A couple of questions from imaging M33 last night

[swag72]

Managed to do some imaging last night instead of beating myself up about the length of guiding I can achieve etc!

So this has led to a couple pf questions really. I was imaging M33 and got 15 x 300s subs and added 15 x 300s darks. I was surprised at the noise as well at the lack of detail I captured overall.

Last night was the first time I used my Astronomik CLS filter, so wondered how much of an influence this had on the final image. Also using 1600 ISO (Haven't found it as bad as this before).

I would have thought that my subs would have produced a reasonable amount of data in the image - So anyone any thoughts?

Would I find a massive difference if I kept adding more 300s subs? I ask as many pictures I see on Flickr have about the same amount of subs at the same time, yet seem much more detailed.

Perhaps I was expecting too much at 300s? Or maybe I'll be better without the filter and my skies aren't as polluted as I thought?!!

I know there's no image to view, but I would welcome general thoughts and ideas.

[carastro]

Hi Sara,

I haven't done M33 yet, but my experience so far has been to use 800 ISO as 1600 will produce worse noise. Also you might just need more 300sec subs.

I use a DSLR and have just reached the end of my first year of guided DS imaging. I have also found that since I had my DSLR modified I am able to capture much more data. You might find looking at my website helpful as it's a warts and all - showing statistics for all my images and you can compare results with length of subs etc, and what the change is once I modified my camera (September 2010).

Regarding the CLS filter it really depends on how much light pollution you have.

I seem to recall you only started imaging very recently, so congratulations on getting into guiding so quickly.

BTW let's see your resulting image.

Carole

[swag72]

Thanks Carole - Really good to see your progress as documented on your site, well done!

I have got a 1000D off to Astronomiser for the filter removal - I look forward to testing that out once it arrives. How much difference did you see in your exposure times once it was modded?

I think I'll have another go tonight without the filter on and see how it goes - Perhaps my skies aren't as light polluted as I think!! Or maybe, once I get the modded camer the filter will come into it's own! Who knows? It's all so very exciting!

No image to post - I've played around and it really is on the very poor side!!

[Psychobilly]

You dont really need to change the exposure settings post mod...

[swag72]

How much extra will I capture? Assuming everything remains equal.

[Psychobilly]

Around 2-3x more of the lovely red stuff with the 1000D and later Canons 4-5x with the earlier ones as they had a harsher "Hot mirror"...

[carastro]

Hi Sara, I haven't changed my exposure times since MOD. However I have found what I do capture in my subs has so much more data in it now (besides the HA) for the same length subs as before, resulting in a much better processed image.

Carole

[RobH]

Hello Sara.

Whatever type of camera you're using, you should be aiming at 30 or more subs per target.

45 minutes worth of data is nothing....you need more.

With 5 minute subs, I would aim for 50, even with a dedicated colour CCD camera.

That's only a little over 4 hours, so no big deal.

For M33, if you want a good enough S/N ratio to really be able to play with the data, go for 6 hours worth.

It may seem a long while, but you'll find that there is significantly less to do when you come to process the image.

This is why some of us total imaging masochists often go for over 24 hours per target with mono CCD's.

Cheers

Rob

[steppenwolf]

M33 is not an easy target as its surface brightness is low. I would suggest that you keep the ISO setting to a maximum of 800 as going further will result in diminishing returns through noise generation. As Rob has said, more subs. is the key to this but additionally, your modded DSLR will help you capture the red knotty stuff in the outer arms making for a more interesting image.

[swag72]

Brilliant folks - Thanks for looking and taking the time to answer. I will have a play tonight (wind permitting) without the Astronomik CLS filter and see what I get. I am really looking forward to the modded camera imaging that's for sure.

[dlp]

Sara - I reckon the CLS filter (not the CCD version) has about 1.5 stops of neutral density, so you would have to more than double your previous (non CLS) exposures for the same result. I think I'm going to ditch mine in favour of the gentler SW screw on, as with the ND and the colour cast it's just not worth the hassle.

David