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My efforts to allow the PST etalon to rotate freely enough, for motor driven tuning, has resulted in floppiness. I never found a suitable substitute for the foolishly stiff, original O-rings. I need to improve this to avoid asymmetric shading and brightness during etalon tuning.
Meanwhile, the subject of suitable blocking filters, for imaging with the new 150mm f/10 objective, has arisen. An etalon produces a "comb" of harmonics of the H-a wavelength. The blocking filter unit is designed block all the different frequencies leaving a single H-a peak. Some light and heat reduction is usually incorporated into their design. They usually contain an ITF and a BF sandwich. The ITF narrows the comb down to H-a.
The tiny, original, 5mm, PST blocking filter reduces the field of view when imaging. It may also be causing some vignetting. Possibly resulting in the outer edges of the captured image appearing darker.
Note that the 5mm PST, BF does work very well for binoviewing. Particularly with a 2x [WO] Barlow nosepiece screwed onto the binoviewer's own nose.
A request for further information on the solar forums suggests I limit myself to 10-12mm diameter, blocking filters to match the PST etalon. A larger BF might increase the field of view. Though this is unlikely within the limitations of a heavily modified, long focus PST. Which sees only a small fraction of the sun's potential diameter. An oversized BF might even cause ghosting at the edges of the field of view due to reflections.
Despite its greater cost, I still prefer the "straight through" Lunt B1200S2 in 2" to T2 form. [See image right] Rather than choosing a Coronado BF10 or the diagonal form of BF1200 from Lunt. A diagonal alters image orientation, left to right, as well as inverting it.
Which is a nuisance when manually slewing the telescope or searching the solar limb for prominences. Text viewed through a telescope with a diagonal may well be upright, but is reversed left-to-right. The "poor man's" terrestrial telescope.
A "straight through" design will maintain the same image orientation. Which becomes completely natural, with practice, to steer the telescope manually via the control paddle. Using the usual, four steering buttons, one can "push" or "pull" the image in any desired direction.
Image reversal could well mean push on one axis and pull on the other to paddle button presses. The resulting confusion might cause the loss of the sun's image altogether from the field of view. Or faulty corrections for the slightest, tracking drift.
Which is a nuisance when manually slewing the telescope or searching the solar limb for prominences. Text viewed through a telescope with a diagonal may well be upright, but is reversed left-to-right. The "poor man's" terrestrial telescope.
A "straight through" design will maintain the same image orientation. Which becomes completely natural, with practice, to steer the telescope manually via the control paddle. Using the usual, four steering buttons, one can "push" or "pull" the image in any desired direction.
Image reversal could well mean push on one axis and pull on the other to paddle button presses. The resulting confusion might cause the loss of the sun's image altogether from the field of view. Or faulty corrections for the slightest, tracking drift.
Before I place an order for a Lunt B1200S2 I am hoping for further, forum responses on the issue of brand compatibility. One, well-respected expert suggests that Lunt BFs may not work optimally with the Coronado PST etalon. Others suggest that the BFs, of either brand, are completely interchangeable.
Neither company is likely to address direct questions on compatibility with a modified PST. The risk of being sued for blindness from somebody taking a silly risk will inhibit open discussions. Several astronomy forums will not even allow solar telescope modding to be discussed.
Thanks to further information the BF10 is the best chance of a match out of the box. The mirror can be removed from the diagonal with difficulty. Allowing the ITF and BF10 to be mounted in a straight through layout.
The mirrors are glued in so local heat is required to melt it free. More on this if/when I get around to straightening it out. It depends how irritating I find the diagonal when I'm actively imaging.
Or not? I'm still looking at the B1200 S2 "straight through" BF as my ideal purchase. It suits my etalon/focuser stack better than 1.25". A male T2 adapter provides 1.25" if desired. While leaving the adapter off provides a male T2 thread.
The other end has a twin screw, band clamp, 1.25" eyepiece/camera socket. Further options exist because a 2" fitting is also mentioned. The 1.25" socket looks removable too. Probably leaving a T2 male thread for direct fitting of a ZWO camera.
The following YT video shows the B1200 S2 in use on a solar telescope. The BF1200 S2 is discussed from about 1:00 minute onwards.
https://youtu.be/AB1z_T5Y1ho
As a side note: The European prices for these Lunt blocking filter is almost exactly double the US retail price. $648 USD = £498 GBP = €572 Euros quoting today's online exchange rates. [On 5.3.20.]
Whereas, the UK online retail price is £924 for the B1200. The European price is 1035 Euros from several German dealers. €1035 Euros = $1175 USD! £924 GBP = $1205 USD!
European VAT is between 20 & 25%. Perhaps the European dealers are buying these things at retail prices to sell them on? Which I seriously doubt! European astro dealers always seem to have doubled US equipment prices.
Neither company is likely to address direct questions on compatibility with a modified PST. The risk of being sued for blindness from somebody taking a silly risk will inhibit open discussions. Several astronomy forums will not even allow solar telescope modding to be discussed.
Thanks to further information the BF10 is the best chance of a match out of the box. The mirror can be removed from the diagonal with difficulty. Allowing the ITF and BF10 to be mounted in a straight through layout.The mirrors are glued in so local heat is required to melt it free. More on this if/when I get around to straightening it out. It depends how irritating I find the diagonal when I'm actively imaging.
Or not? I'm still looking at the B1200 S2 "straight through" BF as my ideal purchase. It suits my etalon/focuser stack better than 1.25". A male T2 adapter provides 1.25" if desired. While leaving the adapter off provides a male T2 thread.
The other end has a twin screw, band clamp, 1.25" eyepiece/camera socket. Further options exist because a 2" fitting is also mentioned. The 1.25" socket looks removable too. Probably leaving a T2 male thread for direct fitting of a ZWO camera.
The following YT video shows the B1200 S2 in use on a solar telescope. The BF1200 S2 is discussed from about 1:00 minute onwards.
https://youtu.be/AB1z_T5Y1ho
As a side note: The European prices for these Lunt blocking filter is almost exactly double the US retail price. $648 USD = £498 GBP = €572 Euros quoting today's online exchange rates. [On 5.3.20.]
Whereas, the UK online retail price is £924 for the B1200. The European price is 1035 Euros from several German dealers. €1035 Euros = $1175 USD! £924 GBP = $1205 USD!
European VAT is between 20 & 25%. Perhaps the European dealers are buying these things at retail prices to sell them on? Which I seriously doubt! European astro dealers always seem to have doubled US equipment prices.
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