Star eater issues on Sony's

Started Jan 13, 2018 | Discussions thread
Tristimulus Veteran Member • Posts: 7,588
Re: Star eater issues on Sony's

Ferguson wrote:

Trollmannx wrote:

Ferguson wrote:

Trollmannx wrote:

Just for the record:

Sony full frame cameras without in camera image stabilization do NOT have the star eater issue when using any settings EXEPT bulb.

So I have an A7Riv and have been happily using it for the last month with both a long sony lens, and (not so well yet) a C11.

The C11 has a very long fokal lenght so unless the seeing is exeptional the stars will be blurred by turbulente. Blurred stars are bloated and usually not affected by the spatial filtering (which is designed to remove single pixel hot pixels). So in this case the star eater issue sound have litte effect.

Well, the main reason I keep using the Sony instead of getting a dedicated AP camera (probably mono) is the 400/2.8 lens. It's a terrific moderately wide field scope and the fast aperture certainly beneficial. There my imaging scale is more like 2 arc seconds per pixel, and tracking much better (because of the F2.8 and shorter exposures), so I assume there I might see this?

There are several things in this thread that confuse me with regard to when it occurs.

You say "without in camera image stabilization"-- but do you mean it is not capable, or is turned off?

Some say, not me.

I say: imaget stabilization MUST be off when doing astrophotography.

Have by accident tried image stabilization on, the result is lots of dancing stars...

so, you say it is good up to 30s but not bulb. So if I use bulb but expose for 25 seconds (which it is aware of and labels in the exif) is it affected?

Not me. But as Mark says, longer than 3.2 sec or bulb mode and a tiny hell is loose...

Plus Jim Kasson in his oft quoted review of the subject says "at 3.2 seconds all hell breaks loose", setting the bar a lot lower.

That is the bar. Just use a sharp short telephoto lens (Just to ensure you can spot the effects of the tiny star eating hell) and expose in steps from 2 sec and longer. By pixel peeping the faintest stars at 100 % something should be seen.

I guess next time out (which at present is forecast to be "later this year" here in SW Florida, continual clouds) I can do some experiments and try to see, but if they have already been done, it would narrow what I need to try.

I guess I also am a little unclear on the effect of dithering and integration on this; I guess to "see" it more clearly I need to look at individual frames. Here's an example.

That's a single, uncalibrated, debayered, stretched version of M33. The detail in there is almost below what you can see at all thanks to Florida community preference for daylight-bright streetlights. Here's what you get with 200 or so stacked, at about the same scale.

I guess what I'm trying to understand is all this very faint, very small detail -- did I lose a lot using the Sony camera? So might 50 subs have done this? Or, you can see massive amounts of color noise in the faint edges, is that partially coming from Sony munging the different channels differently?

The red channel og the A7III is a bit more noisy than the Canon 6D red channel. The blue and green channels are pretty much similar on both cameras.

But the total noise levels are in the same league for the two cameras. Had to work a bit harder to get a more out of the Sony files, so now stretching less in the highlights and taking care not to destoy information close to the noise floor.

But then ordinary cameras are fine tuned in the low, mid and high mid tones that are so important for how we perceive ordinary pictures. The brightest highlights and the deepest shadows are stepchildren in this family. That said, controlling highlights and shadow areas are not easy even when using dedicated astro cameras.

AP is hard enough if the camera is a handicap.

I sometimes use dedicated astro cameras (am curious) but still prefer ordinary cameras for ease of use. The end results does not differ that much (would probably note the subtle differences better if spending hour after hour to fine tweak the results).

It already is from spectral insensitivity. But I love that lens, and I can't put a real astro camera on it (too short of flange depth).

So am trying to understand if it's hurting in particular operational modes, and if there are workarounds. E.g. if I manually set the shutter to < 30s does the impact go away?

No.

(Though there's Kasson's 3.2 seconds still hanging out there).

Practical test:

Have tried stacking lots of 1 sec, 2 sec, 4 sec, 8 sec, 15 sec, 30 sec, 1 min and 2 min exposures. The total integration time was similar for all stacks.

Also note that the results reflect my somewhat light polluted sky and my workflow. Others might discover slightly different results and tresholds but the trend should be clear.

Seems like read noise and pattern noise get the upper hand when exposures are less than about 15 sec. Worsening fast at exposures get shorter.

30 sec is a sweet spot as I can use the in camera intervallometer (am lazy). In my case this is a good balance between noise, bloating by turbulence, and no need for guiding.

1 min sub exposures seems to be optimal at my location. Theory seems to agree...

2 min subs just lead to more bloated stars (have a pretty turbulent atmosphere at my location, quite often the jet stream hoovers above) and there is no additional gain.

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