•

# On solar safety with Herschel and Brewster Angle (Lacerta) Solar Wedges...

Filters Optics Solar Visual Observing Refractor Equipment Accessories
6 replies to this topic

### #1 Spectrum222

Spectrum222

Vostok 1

• topic starter
• Posts: 191
• Joined: 05 May 2015
• Loc: Edmonton, AB Canada

Posted 02 August 2024 - 12:30 AM

There have been numerous posts here and elsewhere on the safety and use of solar wedges.

These are accessories which go on the rear of the telescope (refractors ONLY), and are SOLAR diagonals, for those not acquainted with this solar filtering system as of yet. I will get into more details over time, and I think it important for those considering getting one of these that they are NOT all created equal! Just as a telescope will vary in factors such as optical quality, price, performance, and so on, some wedges DO indeed differ in their ability to safely view the sun with (especially) larger telescopes.

We will start by looking at the math first. Let's talk % Transmission and OPTICAL DENSITY. These quantities come up a lot with solar observing and imaging, especially with Solar wedges, so I think that this is a great place to start:

When we use a neutral density (ND) filter, it absorbs across the entire VISUAL spectrum, with some additional absorption in the UV and NIR/IR regions of the spectrum as well. The absorption curve is rarely flat, but more so in general than colored filters used in astronomy. These are designed to give a relatively NEUTRAL color rendition and dim the view by absorbing light. (hence "neutral" density reference).

The definition of optical density is the negative logarithm of the relative transmission:

OD = -log (T)

where T is the transmission, usually a fraction of the light, passing after the filter or optical system.

So, for example, a filter absorbing 75% of the visible light in this case, and passing 25% through the filter (common ND0.6, or 25%T filter used in lunar observing), we have:

OD = -log (0.25) = - (-0.602) or 0.6. The "ND" refers to neutral tinted filters, looking grey or dark grey. OD is the total remaining light...

Now one can relate these figures better! 0.6 optical density is 1/4 of full transmission. If I were to stack these two, I get:

0.6+0.6 = 1.2, which is now 1/16 T or 0.0625 or 6.25%. We add and subtract logarithms to multiply and divide (respectively).

Okay so hopefully everyone reading this has that concept so far. It is important as we move into how much light is absorbed when doing solar observing and AP later.

I will first duplicate a post I did in the "range of dimming with polarizers" topic recently, as it is highly relevant to this topic:

I have several wedges, the most recent one as of last week is the new Lacerta 2s Brewster angle version. Just got it, about 3 weeks ago.

So, to review, if I have 10% T, or 0.10 T, I have OD=1.0, and the larger the OD, the dimmer the image. Ideally, one should be in the OD5.0 regime for safe solar visual use. One can employ an additional ND/OD filter after the ND3.0 (in lieu of a polarizer) to reach safe levels, and I'll discuss this later below. There are some significant differences between a "standard" Herschel Wedge and the Lacerta Brewster Window type of solar wedges. We will start by discussing the differences between the way these two reflect light:

https://rmico.com/re...-light-tutorial

Has an excellent succinct coverage of this topic. Especially the reflection/polarization "depth"; I include the picture of the graph here for illustration (will be relevant in a moment):

As can be seen in this graphs, we get a noticeable difference in the S-polarization off the surface. at 45 degrees, there is a difference as well, but only PARTIALLY - thus when using a polarizing filter, we cannot totally cross-polarize to nearly null out the light. this is why standard (Baader/Lunt/APM etc.) Herschel wedges have a narrower range of brightness control, and also why they have a lower reflective transmission (OD ~1.35-1.40, or 4.5% approx.) off the wedge's surface. (not including the OD3.0 post-filter)

A Brewster Wedge or plate, being at the Brewster angle, effectively nulls out one polarization, and reflects the other - also, at this angle, the S-pol light is reflected better/absorbed less at the Brewster angle, and hence why a Brewster Solar wedge (like the Lacerta units) pass closer to 8.5%, or OD ~1.07. (again, sans ND3.0 post-filter).

Given the above, this explains why the Lacerta Brewster Wedge has a much wider brightness range; one can go from VERY bright (WAY too much/unsafe for visual!!) to below what might be available for a standard Herschel Wedge system.

Okay - now... can one just employ a ND filter after the Wedge/Plate + ND3.0? Absolutely! so long as you keep in mind you want to be in the OD ~4.9-5.5 range, all safe and good. (so, this is approximately achieved in a Herschel wedge (OD~4.3 to 4.4 with post filter) using a ND0.6 (25%T filter, like a standard one) or a ND0.9 will give in the OD5.3 regime. For a Lacerta Brewster Wedge (OD~4.07), you need a ND0.9 (12.5% T) minimum to be in the regime closest to, say a Baader AS film level for visual.

BTW, a polarizing filter (single) gives an ND(effective) of 0.35, or ~45%T. Stacked in line for max transmission, two are about ND0.4, or 39% (approx.). One could co-rotate a preset dual polarizing filter in lieu of a single if one wished to use that on a Wedge, but I find I prefer a single linear type polarizer, myself.

Now to the "safety" part that seems to confuse many...

There is a link to a German sight on solar observing and quantitative measurements of filtering by Peter Höbel:

http://www.sonnen-fi...de/index-x.html

I will add a ND3.0 (Baader) filter curve from his site, in LOGARITHMIC form - he also has linear values plotted for those interested.

In the NIR (near infrared), the reflectance off a wedge will be in the same range as the optical. Same with UV, at least in the worst cases of 320-400nm, which is the most potentially damaging if unfiltered. First, the curve:

This is a BAADER ND3.0 filter, commonly used on their solar wedges. Note that at no time within the pass band to 1.95um (1950nm), does the OD exceed 2.0 - that is 1%T or 0.01. Now, when used with a solar wedge, the light is reduced to an effective OD of ~1.35 or so. When we have the ND3.0 in the optical path as it should be used for visual, we get 1.35+(>2.0) >3.0, or 0.1% or better.

So, at WORST, before polarizers or additional ND being added, we have 0.1% in the NIR, and even around 2.4um range it is still combined less than (1.35+1.5) = OD1.85 which is 1.4%. Again, this is BEFORE any additional filtering (polarizer or ND) for lowering the visual range brightness. Now, an additional ND filter will reduce this further by some amounts, and I recommend those curious to go to Peter's site to see the curves for other ND filters (Baader) - this will vary with other manufacturers and types of substrates used in the filters.

ISO 12312-2:2015 Eye and face protection — Sunglasses and related eyewear - Part 2: Filters for direct observation of the sun outlines that 3% is the acceptable minimum for safety in the IR. I do not have a copy of this being it is >50 Euro for the standard (ISO ripoff, IMO, but that is another topic!)

Nonetheless, the Baader wedge fulfills the OD5.0 visual and 3% N(IR) requirements by at least 2x in the NIR, when used with Baader filters, which is what we have posted here for curve data.

Now, the Lacerta Brewster Angle Solar Wedge  - the Lac and Lac-2s, have almost double the light throughput, and even with a Baader ND3.0 used, would just pass the ISO requirements for safe solar, if not using an additional blocking filter, that Lacerta recommends if using >5" apertures with their wedges; According to the current ISO criteria, IF one used a Baader ND3.0 filter after the Wedge. I do this myself, BTW - use a Baader ND3.0 on my wedges, and high end Hoya 48mm polarizers (linear). SUPERB results!!!

In the 33+ years I have done solar observing routinely and 25 of these with solar wedges (and AS Film, etc.), I have personally logged 1000s of hours of observing the sun, and have been fortunate enough to still not have cataracts at 59 years of age, and a healthy ocular environment (according to my opthalmologist). So at least my eyes have not had any ill effects using wedges all this time!

Having said this, my three wedges are Baader MK-I, the first original model, an APM 2" wedge, and now more recently, a Lacerta Lac-2m. I call mine an "m" version for modified. I replaced the stock EP setup (wasn't suitable for my EPs and configurations) with a M54 extension tube, a M54-M48 adapter ring (to affix the ND3.0 filter INTO the unit like the Baader systems, and M54a Baader Clicklock system. Works great and allows me to compare both with similar optics aside from the wedge angle/wedge substrate used.

I digress! For other wedges, I urge anyone who has one alternate (and there are many: Lunt, Altair, etc.) to VERIFY that the unit has what is intended for SAFE solar use. I DO know Lunt recommends using 2" wedges for larger scopes due to heat loading on the prism in the 1.25" versions. So follow those guidelines to be safe also!

If one is REALLY concerned, ask their manufacturer or supplier. DEMAND info - IMO, ALL companies (incl. the venerable Baader) should have posted passband results with a wedge and THEIR supplied ND3.0 filters. Heck! APers get lovely passband curves all the time for narrow band imaging filters, WHY can't solar units be not supplied with this? Not cool.

IF someone is truly concerned, I strongly recommend the Anti-Halo filter by Player ONE:

https://player-one-a...y/filter-wheel/

In the link page, scroll down to show either the 2" or 1.25" versions. P-1 claims they have OD4.0 blocking of UV and NIR - add that to the chain and you're totally good and SAFE! Prices aren't outrageous either. In my Achromats, I use an SA (Semi-Apo) filter in the chain and these also have additional NIR/UV reduction. So even in the 5-6" regime, I am pretty fine...

If not sure, ask questions. That is the great thing with CN - so many folks with experience to share. I hope that my information has at least clarified a few things. While alternate filtering systems may vary, safe to say using a Baader ND filter on any wedge should provide enough to at least put one in the safe regime without risking eye damage, so long as additional polarizing or ND filtering is ALSO employed with them!

I will finish this off tonight by saying that a solar wedge is a wonderful accessory, and can provide some of THE finest white-light/continuum images when used with a good quality refractor. However, ALWAYS do a pre-check before doing solar observing - it is a risky endeavor, if not done safely. It takes but a second to change your astronomy career forever!

If not sure - DON'T; ask first. verify, and then proceed.

Clear skies, good sun views (the cycle 25 is off the chart with goodies!), and be safe out there!

Darren

Edited by Spectrum222, 02 August 2024 - 02:06 AM.

• Astrojensen, 0ak3, Prasad and 4 others like this

### #2 norvegicus

norvegicus

Soyuz

• Posts: 3,788
• Joined: 26 Oct 2020
• Loc: en route

Posted 02 August 2024 - 05:52 AM

Thanks.

Ophthalmologist has two h's.

### #3 Sebastian_Sajaroff

Sebastian_Sajaroff

Vanguard

• Posts: 2,255
• Joined: 27 Jan 2023
• Loc: Montreal, Quebec, Canada

Posted 02 August 2024 - 05:57 AM

I have the 1.25" Lunt, bought the ND 0.6 (22%) ND from them as well. I use it on a 70 mm refractor.
I go on a yearly basis to the optometrist for checkups, no issues so far.

### #4 Sebastian_Sajaroff

Sebastian_Sajaroff

Vanguard

• Posts: 2,255
• Joined: 27 Jan 2023
• Loc: Montreal, Quebec, Canada

Posted 02 August 2024 - 05:58 AM

There have been numerous posts here and elsewhere on the safety and use of solar wedges.

These are accessories which go on the rear of the telescope (refractors ONLY), and are SOLAR diagonals, for those not acquainted with this solar filtering system as of yet. I will get into more details over time, and I think it important for those considering getting one of these that they are NOT all created equal! Just as a telescope will vary in factors such as optical quality, price, performance, and so on, some wedges DO indeed differ in their ability to safely view the sun with (especially) larger telescopes.

We will start by looking at the math first. Let's talk % Transmission and OPTICAL DENSITY. These quantities come up a lot with solar observing and imaging, especially with Solar wedges, so I think that this is a great place to start:

When we use a neutral density (ND) filter, it absorbs across the entire VISUAL spectrum, with some additional absorption in the UV and NIR/IR regions of the spectrum as well. The absorption curve is rarely flat, but more so in general than colored filters used in astronomy. These are designed to give a relatively NEUTRAL color rendition and dim the view by absorbing light. (hence "neutral" density reference).

The definition of optical density is the negative logarithm of the relative transmission:

OD = -log (T)

where T is the transmission, usually a fraction of the light, passing after the filter or optical system.

So, for example, a filter absorbing 75% of the visible light in this case, and passing 25% through the filter (common ND0.6, or 25%T filter used in lunar observing), we have:

OD = -log (0.25) = - (-0.602) or 0.6. The "ND" refers to neutral tinted filters, looking grey or dark grey. OD is the total remaining light...

Now one can relate these figures better! 0.6 optical density is 1/4 of full transmission. If I were to stack these two, I get:

0.6+0.6 = 1.2, which is now 1/16 T or 0.0625 or 6.25%. We add and subtract logarithms to multiply and divide (respectively).

Okay so hopefully everyone reading this has that concept so far. It is important as we move into how much light is absorbed when doing solar observing and AP later.

I will first duplicate a post I did in the "range of dimming with polarizers" topic recently, as it is highly relevant to this topic:

I have several wedges, the most recent one as of last week is the new Lacerta 2s Brewster angle version. Just got it, about 3 weeks ago.

So, to review, if I have 10% T, or 0.10 T, I have OD=1.0, and the larger the OD, the dimmer the image. Ideally, one should be in the OD5.0 regime for safe solar visual use. One can employ an additional ND/OD filter after the ND3.0 (in lieu of a polarizer) to reach safe levels, and I'll discuss this later below. There are some significant differences between a "standard" Herschel Wedge and the Lacerta Brewster Window type of solar wedges. We will start by discussing the differences between the way these two reflect light:

https://rmico.com/re...-light-tutorial

Has an excellent succinct coverage of this topic. Especially the reflection/polarization "depth"; I include the picture of the graph here for illustration (will be relevant in a moment):

image.jpeg.30e8941f840424ffdd9922b1de7b6fcd.jpeg
image.jpeg.2001d60dd5206b60afc08596f286505f.jpeg

As can be seen in this graphs, we get a noticeable difference in the S-polarization off the surface. at 45 degrees, there is a difference as well, but only PARTIALLY - thus when using a polarizing filter, we cannot totally cross-polarize to nearly null out the light. this is why standard (Baader/Lunt/APM etc.) Herschel wedges have a narrower range of brightness control, and also why they have a lower reflective transmission (OD ~1.35-1.40, or 4.5% approx.) off the wedge's surface. (not including the OD3.0 post-filter)

A Brewster Wedge or plate, being at the Brewster angle, effectively nulls out one polarization, and reflects the other - also, at this angle, the S-pol light is reflected better/absorbed less at the Brewster angle, and hence why a Brewster Solar wedge (like the Lacerta units) pass closer to 8.5%, or OD ~1.07. (again, sans ND3.0 post-filter).

Given the above, this explains why the Lacerta Brewster Wedge has a much wider brightness range; one can go from VERY bright (WAY too much/unsafe for visual!!) to below what might be available for a standard Herschel Wedge system.

Okay - now... can one just employ a ND filter after the Wedge/Plate + ND3.0? Absolutely! so long as you keep in mind you want to be in the OD ~4.9-5.5 range, all safe and good. (so, this is approximately achieved in a Herschel wedge (OD~4.3 to 4.4 with post filter) using a ND0.6 (25%T filter, like a standard one) or a ND0.9 will give in the OD5.3 regime. For a Lacerta Brewster Wedge (OD~4.07), you need a ND0.9 (12.5% T) minimum to be in the regime closest to, say a Baader AS film level for visual.

BTW, a polarizing filter (single) gives an ND(effective) of 0.35, or ~45%T. Stacked in line for max transmission, two are about ND0.4, or 39% (approx.). One could co-rotate a preset dual polarizing filter in lieu of a single if one wished to use that on a Wedge, but I find I prefer a single linear type polarizer, myself.

Now to the "safety" part that seems to confuse many...

There is a link to a German sight on solar observing and quantitative measurements of filtering by Peter Höbel:

http://www.sonnen-fi...de/index-x.html

I will add a ND3.0 (Baader) filter curve from his site, in LOGARITHMIC form - he also has linear values plotted for those interested.

In the NIR (near infrared), the reflectance off a wedge will be in the same range as the optical. Same with UV, at least in the worst cases of 320-400nm, which is the most potentially damaging if unfiltered. First, the curve:

Ba-ND3-log (1).gif

This is a BAADER ND3.0 filter, commonly used on their solar wedges. Note that at no time within the pass band to 1.95um (1950nm), does the OD exceed 2.0 - that is 1%T or 0.01. Now, when used with a solar wedge, the light is reduced to an effective OD of ~1.35 or so. When we have the ND3.0 in the optical path as it should be used for visual, we get 1.35+(>2.0) >3.0, or 0.1% or better.

So, at WORST, before polarizers or additional ND being added, we have 0.1% in the NIR, and even around 2.4um range it is still combined less than (1.35+1.5) = OD1.85 which is 1.4%. Again, this is BEFORE any additional filtering (polarizer or ND) for lowering the visual range brightness. Now, an additional ND filter will reduce this further by some amounts, and I recommend those curious to go to Peter's site to see the curves for other ND filters (Baader) - this will vary with other manufacturers and types of substrates used in the filters.

ISO 12312-2:2015 Eye and face protection — Sunglasses and related eyewear - Part 2: Filters for direct observation of the sun outlines that 3% is the acceptable minimum for safety in the IR. I do not have a copy of this being it is >50 Euro for the standard (ISO ripoff, IMO, but that is another topic!)

Nonetheless, the Baader wedge fulfills the OD5.0 visual and 3% N(IR) requirements by at least 2x in the NIR, when used with Baader filters, which is what we have posted here for curve data.

Now, the Lacerta Brewster Angle Solar Wedge - the Lac and Lac-2s, have almost double the light throughput, and even with a Baader ND3.0 used, would just pass the ISO requirements for safe solar, if not using an additional blocking filter, that Lacerta recommends if using >5" apertures with their wedges; According to the current ISO criteria, IF one used a Baader ND3.0 filter after the Wedge. I do this myself, BTW - use a Baader ND3.0 on my wedges, and high end Hoya 48mm polarizers (linear). SUPERB results!!!

In the 33+ years I have done solar observing routinely and 25 of these with solar wedges (and AS Film, etc.), I have personally logged 1000s of hours of observing the sun, and have been fortunate enough to still not have cataracts at 59 years of age, and a healthy ocular environment (according to my opthalmologist). So at least my eyes have not had any ill effects using wedges all this time!

Having said this, my three wedges are Baader MK-I, the first original model, an APM 2" wedge, and now more recently, a Lacerta Lac-2m. I call mine an "m" version for modified. I replaced the stock EP setup (wasn't suitable for my EPs and configurations) with a M54 extension tube, a M54-M48 adapter ring (to affix the ND3.0 filter INTO the unit like the Baader systems, and M54a Baader Clicklock system. Works great and allows me to compare both with similar optics aside from the wedge angle/wedge substrate used.

I digress! For other wedges, I urge anyone who has one alternate (and there are many: Lunt, Altair, etc.) to VERIFY that the unit has what is intended for SAFE solar use. I DO know Lunt recommends using 2" wedges for larger scopes due to heat loading on the prism in the 1.25" versions. So follow those guidelines to be safe also!

If one is REALLY concerned, ask their manufacturer or supplier. DEMAND info - IMO, ALL companies (incl. the venerable Baader) should have posted passband results with a wedge and THEIR supplied ND3.0 filters. Heck! APers get lovely passband curves all the time for narrow band imaging filters, WHY can't solar units be not supplied with this? Not cool.

IF someone is truly concerned, I strongly recommend the Anti-Halo filter by Player ONE:

https://player-one-a...y/filter-wheel/

In the link page, scroll down to show either the 2" or 1.25" versions. P-1 claims they have OD4.0 blocking of UV and NIR - add that to the chain and you're totally good and SAFE! Prices aren't outrageous either. In my Achromats, I use an SA (Semi-Apo) filter in the chain and these also have additional NIR/UV reduction. So even in the 5-6" regime, I am pretty fine...

If not sure, ask questions. That is the great thing with CN - so many folks with experience to share. I hope that my information has at least clarified a few things. While alternate filtering systems may vary, safe to say using a Baader ND filter on any wedge should provide enough to at least put one in the safe regime without risking eye damage, so long as additional polarizing or ND filtering is ALSO employed with them!

I will finish this off tonight by saying that a solar wedge is a wonderful accessory, and can provide some of THE finest white-light/continuum images when used with a good quality refractor. However, ALWAYS do a pre-check before doing solar observing - it is a risky endeavor, if not done safely. It takes but a second to change your astronomy career forever!

If not sure - DON'T; ask first. verify, and then proceed.

Clear skies, good sun views (the cycle 25 is off the chart with goodies!), and be safe out there!

Darren

Excellent explanation, thanks for sharing

### #5 gstrumol

gstrumol

Fly Me to the Moon

• Posts: 5,120
• Joined: 03 Oct 2022
• Loc: north of Detroit, Michigan USA

Posted 02 August 2024 - 06:29 AM

Wonderfully detailed!

I use both the Baader solar film and the Lunt wedge. My calculations are simple:

and confirm your note that for a typical wedge to match the reduction in light intensity of the ND5 film one just needs to add ~ an ND0.65, or a filter with max transmission around 22%.

If viewing directly I typically add a basic polarizing filter and a UV/IR cut filter to the EP. In this way, I protect my eyes and, by rotating the EP, I can alter the transmitted light a bit. This has a different advantage that some may not think of. We all know that increasing magnification causes the image to dim. This will happen with the film. You start out at ND5 and things go darker from there. With the wedge and polarizer one can increase the brightness to somewhat counter that dimming.

### #6 TOMDEY

TOMDEY

James Webb Space Telescope

• Posts: 16,483
• Joined: 10 Feb 2014
• Loc: Springwater, NY

Posted 02 August 2024 - 07:23 AM

Yep to all that. In actual practice, the human (and all other fauna) response to light is naturally protective. This is why virtually all animals, left to their own natural instincts --- successfully protect their eyes from damage for as long as it matters = their entire lifespan. Any specular optical system (image-forming or not) can and occasionally will present dangerous incoming radiation to the eye. Our natural blink/divert response prevents this from damaging the retina by limiting the exposure time to small fractional second. Here are some of the specular sources of unwanted solar (and/or other) radiation:

> surface of water - especially at glancing angle --- extremely common (boating, wet roadway)

> sun through trees or scanning horizon --- extremely common (traveling, hunting)

> glint from windows, cars --- extremely common (cities, driving)

> other light sources --- unnatural (welding arc, spotlights, street lights, oncoming headlights, laser pointers)

> optical instruments --- volitions, unnatural (telescope, binocular)

It's that last one that presents a peculiar lemming form of danger. The user (most especially an unexperienced or stupid observer) foolishly presumes that he is "supposed to" look into that hole, even if he has to force himself to tolerate the overwhelming brightness.

The best rule is to immediately avoid / look away if a light seems too bright for comfort, regardless of what any other indicators would suggest.

Emmy Noether's Theorem assures us that any sun glint (including that seen through instruments) is no more luminous, no more radiant --- than looking at the sun directly, with no "optical aid" whatsoever --- which is as dangerous as looking at the sun directly --- which we naturally (should) avoid. In a magnified system (telescope, bino) the sun is presented bigger/closer... which of course adds to the danger. We filter it down to a reasonable level and then are protected to enjoy the view.

Executive Summary: If it looks too bright --- immediately avoid it.    Tom

#### Attached Thumbnails

• Sebastian_Sajaroff likes this

### #7 Spectrum222

Spectrum222

Vostok 1

• topic starter
• Posts: 191
• Joined: 05 May 2015
• Loc: Edmonton, AB Canada

Posted 02 August 2024 - 08:51 AM

Thanks for the kind comments folks - I just wanted to sort of collate a lot of what is out there.

To err is human, to do astronomy is touching the divine! lol...

Well, I did do this up very early this morning, and in fine fashion DID have a few minor spelling errors, and did do a small error in my calculations. I actually was rolling these numbers around in my head during REM. (gotta love that, hey?!)

• firstly: the eye doctor - yes - it has two h's! thanks for that. My spell-check kept overriding me while I was typing.
• secondly: the Baader ND3.0 calculation of total NIR - I said that the total was almost 2x within the ISO standard. But actually, at near OD1.5 peaking, this is right around 3%, since OD1.5 ~3.2%. nonetheless, still JUST passes for safety - right near the edge of that.
• thirdly (omission) - NIR and high mir-IR wavelengths will be out of focus to varying degrees which will vary the amount of effective flux density (not to be confused with OD, I am talking W/mm2 ); this factor is HIGHLY variable. Some high end APOs focus light more precisely beyond the visual (Like most TMB, some Astro-Physics, and so on) usually due to very high Strehls and some medium f-ratios, and that is why they make excellent NIR/UV imaging instruments as well. Defocus past the red (and violet) regimes are perhaps a bit tighter than is some other instruments - though most fine APOs likely fit in this category as well. While useful for UV/NIR imaging, but one still needs to be mindful of this. That one is harder to calculate easily without having all the specs and then the math takes over from there. If anyone knows whether that ISO standard includes effective fluxes (which at a glance from what I understand it does not (?), then it is a sort of useless standard in a way, as throughput in larger apertures may exceed the safe levels, even though the absorbance or effective attenuation met the relative, % specification.

I was going to just edit it, but in fairness to all here, and in the light of transparency (punny?) I thought better to leave it. Hopefully we will not see too much commentary on it per se.

Gary - bang on calculations, sir! having JUST past the 22% at ~25%T is just fine.

and yes - tuning the brightness in a wedge is indeed the single most useful advantage in their use, as you can adjust brightness in the optical to account for variances in cloud cover, transparency, and of course magnification. In fact, even when using my binocular telescopes (APM SD binos) with AS film on them, I often also employ a polarizer on the EP side - I find it not only trims the brightness (esp. in my 120mm bino!), but also by rotating the EPs with them in there, some subtle additional details often pop out and become more easily visible.

I also appreciate Tom's comments. We DO have these animal natural instincts, but sometimes we override it with stupidity, by not trusting ourselves, or failing to also use proper critical thinking skills which are starting to really lack in modern times more and more - but that is a different topic!

He's correct --- too bright? Not right!

I would also suggest since NIR is present but not always immediately detectable by our eye until perhaps hours later, that one limits exposure in a view to <60s or so max at a time. This permits one to not only absorb the view we have, but also to allow the eye to rest for a brief period. I do this anyway, being a lunar/planetary observer as well, so I am accustomed to taking regular breaks (to process the view and rest my eyes).

So far, to date, as I mentioned, no ill effects to using any of my wedges, especially the Baader MK I after nearly 3 decades. But as I also mentioned, it is imperative to check EVERY time your solar kit before training it on "el Sol"! Just as all pilots do pre-flight checks, we should always do a similar check before viewing. Just good sense. Then, we are at least minimizing risks to ourselves and others we are sharing the view with!

Darren

Edited by Spectrum222, 02 August 2024 - 08:53 AM.

• gstrumol and Sebastian_Sajaroff like this

## Recent Topics

### Also tagged with one or more of these keywords: Filters, Optics, Solar, Visual, Observing, Refractor, Equipment, Accessories

 Cloudy Nights LLC Cloudy Nights Sponsor: Astronomics