INSTRUMENTS I USE FOR IMAGING THE SUN

Some of the numerous possibilities for reducing the intense light when observing or imaging the Sun is to use either a front or aperture solar filters such as Inconel or Mylar materials or the use of a solarprism or what is popularly called the Herschel Wedge. I had in the past used numerous kind of aperture filters such as Thousand Oaks Inconel glass filters, Solar Skreen Mylar Filter and lately the very good Baader AstroSolar filters but they are very optimum for my use only with whole disk solar imaging and are not that good for high resolution solar imaging because the filters are dense and thus gave me slow shutter speed when imaging the Sun and thus reduces the sharpness of the image caused by vibrations.

The Herschel Wedge can be used just as well for solar photography as for visible observations. The solarprism used by me is a 2 inch Helioscope with Herschel Optical Wedge made in Russia by INTES.

The main characteristics of the INTES Herschel Wedge are:

Entrance: 2 inches
Exit : for use with 2 or 1 1/4 inch eyepiece and various camera adapters.
Method of reducing light and heat : reflection
Transmission of light : ± 90%
Absorption : ± 5%
Total reduction of light : ± 95%
Type of image : reverted

Filters : 48mm B+W ( Schneider-Kreuznach ) Neutral Density (ND 0.6, 0.9, 1.8 and 3.0) and Linear Polarizer.

Made by Baader Planetarium from Germany, this type of aperture filter is made from optical mylar film that has a density of about 5.0. This filter is normally sold unmounted and comes in sheets of 8.5"x 11". So one has to make his/her own filter cell like the one you will see from the picture. I use illustration boards to make my filter cell and thus save you money. They are generally used for visual and photographic purposes. Image through these filters are very good and gives a whitish color rendition of the Sun. Contrast is very good and you can see good details of sunspots and faculae from the face of the Sun. Please note that careful handling of the filter is a MUST as this film material is very thin and easily torn or punctured.

Photographically, this filter is best use only for whole disk solar imaging only as they require you to use slower speed exposures that tends to make the image a little low in quality due to vibrations.

Also made by Baader Planetarium, this filter is best suited for PHOTOGRAPHIC use only as it has a density of only 3.8 so the image is very bright when use visually. Made of the same material as Baader AstroSolar 5.0 filter, the image it produces still also whitish. Utmost care is also required in handling this type of filter.

I tested this filter and find it still not that great for high resolution imaging of the Sun as the density will give you a fast exposure mostly from whole disk and moderate resolution imaging of the Sun only. For high resolution, it will still give you a slow shutter exposure thus magnifying the vibration easily. Using a very massive mount might help reduce the vibration with the tradeoff of heavy lifting and assembling of the mount itself.

Manufactured by Thousand Oaks from the USA, this type of aperture filter is made from glass and are also mostly called Inconel filter. Coated to a density of 5.0, this filter is best use for visual and whole disk imaging only. This filters produces an orange rendition of the Sun that is very pleasing to the eye. Image contrast is also good but I mostly use this filter for public viewing as this filter comes mounted on an aluminum cell thus is more secure when attached to the from of the telescope. Unlike the mylar type of filter, this filter is more durable and can withstand lifetime use except of course you drop it to the floor! J

Manufactured also by Thousand Oaks, the material is also the same as the type 2 except that this has a density of 4.0 thus is use only PHOTOGRAPHICALLY. Color rendition of this filter is light orange. Best use only for whole disk up to moderate resolution imaging of the Sun as it gives a slow speed exposure when used in moderate resolution imaging. Also comes along in an aluminum cell and can withstand a lifetime use J

Made by late Roger Tuthhill Company, Im not sure if there is still any available for now after his death. Thus the Baader AstroSolar seems to have taken up the slack it vacated. Anyway, this filter is alos mostly sold in sheets and be mounted by yourself, quality of this filter was the best before the Baader invaded the market several years ago. Coated to a density of mostly 2.5 average, this filter needed 2 sheets to make up the safe density of 5.0 for visual and photographic use. I have use this filter before with great results. One good thing about this filter is that if one plans to use this filter for high resolution work, I most of the time use only 1 sheet of filtration thus giving me a density of around 2.5 thus will give me better speed exposure than what the Baader can, but sad to say it it no long er available in the market.

Color rendition of this filter is bluish-white but the background is not that black as that of Baader's which I find a little distrating. Although I still have some more of this filter material stock safely, I no longer is using them because I mostly do my high resolution with the Herschel wedge.

I got this camera this November 2001 only as the trend to digital photography is starting to peak and might make a run for the money against the SLR system. The CP995 has a 3.34 megapixel resolution and uses both Compact Flash Type I / II memory card instead of film. It also has a zoom range up to 4x optical plus 2x digital for a maximum of 8x zoom. I seldom use the extra 2x digital zoom as it only magnify the pixels only so I normally set the extra zoom capability to OFF to avoid accidentally activating it after I made full zoom. Exposure ranges from 1/2400sec down to 8sec plus a bulb exposure of up to 60 seconds. ASA range is from 100 to 800. There are 4 picture quality mode namely, HI, Fine, Normal and Basic. I normally use the FINE mode in astronomical imaging and use the normal mode for terrestrial imaging. The reason I don’t use the HI is that it takes so much memory to process image file (TIFF file) against the FINE mode (JPG file) . There is an LCD monitor of 1.8" for one to see what he/she is imaging. It also has an option to use a remote cable release MC-EU1 but I opted not to get it because its expensive ($125+) and most of the features for that expensive accessory is not suitable for astroimaging use. I just fabricated a aluminum bracket to hold down the shutter using a very inexpensive manual cable release.

Image quality is also very good specially when I use it in conjunction with my 4" f/5.4 TV-101 apo-flourite refractor afocally to image the Sun. Since the CP995 built in lens is not removable, I use Adaptiview-U from Scopetronix to attached the camera to a selected eyepiece for afocal work. Eyepieces that I use are 35mm Panoptic 2" for whole disk solar and lunar imaging and either use the Nagler 4.8mm and the 7mm for hi-resolution close up imaging of the sunspots and craters of the Moon.

FILMS

In order to photograph the smallest details that can be seen, the choice of film used must be exceptionally fine grained, and therefore you have to use films of low and middle speed. I have good experiences with Fujichrome Provia 100 slide film which gave me moderate speed and is fine grained. But there is no doubt that the best film for imaging the Sun is no other than Kodak Technical Pan film. It is extremely fine grained and I have been using this film in conjunction with the Fujichrome Provia 100 slide film. Technical Pan film is not available locally and I have to get it in the US with the help of my friends who live there or are coming back to the country.

For solar photography as in all astrophotography, the general rule is that all photo processing should be do-it-yourself to obtain the most satisfactory results. The film should be developed in an energetic developer to make the best use of the sensitivity and in order to get high contrast. I use Kodak HC-110 dilution B with a ratio of 1:31 which means 1 part concentrated developer and 31 parts of water. The film is developed 5 to 6 minutes at 20°C, agitation the first 30 seconds, after this agitate 5 seconds every 30 seconds thereafter.

As for the slide, I normally just bring the film to the local film developer to let them process it. That's the reason why I still use this film in conjunction with the Kodak Tech Pan as I can readily see the results in a short span of time.

After developing the slides and the negatives, I initially use an Acer 2720 Film/Slide Scanner to scan them and use Adobe Photoshop software to enhance the image to get the best out of the best positive/negative that are selected. I then print the image using EPSON Photo750 printer and EPSON Photo Paper to print the results.

In the near future, I plan to construct my own dark room so that I can also get the best results on a more permanent basis as photo prints last longer than most available photo papers for printers.