Over 10 seconds

[Joshua P]

Hi, I'm new to the forums.

One thing I can't figure out. On a 1 minute exposure, how do you keep the stars from turning into lines? For me, anything over 10 seconds turns into a streak instead of a star, lol.. How on earth do you guys do it? lol :lol:

[R_Metzel]

Hi, I'm new to the forums.

One thing I can't figure out. On a 1 minute exposure, how do you keep the stars from turning into lines? For me, anything over 10 seconds turns into a streak instead of a star, lol.. How on earth do you guys do it? lol :lol:
Its pretty much impossible to do a long exposure and not have moving objects (stars) streak. The earth is always rotating so..... Hope that helps..... and welcome to the forum! :D

[bowtie`]

All those shots that are minutes long that keep the stars looking round and perfect are taken with the camera either monted on top (piggybacking) or through a telescope that is attached to a motorized mount that turns at the same rate of the earths rotation. That way the camera stays pointed at the same patch of sky.

[Adrena1in]

This Wiki Link on Equatorial Mounts (http://en.wikipedia.org/wiki/Equatorial_mount) will explain how to get a camera to accurately track the stars.

The longer the focal length the more accurate things need to be. At 10mm I can shoot for 30s+ with little noticeable trailing even when the camera is static. 4-minute exposures at 10mm with a roughly aligned or a cheap Equatorial Mount is satisfactory. However, at 1200mm (my longest FL scope), the stars appear to move after only a few seconds, even on a roughly aligned mount.

Hope that helps?

[Sorarse]

Bear in mind that without some sort of guiding, even a motorised equatorial mount will display evidence of streaking after 2 or 3 minutes, depending on focal length of lens being used.

[Adrena1in]

... even a motorised equatorial mount will display evidence of streaking after 2 or 3 minutes ...

I dunno...with perfect level and alignment there's no reason why a motorised mount won't track perfectly for hours. I've been able to leave my EQ5, with my 1200mm scope and 10mm eyepiece, for over 15 minutes and the stars have hardly moved at all. The problem with my mount is, I think, the PEC errors and/or slightly loose gears, because I do get minor star-wobble as the mount tracks.

[Celestron]

I have an eq5 mount with dual tracking motors and the best i have had tracking with out alignment was by accident . I happened to set my scope outside one evening and never aligned and it kept Saturn perfect for 6 hrs straight in the dead center of the eye-piece . but thats never happened again . If i start early and get a good polar alignment then do a good drift alignment i can keep an object dead center for hrs but when a camera is attached and i'm manually tracking with a 12mm illuminated reticle and a 2x barlow well i'm constantly making adjustments . 30 secs is the most i can get without manual tracking without star trails and every 1-2 minutes the R.A moves and i have to pull it back to center of the cross hairs . If you really want to know if your mount is tracking proper then get a 12mm illuminated reticle EP and a 2x barlow and watch it for a short time and see if that star doesn't move from center periodically .

[Adrena1in]

That's interesting what you said there Ron. I've had my 1200mm with 10mm eyepiece tracking accurately for ages, but add cameras and stuff, (I do re-do my balancing), and it's never that good. Start Autoguiding and it gets worse.

Perhaps I should take a really long exposure and check exactly what star-drift I do get, and see if I do get erratic errors which could point to mount or gear issues. These wouldn't should up if I align a star, go away and come back 15 minutes later and see it's still in the middle, but would show on a 15-min exposure.

[Joshua P]

Sorry for the late response but.. HOLY CRAP! lol

I guess that rules out star photography for me. Thanks guys.

[Adrena1in]

I guess that rules out star photography for me. Thanks guys.

I wouldn't say that. At 18mm you can shoot for a good 20 or 25 seconds without too much in the way of star trails, and that will allow you some lovely constellation shots and stuff. Plus star trails lasting hours also make for great images. You could do either of those.

If money is an issue, and you are good at taking your hand to making things, you could always have a go at making a Barn Door Tracker (http://en.wikipedia.org/wiki/Barn_door_tracker). These can be made to mimic an equatorial mount, simply with two planks of wood hinged together. The camera sits on one plank and the other is fixed, and you very slowly turn a screw to push the planks apart...kind of like slowly opening the cover of a book. If the hinges line up with the Celestial Pole and you've got it orientated right, the camera will track the stars for quite a while. Fine for wide-angle shots...you could shoot for minutes and get great Milky Way images.

[luigis]

You can always shoot several 10-20 second images and then do Image Stacking to increase the brightness and detail. You can use DeepSkyStacker that is free software and shoot about 30-40 images of the same area of the sky using 10-20 second exposures. The result is similar to a 30x20 seconds exposure.

Luigi