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Hydrogen Alpha Upgrade

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Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Wed Apr 24, 2019 9:32 am

Hi All
Looking for some wisdom! I have the urge to upgrade my H Alpha observing / imaging rig from my current PST. It has served me well for more than 5 years and whilst my primary interest was in Ca-K it did not seem worth going for anything else. Now I am interested to further my H alpha imaging so want to step up. Bearing in mind I like to image full disk regularly with occasional close-ups there are many options with pro's and con's for all:-

1. Quark - With my Evostar scope this will give me very long focal lengths to work with (4.2x1000mm=4200mm although I may be able to use a reducer to bring it back a bit). Not keen to get "that close" at this stage plus still concerned about consistency of the quality of Quarks after all the initial issues. The big upside to the Quark is cost of course.

2. New Lunt / Coronado scope - we are talking circa £2.5K+ for a basic 60mm B1200 and nearly twice that for a DS model :o Plus these will have similar sweet spot issues as the PST (as I understand it). The positive here is I would be able to get a full disk image relatively easily with my ASI178MM.

3. Second hand Lunt / Coronado - second hand Lunt 60 B1200's seem pretty rare and when they do come up they are the other end of the country! I'm watching the market to see what comes up. Both have the sweet spot issue to contend with. On the up side cost is generally lower and focal length is conducive to full disk imaging.

4. External Etalon & Blocking Filter - Add a front mounted etalon and blocking filter to my current scope. The scope does a great job on Ca-K and no reason to think it will not do the same in H Alpha. Buying these new comes up at around £1700 for a 60mm Coronado DS etalon and BF15 and I may be able to pick one up second hand with some patience. I found a supplier of adapters to fit the Etalon to the Evostar for 120 euros.

I'm liking the last idea myself. The front mounted etalon should mean minimal sweet spotting, I can image at the same focal lengths in both HA, Ca-K & WL and could add a Quark later for the double stack experience / super-close-ups. Plus I can keep one scope on my CG-4 the whole session.

So this is where you all tell me the flaws in my plan :( Be gentle :lol: and thanks for taking the time to help :bow2
David

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Re: Hydrogen Alpha Upgrade

Post by Bob Yoesle » Wed Apr 24, 2019 11:10 am

You've covered all the bases David.

Front etalon(s) will generally give you the best performance - especially for full disc views/imaging, and of course will cost the most...
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Re: Hydrogen Alpha Upgrade

Post by MalVeauX » Wed Apr 24, 2019 12:14 pm

Hi David,

Getting a "do it all" scope is tough, on a budget, for sure. I agree that front mounted smaller etalons would do the job. Also, if your seeing supports larger aperture, that would be something to consider. The adapted front mounted etalons would be my pick for a "full disc" every day imaging scope, with the option to double stack. A lot easier to mount and handle a small scope like this. A lot easier in all conditions too. 60mm aperture will resolve quite a lot still, and the small pixels of your IMX178 will record them fairly well. Just depends on what etalon and how you want to set it up, etc. You can always double stack later.

You can totally do full disc imaging with a Quark with a short tube. A 400mm achromat with a Quark and a focal reducer (0.5x) will do a full disc with a larger sensor camera (IMX174, 1600, etc). I do this. It's fast transmission and easy, but again, not ideal in general. Requires a short scope and requires time to warm up and all that. Requires a larger sensor, which may not be an option, and requires focal reducer use. So it's a little more fussy in general to setup.

Personally, I would just save up and get a nice 60mm double stack system of your choice that you can afford that is front mounted if possible.

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Re: Hydrogen Alpha Upgrade

Post by eroel » Wed Apr 24, 2019 4:45 pm

David:
My personal experience after many years of being an amateur astronomer, is to have a small portable scope (I use a set of DS Coronado 40mm with a 76mm f/6.4 Televue, or with a 72mm f/6 Megrez for eclipse imaging).
At home I use a Solarmax 90-DS for FD´s and a 102mm f/7 Stellarvue with a 4X Telecentric and an old Daystar T-Scanner for higher resolution imaging.
At the rural observatory I use a 6" f/12 "Superplanetary" refractor fitted with a 2X telecentric and a Daystar ATM for high resolution imaging. I also got a 265mm Aries ERF to use it in a 10" f/20 Maksutov or with a 12" f/10 Meade SCT and with an appropiate telecentric for the 0.4.5 A° Daystar ATM.
Have not started using the bigger scopes, due to minor mechanical details.
So the truth is that I still have not found a do it all setup. :roll:
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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Wed Apr 24, 2019 10:08 pm

Bob, Marty thanks for your thoughts.

Ha Eric, I can imagine :) Like looking for the Holy Grail! I'm under no illusions that this will be my one and only H Alpha "upgrade" :o
David

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Re: Hydrogen Alpha Upgrade

Post by marktownley » Thu Apr 25, 2019 7:32 am

Oh the dilemma! I think Eric sums it up well for me.

A few thoughts on my 'been there done that' journey...

Front mounted etalons are fickle and unreliable in terms of their performance - I have been through and own quite a few; a couple of them are lovely and flat, and show no banding etc due to needing excess tilt. Then there are quite a lot that do have banding and especially with imaging more so show uneven illumination. (take a look at Pedros recent SM etalon comparisons) - as we become more experienced solar astronomers this is blindingly obvious when an etalon is less than perfect. My advice, try before you buy if you can!

Regards a dedicated solar scope - again, try before you buy - more so with the coronados, for the same reasons above. The pressure tuned Lunts are nice - the 50 is half the price of the 60 effectively but requires more 'fiddling' to get it imaging properly. I like my full disks too, and another option to think about would be (assuming you're happy with the PST performance) to put a SM40 on the front to double stack it. Using a magnimax from astroboot would get you to a point where you're sampling ok with the small pixels of the 178.

A quark is not a bad idea, I think as long as you're buying from somewhere like widescreen where there are no quibbles if there are issues with it being on band then you are ok. It would work well with your 120 for closeups, and another thing to throw into the mix, pick up a cheap 70mm scope (skywatcher Ed72?) then you have some middle ground between the full disks of the PST and the hi-res of the Quark. Imaging with a quark I would use 2x binning on the camera to get the pixel size more in the area you need for correct sampling.

Solar minimum is a buyers market with plenty of kit coming up for sale as peoples interest wanes in a quiet sun. Better to upgrade now than solar max...
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Re: Hydrogen Alpha Upgrade

Post by robert » Thu Apr 25, 2019 9:50 am

David_The_Bears_Fan wrote:
Wed Apr 24, 2019 9:32 am
2. New Lunt / Coronado scope - we are talking circa £2.5K+ for a basic 60mm B1200 and nearly twice that for a DS model :o Plus these will have similar sweet spot issues as the PST (as I understand it). The positive here is I would be able to get a full disk image relatively easily with my ASI178MM.


4. External Etalon & Blocking Filter - Add a front mounted etalon and blocking filter to my current scope. The scope does a great job on Ca-K and no reason to think it will not do the same in H Alpha. Buying these new comes up at around £1700 for a 60mm Coronado DS etalon and BF15 and I may be able to pick one up second hand with some patience. I found a supplier of adapters to fit the Etalon to the Evostar for 120 euros.

I'm liking the last idea myself. The front mounted etalon should mean minimal sweet spotting, I can image at the same focal lengths in both HA, Ca-K & WL and could add a Quark later for the double stack experience / super-close-ups. Plus I can keep one scope on my CG-4 the whole session.
Hi David

I disagree about the sweet spot on a Lunt Pressure tuned 60, absolutely the best option to avoid this PST problem in my experience.

Front mounted etalons are tricky as Mark says. I had a Lunt 75 which was on band in a stripe down the middle only, ok for closeups and narrow FOV but useless for wider angle views. On the other hand I got a Lunt 60 front etalon to DS the Lunt 60 scope and it is tuned at almost no tilt so does a very even DS for full disks.

Pressure tuned Lunt should be without a sweet spot! (PS I use a PST mod 150mm refractor for close ups and the limiting factor is not the gear but my seeing in a wet and windy place)

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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Thu Apr 25, 2019 9:56 pm

marktownley wrote:
Thu Apr 25, 2019 7:32 am

Solar minimum is a buyers market with plenty of kit coming up for sale as peoples interest wanes in a quiet sun. Better to upgrade now than solar max...
Thanks Mark. I had been thinking along the same lines ref the above. Interesting your experiences of front mounted etalons and yes I did see Pedro's comparison threads :(
David

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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Thu Apr 25, 2019 10:01 pm

robert wrote:
Thu Apr 25, 2019 9:50 am

Hi David

I disagree about the sweet spot on a Lunt Pressure tuned 60, absolutely the best option to avoid this PST problem in my experience.

Front mounted etalons are tricky as Mark says. I had a Lunt 75 which was on band in a stripe down the middle only, ok for closeups and narrow FOV but useless for wider angle views. On the other hand I got a Lunt 60 front etalon to DS the Lunt 60 scope and it is tuned at almost no tilt so does a very even DS for full disks.

Pressure tuned Lunt should be without a sweet spot! (PS I use a PST mod 150mm refractor for close ups and the limiting factor is not the gear but my seeing in a wet and windy place)

Robert
Thanks for your input Robert. Interesting comments, it seems experiences with each of my options vary!
David

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Re: Hydrogen Alpha Upgrade

Post by Bob Yoesle » Fri Apr 26, 2019 9:53 pm

"Front mounted etalons are fickle and unreliable in terms of their performance - I have been through and own quite a few; a couple of them are lovely and flat, and show no banding etc due to needing excess tilt. Then there are quite a lot that do have banding and especially with imaging more so show uneven illumination. (take a look at Pedros recent SM etalon comparisons) - as we become more experienced solar astronomers this is blindingly obvious when an etalon is less than perfect. My advice, try before you buy if you can!"

Good advice Mark! However, I would add that if you are getting any banding from a front mounted etalon, then its CWL is tuned too high and needs to be replaced as being defective. This seems to be more prevalent these days as the OEMs seem to intend these front etalons as secondary DS etalons needing additional tilting to remove secondary reflections, and have tuned the CWLs higher than they otherwise should be. I have noted this in a couple of Coronado etalons myself.

On a theoretical basis, front etalons "see" the best possible field angle from the solar limb (equivalent to about a f108 focal ratio instrument angle), and there are no instrument angles. Both these features will provide the very best contrast uniformity provided the etalon CWL is properly tuned just slightly above the H alpha line to allow minimal tilting for tuning (and subsequent removal of ghost reflections).

13062015full disk.jpg
13062015full disk.jpg (490.03 KiB) Viewed 869 times
Two off-the-shelf pre-Meade SM90 front etalons double stacked per below.

If I were to buy a front etalon, it would always be specified for use as a primary single stack etalon, and if it produces any type of banding, it is defective and should be returnable under warranty. When you have two such etalons for double stacking, the one needing the least tilt to be on-band becomes the primary etalon, and the other the secondary double stacking etalon. This was the essence of "etalon matching" when double stacking etalons first appeared about a decade and a half ago.
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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Fri Apr 26, 2019 10:23 pm

Bob Yoesle wrote:
Fri Apr 26, 2019 9:53 pm
"
Good advice Mark! However, I would add that if you are getting any banding from a front mounted etalon, then its CWL is tuned too high and needs to be replaced as being defective. This seems to be more prevalent these days as the OEMs seem to intend these front etalons as secondary DS etalons needing additional tilting to remove secondary reflections, and have tuned the CWLs higher than they otherwise should be. I have noted this in a couple of Coronado etalons myself.



Fascinating Bob. So a question then, of the front mounted etalons on the market are some generally better than others e.g. Coronado vs Lunt vs Solarscope vs ?? Or do the variations in each make it pretty much just pot-luck as to whether you get a good one?
David

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Re: Hydrogen Alpha Upgrade

Post by marktownley » Sat Apr 27, 2019 7:39 am

I don't have direct experience with the solarscope etalons David, but with Lunts and Coronados yes. Personally, I think these days (over here in the UK) it is just pot luck as to the etalon you get if you order one. Retailers have stock sat in packaging and it is lucky guess which one gets picked up and posted to you.

Front mounted etalons should be the best option if the primary etalon is sat squarely at 656nm, if this is what you get then you'll end up with images like Bob's above, or like what Alexandra gets with her 100mm DS solarscope for example.

Something else to consider is how front etalons are physically mounted. Best option is if they screw directly onto the ota as these will be secure and square with no tilt or sag. If this is not possible then a cell is needed. I've had all mine (cells) made via Simon at the widescreen centre (although I believe these are actually made by Telescope Service in Germany) - they are very good quality and I do recommend them, but, the thing you need to keep in mind is that hanging a weight (the etalon) off an interference fit adapter will result in a small amount of sag, especially if this sits on a retractable dew shield. Sag will result in tilt, which in our etalons is bad as it takes them off target band, and this will need to be compensated for.

In my travelling kit, ED60 f6, I can comfortably put my nice flat and onband LC50 etalon with no adverse effects due to sag, however when I double stack with a secondary Lunt50 etalon the load is getting rather too much and there is a sagging moment due to the leverage of the weight, I can make counter effects to this but is fiddly and not the best.
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Re: Hydrogen Alpha Upgrade

Post by skyhawk » Sat Apr 27, 2019 9:04 am

I am not as experienced as these people but I am very happy with my Daystar having moved from the PST
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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Sat Apr 27, 2019 9:22 am

marktownley wrote:
Sat Apr 27, 2019 7:39 am
Something else to consider is how front etalons are physically mounted.
Thanks Mark. I had come across the website below in another thread which looks promising and the linked version should sit on my evostar dewshield (which is removable but not retractable) quite snugly.

https://www.intercon-spacetec.de/zubeho ... 145mm.html

At this point I will just be happy getting reasonably flat single stack disks. Have to admit I have not really thought through what I might do if / when I develop a desire to go to a DS system :?
David

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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Sat Apr 27, 2019 9:28 am

skyhawk wrote:
Sat Apr 27, 2019 9:04 am
I am not as experienced as these people but I am very happy with my Daystar having moved from the PST
Love these ED72's. Something about a small ed frac that just does it for me. I have to say I still have not ruled out doing something similar. Having a second scope on a second mount so I can be watching WL / Ca-K and HA at the same time is quite appealing. It would also mean I could do full disk images in WL and Ca-K in a single frame (and H Alpha in maybe 4 panes with a reducer) with the ASI178.
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Re: Hydrogen Alpha Upgrade

Post by marktownley » Sun Apr 28, 2019 8:31 am

Just as a heads up David, I was watching a SM40ii (double stack unit for PST) that went for £278 on ebay yesterday afternoon, buyers market...
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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Sun Apr 28, 2019 8:57 am

marktownley wrote:
Sun Apr 28, 2019 8:31 am
Just as a heads up David, I was watching a SM40ii (double stack unit for PST) that went for £278 on ebay yesterday afternoon, buyers market...
I saw that, was tempted.... I'm in no hurry with this and the longer I wait the more I have saved and available to spend!
David

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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Sun Apr 28, 2019 9:44 am

I just wanted to thank all who have contributed to this thread. I am still not entirely sure which way I am going to go but your input have given me much food for thought. I am not going to rush in to a purchase, as I said above the longer I wait the more funds I have saved which could be seen as a good or bad thing I suppose :?

I am not sure I have read anything to dissuade me from my original front-mounted-etalon concept but I have read enough to reconsider where I might think about sourcing one from. Having said that the Quark + small Frac idea is still haunting me, as is the idea of a pressure tuned Lunt 60! In fact either of these sat on an AZ GTi sat next to my Evostar on CG-4 is very appealing :?
David

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Re: Hydrogen Alpha Upgrade

Post by Bob Yoesle » Sun Apr 28, 2019 12:18 pm

Good luck with your journey David - but I did want to get back to you about your question:

"Fascinating Bob. So a question then, of the front mounted etalons on the market are some generally better than others e.g. Coronado vs Lunt vs Solarscope vs ?? Or do the variations in each make it pretty much just pot-luck as to whether you get a good one?"

It is more of a pot-luck these days than it used to be, as the market has shifted from better quality but expensive to to higher production and less expensive. If you can find pre-Meade Coronado etalons you have a really good chance of getting an excellent performer. Now days it's a "try before you buy" situation as Mark noted, and when you buy used, make sure you have a no-questions-asked ability to return the item and get a refund.

From what I have seen, Meade Coronado front etalons have the most variability, followed by Lunt and Solarscope, which are generally more consistent, and have more responsive service if problems do arise. The Daystar Quantums and Solar Scope filters also appear to have good performance, but the Quarks appear to be the most variable of any of the H alpha filters - which makes sense from a cost vs. performance perspective.

The two scope/filter system solution is ideal with using smaller DS front etalons for full disc and medium scale, with the Daystar or Solar Spectrum filters being the most viable for hi-res viewing/imaging - if your local seeing allows. The best single scope/filter system generally seems to be an aperture in the 80-100 mm range, double stacked. The most portable system generally seems to be the Lunt LS80 pressure tuned, and it can be double stacked with a second internal etalon system (use a circular polarizer added between the two etalon/collimator systems), or add a front etalon like the SM90. Lunt really should get an 80 mm DS etalon made for this scope...
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Re: Hydrogen Alpha Upgrade

Post by David_The_Bears_Fan » Sun Apr 28, 2019 7:24 pm

Thank you Bob
David

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