Visual Solar Filter

IDAS’s visually-safe ND filter will be available end of March.

– Optical density : 5.2

– Size : 52mm and 82mm

– Response curve

As far as I know, I think IDAS is the 1st company who officially publishes the response curve as solar filters from UV to deep infrared red. Especially the filters are well considered for the safety of the human eye in UV and IR region.  About safety issue, I found out very interesting report published by NASA.


This report mentions the caution in UV for the eye. But unfortunately it doesn’t specify the safety standard. Anyway, it is obvious UV is not the welcome spectrum for human eye. So it looks safer to maximize reducing the UV energy as much as possible. It is same in IR though. Since this report includes other filters’ test data, it is interesting to compare with IDAS.

Another interesting issue is the reflection

As shown here, the popular deposited-aluminum filters have 90% reflection. This means 90% of luminance from the camera sensor repeatedly reflects back to the sensor. This should dramatically reduce the image contrast.

Because of safety for human eye, IDAS filters allows to see camera’s optical viewfinder without any concern while  Regular D5 filters is not recommended.

BTW, I was always wondering why the prominence color looks orange through Ha filters available in the market. I saw it was the deep red for naked eye during totality. So actual color must be the deep red instead of orange. It makes sense in viewpoint of the wavelength. I guess these filters might have spectrum leak somewhere. As a result, the mixed wavelength creates orange color. If those filters totally blocks all other than Ha, it should look deep red for human eye. I wonder my guess is wrong…..



~ by tedishikawa on February 8, 2012.

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