Starship Asterisk*

I want to start trying to take some pictures through my astronomy binoculars a telescope I find uncomfortable, and I am not looking for deep space at this point. I am just starting to enjoy the stars.

To further limit my equipment, I don't have an SLR - just a digital rangefinder. It's advantage is that its compact and pretty light.

My questions:

Any better solutions to holding the camera to the eyepiece than my current rubber band approach?

More importantly - how do i get the aim/focus thing w/o a SLR? Is it just trial and error, or is there a method?

Thanks,
Ted

pmp613 wrote:I want to start trying to take some pictures through my astronomy binoculars a telescope I find uncomfortable, and I am not looking for deep space at this point. I am just starting to enjoy the stars.

To further limit my equipment, I don't have an SLR - just a digital rangefinder. It's advantage is that its compact and pretty light.

My questions:

Any better solutions to holding the camera to the eyepiece than my current rubber band approach? :oops:

More importantly - how do i get the aim/focus thing w/o a SLR? Is it just trial and error, or is there a method?

Exactly what camera do you have? I don't know what a "digital rangefinder" is; normally that means a type of film camera. Perhaps you actually mean some type of point-and-shoot digital camera?

there should be "night mode" icon on your camera mode selector / menu, that typically have moon and stars in it - it has an effect similar to very long exposure (but I think most cameras actually limit that to few seconds any way). so, switch to that mode and connect to the telescope. you should now see some white dots - if you dont, forget about taking any pictures any way, if you see white dots, camera should be able to focus and make a picture with noisy black sky and white dots with colored halos (this "night mode" saturates the colors, on all two olympus cameras I tried). then, if your telescope is any good, you could probably even see a milky way not just dots.

p.s. I think you should also remove ocular lens but I not sure where I heared that.

When I talk about the equipment I have, I feel like I am walking around with my shoes off and holes in my socks.

Yes, it's a point and shoot. I am used to the term rangefinder, since that (used to mean - I am dating myself) focusing through a separate viewer, not through the lens.

I have a Minolta Dimage 3.1 mega pixel.

Thanks,

I recall reading years ago that you need roughly 4.5 megapixels in a digital camera to duplicate the number of grains of silver in the emulsion of a reasonably good film. Obviously this is just a rough approximation, but it indicates that your 3.1 MP camera is below even that threshold -- kind of equivalent to using Tri-X (yes, I'm that old) to take your picture.

Point and shoot cameras with many more pixels are available inexpensively today -- last year I picked up a 10 MP Canon for not much over $100. But that might not help much. As a previous poster mentioned, you're going to get false pixels in the dark areas. This is because the camera simply makes up something when it can't get enough light on the CCD to record any image data. And the only solution to that is to get a larger CCD, which is not now and probably never will be a cheap thing. Currently, larger CCDs are only available in SLR digital cameras, at prices that start at over $500 and go north from there quickly.

I'd be interested to see your results. Maybe you can post some of them on a site (Flickr?) and let us know the URL.

Rob

There are adapters available that replace or attach to the binocular's eyepiece. These may either mount directly to the camera body or attach like a filter to the camera lense. These may also require additional T rings and ring adapters.

Here is an article on building your own telescope adapter. I'm sure building one for binoculars wouldn't be much different.

rstevenson wrote:I recall reading years ago that you need roughly 4.5 megapixels in a digital camera to duplicate the number of grains of silver in the emulsion of a reasonably good film.

You need to distinguish between resolution and information content. When you make an astronomical image, there is a maximum resolution which is determined by your optics and the effects of the atmosphere. As long as your pixels are close enough together that their spacing isn't what limits resolution, that's all you need. This condition is generally easy to satisfy. The number of pixels is then equivalent to the size of film you might have once used, and matters in terms of how big an object you can image. With a few exceptions, astronomical targets are small. There are many cases where a few thousand pixels is all you need to get the highest possible resolution image of a target. In general, a 3.1 MP camera will be more that satisfactory for astroimaging.

As a previous poster mentioned, you're going to get false pixels in the dark areas. This is because the camera simply makes up something when it can't get enough light on the CCD to record any image data.

All sensors, including film, add noise. Some of it comes from simply reading out the data, and is found in all cameras. Some comes from thermal effects, and is also found in all cameras. Cameras designed for astroimaging are cooled to minimize this; other cameras are restricted to short exposures to limit how much this noise accumulates. With a well exposed image, most noise comes from photon statistics. Technological improvements have allowed camera designers to reduce some instrumental noise, but there's still no assurance that a newer camera will perform better than the one being considered here. FWIW, even the worst digital camera is many times more sensitive than the best film emulsions.

A point-and-shoot digital camera attached to binoculars will probably take good pictures of the Moon. With a white light filter it could be used on the Sun. It will capture Venus, Jupiter, and Saturn, but with less magnification than most would desire. That's it, however. Anything more will require some sort of tracking. It is the need to collect more photons that drives larger apertures and fine mounts. The camera is secondary to that.

Chris Peterson wrote:other cameras are restricted to short exposures to limit how much this noise accumulates.

this kind of restriction always seemed dumb to me because it is well-known that adding together several exposures of the same scene make most of noise cancel itself out, while true details survive. there even was flash application somewhere that allowed you to test this in browser using a webcam, but I can't find it

makc wrote:

Chris Peterson wrote:other cameras are restricted to short exposures to limit how much this noise accumulates.

this kind of restriction always seemed dumb to me because it is well-known that adding together several exposures of the same scene make most of noise cancel itself out, while true details survive. there even was flash application somewhere that allowed you to test this in browser using a webcam, but I can't find it :(

No, adding together images does not reduce the noise over a single exposure of the same total length. When you take more individual exposures, you increase the noise from readout (because it is injected from each sub-image). The thermal noise is exactly the same, and the photon shot noise is exactly the same.

The reason for stacking short exposures isn't to reduce noise, but to get most of the benefits of a long exposure (low noise) while allowing short exposures which can mitigate tracking problems, and to keep the total photon count in a single image low enough that the sensor doesn't saturate.

No, adding together images does not reduce the noise over a single exposure of the same total length

That's neither what I was saying, nor what you were:

other cameras are restricted to short exposures to limit how much this noise accumulates.

I'm just saying adding together multiple images does reduce noise - proof.

Thanks for the input.

Rob- When I get a picture that actually shows something, I will put it on flickr.

I am going to borrow my son's camera - it's way better than mine.

Ted