Jump to content

Lunar eclipse and supermoon this month


Recommended Posts

I'm not much of an astro photographer but some people here certainly are! I would have to assume that if you wanted to photograph the night sky effectively, you would want to find the highest spot you can.

 

"It will also be one of the few times when you’ll be able to photograph the moon and stars simultaneously. While it will be a deep blood red, the contrast difference will be low enough that cameras will be able to pick up stars in the background."

 

Link:

 

So, those of you who are astro photographers, answer me this: what is the longest exposure you can take, while tracking the moon, before the stars become perceptively blurred? Does it matter in which hemisphere the camera is? Does it matter what direction you point the camera?

Link to comment
Share on other sites

The longest exposure time you can take, without a tracking device, is roughly 500/F seconds, where F is the focal length of the lens. Some people prefer to use 300/F. There will be some star trailing, but barely noticeable in an 8x10". print. With a motorized tracking device, you can expose up to about 5 minutes before residual errors spoil the results. Above 400 mm or so, you will need lunar tracking to compensate for the moon's orbital motion. This will be at the expense of longer star trails. To fill the frame (short side) with the moon, you need a focal length of about 2500 mm.

 

The closer you point to the astronomical equator, the greater the effect of earth's rotation, regardless of which hemisphere. When tracking, the axis of rotation must be parallel to that of the earth, i.e., pointed toward the pole. In the north, the reference is Polaris, which is nearly 1/3 degree from the true pole. In the Southern Hemisphere, use Sigma Octantis, which is over a degree off axis. You can approximate this setting using a digital level, and a compass which indicates true north (magnetic north is as much as 20 degrees off at mid-latitudes. That's the angular size of the constellation Orion. The moon is about 1/2 deg wide.

 

The luminosity of a full moon will overwhelm all but the brightest stars. I have no idea what the exposure of the eclipsed moon would be. Hopefully someone can fill in the details. A lunar eclipse lasts a long time, so you can experiment freely.

 

A lot depends on how you wish to present the eclipse. If you want a closeup for surface detail, you aren't likely to have many stars in the background. If you want a time lapse with foreground, you need a lens wide enough to include the moon and foreground, typically 35 mm or less. Another possibility is a stacked photo, with separate exposures for moon, stars and foreground.

 

Seeking high ground is probably not necessary if you have a clear view of the sky, good weather and minimal light pollution. In Illinois, "high ground" means another state.

 

The app, "Photo Pills" is very helpful for astrophotography, giving your latitude and with suggestions for exposure and focal length. Other applications will tell you where astronomical objects are located. "Night Sky" uses virtual reality, so you can point the phone in any direction and see these objects on the display.

  • Like 5
Link to comment
Share on other sites

Ed, that's a wonderful answer. I want to go a bit further on the advice against seeking higher elevation. Although astronomical observatories are typically located in mountains, the sites are chosen very carefully, as peaks are often covered in clouds when the surrounding areas are clear. If you're going to leave home for this shoot, heed Ed's advice about light pollution and get away from city lights.
  • Like 2
Link to comment
Share on other sites

" to include the moon and foreground, typically 35 mm or less. Another possibility is a stacked photo, with separate exposures for moon, stars and foreground."

 

Be aware that the moon takes up 1/2 a degree of arc in the sky. The angle of view of a 35mm lens on a 35mm camera is about 65 degrees on the diagonal. So, your moon will look VERY small. Were I to take photos of the moon and include foreground, Ed's suggestion about stacking the photos is good. Or, pick a location where a long lens can be used and get the foreground included, but that presupposes that the foreground will be bright enough as a full moon (not eclipsed) is a sun lit object, meaning that the sunny 16 rule applies.

 

I'd recommend a lens of at least 300mm. And do take several exposures.

 

Attached is a photo I took long ago, The moon was taken with an old pre-set 450mm Soligor f8. The angle of view would be about 6 degrees. Exposure time would have been about a 60th of a second, but that's a guess as it has been many years. The exposure of the refinery was several seconds as can be seen by the blinking lights of an airplane. The photo is "stacked" in that the two images were double exposed in a slide duplicator.

 

Image1.jpg.c00b5def212cbf5eb38bdadb18614f17.jpg

  • Like 5
Link to comment
Share on other sites

1665003124_lunareclipse.thumb.jpg.a28ac4a9a4fa871ff8b10ad73588afd4.jpg

 

I do not have many photos of a lunar eclipse that I would call very good, but this one was taken at 0.4s, f:4.0, ISO 1000, This should point you to a ball-park exposure. It's not like a total solar eclipse in that you have plenty of time to dial in the proper exposure and find a suitable composition while the eclipse is in progress. Here, the sky was clear, so I stayed in the mountains.

  • Like 1
Link to comment
Share on other sites

It is my intention to buy a small (4") Maksutov telescope, which is light enough to use with my iOptric tracker. If the weather is good on the 20th, all the better. If not, there are 0ver 100 Messier objects, well within the capability of a 4" reflector, which I would like to start ticking off my bucket list. It has a mount for a camera, which will permits its use as a super telephoto. Outdoors, on a sunny day, convection currents render the image quality of a 1000+ mm lens. pretty much like wearing eyeglasses in a shower, but whatever.

 

I've wanted to do this for years - over 60 years to be exact. Don't ask me why I waited

  • Like 1
Link to comment
Share on other sites

  • 2 weeks later...
Got up at four a.m., went out to find a foggy day, not even a glow where the moon might have been. Couldn't get back to sleep, now up with a headache and a strong desire to slaughter the first person who annoys me. Since this is generally 99% of the human race, look out for me on the news later ! :mad::eek::(:(:(
Link to comment
Share on other sites

I bought a telescope (4" Maksutov) and used it with an iOptron SkyGuide. In lieu of an intervalometer, I decided to film a sequence in 4K video. Afterwards, about 20 minutes from totality, I took a few stills and went inside to warm up. The sky was clear, the seeing (turbulence) minimal), but the temperature was 4 deg F and dropping. The iOptron has settings for solar and lunar tracking, in addition to sidereal (star) tracking. None account for variations in the earth's orbital speed, which is at a maximum in mid-January.

 

Tracking was good up to 30 minutes, but the sky was too bright to nail the tracker setup. I used a digital protractor and true north compass instead. When arc-minutes count, I was good to degrees. The focus drifted significantly as the telescope warmed up. It took about 30 minutes for it to settle down. Exposure was dicey. Even a small sliver of white blasts the dark part to oblivion. For the full moon, I used 1/100 at ISO 100. For the dark, see below, a still shot taken about 20 minutes before totality. The bright spot is actually the penumbral region, not full sunlight.

 

Sony A7Riii + "Sky Watcher" 4" Maksutov telescope, 1/8 second @ f/12.7 (fixed), ISO 25600 - out of the camera, no enhancement (yet).

_7R34037.jpg.3729c757334dba2730bf4911b9a96fae.jpg

  • Like 5
Link to comment
Share on other sites

Having read that the optimal time for viewing the eclipse was last night at about 9:40PM, I first went out at 10:00, then 11:00, then 12:00. The last time I finally saw the eclipse, but it hadn't yet reached its fullest. So, being too lazy and tired to go back inside to get my tripod, I took a couple of shots handheld. If anyone has even a hint of interest in how the best one turned out, you can see it posted soon for critique in the abstract category.
Link to comment
Share on other sites

Here is a (daylight) photo of the rig I used. For visual observation at low power (30-60x), I find a fluid head for video ideal. Without tracking, it takes objects about 5 minutes to traverse the field of view, so re-positioning, looking and snapping is no big deal.

 

The iOptron SkyGuider tracker comes with the alt-azimuth polar mount, declination bracket and counterweight. It is a brick outhouse compared to the earlier (and still available) SkyTracker, which is rated for only 2.5 lbs (5.5 lbs with counterweight kit @ $80). The polar axis has a clutch, for easy balancing and setting right-ascension. The mount pivots for setting declination.

 

Even at 4 deg F, batteries in the A7Riii lasted an hour with 25% reserve, shooting 4K video, comparable to that under comfort conditions. The 30 minute video clip limit is a bummer. There's no way to change batteries or stop/start the recording without causing a major disturbance to the image. The solution to both would be to use an external, HDMI recorder, which has no arbitrary limits, and batteries which last 2.5 hours to over 9 hours (Anton Bauer rig). Without internal recording, the camera battery last about 3 hours, 10 hours with an external source.

 

_A9_6874_AuroraHDR2019-edit.thumb.jpg.3be8f4678cb7181f1be467a2727338c1.jpg

Edited by Ed_Ingold
  • Like 4
Link to comment
Share on other sites

BTW the A6400 has no time limit for video, AFAIK. FWIW.

Hurrah! I'd pay for Sony to unlock their cameras. Other companies have done that, restricted to a particular camera.

 

You don't need a tracker for visual observation, but you may need to readjust frequently to keep the object in view. the earth's rotation amounts to 4 arc-minutes per minute. Nor do you need tracking if your exposures are short enough. The general rule is 500/FL (or less, for high resolution sensors). 10 seconds, using a 25 mm lens with a 42 MP sensors, stretches star images about about 3 pixels. You need to "peep" to see that effect.

 

The telescope above is relatively inexpensive, and has pretty much everything you need to get started. It includes two eyepieces (52x and 130x), a star diagonal (for easier viewing), and a handy carrying case. I bought the 102 mm (4") because it is the largest telescope I can use with the tracker, yet easily portable. It gathers about 30% more light than the 90 mm (3.5") version. When I was in high school, a similar telescope cost over $1000 ($5000 in today's money). Popularity and improved manufacturing methods have greatly reduced the cost. The mirrors and corrector plate use spherical surfaces, and may be molded, rather than ground, to shape. It sure beats spending three weeks grinding a parabola into a 7 pound piece of glass and mounting it in a carpet tube (or newsprint core).

 

The camera and T-mount cost an additional $25. It mounts directly on the telescope, without an eyepiece.

 

(star watcher) 102mm | B&H Photo Video

 

This is something I've wanted to do since elementary school, but never had the money or the time. I didn't want to pour money into this project until I knew it was something I'd like, and small enough and easily assembled to take with me on a whim. You don't need high power. Most objects in the sky are bigger than you think. The moon is 0.5 deg, the Orion nebula is 0.7 deg, and the Andromeda galaxy (M31) subtends over 2 degrees. Planets need higher magnification to see any details, but you can barely see the rings of Saturn, the Galilean moons and bands of Jupitar, and the polar ice caps on Mars at 50x.

Edited by Ed_Ingold
  • Like 3
Link to comment
Share on other sites

Setting the exposure proved to be much harder than I anticipated. In general, you use manual settings in astrophotography, but that doesn't work well for video. The portion of moon in full sunlight is about 1000x as bright as the part in shadow. An eclipse is not something you have the opportunity to practice with. Still photography is easier, but you need to check the histogram. With everything around. you so dark, the viewfinder looks blown out even when the exposure is correct.

 

The best auto exposure probably uses the spot meter, but only if tracking were good enough to keep it centered on the moon. It wouldn't be a smooth transition, because even the penumbral eclipse, which you see as the bright top-left edge of the moon, is so much brighter than the fully eclipsed part. However it wouldn't jerk around as occurs with even careful handling to change the settings.

 

"Better luck next time," I tell myself. We'll see how it goes in 2021. Meanwhile, there are a lot of interesting things in the sky that aren't so transient.

Link to comment
Share on other sites

Ed, very well done. I like it. I was really disappointed in myself for not having taken the time to sort out the new D810 for mounting to our older telescope. The weather predicted here did not bode well for viewing, and I was feeling lazy. As it was I managed a few images using the 200-500, but focus was difficult to nail, the wind was blowing, and I need more practice. Still, I've posted a few that are illustrative.
Link to comment
Share on other sites

Difficulty focusing could have been due to atmospheric turbulence, which usually accompanies even a light wind at ground level. Similar problems occur during the day for terrestrial viewing due to convection currents cause by the sun. I was not able to get the best focus on the moon with my telescope. By comparison, ground level objects that night were extremely sharp and clear. A full moon is not the best time to see details of craters, whereas they stand in sharp detail near the night/day border for a partial moon. Things to look for include the lunar Apennine Mountains, near the top center, and a peculiar object on the nearby plain called The Piton.

 

The moon is so bright through even a small telescope it obscures many details. On recommendations found on line, I have ordered an ND filter for that purpose ($17).

 

If you're looking for footprints, remember at 42 MP and 1300 mm, each pixel represents 1-1/2 miles. Conversely, you can't see the Great Wall of China from the moon. At Badaling it's less than 20' wide and only exists in short sections.

  • Like 1
Link to comment
Share on other sites

The moon is so bright through even a small telescope it obscures many details.

My astrophoto adapter kit includes a T-adapter, Barlow lens, and a set of filters, including a "moon" filter to bring the brightness under control. I need to get this rig worked out with the D810 (APSC sensors are too small for the best image circle, with the moon exceeding the sensor size). I'm looking forward to the next go-around.

Link to comment
Share on other sites

This begs the question "Why did I use such a high ISO?" In brief, my fingers weren't the only things numbed by the cold. I combined Aperture Priority and Auto ISO for exposure control. I was using a tripod, and could have easily exposed for as long a 10 seconds, but the camera decided to use 1/33 second. And so it goes. Hopefully others can learn from my mistakes. What a hoot of a project, though.
  • Like 2
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...