

My objective was to shoot a double stack, single stack and the Omega CaK behind a single stack for comparisons. Seeing was not so good and has a noticeable impact. I tried to get the same angle but was unable due to the diagonal vs. the straight through inversion. Got as close as I could. You tend to forget to control everything during a 5 hour 72 gigabyte shoot.

All images were 200-400 frames long, shot with the PGR Scorpion, and processed in Autostackkert.
The sharp images from AS were chosen as the comparison images, as with Mark Townleys images, they are straight from the cam.

After the raw cam images I tried to process the single stack and omega images as to duplicate/mimic the DblStk image as best I could(just to see if it could be done).

Now for the good stuff:

Single stack next to double stack:

SSXDS SPOT by Sullij1, on Flickr
Single stack next to double stack processed to look similar:

SSXDS SPOT PROCESCLOSE by Sullij1, on Flickr
Double stack next to Omega behind single stack Lunt:

OXDS by Sullij1, on Flickr

Omega Lunt processed to look similar:


OXDS PROCESSED by Sullij1, on Flickr

Omega Lunt full disc:


OSS SOFT FULL by Sullij1, on Flickr

Sngle stack Lunt full disk:


OSS SOFT FULL by Sullij1, on Flickr

There is no double stack Lunt full disc yet as it was not achievable. I am working on the mosaic for it. To be fair I am also doing mosaics for the other two combinations. They will follow later.

So it looks like double stacking gives a crispier, higher contrast look and tones down the white/brightness in the plague areas.

Can it be duplicated? Not easily!

These compare well to Monsieur Christian Viladrich images from the Barr Associates filter Here:
http://www.astrosurf.com/viladrich/astr ... ntCak.html
and here:
http://www.astrosurf.com/viladrich/astr ... UT-IDS.jpg

There is weirdness in the bandpass as the Viladrich images appear to give a double stack Lunt image look and makes me question whether the Lunt is tight as advertised without double stacking. Still the Lunt is a great filter. Lunt quote 2.4nm FWHM and Barr filter quote 3nm (Valdrich).

So now the price comparisons:

A couple of B1800 Lunt stacked ~2400 USD, Still better than the Barr Associates at 4-5000 USD ( ½ price hmmm, pretty good).

Is crispy contrast worth it? That’s up to you and your wallet; We did verify Mark Townley’s observations.

Perhaps one of our passband experts (Merlin et al spectroscope/spectrum freaks.) can tell us where we are in wavelength and one of our engineers (Mark Thias, Valery D.) can tell us if there is anything more we can squeeze out without stepping up to more expensive Daystar CaK or custom made filter.

Many thanks to our own AstroDan for allowing the use of his filters to verify member results and help answer the CaK passband questions. What an awesome guy. :cheer:

[sullij1]

I do like the look of the double stack though. With a day of good seeing and a large active area this Lunt stack should deliver untouchable results.

BTW the Fliker page has full size images under the select size menu.

[sullij1]

Forgot to say, These were shot with the Celestron 102 f9.8.

[sullij1]

Caught this lil surge prom in the process. things are not optimal in the vid along with the seeing but it was interesting.

http://www.youtube.com/watch?v=_F1lE6g2 ... e=youtu.be

[sullij1]

Here is a color version of the double stack active region:


DS COLOR by Sullij1, on Flickr

[marktownley]

Great read and comparison Joe (and Dan!) - thanks for that.

Yup, same as what i've found - disk area (non plage) is darker and the plage seems to have more dynamic range to it, super granulation is easier on the disk as a whole. I also find the proms and spicule layer easier. In terms of cost for me it ws 2x CaK PSTs £800 + baader K-line £200, so a bit cheaper than the Lunts, I also have 25mm clear aperture through the system.

[sullij1]

Super bargain on your side of the pond, "IF" one can find CaK PSTs!

[swisswalter]

Hi Joe, Dan and Mark

very interesting thread indeed. What I'v seen so far and by my own eyes, the double stack LUNT/PST is the best performer for us amateurs by the time. As Mark showed, you can reach "space Level" on earth. It's a question of time we can do that with open source materials.

It is so interesting to follow the path.

[marktownley]

Just to chuck in a few of my thoughts here as to where i'm going with this: At the moment the setup i'm using is the 2 double stacked coronado CaK filters and a Baader K line as the blocker, this then sits in a Lunt Wedge without any ND filters to act as an ERF and take some of the thermal load off the filters. This works very well up to about f15, but as soon as i'm at f20 and above i'm having to crank the gain up on the camera, which is not good! I tried the filter stack without the wedge, and it worked, but within minutes the temperature on the face of the K-line was too hot to touch, so, a bad idea as I like my K-line intact. I think walter may have had a few thermal incidents with his experiments also :whistle:

The 'problem' we have is a lack of a full aperture ERF to use at CaK wavelengths. The Lunt method is to use an extended nosepiece and mount theirs as high up the OTA as possible. I'm personally against using the KG3 as this is not as optically flat (as I would like!), so this kind of narrows down alternatives. The option i'm currently seriously considering doing is keeping the Tal 100R refractor dedicated solely for CaK and mounting a 50mm Edmunds Optics 394nm 10nm filter halfway down the tube as a sub aperture ERF. This would block to >OD4 out of band but with a transmission of >85% at CaK would give lovely short exposures. I can't find a 2" K-line for sale anywhere.

Anybody think of anymore alternatives?

[astroshot]

Below is an interesting post by Jen @ Daystar FIlters re ERFs.
Post was on the yahoo group page.
---------------
The maximum recommended aperture for the Calcium filter (H line or K line) before a UV/IR cut filter should be used has always been 80mm clear aperture in the past. However, we have recently seen that older filters over 10 years old which operate at that clear aperture over time experience slower damage to the soft 1/4 waveplates inside the filter stack. This happens more slowly, but the same damage that happens at full aperture quickly occurs slowly with a smaller aperture.

We have found damage to occur to those elements in just a few hours of operation while using 150mm clear aperture with no ERF. These 1/4 waveplates are restorable but they do require the filter be sent back to our lab for service with the same service time required as any other job which requires opening the glass, repair, testing and sun testing.

Note that the blockers and trimmers on older 10 year + filters do not age like the Hydrogen Alpha blockers do. This is because of the chemicals used in the coating process of those blockers. Calcium blockers seem to have a 30+ year life expectancy.

So with this new information about the slow aging damage to Calcium filters without UV/IR blocking, we have changed our recommendation to suggest that ALL Ca II filters use the UV/IR cut filter. Conveniently enough; a 2X or 4X TeleVue powermate will accept a 2" UV/IR cut filter threaded directly into its barrel. The TeleVue diagonal also allows direct threading of the UV/IR filter in its male drawtube. So anyone using either component can just screw one in before your filter for full ERF duties before the Calcium filter.

This ERF system is very effective for both Ca II and Halpha because it blocks by reflection instead of absorption. Think of it as a one-way mirror which only lets visible light through. The rest is reflected. It can be used in similar applications that one would a Herschel wedge. This means it is not recommended in telescopes where there are elements (like a secondary in a reflector) that have focused or semi-focused light hitting them. They will gain heat. An SCT would gain heat on the secondary, whose glue would melt and drop off and fall on the primary. Some refractors have corrector lenses toward the rear of the telescope where semi-focused light intersects them. These scopes really need a front-mount ERF. ED, singlets, doublets and cheap baseball bat refractors are all very good scopes for application of the UV/IR cut filter acting as an ERF such as with Calcium. Remember that we are isolating only one wavelength so expensive APO color correction in the glass is moot.

For Calcium H or K line filters, we are recommending Hutech IDAS filters for their excellent transmission at the Ca II wavelengths. Baader offers a UV/IR filter, but its transmission at Ca II is lower.

Correct application would be:
Telescope -> Focuser -> UV/IR threaded on Diagonal -> 2X powermate ->
Calcium Filter -> eyepiece or camera

You can also do:
Telescope -> Focuser -> UV/IR threaded on 2X powermate-> Diagonal ->
Calcium Filter -> eyepiece or camera

Putting the Powermate behind the diagonal uses less backfocus. Less extension tubes. If you can't thread the UV/IR cut filter to the
diagonal, it probably won't burst into flames.. but it might get warmer. Nothing serious.

I don't recommend use of the solar wedge to replace the UV/IR cut filter. These wedge filters reduce ALL light by 99.99%. That means that only .001% of the Calcium light emitted from the sun will hit the filter. That's a pretty dim image - you'd be counting individual photos with that little light.

Baader does make another kind of low density solar film which only reduces the % of transmission a little. This is used in professional observatory research applications like a 20" telescope we work with. You would still have the same problems as the wedge, just not as severe. The UV/IR Cut filter passes the highest percentage of desired light, while blocking sufficient off-band light. It's easy to install and pretty cheap to buy at $50 to $100 for 1.5" or 2" sizes. Then you can go up to 150mm or even higher in a refractor application. Ted at Hutech is aware that we're using them for this application now and has ordered a bigger lot so he'll have more in inventory for us.
-------------------

[astroshot]

More info:
http://www.daystarfilters.com/calcium.shtml

[marktownley]

Below is an interesting post by Jen @ Daystar FIlters re ERFs.
Post was on the yahoo group page.
---------------
I don't recommend use of the solar wedge to replace the UV/IR cut filter. These wedge filters reduce ALL light by 99.99%. That means that only .001% of the Calcium light emitted from the sun will hit the filter. That's a pretty dim image - you'd be counting individual photos with that little light.

-------------------

Now I guess Jen is referring to a wedge here with ND3 filters in place, however remove the ND filters so 5% of the light goes through (the other 95% goes into the wedge heat sink) and at short to mid focal ratios there is definitely enough light.

[swisswalter]

Having had a cracked UV/IR cut filter unsing it with the TEC140 at the focuser I was looking also for another solution.

Oliver suggested this:

http://www.ebay.de/itm/221289928124?ssP ... 1558.l2649

Now that looks very good in my eyes but I would like to have a 152 mm version. At the Moment there are not enough people to maka a run :whistle:

[marktownley]

That is most definitely a solution Walter!

[astroshot]

Any idea what a batch of 6 would cost in a size suitable for a TEC140?

[sullij1]

If we could get Olivers attention he could tell us how much or if possible. I will drop him an email.

[sullij1]

Sent Oliver an E. Perhaps he will turn up and help us.

[sullij1]

I lied! I forgot to get the single stack mosaic. No big as many of my Cak are 2 panel mosaics from the single stack. Here are the 9 panel mosaics from the double stack and single stack with the Omega pair. IMHO if a way to tone down the plage in the omegas can be found the Omegas will give the DS Lunts a run for their money on the full discs.

I am working in PS3 for the mosaics and PS3 merge is not kind to me so I hope you will forgive some of the artifacts.

Lunt Double stack out of cam:


DS MOSAIC DISC by Sullij1, on Flickr

Omega and Lunt single stack:


OMEGA FULL MOSAIC by Sullij1, on Flickr

[swisswalter]

Hi Freaks

thanks. I'll send another email to Oliver too

[swisswalter]

Hi Freaks

Oliver is out of office and back again on the 8th