Basic focussing for an EOS 10D

[daneel]

I've tried to get some wide-field sky images with my 10D. I tried the following:

- auto-focus on Jupiter (which is bright enough for the auto-focus to work)

- switch to manual focus

Then I tried a 30 second exposure in "bulb" mode at 400 ASA. The image looks okay with a pretty star-field but it's out of focus. Also tried manually focusing on a bright star but the image was still soft.

This is really frustrating as each image takes about 30 seconds to acquire so the feedback is too slow to focus, look at the image, focus, look at the image etc.

Has somebody worked out a good way of doing this? Or am I using the wrong camera? It would be a good start if I could see the image in the LCD while it's acquired but this ain't going to happen on the 10D.

Thanks!

Ramin.

[barkis]

Hi. Ramin,

What focal length lens do you have in your camera. Jupiter is very low down in the sky, at a low declination, which means that at 30 secs exposure, you may be getting slight trailing which you may perceive to be bad focusing. You can use Jupiter as your test object as it is very bright. Does your camera have a diopter adjuster, that allows you to sharpen the cross or whatever reticule is on your camera focus screen. Make sure that is set properly, then focus on Jupiter. Focus until you get the image as small as you can, and don't try to look for detail as I Don't think it will be visible in a lens anyway. Normally, a lens is focused to Infinity for the stars

Once you have focus, take a series of exposures, and bracket them, that is note the exposure time for each shot you take, so when you download them, you can Identify which exposure worked best without trailing. I take it the camera is on a tripod or mount of some kind.

Ron.

[daneel]

Hi Ron - thanks for your excellent suggestions. The lens is a cheap 28-80 mm zoom that I got with the camera.

Looks like I'll have to spend time adjusting the diopter setting on the camera - it's amazing that it doesn't let you show the image being acquired on the LCD screen. Is there a camera review section somewhere on SGL? Might trade in the 10D for something more astro-friendly.

I got a reasonable picture of Cepheus which was quite close to the zenith. Was narked that I couldn't see M52, but suppose with just a camera it's going to be a fuzzy blob at best.

The tripod was a Joby Gorillapod. Suppose I could clap it onto the HQ6 for long exposures once I get the focusing sorted as a Heath-Robinson version of an Astrotrac.

[Mark at Beaufort]

Hello Ramin

The first thing to state is that the Canon 10D is a quality digital SLR and when it was introduced, 3+ years ago, it was classified as a serious amateur/semi pro camera. Ron is correct in that you need to check that the diopter settings is correct for your vision. You can take a normal daylight photo and check that it is sharp by zooming into the photo on your computer.

All Canon SLR cameras have similar user friendly layouts and it is only the most recent cameras 450D and 40D that have live view settings.

I would suggest that you check the diopter position and then take a photo of the moon over the next few days. Set the ISO to 400 and f number to it fastest setting on the 80 position of your lens. I guess it will be f5.6. Switch the lens to manual and the camera to manual. Depending on your computer software I would take the photo in RAW. Place the camera on a photo tripod and if possible use a remote release cable take a series of photos and bracket your exposures. Play back the results on the computer to see the best exposure.

If everything is okay you will know that the camera and the lens are working. Check where the focus position was on the lens and if necessary hold it by using some masking tape. You can now experiment by taking star fields. As Ron said take a number of photos and bracket them and check the results again on the computer. Your computer will be able to identify shutter speed and f number from the compact flash card. If you get star trails increase the ISO to 800 or 1600 and check again.

If all this works then to improve you will need to stack photos and really you will require an equatorial mount.

Have fun.

Mark

[daneel]

Thanks Mark. If the sky is ever visible again I'll adjust the diopter setting. Nice tip about the masking tape - the focus is very sensitive so just touching it throws it off. I've got an EQ6 so will try that for longer exposures at a lower ISO setting. At ISO 400 I was getting a lot of noise.