Remove star trails

[majestic0110]

HI all, I hope you are well!

Just a quick question, I have been taking some snaps of the stars using a canon 500d DSLR and my telescope. I've kept the exposures short (1"6 seconds) but I am getting noticeable star trails in my images. I have an HEQ5 mount but no autoguiding (yet!). Is there any thing I can do in GIMP to reduce/remove the star trails themselves? I must say in advance I have no idea what I am doing in GIMP and I do not own PhotoShop.

Thanks

Phil

[Digz]

With a well balanced scope with good polar alignment you should be able to get at least 60s exposures without any trails.

Can you expand a little more on what your set up is?

[majestic0110]

Hi Lee, thanks for the reply - nice to see a fellow Bristolian on here (though I live in Dublin, Ireland now). I have an HEQ5 PRO with a skywatcher 200PDS. I have not yet got the nack of accurate polar alignment simply because on the HEQ5 the red LED is EXTREMELY bright, so much so that I cannot even see Polaris when it's on. And when it's off I cannot see the reticule guiders. From what I have googled around this seems to be an issue with the HEQ5's, and I have not really found a suitable work-around. What might you suggest?

[Digz]

Eh up me babber, what part of Bristol be ye from?

I wasnt aware of an issue with the brightness of the HEQ5 LED. Having a quick search of the forum check out these couple of threads:

Hopefully there is something useful there.

Once you have nailed polar alignment then you should easily be able to get subs of upto 60s maybe even slightly longer.

HTH

[majestic0110]

Cheers mate, I'll take a look at them. Polar alignment seems a little tricky, I am very new to my EQ mount having had Alt-Az previously. Daunting! I was born in Frenchay! But I gre up in Weston super Mud! What about yourself?

[Digz]

No problems. I found it quite daunting myself when first trying to polar align. For me I tend to use the information displayed on the synscan handset to help polar align. There is a good thread here about it but Im struggling to find it at present. Ill see if I can dig it out.

I was actually born in the Isle of Man but grew up in Bishopworth and currently reside in Dundry :-)

[majestic0110]

cool! Your gallery on your blog is seriously impressive !

[Digz]

Thank you

Still cant quite find the right post but check these out:

Hopefully something useful in there which wont confuse you too much!

[dph1nm]

Once you have nailed polar alignment then you should easily be able to get subs of upto 60s maybe even slightly longer.

Hmm - don't expect too much. At 1m focal length with a 500d you have ~1" pixels, so for this not to trail in 60s (~1/10 of the worm period for an HEQ5) you are going to need PE of +/-5" or so (OK, so you might get away with twice this). That is getting towards £5K mount territory!

NigelM

[mikehab]

When I saw this topic I thought "hmmmm... what an interesting/great idea" ... as I thought it was a request for help on how to remove star-trails from pictures. Obviously it wasn't .... however my thought process continued..... and I'm now wondering whether there is any software (or even a photoShop 'Filter' plugin for example) that could automatically remove star-trails from pictures by effectively 'de-rotating' the image by the same amount as the length of the star trail. Thinking logically about the process that causes the star-trails in the first place, could it be possibel to reverse the 'trail' post-processing? Then having removed the trail the subs would be nice and 'clean' and could be used for stacking. Image processing has come a long way in recent years, especially in the area of astro-photography processing techniques - and there are a lot of very clever people out there ... just wondering whether there's something out there that might be able to do this?

Mike

[Digz]

Hmm - don't expect too much. At 1m focal length with a 500d you have ~1" pixels, so for this not to trail in 60s (~1/10 of the worm period for an HEQ5) you are going to need PE of +/-5" or so (OK, so you might get away with twice this). That is getting towards £5K mount territory!

NigelM

Interesting you should say this. Now I know my mount is an NEQ6 but on one lucky occasion I was able to get 3min unguided subs allbeit every third sun (IIRC) was useless.

The basic principle is the same and I've struggled to articulate it well and you've made it nice and clear for me cheers.