a question on astrophotohy

Hi, since I am new to the 10D (coming from the G3) I have a question about taking shots of stars.

With the G3 I could point the camera in to the sky and with an shutter speed of 15" I would get nice points of lights, however I have noticed that with the 10D the points of lights at 15" become small streaks

Why? I am using the same tripod that I used for the G3 so why is this happening?

It could be shutter slap.

The force of the mirror opening actually moving the camera. There is a custom function that will hold the assembly open. Try that.

Also,. are you using a shutter release cable? Try using the time delay shutter release if you don't have a cable.

With the g3 the shutter lag may have been enough to limit the effect of your pressing the shutter button on the image.

Question about saving my digital pictures for printing

Mark,

I am not an expert by any means. However, I would be very surprised if you can get the rich detail that you probably want by using only a 15 second exposure.

So far, I have only used my 10D for imaging the moon:

http://mywebpages.comc​ast.net/bearss/

The camera was mounted to my Meade ETX-90 in a prime focus setup. I focused and let the camera set the exposure!

It seems like the streaks you are getting are star trails caused by the rotation of the Earth. However, I've only noticed star trails for exposures of around 30 seconds or more. I have had good luck with my film camera taking pictures of the night sky. I purchased an inexpensive "piggyback" adapter to mount the camera on top of the telescope scope. That way, the scope's motor tracked the sky and I could get much longer exposures without noticing the star trails.

If you don't have a motorized telescope, you could consider building a rig that would allow your camera to track the sky. I've seen articles in Sky & Telescope on how to do it. Basically, you tilt your tripod according to your latitude and make a sort of hing that swings the camera.

Brian

Those thoughts make sense. Another idea is the lens...what lens are you using? The longer the lens, the sooner star trails will start to show up. And another thought, what ISO was the 10D at? If you had it set to Auto, it may have choosen 800 or 1600, while the G3 I think will only go up to ISO 400.

On the subject of tracking drives, Orion sells one that is specifically designed for wide field tracking using a 35mm or smaller camera. It comes with table top legs, counterweight, and a plate with 1/4" thread on it. It costs about $50. Throw in the motor drive for it, and you have a total of about $100. I have done some exposures at about 5-10 minutes with this setup, using my D60 and 17-35mm lens with pretty good results. www.telescopes.com (just checked the site, they are redesigning it and for some reason, everything says "we no longer carry this product".)

One thing to consider though, the unit comes with tabletop legs. I would recommend getting a real tripod for it, such as a small Bogen (I think I have the 2020) which would cost another $50-60. Get the kind that doesn't come with a head on it, just has the screw sticking out the top. The tracking unit comes apart and has a screw hole on it that fits the screw on Bogen and other tripods. It is the larger diameter screw though, not 1/4"...but if you end up getting a tripod that has the 1/4" threads on it, that's ok too. Most good camera stores also have adapters to go from 1/4" up to the larger diameter threads.

Good luck!

Yes!

This answer makes more sense than the star trails I mention below. Still, I think longer exposures will be needed to get a lot of detail or to reveal faint stars.

Brian

thanks for the input.

extra info that might be useful, I am using ISO100, with the only lens that I have, which is teh 28-135mm IS USM

I don't have a telescope to connect the camera too, and that is down the track.

the 15secs is only just a start. I only had the camera for 4 days so far and only one night has been good enough for a few hours. dam the winter.

I am using the timer so I am not touching the camera when the shutter opens.

I had figured that 15secs would not be long enough for star trails.

I will keep all that you have said and when the sky gets better I will see if I can improve the results.

I took a shot of the Milkey Way with my 10D and a Sigma 17-35mm f-2.8 lens at ISO 400 for 72 seconds. I enabled mirror lockup to prevent mirror "slap" and used the timer remote shutter release (an indespensible but expensive tool!) and a steady tripod. I cranked up the exposure to +3 and increased shadows in PS7. I did an unsharp mask and then ran it through the Imaging Factory Noise Reduction Pro to eliminate roque red and blue pixels. I believe that the 17mm lens prevented the streaks. I connected the 10D to my Meade 8" telescope last night and got nothing but blurs. The tracking computer on my scope blew up though and I'm waiting for another which should correct the "streaks." Either a very wide angle lens or a tracking tripod should do the trick. If you want 'deep sky' shots, you'll probably need a scope. I read where you can attach your camera in piggyback fashion to a scope and use the tracking features of the scope to keep the pictures in focus. Here is the shot I got...

Patrick

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I took a picture of the Big Dipper last week in a moonlit sky, and saw no discernable star trails with a 30-second exposure. I used f/5.6 at ISO 800, and can see stars down to magnitude 5 or 6 in the image. The Moon lit up the foreground and sky enough to make the image look nearly like daylight, and it is rather surreal to see stars in an otherwise daylight-looking image.

But I was using a 14mm lens to get a very wide sky field. The longer the lens, the more the movement.

Think of it this way. If a normal lens (28mm on a 10D) has a 45-degree field of view, then one pixel subtends an angle of about 0.0125 degrees, or 45 arc-seconds. Now, there's a convenient equation: the angle of view of the lens in degrees is equivalent to the number of arc-seconds of angle for each pixel. (This convenient relationship is because the there are 3600 pixels diagonally across the 10D frame, and 3600 arc-seconds in a degree).

If the sky rotates 360 degrees in a day (it isn't that exactly, of course, but it's close enough for this calculation), then 24 hours means a sky movement of 28,800 pixel-widths. Thus, one pixel width of sky movement happens every three seconds with a normal lens. With a normal lens, you will therefore get streaks five pixels long in 15 seconds. Remember that the brighter stars will flare in the lens, and this flare will cover up some streaking. My bright Big Dipper stars, even with the 14mm lens, were spots three or four pixels around, and that's probably why I didn't see any streaking.

It is not mirror-slap, by the way. Vibration from mirror slap will only last a tiny fraction of a second, and therefore will only affect images of a tiny fraction of a second. With a 15-second exposure, the part of the exposure made during that vibration would not even be visible in the image, except for point source lit well enough to be exposed visible in a small fraction of a second, and those would flare out completely in a 15-second exposure.

Rick "doing the arithmetic" Denney

>>> extra info that might be useful, I am using ISO100, with the only lens that I have, which is teh 28-135mm IS USM

Wow! It reminds me the fun from my childhood days where you can watch bright stars and the milky way outdoors...

Okay, just one small remark: the latest generation IS, say on EF70-200mm f/2.8 L IS USM, automatically detects whether the lens is mounted or not. But I guess it is not the case for EF28-135mm f/3.5-5.6 IS USM.


Griffin.

I have read that the IS should be turned off when having it turned off. in this case I have done so.

the camera is in full manual mode, so I have control over everything.

it would seem those that are wiser and have had the camera longer than I, that I would have a tracking device to keep the stars in the right frame of mind.

Just typical, the universe never plays by the rules.

Since I have only had the camera for a total of 5 days, this will be the first weekend that I will have the camera and I am looking forward to using it.

Untill the weather improves I will not be taking any night shots. by stay tuned.