COMET Side Challenge - DPChallenge Forums

07/18/2020 12:38:49 PM · #26

Originally posted by vawendy:

I'd love to hear your process from beginning to end! What are your difficulties? What do your originals look like? How do you get rid of noise without losing clarity?

Well, one critical factor is that I have the advantage of a Star Adventurer equatorial tracking mount for the camera, so I can follow the stars and comet without blurring. This mount can also track at 1/2 rate, so I can get exposures that minimize blurring on both the comet AND the foreground.

That said, the process is fairly simple. I'm using a full frame camera to hold down the noise. Autofocus on a bright star, the moon, or a distant land object, then switch your camera to manual focus. You'll need to use a solid tripod, a remote shutter release or delay timer, and mirror lockup or live view to minimize vibration. The slightest movement will be obvious. If there's any wind, try to shield your camera from that, too. Divide your total focal length (including crop factor) into 500 to determine the maximum theoretical exposure time in seconds. The comet itself moves at a slightly different rate than the stars, so even with tracking you're limited to about a minute before the nucleus blurs. If you have an interesting foreground, it's a good idea to take separate shots with more exposure time so you have a brighter image to combine later (you can shoot those at ISO 200-400 for less noise).

Try to catch the comet as high in the sky as possible, which now means soon after sundown, so you're looking through less atmosphere and it's easier to avoid foreground obstructions. Find a location that faces northwest over a large field, body of water, or lower ground.

Stacking 10 or more frames can bring out considerably more detail and knock down the noise, but it's a somewhat complicated procedureâ�� especially with comets.

Any other questions?

Message edited by author 2020-07-18 12:40:24.

07/18/2020 12:46:13 PM · #27

This was the original for the Tappan-Zee image, before unleashing the full fury of Photoshop upon it.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

07/18/2020 12:52:12 PM · #28

This is a lightly-processed shot from the first time I caught Neowiseâ�� before dawn on July 9. That streak passing above the comet is the International Space Station. I didn't know the ISS was going to make a cameo appearance or I would have been better prepared for it.

GeneralE

Canon PowerShot S3 IS

07/18/2020 01:39:56 PM · #29

Before dawn? Was that before it went around the sun, or is it actually in the sky all day but washed-out?

07/18/2020 01:52:39 PM · #30

Neowise was visible before dawn last weekend, but now it's more of an evening comet as it rapidly moves away from the sun and loses brightness. Note that the tail has flipped between my Westport and Tappan-Zee shots since the sun is on the other side. If you're far enough north, it doesn't dip below the horizon all night. Yes, it's up in the daytime, but washed out.

Message edited by author 2020-07-18 13:53:35.

westford

Sony FE 24-105mm F4 G OSS

07/18/2020 07:28:07 PM · #31

some great shots, down in the southern hemisphere the comet doesn't become visible until the end of July, but is unlikely to be a such a spectacle by then
as it is already moving away from the sun, so will fade from view very quickly, so enjoy in the north

Lydia

Canon EOS-6D

07/18/2020 07:45:31 PM · #32

You people are amazing me with your comet knowledge and shots!

07/18/2020 10:27:35 PM · #33

So how do I know what type of exposure I'm looking for? I'm setting my aperture at 2.8 (widest for that lens), the shutter speed to ~2.5 (anything over 3 and stars are blurring (which I thought I was supposed to have close to 30 seconds of exposure before they streaked??)), but my ISO I can set to anything I want. I can have dark sky and foreground dark, or I can get twilight type sky, etc. Is there an optimum?

E.g.,

Message edited by author 2020-07-18 22:35:43.

07/18/2020 10:48:55 PM · #34

Wendy, your last image looks to be about the correct exposure. Looks like your FL is about 100mm or so, which means you will see trailing starting at about 5 seconds, or even a bit sooner.

07/18/2020 11:13:15 PM · #35

Originally posted by kirbic:

Wendy, your last image looks to be about the correct exposure. Looks like your FL is about 100mm or so, which means you will see trailing starting at about 5 seconds, or even a bit sooner.

But how do you know it's the right exposure? It looks overexposed to me. But is it just guesswork or is there a way of knowing?

07/19/2020 08:28:28 AM · #36

Originally posted by vawendy:

Originally posted by kirbic:
Wendy, your last image looks to be about the correct exposure. Looks like your FL is about 100mm or so, which means you will see trailing starting at about 5 seconds, or even a bit sooner.

But how do you know it's the right exposure? It looks overexposed to me. But is it just guesswork or is there a way of knowing?

The real answer is a long one. For a single exposure, you need to decide how much detail in the core you want to sacrifice to overexposure vs how much detail in the tail you want to capture. For your third image, I can see that the sky background is already brightening substantially, so going higher in exposure is going to gain you little in detail in the tail. The core does not look overexposed to any great degree.
Your image now needs post-processing to bring out the detail. That is one of the difficult things about astrophotography.

07/19/2020 09:19:26 AM · #37

Originally posted by kirbic:

Originally posted by vawendy:

Originally posted by kirbic:
Wendy, your last image looks to be about the correct exposure. Looks like your FL is about 100mm or so, which means you will see trailing starting at about 5 seconds, or even a bit sooner.

But how do you know it's the right exposure? It looks overexposed to me. But is it just guesswork or is there a way of knowing?

The real answer is a long one. For a single exposure, you need to decide how much detail in the core you want to sacrifice to overexposure vs how much detail in the tail you want to capture. For your third image, I can see that the sky background is already brightening substantially, so going higher in exposure is going to gain you little in detail in the tail. The core does not look overexposed to any great degree.
Your image now needs post-processing to bring out the detail. That is one of the difficult things about astrophotography.

Ok -- that was helpful. That's what I was thinking (although just about the tail, wasn't considering the core. Friday I didn't see much core. Yesterday was a lot more evident.)

That was my next question for you and Shannon. Post processing.

I've downloaded seaquater, and played with stacking multiple images.

1. Should I be using a different (yet free) software package?
2. If I found a place to put the full, resulting tiff (or whatever format you want) up on the web, could you guys take a stab at processing it? I'd like to see what results you come up with for the same file. I'm working on processing it, but I don't quite know what I'm looking for. I'm coming up with many different options, but since I haven't looked at much astrophotography, I'm not sure what a "natural" shot should look like.

Shannon: that tracking looks awesome!!! I always thought I'd have to get a tracking telescope! You've opened up a whole set of possibilities!

Question: with my gear and that tracking mount, could I photograph nebulae? What lens would I need? (and how do I talk my husband into another $400+ ;) )

And do you recommend that one? Are you happy with it? Do you wish you had purchased something else?

Message edited by author 2020-07-19 12:26:01.

Melethia

Canon EOS-80D

07/19/2020 02:32:00 PM · #38

Butting in uninvited - Wendy, if you want the font of all knowledge of astrophysical photography, check with cgino. She's a master.

07/19/2020 03:01:18 PM · #39

Here's an image created from sixteen 5-second exposures stacked:

The full resolution photo is there as well, feel free to check it out.

Edit to add: this was from the same source image set as my previous image post.

Message edited by author 2020-07-19 15:01:49.

07/19/2020 08:40:08 PM · #40

Originally posted by kirbic:

Here's an image created from sixteen 5-second exposures stacked:

The full resolution photo is there as well, feel free to check it out.

Edit to add: this was from the same source image set as my previous image post.

oh my!! Now I definitely have to go out again, I didn't get anywhere near that detail in the tail.

@ Deb -- Looks like she hasn't been here in quite awhile? I'll have to track her down. :)

07/20/2020 12:59:27 PM · #41

Wendy, I have the Sky-Watcher Star Adventurer mount (without a counterweight, which I probably need). That seems to be the most popular option among the basic camera tracking mounts. The iOptron SkyGuider Pro is similar, but offers a much better polar alignment feature. Both are rated to support up to 11lbs, but realistically I wouldn't use more than about 7lbs. You'll need to know how to find the North Star for alignment, but once aligned the rest is easy: just attach your camera with a ballhead, point it where you want, and turn on the tracking. Pretty much any lens is fair game provided it's not too heavy, although longer focal lengths require more careful polar alignment to get the tracking right. I caught the green coma and a bit of the blue carbon monoxide ion tail on Saturday with the Star Adventurer and a 400mm lens, but it's a little grainy due to ISO 6400.

I still want to get a "proper" closeup with a telescope, and last night's attempt was scuttled by a thunderstorm. Will try again tonight.

While you technically CAN shoot bright nebulae, the Andromeda Galaxy, etc., these mounts are primarily intended for Milky Way shots. You'll need to capture many exposures and use stacking software for deep sky targetsâ�� ranging from Deep Sky Stacker, AutoStakkert!, and Registax, to the powerful (and expensive) Pixinsight software I use. This was the Veil Nebula from last week:

07/20/2020 04:36:41 PM · #42

Sure wish I had proximity to a dark sky site... see this result achieved with moderate equipment!

07/20/2020 06:37:11 PM · #43

I won't be winning any awards with this but at least I got out (to my garden) and captured it. Now I know how easy it is to find in the sky I may travel to somewhere with a more interesting foreground if we get another clear sky night.

07/21/2020 04:04:02 AM · #44

I took my shot with a 85mm 1.4 lens at F-STOP 1.4 and ISO 400 with 6 second exposure.

It looks like it could be clear skies tonight again so I would like to go to a dark sky site (Exmoor) and have another go.

So if anyone has any suggestions for alternative settings or alternative lens please let me know.

It sounds like taking multiple exposures and stacking is not straightforward? I have had a successful attempt at star trails before using Star Trails application but I get the feeling it is not as simple as this with a comet? If it is doable, is it simply a case of taking multiple exposures at the same settings and combining them in a program? If so, would it be the same settings for each exposure?

As you can see I have very little knowledge of astrophotography :)

07/21/2020 08:00:32 AM · #45

Paul,
Take a look at the details posted on my last image. That walks you through the basics of stacking manually. Post back with any questions, and I'll try to keep an eye out and answer you.

07/21/2020 09:30:11 AM · #46

Thank you Fritz - that is really helpful.

Couple of questions. You have used a shutter speed of 5s - was that decided upon by trial and error, super intelligence or some formula? I more or less used the 500 rule (500 / 85 = 5.8823 rounded up to 6)

I see you manually aligned and rotated your images - do you know if there is any cheap/free software that would have attempted to do this process for you? I would have no idea what rotation to use or where the rotation point would be.

Your ISO was rather high - I took mine at ISO 400 so perhaps I needed to have the ISO much higher?

07/21/2020 10:01:00 AM · #47

Originally posted by P-A-U-L:

You have used a shutter speed of 5s - was that decided upon by trial and error, super intelligence or some formula? I more or less used the 500 rule (500 / 85 = 5.8823 rounded up to 6)

I knew that was about the max for my 135mm focal length to avoid too much trailing. I started with 10s, looked at the amount of trailing on the LCD at full magnification, decided it needed to be reduced a bit, so reduced exposure to 5s

Originally posted by P-A-U-L:

I see you manually aligned and rotated your images - do you know if there is any cheap/free software that would have attempted to do this process for you? I would have no idea what rotation to use or where the rotation point would be.

Yes, there are a number of packages that will do it. You may find this more trouble than it is worth if you don't do it often. The rotation calculation is rather easy. The sky rotation is 15 degrees per hour if you are pointed at the pole. We're not too far away from that, so OK to use that as a starting point. I estimated one shot per 6 seconds (5s exposure, 1s between shots) which is 1/10 minute, or 1/600 hour. So my rotation per image is 1/600*15 degrees = .025 degrees/image. Rotation is counterclockwise when facing north.
The rotation point doesn't matter. Ps uses the center, and that's fine. You are going to translate the image later to line it up.

Originally posted by P-A-U-L:

Your ISO was rather high - I took mine at ISO 400 so perhaps I needed to have the ISO much higher?

Yep, it was high. Based on getting a good exposure while maintaining my maximum exposure time and my available maximum aperture. I used f/2.5 even though the lens goes to f/2. From experience, this yields a little better resolution in the corners.

Message edited by author 2020-07-21 10:03:54.

07/21/2020 11:00:06 AM · #48

Thanks again Fritz - that all makes sense and will be helpful for my attempts tonight.

07/21/2020 12:44:03 PM · #49

Originally posted by P-A-U-L:

I see you manually aligned and rotated your images - do you know if there is any cheap/free software that would have attempted to do this process for you?

DeepSkyStacker is free and has a comet align module.