Hi all,

Hope everyone is doing great! I just have a few quick questions. I've shot astrophotography on DSLR and it is my favourite type of photography. But I want to try and get into doing it on film. I have the MZ-7 with the 50mm 1.7 lens. I also have a tripod and the remote for bulb mode.
Is exposure the same as a DSLR? When I normally shot on my D3300 I'm using iso 200 and anywhere from 15 to 30 seconds. would 200 iso film be the same as the digital?

Sorry if this isn't a great post by thanks

Probably not. With film you have reciprocity failure to contend with. For shot exposures you may only need 1 or 2 stops extra for time or ISO but the longer you ideally would expose for the faster the increase. Different films have different recommended ways of handling reciprocity failure so for example here is Ilford's document on it for long exposures and their films. It looks like if you search for specific films you can find data for them and how the manufacturer recommends compensating for it.

Astrophotography is actually what caused me to make the jump to digital after burning through a roll of film and not getting anything. I'm not trying to disuade you from trying just offering some caution and trying to set expectations. I would love to see what an adept amature could do with film astro photography of deep sky objects or even tracked star fields. All of that said film is a great way to do star trails especially with a all manual mechanical camera that doesn't need a battery since all you need is a bulb cable to hold the shutter open for hours at a time.

Here is an image of the area of M8 and M20 taken with a DSLR (a Pentax K-3II). It is a 4-minute total exposure with a 200mm f/4 lens stopped down to f/5.6.



Here is an image of the same area with a similar framing (but without Saturn photobombing the shot!) taken with a 35mm film camera (an Olympus OM-1 with Fuji Provia 400F slide film). It is a 30-minute exposure taken with a 300mm f/4.5 lens stopped down to f/5.6. (Note that chromatic aberration from the lens has not been corrected in either case.)



Given the lenses and the detector sizes used in each case, the image scale is nearly the same (it would be identical except for a difference in cropping). In the case of the film image, the 300mm lens collects 2.25 times as much light, resulting in 2.25 times the photon density at the image plane. Despite this significant advantage, the film image doesn't show nearly the number of faint stars nor nearly as much Milky Way dust as the DSLR image, despite almost eight times the exposure time. The amount of reddish nebulae recorded is about the same but the pink color of those areas in the DSLR image is actually more accurate. And the DSLR image shows much more of the blue reflection nebula in M20 than the film image. (It's not clear, in fact, if the film image captured any of it at all!)

I did film for several years. I would never go back.

PS. The digital capture used ISO 1600 while the film capture used ISO 400. Knowing this, it would then be fair to ask if the ISO difference is responsible for the better performance of the DSLR. Not really. I could have used ISO 400 with the DSLR and got just as good an image. (I would have stretched the contrast more in post processing to achieve the same peak brightness.) The amount of noise would have been ever so slightly higher and probably not perceptible. Conversely, if I had used ISO 1600 film, the film image would have showed more nebulae and dust than it does at ISO 400 but would have looked distinctly "noisier." That's because in order to achieve higher speed the film would have been very much grainer.

Wow I love those deep sky shots. Most of what I've been able to do has been landscape stuff.

Thanks for replying,

So if I really wanted to shoot astro I should probably stay in digital until I get more confutable? The idea of shooting astro with film is kinda just something I would do for fun. Not something that I would take seriously. Another thing, back in the day did you ever shoot on the k100d/k110d? I know they're old but I think you could probably still get some great night sky images with them!

Really, it's the availability of processing that makes digital astro so, so much better than film.

Digital lets you stack multiple short exposures to yield an image with the same quality and signal/noise ratio as one long-exposure image. If one airplane or satellite passes through your frame during a 30-minute exposure (and for deep sky, we're often going for 2-6 hours' total integration time or even more), or you happen to kick the tripod, too bad so sad you lose. The whole night.

Heck the multiple-short-exposure trick even works if you're doing star trails (linked image was dozens and dozens of 30-second sub-exposures). If you want stars to look like stars, you need some kind of tracking (whether internal to the camera as with AstroTracer, or externally with a clock-driven mount). But those mounts have imperfections. Again, almost any clock-drive mount can do, say, 30 seconds' worth of exposure and have it come out OK, especially at shorter focal lengths. 30 minutes? It is to laugh. My thousand-dollar mount can do a few minutes at a time. For a half-hour exposure, especially without autoguiding, you're in the ten-thousand-dollar mount range.

Lew Dite casually posts the 30-minute film exposure as if anybody could pull that off, but believe me as an old film guy, that image is an amazing achievement. (Hand-guided, right?)

Then there's stuff like contrast enhancement (stretching), localized contrast enhancement, noise reduction...the list goes on for quite a ways. A single sub-exposure straight out of our cameras would make you laugh. Where's the nebula? Why are there only 10 stars? But when we run a night's work through stacking and processing, magic happens. And it's repeatable, undo-able magic, too. If I never spend another hour in the dark dodging and burning, only to put the print in the developer and find out I screwed it up and have to start from scratch, it'll be way too soon!

None of this is meant to discourage you. Film is an art form, and more power to those who can make it sing. But wow, I would never go back.

If you can get ahold of a copy of Charles Bracken's The Deep Sky Imaging Primer, you'll learn much more about the sort of thing we're talking about. It's really fascinating stuff. I've pored over that book a dozen times, and I took it out to the local pub for dinner company last night. Learned some new things, too! I also got some...looks...from the bar patrons. Not from the staff, they know I'm a nerd. Also they've seen some of the images I can produce with my digital gear and workflow.

Thanks. Yes, manually guided. (I STILL don't have an autoguider.) The mount was a Vixen GP-DX with S2KPC, pictured here as I used it with the 300mm lens. Very good tracking. 300mm is easy to guide with that mount. I still have the mount and still use it, at least when I'm imaging with a telescope. Astrotracer, which was used for the first shot I posted above, has for me completely replaced using a telephoto on that mount.

I remember a guy in my club doing film astrophotography back in the early 90's. He was doing long exposures - like 30 mins or more as I recall - on a Losmandy GEM mount, fairly wide field with no guiding. He was exposing straight to slide film and showed the results a couple weeks later at a club meeting and I was kind of blown away. I always remember that. Maybe having no experience at that time made me more impressionable but I think using slide (positive) film would be the ultimate in purist astrophotography :-)

I think the advantage of film is that you can use a much larger sensor. 6x7 film has 4 times the area, and consequently gathers 4 times the light for a given physical aperture (focal length/f#)..

Might want to check the math on that. For a given aperture, expanding the image makes it dimmer, not brighter. Same number of photons hitting the objective, it's not as if it magically sucks in more if you spread them out at the back end.

Math is my strong suit, not magic.

@weverka, Yes, you do get four times the photons (simplistically speaking, not accounting for vignetting). The extra photons are all in the extra image you get from the wider field of view provided by the larger sensor. However, your reply was to a question from justoboy about ISO, which has nothing to do with field of view. Can you understand how someone would conclude from the context of your reply that you thought the larger sensor alone would lead to a brighter image? Unfortunately, many people do think exactly that.

Never mind photons. Exposure is dependent on only two things, focal ratio and shutter speed. ISO is simply the gain in the sensor amplifier - that is related to ISO of film days - and is an expression of sensitivity, not exposure. Most digital sensors have a "native" ISO of 100. Any ISO greater than that is simply due to gain in the sensor amplifier and does not affect exposure. Thats why increasing ISO also increases noise and does not improve the SNR of your image.

The effects of shutter speed is obvious.

Lens focal length, pupil diameter are taken into account with one figure called focal ratio or f-stop.

It doesn't matter what lens you have nor the size of the sensor, if you have an f/4 lens, you have an f/4 lens regardless if its a giant newtonian or camera lens, the exposure at f/4 is the same, regardless of whether you're exposing a 7mm or 25mm sensor or 35mm film.

You're of course both right...and so was I! Danged human languages, anyway, eh?

What I thought you meant was that a larger "sensor" (e.g. 6x6 film) would have a brighter photon flux on each "pixel" (or each pixel-equivalent chunk of light-sensitive silver compound), so a big film camera would have a light-gathering advantage in the time domain. Which clearly is not what you meant to assert (which is good!). I was misled by "4 times the light".

Of course you can exploit a larger image circle (if your optics provide one!) via a larger-format sensor too. If you stuck a medium-format digital camera on the back of a scope with a whacking great image circle, your FOV would of course be greater; the image scale (arcseconds per pixel) would depend on the pixel pitch of the sensor. But the brightness (# of photons per second) per unit area on the sensor would be the same regardless of whether the sensor is a 1/3", APS-C, or medium-format -- UNLESS you modified the optical train to concentrate the same FOV onto a smaller sensor, as one does with a reducer.

This is a good clarification. As you said, the brightness per unit area on the film depends on the f number, not the size of the film. ( the thread is about film astrophotography, not digital.) And to frame the image on a bigger piece of film, you need a longer focal length lens. So if you can get long enough lenses with the same f number, you get 4 times light going to 70 mm from 35 mm.
I was imagining a Pentax 6x7, for which there are numerous lenses that will give the field of view for Milky way shots. For Andromeda, the 600mm f4 for the 6x7 has about the right field of view.

This would be your resource for film astrophotography. Film Astrophotography Techniques

In the old film days, photographers used to "hyper" their film to make it more suitable to astrophotography. Gas Hypersensitization. Even with that though, if you are going to compare your results to digital:



I built a simple barndoor drive (tangent drive) back in the day and had no time to motorize it, so I hung a ticking wind-up wristwatch (remember those?) over the temple of my eyeglasses, so it hung over my ear and I could hear the ticks. Then I manually turned the screw, trying to be smooth like a second hand and concentrating on moving 90 degrees every 15 seconds. Believe it or not I did up to 7 minute exposures that way. The 5 minute exposures were the best and I got my target (Comet Hyukatake). Still proud of the accomplishment, but in the way I would be proud of myself if I rode a bicycle to/from my work (35 miles). I wouldn't choose to do it (again) if a motorized vehicle was available. That's the way I feel about digital with astrophotography. (Especially if you have a Pentax DSLR with AstroTracer).