17 replies to this topic

[Marcin_78]

Once again I used my inexpensive astrophotography equipment just for fun. This time I took some pictures of high-flying planes using just an astro camera and a telescope on a simple alt-azimuth mount. Well they were actually two different telescopes on two different alt-azimuth mounts, so you can see it's possible with different kinds of telescopes.

 

My home city lies very far from any decent airport (over 100 km to the nearest such one), so almost every plane that I can see is flying at a cruising altitude of at least 10 km (32800 ft). The crucial things for me to succeed were (1) using a focal reducer 0.5x (in order to get a bigger field of view) and (2) using the program FireCapture_v2.7 in the timelapse mode, with the minimum possible delay of 1 second.

 

Thanks to the timelapse mode I don’t need a “third hand”, nor anybody else to push the “capture button” while I am moving my telescope (aiming at a plane) and setting/correcting the focus. It’s actually good to set the focus in advance while aiming at clouds that are roughly in the direction where the plane should appear (you can predict it thanks to the site www.flightradar24.com), but don’t expect to find perfect focus this way. Well, don’t expect to find perfect focus EVER, so you won’t be disappointed. And forget about all the plane-spotting pictures (that are all over the net) taken with expensive non-astro cameras.

 

I used two different telescopes, so the results vary significantly. The difference is actually overblown because the planes pictured with my 70/700 refractor were very far (first two pictures), while the plane pictured with my 102/1300 Mak (Maksutov-Cassegrain) was very close (third picture).

 

The original pictures were 1920x1080 pixels, so they were too big to be posted here and this is why I cropped them to 1600x1080 pixels.

 

Click to enlarge!

 

 

 

 

By the way, has anybody any idea what kind of plane is the last one? And what are the circles on its belly?

 

Aiming with the refractor was much easier than with the Mak, for two different reasons. First reason is that the refractor is physically longer, so there is more precision to its movements. Second reason, more important, is that the field of view is almost twice as big (with the same camera) because it has a much smaller focal length (700 vs. 1300). It's worth to point out that the field of view AREA is actually 3.45x as big ((1300/700)^2), so it's a BIG difference. But a particular plane at a particular distance will be proportionally bigger on the picture taken with the Mak, so it's a double-edge sword.

 

I attempted also several other planes, but the results were either weak or non-existent because:
1. The initial focus was very bad and I couldn’t fix it in time while keeping the plane in the field of view.
2. The plane was practically invisible because the sun was on the “wrong side”.
3. The plane didn’t leave any contrails and I couldn’t “find it” at all with a telescope.

 

I have to point out that I used my better (more expensive, but still affordable) astro camera ZWO ASI 482MC-S (sensor pixel size 5.8 µm) because it has a much bigger field of view (with a particular telescope). This camera, combined with a reducer 0.5x (official reduction factor) and with my refractor gives me more than 1.8 degrees field of view. With my Mak it's almost 1 degree.

 

 

Now it's time for some math. The crucial questions (and answers) are these:

 

How can I predict the size of a plane in pixels on a captured picture? By dividing the angular size of the plane in arcseconds by the equipment resolution in arcs/pixel.
How can I predict the angular size of the plane? By using my formulas that I described here:

https://www.cloudyni...ing/?p=12775631

 

The example in that post of mine was made for:
1) a plane 35m big,
2) flying at the altitude of almost exactly 10km,
3) being 10km away (horizontally).

 

The two distances created almost exactly a square 10km x 10km, so the view angle (when looking at the plane) was almost exactly 45 degrees above the horizon.

 

At the bottom of that example there was the angular size of the plane (8.509 arcminutes), so the size in arcseconds was 510.54 arcseconds (8.509 arcminutes * 60 arcseconds/arcminute).

 

Now we can calculate the size of plane in pixels:

 

Refractor:
Plane size in pixels = 510.54 arcseconds / 3.42 arcs/pixel = 149 pixels

 

Mak:
Plane size in pixels = 510.54 arcseconds / 1.84 arcs/pixel = 277 pixels

 

The result for the Mak is very close to the actual plane size in pixels on the picture taken with the Mak (third picture). The result for the refractor is much bigger than on the pictures taken with the refractor (first and second pictures), simply because the planes were much farther away than 10km.

 

I can't post any more pictures here, so I will continue in another post.

Edited by Marcin_78, 16 April 2024 - 01:20 PM.

[Marcin_78]

There's no time to make such calculations on the fly, but it's good to make some tables in a spreadsheet to roughly know what to expect from different planes being at different distances (horizontally). Here, I will save you some time:

 

 

One thing I can't help you with is a cheat-sheet for distances – it has to be done for a particular location like this:

 

 

From my own experience I can say that any plane within the smaller circle (20km radius from my location) is great. And any plane outside the bigger circle (40km radius) is usually invisible or very weak because it's very low above the horizon, so there is lots of air in the way.

 

It was very fun and my 9-year-old son enjoyed helping me (he was using the site www.flightradar24.com on my smartphone). I will definitely do it again. The next time I will use the refractor with the same camera, but without the reducer (the FOV will be similar to the FOV in the Mak with the reducer, but the refractor is easier to operate).

 

Clear skies!

Edited by Marcin_78, 16 April 2024 - 01:52 PM.

[Echolight]

Looks a lot like a Boeing 757.

 

...looking again, maybe a 737 Next Generation.

https://en.m.wikiped...Next_Generation

 

Those circles are likely air currents. Notice the projection from the bottom of the plane about where the most forward circle is.

 

Edited by Echolight, 18 April 2024 - 06:09 PM.

[BlueRidgeSky]

https://globe.adsbexchange.com/

 

International flight tracker. Fun to play with and see what is flying over. Click on a plane and it tells some stuff about it. Maybe next time you can see what is flying overhead.

 

Edit: Should probably say worldwide flight tracker instead of international.

Edited by BlueRidgeSky, 24 April 2024 - 09:35 AM.

[Marcin_78]

(...) Click on a plane and it tells some stuff about it. Maybe next time you can see what is flying overhead. (...)

 

The site flightradar24.com allows that too, but I was generally focused on preparing for another plane and I wasn't checking and writing down any plane info then. The next time I will try to write down as much info as can, including the info about the distance to a plane, so I can verify how precise my calculations are.

 

As for the site globe.adsbexchange.com I must say that it is very good and the info about planes is very concise visually – on my computer I don't even have to scroll down at all in order to check the most important info, except for the destination (apparently there is no info about destination on that site at all). Thanks!

 

EDIT: I LOVE the site globe.adsbexchange.com because the planes' colors show right away (without clicking/selecting a plane) which plane is at which altitude! GREAT for my purposes! THANKS again!

Edited by Marcin_78, 24 April 2024 - 03:32 PM.

[BlueRidgeSky]

A site that combines the info from both would be nice.

 

Edit: And combine the way all the info is presented. 

Edited by BlueRidgeSky, 25 April 2024 - 11:13 AM.

[Rutilus]

The plane looks very much like a Boeing 737 Max 8, operated by the airline Ryanair  (Dublin Ireland).

I'm in the U.K., and on the flight path from Dublin, Liverpool, Manchester and Leeds Bradford airport.

I see them all the time, their blue and yellow livery shows up well in binoculars and photos..  

[Marcin_78]

(...) The next time I will use the refractor with the same camera, but without the reducer (the FOV will be similar to the FOV in the Mak with the reducer, but the refractor is easier to operate). (...)

 

I didn't do it because I didn't want to use the refractor (70/700) with the focuser racked very far out in order to compensate for the lack of a mirror diagonal. The backfocus of the reducer “cancels” the difference of the missing mirror diagonal and I wanted to stick with that.

 

Nevertheless, I still wanted to get more details out of the planes, so I did something that I had been pondering about as far as the planets were concerned – I bought a new (planetary) camera (ZWO ASI 715MC) with a very small sensor pixel size (1.45 µm). I hadn't bought it earlier because I didn't want to spend my money just for imaging 4 planets from time to time. My planespotting hobby changed it completely – now I have a HUGE number of targets I can go after!

 

Here are some (cropped and slightly processed) pictures of planes taken with the new camera (ZWO ASI 715MC), combined with the refractor (70/700) and the focal reducer (0.5x):

 

 

 

 

 

My new camera allowed me to greatly improve the resolution in arcs/pixel while still using the refractor with the reducer:
 

 

Please notice that I wouldn't use the Mak with the new camera because the field of view would be definitely too small for planespotting (although the resolutions in arcs/pixel would be even better):
 

 

I have to also point out that all the pictures above were SLIGHTLY processed in GIMP (Color Curves and a very delicate sharpening) because this time I took all the pictures as monochromatic pictures, but after debayering they all turned out kind of weird/poor and I HAD to “smooth them out”.

 

The worst thing, however, was that a single monochromatic JPG was VERY BIG (much bigger than I expected). Later I did some experimenting and I discovered that a single monochromatic JPG is ALWAYS significantly bigger (by at least 60%, but in some cases much more) than a color JPG! It's probably because on a monochromatic picture there is hardly any compression typical of JPGs due to big differences between adjacent pixels.

 

In the next post I will present pictures of planes taken with the same setup (ZWO ASI 715MC + 70/700 refractor + focal reducer 0.5x), but with the Debayer algorithm Bilinear (that is clearly better than NearestNeighbor) used right during capturing (in the program FireCapture_v2.7.14), exactly like I had done it with the pictures in the post # 1, but this time with the new camera.

 

EDIT:

 

The colors on the first screenshot above connect things in a way that means “in spite of”, so the new camera gives:
1 – green color) big enough FOV in spite of using the reducer,
2 – yellow color) very good resolution in arcs/pixel in spite of small aperture.

 

In reality aperture influences the Dawes Limit (also present on the screenshot above), but in this case the resolution in arcs/pixel is still within acceptable limits – around 1/2nd of the Dawes Limit (0.85 / 1.66 = 0.512).

 

According to the FAQ on the planetary-imaging sub-forum it's good for seeing that is a little better than “ok-to-fair seeing” – the rules of thumbs in the FAQ are based on the sensor pixel size):
1) focal ratio for “ok-to-fair seeing” = 1.45 * 3 = 4.35
2) focal ratio for “good seeing” = 1.45 * 5 = 7.25
3) focal ratio for “excellent seeing” = 1.45 * 7 = 10.15

 

My focal ratio with the reducer 0.5x was 5 (f/5), so almost exactly half of the maximum useful focal ratio (for “excellent seeing”).

Edited by Marcin_78, 15 May 2024 - 09:39 AM.

[Marcin_78]

(...)

 

The colors on the first screenshot above connect things in a way that means “in spite of”, so the new camera gives:
1 – green color) big enough FOV in spite of using the reducer,

 

(...)

 

I messed it up. Obviously a big enough FOV is possible thanks to the reducer, not in spite of it.

[Marcin_78]

(...)

 

In the next post I will present pictures of planes taken with the same setup (ZWO ASI 715MC + 70/700 refractor + focal reducer 0.5x), but with the Debayer algorithm Bilinear (that is clearly better than NearestNeighbor) used right during capturing (in the program FireCapture_v2.7.14), exactly like I had done it with the pictures in the post # 1, but this time with the new camera.

 

(...)

 

Before I post any new pictures I have to add some additional comments on debayering, if anybody (a potential newcomer) were interested.

 

The program Registax6 probably uses a poor Debayer algorithm NearestNeighbor, but it is not really specified. Reportedly the program AutoStakkert is better for debayering, but I don't know how to save a color picture. When I use the option “Export Frame(s) As displayed here” the saved file is still monochromatic, even though it was displayed as a color one. No idea why.

 

The program FireCapture is simply fantastic because it has lots of different Debayer algorithms. Obviously the more advanced they are, the more time and the more CPU usage they require for debayering, but the Debayer algorithm Bilinear is more than good enough for me. On the Wikipedia site Bicubic_interpolation there are great visual examples how different debayering algorithms work. To me the Bilinear algorithm seems to be the most natural one anyway.

Edited by Marcin_78, 16 May 2024 - 03:27 AM.

[Marcin_78]

All (cropped) pictures below were taken as color JPGs (Debayer algorithm Bilinear in the program FireCapture_v2.7.14) with the equipment combination: the camera ZWO ASI 715MC + 70/700 refractor + focal reducer 0.5x. I used a very short shutter speed of slightly less than 0.5ms because the planes are generally moving very fast across the sky, even when they are at very high altitudes. When it's getting darker (around sunset) I increase gain to make the view a little brighter, but it's very hard to “guess” a proper gain setting in advance (especially already AFTER sunset), so I ended up with some pictures being underexposed or overexposed.

 

Because of the unpredictability of the brightness of the view I (slightly) processed every picture in the program GIMP by changing (slightly) the Color Curves (either for brightening or for darkening the view). I don't use sharpening at all because it introduces more noise (or rather enhances what noise there already is). Additional notes are below the pictures.

 

 

 

 

 

 

 

I can't attach any more pictures here, so I will continue in the next post.

Edited by Marcin_78, 16 May 2024 - 03:15 AM.

[Marcin_78]

 

 

 

 

This time I was more lucky and there were more planes flying close to my home city, but there was only one flying almost directly above me (previously there were 3 such planes). This closest plane ended up being the biggest (and most detailed) so far – 680 pixels!

 

The visibility was great and the range at which I could clearly see a plane's contrails was remarkable. There were 2 cases when I was really surprised that I could clearly see the contrails of a plane that was AT LEAST 60km away. At such distance a plane is only (around) 10 degrees above the horizon (the precise angle depends also on its altitude), so there is lots of air in the way. When I was using the site globe.adsbexchange.com I had discarded the planes (previously such distant planes were completely invisible probably because of bad transparency), so I saw them without even looking for them (this is why it was so surprising).

 

I started the imaging session 2 hours before sunset, which was not too early and not too late. Once, when I tried to image planes at an earlier (relatively to sunset) hour, I was blinded by the brightness of the sky and I had trouble seeing anything on my computer screen. Not recommended at all.

 

On the other hand when it's close to sunset the planes are still very bright on the side closer to the Sun, but clearly darker on the other side. Especially AFTER sunset, very much depends on whether you are looking/aiming at a plane towards the Sun (most of the plane is very dark then) or away from the Sun (most of the plane is very bright relatively to the background). Fortunately such pictures are still very good/interesting, but waiting just for the sunset is wrong because there is too little time to image numerous planes. Like I wrote – 2 hours before sunset is a great time for starting an imaging session.

 

Clear skies!

Edited by Marcin_78, 16 May 2024 - 05:43 PM.

[Marcin_78]

I have some new pictures (taken on 29 May 2024) to post, with very short comments. By the way, this hobby of mine is great for the terrible time of astronomical white nights currently present at my location (the Sun sets only after 21:00 and the nautical twilight ends only after 23:00).

 

This time I processed my pictures (in the program GIMP v2.10.30) a little more: Color Levels + Color Curves + very delicate sharpening (the filter Sharpen (Unsharp Mask)).

 

The first picture (in this post, not chronologically) is by far my best ever – you can see particular windows of the plane (click to enlarge):

 

 

Taking such a picture with my poor equipment (inexpensive 70/700 refractor + simple alt-azimuth mount + focal reducer 0.5x + the camera ZWO ASI 715MC) feels like a miracle – everything has to click: relatively low altitude of a plane (close direct distance to a plane, so it appears big enough), not too steep angle of viewing (horizontally, a plane has to be not too close, so its side is better visible), good sunlight reflection (a lottery) and perfect focus (very hard to find).

 

Here are two “standard” pictures:
 

 

 

This time I got a bonus – by sheer accident I spotted (while using my binoculars) two gliders from the local aerodrome. Obviously gliders fly at much lower altitudes and have no engines, so they leave no contrails, which makes them very hard to spot. When I knew they were flying nearby I was more alert, so from time to time I could find them with the naked eye.

 

From afar a glider looked like this (to my camera):
 

 

The weather must have been good for gliders, because they roamed even beyond my location, which means that they were relatively far from the local aerodrome. As always, at close direct distance the result was the best (click to enlarge):
 

 

Clear skies!

 

EDIT:
I dug out a video I recorded last year (at the local aerodrome) of a glider taking off without a plane pulling it (thanks to a rope pulled by a machine on the ground). If anybody is interested, I uploaded it to Youtube:

 
https://www.youtube....h?v=gqTPDAoXie4

Edited by Marcin_78, 01 June 2024 - 04:39 AM.

[Tamiji Homma]

I also like taking photograph of high flying aircraft.

 

Here is SpaceX Falcon 9 right after ECO (Engine Cut Off) from front yard on April 6 2024.

 

 

Original shot: https://pbase.com/ta...09/original.jpg

 

Tammy

[Marcin_78]

Recently I have realized that an IR-cut filter is very important for achieving correct (more or less) colors. I described it in detail in this topic:
https://www.cloudyni...t-wrong-colors/

 

In that topic I focused on the camera ZWO ASI 482MC and among other things I posted terrestrial day-time pictures to show the difference between not using and using an IR-cut filter.

 

The camera ZWO ASI 715MC, which I use for taking pictures of high-flying planes, “suffers” from exactly the same problem – it doesn't have a built-in IR-cut filter, so you have to buy one in order to achieve correct (more or less) colors. Here's the same terrestrial day-time comparison for this camera:

 

ZWO ASI 715MC - without an IR-cut filter – cropped (the focus is a little off, but it doesn't matter for colors at all)

 

 

ZWO ASI 715MC - with an IR-cut filter – cropped
 

 

A you can see there is a GIGANTIC difference!

 

In the linked topic it was pointed out to me that I overdid the yellow color with the camera ZWO ASI 482MC and I did the same with the this camera (ZWO ASI 715MC). Here's a better version (adjusted in GIMP):

 

 

I was wondering why I overdid the yellow color and I think it was because I was adjusting the values WBlue and WRed when I was sitting on my balcony and looking at the laptop screen while the sunlight was still quite strong. It's hard to perfectly see colors under such circumstances.

 

For the record: it's impossible to achieve in GIMP natural colors on the picture taken without an IR-cut filter, so the fact that was adjusting the values WBlue and WRed under difficult circumstances had hardly any significance overall – an IR-cut filter is crucial for achieving correct (more or less) colors anyway.

 

Below there are some pictures of planes taken with an IR-cut filter. The colors are a little better, but there is also less glow around the planes and everything appears sharper.

 

 

Continued in the next post.

Edited by Marcin_78, 15 July 2024 - 11:25 AM.

[Marcin_78]

 

 

 

The last 2 pictures are of the same plane but taken at different distances.

[Marcin_78]

This will be my last post in this topic for a long time.

 

The planetary season has already started and I am about to unscrew the focal reducer 0.5x from the nosepiece of my camera ZWO ASI 715MC. I hate unscrewing and screwing things like focal reducers back and forth, so for a long time I will be unable to capture high-flying planes with this camera, simply because the field of view will be too small without the reducer.

 

This hobby (high-flying-plane spotting) kept me alive through the “dark times” (or rather “bright times”) of astronomical white nights present at my location from 20 May till 22 July. More importantly this hobby actually made me buy this planetary camera (with very small sensor pixel size) that now should give me great results with the planets Saturn, Jupiter, Mars and Venus.

 

All the pictures below were taken on 21 July 2024. As always during processing of my pictures, I slightly adjusted color curves and used a little sharpening. All the pictures were cropped in order to focus on a given target.

 

 

 

 

 

 

Clear skies!

[Marcin_78]

This will be my last post in this topic for a long time.

 

The planetary season has already started and I am about to unscrew the focal reducer 0.5x from the nosepiece of my camera ZWO ASI 715MC. I hate unscrewing and screwing things like focal reducers back and forth, so for a long time I will be unable to capture high-flying planes with this camera, simply because the field of view will be too small without the reducer.

 

(...)

 

The first TWO pictures below are probably my LAST pictures of high-flying planes taken through a telescope. My old 70/700 refractor, which with a focal reducer 0.5x gave me focal length of 333mm (the precise reduction factor was 0.475x), is stored away in my garage and now I use a 90/500 refractor. The new refractor is too fast on its own to be used with a focal reducer, so I have to use it at nominal focal length, which means that the FOV is much smaller as far as area is concerned (FOV is inversely-proportional to focal length):
(333/500)^2 = 0.444

 

This time I didn't even try to use a tripod – the one that I use with the new refractor is more jerky (but more sturdy), which in combination with the much smaller FOV is a complete no-no for plane-spotting. Instead, I was sitting on a chair, stabilizing the telescope on my upper leg and shooting from the hip. It's very hard to aim this way, so I ended up with pictures of only 2 planes.

 

 

 

I have to point out that I used a too long shutter speed of 3ms (it should have been around 0.35ms), which explains the low quality of pictures. It doesn't really matter because the worst thing was that I missed SEVERAL planes that were flying really close! ANY picture of those planes would be awesome, but I couldn't find them in the very small FOV.

 

On the very next day I went the opposite way and I used a GUIDESCOPE 40/160 (achromatic doublet) – the FOV AREA was more than 9x times bigger than in the new refractor and more than 4x bigger than in the old refractor (FOV is inversely-proportional to focal length):
(500/160)^2 = 9.77
(333/160)^2 = 4.33

 

The downside was that the planes were that much smaller (as far as area was concerned), BUT I was able to aim at them in VERY easy way, especially when they were closer to my position, so they looked bigger. I held the guidescope like a pistol (see the picture below), but I was still shooting from the hip because I had to look at the computer screen to see if the image was sharp and correct the focus if needed.

 

 

In the guidescope the focus is set by turning its FRONT part, which is VERY handy in this case.

 

The very first picture in the guidescope was interesting – the plane apparently had engines placed differently than big airliners, like this:

 

 

 

The second plane in the guidescope left no contrails, which was strange:

 

 

Maybe the plane was flying at a lower altitude and the air was warmer there? On the other hand the plane wasn't much bigger, so the difference in altitude couldn't be all that big.

 

Starting from the next picture the shutter speed was 1.3ms (almost perfect for the guidescope).

 

 

The plane on the next picture was surprisingly big AND detailed:

 

 

Everything was perfect – I managed to capture the plane when it was almost directly above me (very short direct distance to the plane), the plane had to be one of the bigger ones (airliners' sizes range from 35m to over 70m) and I was able to find perfect focus – the word “Emirates” is VERY clear! I think this is my best picture of a high-flying plane so far, even better than the first one in the post #13.

 

The final picture was very important for theoretical reasons:

 

 

As you can see the plane was captured from a side when it was about to disappear behind a nearby apartment building. I instantly took my smartphone and took a screenshot of the plane's position and other info (I was using the site globe.adsbexchange.com for preparing for new planes – checking from which direction a plane should appear, so I had the site running constantly). This way I could check if my formulas were correct – my calculations gave me 140 pixels while the actual size of the plane on the picture was 143 pixels. The precision of my calculations was 97.9%, so it was fantastic! I am going to update the topic linked in the post #1 and describe those calculations in detail, but I need some time to do it.

 

Back to the pictures:

 

In the future I will try the shutter speed of 1ms – I checked my earlier logs and I achieved the best results in a telescope (with effective focal length of 333mm) with the shutter speed of 0.47ms, so with my current focal length of 160mm the shutter speed should be around twice as long.

 

Clear daytime skies full of planes!

Edited by Marcin_78, 26 January 2025 - 04:42 AM.