11 replies to this topic

[Rustler46]

Here is a composite image from the 2015 Perseid meteor shower, one that I call "Polar Perseids". The shower radiant is outside the FOV on the right. It shows the result of a simple method of capturing meteors.

 

 

This was assembled from a series of 35-second exposures on a fixed tripod (no tracking). The lens was a fast, middle wide field lens - a Sony 35mm f/1.8. The technique is quite simple, at least for capturing the individual meteor trails. One just points a fast lens at the celestial pole. Polaris is near the center of the FOV, with the rest of Ursa Minor extending to the left. This allows for 35-second exposures with minimal star trailing. The longer exposure results in fewer individual frames that must be sorted through to find bright meteors. The number of meteor trails captured depends mostly on the lens aperture (19mm in this case) along with the focal length & sensor size (or equivalently the field of view covered). The length of exposure (35 seconds) is mostly irrelevant. Individual meteor trail exposure is set by the duration of the meteor, around a second (depending on the characteristics of the shower). Some showers produce fast and colorful meteors, like the Perseids. Others like the Geminids are slower and less colorful. One must balance field of view with aperture. Too wide a field (i.e. fisheye) results in small aperture (i.e. 3mm). While the entire sky is covered, only the very brightest ones will be well captured. So a focal length from perhaps 15 to 35 mm is a nice compromise. But it must be fast, that is large aperture.

 

Edit:

Important note:

In my opinion (we all have one, don't we), ​shoot wide open. Don't worry about what that might do to the background stars. You can always shoot a single separate background star image, stopped down to give nice star images. Individual meteor trails (with bad star background cropped out) will be added to the background image with nice stars. Any wide open lens aberrations will have little effect on the meteor trail. Since the meteor isn't a single point like a star, the worst effect will be a broadening of the trail's width. Better to have a slightly wider meteor trail than not getting one at all, or having the trail be weak. You want to gather the most light possible for a swiftly moving piece of sand blasting into Earth's atmosphere. So my best advice is shoot wide open!

 

The only complicated part is assembling the composite image, showing all of the bright meteor trails captured during the shower. I will supply the technique used for that in later replies to this thread. But the overall simple process can produce some nice results that could be employed in the upcoming Geminid meteor shower. Most years this one is the best shower.

 

Clear Skies,

Russ

Edited by Rustler46, 28 November 2020 - 12:00 AM.

[iwannabswiss]

Here is a composite image from the 2015 Perseid meteor shower. This shows the result of a simple method of capturing meteors.

 

All I see are clouds. 

[Rustler46]

The number of meteor trails captured depends mostly on the lens aperture (19mm in this case) and the focal length (or equivalently the field of view covered). One must balance field of view with aperture. Too wide a field (i.e. fisheye) results in small aperture (i.e. 3mm). While the entire sky is covered, only the very brightest ones will be well captured. So a focal length from perhaps 15 to 35 mm is a nice compromise. But it must be fast, that is large aperture.

Here's an example of using a wide field but small aperture lens, this one from the 2017 Geminid shower.

 

 

The lens was a Samyang 8mm fisheye, f/2.8 (less than 3mm aperture). Wide field yes, but slow. So only the brightest meteors were captured. This composite was from two night's observing, over 800 individual frames.

 

Russ

[Sheol]

       Man, those are really nice! I see the typical yellow color of the Perseids, plus a red one or two. The Geminids are looking more white or blue. Is this typical for them?

Again a shower I must check out, weather allowing.

 

           Clear Skies,

            Matt.

[Rustler46]

       Man, those are really nice! I see the typical yellow color of the Perseids, plus a red one or two. The Geminids are looking more white or blue. Is this typical for them?

Again a shower I must check out, weather allowing.

 

           Clear Skies,

            Matt.

Thanks, Mat. I must admit to shamelessly boosting color and saturation of the meteor trails. I do whatever is necessary to make the trail stand out better, more contrast or color. For certain colors to be seen, the meteor must have a minimum velocity. The average velocity varies among the showers. Here is a good resource for that:

• 2020 METEOR SHOWER LIST

Of the two best showers of the year, the Perseids  (59 km/sec) are more colorful than the Geminids (33 km/sec). The following are good resources:

• Wiki - Meteoroid
• HOW TO PHOTOGRAPH METEORS WITH A DSLR

These are fascinating solar system objects. So Sunday night, December 13/14 is the peak for the Geminids. A day or two before will also produce goodly number. But after the peak it very quickly subsides.

 

I hope many of us can have clear skies. Dress for the cold temperatures. I plan on foregoing photography this time. My wife has taken the next day off from work. So we'll go to our dark site with lounge-chairs and warm sleeping bags to watch the show.

 

Best Regards,

Russ

Edited by Rustler46, 27 November 2020 - 08:02 PM.

[iwannabswiss]

Those are some beautiful shots.

[Rustler46]

Thanks for your kind comment iwannabswiss.

Edited by Rustler46, 28 November 2020 - 04:26 PM.

[Rustler46]

The only complicated part is assembling the composite image, showing all of the bright meteor trails captured during the shower. I will supply the technique used for that in later replies to this thread. But the overall simple process can produce some nice results that could be employed in the upcoming Geminid meteor shower. Most years this one is the best shower.

Directions for Making Composite meteor shower image

1. Capture background image, perhaps a stack of multiple frames. This can be with lens stopped down a bit to improve edge of field star images. This should be captured at a time midway through your meteor capture period.
2. Capture a continuous series of meteor capture frames, wide open, moderate ISO.
3. Sort through the many meteor capture frames to find the frames that actually captured a meteor. In the image I shared of the 2017 Geminid Meteor shower there were around 80 out over 800 frames that actually had a meteor.
4. Process each meteor frame to emphasize the meteor trail. Increasing contrast and boosting color can often help in this regard. You can largely ignore what this does to the stars in the background because these will not be included in the final composite. I use Adobe Lightroom-5 for this step.
5. In a photo processing program with layers capability start with your background stars layer. I use Photoshop Elements 2.0 - a very old version.
6. For each meteor containing frame add that as another layer.
7. For that layer change the "opacity" to 50%. This is so that you can see through the meteor layer into the background layer.
8. Rotate and move the meteor layer until the bright stars in it match then location of the bright stars seen in the background layer. This will be particularly necessary if you were not tracking. But even with tracking there could be some minor adjustments needed. Without tracking each frame will have rotated with respect to frames captured at different times. So this step adjusts all meteor trails to match the background frame orientation.
9. In the meteor layer draw a selection line tightly around the meteor trail. This selects the meteor trail.
10. Select "Invert Selection" which selects everything on the meteor frame except the meteor trail.
11. Delete the selected background stars in the meteor frame. You now have a single meteor trail that has been rotated to match the background frame.
12. Remember to change opacity back to 100%. Otherwise the meteor trail will be weaker.
13. This meteor trail can be merged down (copied onto) the background frame. But l like to keep a separate meteors layer, along with the background layer. So the first meteor created in this step can be the basis for the meteors layer. See * below.
14. Repeat steps 6 through 13 for each addition meteor containing frame. Merge each added meteor down into the meteors layer. This will be necessary to avoid having (for example) 50 layers for the 50 meteors you captured.
15. When you have done this for all your captured meteors you should have just two layers - meteors and background. Each meteor will have been rotated to match the background.
16. Save this result in two forms - one file with meteor and background layers (photoshop file format) and second file with all layers merged together in a single frame. The best file format would be something like TIFF. JPEG is lower quality. So save in different file types to see what works best for you.
17. Post process your final composite image in your favorite program. I like Adobe Lightroom-5.

* In step 13, you might want to keep a separate layer for sporadic (non-shower) meteors. That way you can include or exclude sporadics in different versions of your final image.

 

It sounds complicated. But once you do it a few times it isn't that hard. But it is time consuming. So the single frame meteor capture (not composite) method is much easier. But the composite method can often produce a nice single image record of the meteor shower.

 

Best Regards,

Russ

Edited by Rustler46, 28 November 2020 - 04:36 PM.

[Rustler46]

Important note:

In my opinion (we all have one, don't we), ​shoot wide open. Don't worry about what that might do to the background stars. You can always shoot a single separate background star image, stopped down to give nice star images. Individual meteor trails (with bad star background cropped out) will be added to the background image with nice stars. Any wide open lens aberrations will have little effect on the meteor trail. Since the meteor isn't a single point like a star, the worst effect will be a broadening of the trail's width. Better to have a slightly wider meteor trail than not getting one at all, or having the trail be weak. You want to gather the most light possible for a swiftly moving piece of sand blasting into Earth's atmosphere. So my best advice is shoot wide open!

 

The only complicated part is assembling the composite image, showing all of the bright meteor trails captured during the shower. I will supply the technique used for that in later replies to this thread. But the overall simple process can produce some nice results that could be employed in the upcoming Geminid meteor shower. Most years this one is the best shower.

I realized that I have yet to completely processing my images from this year's Perseids. To illustrate the above note, here is an image taken with a 50 year old film-era lens - a Mamiya-Sekor 55mm, f/1.4 (with Pentax screw mount). The FOV shows the familiar W of Cassiopeia.

 

 

While lens aberrations make the stars atrocious, the 39mm aperture gathers a lot of light to give a strong meteor trail. Seagull stars will be cropped away, leaving only the meteor to add to the composite. The drawback here is the field of view covers far fewer square degrees of sky, compared to the 35mm f/1.8 lens. 

 

Next I'll show the same lens stopped down, used to capture a nice background image for the composite.

Edited by Rustler46, 28 November 2020 - 08:16 PM.

[Rustler46]

While lens aberrations make the stars atrocious, the 39mm aperture gathers a lot of light to give a strong meteor trail. Seagull stars will be cropped away, leaving only the meteor to add to the composite. The drawback here is the field of view covers far fewer square degrees of sky, compared to the 35mm f/1.8 lens. 

 

Next I'll show the same lens stopped down, used to capture a nice background image for the composite.

This background image was taken at f/2.8, which greatly improves star images, but is poor at catching swift-moving meteors.

 

This will form a suitable background for several Perseids captured this year. Notice it captures some DSOs, like NGC 7789, "Caroline's Rose" open cluster in upper right.

 

I've learned with these longer focal lengths pointing at the radiant is a mistake. It's better to point away from that area where the trails are longer and more numerous. 

Edited by Rustler46, 29 November 2020 - 01:46 AM.

[Rustler46]

Heres a composite using the same lens of the 2016 Perseid shower.

 

[Rustler46]

I realized that I have yet to completely processing my images from this year's Perseids. To illustrate the above note, here is an image taken with a 50 year old film-era lens - a Mamiya-Sekor 55mm, f/1.4 (with Pentax screw mount). The FOV shows the familiar W of Cassiopeia.

 

Screen Shot 2020-11-28 at 3.51.07 PM.jpg

 

While lens aberrations make the stars atrocious, the 39mm aperture gathers a lot of light to give a strong meteor trail. Seagull stars will be cropped away, leaving only the meteor to add to the composite. The drawback here is the field of view covers far fewer square degrees of sky, compared to the 35mm f/1.8 lens. 

Here's some research I did on these two lenses:

• Mamiya 55 mm, f/1.4
  • Aperture = 39.3 mm
  • Aperture area = 1213 mm²
  • Field of view - 24.0° x 16.2°
  • FOV = 389 square degrees
• Sony 35 mm, f/1.8
  • Aperture = 19.4 mm
  • Aperture area = 296 mm²
  • Field of view - 36.9° x 25.1°
  • FOV = 926 square degrees)

Now using these figures the relative light-gathering power of these lenses is given by the ratio of the aperture areas.

• (Aperture Area 55 mm) ÷ (Aperture Area 35 mm) = 1213 ÷ 296 = 4.10

This means the larger aperture gathers 4.1 times as much light as the smaller aperture. Using an external magnitude calculator the difference in star brightness is 1.23 magnitudes. In other words with a given exposure, the larger aperture will reach 1.23 magnitudes fainter. I suspect the actual difference would be less considering the poorer star images given by the 55 mm lens. Fainter stars would be spread out by lens aberrations, becoming less discernible. 

 

The ratio of FOV areas is another measure:

• (35 mm FOV area) ÷ (55 mm FOV area) = 926 ÷ 389 = 2.38

So the wider lens covers over twice the area in the sky. While this doesn't compensate for the narrow lens' greater aperture, I still think the wider lens is better by far in capturing meteors. That is what my experience has shown.

 

Roger Clark in Clarkvision.com has done an extensive job in evaluating lenses for meteor photography.

 

Russ

Edited by Rustler46, 30 November 2020 - 05:41 PM.