Electronic shutter on the Sony A7R II

Started 4 months ago | Discussions thread
Alen K
Alen K Senior Member • Posts: 1,266
Re: Electronic shutter on the Sony A7R II

1llusive wrote:

Alen K wrote:

For deep-sky astrophotography, mechanical shutter life is not much of a problem because most people mount the camera or telescope/camera combination on some sort of tracking platform, be it a portable tracker or a full-blown equatorial mount. Exposures in that case are typically at least 30 seconds to several minutes long. Only tens to hundreds of sub-exposures are then required for typical total exposure times.

Shutter life could potentially be a problem if attempting to do long total exposures with an untracked camera, since sub-exposures would necessarily be much shorter, perhaps only a couple of seconds. If you try this, you will soon tire of it and buy a tracker.

Planetary and lunar close-up astrophotography, on the other hand, is best done with thousands of short (1/30 second or shorter) exposures in order to get enough candidates that are either wholly or partly minimally effected by atmospheric turbulence. (I am oversimplifying.) Special stacking software is then used to automatically sort through the frames to find the best ones and then aligning and combining them.

Practically speaking, that means taking video, not individual exposures. Furthermore, the video should preferally be uncompressed, something that most of today's DSLRs and mirrorless cameras can't do without extra secondary equipment. It is far more practical (and less expensive) to use a dedicated planetary camera feeding video over USB to a computer.

I believe taking fast electronic shutter frames is better than video. Part of the reason you alluded to is compression, but the other reason is avoiding over sampling or line skipping of the sensor and just getting a raw 1:1 pixel mapping.

Better for quality, yes. But I'm not sure the stacking programs I alluded to (e.g., Autostakkert!) can handle thousands or even mere hundreds of such frames. They are happier with video files, which even if uncompressed are usually smaller than the equivalent number of still pictures because each frame in the video file will have lower resolution. (Even if you were to use 4K video, which is equivalent to around 8 megapixels.)

And how many frames per second can be achieved using the electronic shutter still-image mode? Most planetary and lunar imagers recommend at least 30 fps, with 60 fps being better. The idea is to freeze the seeing as much a possible in each frame and to collect as many frames as possible in a given time in order to have more candidates for selection.

One of the other problems with using video from most DSLRs or mirrorless cameras, besides video compression and line skipping or averaging, is that you don't usually need the field of view their large sensors provide. Certainly when imaging planets, most of the frame will be empty and hence wasted.

That is yet another reason to use a dedicated planetary/lunar camera with their smaller sensors. Such cameras avoid all of the problems we have mentioned. All of the top planetary and lunar imagers use them. I'm not saying that a mirrorless camera can't be used for imaging planets or lunar close-ups. But they are not ideal for that.

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