Comet - what did I do wrong

Started Jul 25, 2020 | Discussions thread
WJaekel Regular Member • Posts: 179
Re: Comet - what did I do wrong

The blur/blob of the stars in your shot primarily is caused by misfocus. As others pointed out, you would have needed to focus manually on a bright star etc by using live view and loupe. Of course, your setup (tripod) must be stable. I normally use Mirror lock and a cable release, too, IS off.

That said, there's another problem I personally came across with my shots I took towards the end of the visibility of the comet on July 24th (see downsized example below) : I had used my 400mm/f2.8 IS II lens mounted on the 1Dx III, set to ISO 4000, f4 and shutter speed to 6 sec, correction + 1.3. Towards the end of the period, he comet was almost invisble with the naked eye here. Viewing the results at 100% ,I was surprised that 6 sec already were too long to capture the stars as points. Instead, I got short lines (trails) and I don't think that there was any blur caused by my very stable setup.

Back home I did some search and I obviously didn't respect the 500 rule " SS = 500 / (CF x FL)" to avoid star trailing :SS = limit of shutter speed, CF = crop factor (FF 1,0, APSC= 1,6 for Canon), FL = focal length.

So for my combination the limit would have been just around 1 sec !! If you do the maths for your setup the limit would be 1 sec, too - with CF= 1.6 on your 7dII and focal length 300mm. But for your image you had zoomed back to 70mm. The limit would be around 4.5 sec by then. So 2.5 sec is well below that and trailing couldn't come into play.

In my case, it would have been better to use a shorter lens and crop if I want the perfect shot with no indication of star trails. But as for the overall images, I'm content with the results so far.

BTW, there's also a good calculator in the Photopills App, I unfortunately had not used at the location.

As said, the stability of the setup is important, of course



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