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07-18-2020, 05:00 PM - 5 Likes   #1
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Shooting Comet NEOWISE

We've already seen some Comet NEOWISE photos: Astrotracker advice linking focal length to time, Neowise Comet - PentaxForums.com

along with some questions about astrotracker usage and comet exposures.

I'll bet there are a lot of comet shots out there, just waiting to be seen.

I'll put out a few from last night, with some comments on exposure details, and hope for many more to follow.

I was set up with my K-1 and DA* 60-250mm F4 lens, on a non-too great tripod. I wasn't sure the sky would be clear (it's monsoon season here in Arizona, and we had 1.15 inches of rain yesterday!) but by 8 PM things were looking good.

I did not bother to set up the astrotracker, so these images all have some trailing.

Focus was in manual, and focusing was done in magnified Live View, on a star near the comet or even the comet itself - it's that bright! I used the 2-second mirror lock-up mode.

For most of my shots, I had the zoom at minimum (60 mm) so I could get a modest field of view to emphasize the comet tail. Even at 250 mm, though, the trailing was not bad for the 8 second exposure below.

I had the ISO cranked up substantially - 12800 to 25600 for most shots. One try at 51200 was pretty poor! But, otherwise, I was rather impressed with the quality of the images. At these ISOs, the sky background is well above zero - a typical histogram of the sky peaked at 40 or more in PhotoShop Elements.

These images are jpeg's from the camera, run through DxO PhotoLab to up the contrast a bit and do a bit of noise reduction.

Here's a shot at 60 mm focal length, ISO 16000, 15 second exposure, and f/4; the first image is the DxO version, the second is the sooc jpeg





Note the bonus (?) satellite trail! I have these in many of my shots. These are Starlink satellites - the ones being launched by Elon Musk by the hundreds (soon to be thousands). They will be the bane of astronomers!!!!!

Here a zoomed-in version: 250 mm / ISO 25600 / 8 seconds / f/4.0



A faint satellite trail in this one, too (left of the comet)

Note the greenish color at the front of the comet nucleus - I think that color is real: comets often have a greenish hue, thanks to the particular gases (Cyanogen in this case) that comprise the comet.


Back to 60 mm and ISO 12800 / 15 seconds / f/4



And, finally, similar to above, but a higher ISO: 20000



Thanks to the higher ISO, the background sky is somewhat brighter.

A bit of comet physics: the physical head of the comet is the nucleus - this is a ball of ice, rocks, and dust (the ice being of several kinds: some water ice, but also frozen carbon dioxide and ammonia (it's cold out there, baby - even colder than MossyRocks's Minnesota fingers!), typically a few kilometers in size; surrounding the nucelus is the coma - a cloud of gas that has evaporated from the nucleus and glows in the sunshine. The the wide, prominent curving tail seen in NEOWISE is a "dust" tail of material that has been emitted from the nucleus, and the long, thin, relatively straight blueish tail to the left in many NEOWISE images is the ion tail (gas that is ionized (lost an electron or 2) by solar radiation and subsequently glowing/fluorescing).

07-18-2020, 05:35 PM   #2
maw
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Beautiful images...

I can't see it from my house because it's south-facing, in Italy I should orient myself to the Northwest.
I've decided I'll photograph it in the next round, jokes aside,
maybe by using a brighter lens like 50mm f/1.4 or f/1.8 you would have gained something.

"There are more comets in the sky than fish in the sea'', cit. Kepler
07-18-2020, 06:22 PM   #3
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QuoteOriginally posted by maw Quote
maybe by using a brighter lens like 50mm f/1.4 or f/1.8 you would have gained something.
That's my plan for this evening - my venerable M (or A, I don't remember which) 50/1.7

It looks like it is clearing up! Yeah!
07-18-2020, 07:07 PM   #4
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QuoteOriginally posted by AstroDave Quote
That's my plan for this evening - my venerable M (or A, I don't remember which) 50/1.7
It looks like it is clearing up! Yeah!
Both A and M, but I know the comet will be visible for a while, so you can try various alternatives.

Enjoy.

07-18-2020, 07:29 PM   #5
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Very nice !
07-18-2020, 07:51 PM   #6
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Why did you use such a high ISO?
07-19-2020, 05:51 AM   #7
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QuoteOriginally posted by bwgv001 Quote
Why did you use such a high ISO?
I wanted to go as faint as possible for the comet tails, and was not tracking, so shorter exposures are desirable.

I could have used even shorter exposures and stacked several shots. And, I suppose since the background sky is well above zero, I could have used lower ISOs. If you want to shoot, this is a place to experiment.
07-19-2020, 09:34 AM   #8
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great job!

07-20-2020, 09:18 AM - 5 Likes   #9
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Here's what I've been able to do over the last few nights.

Started super early in the morning on the 11th and went up to an area where I knew I'd be able to get some foreground interest and still have dark skies. Used my FA-77 at 1.8, and 8 seconds exposure.


Also tried a "selfie", and ended up a bit blurry.


As it's now visible in the evening, I'm having to wait a long time after sunset. This is from 11pm, and there was no color visible in the sky to the naked eye (15-30 DFA picked it up though).


And then a bit later it descended enough to get the reflection. This is 60s with the astrotracer (which I forgot to calibrate, so it's not as sharp as it could be). Had a lot of color noise, so I thought it looked better in B&W.
07-20-2020, 09:40 AM   #10
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Lovely photos! Amazing to see how good that ISO25600 is at bringing out the ion tail. Fascinating stuff!
07-20-2020, 12:29 PM - 1 Like   #11
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Neowise over Northumberland

Nice images so far
Here’s one from my holiday last week that I took for the Single In July Challenge here on the forums.
07-21-2020, 04:45 PM - 2 Likes   #12
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Good stuff here. Here was one of my efforts on July 11th. Shot with the 645z + FA 645 80-160 @ 118mm, 5 sec., f4.5, 3200ISO.


and just for comparison, this was on the same shoot with the K-1II, DFA*70-200 @ 160mm, 5 sec., f5.6, 3200ISO
07-22-2020, 12:09 AM - 1 Like   #13
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We had wonderful clear skies tonight over Pugetropolis, so we went out to try our luck. The family was not impressed, they thought it was going to be a bit more on the spectacular end of the scale. I tried my K50/18-135 combo (results were a shambles). Fortunately, I also dug out the old K30 body (with the bricked aperture control module) and topped it with my M-series 80-200 zoom. That one actually gave a couple of usable photos. Had the ISO maxed at 6400, exposures of 10 and 15 sec, the lens set to f/4.5 but Dog only knows if that was used. Put it into "M" mode, still thought it was in TAv no matter what. Boosted saturation, fiddled with brightness and contrast in PS Elements 15.

At any rate, here is the 15 sec shot


And the 10 sec shot
07-22-2020, 02:22 AM - 1 Like   #14
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QuoteOriginally posted by jlev Quote
Here's what I've been able to do over the last few nights.
QuoteOriginally posted by W412ren Quote
Neowise over Northumberland
QuoteOriginally posted by blackcloudbrew Quote
Good stuff here. Here was one of my efforts on July 11th. Shot with the 645z + FA 645 80-160 @ 118mm, 5 sec., f4.5, 3200ISO.
Very beautiful all the images, they will be difficult to capture once the comet will disappear, but beautiful to show to our children, friends etc..
in addition are shot from many parts of the world.

Congratulations to everyone.
07-28-2020, 03:43 AM   #15
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Here's the best I got. DA 50 1.8 with K1, 6s f/1.8 ISO1600 (single exposure).
Unfortunately I saw too late on the media that we a comet was visible and didn't had the time to learn how to setup astrotracer properly .
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