The 2″ IDAS-D2 LPS filter for use with my William Optics Zenithstar 61 refractor telescope with a Canon 5D MkIV camera.
This is a quick play using the IDAS-D2 filter on the Canon 5D MkIV camera and a Canon 100mm macro lens to see what the colour cast was like in diffused daylight.
The filter bandwidth rejection ranges can be seen below;
For info, I used a standard M58-M48 stepdown ring to mount the filter to the Canon macro lens and I think that configuration will work for normal DSLR night photography with the Canon lens without any significant vignetting.
In the ‘real’ world the IDAS-D2 filter is performing very well
A lot of Nikon camera sensors are ISO invariant and unexposed images taken at ISO 100 can be recovered in post processing without any significant image degradation.
Most of the earlier Canon sensors are ISO variant and suffer from a purple colour cast when any underexposed shadows are recovered in post processing.
The Canon 5D MkIV sensor, at first glance, is also ISO variant but after testing it appears like the 5D MkIV sensor in ISO invariant from ISO 400 upwards (at least to ISO 3200) which is where I stopped testing.
Baseline exposure @ ISO 3200, f/8.0 1/50 second correctly exposed
Underexposed by 1 stop @ ISO 1600, f/8.0 1/50 second and then increased by 1 stop in Lightroom
Underexposed by 2 stops @ ISO 800, f/8.0 1/50 second and then increased by 2 stops in Lightroom
Underexposed by 3 stops @ ISO 400, f/8.0 1/50 second and then increased by 3 stops in Lightroom
Underexposed by 4 stops @ ISO 200, f/8.0 1/50 second and then increased by 4 stops in Lightroom
Underexposed by 5 stops @ ISO 100, f/8.0 1/50 second and then increased by 5 stops in Lightroom
By comparing the ‘corrected’ images above it is clear that if the exposure is correct metered at ISO 3200 and then an image is shot at ISO 400 it is possible to comfortably increase the exposure in software by at least 3 stops without any image degradation.
There is obvious image degradation at ISO 200 and ISO 100 where the purple cast starts to appear in the dark colour square and image noise increases but ISO 400 seems to be the ideal ISO to work with if you want to retain highlight details and increase the dark regions thereby maximising the dynamic range of the camera.
Just when you thought you could put the cameras away after chasing the Northern lights through the winter the season for hunting the Noctilucent clouds is almost upon us again. This page will be updated as and when I manage to capture some NLC images for this year.
Noctilucent clouds or NLCs are the jewels in the twilight summer skies, they are also called Polar Mesospheric Clouds or PMCs. For a month or so before and after the Summer Solstice, which is June 20th in 2016, they can shine and dance brightly in the rich blue background of the twilight and dawn skies.
It is only during this short period that the very high Noctilucent clouds can form just below the mesospause layer of the atmosphere approximately 80-85km above us. They require temperatures below -123c which only occur at these high altitudes around the summer solstice period and are created from microscopic particles surrounded by ice crystals which scatter the sunlight. This website provides details of the daily temperatures in the mesopause layer which might aid in forecasting the appearance of the NLCs.
Because of their very high altitude they are the only clouds illuminated by the sun when it is at least 6 degrees below the horizon (approximately 40 minutes after sunset or before sunrise). When the sun reaches 16 degrees below the horizon (about 2 1/2 hours after sunset or before sunrise) the clouds will not be illuminated and they disappear into the night sky waiting to be reborn by the predawn light of sunrise.
They are commonly confused with high white Cirrus cloud which is still illuminated by the sun shortly after sunset or before sunrise or by the moon against a dark sky, but on a moonless night with the sun more than 6 degrees below the horizon you are probably seeing the white or bluish white NLCs.
To view the NLCs you need nothing other than patience, clear skies with little or no light pollution, the right atmospheric conditions and a clear view to the northern horizon. They appear in the Northwest to Northeast direction above the sun’s position below the horizon. Before midnight they are in the Northwest and as the night progresses drift further to the North and Northeast.
To photograph the Noctilucent clouds I would recommend a decent DSLR but a good bridge camera can also capture them. Fast wide angle lenses, with an aperture of f/2.8, will allow you to use a relatively fast shutter speed of around 10-15 seconds. Longer exposures will tend to blur the fine detail in the clouds as they move across the sky. If you use telephoto lenses to capture the very fine detail in the clouds then the exposure times will need to be reduced to a few seconds to avoid motion blur spoiling your photographs.
A tripod, or a good solid wall, is essential to support the camera during the long exposures and a remote intervalometer is ideal to minimise any camera movement. Manually focusing on a star and then turning off the autofocus function will ensure the lens remains focused on the clouds rather than hunting for the correct focus point and manual exposure, or exposure compensation, is necessary to avoid overexposing the surprising bright NLCs.
Some beautiful still photographs can be taken and if you have the time then taking a lot of images for a timelapse can be very rewarding as you will see the structure of the Noctilucent clouds change as they flow and ebb across the night sky.
If you are very lucky you might catch the NLCs and the Northern lights in the same evening. The timelapse below was captured on the 23rd of June 2015 and shows the Northern lights and Noctilucent clouds from Cemlyn bay on Anglesey.
For more information and scientific details of NLCs I would recommend visiting the Atmospheric Optics and NLCNet websites and the website of the NightSkyHunter for a fascinating insight into the classification of the NLC structures. Spaceweather.com also get some beautiful NLC images when the season kicks off.
The countdown has begun for the new season. Good luck and good hunting !
This is a small collection of photographs and a 360 degree digital tour which will grow over time as I revisit the Tewkesbury Abbey. If you wish to read more about the Tewkesbury Abbey I would recommend visiting the official website
Tradition, originating in the desire to account for the name of the town, would assign the foundation of a cell or chapel to Theoc, or in Latin form Theocus, in or about 655. In support of this theory Camden and others assert that it was called in Anglo-Saxon times Theocsburg or Theotisbyrg. Others would derive the name from the Greek “Theotokos,” as the Church is dedicated to St. Mary, and others again refer us back to a very early name, Etocisceu—Latinised as Etocessa. In Domesday Book the town is called Teodechesberie, and throughout the Chronicles of the Abbey is called Theokusburia.
The Chronicles of the Abbey tell us that the first monastery at Tewkesbury was built by two Saxon nobles, Oddo and Doddo, in or about the year 715, a time when Mercia was flourishing under Ethelred, and later, under Kenred and Ethelbald. It was dedicated to the Virgin Mary, and endowed with the manor of Stanway and other lands for the support of the Benedictine monks who, under a Prior, were there installed. Oddo and Doddo died soon afterwards, and were buried in the abbey church of Pershore.