Use of vintage eyepiece sun filters.
Posted 03 June 2011 - 12:12 PM
Posted 03 June 2011 - 12:30 PM
This is probably the best result we could hope for in a way. In at least one case (this one), the filter cracked when used per the manufacturer's instructions! And that was in a 60mm scope. That said the filter is really old but that's what we have to use and test these days.
It's looking like the data is pointing in a clear direction although not statistically significant.
If anyone has any extra sun filters that would help me here. I only have a couple left and I want to repeat some of the experiments. So if you can send me one or two please PM me. I will return any unused filters.
I have included a shot using my Canon PowerShot SD400 (Elf) looking directly through the cracked filter. This is the best shot I could get of the crack. It is extremely fine but you can see the visual anomaly it causes in the picture.
Posted 03 June 2011 - 12:32 PM
Posted 03 June 2011 - 12:35 PM
Posted 03 June 2011 - 03:00 PM
Note that in this test, my sun filter's lock ring is a bit corroded and I can't get it to loosen up a bit. That might cause it to crack faster then if it was loose due to heat expansion.
Great detail. In the real world, the quality of any given sun filter is unknown. Your noting flaws helps to show the kinds of breakages that could occur if people made the mistake of extrapolating theoretical opinions about safety into their own observing.
Neat to have already shown that even with 60mm objectives, these filters are not reliable, even if it is not yet clear how often the failures are hairline versus catastrophic (nor ever may be, with the limited number of filters available). Are you 100% sure the crack did not exist prior to your starting the test?
Posted 03 June 2011 - 03:20 PM
Posted 04 June 2011 - 05:13 PM
Actually being a survivor of two glass sun filter failures while observing I thought I should chime in.
In 1966 in SoCal probably in February, maybe March, while looking into the soul of Sol the screw in sun filter snapped big time exposing me to a "blinded by the light" experience. I was 14 and using a Tasco 11 te 4.5" reflector. This was a scope that I only had for a few months while I was visiting the "dark side" of reflectors and soon came back to a 3" Edmund refractor. The Tasco sold for $89 and would have been da bomb except there was a collimation or secondary mirror issue. Anyway there was an offset opening as I recall in the tube cap. This was to reduce the amount of light for solar observing. I know that now but then... I was much too smart to read the instruction manual I can't say if I was viewing with reduced aperture but in any event the filter snapped leaving a pretty wide gap and a momentary exposure to unfiltered sunshine. I experienced a few minutes of panic and darkness in the exposed (left) eye. Eventually things became "normal". I can still feel the heat generated in that moment.
Being a big fan of the sun which was in a pretty intense sunspot stage I was more disappointed that the filter broke than anything else. Anyway because the Tasco 11 te never could be collimated to specs. (less than four images of Jupiter in the ep at any one time) the owner of "Optech Precision Instruments" (I bet Lew knew this gentleman) offered a deal on an Edmund 3" refractor as a upgrade/substitute. I believe the Edmund was $125 at that time and I'm quite sure we paid somewhat less. The Edmund used 1.25 ep's and I recall digging deep to purchase a solar filter with a rubber cup that fit over a 1.25" ep like a eyeguard. I was told this wouldn't break like the other kind. It must have cost a lot then... like $2.50. I used this for zillions of hours with the Edmund scope. I was hooked on sunspots and granulation and didn't let a day go by for the next few years without taking a good look at the sun. I never had a failure with this filter.
In 1995 or so I picked up an old orange C-8. I was surprised that when looking at bright objects like Jupiter or Saturn my left eye (eye for observing) gave me a mellow view and my right eye was overwhelmed by brightness unable to discern much detail. It was like my left eye was looking through a ND filter. I remembered the Tasco experience. I believe that that burst of light affected some rods for sure. The difference between what my eyes can see as far as magnitude is apparent. I don't notice this except in the eyepiece. Of course my left (primary) eye is the one that talks to what's left of my brain... I do need it!
And knowing that sun filters break but being quite risk tolerant I recently was observing sun spots once again with a 60 mm scope when the screw in filter snapped. The split was minimal the light was very bright but nothing like the first exposure back in the 1960's. I don't believe this second exposure has contributed to the dimming down of my left eye. I do like the filtered view, the orange/yellow/green (whatever) that they provide. Projection isn't really viewing for me so I don't use that technique. I actually have a device that came with an old Goto telescope that can project a solar image onto a wall for a classroom of students to see. I haven't tried it yet.
The Goto Kogaku and Nippon Kogaku scopes that I have came with solar filters that cover the eyepiece like the one that I bought for the Edmund 3". Even though the filter glass is right there at your eye surface (being on top of the ep) I don't think it absorbs much heat. The Goto Kogaku even came with a Herschel wedge/ star diagonal for sun viewing. If it ever clears here I'll try it out.
Here are some pics of how the Nippon Kogaku filters attach to ep's. They might be safer but as metioned before a full aperture filter is the best way to go.
Posted 04 June 2011 - 05:16 PM
Posted 04 June 2011 - 07:16 PM
Unitron made a similar over the top of the EP filter for both solar and lunar versions. I have a pair of them. Does anyone else have experience with this type of solar EP filter?
Posted 05 June 2011 - 08:03 PM
Posted 05 June 2011 - 10:30 PM
Posted 05 June 2011 - 10:48 PM
Posted 05 June 2011 - 11:32 PM
Send them on over. I can definitely use more for this experiment. I believe you have my address.
Posted 05 June 2011 - 11:38 PM
Posted 06 June 2011 - 06:56 AM
Posted 06 June 2011 - 10:14 AM
Since blindness is a serious handicap to observing,I would always err on the side of caution.
Looking through some old filters that are KNOWN to be risky just seems ,well, foolish!Use a full aperature filter of proven safe design and preserve your eyesight.
Posted 06 June 2011 - 10:27 AM
Please understand these are a layman's opinions ,not advice, and you do any such experiments entirely at your own risk.
Posted 06 June 2011 - 10:58 PM
Posted 08 June 2011 - 09:16 PM
Posted 08 June 2011 - 09:35 PM
Does anyone know how one of these solar filters compares to an ND 3 filter?
A ND-3 filter reduces the light by 10^3 or 1000:1. For safe solar viewing you need 100,000:1 or a total of ND-5.
Welder's glass Shade numbers is SN = 1 + (7/3)*OD were OD is the optical density. Welders glass #14 works out to optical density of 5.57 or over 100,000:1 in the reduction of intensity.
The eyepiece Sun filters should be at least ND-5.
Posted 08 June 2011 - 09:43 PM
Posted 08 June 2011 - 09:56 PM
Thank you. That is what I am looking for. So, a "sun" filter with a herschel wedge should be more than ok, right? Maybe actually too much blocking?