Here is My Approach to Shooting the Eclipse

What I Want To Photograph

• Several shots of the eclipse before and after totality.
• Several near totality shots.
• The solar corona during totality
• Using a second camera a time-lapse of the location darkening and brightening into and out of the eclipse

Factors in My Equipment Selection

I will be on location broadcasting live on FOX19 NOW and social media so I cannot manage a large, cumbersome set up. - Light weight equipment, easy t hadle and adjust, no astronomical telescope, a modern DSLR fits the bill.

I will need to broadcast as I shoot. - Maybe handheld shooting - requires fast shutter speed for sharp image and to reduce light to sensor.

When the sun is un-obscured the amount of light is way too bright for a digital DSLR. - Special Filters are needed to reduce the radiation load on the sensor.

As the sun becomes obscured the amount of light decreases dramatically so I will need to adjust the camera sensitivity. I will use the camera in manual mode, change f-stop, or shutter speed or adjust a variable ND filter.

I do not know how large the solar corona will be at totality, so ... I need to use a Zoom Lens

Guiding Principles

•  I need to reduce the amount of solar radiation reaching the camera sensor. 
• About half of the sun's light reaching the surface is visible or shorter wavelengths (diagrams below).
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• I will use a 720nm IR filter - it allows only IR radiation through the lens to the sensor. The R72 filter should reduce the amount of solar radiation reaching the camera sensor by approximately 50%.

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  Transmission curve for Hoya R72 glass. Courtesy: Hoya.com

• Hoya R72 glass eliminates almost all of the solar radiation with wavelengths shorter than 700nm. There is a transition from 0% to 97% transmission between 700nm and 750nm. Some very long wavelength visible red will leak into the photographs creating a red hue. For my final photos I will adjust color saturation, brightness and contrast in Photoshop. But this drastically reduces the light levels on the camera sensor.
• All DLSR cameras have a built-in infrared blocking filter which will reduce the amount of  radiation further. Even though the R72 filter has cut the total solar radiation reaching the sensor in half the amount of IR still reaching the sensor could damage the sensor.
• The combined transmission corves of the IR cut filter and the R72 filter show that what the camera will record is in the grey zone where both allow some solar radiation through.

Typical Canon IR cut filter transmission, Courtesy kolarivision.com

Combined transmission curves of the Canon IR Cut filter and the R72 what gets to the sensor is in the grey zone.

• To further reduce the amount of radiation reaching the sensor I will use a variable ND filter - this also makes it easy to adjust the settings as the eclipse progresses.

Test Results Saturday 8.19.2017

Canon Mirrorless M3 (Crop Factor 1.66)
Canon Lens EFS 55-250mm Full Zoom (Equivalent Lens Focal Length 415mm)
Canon Mount Adapter EF - EOS M
Manual Focus
Image Stabilization On
1/4000 sec.
F 32
ISO 100
Hoya R-72  720nm IR Filter
Tiffin Variable ND, Set at approximately 4 stops light reduction
Tripod

Contrast increased (100) and brightness decreased (60), color adjusted in Photoshop

200% enlargement of above

Test Results Sunday 8.20.2017

Canon Mirrorless M3 (Crop Factor 1.66)
Canon Lens EFS 55-250mm Full Zoom (Equivalent Lens Focal Length 415mm)
Canon Mount Adapter EF - EOS M
Manual Focus
Image Stabilization On
1/4000 sec.
F 32
ISO 100
Hoya R-72  720nm IR Filter
Tiffin Variable ND, Set at approximately 6 stops light reduction
Tripod

Contrast decreased (60) and brightness decreased (50), no color adjustment, in Photoshop

De-saturated the color, did some noise removal and tweaked brightness and contrast, enlarged.

Final Test

Compare to NASA High Resolution Image in Visible Light

Not bad for prosumer equipment vs. a multi-million dollar imaging system.

Test Results II Sunday 8.20.2017

Canon Mirrorless M Modified to Full Spectrum (IR cut filter removed) (Crop Factor 1.66)
Canon Lens EFS 55-250mm Full Zoom (Equivalent Lens Focal Length 415mm)
Canon Mount Adapter EF - EOS M
Manual Focus
Image Stabilization On
1/4000 sec.
F 22
ISO 100
Hoya U-340 UV Band Pass Filter
Tiffin Variable ND, Set at approximately 4 stops light reduction
Tripod

Hoya U-340 Transmission Curve

• Hoya U-340 glass transmits virtually no visible light (400nm - 700nm).  
• This chart is for glass 2.5mm thick. The filter I am using is 2mm thick so I can expect to see some visible light in photos.
• Spec sheets say that <0.1%, not zero, is transmitted in the visible range by 2.5mm glass.
• Visible light output from the sun is immense so with a thinner than spec'ed filter and an intense source my camera should record UV, some Visible (skewed to red) and some IR. and yield a creamsicle orange sun before color correction.
• This set up should decrease visible and IR by 99% and allow through plenty of UV. 

Conclusions

Either set up should work well but using the full spectrum camera with the U-340 filter will mean lower contrast, but less red in the images.

In IR, the first set-up, I will have to be meticulous when focusing manually.

I can reduce the amount of light further by increasing the effect of the variable ND filter up to when the criss-cross pattern appears and reduce reliance on Photoshop.