BF30 ITF replacement

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BF30 ITF replacement

Post by Bob Yoesle » Thu Oct 18, 2018 6:09 pm

I just got a note from Oliver Smie that he can now provide his drop-in replacement for the ITF in the BF30 size:

"After endless time I have also durable ITF replacement filters for the
Coronado BF30 in stock, a batch of 18pcs. Filter design is the same to
my smaller ones for PST, BF10...

https://beloptik.de/en/itf-replacement-filter/

Diameter is 35mm, thickness 3.5mm for drop-in, price 250 EUR (210 EUR
without 19% german VAT)

Have fun with sun!

Clear skies
Oliver"

This would be of superior longevity compared to the traditional OEM ITF used by Coronado.
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Re: BF30 ITF replacement

Post by marktownley » Thu Oct 18, 2018 6:29 pm

Brilliant! Thanks for the heads up Bob.
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Re: BF30 ITF replacement

Post by TheSkyBurner » Thu Oct 18, 2018 7:40 pm

But its glued, and the epoxy is the achilles heal of these filters.

Its a nice offer but I would of eliminated that lamination to rg630 glass with the h-alpha coat on the back of the kg3.

Anybody can glue a kg3 filter right to a baader planetarium 7nm h-alpha filter using canadian balsam in a heated vacuum chamber!

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Re: BF30 ITF replacement

Post by Valery » Sat Oct 20, 2018 4:46 pm

TheSkyBurner wrote:
Thu Oct 18, 2018 7:40 pm
But its glued, and the epoxy is the achilles heal of these filters.

Its a nice offer but I would of eliminated that lamination to rg630 glass with the h-alpha coat on the back of the kg3.

Anybody can glue a kg3 filter right to a baader planetarium 7nm h-alpha filter using canadian balsam in a heated vacuum chamber!
And who will really do it? And if one will do this, he will come out with about the same or even higher price!
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Re: BF30 ITF replacement

Post by TheSkyBurner » Sat Oct 20, 2018 5:39 pm

Valery wrote:
Sat Oct 20, 2018 4:46 pm
TheSkyBurner wrote:
Thu Oct 18, 2018 7:40 pm
But its glued, and the epoxy is the achilles heal of these filters.

Its a nice offer but I would of eliminated that lamination to rg630 glass with the h-alpha coat on the back of the kg3.

Anybody can glue a kg3 filter right to a baader planetarium 7nm h-alpha filter using canadian balsam in a heated vacuum chamber!
And who will really do it? And if one will do this, he will come out with about the same or even higher price!
That was the point I was trying to make Valery :) Beloptik should of just got a single element solution manufactured. Unmounted 7-10nm filters are cheap with only Od4 blocking, especially in a batch of 25. The ir/uv cut coating can be applied to any filter!

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Re: BF30 ITF replacement

Post by Valery » Sat Oct 20, 2018 11:45 pm

OTOH, my point, Apollo, was that you should finally understand that peoples like you, who trying to make all theirselves, as cheaper as possible, are quite quite rare. I know only one such person - you. I believe we should give small manufacturers a freedom to make the things the way they see. They always compete each other. Their overall view on a subject/problem usually wider and smarter than one single person's point of view.

And Oliver's solution is best on the market. The solution you offer is exactly the same as Coronado does/doing and now these filters should be replaced. Oliver's filters will work decades. Good enough, I believe.

I will buy Oliver's ITF filter despite the ability to make such a filter myself. The best way is: we need to earn money doing what we can do best - at our job or extra job, but still where we are good. Then buy the things we need and which we can't do right. Unless we are peoples like you are.
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Re: BF30 ITF replacement

Post by Bob Yoesle » Sun Oct 21, 2018 3:59 am

The ITF of the solar blocking filters do not fail from lamination separation or de-contacting between the filter components, they fail from thermal cycling and loading. This compromises the edge seal, which results in atmospheric moisture being able to penetrate the filter and degrade the silver layers of the ITF coating. Oliver’s solution therefore completely removes this silver layer deterioration mechanism.

Secondly, the purpose of the ITF is mostly long IR blocking out to about 4000-5000 nm, and why Oliver’s solution is to incorporate the KG3 element instead of the silver layer ITF. Although the ITF also incorporates a RG630 substrate for UV blocking, this long IR blocking is something the standard nighttime H alpha RG filter with standard UV/IR blocking to 1200-1400 nm cannot do.

However, if one already has an RG630 element elsewhere in the system, preferably also with standard IR blocking to 1200-1400 nm such as the ERF’s used by Lunt and Solar Scope, one then does not need the RG630 element in the ITF portion of the blocking filter. Solar Scope therefore has eliminated the ITF from their blocking filter(s), and so has Lunt. Solar Scope uses a KG filter instead, and Lunt uses a BG element.

Since my systems incorporate RG630 ERF elements, I have used Oliver’s other ITF replacement filter - a KG3 UV/IR filter - to replace a rusted BF30 ITF with great results and improved image brightness.
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Re: BF30 ITF replacement

Post by Merlin66 » Sun Oct 21, 2018 8:44 pm

I’ve mentioned previously, but repeat my myself again.
Why do we think blocking IR beyond 1400nm is an important issue in solar filter design?
This region is heat not light and well beyond the sensitivity of the eye or current imaging sensors.
I accept that extended and prolonged exposure to IR can be harmful, but this is not the case with the average solar observer.
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Re: BF30 ITF replacement

Post by Bob Yoesle » Wed Oct 24, 2018 4:15 pm

Hi Ken,

"Why do we think blocking IR beyond 1400nm is an important issue in solar filter design?"

For one reason it seems most of the solar filter manufacturers think it's important, and spend additional funds and increase the costs of their products to provide blocking to 3000 nm or beyond.

https://luntsolarsystems.com/lunt-solar-safety/

"This region is heat not light and well beyond the sensitivity of the eye or current imaging sensors."

There appear to be other structures of the eye besides the retina that are susceptible to mid and long IR:
Occular absorbtion.jpg
Occular absorbtion.jpg (162.2 KiB) Viewed 505 times
Here's what our friend Mark Wagner of Solar Spectrum filters had to say in this regard:

The ITF is used to block what the main bandpass doesn't, the one that only lets one peak from the etalon through. The bandpass will normally turn back on at around 800 nm. So the ITF is designed to block any light from 690 nm to the FIR (past 2500 nm). It is not uncommon to be still blocking past 3000 nm. They will use a red glass (RG630) to help block the short side (lower wavelengths). These filters will be spec’d as blocked from X-ray to FIR with a of OD4. This is how a standard bandpass keeps the level of IR low for safe viewing.

Filters that are blocked to only 1000 nm (like most stock filters) are not safe for viewing the sun, but maybe fine for imaging depending on the camera. To decide how far in the IR is safe for viewing I would say nothing shorter then 2000 nm. I wanted to see what a filter looked like with a dim etalon that I only blocked to about 900 nm. I did this test because the hard coated filters I use have more transmission than a standard one. And it would be closer in brightness. I only looked for about 5 minutes. When I was done I noticed that I couldn't focus the eye I had been using. It took about 45 minutes before I could focus with that eye. Didn't get hurt but got scared that I had damaged my eye. So don't try viewing with filters that are blocked anything shorter then 2000 nm on the sun.

KG glass is also used in blocking the IR.


Mark's description sounds very similar to what one expects with corneal edema (swelling) and irritation likely from IR exposure.

George9 followed up with a well-regarded expert in eclipse filter safety:

Thanks, Mark. Dr. Ralph Chou was nice enough to answer a couple of email questions in this regard, too. He let me quote him here.

First, with regard to solar eclipse eyeglasses: "You are correct that the specification for solar filters does not need to go beyond 1500 nm since water within the ocular media prevent longer wavelengths from reaching the retina. As for the cornea, the thresholds for damage by infrared radiation are extremely high, and even with a telescope, the danger to the cornea from IR between 1500 and 2500 nm while observing the Sun is not significant. The solar filter materials do block IR quite well out to about 3000 nm, so the eye is well protected across the entire UV-visible- NIR waveband." There is an existing eclipse eyeglass standard (EN1836) and a new draft ISO standard (ISO 12312-2), for which Dr. Chou is lead writer.

But with regard to telescope filters: "I expect that the manufacturers are well aware that they need to ensure that all of the optical waveband in sunlight (280 to 3000+ nm) has to be attenuated for eye safety, no matter what their technology is."

In other words, while the cornea is relatively resistant to damage in the 1500-3000nm range and should be fine without magnification, you still really need to make sure it is blocked in a telescope. And it would be possible to create a filter that is perfectly safe for solar eyeglasses but would not be a great idea to use by itself in front of a large telescope.


If we do a little math, we can see that my 4 inch (102 mm) telescope will present 650 times the amount of light (hence IR) than the unaided (naked eye) alone:

Area = pi r^2

Pupil D = 4 mm, then A = 3.14 x 2^2 = 12.56 mm^2
Objective D = 102 mm, the A = 3.14 x 51^2 = 8167 mm^2

8167/12.56 = 650.2

Applying this methodology to H alpha filters, we can see there is also potential here as well. For example, if the etalon has a free spectral range of 10 Å, and a FWHM (50%) transmission of 0.7 Å, the native 650 times the pupil transmission would be:

0.7/10 = 0.07
0.07 x 650 = 45.5 x 0.50 = 23

So if a solar H alpha blocking filter is not blocked at all beyond 1400 nm, in the case of a 102 mm refractor it could present the eye with about 23 times as much mid and far IR as the pupil would receive alone, and additionally is focused at the eye itself. And who is to say what an individuals specific susceptibility to any form of radiation could be based on their genetics and previous exposures, which generally are cumulative?

"I accept that extended and prolonged exposure to IR can be harmful, but this is not the case with the average solar observer."

Why take the chance, especially when a KG3 filter (or ITF, BG38, etc.) is relatively inexpensive insurance? And if for no other reason, in our litigious society, it wouldn't take much for a casual observer at one of my solar outreach events to show up and claim my solar filters were not safe and caused their eye issues. We go to court, and I state because Ken Harrison said it was safe I didn't use any IR blocking beyond 1400 nm. The plaintiff's attorney points out with documentation that every solar filter and H alpha telescope manufacturer incorporates IR blocking to 3000 nm or more. He or she also quotes the above information from Wagner and Chou, readily discoverable on the internet. The plaintiffs then ad you to their lawsuit for contributory liability. Who do you think the jury or judge is more likely to side with?

If you truly believe there is no harm from 1400 nm and beyond, this should be the acid test:

Get yourself a THORLABS FEL 1400 1 inch filter, which is only $76 USD
FEL1400_Transmission.gif
FEL1400_Transmission.gif (7.91 KiB) Viewed 505 times
https://www.thorlabs.com/thorproduct.cf ... er=FEL1400

This filter is blocked OD 4 from 200 nm to the cut-on of 1400 nm. Focus your equatorial mounted 6 inch f 8 refractor on the sun using a standard piece of Baader astrosolar filter material. Add the FEL 1400 to your eyepiece, remove the Baader astrosolar material, and "observe" only with your non-dominate eye for couple of hours every week for a year or two, and let us know how it goes. I hope you are right.
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Re: BF30 ITF replacement

Post by TheSkyBurner » Wed Oct 24, 2018 8:51 pm

Bob Yoesle wrote:
Wed Oct 24, 2018 4:15 pm
Hi Ken,

[
I think at f/30 and beyond, the intensity is greatly diminished. It is the refocus lens that is going to be the ultimate source of death rays because it brings the intensity back to f/6.6 on a solarmax 60 .

Obviously the parameters for a front mounted filter will never achieve f/30 without a barlow so the intensity is at maximum.

I am curious to how much the damage is reduced at f/30+

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Re: BF30 ITF replacement

Post by christian viladrich » Wed Oct 24, 2018 9:12 pm

Hello Bob,
Thanks for the valuable information.
What is the orginal source of information for these figures :
download/file.php?id=34786
Thanks !
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Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

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Re: BF30 ITF replacement

Post by Bob Yoesle » Thu Oct 25, 2018 1:54 am

Image re-proportioned from here:

https://www.phys.ksu.edu/personal/macf/ ... aining.htm

Original figure source document described here:

https://www.lia.org/resources/laser-safety-information
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Re: BF30 ITF replacement

Post by Merlin66 » Thu Oct 25, 2018 4:05 am

OK......
I yield.....
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Re: BF30 ITF replacement

Post by TheSkyBurner » Thu Oct 25, 2018 4:44 am

in kens defense, i would like to point this out as quoted from lunts own website about safety. Focus on Paragraph 3 and 4. http://luntsolarsystems.com/lunt-solar-safety/

Energy Rejection Filter – The filtering of a Lunt system starts with a “true” energy rejection filter at the front of the system. This filter is unique to Lunt, and blocks both dangerous UV and IR.

"Etalon – The next “filter” in the system is actually the etalon. While the etalon was not designed as a safety filter. However it does have a very high reflective surface that rejects most UV (T). Significant, this would reject the majority of all IR if no prior IR filters were present."

The etalon combined with the supplied erf will reject the majority of all IR if no infrared filters are present.

Now where does this argument go about the additional IR blocking at the ITF? Is it still required, or is it just a failsafe countermeasure?


paragraph5
BG Filter – The third filter is the Schott-designed BG (Blue Glass) filter. This filter is also created to absorb any residual IR.


The BG filter is only installed to absorbe "residual IR." So it really is not blocking much at this point behind the first erf, and the etalon itself.


(lunt does not use an ITF filter in their system, it is a coronado part) Solar spectrum filters? So I would say that lunt knows you dont need the ITF in there, and it seems like they are just playing safety patrol with the bg glass. (specifically to avoid any liability whatsoever)

John Herschel once made a great discovery by sitting in front of a living room fireplace. He realized that when placing a piece of glass in front of it, less heat radiated outward. He experimented with various types of glass in front of his fireplace, of varying thickness and then thus herschel wedge prism was born. He understood a glass of certain type of a certain thickness absorbed the longwave radiation. I would like to conclude that the very thick, dual pane etalon is doing the same thing, but to what extent?

Would i sacrifice my eyeballs? NO WAY. But I would totally love to test how much infrared is actually coming out of the back of etalons. It seems like it should be publicly disclosed by all companies.

All laser products are rated in "exposure class" for emitted radiation. So if the etalon is actually dumping a hazardous amount of emitted long wave and shortwave radiation the exact amount should be disclosed.

https://en.wikipedia.org/wiki/Laser_saf ... sification


Now back to the lunt safety page, focus on paragraph 9 "Redundant Filters"
"People are protected even if they use our products improperly. For instance, should a person accidentally place a standard night time diagonal in the rear of a solar telescope, the view would be bright, but safe."

Now it says right on lunts own safety website, that if you were to not use the blocking filter, and insert a regular diaganol mirror. The view is "safe"

Im not here to tell anybody they are wrong, I am just here because sometimes even the smarties, still make mistakes.

It would appear that ken is actually right to state the extra infrared blocking is not required on a Lunt telescope. Other brands however, use different methods to filter their products. It is already known that parts should not be interchanged with other solar scope brands.


Now whats the story with coronado bf30 blocking filter. Does it even have an ITF? From the front it appears to have the same BG glass as the lunt b3400.

Image

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Re: BF30 ITF replacement

Post by Bob Yoesle » Thu Oct 25, 2018 8:48 pm

Individual biological tissue susceptibility, dose, exposure time, and recovery time, are all variables which need to be accounted for with any kind of energy exposure, whether it is electromagnetic, acoustic, or kinetic. With IR there seems to be a paucity of data related to optical instruments in general, and even more so related to telescope observation and specific solar telescope and filter systems:

https://www.icnirp.org/cms/upload/publi ... frared.pdf

While I consider myself to be a solar enthusiast, I am by no means an expert when it comes to solar equipment and safety. My perspective is that I generally don’t have enough knowledge or information about what we are dealing with to make perfectly informed decisions. Filter components and coatings change between companies, over time, and within product lines. Hopefully the amount of IR B for most solar telescopes and filter systems falls well within acceptable limits. However, stating there is no concern at all for IR B did not seem “reasonable,” especially when others who have some expertise with solar radiation apparently believe IR blocking beyond 1400 nm is important at least to some degree for safety.

Moreover, you can not use qualitative marketing verbiage to make definitive or quantitative conclusions about specific filter components. While we do have some dated independent data about the Coronado ERF (no IR blocking), Baader ERF (IR blocking to ~ 1400 nm), and Solarscope ERF (IR blocking to ~ 1000 nm), and the Coronado ITF (blocks to 2500 + nm) http://www.sonnen-filter.de/index-x.html , we don’t have specifics on what the current Lunt ERF or other components transmit or block to, other than the Schott catalog for the BG and KG filters.

So the fact that Lunt now uses a BG element instead of an ITF, and states that the BG element takes care of “residual” unspecified IR and may be redundant actually may mean little. Maybe Lunt has placed all needed UV and IR blocking ahead of the blocking filter diagonal. But we don’t know for sure because we lack sufficient information about the filter system components and their transmission characteristics, and have only rather vague descriptions that an unspecified level of blocking to 3000 nm is needed for telescopic (not naked eye/eclipse filters) observation.

I do know for a fact that etalons can allow IR harmonic peaks to pass. I used an ERF/etalon and blocking filter system from a very highly regarded solar filter manufacturer, which produced noticeably defective images. It turned out that the blocking filter was letting IR A from the ERF/etalon through, which was invisible to the eye but quite noticeable from imaging:
IR leak.jpg
IR leak.jpg (218.44 KiB) Viewed 407 times
Top image H alpha filtergram with out-of-focus IR A leakage, bottom same system with added IR blocking filter.

Whether or not this IR was significant or posed a safety issue I could not tell, although I did not observe for more than a minute or two at a time. Luckily, my 100ED semi-APO telescope couldn’t focus the IR A with the H alpha. Had I used a “better” APO that could, the situation might have been more serious. A simple IR blocking filter cured the problem, and after I supplied photographic documentation, the manufacturer quickly remedied the situation for me and future customers.

This experience, and my background in health care ("if something bad can happen it will happen - to somebody"), make the bottom line easy for me. When it comes to solar radiation and unknown amounts hitting and entering my eye, I believe prudence is warranted - and to paraphrase - a gram of prevention is worth a kilogram of cure.
Last edited by Bob Yoesle on Fri Oct 26, 2018 3:27 pm, edited 4 times in total.
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Re: BF30 ITF replacement

Post by TheSkyBurner » Thu Oct 25, 2018 9:34 pm

Bob Yoesle wrote:
Thu Oct 25, 2018 8:48 pm
Individual biological tissue susceptibility, dose, exposure time, and recovery time, are all variables which need to be accounted for with any kind of energy exposure, whether it is electromagnetic, acoustic, or kinetic. With IR there seems to be a paucity of data in general, and even more so related to telescope observation and specific solar telescope and filter systems.

While I consider myself to be a solar enthusiast, I am by no means an expert when it comes to solar equipment and safety. My perspective is that I generally don’t have enough knowledge or information about what we are dealing with to make perfectly informed decisions. Filter components and coatings change between companies, over time, and within product lines. Hopefully the amount of IR B for most solar telescopes and filter systems falls well within acceptable limits. However, in my non-expert opinion stating there is no concern at all for IR B did not seem “reasonable,” especially when others who seem to be experts apparently believe IR blocking beyond 1400 nm is important to some degree for safety.

Moreover, you can not use qualitative marketing verbiage to make definitive or quantitative conclusions about specific filter components. While we do have some dated independent data about the Coronado ERF (no IR blocking), Baader ERF (IR blocking to ~ 1400 nm), and Solarscope ERF (IR blocking to ~ 1000 nm), and the Coronado ITF (blocks to 2500 + nm) http://www.sonnen-filter.de/index-x.html , we don’t have specifics on what the current Lunt ERF or other components transmit or block to, other than the Schott catalog for the BG and KG filters.

So the fact that Lunt now uses a BG element instead of an ITF, and states that the BG element takes care of “residual” unspecified IR and may be redundant actually may mean little. Maybe Lunt has placed all needed UV and IR blocking ahead of the blocking filter diagonal. But we don’t know for sure because we lack sufficient information about the filter system components and their transmission characteristics, and have only rather vague descriptions that an unspecified level of blocking to 3000 nm is needed for telescopic (not naked eye/eclipse) observation.

I do know for a fact that etalons can allow IR harmonic peaks to pass. I used an ERF/etalon and blocking filter system from a very highly regarded solar filter manufacturer, which produced noticeably defective images. It turned out that the blocking filter was letting IR A from the ERF/etalon through, which was invisible to the eye but quite noticeable from imaging:

IR leak.jpg
Top image H alpha filtergram with out-of-focus IR A leakage, bottom same system with added IR blocking filter.

Whether or not this IR was significant or posed a safety issue I could not tell, although I did not observe for more than a minute or two at a time. Luckily, my 100ED semi-APO telescope couldn’t focus the IR A with the H alpha. Had I used a “better” APO that could, the situation might have been more serious. A simple IR blocking filter cured the problem, and after I supplied photographic documentation, the manufacturer quickly remedied the situation for me and future customers.

This experience, and my background in health care ("if something bad can happen it will happen - to somebody"), make the bottom line easy for me. When it comes to solar radiation and unknown amounts hitting and entering my eye, I believe prudence is warranted - and to paraphrase - a gram of prevention is worth a kilogram of cure.

COMPLETELY AGREE!

So much has changed over the last 8 years that it is anybodies guess how these new things are operating now from the "old school" etalons.

manufacturing practices typically get better with experience, but sometimes they also take short cuts. I think that safety is the main concern and that every bit necessary to protect kids is important.

I was informed today that the first filter in lunt CaK systems, is an ITF with total infrared blocking. So although there is no bg/kg glass they have that long wave covered in both systems.

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