The choice of the optical setup for a solar eclipse - if one wants to reach some good results and not just shoot casually - is not so straightforward. I did not want to shoot the partial phase and I was basically interested in taking pictures of the prominences and of the solar corona. The unknown part of the event is the extention of the solar corona which varies according to the solar activity, the transparency of the sky, the height of the sun on the horizon, the height of the observation site above the sea level, etc.

An additional variable to take into account is of course the equipment one happens to have and decides to and/or can carry. If one has several telescopes and cameras and wants to cover all aspects of the eclipse, it is worth having a look at Bob Yen's site on internet (http://www.comet-track.com/eclipse/secl98/secl98.html) where he explains how he took 11 cameras and 21 lenses to Cura�ao and how he made them work thanks to some electronic equipment described in the Eclipse Chaser site (http://www.eclipsechaser.com/).

Otherwise, if you want to travel light, you might be interested in reading how I decided on a single telescope, a single camera and a very simple mount.

I began taking notes for this article before the eclipse. For a good reason. Such an unpredictable event always leaves the observer and the astro-photographer in the uncertainty. Each decision, although correct, tends to give preference to certain aspects of the phenomenon while putting aside equally important ones.

The choices made are no more than working hypotheses in a complex system of questions and answers. It seems useful to share, as far as possible, the thoughts and criteria generating the choices, and which would suggest different solutions if/when a single variable would change.

For the final part of this article the notes were taken after the eclipse, to show which solutions worked, how they did, and where some weak points were found. But, once more, only by making the criteria explicit one gives meaning to these choices allowing better ones to be made in the future.

Eclipses are similar, but never identical: most solutions may simply not be adequate! And during a total eclipse seconds fly. If one makes a mistake, there is no second chance (as I personally learned).

Optical Setup (first part)

This was a rather difficult selection I was forced to make in the last few days late in the evening after working hours. I used mainly some optical targets and the reflex of a small laser pointer inside my flat because the weather in Paris was almost always cloudy.

My first hypothesis was a rather cheap, even though good, telelens 400mm f.6.3 which I have not been using for few years and I could have coupled either with a 1.6x or a 2x teleconverter. On paper this setup is tempting: it is very light (1/2 kg) and it would have not given any carrying problem easily fitting into my hand-luggage. The equivalent focals are either 640mm or 800mm, with a solar diameter on the focal plane of 5.8-7.3mm (see under "Focal Length"), enough to get some good resolution prominences and to frame a corona of 3-4 solar radii (what I was expecting and hoping). But when I made some optical test by putting an eyepiece behind the 400mm and trying to use it as a small telescope to evaluate its quality, I found out that the performances were decent only at f/16. This would have given an aperture of 25mm and an equivalent f/32 when coupled with the teleconverters. The whole setup having then 11 lenses and a theoretical resolution of only 5 arcseconds. I told myself I was not going to cross the ocean just to get some 5 arcsec pictures at the best, and I decided that the hassle of carrying something bigger would pay me back.

Second hypothesis was a higher quality telelens 500mm f. 5.6 with an excellent reassuring mechanical quality and with a higher weight (3.5kg). This otherwise perfect lens failed like the previous one on the eyepiece test. Images were good only at f/11 which means a 45mm actual aperture and 2.7 arcsec resolution. Not too bad if one considers the daily turbulence.

On the other hand I also happen to have a 90/1000mm refractor which was giving definitely better performances for less weight (2.5 kg) but a longer tube.

This third hypothesis sounded fine to me. The optical performances were correct. The 90mm lens was promising (and reaching) 1.3 arcsec resolution: more than twice what I would have had with the telelens. I had the additional advantage of using a simple two-lenses achromatic refractor (against the fuzzier 11-12 lenses setups envisaged above) with an evident improvement in the contrast of fine details of prominences and corona. And the 1000mm focal length was a bit long but still fine for my needs.

Focal length

I would open here a parenthesis on the selection of the focal length. Ideally speaking, to best frame both the prominences and the corona one needs two telescopes. The prominences photographically speaking are small (actually they can vary between some 20.000 and 100.000 km) and they look just detached from the solar limb. On the other side, the corona can shine for 2-3 solar radii and more.

To take pictures of the prominences one should make maximum use of the film format, knowing that on the focal plane the diameter of the Sun's image is approximately equal to the focal length divided by 109. With a 24x36mm camera one should use a focal length of about 2.000mm to get an image of 18mm which would give an additional 3mm circle for prominences to fill up the 24mm short side of the frame. This of course requires a solid mount with a motor drive to keep the sun at the very center of the frame and, additionally, a separate scope for the corona which - apart from its inner part - would be entirely out of the frame.

For the corona, as already said, the choice is a bet. I was personally guessing some 4 solar radii and then being oriented on a 600-800mm instrument. That is why a focal length of 1.000 mm sounded in principle a bit long - but acceptable - to me.

Optical Setup (second part)

I had a couple of reasons to drop the 90/1000mm refractor. First of all the mirror in my flat. I had with me a briefcase with some working documents and a 55x35x20cm cabin-luggage for astronomical and regular photographic equipment plus some personal belonging. In addition I put the 90/1000 in a sort of rifle carrying bag. Then I stood in front of the mirror and I played out a scenario of me trying to convince the customs officers to let me take all this as carry-on luggage. The mirror looked at me and screamed: "no way!"

Furthermore, the long tube would have been very unstable on the photographic head I was planning to take (see under "Mount") and it would have required a more serious astronomical mount.

The other reason was my Vixen 80mm f.5 Shortfocus refractor whose optical quality is surprisingly good, even though not exceptional, for a regular achromat. I had a side by side test: the 80/400 was (obviously) softer than the 90/1000. Then I slipped into the focuser a 3x TeleVue barlow. Wow! The residual chromatic aberration got drastically reduced. The image was still not as good as in the 90/1000 but it was coming out of a 30cm refractor (1.5 kg)! This needed some consideration.

My only concern was the mechanical reliability. The focuser is fine when used with 1.25" eyepieces but evidently was not designed to support a heavy camera with a barlow in between. Dropping the barlow for the teleconverters would have taken me down to fuzzier images. I had a 45 cm setup with 1.5kg in the front, 1.5kg in the back and a tiny tube in between. I would have needed either two tripods (one to put under the Vixen and a shorter one under the camera) or a sort of platform to support both. Too tricky I thought. And I realized I did not have a solution to my problem.

In this report I am intentionally not mentioning two Maksutovs - a 100/1000 and a 150/1800 which - due to their greater sensibility to the daily turbulence - did not really make me enthusiastic about their performances on the sun against the lens-based telescopes.

After all these tests, I was definitely captured by the idea of using a small highly corrected refractor to perform the task. And I found out that my equipment, even though excellent for other purposes, was not good enough for what I wanted to do. Furthermore I started considering that since I was travelling to the other side of the world, this might justify an additional "investment"...

I started considering a sturdier alternative (e.g. a semi-apo like the TeleVue Pronto) - due to the practical unavailability of what I would have considered an excellent choice (read Astro-Physics Traveler, an apochromatic refractor 105/610mm) - when I ran into the instrument which I eventually selected: a Takahashi FS-78.

Even though what follows might look like a subtle advertisement, it is just a faithful report of what I told myself.

This 78/630mm two lenses fluorite refractor is the entry-level of the Takahashi line. For 24mm less in diameter than the bigger FS-102, it pays back with half the price and almost half the weight. Astonishingly, the French price of the FS-78 is 6.000 FF (i.e. some 136.000 €, its price in Japan!). In France a TeleVue Pronto is more expensive without having the same optical performances. The FS-78 weighs 3kg against the 2.7kg of the Pronto and the 5kg of the FS-102. The FS-102 would not fit into my hand-luggage and, more importantly, it would be a bit too shaky on a photographic tripod. And, once more, I could not carry a real astronomical mount to support it. On the other side the Pronto looks very small. When operational it is some 45cm long against the 74cm of the FS-78. But in the Takahashi both the eyepiece holder and the lens-shade can be easily unscrewed to reach the final length of 52cm. One could unscrew also the focuser and even the objective cell, but this might be less straightforward for many. Anyway, to break an FS-78 down to 52cm takes some 10 seconds. Now, even like this, the FS-78 did not smoothly fit in my cabin-luggage. Of course, if one wants to stretch the luggage a bit (mine has a metallic frame!) the tube does fit. But - I thought - why not just put it diagonally! And this still left space for the Vixen 80S (which I decided to also carry), two 24x35mm cameras, two medium-format cameras, 5 lenses, 7 eyepieces, various accessories and some clothes!

But, apart from this mere physical considerations, what really convinced me was the optical performances. As already mentioned, I happen to have a Maksutov 150/1800, what I call my "mirror-based refractor". This maksutov has an excellent star test and it's a pleasure to use with all my eyepieces, even 65 and 55mm Plössl or 35 Panoptic. Stars are pinpoint up to the edge and they do snap into focus. I did not intend to use it for the eclipse but - although the mirror was screaming: "forget it!" - I was still considering whether to bring it with me for deep-sky observations. After three side by side tests I found the two instruments of comparable quality. While the Maksutov was obviously superior in brightness since its receptor surface is four times bigger, the small fluorite refractor was catching up with its contrast delivering more pleasant images. This fluorite doublet does transmit a lot of light: stargazing at 18 and 23x with the 35 and 27 Panoptic was just superb. On the other hand the ease in holding the 250x provided by a 2.5mm Vixen Lanthanum was simply amazing.

For the sake of objectivity, it has to be mentioned that the tests were made in evenings with medium seeing conditions and without the Maksutov reaching its thermal equilibrium (which would take 1.30h against some 5-10 mins!). On the Sun, as already said, the FS-78 was clearly superior.

The bottom line is that, while the Maksutov remained in its native Europe, the Takahashi traversed three continents in two weeks.

The only modification I made - and I would advise to make - to the Takahashi was a custom 2" eyepiece holder instead of its 1.25". My camera was held without any problem, and on deep-sky observation the FS-78 took advantage of bigger eyepieces.

Focal Length (again!)

Having decided on the FS-78, I came back to the focal length issue. I had basically two possibilities: one more corona-oriented (using the Takahashi as it is), and the other prominences-oriented (adding a barlow or a teleconverter). I set aside the 3x and 2x barlows as well as the 2x teleconverter because the equivalent focal length was going to be too long: with 1300mm or 1900mm I was afraid of missing the corona on one hand and - despite the added ease in focusing on a bigger image - to loose details on the prominences for the amount of vibrations. On the other hand, the 1.6x teleconverter, providing an equivalent focal of 1.000mm seemed a good compromise to consider.

But the use of the Takahashi at 630mm without additional optical elements had its advantages. The purity and correction of the fluorite doublets would have given only a minimum of light absorption and probably the best resolution, if one would reach the optimal focus (see under "Focus"). Additionally, still following my hope for a big corona, as already said, a focal length of 630mm would have given a solar image of 5.8mm allowing me to record a full 3 radii solar corona in the 24mm circle.

However, to reach the final decision, some tests on film were needed.

Film

I like slides more than negatives and I decided to use a Fuji Velvia 50, a film I know very well. I also had the possibility of using a Kodak Panther 50 but, being not so familiar with it, I did not feel like taking risks. If one likes better the negatives, the Kodak Ektar 25 would be an excellent choice, which I shall consider as well the next time: I found out that developing and printing slides in some countries can be a hassle. With the negatives I would have had an easier life.

Mount (kind of!)

I actually could not carry anything bigger than a photographic tripod. And I wanted to take the best out of this limitation. I have several tripods and even quite sturdy ones. But I needed to travel light and after a few comparison I picked up a Manfrotto 190 with a fluid video head. This tripod has a special feature I have been appreciating during the last few years: the legs have three different position locks and can be opened at 45, 60 and 75ƒ. When opened at 75ƒ the tripod looks like a small spider and, despite its light weight (some 3.5 kg.), is extremely stable.

Once a tripod has been selected, there is a need to follow the sun without slow motions. I thought to solve the problem by putting between the telescope and the tripod a micrometric head designed for piggy-back photography. But although I gained in fine tuning, the head with the optics and the camera became too unstable. I had to think of an alternative.

I put the lower limb of the sun at the center of the viewfinder, I locked all the movements and I tried to counterbalance its motion just by small vertical shifts of one leg. Making a correction only when the higher limb was touching the center, I found out that I probably needed to touch the leg no more than three times during the whole event to recenter the sun which was moving in my viewfinder from top right to bottom left.

The setup was now extremely stable. It worked very well: both during my day-before test in Venezuela (sun at 65ƒ on the horizon) and during the eclipse.

Camera, Focusing and Visual Observation

I have two 24x36mm cameras and both were valid alternatives. A Nikon FM2n to be used with a DR-21 90ƒ Viewfinder, a MD-11 Winder and an E entirely mat focusing screen. A Nikon F4s with either a DW-20 Waist-Level Finder or a DW-21 6x High Magnification Finder and focusing screens E (architecture) and M (photomicrography).

A priori, the lighter FM2n seemed preferable. But the manual winding did not seem to me a very safe procedure in the three minutes concitation of the eclipse. The use of the MD-11 filled up with 6 AA batteries makes the weight of the two cameras rather similar. Additionally, the architecture designed E screen looked a bit too coarse to reach a fine focusing. The F4s is very heavy but has the advantage of a higher flexibility for the vast choice of focusing screen and viewfinders.

My first tests were based on the DW-20 + E combination. The focusing procedure was a bit easier (but still uncertain) than with the FM2n due to the slightly brighter screen and mainly to the 6x additional magnifying lens of the DW-20.

The waist-level finder had the advantage of allowing the monitoring of the sun position from a distance and - at the same time - to let me watch the eclipse.

For the visual observation, after having gone through several hypotheses (a big 20x70 binoculars, a regular 8x30 model, a 7x50 finder, a 6x30 finder, etc.) I had selected a combination of either 85mm or 180mm Nikon lenses coupled with a Lens Scope Converter giving either 8 or 18x.

Nevertheless, further tests made me change the whole setup. I had the chance of coupling the almost transparent microphotography screen M with the 6x High Magnification Finder DW-21. The quality of the view increased so much that not only did I discard immediately the lightweight FM2n hypothesis but I also put aside my visual setup deciding to observe directly through the camera.

To give an example, the DW-21 + M screen allowed me to focus on the penumbral part of the sunspots and even on the solar granulation using the FS-78 at its 630mm prime focus. The same setup allowed easily spotting and focusing Venus at 10:30 a.m., giving a clear view of the phase only a couple of days before the eclipse. I would definitely advise anybody who can, to seriously get/modify a camera with a combination of very bright (or, better, transparent) screen coupled with a magnifying finder.

This choice was the most successful part of the whole eclipse. I was able to see as clearly as using a telescope and, at the same time, to take pictures. The vision of the corona is something so beautiful, awesome and unbelievable that no picture can come close to the real thing. And the direct magnified view through the transparent screen made me so satisfied that I was even ready to accept the lose of all my shots when, at the beginning of the eclipse, the shutter release cable on the F4 got locked providing me with the most tangible example of Murphy's law: "if something can go wrong, it will". But we shall see this later.

Tests

One important - very important - thing to take into account, which I luckily found out before the eclipse, is that while the transparent screen gives wonderful views, the focusing operation is entirely unreliable because the eye re-focuses automatically the image as through a window.

To focus I could not use the sun: I needed to focus without a filter to avoid any focus shift. The moon was practically invisible and I started looking for buildings and tv-arials on the horizon. It has to be known that to have a reliable infinite position one has to focus at least at 10.000 times the focal length. In my case not less than 7 km. The further the better. By casually focusing and re-focusing buildings on the other side on Maracaibo Lake, I was led to mark the infinite in different points on the focuser!

The only solution was then an actual photographic test. I started putting 8 marks at 2mm each on the focuser and I shot a roll with different speeds for each sign to avoid turbulence effects.

This was the day before the eclipse: I got the film back just 20 minutes before the first contact. Luckily I was not interested in shooting the partial phase! I definitely advise anybody who is interested in trying the experience with the transparent screen to perform some tests well in advance!

On my tests, the 3rd and 4th marks gave a similar focus. I then put the focuser just in between and I locked it by the focuser knob. This was another crucial point. I had to move the camera at the very beginning of the eclipse to solve the shutter release problem and to re-frame the corona. Without a locking knob on the focuser, all the preparation would have been lost: during the totality it gets suddenly very dark!

Exposure times

The weird magic formula to keep in mind for solar eclipses is T = f^2 /(I x 2^Q), where T is the exposure time, f is the focal ratio of the instrument, I is the ISO film speed and Q a brightness exponent whose value is 12 for the Baily's Beads, 11 for the Chromosphere, 9 for the Prominences and from 7 to 0 for the Corona.

To make it easy, using a 78/630mm (f/8) with a 50 ISO film my reference time would be 1/4000 sec for the Baily's Beads, 1/2000 for the Chromosphere, 1/500 for the Prominences and from 1/125 to 1 second for the Corona.

Actually, because one does not have control on the transparency of the sky, each reference time should be bracketed of ± 1EV at least. For the prominences, for instance, it is difficult to decide a priori a good time between 1/1000 and 1/125. All of them have to be tried. Additionally, I know that the Velvia 50 rarely has a sensibility of exactly 50 ISO: often values of 40 or 32 ISO are more appropriate.

The solution is just to slowly try all the shutter speeds of the camera. Waiting a few seconds between each shot to allow the vibrations to stop and not to run out of film. Shooting once every five seconds, a roll of 36 frames lasts about three minutes.

Totality!

Here we are finally! Everything is ready. I am sitting like a Yogi on the terrace of the Simon Bolivar Planetarium in Maracaibo: with the tripod legs open at 75ƒ, and at their minimum height to gain in stability, the DW-21 eyepiece is at some 40cm from the floor. This is something I did not mention before: such a setup is not for everybody! The head of the tripod is locked, the camera adaptor is in the focuser which is locked as well between the 3rd and the 4th mark. The camera is loaded with a roll of Velvia 50. To reduce the vibrations I am using a shutter release cable that - of course - worked smoothly in all my tests during the last two days. I am using a solar filter and I am following the sun by shifting the left leg of the tripod every 45 secs.

The sun is now only a very tiny crescent. The light has been decreasing drastically during the last five minutes and a cool breeze has started blowing. The excitement in the air is palpable.

My friend Alejandro is waiting for me to yell out when to start shooting! Everything suddenly gets dark. I get rid of the solar filter and I scream: "goooo!" He starts shooting: he will get his Baily's Beads and the Diamond Ring. I try to do the same: no reaction! Geeezz! I do not know whether to watch the eclipse or to have a look at my camera. I give another couple of tries with the shutter release and then I give up. Fortunately the F4s - I love this camera! - has the hole for the shutter release separated from the shutter button. I try to stay calm, but it is gone! The eclipse started and I lost the very beginning. Fine: I cannot go back in time.

I try to mentally follow my shooting programme: I just know that I have to go down from 1/2000 to 2 secs and then come up jumping two steps every time. But I get awestruck by the beauty of the event, and I forget I need to count 3 secs between each shot: I am going too fast. I will run out of film eventually.

Suddenly the corona appears. Oh my God! I had never seen it so close and so clear at the same time: using the M screen I feel like I could touch it if I just reach out my hand. It is so delicate, so alive: it looks like a pearly transparent veil of pure energy shaped in the wind of ionized electrons. I see solar brushes on the north and south pole and small prominences all around. I see the equatorial streamers so unbelievably three-dimensional. And I see something more: I realize the corona is enormous; even bigger than what I've been expecting (in the discussions before the eclipse I was considered an "optimist" on its size...). The eastern and western coronal streamers are going outside my viewfinder. In a fraction of second I think I'd better use the diagonal of the frame (I should have thought of this in advance, of course!). Confident in the focus-lock knob, I unlock the camera, I turn it 45deg. and I lock it back. Perfect! The very external part of the corona is still outside the viewfinder but now I can see almost everything.

I start shooting again a bit, but then I stop to watch how the eclipse looks with the naked eye. All around is dark. There is an unreal electric blue light with a bright band around the horizon where the shadow ends. I see Venus, Jupiter, Mercurius and few stars. There is a hole in the sky and all our thoughts are swallowed by it. I cannot see more. I want to go back to my viewfinder and watch again the corona in details. I go on shooting and shooting, but this is no longer important: I am just trying to memorize everything I see. I am crying with joy and astonishment. Suddenly I remember the words of A. Stifter in his report of the total eclipse in 1842:. "...this was the time God spoke and all men listened". I have read this page several times. I am getting to understand it better today.

The shadow moves at more than 2.000 kmh: the darkness is suddenly over! I fall back on the floor, arms flung open, eyes closed, still savouring the glorious few minutes of total utter magnificence.

The totality was so overwhelming that nobody cares anymore about the partial phases of the eclipse restarting. The TV cameras are all around us: this eclipse is a big event! As several times in the last two days we get interviewed again. I am still crying and they want to know my first impression. What to say: "in these moments one would like to have two telescopes, four hands and six eyes!". I start describing the corona, its extreme brightness range of 10.000:1 that only the eye can capture and how our films cannot handle it. I tell them we are going to get a recorded image that will be only a distant pale epiphany of what we actually got to see and feel! I make a drawing. I do not want to forget this corona: it is the most beautiful thing I've ever seen.

Thanks God even today - as the faces of disappeared beloved people - this faint corona is still with me when I close my eyes and I want to see it.

Final Wisdom

The pictures came out fairly well, in the end! Prominences are nice while a digital image processing would definitely help some faint details in the corona to come out (see again Bob Yen's site for some examples of this). I realize that all my choices have been quite good. Going back in time I would just add a 250 fotograms back to my equipment to be able to shoot without problems (I did run out of film!). And maybe I would use the Ektar 25 to gain a bit more detail and for the ease in developing. As of the focal length, I would have loved to have something longer to reach a higher resolution on the prominences, but I do not regret the view I had of the entire corona.

Some important things I would remember: to perform very accurate focus tests, to select a sturdy and high quality optical setup, to shoot less and to watch more: one will always find a lot of good pictures around. The first-hand visual experience can be found nowhere.

Next year the shadow of the eclipse will cross northern France. Hopefully we shall have nice weather and we shall have two minutes of totality. Not having any weight limitation, I am planning to use two telescopes on heavy mounts and medium format cameras to gain at the same time in resolution and in field. But I am also planning to bring with me a couple of friends and let them play with the equipment. I would just observe through a good refractor: a zoom eyepiece would be the final wise choice!