Alternative to the Coronado/ Lunt IFT (mini-erf)???

[Merlin66]

The 35nm CCD Ha filter is very close to the D-ERF spec.
Baader recommended the 35nm over the 7nm.

[etatsolarchat]

Sounds good.

BTW that German site seems to have contact info here,
http://www.mikroskopie-ph.de/Impressum

[Merlin66]

A follow up on the possible health hazards of N-IR and IR radiation on the eye...
http://www.google.com/url?sa=t&rct=j&q= ... v6Z0qgRn8Q
Heavy stuff....but if you keep reading you'll find they come back to the ICNIRP recommendations (p524) and summarise the "potential hazard index"


[attachment:1]NIR_radiation.JPG[/attachment]


Which basically shows IR above 1150nm has no significant safety concerns for the human eye.(This matches the ICNIRP documents)

[markthais]

Well the post was about using and alternative source to an ITF.
The first thing you need to worry about is where the narrow bandpass that works as a order sorter for the etalon turns back on in the red. The shorter wavelengths are cut out by the color glass, RG630 works well for the short side. Now the long side of the bandpass can turn back on anywhere from 700nm to 1200nm depending on the design.
There is no magic, you want to keep the IR down. And block the filter as far to the IR as possible.
Ok, the advantage of and ITF is that it will block the IR down to OD 4 to 2500nm and OD 3 all the way to 3500nm.
They usually have a peak transmission of 60% or better.
Now KG glass can be used to block the IR. It starts at about 60% T and gets down to about OD2 in the IR. But you don,t have any optical coating to worry about. If the pre-filter where blocked to 1500nm then adding a KG3 glass this would keep the IR low.
If the Badder 35nm filter can block the pre-blocker then add some KG class and some red glass (so you are not looking at the mirror of the Badder filter) then you would have a petty good IR filter.
With today's new coatings they are able to make very hard coated filters that would be blocked to 2500nm on only one surface. The problem is that these filters are very expensive.

The paper about IR limits is for LED's and solid state lasers. They still make you wear the glasses when you are using them even if it is safe. The paper is not for looking at the sun.

SO, ITF's where around long before any Lunt filter designs where on the market. The soft coated ones have the problem of sometimes they last and other times not so well. They are proved safe, and the cost is low compared to hard coated filters. The main problem is that they usually fail from the outside to the inside. So the smaller the filter the faster it should fail. A 25mm ITF filters and up are the most reliable.
I can see in the future where the soft coated filters will be phased out as the cost of hard filters drop.
Note: The cost of a BF30 at $1500 seems high to me also, unless you are buying the run, and they are only getting one out of a run. Then that would be about right.
Mark W.

[Bob Yoesle]

Thanks Mark

List price of the Coronado BF30 is $1599.00 USD:

http://www.meade.com/product_pages/coro ... sories.php

Lunt's equivalent sized B3400 lists for $1789.00 USD:

http://luntsolarsystems.com/blog/h-alph ... ng-filters

I don't know if anyone has ever asked to be able to purchase the ITF itself from Meade or Lunt and do the install oneself. I do know what a hassel it is to get replaced even under warranty. When I had my second ITF failure, the replacement came back with the bandpass filter being scratched, and I had to return the filter for a third time...

Rather than mess with all the guessing about what would be a good DIY ITF relpacement, what we really need is a reliable OEM source for the 1000 nm ITF's themselves (should be quite adequate when used with a Baader or Lunt DERF) in the common sizes used so we can replace them ourselves when they fail. As you state, the cost is low, especially compared to the bandpasss (trim) filter, which doesn't seem to have the short-term failure issues.

Having to buy a complete new BF system just because the ITF fails would be ridiculous.

Bob B)

[Merlin66]

By way of comparison the Baader 35nm ITF in a 1.25" threaded cell is A$90.

[etatsolarchat]

What is it that makes BG glass better than KG, KG attenuates far infrared more and the 656 less. The BG is better around 700-1000nm is that why?

The baader 35nm doesn't block above 1500nm, don't think it can do the job.

[Bob Yoesle]

Better for what?

The problem is that these filters are complex and complimentary filter systems, and the various coatings and glasses can be located in different areas of the optical train, and indeed seem to change over time. Since we don’t know the far IR properties of most of these filters, it would be difficult to make recommendations without the data.

But it appears all manufacturers utilize the same basic components regardless of where they are located, and this includes using an ITF for IR blocking out past 2500 nm (3500 nm per Mark). For those of you who don't know, Mark W. is Mark Wagner, formerly of DaysSar and now the owner/manufacturer of Solar Spectrum Filters, so he knows a thing or two about this subject.

The most modern designs appear to use the following components and coatings.

Etalon filter: The heart of the system, the narrow bandwidth component. Can be located at the objective, between collimating lenses, or after a telecentric lens system.

Heat reflective coating: In the diagram below (early Lunt design) this is located on the collimating lens, and protects all subsequent components farther downstream. Baader and Lunt apply similar coatings to their stand alone ERF’s for use at the objective. Early Coronado scopes and filters systems lacked this coating, and may be part of the reason the ITF’s failed more quickly than expected. DayStar RG ERF’s apparently lack any heat reflective coatings as well.

ERF: this is usually used to block UV radiation. With the Baader D-ERF, this is the above heat reflective coatings applied to a crown optical glass with additional UV blocking coatings; in the Lunt ERF this is the RG glass with the heat reflector coating. In the Lunt schematic shown below, this is likely red “filter glass” with the blocking filter coating applied to it. DayStar is also advocating using UV/IR filters as an ERF to replace the objective mounted ERF, which therefore also have some IR blocking, and thus may extend the life of their blocking/trim filters. This would therefore be what is being called a “mini ERF.”

ITF: This is a metallic silver IR blocking filter, and is generally located as a smaller element near and ahead of the trim blocking filter. On the Coranado PST, this was at one time located on the objective, giving new meaning to the word “rust” when it deteriorated. Calling this a “mini ERF” can be somewhat confusing, as the ERF is typically the UV blocking component as described above.

Blocking (trim) filter: This is a relatively narrow band filter coating to block the side band harmonics of the etalon. This constitutes most of the expense of the blocking filter component. It appears to be either a stand alone filter, or may be sandwiched with a BG substrate.

Blue Galss: This is apparently used as a substrate for some of the coatings above, and/or is used to control image brightness and possibly provides some additional IR filtering. In the Coronado BF it was combined with the trim blocking filter. In the current Lunt blocking filters, it may be located where the ITF used to be located, and is apparently just AR coated. The ITF likely has been moved to the collimating lens, possibly combined with the heat reflector element as in the Baader DERF.

The salient point appears that you need to incorporate just about all these filters - from UV to far IR - for safety or product durability. I doubt the manufacturers would incorporate all these items and increase their costs unless they were necessary to meet product safety standards. Inferring that you can substitute or eliminate one or more of these components - based on a changed system design of a particular manufacturer - is problematic, if not possibly dangerous. Unless used only for imaging, I personally would not look through a H alpha telescope that does not incorporate an ITF for blocking to extended IR wavelengths.





Bob B)

[Merlin66]

Where did you get data for the Baader 35nm above 1500nm?
According to my sources the transmission above 1100nm is "insignificant".
Mark,
the document cited looks at the structure of the eye and the possible impact of IR radiation. There's quite a bit of data on the total energies involved in possible hazard conditions and these can be easily equated to the solar IR spectrum.
Why do you feel that IR energy above say 1500nm is deterimental? ( The Schott datacurve for RG630 shows a transmission of >95% out to around 2500nm)
http://www.us.schott.com/advanced_optic ... g630_e.pdf
http://en.wikipedia.org/wiki/Sunlight
The intensity of the IR drops significantly above 1750nm to >0.2 W/m^2/nm (from almost 1.5 W/m^2/nm at 750nm)

[Merlin66]

Bob,
A great summary of the filter system used in most Ha scopes.
Many thanks.
I think the ERF besides blocking UV also suppresses a lot of energy from the visual spectrum...<600nm
In the current PST there's no up front ERF element. There's only the ITF between the etalon and the blocking trim element. Based on the spectroscope curves it seemed to block a significant amount of UV and visible hence in the PST I called it a "mini-erf"

[marktownley]

Where did you get data for the Baader 35nm above 1500nm?
According to my sources the transmission above 1100nm is "insignificant"

Well if the coatings are the same as on the Baader D-ERF then transmission above 1100nm is far from insignificant...

[Merlin66]

Hmmmm
Point well made Mark!!!

[Bob Yoesle]

And here's the Log plot of an ITF:





Bob B)

[Bob Yoesle]

Hmm,

Also noticed the second peak at 375 nm - wondering if an H alpha ITF can be used a s a IR blocking filter / CaK attenuator with CaK emission line filters? I know my home brewed CaK filter module has plenty of throughput from shortness of the exposure times. Perhaps a “dual mode” ITF could be designed that had the second peak at ~ 395 nm...

Bob B)

[Bob Yoesle]

I had speculated from a conversation I had long ago with Bill Dean (formerly w Coronado) that ITF failures were a result of sealant (epoxy?) cracking at the periphery of the ITF. This cracking appeared to be caused by thermal loading and cycling, and is stated why Lunt and Baader (Solar Spectrum) have incorporated enhanced thermal cycling and loading preventive measures. This would prevent atmospheric moisture from invading the filter, which as Mark notes above then progresses inward form the edge of the filter.

I now have it confirmed from a filter supplier that:

...[The ITF is] a conventional immersed design, which is to say it is multiple elements laminated together and includes moisture sensitive materials. The reason these filters seem to have erratic performance in terms of long term durability relates to the edge seal. As long as it is intact, the exterior surfaces are highly durable. The problem is that the edge seal can be compromised if it is cracked. This can be invisible to the user but will result in failure over time due to moisture intrusion. This manifests itself as a haze creeping in from the edges towards the center, and eventually as progressive degradation of the filter's performance.

Meade’s approach to prevent ITF failure appears to be additional sealing of the ITF itself. Note the pre-Meade Coronado ITF on the left ( with “rust” around the periphery), and the newer Meade Coronado BF 30 with the seal showing just under the filter holder ring’s edge on the right (arrow).





So we can now definitively state the best ways to avoid ITF failure is to reduce/eliminate thermal loading and cycling as much as possible (i.e. using Baader/Lunt IR blocking ERF’s) to eliminate seal cracking, AND to reduce moisture exposure as much as possible (such as use of descants, nitrogen/argon purging and sealing, storage, etc.)

I’m attempting to locate a suitable OEM ITF replacement source... stay tuned.

Bob B)

[swisswalter]

Hi Bob

thank you for the inside information. Good luck on finding an ITF source

[Bob Yoesle]

Thank you Walter.

What follows is some additional speculation:

As noted earlier, Lunt has adopted IR reflector coatings onto the UV absorbing ERF (or elsewhere). In addition, Lunt specifies the ITF meets the MIL-STD 810:

http://www.luntsolarsystems.com/technical-manuals.html

This then might mean Lunt is using a “hard coated” ITF which is specifically designed for moisture protection and durability:

Stabilife® optical filters and coatings are manufactured using two patented processes for the deposition of metal oxide thin film optical coatings; Reactive Ion Plating (RIP) and Hybrid Plasma Deposition (HPD). Both processes yield highly dense, thin film coatings with extraordinary hardness, abrasion resistance, and adhesion to the substrate.. and for humidity resistance using the aggravated test specified in MIL-STD-810E. Stabilife® thin-film optical coatings require no additional protection such as hermetic sealing using lamination or other processes, to achieve their exceptional durability.

Coating Operating Temperature Range:

-100 º C to 300 º C **

Coating Humidity Resistance:

MIL-STD-810, Method 507.3, Procedure III, Modified to 40 cycles**

** The specifications for humidity resistance and coating operating temperature range listed above apply to exposed coatings only. Humidity resistance and operating temperature range of filters manufactured using Stabilife® coatings and assembled using epoxy systems revert to the humidity resistance and operating temperature range of the epoxy system.

http://www.newport.com/Stabilife-Coatin ... ntent.aspx

It looks like epoxy is the standard sealant used in both the “ordinary” and “hard” coated ITF’s - and why protection from thermal loading and thermal cycling is still needed even with hard coated filters.

Ideally both the ITF and the blocking bandpass filter system would use such “hard” coated filters, but as Mark Wagner states, these likely would be much more expensive. This also may in part explain the high cost of Solar Scope filters, which are stated by many to be without any BF degradation issues. Note however that Solar Scope's ERF - apparently a RG ERF - also incorporates an IR reflector/blocking, but has a significantly different transmission profile from the Baader DERF:







Bob B)

[Merlin66]

Great stuff!
Could we therefore envisage a solution where a Baader 35nm is placed independently after an IR absorbing element (RG630?)

[marktownley]

RG630 passes IR, it blocks below 630nm, however, if we can find it commercially to buy with these coatings that also block from just above Ha up to 2500nm than yes it would work. Otherwise the easiest way is to use the KG3 in conjunction with the Baader 35nm. We're going full circle here

[Bob Yoesle]

KG5 would appear to have superior IR blocking ability, though the transmission is a bit less (~10%) than KG3 at 656.3 nm:







I have no direct experience with the KG, but when I did try and get quotes on buying it optically polished to 0.25 lamda, it became very expensive. In all likelyhood it would not be cost effective compared to a "regular" ITF. Used in its “native” optical quality I would think it would have to be placed very near the focal plane to avoid any deleterious wavefront effects. So again it might be better to use an ITF and replace it if and when it fails (here’s where the IR reflector such as the Baader/Lunt DERF or 35 nm comes in).

...Still waiting to find out what might be available in an off-the-shelf ITF with a 656.3 nm peak.

Bob B)

[Merlin66]

Sorry guys I did mean the KG series.....
If it works by absorption, when it does heat up with exposure it will re-radiate in the far IR (wein law) depending on it's temperature....???
I'm still not convinced that the amount of IR radiation capable of getting through (>1200nm) to the final eyepiece/ CCD (in W/m^2) is a significant issue......

[marktownley]

I used the bog standard KG3 here http://www.uqgoptics.com/catalogue/Filt ... LTERS.aspx - at £20 can't go wrong, even at long focal lengths i've not had any issues with the optical quality. Go on Bob, get a 25mm peice and give it a try

[Bob Yoesle]

OK Mark, I’ll give it a try

I’m likely going to get two of these:

http://www.edmundoptics.com/optics/opti ... lass/49095

My tests will involve using a KG5 (or maybe a KG3) ahead of my Baader R CCD pre-filter in my H alpha sealed blocking filter holder (BF30 inside). Placing it ahead of all the other filters (except the DERF and etalon of course) - in a vented filter holder - will allow it to protect all the downstream elements and hopefully not to build up any excessive heat as mentioned by Ken - good point by the way!





I plan to also use the second KG filter in a similar fashion to protect my CaK module, as the transmission at 394 nm looks great. This may help to protect the Baader B CCD pre-filter ('mini ERF'), in addition to the PST’s internal filter (which may already be showing signs of deterioration as shown above) as well as the Baader CaK filter...

I'm still not convinced that the amount of IR radiation capable of getting through (>1200nm) to the final eyepiece/ CCD (in W/m^2) is a significant issue...

Neither am I Ken, but the fact that Mark (Solar Spectrum) advocates an ITF's continued use for far IR blocking, and they apparently are still incorporated by Solar Scope, Coronado, DayStar, and perhaps Lunt, gives me pause to think it wiser to exercise an ounce of prevention until more definative information is available.

So for me the KG would be an ITF and bandpass filter conservation measure and not an ITF replacement measure.

Bob B)

[solarchat]

unfortunately, a corporation could not sell a scope at the demanded low price if they only used the best available coatings ,flatness, and hand selected parts.

[Merlin66]

Yea...
In the automotive industry we used to call it a "commercially acceptable solution" - to meet the minimum "fit and function"

[Bob Yoesle]

From Light and Infrared Radiation by David H. Sniley

http://www.ilo.org/safework_bookshelf/e ... =857170572

Biological Effects

The eye is well-adapted to protect itself against acute optical radiation injury (due to ultraviolet, visible or infrared radiant energy) from ambient sunlight. It is protected by a natural aversion response to viewing bright light sources that normally protects it against injury arising from exposure to sources such as the sun, arc lamps and welding arcs, since this aversion limits the duration of exposure to a fraction (about two-tenths) of a second. However, sources rich in IRR without a strong visual stimulus can be hazardous to the lens of the eye in the case of chronic exposure. ...

There are at least five separate types of hazards to the eye and skin from intense light and IRR sources, and protective measures must be chosen with an understanding of each. In addition to the potential hazards presented by ultraviolet radiation (UVR) from some intense light sources, one should consider the following hazards (Sliney and Wolbarsht 1980; WHO 1982):

1. Thermal injury to the retina, which can occur at wavelengths from 400 nm to 1,400 nm. Normally the danger of this type of injury is posed only by lasers, a very intense xenon-arc source or a nuclear fireball. The local burning of the retina results in a blind spot (scotoma).

2. Blue-light photochemical injury to the retina (a hazard principally associated with blue light of wavelengths from 400 nm to 550 nm) (Ham 1989). The injury is commonly termed “blue light” photoretinitis; a particular form of this injury is named, according to its source, solar retinitis. Solar retinitis was once referred to as “eclipse blindness” and associated “retinal burn”. Only in recent years has it become clear that photoretinitis results from a photochemical injury mechanism following exposure of the retina to shorter wavelengths in the visible spectrum, namely, violet and blue light. Until the 1970s, it was thought to be the result of a thermal injury mechanism. In contrast to blue light, IRA radiation is very ineffective in producing retinal injuries. (Ham 1989; Sliney and Wolbarsht 1980).

3. Near-infrared thermal hazards to the lens (associated with wavelengths of approximately 800 nm to 3,000 nm) with potential for industrial heat cataract. The average corneal exposure to infrared radiation in sunlight is of the order of 10 W/m^2. By comparison, glass and steel workers exposed to infrared irradiances of the order of 0.8 to 4 kW/m^2 daily for 10 to 15 years have reportedly developed lenticular opacities (Sliney and Wolbarsht 1980). These spectral bands include IRA and IRB (see figure 49.1). The American Conference of Governmental Industrial Hygienists (ACGIH) guideline for IRA exposure of the anterior of the eye is a time-weighted total irradiance of 100W/m^2for exposure durations exceeding 1,000 s (16.7 min) (ACGIH 1992 and 1995).

4. Thermal injury of the cornea and conjunctiva (at wavelengths of approximately 1,400 nm to 1 mm). This type of injury is almost exclusively limited to exposure to laser radiation.

5. Thermal injury of the skin. This is rare from conventional sources but can occur across the entire optical spectrum.

Note: For item 1, the sun would fall into the “nuclear fireball” category. :blink:

Per items 3 & 4 it appears there may be a risk from the longer IR wavelengths to the eye’s lens and cornea, verses the retina as is the case for shorter IR wavelengths. It might be OK at the power levels encountered (?), but I believe the solar filter makers are being conservative by using an ITF for blocking 1400 + nm - as they should be - when it comes to eye safety.

And as Steve notes, the commercial solar filter suppliers have an interest in keeping costs down, so if they are including such filtering, is seems it would be due to a safety feature or concern.

Bob B)

[solarchat]

^^^^^^^
excellent post Bob

[Bob Yoesle]

Thanks Steve

I had a question mark in the quote above regarding the power levels encountered, and did some rough calculations. I hope I figured these values correctly - they seem to be what one would expect.

If we use one of the largest refractor telescopes available - a TEC 180mm f/7 apochromat - it will produce a prime focus solar image 11.5 mm in diameter. This represents a circle with an area of 1.04 cm^2. The objective itself has an area of 254.3 cm^2.

The sun's energy output at the surface of the earth is 1004 watts/m^2 (essentially a kilowatt per square meter), composed of 527 W IR, 445 W visible, 32 W UV (per Wikipedia).

1 m^2 = 10,000 cm^2, which means this is 0.0527 W/cm^2. 254.3 cm^2 (the area of the 18 cm diameter objective) x 0.0527 W/cm^2 yields at total of ~ 13.5 watts of IR entering the telescope. But this 13.5 W can be focused to an “IR image” of the sun 1.04 cm^2 in area (and smaller if we consider the exit pupil image of the eyepiece as the area). To see how this relates to the power level described in the reference above, we have to convert 13.5 W/1.04cm^2 to m^2 > 13.5 W/1.04 cm^2 x 10,000 cm^/m^2 yields an equivalent of 130,000 W/m^2 IR radiation!

So we can now see the reason for having E5 to E4 levels of IR blocking to reduce this to 1.3 to 13 W/m^2 for safe solar observation with a telescope that could be used for solar observation, which is indeed under the 100W/m^2 per 16.7 minutes guideline cited. E3 blocking (130 w/m^2) would not in general be sufficient.

Bob B)

[Merlin66]

Bob, et al,
A few years ago I also looked at all the available safety and health recommendations and prepared a summary document.
I'm attaching the pdf file of the summary for info...
For Ha observers you need to consider the W/M^2/nm.
Also remember the etalon by design automatically reduces the transmitted energy by 1/10 (1A bandwidth, finesse 10A)across the whole spectrum.....
(right click on the attachment - and "save as")

Attached files ICNIRP_review_2013-02-17.pdf (687.6 KB)

[Bob Yoesle]

Thanks Ken, I look forward to reading it :cheer:

Bob B)

[Spectral Joe]

I like that sort of analysis, Bob. Be sure to consider that transmission of the optics, though. Some of the bad stuff is cut off that way.

[Merlin66]

We can also safely assume that 50% of the IR (the region between 700nm and 1200nm) is already suppressed by a "conventional" ITF ie Baader...
That leaves about 0.1 x 0.5 x 500 = 25 W/M^2 of IR above 1200nm to be considered. Then we have the transmission efficiency of the optics....
(Everything else seems to be blocked by the combination of ERF/etalon/ITF/BF...)
If the BF is again passing nothing but the 1nm bandwidth around the Ha line, the energy transmitted is only 0.15W/m^2 (from the standard solar energy distribution curve). As the only energy evident in the BF bandwidth is actually only the 1A spike from the etalon, the actual transmission is only 0.015W/m^2 getting through to the CCD and or the eye. The rest being reflected/ absorbed away.....

[Spectral Joe]

A useful exercise will be to convolve all of the available data into one transmission plot, they are difficult to assess on their own. To add more noise to this discussion, has anyone considered using a cold mirror as a diagonal? They show up surplus (and don't cost that much new) and would eliminate that pesky IR.

[Merlin66]

Joe,
I did look at a couple of the Edmund cold mirrors, but the cut off (Visual reflectance/ IR transmission) appeared to be just below 650nm...so the Ha would have been blocked.
There may be others with better curves....

[Spectral Joe]

Thor Labs has one that cuts off at a little above 750, but it comes back on near 1200....

[Merlin66]

In the light of the above discussions, maybe we should call it a "warm mirror" ;-)

[marktownley]

Also remember the etalon by design automatically reduces the transmitted energy by 1/10 (1A bandwidth, finesse 10A)across the whole spectrum.....

I genuinely believe that this only happens at and to a lesser degree around the resonant frequency of the etalon. If the spacing of the etalon plates is essentially fixed and we vary the wavelength, I don't see how at say 350nm or 2000nm a etalon designed for 656nm can operate the same...

[marktownley]

Thanks Steve

I had a question mark in the quote above regarding the power levels encountered, and did some rough calculations. I hope I figured these values correctly - they seem to be what one would expect.

If we use one of the largest refractor telescopes available - a TEC 180mm f/7 apochromat - it will produce a prime focus solar image 11.5 mm in diameter. This represents a circle with an area of 1.04 cm^2. The objective itself has an area of 254.3 cm^2.

The sun's energy output at the surface of the earth is 1004 watts/m^2 (essentially a kilowatt per square meter), composed of 527 W IR, 445 W visible, 32 W UV (per Wikipedia).

1 m^2 = 10,000 cm^2, which means this is 0.0527 W/cm^2. 254.3 cm^2 (the area of the 18 cm diameter objective) x 0.0527 W/cm^2 yields at total of ~ 13.5 watts of IR entering the telescope. But this 13.5 W can be focused to an “IR image” of the sun 1.04 cm^2 in area (and smaller if we consider the exit pupil image of the eyepiece as the area). To see how this relates to the power level described in the reference above, we have to convert 13.5 W/1.04cm^2 to m^2 > 13.5 W/1.04 cm^2 x 10,000 cm^/m^2 yields an equivalent of 130,000 W/m^2 IR radiation!

So we can now see the reason for having E5 to E4 levels of IR blocking to reduce this to 1.3 to 13 W/m^2 for safe solar observation with a telescope that could be used for solar observation, which is indeed under the 100W/m^2 per 16.7 minutes guideline cited. E3 blocking (130 w/m^2) would not in general be sufficient.

Bob B)

This is exactly the reason an ITF is used that blocks out to 2500nm+ - it's the old ant and the magnifying glass anology, but in this case the ant is our eye, and the magnifyying glass is the scope...

[swisswalter]

Hi Mark

what a cute pic. So we can use the ants to proof our ITF solutions on our scope mods ;-)

[Merlin66]

I need some stickers designed....
"Disclaimer - No ants were killed in the making of this Filter"
;-)

[marktownley]

[Merlin66]

Mark,
the etalon isn't only designed for 656.28nm... It's designed to give a narrow bandwidth (0.7A) with a finesse (around 8-10A).
The "comb" spreads across various wavelengths, one of which coincides with the Ha wavelength.
You could equally use it at 10A intervals....

[swisswalter]

I need some stickers designed....
"Disclaimer - No ants were killed in the making of this Filter"
;-)


great Ken

[Merlin66]

Mark questioned the spectral coverage of a "bare" PST etalon....did it cover the whole spectrum or just the region around Ha?
i've just set up the "bare" PST etalon on the spectroscope and the attached images show it does indeed cover the whole solar spectrum!
The resolution of the MG80 doesn't bring out all the resonance lines, but I'm sure you can see enough to get the picture ;-)
The first image is a solar spectrum reference...the ADU count around 700nm was 30K
#2 is the calibrated spectral profile
#3 is the result with the PST etalon, the ADU count around 700nm was only 5K
#4 the calibrated PST etalon profile
and I've added a hi-res profile I obtained previously for a similar etalon..the absorption "dip" in one of the spikes is the Ha line.
So, based on these results the etalon covers the full spectrum (and probably into the IR), the transmission of the etalon is approx 5/30 = 1/6 the incoming energy....

[etatsolarchat]

Looking over IR blocking glass noticed that they may have a plot for 1mm but sold in 2 or 3mm changes the plot. For example KG3 filter, that's made of 2mm KG1. So when buying you should verify composition and thickness...

[marktownley]

Thanks for that info regards the plots Ken, it is always good to learn new things.

In the meantime this http://solarchat.natca.net/index.php/en ... lter#59297 in conjunction with the Baader Ha filter is the answer to our ITF replacement issues.

8)

[BelOptik_Oliver]

Yes Mark.
Instead of Baader H-alpha filter is sufficient also a simple red filter (Wratten #29 or B+W091 or Schott RG630) in conjunction with UVIR cut on KG3.

[MjrTom]

Thanks for that info regards the plots Ken, it is always good to learn new things.

In the meantime this http://solarchat.natca.net/index.php/en ... lter#59297 in conjunction with the Baader Ha filter is the answer to our ITF replacement issues.

8)

Very interesting!
Thanks for the info, I shall probably be in the need for an ITF as the PST I used for my mod did not have one in the eyepiece stalk.
BTW, I use a 105mm BelOptic ERF in my 100mm PST Mod Scope.

Mark

[Merlin66]

Hmmm
Oliver's UVIR filter certainly looks interesting....has anyone on the forum tried this yet?

[DSobserver]

I've so many questions...

1-Do you confirm that your Infrared Blocking Filter - UV/IR cut on Schott KG3 can replace ITF filter?
2- why do we need to complete it with a red filter?
3- What is an AR coating?
4- I see that you also offer H-alpha interference filter FWHM 1.5A (0.15nm). Can we use them as a BF on a PST?

Thanks!