New Year, New Setup & the Blocking Filter Experiment - 3rd February

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New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 2:22 pm

Sometimes life goes in directions you weren't thinking of going, and the past couple of months have been just that. I've just recently bought a Coronado SM90ii, not just any, but one with a bit of history and pedigree. Way back in 2010/11ish the BBC commissioned a SM90ii for it's Sky at Night TV programme on solar astronomy. The scope ended up briefly with Pete Lawrence where it was reviewed for Sky at Night magazine, before ending up with Gary Palmer for a few years, then, with it's last owner Pete Williamson. Correspondence with Coronado reveals it was a somewhat unique scope, a prototype where they were looking at producing higher finesse etalons for higher contrast (tighter bandpass?), a route they ultimately did not take sadly with production as a whole. I've used this scope on and off quite a number of times over the years and was very familiar with it's optical quality. 90mm is also a nice size for the seeing I get regularly. It also has a rather nice 2.5" Starlight Feather touch focuser...

Imageimage by Mark Townley, on Flickr



The weight of this shifts the balance so that the clam shell sits behind the tuning ring, opposed to the 'infront of' configuration normally...

Imageimage by Mark Townley, on Flickr

Sunday morning I was out and ready for the sun:

Imageimage by Mark Townley, on Flickr

Alas the skies were not the clearest, and the sun is only just starting to poke out of the tree's on my southern horizon, but there are gaps in the tops now ;)

Imageimage by Mark Townley, on Flickr

Imageimage by Mark Townley, on Flickr

Halos and circumzenithal arcs weren't really what I had in mind for observing, but a few clearer windows presented themselves.

It also gave a my first semi decent opportunity to try out my new camera - a PGR Grasshopper 3 with a 9.1Mp (sony ICX814) chip - this was an impulse buy before Christmas, they had a stock clearance sale where I picked one up for 25% of the RRP. It only does 9fps, but, for full disk scale this is fine, and with 3.69um pixels and a 3376x2704 chip size means full disks up to 1000mm focal length. The 800mm focal length of the SM90ii easily fitted on with room to spare.

This was the first trial of my grand blocking filter experiment: each Coronado blocker has 3 parts that can affect the brightness - the ITF, the mirror, and the blocking filter itself. With 3 blockers to hand, 2xbf15 and a bf10, my winter project has been to construct a blocker with the highest transmission. That I achieved by simple holding each of the 3 sub components to the light and visually rating the brightness, then I assembled a blocker with the highest transmission which I used today. Yup, it has high transmission, todays disk was too bright at zero gain and 1ms exposure, so I ended up using some improvised ND filters to get the brightness where I could get a 70% histogram. This is gonna be fun - Valery, you need to do this if you haven't already!

Anyway, to todays disk. Visually there is little to see, a few small proms and filaments and the relic plage from active regions of old. On the screen and through the camera there was quite a lot of contrast, similar to my quark. I want to make a custom barlow to give me about 1.2x magnification to fill the chip, till then i'll take this scale:

Imageha-fd-bw by Mark Townley, on Flickr

Imageha-fd-colour by Mark Townley, on Flickr

The scope has a very even field of view, there are no flats used above and absolutely zero tilt on the camera. The tuning is smooth and precise with no obvious sweet spot, the focuser is a dream. It kinda reminds me of a decent PST on steroids. With larger pixel size cameras it will be nice to zoom in with this setup, but that needs to be later in the year. Till then i'm a happy bunny!

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by MalVeauX » Sun Feb 03, 2019 3:06 pm

Very nice Mark, very sweet even field.

Very best,

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 3:37 pm

Thanks Marty, I'm really looking forward to using this scope this year. In the meantime I fitted a couple of finder shoes on the focuser which will make mounting my SSM and Hinode guider a doddle.

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Alexandra, this is the scope we looked through at the IAS when it was double stacked with that SM90 etalon I bought from Walter. The view was awful! I still remember your face when you looked through, you looked at me, grimaced and shook your head. With that double stack unit it just didn't work - it was a dead duck.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Valery » Sun Feb 03, 2019 4:54 pm

Congrats, Mark!

I dodn't understand how SM90 front mount etalon can't work in a DS with this scope.

About BF's selection. I already did this and I beleiev my BF10 now is very bright. It works fantastic with my PST etalon. Even in a telecentric mode (with some bandwidth widening) at F/43-45 the view is as contrast as in my former 0.38A Quark and close to 0.25A Quark.

I was stupid when I sold my first Ha filter - SM90 Serial #005 with BF30. It was probably made at Isle of Man. As far as I remember, the image contrast was same good as in my 0.2A Quark.


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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 5:01 pm

Valery wrote:
Sun Feb 03, 2019 4:54 pm

I dodn't understand how SM90 front mount etalon can't work in a DS with this scope.

Valery
It needed so much tilt the fov went from ridiculously detailed at one edge to featureless at the other... Reducing the tilt just made the whole fov more even but completely off band and washed out.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by MapleRidge » Sun Feb 03, 2019 6:32 pm

Hi Mark...

Beautiful scope and write up of its history, your blocking filter setup, and your first light perceptions. The skies looked poor to a trial run but good skies are few and far between...the first image form the scope and new camera do look exceptional.

Looking forward more images as you continue to refine the setup.

Brian
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 6:36 pm

Thanks Brian. I'm very excited about the scope. With better conditions and 'blue' skies contrast on the disk will only be better. It's a heavy piece of kit - over 10kg...
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by bart1805 » Sun Feb 03, 2019 6:48 pm

Congratulations Marc!

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Astrophil » Sun Feb 03, 2019 7:21 pm

Mark,

Looks like that's going to be a great scope for FD images with the new camera. The scope's history makes it very special as well. Congratulations on the acquisition. I think we all are eagerly awaiting additional images. Is it just me or does the image showing the finder shoes have the Chromosphere in the background?

Phil

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 7:37 pm

Tee hee hee! I know what you mean Phil, looks like it's on a spicule carpet ;)
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Bob Yoesle » Sun Feb 03, 2019 8:14 pm

Awesome and beautiful scope Mark, and the contrast uniformity looks great. I'm assuming it uses an internal 60 mm filter for minimum field angle magnification.

It sounds like the front etalon you tried was a dedicated DS filter, and apparently required excessive tilt. I experienced this with a 60 mm that was similarly useless, just a very narrow on-band banding stripe, and everything else was off-band. Perhaps the SM90III filters will behave better - especially those meant to be the single stack etalon.

The pre-Meade etalons seem to be in a whole different league than what is available today, and the reason they were twice to three times as expensive. They likely took longer to produce and were much more labor intensive. My first view through a double stacked scope was a pre-Meade external 90 with an internal 60, and it was a religious experience. Seems you have something similar to that era - you need to find an equivalent external 90!!!

I wish the companies would offer that kind of quality again - like with cars you could get the standard consumer version or the "premium" version.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Sun Feb 03, 2019 8:22 pm

Thanks Bob, yes it has an internal 60. You're right, I do want the external 90 for it, but it has to be a good one. I can see it is going to be a long process that involves lots of 'try before you buy'.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Mon Feb 04, 2019 7:48 am

And zooming in with a 2x cemax barlow. This time full frame with the ICX814, again no NR and no tilt needed :)

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Montana » Mon Feb 04, 2019 12:41 pm

Wow!! that scope looks magnificent :hamster: I have used Andy Devey's version and it is a glorious scope indeed, they are a real winner to get the originals.
I asked Pete about the camera, sadly it is an Altair Astro version of the 174 chip and it seems it can only get 60fps in 12bit mode? I have no idea why as the Grasshopper and ZWO get 128fps at 12 bit. So it is no good, I need high speed ;)

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by MAURITS » Mon Feb 04, 2019 1:44 pm

Nice solar equipment and captures Mark …
I like the looks of the coronado.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by robert » Mon Feb 04, 2019 2:48 pm

Nice scope Mark. Lovely even filter! :shock: :roll: ;)
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Tue Feb 05, 2019 7:31 am

Thanks everyone! I think as we become more seasoned and experienced solar observers our expectations in terms of how even the illumination of our filters are gets higher. I think back to some of my earlier setups and the illumination of the etalons and while I was happy then I wouldn't accept it now. I have a Lunt50 etalon which is very good, tight bandwidth and requires zero tilt. I need to look at an adapter plate but I think could make an interesting combination with this scope to double stack for a while. Certainly something to have a go at for later in the year!
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by krakatoa1883 » Tue Feb 05, 2019 12:12 pm

Great and even images, Mark, and interesting experience too. Thanks for sharing.
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by ffellah » Tue Feb 05, 2019 12:17 pm

Congratulations on your new SM 90 Mark. It already looks like you got a really nice and performing scope. I am sure you will have lots of fun with it. Eric and I like our SM 90s a lot. Yours seems to have a really even illumination, judging from these first results.

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Bob Yoesle » Tue Feb 05, 2019 3:56 pm

"I think as we become more seasoned and experienced solar observers our expectations in terms of how even the illumination of our filters are gets higher. I think back to some of my earlier setups and the illumination of the etalons and while I was happy then I wouldn't accept it now."

Hope the new SM90III's might be able to get you there Mark. If the etalon itself is of high enough quality, then the ability to both optimize the tuning while achieving minimal tilt makes them ideally suited for double stacking. Are there any dealers who would carry two or more at a time so that you could try before you buy?

Unfortunately, the goals now seem to be high production and lower cost at the expense of overall quality. But sometimes an outlier may slip through!
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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by marktownley » Tue Feb 05, 2019 11:48 pm

Hi Bob,

There are a few places here in the UK that show stock for external 90 etalons, whether this is actual 'live stock' or they are all showing the same 'virtual stock' from the same importer company warehouse remains to be seen. I would certainly like to try before I buy, but whether any would be obliging in this remains to be seen. I could ofcourse 'visit' the shop, but this would require a sunny saturday which is rarer than i'd like, and i'd prefer a more protracted trial period than a quick look and making a decision. Pricewise, whichever series of etalon, the 90 is a bit rich for me buying 'blind' to resell and buy another unit until I get the right one.

I think I will go with the plan that the right double stacking etalon for it will find me, rather than me find the etalon, a bit like the scope itself ;)

I tried my adapters for the Lunt50 to fit on the scope but all are too small, the scope is chunkier than it may seem. Will have to get one made up.

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Re: New Year, New Setup & the Blocking Filter Experiment - 3rd February

Post by Carbon60 » Wed Feb 06, 2019 7:55 pm

Just catching up on this post, Mark. Looks excellent....a nice new toy to keep you busy. :)

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