my comments may be a bit misleading. They are a bit tongue in check in that The good Fuji films we have been using, both the Superia Xtra 400 (FSX 400) and the Superia 200 (FS 200) are readily available right now. The big question is the unkown quantity of, for how long. There have been good films available to us in the past that were around for several years until the film companies changed the chemistry. We are at the whims of the film companies on this, and beleive me they don't even consider the astrophotographers at all. My mate Noel thinks that in a few years time we not be able to get film at all because of the continuing developments in digital photography.
Widefield or telephoto focussing of the film camera is the easiest of all. Film camera lenses have focus point called, 'infinity,' which looks like a stretched side-ways figure 8. Filming through a telescope requires a different technique called, 'knife-edge focussing.'
First you need a knife edge device. This needs to have a bevelled edge like a knife edge. We lost our purpose built knife edge and so we used three Stanley Safety knife blades, which by nature are very sharp so you have to be careful. You slide the knife edge along the film rails in the back of the camera (see pic attached). by this stage you have attached the camera to the 'scope, opened the back of the camera, inserted the cable realease and started an exposure on the "B" setting (B for Bulb) which holds the aperture open for however long you want. You can directly view the star by moving your head around so that the star avoids the central obstruction caused by the secondary mirror.
You point the telescope at a fairly bright star. with the aperture open you look through the back of the camera and see the star as a bloated, out of focus disc. This is because you can't get your eye to the actual focus point (see diagram attached). The third diagram shows what happens to the appearance of the star disc as you go in and out of focus.
As you slide the knife edge across the star disc you may notice the knife-edge crossing from the direction that you are moving the device. Change the focus and see if you get a difference. When you hit the sweet spot of focus the star blinks out instantly. There is no gradual drop off in light intensity. Then you load the film into the camera and you are ready to start shooting. If you accidentally change focus at any stage then you will have to rewind the film and take it out of the camera and repeat the focussing again (avoid this at all times. It can be done but it aint no fun!)I
Thanks for the heads-up on the film - yes, I see where you're coming from. If memory serves, fuji provia 400 was all the go until it disappeared from the market. Then kodak E200, etc. etc.
I would be keen to know your thoughts on slide v film?
Thanks also for the detailed knife edge focussing explanation - nice reference. I have read about this procedure before - sounds a little scary! But this game is not easy.
we used to use hypersensitized 100 ISO slide film in the late 80's. It was Fuji D-100. A brilliant film, grain structure, colour balance just superb, but we found the 1 hour long exposures for things like NGC 253 were a bit inhibiting, so in the end we went for the faster but grainier films, including Konica 3200.
This is what i like about the new films out now. you don't have to reach out to 3200 ISO to get a quick result. Even the Superia 200 we used the other night has a great colour range and very acceptable grain. It could be more than 20 years since I used slide film so I can't comment on things like suitability. I guess we could just try a few shots to see.
As for knife edge focussing, it is a skill that you just have to practice a fair bit of to get good. You can shag around for 15 minutes or so before you get the first attempt sorted, but after awhile you can cut this down to a few minutes.
As with everything to do with film, you just have to get into a good regimen with your procedures to ensure the right results. There is no way of doing a check as you go along as you can do with digital.
The other difference between now and twenty years ago is the way you can combine the simplicity of film and the subtleties of the digital process these days to get the best result. All the things that were very complex or unattainable in a dark room situation are relatively simple in many of the imaging software programmes available now.
There is no doubt that the march of the digital revolution is picking up pace, and in many respects leaving film way behind, but film is not dead just yet. It just smells funny
Loooong time ago I made for my Practica VLC3 (still working, BTW) a special focussing microscope, that was plugged into it instead of prism (I cannibalised one of it's frosted glass viewfinders, they were cheap).
Of course, I needed to adjust the mirror, so the correct focus in viewfinder was corresponding to focus on the film plane.
I was using it couple of years back, for a Moon eclipse.
Perhaps I should try it again
I've never gone down this track but I'm very much aware of hypersensidising film to slow reciprocity. I was introduced to this process in the 80's by Chris Floyd here in Adelaide who used to sell his astrophotos at the brickwork market - fantastic work, and what got me initially interested in astronomy and imaging.
Ian, are you simply scanning your prints to produce a digital image? Hope you don't mind all the questions.
that is an intriguing way of doing it. The frosted screens are just anathema to astrophotography. One thing I forgot to mention to Nix earlier on is that before you start the knife-edge focussing you can get it really close and save a lot of time by focussing through the camera first to at least get you in the ball park.
Yes Nix you can just scan the print to get a quick digi image, but if you have access to a neg scanner then I would recommend this process to obtain a better digital image to work with. If you can scan to 2400 dpi I would suggest that this is the way to go.
It was an interesting read about film photography, I guess I am one of the many budding Astro-Photography amateurs that has not seen this process in action. I can only imagine the paradigm shift in skills and acceptance necessary for the digital method to take off, all the while un-be-known to me.
Maybe I will have a go at it once I get my skills up a bit in the basic's
Whats interesting is the resolution. I punched 70mm apature at f6 (420mm FL, close) with a 40D into CCD calculator and got 2.8 arc/secs/pix image scale. On zooming right in your stars are much smoother than what a 2.8 asp would render on a DSLR, nice work.
if you are thinking of trying out some basic film astrophotography firstly you need the right sort of camera. A fully manual (no batteries required) camera, which tend to be the older models from the 60's and early 70's, that have a "B" and or a "T" setting enable you to do long exposures. If the camera has a B setting then you will need a cable release to hold the shutter open.
If the camera has a T setting then a cable release is not required (see the picture of the top of my old Nikon F, made in 1967, which has both settings on the exposure dial). Because the mirror flip in a single lense reflex (SLR) camera is quite aggressive and creates a large vibration at the start and end of an exposure, it is best to cover the front of the lense with a dark card prior to the start and finish of an exposure. With the T setting you just push the firing button to start, and turn the exposure dial to another point such as 1000th of a second to finish the shot.
Some of the later automatic cameras do have a manual override when it comes to doing time exposures so that the batteries aren't worn out at all.
A simple test of the film and camera is to do a few trailed shots on a tripod. I've attached an example here taken with a 50mm lens at f/2 (the lense wide open to get the most light) and let go for one minute showing the Pointers, Crux and Eta Carinae using FSX 400. To cut the star trails down you could shorten the exposure to say 45 seconds. Nearer to the equator you have to make it no more than 25 seconds to keep the stars close to round. Always record what you are doing so that you can learn from each session. Camera details, lense, f/ stop, exposure , subject, location, sky conditions etc. Give it a go sometime. You will be surprised at what you get
Bassnut,
I hadn't gone into it to that extent so I find that very interesting indeed! After 35 + years of doing this I find I still use the old (with the emphasis on old!) eyeometer. If it looks good then I am happy. If it looks coarse then I try to figure a way to overcome that. Even the grainiest of films can come up with a good result as long as the film is really saturated, i.e. exposed properly. No good doing short exposures with coarse grained films, unless you like that sort of effect.
Hi Bojan,
that is an intriguing way of doing it. The frosted screens are just anathema to astrophotography.
It worked absolutely fine
Here you can see the microscope disassembled - the front lens is objective from 8mm movie camera - reversed of course, and eyepiece is from old broken binos. The magnification is around 50x, so every detail of frosted glass and projected stars are clearly visible.
Prakticas are still available from time to time on ebay.. very under-valued camera here in the west, but very fine quality stuff, absolutely comparable with much more famous brands from those times, me thinks. There was also a magnifying lens (10x) offered by Pentacon but I never found it in the shops, so I decided to build my own.
some good points there regarding there being brands other than the usual suspects that are perfectly good cameras. You are proof that astronomers have been leading the way in recycling for years. Broken binoculars are never really broken, they are just transformed.
I gather from this that you were able to do direct focussing as one does through a standard eyepiece? I'm guessing that the 10x magnification made it that much easier to achieve focus.
