a7RIV eats stars

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thiefofpresence
thiefofpresence Contributing Member • Posts: 770
Is the lead buried after all?

JimKasson wrote:

And it starts sooner than the a7RIII.

My question is this, is the (buried) lead that despite more resolution, don't expect more un-eaten stars than A7R3? That would be a disappointing result for enthusiast astro-photographers lusting for the higher resolution sensor and thinking they will see their money in the more star-endowed images.

It would also be nice if the cutoff could be expressed in star magnitude. What magnitude does the squelch of "star-eating" kick in? For some really small magnitudes, one would imagine the enthiusiast would say - oh well - enough for me (unlike the professionals who as others have pointed out would invest in gear that worked at fainter magnitudes.

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waldoh Contributing Member • Posts: 662
Re: Making the menus more complicated

I’m curious, does stat eater remove less or more stars than the A7RIII?

Didnt it only remove stars that were 1 pixel wide or something? Now that the pixels are smaller, how does that effect star eater?

JimKasson
OP JimKasson Forum Pro • Posts: 26,986
Re: Making the menus more complicated

waldoh wrote:

I’m curious, does stat eater remove less or more stars than the A7RIII?

Algorithm looks about the same to me, but the smaller pixels in the a7RIV will slightly increase the probability that the star illuminates enough pixels to be safe from munching.

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Magnar W
Magnar W Senior Member • Posts: 4,255
Re: Making the menus more complicated
1

waldoh wrote:

I’m curious, does stat eater remove less or more stars than the A7RIII?

Didnt it only remove stars that were 1 pixel wide or something? Now that the pixels are smaller, how does that effect star eater?

How could 1 pixel stars be recorded faithfully with a Bayer matrix sensor?

And what about the effect of turbulent air?

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JimKasson
OP JimKasson Forum Pro • Posts: 26,986
Re: Is the lead buried after all?

thiefofpresence wrote:

JimKasson wrote:

And it starts sooner than the a7RIII.

My question is this, is the (buried) lead that despite more resolution, don't expect more un-eaten stars than A7R3? That would be a disappointing result for enthusiast astro-photographers lusting for the higher resolution sensor and thinking they will see their money in the more star-endowed images.

It would also be nice if the cutoff could be expressed in star magnitude.

That would depend on the aperture and quality of the prime lens, and on how well it was focused.

What magnitude does the squelch of "star-eating" kick in? For some really small magnitudes, one would imagine the enthiusiast would say - oh well - enough for me (unlike the professionals who as others have pointed out would invest in gear that worked at fainter magnitudes.

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Trollmannx Senior Member • Posts: 5,743
Re: Is the lead buried after all?
3

thiefofpresence wrote:

JimKasson wrote:

And it starts sooner than the a7RIII.

My question is this, is the (buried) lead that despite more resolution, don't expect more un-eaten stars than A7R3? That would be a disappointing result for enthusiast astro-photographers lusting for the higher resolution sensor and thinking they will see their money in the more star-endowed images.

Astrophotography is about sinking money anyway, lots of frustration and success only now and then. So no traditional value for money here anyway. But the disease is permanent and non cureable - and we believe we get lots of fun from it all...

Well, at least it is an interesting and rewarding hobby for those peristent ones!

It would also be nice if the cutoff could be expressed in star magnitude. What magnitude does the squelch of "star-eating" kick in? For some really small magnitudes, one would imagine the enthiusiast would say - oh well - enough for me (unlike the professionals who as others have pointed out would invest in gear that worked at fainter magnitudes.

Limiting star magnitude depends upon a lot of factors like transparency, altitude, turbulence and then some. So no hard answer here.

Also note that 0.4 magnitudes corresponds to about 100 %. One magnitude difference is about 2.5 times fainter or brighter.

Just took an image of M51 with the a6400 and a dedicated astro camera.

32x30 sec exposure (32 stacked exposures each 30 sec - that does the job nicely, no need for longer sub exposures if you know what you are doing and why).

106/530-5 Takahashi astrograph (so the optical quality is as good as it bets.

At least 18.5 mag limiting magnitude by the Sony. Just hook the camera to the telescope and use the Bathinov mask and Live View to focus - and go.

The dedicated astro camera did go 0.2 or so magnitudes dreper. The camera must be tethered to a computer and cooled to operating temperature before using, a slow focusing procedure before opening the shutter - and then go.

My A7III does about as well as the a6400 when catching faint stars, but resolution is a bit limited compared to the a6400 and my dedicated astro cameras.

Sony cameras are not that bad even under a starry sky! And the ease of use is appealing.

sharkmelley
sharkmelley Senior Member • Posts: 2,252
Re: a7RIV eats stars
1

Thanks for the analysis!

But it's not a surprising result.

Mark

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JimKasson
OP JimKasson Forum Pro • Posts: 26,986
Re: a7RIV eats stars
2

sharkmelley wrote:

Thanks for the analysis!

But it's not a surprising result.

Please don't shoot the messenger.

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Astrophotographer 10 Forum Pro • Posts: 13,345
Re: a7RIV eats stars
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Thanks for doing this Jim. Its as I expected unfortunately.

Do you know if there is the same blue/red speckle noise in shadows of longer exposures as well?

That marred the A7rii and iii cameras although it cleans up with a mild "dust and scratches" filter in Photoshop.

Also is there any evidence of "amp glow" - reddish/magenta areas of the image in long exposures?

The iv does not seem to be any sort of advance for nightscapes. The 16X pixel shift is probably not much use compared to the 4X pixel shift. It would be easier to simply stack 2 lots of 4X and avoid any artifacts from slight motion the tracker creates.

61mp would mean larger files and slower processing time as well.

The "intervalometer" Sony added is also not really that useful. It does not allow exposures longer than 30 seconds.

So to improve these cameras for astro Sony would need to:

1. Provide a disable menu item for this filtering. So easy to do one wonders why they don't.

2. Have a menu item for long exposures allowing multiple exposures of any duration perhaps up to a 15 minute or one hour limit.

3. An intervalometer that does time lapses like the old app and outputs in a movie file output option as well as RAW output.

4. Put a timer countdown on the LCD when doing a long exposure so you can see how long is left to go.

Several other manufacturers already offer the above to a greater or lesser degree, notably Fuji. Canon and Nikon do well here especially Canon.  Sony is way behind here.

Given how this topic has received little attention from Sony in the past its probably better if you want to do nightscapes to use other brands. Canon EOS R and Nikon Z are probably 2 of the best out there. Fuji is not far behind although it too does some filtering.

Greg.

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Re: a7RIV eats stars

JimKasson wrote:

Brick Wall wrote:

Nice analysis, thanks!

Anyone know if other cameras (e.g., NIkon Z's, Olympus, etc) also eat stars? Is this a common thing?

The older Nikons used to, but they fixed it after years of complaints.

I believe there are some current models that do. Fuji as well.

Mark Shelley is the guy on this. He has tested a number of cameras.

The only brand that does not seem to do this at all is Canon. Anyone else is suspect.

The Z6 I believe does not. Not sure about the Z7. Fuji GFX does. You can expect some fake green stars with these if the stars are pinpoints.

Greg.

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Re: a7RIV eats stars

When the iv was first released there was mention of a menu item to turn NR off. I am not sure if this is the same as they have always had where you can turn long exposure NR off. But it was said the menu item was to turn NR off.

Its unlikely, but is there a menu item for this and if so does it turn off this RAW filtering?

Greg.

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JimKasson
OP JimKasson Forum Pro • Posts: 26,986
Re: a7RIV eats stars

Astrophotographer 10 wrote:

When the iv was first released there was mention of a menu item to turn NR off. I am not sure if this is the same as they have always had where you can turn long exposure NR off. But it was said the menu item was to turn NR off.

Its unlikely, but is there a menu item for this and if so does it turn off this RAW filtering?

Greg.

I turned off all the NR settings I could find.

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Re: a7RIV eats stars
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golfhov wrote:

waldoh wrote:

Does star eater matter if all your after is a nice Astro Image?

Probably not. The artifacts introduced and stars removed so minuscule as to ALMOST be indiscernible in all but the largest prints

Not scientific accuracy?

If you want more detailed reading check Jim's blog or hunt down some of the other detailed writings on it.

I have done nightscapes with star eater on and off on an A7rii where you could turn it off by activating hi or lo drive mode.

The difference to the image is not great but its there. A drop in vibrancy of the stars as a look in the image and excess green in the star fields. What complicates it is the fact that there is airglow often in the night sky which is often greenish. Its an emission from a chemical reaction in the atmosphere.

But compare an A7rii/iii to an EOS R and you see a bit more noise in the EOS R but the star colours are way better in the Canon. That seems to be the damage.

There are no green stars. A7r* night sky images with a tracker (no tracker means the stars will elongate and this tends to protect them from the star eater), will have a fair amount of finer dimmer stars turned green. A little hard to correct.

I do find Pixel shift helps as it deepens the colour to start with (only when using  tracker).

It probably is overexaggerated in importance and noone is making scientific images using mirrorless cameras (what science would that be?). So its really the subject of pretty pictures and in that regards the A7r* series do very well with their very sensitive sensor. Colour speckle in shadows is a more destructive aspect of their performance as is magenta amp glow that can occur.

Additionally A7r* cameras cannot be converted for astro use (removal of the restrictive UV/IR filter) as they use an IR light for shutter timing that can leak into long exposures.

There is little to no software to control these cameras so all in all they are not a great choice overall for nightscapes but they are still plenty good. EOS R is way better in my opinion. Nikon Z6 perhaps even better.

Its a shame Sony does not cater to the Astro crowd as I see many people these days post about wanting a camera for family etc and they want to do astro as well.

At this stage smartphones cannot do astro so its one of the last areas where these larger cameras outperform smartphones yet this is being ignored by one of the bigger players.

Greg.

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Re: a7RIV eats stars

sharkmelley wrote:

Thanks for the analysis!

But it's not a surprising result.

Mark

Hi Mark,

You've done testing on a number of brands. As I recall you found similar filtering in some Nikon models and Fuji models. Which were they again? I think it was the D5700 Nikon and the X Fuji cameras. Also the GFX Fuji.

Greg.

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Re: a7RIV eats stars

Magnar W wrote:

JimKasson wrote:

My guess is that if you're happy with the a7RIII in this regard, the you'll like the a7RIV, too.

Yes, I suppose so.

Is there any differences with uncompressed raw?

If you've been averaging a7RIII images made at 3.2 seconds as a workaround, you'll have to drop the exposure time by a third of a stop.

For real world astro work I prefer longer single exposures for stacking, since loss of faint stars doesn't matter that much for the look & feel of the end results.

People don't notice stars that are not recorded anyway.

The tradeoffs made by the a7RIV in terms on conversion gain and the "Aptina trick" are not as good for astro as the way the a7RIII works.

Ideally, I would prefer a on-off filtering/"star eater" setting in the camera and then deal with noise when processing the frames.

Its not so much faint stars being removed as some stars being turned green that is the problem. Its also a bit hard to correct. HLVG (green noise removal tool) free Photoshop plugin helps but its not the best fix as it can throw colour balance off as well.

Greg.

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Re: a7RIV eats stars

JimKasson wrote:

Magnar W wrote:

Looking forward to see how this affects real world results. I will not buy the A7rIV myself, since I am satisfied with the A7rIII also for night sky work, but I hope experienced photographers who buy the IV will do some tests.

My guess is that if you're happy with the a7RIII in this regard, the you'll like the a7RIV, too. If you've been averaging a7RIII images made at 3.2 seconds as a workaround, you'll have to drop the exposure time by a third of a stop.

The tradeoffs made by the a7RIV in terms on conversion gain and the "Aptina trick" are not as good for astro as the way the a7RIII works.

Jim

I thought the filtering has been on a 3.2 second exposure cut-in for several years now?

It matters little as no one is going to take nightscape images with 3.2 second exposure lengths. Realistically 12 seconds is about as short as you are going to use for longer focal length lenses and take 6-8 of them and stack. 30 seconds is a workable length but that requires a tracker on anything but the widest of lenses depending on your tolerance for elongated stars.

Greg.

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Re: a7RIV eats stars

PWPhotography wrote:

Magnar W wrote:

JimKasson wrote:

My guess is that if you're happy with the a7RIII in this regard, the you'll like the a7RIV, too.

Yes, I suppose so.

Is there any differences with uncompressed raw?

If you've been averaging a7RIII images made at 3.2 seconds as a workaround, you'll have to drop the exposure time by a third of a stop.

For real world astro work I prefer longer single exposures for stacking, since loss of faint stars doesn't matter that much for the look & feel of the end results.

People don't notice stars that are not recorded anyway.

The tradeoffs made by the a7RIV in terms on conversion gain and the "Aptina trick" are not as good for astro as the way the a7RIII works.

Ideally, I would prefer a on-off filtering/"star eater" setting in the camera and then deal with noise when processing the frames.

As I always said if you really want a dedicated camera for stars then none of regular cameras are the best but specialized modified ones. Otherwise most like me only interested stars and sky as background then nothing to worry about some weak stars faded away

A7r IV should not be that much difference from A7r III. Personally I might interest to get if a discount (just want a reason) in the holiday season or early January before my big trip to the Antarctica and the Torres del Paine NP in mid January, mainly team with A7r III better than A9 with both high resolution and similar DR.

You know this same 61mp Sony sensor is coming out in a dedicated astro camera from QHY and ZWO. But its a lot more expensive. They also claim no amp glow which is not something I have had a lot of trouble with using Sony's but I have seen it a fair bit on A7rii images. Its a magenta band on one edge or corner of the camera.

So if you really want the 61mp full goodness get one of those.

They have been selling the 36mp A7r sensored camera for a while.

I believe its only in one shot colour which is a compromise but its 61mp if that floats your boat.

Greg.

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Re: a7RIV eats stars

JimKasson wrote:

Astrophotographer 10 wrote:

When the iv was first released there was mention of a menu item to turn NR off. I am not sure if this is the same as they have always had where you can turn long exposure NR off. But it was said the menu item was to turn NR off.

Its unlikely, but is there a menu item for this and if so does it turn off this RAW filtering?

Greg.

I turned off all the NR settings I could find.

Thanks Jim. So nothing new there.

Well if one really wants the 61mp full goodness without the star eater and any threat of amp glow then you get the much more expensive dedicated QHY or ZWO cooled camera version. It seems they are picking up the market that Sony is not interested in.

Makes you wonder how bad the noise would be if they turned it off. Would we be shocked? Are they concerned the Canikon fanbois will make a huge deal out of how noisy Sony sensors really are or are they simply disregarding what they consider is too small a section of the market to bother with?

Greg.

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Re: Agreed

SilvanBromide wrote:

golfhov wrote:

Just a few questions.

How many "professional astrophotographers" do you think there are........

Six!

But I think the discussion was more about astronomers and astrophysicists. There are twenty-three of those. ; )

And I think the fact that Sony cannot just tuck the option into the menus somewhere to disable it is unfortunate. Of course then I guess some would complain about the extra menu item.........

Oh well

They may well view it as a no-win scenario along those lines. Or simply as a lower priority than some of us would like.

It's not as though there aren't more than a few esoteric menu options already firmly ensconsed in the alpha UI. I wouldn't have thought that one more (that people have clamoured for) would sink the boat...

LOL! Funniest post of the week!

Greg.

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Re: Making the menus more complicated
1

JimKasson wrote:

waldoh wrote:

I’m curious, does stat eater remove less or more stars than the A7RIII?

Algorithm looks about the same to me, but the smaller pixels in the a7RIV will slightly increase the probability that the star illuminates enough pixels to be safe from munching.

Yes good point. I hadn't considered that. As the MP race continues (and likely to hot up with a 102mp Sony sensor already ready and an upcoming Canon 83mp model) it will be less of an issue if they stick to one pixel for noise which I am not sure they are but they might be.

Greg.

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