Dress Rehearsal for Venus Transit

It was a full dress rehearsal. Both telescopes, two cameras, the entire streaming rig set up on the lanai. No less than three computers with cables all over the driveway! Surprisingly enough, everything went pretty well!

Sol 2Jun2012
The Sun on June 2, 2012
If you had been watching the Keck Transit of Venus stream, you would have been looking at a live image of the Sun for several hours. The seeing from my driveway was pretty poor, but there is a nice collection of smaller sunspots across the disk.

Everyone wandering by the house noted the telescopes. I gave peeks to our mail-lady and a couple young women who stopped by, intending to read me a bible verse or two (that was fun;)

Two technical issues were key today… Using thirty feet of active USB extension cables to run the streaming camera remotely, no problem. Co-aligning the two telescopes to aim at the same point, no action needed, aligned from the start. I had thought I might need to shim the mount for the piggyback ‘scope. I was also able to play with the streaming camera further. The Baader film filter gives a blue-white image. Adjustment of the camera white balance will restore a little yellow cast. I do not have much problem with the white, but a hint of yellow will allow people to instantly realize they are seeing the Sun. The same reason I adjust my processed photos for a golden orange hue.

We are all swapping gear around to get the set-up ready. Chris was nice enough to loan me a Canon T-ring and some Baader film. I built a battery pack and some sun-finders for several telescopes. Last night I picked up a whole solar rig from Cliff for delivery to Olivier. Olivier lent a 40mm eyepiece to Keck for the public telescope that will be setup at HQ. The list goes on…

I was not the only one doing a dress rehearsal. So far today I have been on the phone to other folks setting up and using a sunny Saturday to check gear. Some of the guys over on Maui even posted a video of their test run. I should have thought to do the same thing! Will have to time lapse the summit setup.

Photographing the Transit of Venus

With the Transit of Venus looming on the calendar, a discussion of solar photography is in order. Taking good photos of the Sun is not that difficult, but can be aided with a little information. There are some unique challenges in solar photography.

Solar Filter
A solar filter mounted on a refracting telescope
The one obvious problem is dealing with the sheer intensity of the Sun. An intensity that can easily damage a camera if placed behind unfiltered optics. A proper solar filter is the easiest way to reduce the light to a safe level.

A solar filter will also produce the most pleasing images of the Sun. Indirect techniques like projection can be used. But for good solar photos, a proper filter in front of your optics is the single best method.

Solar filters for optics are constructed with a thin film of metal such as aluminum or stainless steel vacuum deposited on a substrate. This substrate is usually glass or a thin mylar film. The resulting filter allows only a small fraction of the light through, about 0.01% or 1/10,000 of the unfiltered value. Importantly, the filter blocks the ultraviolet and near infrared part of the spectrum as well. The result is a safe filter than can be used on a telescope or telephoto camera lens.

Sufficient magnification is needed if details of the Sun’s surface are to be well recorded. A few hundred millimeters focal length, found in common telephoto lenses will produce a reasonable solar image. The image will still be fairly small. To fill the sensor requires more. For an APS-C sized sensor (Canon T2i, 60D, 7D, Nikon D5000, D3200 or similar) a telescope with 1,000mm focal length will create an image filling a good portion of the image.

Image sizes for APC-C Sensors


Focal Length     Image Size (arcmin)
100mm   760×510
400mm   190×128
800mm   95×64
1000mm   76×51
1500mm   51×34
2000mm   38×25

The table to the left shows the resulting images sizes, in arc-minutes, given various focal length lenses, on an APC-C sized sensor. Recall that the Sun is about 30 arcminutes across as seen in our sky. With 100mm the resulting image is 510 arcminutes from top to bottom in the frame. This is 17 times the width of the solar image, a pretty small image indeed. With 400mm this improves to about 4, thus the Sun will reach about 1/4 the height of the image. At 1000mm this is about ideal, the Sun will reach more than halfway across the frame.

1500mm will just fit the solar image. While this may seem ideal, there is an issue. A small amount of drift will put part of the Sun out of the image, cutting off part of the disk. Sizing the image to fit in the frame with a good margin will allow some drift, while still giving a good image scale.

If you have a full frame camera (Canon 5DMkII, Nikon D800, etc.) a larger image can be used to fill the larger sensor, thus a longer focal length can be used. A telescope with 2000mm focal length will produce an image 17mm across, neatly fitting in the area of a full frame sensor.

Few compact cameras can boast a lens that will zoom far enough to produce an image of the Sun filling the frame. For these cameras another technique can be used, afocal photography. This can also produce good images, but will require experimentation to find the right combination of telescope, eyepiece and camera to produce a correctly sized image.

Solar Framing
The full frame solar image with about 1000mm of focal length and a Canon 60D
If you want to calculate the image scale for your optical combination, lens and camera, I suggest downloading the CCD Calculator from New Astronomy Press. You can enter the optical parameters and see exactly what the resulting image will look like with a sample image of the Sun, Moon or other selected objects.

Another issue is resolution. Our atmosphere usually limits the practical resolution to about one or two arcseconds, blurring any finer detail through atmospheric distortion. This can be much worse in the daytime with solar heating of the ground and air around the telescope. Thus the limit for resolution will be reached with about 1000mm focal length and a modern 10-15 megapixel camera. Any further magnification beyond about 1000mm will simply result in magnifying the blur. There are techniques for overcoming this (image selection and stacking), but if you know how to do that, you already know what you are doing.

Just a bit of summing up… You need a proper solar filter or other method of safely reducing the solar intensity. A long telephoto (400mm or more) will produce a reasonable solar image. A small telescope with about 1000mm of focal length is ideal for photographing the entire disk of the Sun with a DSLR camera.

Preparing for the Venus Transit

The Sun
The Sun on 13May2012
Time to start preparing the gear for Venus Transit! This means dismantling the astrophotography rig in the garage and reconfiguring for solar work. Taking the the AT6RC telescope off and remounting the 90mm APO. The APO has just the right focal length to produce a nicely sized solar image on an APC-C sized sensor, such as the sensor in the Canon 60D.

First up? just setup the ‘scope in the driveway and take a few photos of the Sun. Just checking the photographic setup, the necessary parts and pieces. Nothing misplaced? Where did I store the solar filter? A nice focus on the camera? Perhaps take some nice photos of the large sunspots that current grace the surface of the Sun while I am set up. I hope we have some nice spots during the transit, they make focusing so much easier!

Next step is to get autoguiding operational, this will be a seven hour event and I really do not want to manually guide for the entire duration. Particularly with a telescope that was setup in the daytime and is not properly polar aligned.

A couple other steps remain in the preparation. Automate the camera to take photos at a regular interval. Insure I can provide a good video feed to the computer sending out the webcast. I do have a few more weeks to accomplish this. I am certain those weeks with speed by surprisingly quickly. Time to get ready!

Canon Introduces the 60Da

Most of my astrophotos are taken with my venerable Canon 20Da, a special version of the EOS 20D that was produced for astrophotography. Normal DSLR cameras work quite well for astrophotography, with one major drawback… The filter placed in front of the sensor blocks much of the Hα light emitted by many nebulae.

Orion Nebula
NGC1976 or M42, the Great Orion Nebula, taken with the Canon 20Da and a AT6RC telescope.
This light, emitted at 656mn, a wavelength deep in the red, give emission nebulae their characteristic shades of rich red. Hα is the strongest component of light produced by emission nebulae. Without this light, the nebulae will often appear bluish in photographs, as the next strongest component OIII dominates.

Specifically for astrophotography, Canon produced a special version of the 20D with a re-designed filter that allowed Hα light to reach the sensor, the Canon 20Da. The camera also featured on-screen focusing, a feature now found on most DLSR cameras, but unusual back in 2005.

The 20Da was discontinued in 2006. Astrophotographers wanting a DSLR camera with a filter that admits Hα light must buy a standard camera and remove the filter, or have it modified by specialist that offers a conversion service.

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iPhone Moon

Despite numerous attempts, I had never managed a decent shot of the Moon using an iPhone. When showing people how to do afocal photography, I have leaned how to make just about any compact camera perform nicely, but routinely seen nothing but trouble with cell phone cameras.

Lunar photography is incredibly popular with folks using the telescope, a great activity for a night with a bright moon. Long ago I found that an inexpensive 20-25mm Plössl is a good match for the lens of most compact cameras. On a 1-2m focal length telescope this combination can produce very nice lunar photos. The setup does not work with cell phone cameras. Though people do try, the results have been routinely disappointing.

Working a resort star party recently, I discovered a combination of telescope and eyepieces that works very well. A C11 telescope, an f/6.3 focal reducer, and a 20mm Nagler type 2 eyepiece produced very nice photographs with several different cell phone cameras. The result was a very happy audience and a lot of great lunar photos. As people walked away from the telescope they were rapidly replaced by a crowd holding glowing screens, all wanting to get a nice lunar shot for themselves. I will have to explore other telescope/eyepiece combinations to find another solution that does not involve a $500 eyepiece.

iPhone Moon
An eleven day old Moon, taken with an iPhone 3GS, a C11 and a 20mm Nagler 2 eyepiece

Afocal Photography

When doing any sort of public astronomy, showing folks the beautiful sights available to a telescope, I often hear the question “Can I take a photo of that?” The person asking the question is usually holding the ubiquitous compact digital camera. They are often surprised when my answer is “Yes”.

Afocal Photography
Taking a photograph of the Moon using afocal photography

It is indeed possible to manage hand held shots of bright astronomical objects by simply holding the camera up to the eyepiece. There are a few tricks to making it work, but nothing that can not be demonstrated in a minute or two. The resulting photographs can be quite pleasing, definitely worth showing to friends and family along with the rest of the Hawai’i vacation shots.

The method of positioning a camera with a lens in front of an eyepiece is called afocal photography, or sometimes digiscoping. Afocal has been around for a while, but was not considered a practical photographic method by most. The advent of common digital cameras without removable lenses has changed this.

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WP Plugin Confusion

The world of WordPress plugins is a stew of confusion to a new WordPress user. Thousands of options are available for use with your blog, an amazing array of interesting features to add useful capabilities. From this, you are trying to choose what works for you. You really do need a few plugins to add key features.

For Darker View there a number of things I have determined I need to get working… Spam comment filtering, backup capability, statistics, social site support, threaded comments, and a decent photo gallery. I have the backup utility working now using the very nice WordPress Database Backup by Austin Matzko. Social site functions and statistics from Jetpack work smoothly.

The latest experiments center around getting a decent gallery function integrated. Two options appear to be worth considering… NextGEN Gallery seems to be the standard, but I had read that it was flash based, and I want things to work on an iOS device. In a later experiment I found that it does work on my iPad, so it is back on the list.

In the meantime I have experimented with DM Albums. This is a straightforward plugin with a decent interface. Just load the photos and put a single tag into the post. I like the effect, it seems to play well with my theme. The result is a nicely functional gallery.

DM Albums does have some sizing issues in the full screen mode, pretty annoying issues. The package has seen very active development lately, with two major releases already this year as they clean up the bugs and get everything working. Thus I am not giving up on this package just yet.

This issue is not done yet, I am just out of time to play with it for now.

[dmalbum path=”/wp-content/uploads/dm-albums/Hawaii 100/”/]

Keck in Motion Scene Guide

I have been getting a few questions about the video. To answer a few of them I have compiled a guide to the scenes. Some quick explanations to what you are seeing, information on the camera used as well as the exposure information.

The video is a combination of two techniques. Many scenes were filmed as standard video then accelerated during editing to allow the motion to become clear. Examples of this are scenes of telescopes slewing and the interferometer delay lines moving.

Slower subjects, such as clouds or the stars moving across the sky, were photographed as time lapse. Here a large number of still images were taken. These are then processed and converted to video using Photoshop CS5 before loading into the video editing software, Adobe Premiere Elements. To construct the time lapse sequences sometimes required thousands of separate images, quickly filling memory cards and exhausting batteries. After dark it is long exposure time lapse that is used, with individual exposures often 15 seconds to one minute long.

Continue reading “Keck in Motion Scene Guide”

A Premiere

Tomorrow night will see the premiere of my latest work. Over the last few months I have been assembling a video on Keck titled Keck in Motion. The nice part is that the first public screening will see the video on a big screen indeed… The showing will be at the Kahilu Theater. It will be run as a introduction piece before the Keck lecture

The video has seen the usual creative cycles during production… Enthusiasm followed by disillusionment, in alternating phases. Despite some doubts along the way, I have to admit the final version is not all that bad. Everyone who has seen it uniformly gives great reviews, but as the author, I see all the flaws and things I could improve. Whatever reservations I might have, the time has come to simply say… It is done. I have turned over copies to Larry and Mariko, ready for projection on a big screen tomorrow night.

The video has been seen a couple private showings to a selected audience. In particular it has been seen by the guys on the summit crew, many of whom appear in the video. Some bits of the video have been seen here before, particularly the three lasers sequence. Some of the material was stuff I had accumulated across the years, many pieces were custom shot to complete the project. Somehow it works into a very nice narrative and a complete story in three minutes, thirty-six seconds.

Look to see the video posted here after the premiere. Peeking at my Vimeo account will not help, I have not uploaded it yet. I suspect it will get spread around a little, used for Keck PR. It does show what a special place Keck is. Better yet, it highlights the hard work it takes to keep Keck on-sky every night. Because of that, this video is dedicated to the guys of the summit crew.

Lasers 3 over Mauna Kea from Andrew Cooper on Vimeo.

Repairing the Broken

There are some devices that folks still try to repair if possible, camera gear seems to be at the top of the list. I suppose this should not be a surprise, the gear is expensive, and seems to get damaged from hard use. Particularly on this island, where cameras see a wide range of harsh conditions, from tropical heat to salt water.

A month back I repaired a Pentax waterproof camera for a co-worker. Salt water had penetrated around the shutter button and corroded the switch. The camera, rated to 10m (30ft), had probably experienced pressures even higher. Her teenage boys can easily exceed that depth while free diving the island reefs. It was necessary to completely disassemble the camera to get at the button. Well over an hour of tiny screws and gaskets to replace a $1.35 switch.

There have been other items this year… A classic chrome stand microphone that required a little rewiring to work with a modern computer. A pair of very nice computer monitors now found on my desk. A toy RC aircraft with broken motor leads. I do appear to have gained a reputation for fixing this stuff.

Last week it was an underwater video camera case brought to me. None of the external controls were working, no way to hit record once in the water. The repair turned out to be fairly simple, a broken conductor in the LANC cable used to control the camera. A bit of scrounging around in my spare parts to build a replacement cable was all that was required to put everything right. Most repairs are that sort of simple, just the effects of wear and tear taking their toll.

After the repair J sent me a link to his YouTube channel and I spent a lunch watching video. Well edited, nicely crafted videos of the local paddling sport community. Canoe races and special events covered with a personal touch, with respect for the people and traditions. I was very happy to see I had done a bit to help someone who was producing such excellent material.

The repairs serve me as well. Each time I take apart an unfamiliar device I learn, I refresh my skills, I experience the simple joy of using those skills. Each device is a challenge, to successfully disassemble the gear, find the fault, and put it all back together properly. On occasion I fail in that challenge, either I do not have the skill, or the repair is impractical, or the device too badly damaged. There is often little real risk, if it is broken the attempt to save something useful from the trash is an easy choice, the only thing lost is the effort. The reward is seeing the gear returned to useful service and knowing you prevented that little bit of waste.

I wonder what will come my way next time?

An example of J’s Videos