Within a month or so, it's the first time I'll see fireworks as an owner of a good camera and naturally I'm planning to take photographs of them.
By researching various fireworks photography sources, I have found that the lens does not need a fast aperture: f/8 is plenty, some sources recommend as low as f/22. ISO speed will be of course 100. Shutter speed will naturally be bulb exposure on a tripod with remote camera connect smartphone app.
However, focusing will be a problem. I have understood that manual focus to infinity should be used, with the focusing done during daylight. This makes it problematic to use some externally zooming lenses as they may not be parfocal and will shift focus during transportation. Thus, the lenses I'm most interested in using for fireworks photography are:
- Canon EF 85mm f/1.8 USM prime
- Canon EF 135mm f/2L USM prime
- Internally zooming (probably non-parfocal?) Tamron EF 70-210mm f/4 Di VC USD
- Externally zooming electronically parfocal Canon RF 24-240mm f/4-6.3 IS USM
With prime lenses, there's no focus shift during zooming so I can easily set the focus and try to avoid accidental refocusing during transportation. With Tamron EF 70-210mm internal zoom, I can set the zoom to the desired focal length prior to focusing during daylight and then maintain that zoom setting, but then the advantage vs a prime would be minor unless the focal length I'll choose is far away from 85mm and 135mm.
The problem of non-parfocality made me consider Canon RF 24-240mm. I understand that while not truly mechanically/optically parfocal, it maintains focus by shifting focus electronically during zooming. Also, being focus-by-wire, there's no possibility to accidentally refocus during transportation if the camera is turned off.
My question is: do the electronically parfocal Canon RF lenses maintain infinity focus well enough for fireworks photography that I can focus to infinity at one focal length (probably the longest) and use the lens at any focal length afterwards without needing to refocus?
Of course one option could be to use several lenses with different focal lengths, but changing a lens outdoors with air dark from particulate matter from fireworks sounds like a possibility to self-caused sensor cleaning need, considering that my mirrorless camera lacks mirror protecting the sensor (obviously) and the mechanical second-curtain shutter does not close to protect the sensor when the camera is off. Also, reacting to changes in firework shooting distance is easier and faster with zoom than by changing lenses.
I calculated that at 135mm and f/11, hyperfocal distance is 53.8 meters. Thus, even a shift from infinity to 30 meters would be a problem.