Skip to content

Recent Articles

24
Feb

A View to the Infrared

With the huge popularity of smart cell phones has come the rise of the portable infrared camera. One can readily go to Amazon and slew through a series of miniature attachables for your phone, each with their features and abilities. This is a look at two widely accepted models by two companies: FLIR and Seek Thermal. As an educator, having an IR camera is a very cool way to SHOW students what seeing in different wavelengths is all about. Great strides have been made in astrophysics and other sciences due to our abilities to “see” in multiple wavelengths with some very cool tech. So lets look at these two units.


On the left is the Seek Thermal Compact model. This is available now for iPhone series, and will be coming to Android later this summer. Three models are available each with progressively more features/abilities and with increasing price tags. This unit comes in at $249 US. The more expensive they get, the better they are at resolution and frame rate. More can be seen for comparison at their site here: Seek Thermal Compact

On the right is the FLIR One unit for the iPhone. This is a Gen2 unit, as FLIR have a redesign out there for Gen3: a whole new look there, so you likely can find one of these Gen2 units out there for less money.

Cases: The case for the FLIR is not a case so much as a neck lanyard with a rubbery wrap for the camera. It’s difficult to get the camera out of the case, and your finger is likely to hit one of the lenses. The Seek unit has a very nice water proof case with a strong latch and foam insert.

Image Quality: both are fine for image quality given their tiny size. The thing about long wavelength IR is that resolution will suffer, period, unless you are able to fork out many hundreds for a pro level, stand-alone unit from FLIR often used by law enforcement or the military. You wouldn’t be reading this either 😉 The cool thing about the FLIR system is that it has two lenses: one takes images in IR the other in visual wavelengths. The system then does a edge find algorithm on the visual image and uses that to draw outlines in the IR image to accentuate the subject matter. This is a boon and a bust: it makes your subjects obvious. It also fools people unfamiliar with the system into thinking that these edge lines are part of the IR light being received. Nope. Some educational extra work is needed to make sure that people are not fooled.

The FLIR default image: note the edges drawn in by the software to make subjects more visible. This is a nice feature when using the unit to ID small features or plumbing issues in the basement 😉
This is the same subject though I placed a finger over the visual light lens to prevent it from generating an edge to the subject…. except at the far left of this image. The blurriness is typical of IR images.
Here is the same subject taken using the Seek system. No edges here.

Abilities: Both are pretty much equally capable. The abilities of the system (other than the edge drawing feature of the FLIR) are within the software. Seek’s software has the annoying feature of wanting you to join their Seek online group. This can be circumvented, but you have to do this every time you launch the app. Both allow different palettes. Both have spot measurement of temperatures. Both have temperature scales available with the palettes. Some examples for you to enjoy:

Spot temperature reading on the FLIR: looking at the wood of the basement door. Note the cooler air below the door.
Cooler portion of the same door where cool air is being pulled up into the house by the air circulation system in the house.
Can you find the hot cup of coffee in this busy kitchen?
We always know when the dog has been sleeping on the couch…. she leaves her thermal signature wherever she has been. This image had my thumb over the edge-making visual light lens.
Seek’s spot temp measurement of my hot Comcast set top box. The stereo amp is below the Set top unit…. yeah – that is one HOT set top. Shame on Comcast.
Same image but with the temp scale turned on. A nice feature.

Other oddities? Yes! The Seek Thermal systems have no internal battery, so…. it draws all its power from your iPhone and will eat up batteries pretty rapidly. Your phone will also heat up. The FLIR unit has an internal rechargeable battery. This requires a tiny USB plug wire for charging, time to charge, etc. Don’t lose that cable! The internal battery cannot be replaced, though I have had mine for years and have had no issues. Recharging is slow but it lasts a day. Pick your poison. Both units are pretty good given that they are small and limited in resolution. If you like the FLIR edge drawing ability, and its internal battery, then the choice is to go with FLIR. If you do not want/need that edge finding ability, then the Seek is a good choice. Just know that it will consume your phone’s battery for you.

2
Jan

Then and Now: Astrophotography on the Simple Side?

I spent some time this morning with PixInsight on a stack of M-42 images. This is the result. PixInsight is an impressive, though oddly challenging, piece of software. The interface still eludes me at times. The results are splendid, however.

This image was taken through a Nikon D-810a at f/4, 200mm, tracked on an iOptron mount in gusty winds. This piece is the result of three major processes:

  • All images were aligned using stellar centroids.
  • The images were then stacked… this is an image integration of 100 seconds worth of exposures.
  • PixInsight was then used to do a Dynamic Background Extraction to essentially perform a flat field thus removing the lens’ vignetting. I still can’t get over this process: no flat fields required… though I bet real flats would result in a better overall image.

The camera does its own internal bias and dark subtraction. The image was then brought into PhotoShop for adjustment to levels and cropping.

M42 color stack using Nikon D-810a

Now… compare that colorful image with the monochrome one: that was taken way back in 1986 on Tri-X Pan film pushed to about 1000 ASA by boiling it in nitrogen. The image is a 20 minute exposure through a Celestron C-8 at f/10, manually guided with an illuminated reticle eyepiece. I developed this in my bathroom using duct tape and towels to block all external light from entering.

M42 film

What a difference! New technology brings better sensitivity and a whole new world of imaging…. but we knew this. I’ve been playing with CCDs since the early 1990s. No surprises. The real surprise? Cost! All this tech adds up in cost. I am not really sure that it saved me a whole lot of time to make the new image with the new tech… perhaps if both images were color? Then, yes, the new tech has saved me time. Simple? M’eh. It’s about the same level of technical detail. It ends up being about one’s knowledge base: software or film developing? You choose. Certainly some of my best images were taken with film. Which do you prefer? It’s totally up to you. Like vinyl records, film is making a comeback, but hasn’t made its way to the realm of astrophotography again. I am pretty sure that CCDs and CMOS sensors are here to stay for astro-art imaging.

  • PixInsight sounds interesting: check out their site here.
  • iOptron? Check out their site here.
27
Dec

Comatic Aberration and Chromatic Aberration

These two phrases are pretty much guaranteed to raise the blood pressure of optical aficionados: Comatic Aberration and Chromatic Aberration. There. Did your blood pressure go up? Then it is likely you have dealt with one or both of these issues before… and it is likely that you do not need to read further! For those looking around the internet for an example of these aberrations, seek no more!

Let us start with an image. This shot is of the December sky taken through a wide angle 20mm AFS Nikkor 1:1.8G ED lens on a Nikon D-810. The images were raw NEF files without any processing (except resize), either on board the camera or using software. Click on any image to see it in larger format.

Taurus and comet Wirtanen
Taurus and Comet Wirtanen

The image is a pretty typical night shot: 10 seconds focused at infinity and using 5000 ISO at f/2 (a little stopped down). The constellation Taurus is dominating the right side of the image. There is an airplane top-center moving to the lower left. If you follow the airplane’s future trail it leads to a faint greenish fuzzy object, Comet 46P/Wirtanen. This image is reduced in size…. but upon close, full-scale viewing, this image displays two of the common issues that astronomers and photographers aim to rid themselves of. Funny thing is that this lens gets fabulous reviews on sites like Amazon, and when I complained about these issues I was actually chastised! “Are you kidding? This is such a great lens!” Well, no. It’s not, and for the price, it really should perform a lot better. Add to this story the fact that the Nikkor 16mm fisheye actually is BETTER than this 20mm lens, and there you have an argument to not buy this 20mm lens. So, read on….

May I present to you comatic aberration:

comatic aberration in star images
Classic coma on the images of stars. These should be small round dots, not winged things….

This aberration is off to the sides of the image, off-the central axis. The further from the center, the worse this aberration gets. Some systems sprout seagull like wings from stars. This lens sprouts more than that. Ugly. The cause of this problem is in the optical design and is usually found in parabolic mirror systems like Newtonian reflectors. Alas, it also happens here in lens designs.

May I now present to you chromatic aberration:

Chromatic aberration in star image
An example of chromatic aberration: note the violet halo surrounding the bright star. The violet wavelengths focus at a different distance than all the rest. The fuzzy green object to the left is Comet Wirtanen.

Chromatic aberration has been the bane of the optical world for a long time, starting with those who first pointed telescopes up at the stars (i.e. those like Galileo, etc). A single lens acts very much like a prism in how it bends (refracts) light. The angle of refraction has to do with the light’s wavelength, so not all colors of light will come to focus at the same spot. This is usually handled with complex, multiple-lens systems like Petzval lens groupings using unique glass recipes than minimize chromatic aberration. Well, this lens? It suffers. When pointing at a bright white star, this lens gives an image very much like that of a simple two-lens refracting telescope, what is called an achromatic refractor. Well, they are notorious for having a violet to blue ring of light surrounding bright objects… and halos of blue around the moon and Jupiter. Not fun. Nope. This is why we have monstrously expensive systems like apochromats and Petzvals. We are talking expensive!

8
Dec

Comet 64P/Wirtanen

Comet Wirtanen has been giving us a moderate showing this time around the Sun. As it has been closer to Earth than it usually gets, we are enjoying a comet that might just get bright enough by December 16th to see without a pair of binoculars.  Last night we checked it out through the school’s 16″ telescope and took some images as well.

Comet 46P/Wirtanen: One is through the 16″, the other is a wider field view through a telephoto lens. The brilliant green color is striking and caused by the excited gases: cyanogen (CN)2 and diatomic carbon (C2).

Wirtanen
29
Nov

20-21 January 2019: Total Lunar Eclipse

We have a splendid opportunity to see a total lunar eclipse this January. It will be taking place late on a Sunday night into the early hours of Monday morning. That Monday is also Martin Luther King, Jr. Day here in the USA, so many schools will not have classes that day. Eclipse timings are given in the above graphic, in Universal Time.  Converting that to the various USA time zones: 

Event Pacific Mountain Central Eastern
Partial eclipse starts 7:34 pm 8:34 pm 9:34 pm 10:34 pm
Total eclipse starts 8:41 pm 9:41 pm 10:41 pm 11:41 pm
Total eclipse ends 9:43 pm 10:43 pm 11:43 pm 12:43 am
Partial eclipse ends 10:51 pm 11:51 pm 12:51 am 1:51 am

Usually the real eclipse visibility starts to take place late in the penumbral phase approaching the first contact of the umbra. If you have not seen a lunar eclipse before, it is quite a special event. The moon will appear to have a charcoal chunk missing from it as the eclipse progresses.  Deeper into the eclipse, the moon will take on a rusty red hue caused by the sunlight passing through the earth’s atmosphere before arriving at the moon. Telescopes are not required, as one can see the whole event easily with the eye. Binoculars and telescopes will offer a nice closeup view.  Photography of the event is a relatively simple affair. A good tripod and telephoto lens will work well with the moderate shutter speeds required.  Tracking is not needed.  An example of a series of photos I took of the last total lunar eclipse is below. The camera was a Nikon D7000 with 200mm telephoto on a tripod. Click for a larger image.