Optimum BF for 6" f/10 with PST etalon and ASI174?

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Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Hi,

Am I "wasting my time" trying to image with the original PST BF5 with the set-up in the thread title?

Lunt would have me believe I automatically need their BF1800 for my 1500mm focal length.
Not that they mention PST mods in the same breath, of course. ;)

I'm now using an iStar 150/10 H-a objective with full aperture Baader D-ERF. Baader H-a 35nm + Beloptik KG3 and PST etalon.

Previously I used an old, very secondhand, Celestron 150/8. Fitted with internal 90mm D-ERF, PST etalon, Maier ITF and PST BF5.
No diagonal or black box.

Endless searching online produces rather incomplete reasons to "upgrade." At very considerable expense with increasing size!
I even found threads criticizing the BF1800 as "rather variable." With warmer praise for the 1200 for "greater consistency."
Most forum threads were dealing with much smaller commercial telescopes than mine and often more about observing rather than imaging.

I'd really value the opinions of the experts here before investing further. Are there valid alternatives to the Lunt series in this context?

For the benefit of all who follow this path, may we, please, have the reasons for your recommendations and strictly for imaging only.

Thanks,


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by MalVeauX »

Heya,

So your scope's focal length is 1500mm approximately (give or take a bit due to the PST mod). I think if you divide the focal-length in millimeters by 110 or 115, it will give you the size of the disc in millimeters. So 13.0 to 13.6mm I think is that range, so you would want a 15mm blocking filter ideally if you wanted to get all of that onto a sensor; thing is, your IMX174 has a 11.3x7.1mm surface, smaller than that image circle, so its not capturing the full image. So really you'd be fine with a 12~15mm blocking filter with that size sensor; and if you have a smaller sensor, 10mm blocking filter is plenty.

And really that's assuming the entire image circle is good, and in the sweet spot. Which it will not be. The sweet spot on the PST etalon is small. So really, I don't see any reason to use a larger than 10mm blocking filter for a PST mod for imaging, since you likely will not get a larger area in the sweet spot than that anyways.

Very best,


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by marktownley »

Marty is right. The sweet spot of a 150mm/f10 is going to be a relatively small part of the sun (a circle ~8 arc minutes), so no benefit to getting a larger blocking filter. A BF10 is about as large as I would go.


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thank you Marty and Mark.

Taking your advice on size: A BF10 or BF1200 are the obvious candidates but at different price levels.
With the BF 10 much cheaper but 1.25" push fit only.
The BF1200 has a 2" option to T2. I much prefer 2" or T2 fittings for mechanical reasons.
The BF1200 is also available as a "straight through" fitting.

How does a diagonal BF fit in the short space available inside focus, after the etalon, with a 2" helical focuser in-line?
Can the BF10's straight, tubular fittings be unscrewed to fit T2 adapters?
Or is it another "unique" thread size? Any locking compound on the Coronado BFs?

My online research suggests that Lunt BFs are much more popular than Coronado on the forums.
Though I may be biased or merely mistaken from my small sample. Coronado BFs hardly get a mention.

What price Coronado support now Meade is in trouble?
Lunt has a decent online reputation for after-sales support.


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by AndiesHandyHandies »

Hi

This 25mm filter would work as a comb filter, also called a blocker after the PST Etalon.

https://www.ebay.co.uk/itm/153170511303

Optical Interference Filter 656.3 H Alpha 0.15nm Band-Pass for Normal Incidence

Provided its a production quality one, not one described as 'old new stock' which are cosmetic re-jects.

I bought two packages of the 'old new stock' which Bob sells as a H-Alpha project kit. For £150?
The ones which came had one of the above bonded to a 40nm ERF which had lots of reflections.
He replaced them with the 40nm on its own, but forgot 2 of the above!
It seems he had to send two production quality ones to make up the return which look perfect on the coatings.

You could contact Bob as he owns Omega filters who made the filters for NASA on the Mars landers. You can buy the same filters for comparing earth rocks with the martian rocks.

He has his own store on ebay for 'seconds' which this could be one of.

Personally I have a 2" and 1.25" sodium light pollution filters and they are perfect, £145 for the 2".
So when I saw the kit I did not think to do 'due diligence' and find issues on this forum with his seconds. To be fair he will replace what he sends, one guy tried 8 seconds and then got his money back.

I have asked him if this is a production one.

He takes time to reply sometimes so I have contacted him via his companies sales rep.

Worth a look?

Andrew.


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thanks Andrew.

I think your Omega H-a filter recommendation is far too unreliable on quality control to seriously warrant my importing one.

Cost + freight + import tax + customs clearance charges by Danish P.O. [£14 equivalent per package] + 25% purchase taxes on literally everything adds a serious load of extras on the basic price.

Getting the Danish PO to recognise up to eight potential returns to the US, before I was sent a good one, could bankrupt my piggy bank while they thought about it.


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

How does one judge the image quality of a PST Mod?
So much depends on the processing. Here is a series of images from this morning.
Do they suggest it is worth investing a further 1000 Euros in this PST mod in the form of a shiny new BF1200?

The first image shows unprocessed surface texture.
Only a touch of histogram to improve the contrast.
The dark area in the center is a circle of dew on the inside of the D-ERF.

12_00_10_g4_ap1338 no imppg.jpg
12_00_10_g4_ap1338 no imppg.jpg (54.67 KiB) Viewed 11814 times
These two images are of the NE quadrant showing a likely filament over a disturbed area near the limb.

sun surface texture NE imppg  rsz 600.jpg
sun surface texture NE imppg rsz 600.jpg (74.19 KiB) Viewed 11814 times
The second image is badly and deliberately overcooked.

sun surface filament NE 1230 imppg histo rsz 600.jpg
sun surface filament NE 1230 imppg histo rsz 600.jpg (83.63 KiB) Viewed 11814 times
The last image shows proms on the SE limb.

prom 232020 1130 imppg pf7 txt 2.jpg
prom 232020 1130 imppg pf7 txt 2.jpg (40.33 KiB) Viewed 11814 times
I know the processing is short and shoddy but I just wanted capture something quickly to prove the new OTA.


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by MalVeauX »

Heya,

The processing isn't what matters as much, we can all process something out; what matters is seeing conditions first and foremost if you're trying to image at these image scales. If your seeing is excellent, you can maximize the resolution of that 150mm aperture if you image at the critical sampling limit and seeing allows it to be resolved to that point (which is the point of the airy disc essentially). This is not common though. Your best bet, just looking at these images, is actually to reduce your image scale. F20 is the practical focal-ratio for HA wavelength with your IMX174 sensor. But, your conditions likely don't allow you to get that resolution, so you might want to drop it down a bit more... maybe F14~F16. Your blocking filter at 5mm is causing vignetting for sure. If you wanted to maximize this setup it would need a 10mm blocking filter or larger, and again, good enough seeing to support this image scale, or back off image scale a little, and make it easier and still get good resolution.

Very best,


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thank you Marty. I am most grateful for your continuing patience with all my questions.
Over half a century of the dark side and ATM seems to be no guarantee of holding relevant information on solar imaging.
I hope my endless questions and your answers are helping to spread the knowledge to other solar enthusiasts.

I see your point about focal ratio and seeing conditions. I simply haven't thought of it in those terms until now.
Adding a 2x Barlow, to get closeups of fine detail and proms, should be strictly limited to the best seeing.
Though I have been enjoying surprisingly steady conditions recently in the early to mid-morning during rare, cloud free moments.

Even timing my video captures to the very best moments is relatively easy on my large monitor.
By capturing many, short duration videos [<6 seconds ] 1-2k frames at high [300+] fps I hope to further maximize moments of lucky seeing.
Gain can be balanced against exposure to maintain high fps. I use SSDs and a fast laptop to that same end.

My tracking is usually accurate and steady thanks to my massive mounting and drives. It all helps at these focal lengths.
Since it is of such importance, it follows that anything I can do to improve my local, or instrumental, seeing conditions is a plus.
So the whitewash brush and can opener may well get an outing after all. :?

PS: A larger BF is on my immediate shopping list.

Thanks again. :bow


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by AndiesHandyHandies »

Hi

The 8 returns were for some one trying seconds CAK filters I recall.

Bob the owner of Omega Opticals reply was:

This is new production of a single cavity FP etalon. It is only the narrow passband, that controls from 0.8 to 1.3 times the CWL.

I have asked him a clarification question about it being suitable as a PST Blocker.

I have used one of his 0.15nm filters, which looks lke a production one, as a Blocker on a Stage 2 PST mod.

RodAstro has used Bobs 40nm ERF and 2 0.15nm from the 'seconds kit' as an etalon on a 6" F15 telescope. Some reflections and variable illumination issues. But it works. One only is good for prominences.

The filters are USA 25mm size and fit in plastic Celestron/Skywatcher Moon filters.

Andrew.


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by MalVeauX »

Heya,

No worries! And really its just my opinion, others may feel differently about it. I'm learning still too. But it's a great place to be able to share everything both ways!

Something to consider, steady seeing is good usually, but doesn't always mean it's sub-arc-second good, so it still is the great limit for high resolution. You can have steady seeing but it's 2~3 arc-seconds and won't support the maximum resolution potential of a 150mm aperture or more, at the critical sampling limit. Depends on how patient you are too. Some days will be better than others of course. Having the option to change your image scale rapidly is good. You can start with a courser image scale and if seeing seems to be holding up well, you could try to sample at a finer image scale. When it comes to larger apertures like this, past 102mm and up, it's amazing how bad the seeing conditions become resolved. And now all locations support the larger apertures. It's all about optimizing and maximizing the best times of the day with the best seeing conditions for your local area and of course, lucky imaging.

Very best,


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thanks Marty.

My next problem is deciding if the "straight through" Lunt B1200S2 or the diagonal version of the Lunt B1200 has the shortest light path or the same. The information available online is almost nil. I have been searching the forums for images and information on the straight through version but there isn't anything so far. I may simply be using the wrong search terms. For imaging I'd probably prefer to avoid the diagonal. The one advantage for the diagonal version is comfortable use for solar viewing with a binoviewer. They are both the same price in Europe. Now I can't make up my mind before placing an order. :D


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H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by rsfoto »

Hi Rusted,

My logic tells me that the shortest light path is always straight through as a diagonal adds a lot of light path.

¿?

Rainer


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

rsfoto wrote: Tue Mar 03, 2020 5:14 pm Hi Rusted,

My logic tells me that the shortest light path is always straight through as a diagonal adds a lot of light path.

¿?

Rainer
Thank you Rainer and fully agreed in principal.
But, the [normally] spaced ITF/BF components might well be placed each side of the diagonal flat. [I'm guessing!]

I have been advised to go for a Coronado BF diagonal with my PST mod to avoid potential clashes with Lunt's filtration.
The Coronado BF is a 1.25" fitting so doesn't add as much path length as a 2".
So now I'm probably looking at a BF15 for imaging with a 1500mm f/l.
Or a BF10 if I want to completely avoid the risk of peripheral ghosting.
Choices - choices.. :lol:


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by marktownley »

Rusted wrote: Tue Mar 03, 2020 6:28 pm So now I'm probably looking at a BF15 for imaging with a 1500mm f/l.
Or a BF10 if I want to completely avoid the risk of peripheral ghosting.
Choices - choices.. :lol:
The Bf15 / 1500mm rule works only if you're imaging a full disk - which you definitely wont with a PST mod. BF10 is fine with the limitations of a sweet spot - and cheaper...


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by rsfoto »

Rusted wrote: Tue Mar 03, 2020 6:28 pm
rsfoto wrote: Tue Mar 03, 2020 5:14 pm Hi Rusted,

My logic tells me that the shortest light path is always straight through as a diagonal adds a lot of light path.

¿?

Rainer
Thank you Rainer and fully agreed in principal.
But, the [normally] spaced ITF/BF components might well be placed each side of the diagonal flat. [I'm guessing!]

I have been advised to go for a Coronado BF diagonal with my PST mod to avoid potential clashes with Lunt's filtration.
The Coronado BF is a 1.25" fitting so doesn't add as much path length as a 2".
So now I'm probably looking at a BF15 for imaging with a 1500mm f/l.
Or a BF10 if I want to completely avoid the risk of peripheral ghosting.
Choices - choices.. :lol:
Hi,
Or a BF10 if I want to completely avoid the risk of peripheral ghosting.
I see that people choose their blocking filters according to the recommendations of the H-alpha telescope producers in regard to used focal length and so now I ask myself if I made a totally wrong decision to use a BF 30 (29.5mm Ø) and using a 900 mm focal length telescope.

¿ or do they just care about our Wallet ? :lol:

Why do they not make straight through BF with the low diameters ?

BF_Wallet.JPG
BF_Wallet.JPG (54.48 KiB) Viewed 11754 times


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by MalVeauX »

Heya,

As for straight through versus diagonal; get straight through for pure imaging setup (no mirror to change orientation of image, less work in post to correct orientation; also mirrors have a bit of transmission loss, small, but every 1% counts if you care at higher resolution; also one less surface to have dust on to have to do a flat frame for). Diagonal is better when you might use it visually.

Very best,


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thank you all for your kind and useful responses.

I must take Mark's experienced advice and limit myself to a BF10 or B1200.

May I ask a straight question?

Do Lunt BFs always work well with PST etalons?
Is it acceptable to "mix and match" brands with the PST etalon without thought or consequence?

Coronado don't do a straight through BF10. Only the 1.25" diagonal/elbow.
Which leaves me with my original choice of a "straight through" B1200 S2.
Which I still cling to as my favourite option.

Or, I must accept an elbow. With its obvious, image orientation issues.
Which is always a bore when centering a feature on the paddle and mitigating unexpected drift.
Or quickly scanning the entire limb of a huge [round] sun for promising proms.

I routinely set my camera orientation to match Gong Ha at the start of every imaging session.
It's a great time saver and avoids having fuzzy images of the only "low hanging fruit" on the Internet.
While all others are posting wonderful images and animations of "The Leaning Tower of Pisa." :lol:

From searching for "BF" and reading numerous threads and posts here some members have a drawer full of BFs.
Many of you have been "doing H-a solar" for years and must have built up a brand preference when you still use the PST etalon.
Does brand really matter?

Thanks again


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by MalVeauX »

Heya,

The blocking filter is going to be around 6 angstrom at 656.28nm, by all makers, since that's removing the off-band harmonics that the comb filter (etalon) is outputting. It should work the same regardless. There may be quality, transmission, durability, etc, differences, but the actual function is the same.

You can convert a Coronado blocking filter from diagonal to straight through. Some components might be glued, but you can break the glue. Inside you'll find a mirror, ITF filter and the actual narrowband blocking filter. The threads are the same as what's on the eyepiece holder going into the diagonal (there are adapters to allow this to be converted to 28mm for 1.25" gear, letting you use it just like an eyepiece would, but without the mirror). I did this in my "non destructive" thread where I took the PST and made a straight through blocking filter with internal helical focuser if you want to take a look.

Very best,


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by christian viladrich »

Just a word of caution about the Omega filters, I have four of them in Ha and one in Ca K.
They are all completely rubbish.


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Bob Yoesle »

Unfortunately, Christians' experience with Omega filters is also my experience.

FYI - Not all blocking filters are 0.6 nm - it depends on the etalon and blocking filter generation. Some of the early Coronado BFs were closer to 0.2-0.3 nm, and the etalons themselves had a narrower FSR. Using a Lunt BF with a narrower FSR etalon would not work, as one or more of the etalon harmonics contaminated the detail from the CWL peak, and some of these could extend into the IR...


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

MalVeauX wrote: Wed Mar 04, 2020 3:09 pm Heya,

The blocking filter is going to be around 6 angstrom at 656.28nm, by all makers, since that's removing the off-band harmonics that the comb filter (etalon) is outputting. It should work the same regardless. There may be quality, transmission, durability, etc, differences, but the actual function is the same.

You can convert a Coronado blocking filter from diagonal to straight through. Some components might be glued, but you can break the glue. Inside you'll find a mirror, ITF filter and the actual narrowband blocking filter. The threads are the same as what's on the eyepiece holder going into the diagonal (there are adapters to allow this to be converted to 28mm for 1.25" gear, letting you use it just like an eyepiece would, but without the mirror). I did this in my "non destructive" thread where I took the PST and made a straight through blocking filter with internal helical focuser if you want to take a look.

Very best,
Thanks again Marty. There was a wealth of information in that thread.
Somehow I had completely missed the BF dismantling.

Your creativity in the art of building solar H-a equipment is a blessing.
You get to do all the work and we can tag along once its proven to work.

The BF10 looks like a better PST match than a 'straight through' B1200S2.
I can learn to live with the BF10 diagonal until I'm tempted to take it part.


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H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Bob Yoesle wrote: Thu Mar 05, 2020 3:27 am Unfortunately, Christians' experience with Omega filters is also my experience.

FYI - Not all blocking filters are 0.6 nm - it depends on the etalon and blocking filter generation. Some of the early Coronado BFs were closer to 0.2-0.3 nm, and the etalons themselves had a narrower FSR. Using a Lunt BF with a narrower FSR etalon would not work, as one or more of the etalon harmonics contaminated the detail from the CWL peak, and some of these could extend into the IR...
Thanks Bob.

I have no idea as to the age or spec of my PST donor. Blue objective.
I'll play safe and go for the BF10 as the most likely best match straight out of the box.
There's a pun in there somewhere. Given the context of this thread. ;)


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Merlin66 »

Bob,
The ITF should suppress any etalon harmonics outside the target CWL.
Maier_ITFgraph.jpg
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Merlin66 wrote: Thu Mar 05, 2020 11:37 pm Bob,
The ITF should suppress any etalon harmonics outside the target CWL.
Maier_ITFgraph.jpg
Thanks Ken.

My searches here [and elsewhere] suggest that the advice has always been that both Lunt or Coronado BFs are acceptable for PST mods.
I presume that nothing has really changed in that respect?

The big brands are very unlikely to actively support "home brews." If only for safety reasons.They are too far removed from "DIY solar activists" to be able to monitor "total user idiocy." No doubt they'd be snowed under with emails asking daft questions, like mine. Then sued if an idiot hurt their eyes using any of their products badly. The wording on their sales literature is heavily biased towards matching same brand components.

I'd be using a Quark if it wasn't such a gamble buying a good one at very considerable expense. :roll:


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by marktownley »

Rusted wrote: Fri Mar 06, 2020 9:34 am I'd be using a Quark if it wasn't such a gamble buying a good one at very considerable expense. :roll:
In my experience there's plenty of variability with PST etaons too...


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

marktownley wrote: Fri Mar 06, 2020 3:58 pm
In my experience there's plenty of variability with PST etalons too...
Thanks Mark.

That sounds as if one can never be certain of a match made in heaven.
I'm using a Beloptik KG3 and Baader 35nm H-a after the full aperture Baader D-ERF.
So, presumably, have a better chance of avoiding problems with unwanted harmonics.
The downside is likely to be less than optimum bandwidth providing inferior H-a images.


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H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Merlin66 »

Rusted,
the ITF etc etc will have no impact on the H alpha bandwidth...this comes from the etalon.
The final sort/ blocking filter can affect the bandwidth if there is a serious miss-match by cutting off/ into the etalon bandwidth.


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Merlin66 wrote: Sat Mar 07, 2020 9:49 am Rusted,
the ITF etc etc will have no impact on the H alpha bandwidth...this comes from the etalon.
The final sort/ blocking filter can affect the bandwidth if there is a serious miss-match by cutting off/ into the etalon bandwidth.
Thanks for the clarification.


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

I ought to update this thread to say that my Lunt B1200S2 "straight through" blocking filter arrived.
Excellent service from Bresser.De and DHL for express delivery.
I didn't want to miss a deadline for closure of international postal postal packages due to the virus.

I quickly discovered that the new BF needed more inward focus than the PST BF.
So the previous fittings were removed. As was the 1.25" receptacle from the new BF body.

By sheer luck I had a T2 male threaded adapter which contained the BF's 2" barrel and fitted my camera.
While the female 2" thread fitted my 2" helical focuser. The new BF is invisible inside the adapter.

The immediate impression was of a much larger field of view on my monitor
The PST BF provided more even illumination on larger frame sizes in SharpCap.

I had some brighter corners and shaded rings from the Lunt BF. Probably from the PST etalon.
I could overcome these problems with flats but soon found 800x600 provided acceptably even brightness across the field.

Sadly I haven't had a continuously clear sky nor more than moments of a clear sun since the new BF's arrival.
There is definitely a real sense of 3D surface texture in iMPPG. Though not to the standard of the processing experts here.

Pictures are worth more than my usual excess of words:

P1410297 rsz 600.JPG
P1410297 rsz 600.JPG (138.43 KiB) Viewed 8290 times
P1410316 rsz 600.jpg
P1410316 rsz 600.jpg (104.41 KiB) Viewed 8290 times
P1410300 rsz 600.jpg
P1410300 rsz 600.jpg (122.07 KiB) Viewed 8290 times

My only capture shows the dying remnants of AR2758 near the limb.
Cropped from 800x600 to remove the brighter corners.
sun 17.3.20 11.07.jpg
sun 17.3.20 11.07.jpg (73.22 KiB) Viewed 8290 times


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by marktownley »

Nice mod and looking promising with the results!


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Thanks Mark.

I shan't be able to confirm any real improvements until I catch some clear sunshine with decent seeing.

The eternal optimism of the apprentice, solar imager. ;)


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Solar-Cologne »

Hi Rusted,

Coronado and Lunt are not the best BFs.

I am tested the BFs from Wolfgang Lille Heinbokel / Germany.......they are the best

I use an Lille 30mm and 50mm Blockingfilter.

http://sonnenfernrohr.de.w0199a68.kasse ... a-systeme/

Sorry, Wolfgangs Website is only in German.

If you have Questions, pleas ask me.


Best Regards
Achim


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Merlin66 »

The Ha systems are listed and documented, but I can't see any specifics on the BF (LS1800 is mentioned), there no information on compatibility with other etalon suppliers (ie Lu,t Coronado, Solar Spectrum, SolarScope etc.)


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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Solar-Cologne wrote: Mon Mar 23, 2020 5:34 am Hi Rusted,

Coronado and Lunt are not the best BFs.

I am tested the BFs from Wolfgang Lille Heinbokel / Germany.......they are the best

I use an Lille 30mm and 50mm Blockingfilter.

http://sonnenfernrohr.de.w0199a68.kasse ... a-systeme/

Sorry, Wolfgangs Website is only in German.

If you have Questions, pleas ask me.


Best Regards
Achim
Hi Achim,

Many thanks for that information and link.

Google auto-translate solved any problems.

I didn't see any price list for Lille's products
What does such a large BF cost in Euro?

There is an English saying: "If you have to ask the price, then you can't afford it!" :shock:


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Optimum BF for 6" f/10 with PST etalon and ASI174?

Post by Rusted »

Merlin66 wrote: Mon Mar 23, 2020 6:10 am The Ha systems are listed and documented, but I can't see any specifics on the BF (LS1800 is mentioned), there no information on compatibility with other etalon suppliers (ie Lu,t Coronado, Solar Spectrum, SolarScope etc.)
Thank you for that.

I am very happy with my new Lunt B1200S2 BF so far. After making repeated back and forth comparisons the Lunt easily wins over the BF5. There is a difference in focus between the two. So one of them must have some optical power.

The Lunt BF image is very much duller but there is none of the obvious vignetting of the BF5. I often ran into minimum exposure with zero gain with the PST BF5 in SharpCap with my 6" and the ASI174! Now I have a much wider, safety margin to play with and must adjust gain upwards to have enough light at 1-2ms exposures. With the BF5 I would always be on zero gain and under 1ms on a clear sun!

You may remember that I had motorized my PST etalon which was discussed in another thread here. That worked rather well with the BF5. With the Lunt the looseness of the thinner packing rings I had used, meant very non-optimum, brightness levels across the much larger field on the monitor.

I removed the rubber band and thin metal shell and played with the PST etalon's tuning with a rod in the tuning holes. Naturally there was a lot of play and this changed the "lighting" across the field.

So, I have returned to the original, ridiculously stiff, O-rings and was pleased to see much larger fields of smooth surface detail with much more even brightness.

Downside is I now have to manually tune the etalon again. Even with thin and very grippy, industrial, rubber gloves it is hard work turning the PST tuning band smoothly. Which is what drove me to motorize the etalon in the first place. Except it was far too stiff to turn with a motor as standard.

Despite considerable expense and many trials with different materials [all bought online] at 1.5-1.7mm Ø I never found a perfect match between freedom [i.e. desirably low friction for driving] and the necessary stability of the PST etalon in rotation.

I've had a couple of days of sunshine between cloud now but with rather indifferent seeing conditions. I shall continue to experiment and will report any useful improvements. My blog shows some of the images I have been capturing. I don't think the experts here have much to worry about! ;)

Sorry for this long winded update. :oops:


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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