Long Image processing time after shutter is closed [duplicate]

Question

This question already has an answer here:

• Why does storing a long exposure photo take almost as long as the exposure time itself? 3 answers

I have a entry level dslr (Nikon D3300) and was practicing long exposure photography. I noticed one behviour from the camera and was inquisitive whether this can be tweaked in any way: I kept the shutter open for 2 minutes. When I clicked the shutter the release the second time to close the shutter, the camera took another 2 minutes to process and save the image. I tried this for multiple timings and observed and the longer the shutter is kept open, more is the time required by camera to process and save the image. Its almost 1:1 ratio. Is that expected?

I am going on a trip where I am expecting to take star photos. I am planning to keep long expose (20min +) to capture rotation of earth in the star. My concern is after keeping shutter open for 20 minutes, if the camera takes another 20minutes to save the image, I would get limited time to multiple shots. As one photo would take close 40 minutes to store in my camera. It would get frustrating waiting everytime to wait for camera to save the image. It would even feel worse if after waiting for so long, the imagedoes not meet your expectation.

Is there a way I can improve the time if takes to process and save the image after I have released the shutter? If possible how to do so and are there any repercussion to image quality if thats done?

Thanks

Answer 1

This is caused by the camera performing a so-called "long exposure noise reduction", which means that after the exposure a dark frame exposure of the same duration is made and then the two images are subtracted. You can opt to shut off long exposure noise reduction and instead take only a few dark frame exposures yourself.