What 1800 Second subs can give you : M1

[Catanonia]

EDIT : After posting the JPG's don't do it as much justice.

Well as some of you will know, I have now got an Off Axis Guider and can pretty much guide as much and as long as I can.

I did M1 a few months ago with standard 5 and 8 minute subs with the EOS 1000D Modified via the ED120 Skywatcher Diamond Pro.

Well decided to try again with roughly the same total exposure length and roughly the same visibility.

So here is 3.5 hours on the M1 Crab made up of 50% 30 min subs and 50% 10 min subs.

Off Axis Guider with 1800 Second and 600 Second Subs

SW ED80 Guide scope with 300 second and 480 second subs

I think that the differences in detail are quite striking.

Done roughly the same processing on both.

So i am officially an OAG fan

Both images taken with a SkyWatcher ED120 Pro Diamond / EOS 1000D Baader modified with Astronomik CLS clip filter. Guided on EQ6 Pro mount with QHY5 / PHD. Only difference was the ED80 guide scope mounted ADM side by side compared to Lumicron OAG directly on the image train of the ED120.

[Catanonia]

Major differences to point out as JPG conversion is a bit tad, is that I have not had to push the processing so much as to blow out the core star due to the detail I got with the 10 and 30min subs

[themos]

That's pretty cool!

[Tim]

Steve, dont get tempted to go too long. You still need the quantity of subs to make them smooth, and there comes a point where SNR does not improve with length of sub, in fact may degrade. I'd be surprised, or shocked if 1800 secs produced as good a result as say 600secs with an uncooled dslr, and it would take you 3 times as long to get your 20 or so subs to smooth it out. Not to mention that you'd need a whole night taking darks

There's a little bit of star trailing too, might want to look at that, could be PE effects over that length of time if your polar alignment is perfect? It's time to get the hang of what the graphs mean in PHD

Good to see you got it working. Wait till you try a really rich nebula area, you will see a real difference then with long subs.

[MartinB]

Well done Cat and thanks for sharing, the results are very interesting. 2 very very good M1 images

I actually prefer the image taken with the shorter subs. It's a bit difficult to compare because of the different sizes here but the detail seems as good, the stars are a better shape and there are some odd flecks in the image with the longer subs.

It is very true that you don't have to do as much histogram stretching with the longer subs but that isn't necessarily a huge deal

Craig Stark has written some excellent articles on signal to noise which cover optimum sub exposure length. He has created a very neat spread sheet.

Articles & Reviews

You will find the articles under the 2009 section. Highly recommended reading

[MikeD]

2nd image looks a lot nicer to me, cleaner, more natural and with no loss of detail as far as I can see.

Still, well done on hitting 1800 sec subs.

Mike.

[Catanonia]

Thanks guys for the comments, just what I was after.

I would have to agree with you. 1800 Second subs are pushing the limits a bit and in this case seem to be worthless.

More of an exercise to see if it was possible when needed.

I will probably be sticking with 600 second subs for the majority of my work hopefully with the knowledge that I can do it nicely with the OAG and not hit and miss with the ED80 guidescope.

This should give me the level of detail I want as well as allow enough images to cancel out the noise.

Now just need to find a nice target to give this a go at.

Certainly can't wait for the American and Pelican season again, really want to hit this one with a big mosiac

[johnh]

Very informative comparison.

John.

[adamsp123]

Nice comparison and great pics! but I am with the crowd number 2 for me

[barkis]

They are very fine Images, and the Crab is superb.

The larger Image seems to have a flare from the brighter stars which I though might be due to the pick up being too far into the light path.

Is that a possibility?

Ron.

[Catanonia]

They are very fine Images, and the Crab is superb.

The larger Image seems to have a flare from the brighter stars which I though might be due to the pick up being too far into the light path.

Is that a possibility?

Ron.

I spose it is possible with 30min exposures, the brighter stars will get more signal and maybe give what you mean.