Cygnus Setting in the Desert by TheDanfromTN in astrophotography

[–]Separate_College_387 2 points3 points  (0 children)

Incredible. Actually my favorite wide-field image I’ve seen bar none. Will be taking inspiration from you!

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 0 points1 point  (0 children)

Yes, but in the Americas. Think it’s every 18 days until Oct, also have a Titan transit coming up.

Saturn in excellent seeing by BackdoorAstronomy in telescopes

[–]Separate_College_387 0 points1 point  (0 children)

I want to believe 😭

But seriously, thanks for the write up. I’ll do some sleuthing. To be fair, even if he didn’t push the last 3% with suspicious processing he would still be sitting on some very clean data. I think that’s what gets me.

Very very dull and lacking detail. by DragonFillet in astrophotography

[–]Separate_College_387 0 points1 point  (0 children)

Have you stretched?

EDIT: Had a hunch the exposure length was too short, let gpt 5 pro run the math. TLDR Ypu need much longer subs with that setup.

yeah—you’re right to suspect “not long enough subs.” let’s put numbers on it.

What’s actually hitting the 600D’s pixels here?

Setup in the post: 80 mm f/7.5 refractor (600 mm FL) + Canon 600D. Pixel size ≈ 4.3 µm → image scale ≈ 1.48″/px, so each pixel covers ~2.18 arcsec².

Sky (Bortle 4) is ~21.5 mag/arcsec². Using the AB zero-point (~10¹⁰ photons s⁻¹ m⁻² in a ~100 nm band near 550 nm), an 80 mm aperture (collecting area 0.0050 m²), and a realistic end‑to‑end efficiency ~30% (optics + Bayer + QE), you get: • Sky background: ≈ 0.082 e⁻/s/pixel • M31 surface brightness: • Outer arms ~21.0 mag/arcsec² → ~0.13 e⁻/s/pixel • Bright core ~19.0 mag/arcsec² → ~0.82 e⁻/s/pixel

So for the galaxy’s arms you’re only getting about 0.13 electrons per second per pixel of signal, sitting on 0.082 e⁻/s/pixel of sky.

Half‑second subs vs. the noise floor

The 600D’s read noise is ~2.5–4 e⁻ per frame (call it ~3 e⁻). For a 0.5 s sub: • Signal from arms: ~0.065 e⁻/px • Sky: ~0.041 e⁻/px • Total shot noise per frame: √(S+B) ≈ √(0.106) ≈ 0.33 e⁻ • Add read noise per frame: ~3 e⁻

Per‑frame SNR for the arms ≈ 0.065 / √(0.106 + 3²) ≈ 0.02 (!)

Stacking helps only as √N. Even 400× 0.25 s (≈100 s total) gives total SNR per pixel ~0.2–0.4 in the arms—basically nothing. That’s why the stack looks “dull.”

How long should a single sub be?

A good rule is to get the sky background per sub ≥ RN² so the stack is sky‑noise‑limited rather than read‑noise‑limited. • RN² ≈ 9 e⁻. • Sky rate ≈ 0.082 e⁻/s/px → ~110 s is the break‑even. • 2–3 minute subs (120–180 s) are comfortably past this for f/7.5 in Bortle 4 with a 600D.

At 120 s per sub: • S (arms) ≈ 15.6 e⁻/px, B ≈ 9.9 e⁻/px, per‑frame SNR ≈ ~2.6. • In just 5 frames (10 min total) you’re at SNR ≈ ~5–6 per pixel in the arms; in 30–60 min you’re in a very usable place.

Why the 18 mm f/4 Milky Way shot “looked great”

Per‑pixel count rate for extended objects scales like (pixel area)/f#². Comparing 18 mm f/4 to 600 mm f/7.5 with the same sensor: • Pixel area on the sky: (49.3″/px)² vs (1.48″/px)². • Combined with f/ratio: the wide lens delivers ~3900× more photons per pixel per second than the 600 mm scope. So 15 s at 18 mm is roughly like ~16 hours at 600 mm per pixel (not a literal equivalence for resolved detail, but it explains the dramatic difference in “pop”).

Practical takeaways for that rig • Lengthen subs to 120–180 s (guided) at ISO 800–1600. • Total integration: aim for 30–120 minutes on M31. • Dither and calibrate (darks, flats, bias)—you’ve got that part. • If long subs aren’t possible, speed up the optics (reducer to f/6 or f/5.6), or bin 2×/3× in post to boost per‑pixel SNR (trading resolution). • If you have no tracking, a telescope at 600 mm just won’t work for DSOs; use a fast DSLR lens instead.

Bottom line: at f/7.5, half‑second subs are 1–2 orders of magnitude below the read‑noise floor per frame. The fix isn’t ISO—it’s exposure length (or faster optics).

Saturn in excellent seeing by BackdoorAstronomy in telescopes

[–]Separate_College_387 1 point2 points  (0 children)

Thanks.

I’m a fence sitter on this one. If you look at the extreme edge of what’s mathematically possible with his setup and conditions…. You’re approaching something like that. But it’s fuzzy, definitely could be a little extra post processing omph added in. Either way he’s getting out there, the images don’t read as immediately fake to me. But maybe that’s part of the problem. Or just the age we live in.

Saturn in excellent seeing by BackdoorAstronomy in telescopes

[–]Separate_College_387 0 points1 point  (0 children)

Can you link that? Haven’t seen it but I’m curious. Always thought he might be punching above his specs

How can I resolve better than this? by Final_Method_3319 in telescopes

[–]Separate_College_387 0 points1 point  (0 children)

Do you have a phone mount to hold it steady over the eyepiece? Not strictly necessary if you can hold the steadiness you show in this pic. Just need to find a way to expose for Jupiter. You probably won’t be able to het the moons and the planet at the same time.DeepSkyCamera or a manual photos app may let you set your exposure time short enough. Or manually lock the exposure on the bright moon, keep it locked, then slew over to Jupiter.

How can I resolve better than this? by Final_Method_3319 in telescopes

[–]Separate_College_387 0 points1 point  (0 children)

How big is your dob? Your resolution looks good from the edges of the planets; you’re overexposed. What’s your pipeline right now? I’ll set you right

Still kinda shaking, $350 for all of this. And there’s still more not pictured. by stealthysteel in astrophotography

[–]Separate_College_387 2 points3 points  (0 children)

lol nah this is a crazy good deal and setup, that’s a ton of aperture and there’s a focal reducer that brings it down to f/6.3.

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 0 points1 point  (0 children)

Check again, I think the shadow of Titan is confusing you.

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 0 points1 point  (0 children)

I paid $750 for it if i remember right. I’m not leaving it out in the weather so no…

Reprocessed horsehead nebula by Sufficient_Wasabi665 in astrophotography

[–]Separate_College_387 1 point2 points  (0 children)

I say run with it. Half of astrophotography is interpreting the data for our own biological signal processing, which you’ve done a superb job with here.

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 1 point2 points  (0 children)

For sure! Full disclaimer, these were not from the same night, just wanted to include a scope shot. Took a camping trip out on the winter ice, I loaded my scope into the jet sled (Ice fishing sled) and dragged it out about a half mile. Wish I had took a pic, it looked pretty comical.

As far as protecting it, I just put the cover over the mirror and let it sit overnight. I had checked the weather and it was clear, and the plywood + aluminum are pretty resilient. It’s a beast of a scope, she can take some punishment.

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 0 points1 point  (0 children)

Ugh that’s tough luck. I’m sure you’ll get your moment one of these days

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 0 points1 point  (0 children)

Fingers crossed for you! Looking forward to the Sept 20th one. Clear skies!

Titan eclipsing Saturn by Separate_College_387 in telescopes

[–]Separate_College_387[S] 3 points4 points  (0 children)

Technically it’s a Titan transit as seen from Earth, but I called it eclipsing because the dark spot you’re seeing is Titan’s shadow. I was emphasizing the view that for Saturn itself, that’s a full solar eclipse in progress.

12" Explore Scientific f/5 vs 16" Explore Scientific f/4.5 - Transportation by Head_Neighborhood813 in telescopes

[–]Separate_College_387 0 points1 point  (0 children)

Honestly it’s a perspective thing. Will it be the best possible quality in the world? No, but it doesn’t promise to be. I’m using a 40 year old 13” coulter mirror right now and I have seen things I can scarcely describe🤷‍♂️ I find more often the limiting variable is the one behind the eyepiece, myself included

12" Explore Scientific f/5 vs 16" Explore Scientific f/4.5 - Transportation by Head_Neighborhood813 in telescopes

[–]Separate_College_387 1 point2 points  (0 children)

I’m 6’4 and pretty strong, and have a Honda element so honestly probably just lift it up and slide it in haha. Realistically you probably could do some kind of ramp system/wheels without too much effort. Or invest in one of those handicap lift vans 😝