Sunday, November 25, 2012

Some more backyard astrophotography with Sigma 100-300mm f4 and D800

There have been four (not too many) clear nights after last post on the subject. I've imaged M45 and M31 with its sister galaxies using Astrotrac tracking device and Sigma's 100-300mm f4 telezoom on a Nikon D800 DSLR.

Here is Messier 45 or Pleiades at 300mm after some heavy cropping. Twenty four images at ISO800 and 30s each were stacked together. Contrast was boosted in GIMP 2.9, which handles 16bit files but is just too slow for general use - yet. However, the nebulosity is well shown even with all the light pollution in the sky.

By the way, one cheap way to reduce light pollution when using a unmodified DSLR is to use a redhancer filter. It's exactly the same filter as the expensive Baader one but comes in bigger sizes such as 77mm. Baaders are limited to 2" or around 50mm. The filter works because there's neodymium element blocking the wavelengths that high pressure sodium vapour lamps emit. Most of the orange glow in the sky is gone with such a filter.

Messier 45 with D800 and Sigma 100-300mm f4

And here's another take at same subject, now with 40 images stacked together. There's less noise and more detail when compared to the earlier attempt. I'm pretty satisfied with this one.

Saturday, November 24, 2012

Explosion in the sky - northern lights in Maaninka

A week or so back, I was photographing M45 (Pleiades) when I noted a bright green band in the northern sky. Northern lights were suddenly active. So off to Maaninka we head since the skies are darker there. We were greeted by this band of green and red(!) lights as soon we stepped outside of the car.

Revontulia 2012-11-13

I used mostly the Samyang 14mm f2.8 on a D800 to shoot these. Exposure times were in the 15 to 30 second range and ISO was 1600. As the aurorae became more active, the exposures were shortened to avoid blurring details from the bands.

Revontulia 2012-11-13

There's quite a bit of spherical aberration in the centre of the image up until f4 or so. Bizarrely it goes away in the corner of the frame. Strange lens I must say.

Saturday, October 27, 2012

Gigapixel from Puijo tower, Kuopio

Yesterday it was such a nice evening, so I went and shot a 360 degree cylindrical panorama from the viewing platform of Puijo tower in Kuopio. The tower itself is 75 meters tall and it stands atop of a 200m tall hill, Puijo. Breathtaking view opens from the height, showing the viewer the whole city of Kuopio and its surroundings. On a good weather, the visibily is almost 100 kilometers, but this time there was some fog or mist rising from lake Kallavesi which hindered the view a tad.

Without further ado, here's the whole panorama embedded with Saladoplayer. Click theyourself to full screen mode and enjoy the view.


Sunday, October 21, 2012

Astrophotography with Sigma 100-300mm f4 and D800

Last night was the first clear sky in about a month. That's quite long time to wait, si I didn't want to waste this opportunity and went straight outside with Astrotrac. The first target was Andromeda's galaxy or M31: big, bright and overall easy target to photograph even with heavy light pollution.

I'm continuously amazed by the D800 and its sensor and this time was no exception. This time I mounted Sigma's 100-300mm f4 telezoom to D800. Astrophotography is the most demanding subject lens-wise: any chromatic aberration, coma, halation, spherical aberration, focus shift will ruin the pictures very fast. Luckily, the Sigma had no problems image quality wise.

Here's nine image long stack of M31 (250mm f4, ISO 800 and 2 minutes per exposure) stacked together in Hugin and Enfuse:

Messier 31

And here's 100% crop of the galaxy's center region, the dust clouds in the spirals are clearly visible:

M31 (crop)

When stacking images in Enfuse, one must remember to set the sigma parameter to maximum value (1) and weight only exposure. This way, the images get averaged together very cleanly. One good thing about Hugin is that is quite fast aligning the images, I'm processing the same images in DeepSkyStacker and it's been going for an hour and a half no and haven't yet produced anything. Of course, DSS works straight with raw files whereas Hugin uses TIFFs, but even factoring the raw development time with Raw Therapee, Hugin is still faster - by a fair margin.

Lyyran rengassumu (M57)

Above is a test shot from the Lyra's M57, a small planetary nebula. That was the last image before the clouds rolled in.

Friday, September 14, 2012

Suddenly, northern lights

According to spaceweather.com, there has been a minor storm around the poles. Northern lights have been seen in as south as Southern Finland.

Reposten ja pilvien tanssi taivaalla

Here, the sky only opened for couple of hours. But that was enough to photograph some of the action in the sky. Below is a spherical panorama, where one can see the green glow among the yellow suburban sky.

Aurora borealis midst the light pollution in Finland

Sunday, August 19, 2012

Dark side of ETTR

Three weeks back I was photographing a show of noctilucent clouds. Since there was enough light, I exposed the images to the right (or ETTR for short) to gain better signal-to-noise ratio. As exposure increases, the read noise of the camera can be regarded as a constant when exposures are short, hence better SNR. Images will have less noise, gradations will be smoother and colors better. ETTR works best when dealing with raw image files.

However, there were some unexpected consequences because of ETTR: as I brought the exposure down in Raw Therapee, I noted that there was visible posterization in the gradients on the sky. Paradoxically this artifact is caused by too good image quality, the steps between the tones in 8 bit image are so far apart that they become visible.

ETTR banding

As mentioned the problem only exists for 8 bit images displayed on 8 bit displays. Cheapest TN panels are usually 6 bit and they dither everything displayed. Dithering is the act of adding a small amount of noise to salient parts of the image to mask the posterization. Human vision likes details even if they're not real.

Above image has taken an adjustment of three stops in exposure, the posterization/banding is clearly visible in the sky part of the image. Below is an untouched exposure, here the noise from the camera acts as a dither, helping to hide the posterization. However, the image quality is clearly inferior due to the worse signal to noise ratio.

ETTR banding, alivalotettu kuva

From further testing I was able to rule out lossy NEF compression as the reason to this artifact, as both losslessly and lossy compressed raw files showed the same amount of banding (the lossy compression in the NEF files works by cutting some tones from the highlights as shown here).

Hopefully Raw Therapee implements some form of dithering for 8 bit images. I was unable to test other raw converters, but I assume the results will be similar - there would be too many people complaining about small amount of added noise because they wouldn't recognize it as a good thing.

This post was originally posted in Pallopanoraamablogi as "ETTR:n varjopuolet" at 2012-07-12.

Saturday, August 18, 2012

Astrotrac, first light

I recently acquired a tracking device for my camera, specifically the Astrotrac TT320X-AG with Tele-Optic wedge. AG in the product code means that it has auto guiding port, but I don't (yet) have such appliances.

This is how it sits on my tripod; first the wedge is on the tripod, and on the wedge is the Astrotrac and on the on the Astrotrac is the ball head and on the ball head sits the camera or lens. The wedge is used to align the axis of rotation to the celestial pole, as the sky rotates around that point and the camera must follow the stars while they move to avoid streaking of the stars.

Astrotrac TT320X-AG ja wedge Astrotrac TT320X-AG

The tracking device is basically built around the 20cm long screw and a motor which runs the screw and rotates the upper aluminium arm. As the arm moves, so does the camera mounted atop. Motor is powered by 12 volt power source, which can be a battery pack, transformer if the mains are close or accumulator such as lead-acid battery. Personally I built the power source from latter, a cable with 5mm round plug was needed to connect the two. If using rechargeable AA batteries, one must use ten of them because their voltage is lower than regular batteries (1.5V versus 1.2V from rechargeables).

Astrotrac TT320X-AG Operating the device is quite straight-forward: after aligning the axis of rotation to celestial pole and and the camera to chosen subject, the play button is pressed in the control panel. The star-like symbol controls the brightness of the indicator LEDs and and the volume button the... volume of the beeps. There's also button to rewind the screw. Volume and brightness buttons also choose the tracking rate if pressed while starting the apparatus.

After two hours of tracking the system must be rewound to continue. Depending on the batteries, there's enough juice to power the device for several nights of photography.

Anyway, here's the first light from the device. Polar alignment wasn't perfect as I did it by eye rather than drift-align or even polar scope.

Tähtitaivasta ja valosaastetta venerannalta
(Two and half minute exposure, it's not the tracking accuracy that's the problem but the sensor heating up as you can see in the corners.)

Nights aren't yet dark enough to capture the Milky Way very well, but in a week or so the night should be dark enough. The faint green glow is from northern lights that were present earlier, even though it was invisible to the naked eye, long exposure captured the glow in the sky.

Illan ja syksyn ensimmäiset reposet

Linnunrata ja revontulten kajo pohjoistaivaalla

Thursday, July 19, 2012

The best of northern lights of 2011-2012

Last winter's aurora borealis season got a head start in September after and X2 class eruption on Sun hurled charged particles into Earth.

Revontulien ensikajastus
(Panorama of three vertical images, projected as Panini to give an exaggerated sense of perspective without stretching the image.)

Revontulivyö heijastuu tyynen järven pinnasta

Revointulikiekura Siilinjärven yllä

The northern lights even surpassed the light pollution and covered most of the sky:

Revontulet kirkkaimmillaan

Monday, July 9, 2012

Opportunity's latest 360 degree panorama

Below is a spherical panorama shot and stitched by NASA from 817 images taken in Mars by Opportunity rover using the one megapixel Pancam. Images were shot between December 2011 and last June.

It's a false-color image meaning that the colors differ from what human eye would see. As the landscape is mostly orange, using narrowband filters enable the scientist to see better the interesting features of Martian lansdcape.

The local south is located at the visible seam. Above the metal pole is the crater Endeavour, where the little rover visited in 2011. There's lots of dust settled on the solar panels, which will probably be the end of the rover as power output of the panels falls under the threshold needed to operate the vehicle.

There are more (spherical) panoramic images available at Cornell's Pancam site.

(Image credit: NASA/JPL-Caltech/Cornell/Arizona State Univ.)

Monday, July 2, 2012

Viannankoski, Maaninka virtual tour

Below is a virtual tour of Maaninka's popular fishing resort Viannankoski. Press the compass button to bring up the image list. Last two panoramas in the list are high resolution partial spherical panoramas, about 180 degrees wide each.



Tour made with Saladoplayer.

This post was originally published on Pallopanoraamablogi on 2012-04-12 as "Maaningan Viannankosken virtuaalikierros".

Sunday, July 1, 2012

Huosiaisniemi, Juankoski conservation area virtual tour

On the border between Juankoski and Nilsiä, there is conservation area of Huosiaisniemi, where rare lady's-slipper orchid cypripedium calceolus grows.

Lehtotikankontti, Cypripedium calceolus

The yellow part of the flower reminds a slipper or shoe, hence the flower's name.

Kielonkukat Lehtotikankontti, Cypripedium calceolus


Below is a virtual tour made with SaladoPlayer. Navigating is done with the arrows which can be seen when pointing the camera straight down, green arrow takes you forward in the tour and red takes you back to previous panorama.

Thursday, June 28, 2012

View from Puijo tower

Below is 360 degree panorama from the observation deck of Puijo tower in Kuopio. The tower itself is 75 meters in height and resides on a 225 meter tall hill.

The panorama is over six hundred megapixels in size, one can zoom in quite deep into the image.


OpenZoom, press F for full screen mode or use the controls in image.

The observation deck looks like this:


Puijon tornin näköalatasanne in Kuopio

This post was originally posted on Pallopanoraamablogi on 2012-05-18 as "Puijolla".

Wednesday, June 27, 2012

Flat field box for fisheye

Flat field images are used in astrophotography to rid images of vignetting, dust on sensor plane and to even the general unevenness of light field. Shooting flat field images for longer lenses is relatively easy, one only needs an evenly illuminated featureless object. However, with fisheye lenses and their immense field of view and depth of field, there are certain problems one must solve.

Because the field of view is usually about 180 degrees from corner to in case if diagonal fisheyes and the same 180 degrees from edge of the imaging circle in case of circular fisheyes, one cannot just point the lens to something white and featureless and expect a good result. The lens needs to be quite close to the surface and the surface must be curved or round to cover the whole field of view.

The surface also must be non-reflecting. This can be achieved using white acrylic glass which is then sanded with very fine grit, around one thousand in CAMI grit designation. Coarse sandpaper should not be used to avoid visible streaks.

Unusable flat field image from fisheye
(Stuff gets reflected into the flat field image.)

Another problem is that the camera and lens casts a shadow on the acrylic glass. One must block the light entering behind the camera, black cloth or black painted flat field box can be used to counter the extra light.

Here's one version of a flat field box for fisheye lenses:


1: inner walls should be painted black, 2: curved acrylic glass sanded matte 3: diffuse light source, be it a window or similar. Top and bottom should also be covered.

For circular fisheyes the acrylic glass should be curved in two dimensions, not just one to cover the field of view. Hot air blower can be used to help making the curvature. Paper should not be used in place of the plexiglass as it is not homogenous enough.

Below is an example of the effect of flat field correction on spherical panorama embedded with Saladoplayer.



Look straight down for the most visible effect. Here's single image, with flat field correction enabled and without:

Kalansilmäobjektiivin värivääristymien korjaus Raw Therapeen flat field correction -työkalulla

Flat field correction was done in Raw Therapee. It detects the lens used and loads the corresponding flat field image automatically. If there are multiple falt field images, the images are either stacked or the best one is selected using various criteria.

This article is adapted from post on Pallopanoraamablogi titled "flättiboksi kalansilmälle" and "flättiruutujen vaikutus pallopanoraamoihin".

Tuesday, June 26, 2012

Sirui K-20X ball head in review

I've been shooting for years with my Chinese-made unbranded KS-0 ball head that I bought from Dealextreme.com. While it is quite sturdy ball head, it has some quirks, which've led me to look for a better alternative. The alternative which I've now bought is Sirui K-20X which I'll now review.

Sirui is also made in China, but it tries to separate itself from the numerous white box manufacturers as a premium brand. Sirui's K-20X ballhead was purchased from Poland, Foto-tip.pl's online store to be exact. Amazon also sells the same head for about the same price.

Below are the main specifications of both ball heads:

KS-0 Sirui K-20X
KS-0 Sirui K-20X
Approximately 31€ at time of purchase, now a tad more (Dealextreme.com) approx. 100€ (foto-tip.pl)
The tightening mechanism of the ball is with two screws. Panning has also its own screw. Screw handles have rubber coats. The tightening mechanism of the ball is made with one screw with a limiter. Panning has its own screw. Screw handles have rubber coats.
Arca-Swiss compatible quick release plate with anti-slip rubbers. Can be attached to tripod with either 1/4" or 3/8" screw, adapter supplied. Arca-Swiss compatible quick release plate with anti-slip rubbers and anti-twist feet. Can be attached to tripod with either 1/4" or 3/8" screw, adapter not supplied.
approx. 475 g approx. 400 g

Build and construction

Whereas KS-0 was delivered in white, partially crushed cardboard box without any documentation whatsoever; had the Sirui's ball head instruction written in good English, nice neoprene pouch and Allen key. Even though the pouch probably won't be used and the instructions for simple accessory aren't really needed, it gives warm and fuzzy feeling in the customer.

Both ball heads have Arca-Swiss compatible quick release plates. Sirui's supplied TY-60 quick release plate is tad larger (60mm x 48mm) than KS-0's plate (40mm x 50mm) and features anti-twist feet for attaching heavier cameras. Sirui's quick release plate's screw also has hexagonal socket to tighten the screw further than is possible using bare hands. KS-0's quick release plate's screw has a slot that can be tightened using a coin or similar, it has no handle unlike the Sirui's screw, which is a nice detail.

Thursday, June 21, 2012

Our galaxy and sky in infrared light

NASA released some time ago full sky image taken by WISE (Wide-field Infrared Survey). Unluckily NASA only released the image as a flat, zoomable image instead of spherical panorama which it is so I'm releasing one.

Below is embedded spherical panorama with SaladoPlayer of the sky in infrared light. In the middle is our galaxy - The Milky Way - as a bright stripe of stars since we are observing it from the inside accompanied by the surrounding skies.


Image credit (IR): NASA/JPL-Caltech/WISE Team, image credit (visible): PhotoPic Sky Survey, cc-by-nc

From the drop-down menu one can change between visible light sky as captured by Photopic Sky Survey and the infrared sky. I've also added some informational hot spots to the image to help navigating oneself in the image. The panorama can also be seen in 360cities.

This post originally appeared on Pallopanoraamablogi as "Infrapunanäkymä galaksiimme" at 2012-03-17.

Kuopio's marketplace in a gigapixel panorama

Below is 2.7 gigapixel panorama of the Kuopio's market square renovation. You can zoom into the image and drag it around.


(One can change the panorama on the fly from the drop-down menu.)

Technical notes: middle portion of the image is shot with the venerable 105mm f2.8 VR Micro-Nikkor. Four rows of images were shot and stitched together in Hugin. Additionally, two rows of images were shot with Tokina 11-16mm f2.8 lens at 1mm setting and stitched together. These two panoramas were then combined to offer both resolution and good coverage over the scene.

Because handling and processing of images that are in the size of several gigabytes or -pixels is quite challenging, the panorama was stitched straight into cube faces with Hugin and Multiblend. Surprisingly, this worked quite well as no seams between the cube faces can be seen.

However, the tiling of the image for displaying didn't go so smoothly as SaladoConverter kept crashing. So, the tiling had to be done with Zoomify's ZoomifyConverter and the tiles renamed to conform to file and folder structure SaladoPlayer uses. Since Zoomify doesn't use any overlap between tiles, some seams can be seen when zooming is set to minimum.

This post originally appeared on Pallopanoraamablogi as "Kuopion torityömaa gigapikselipanoraamassa" at 2012-05-19

Adobe Lens Correction Profiles compared

Adobe Lens Profile Downloader profile info window Version 4.0.9 was released of the raw photo process raw Therapee, which has the ability to use Adobe's Lens Correction Profiles (LCPs). LCPs can correct light falloff (vignetting), lens geometry (distortion) and chromatic aberration. Raw Therapee itself doesn't have any correction profiles built-in, but one can acquire most of the by installing Adobe's Camera Raw with Photoshop or DNG Converter. Not all lenses have correction profiles, for example the Tokina 11-16mm f2.8 lens wasn't included so it had to be downloaded separately using the Lens Profile downloader, a small AIR applet. Funnily though, Samyang's 8mm fisheye lens didn't have a correction profile at all.

Care must be taken when downloading the profiles. Most user-supplied profiles only have vignetting correction measured for only one small aperture. For example profile that has light falloff correction only for aperture f/11 can't be used to remove vignetting at larger apertures. It's a good idea to take a look at the calibrated apertures and focal length before applying or downloading the profile, see the screen capture on the right-hand side of the page for example of a quite thorough profile.

Below is a mouseover image with a lackluster profile that has the light falloff correction only for aperture f/11. Even though there seems to be some extrapolation of vignetting correction values, it is just not enough to rid of all of the vignetting.


Move mouse over the image to see the LCP corrected image, flat field corrected image acts as a reference. Image taken with the Tokina 11-16mm f2.8 lens with wide open aperture and at the lenses widest setting.

Below is another example image pair with a better profile, that corrects most of the vignetting. Do note however, that the corner color shift can't be corrected, hence the greenish cast in the extreme corners.


Move mouse over the image to see the LCP corrected image, flat field corrected image acts as a reference.

For example, there's user submitted profile for the old Nikon 50mm f1.8D AF lens that's been calibrated twice for each aperture at different focusing distances. Focusing distance can affect the vignetting and most probably the distortion of the image. However even that profile can't correct for the hot spot problem the lens has; at smaller apertures (f/5.6 and onwards) a round, brighter area appears in the center of the image. It's cause by the aperture blades reflecting light back from the sensor.

Below is a mouseover image pair, flat field corrected photo is used as a reference.


Move mouse over the image to see the LCP corrected image, flat field corrected image acts as a reference.

Both Sigma and Tamron offer 'official' profiles straight from the manufacturer, Nikon and Canon seem to want to keep the users on their own respective pieces of software.

This post originally appeared on Pallopanoraamablogi as "Adoben korjausprofiilit" at 2012-05-12

Welcome

Tukkimiehentäi (hylobius abietis)Welcome to Equirectangular, the blog with and about photography, panoramic photography, spherical panoramas and virtual tours.

This blog will (hopefully) be the English language off-shoot of Pallopanoraamablogi, which I've been writing since spring 2010. Most posts shall be translated from the master blog, but we'll see if there's any exclusive content to be posted here.

Siilinjärvi's Tarinaharju forest path virtual tour

Tarinaharju virtual tour thumbnailsSiilinjärvi's esker area known as Tarina has some very popular pathways. Housing an old TB hospital, the area was known for its fresh air in the beginning of the 20th century.

Below is embedded a sixteen image long virtual walk, the green arrow takes you deeper into the forest and the dark orange/red moves you backwards in the tour. A thumbnail list of the images can be seen when clicking the middle button (compass) in the bottom-right corner of the player. All the beautiful places of Tarina without the annoying mosquitoes.



This post originally appeared in Pallopanoraamablogi at 2012-06-08, titled "Virtuaalinen metsäreissu Tarinaharjulla"