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M57 C8 @ 2032FL


Ewan
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Thanks everyone, i did shoot this 3 days ago but i had my reducer on while i was testing phd2 as i thought the lower fl might make things a bit easier but im very happy finally getting some longish subs at f10.

Longer focal length does help but it is do able on lower.

I have seen a couple of shots of this done with the DMK & the image lookex considerably bigger so that's one thing im looking at trying with rgb, anyone know rough settings for doinv long exp using the DMK or have tried simlar ?

I will add some more to this but i must reach a 'data' limit using a dslr ?

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Thats a great image! Can't believe you got all that at F/10!

You will reach a data limit with your DSLR but not for a while. Obviously it changes from target to target but I've got 8hrs on M31 and M42 and that was getting close to the limit but I was only using 2min subs. Now that I have guiding I will be going back at those targets but with 5min subs and I'm sure I will be adding a lot more data.

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It is a tiny target. I'd love to get a C14 pointed at all night it with a decent camera on the back. Not sure how I'd smuggle a C14 in though :)

James

As in the wife don't see eh James :-)

Thats a great image! Can't believe you got all that at F/10!

You will reach a data limit with your DSLR but not for a while. Obviously it changes from target to target but I've got 8hrs on M31 and M42 and that was getting close to the limit but I was only using 2min subs. Now that I have guiding I will be going back at those targets but with 5min subs and I'm sure I will be adding a lot more data.

How & when do you know when that limit is reached ? visually when you can see no more detail is comming through ?

Good luck with those longer subs & i look forward to seeing them finished.

Tidy image on a tiny object well its actually very big but you know what i mean

:-) i know exactly what you mean it is pretty small, i can make it out in my 6 x 30 finder as my 10 x 60 is used for guiding, i need some software, i think Gina uses a neat thing, that will let me mix & match different fl shots from different cameras.

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Ewan,

I honestly don't know if there is a way to find out with out just going until you feel like your data hasn't improved with the latest batch of subs or has only improved a little. That would tell you you've reached or getting close to the limit. Maybe there's some crazy math equation out there to help narrow it down to a closer set number of time but I don't know of it or could figure it out even if I did. I think I remember reading something about it on the web a while ago but it was a while ago. You'll have to do some google searching. What I have found out is that the longer your subs are the more data you can aquire before you reach that limit. I've only tested that personally from 30sec to 120sec subs. And I'm sure its a whole different game when you switch over to CCD from DSLR. I know with my dslr at 2min subs I found 8hrs to be about the limit. Now whether more subs will help bring down the noise even if you aren't increasing the data....I'm not sure. With a dslr I would think there's a limit on that as well just because of the fact the dslr are very noisy. I do plan on doing some of my own tests on this to find out once the weather allows me to go out...which will probably be another month at least till it starts getting cold enough.

Edited by nmoushon
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Quite. It's unlikely to go unnoticed unless I get into the habit of buying large numbers of dustbins :D

James

Or just get a dustbin to hide it in, bring it out a few months later and use the excuse of 'oh, this old thing?' 'that's always been there!' :D.

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Ewan,

I honestly don't know if there is a way to find out with out just going until you feel like your data hasn't improved with the latest batch of subs or has only improved a little. That would tell you you've reached or getting close to the limit. Maybe there's some crazy math equation out there to help narrow it down to a closer set number of time but I don't know of it or could figure it out even if I did. I think I remember reading something about it on the web a while ago but it was a while ago. You'll have to do some google searching. What I have found out is that the longer your subs are the more data you can aquire before you reach that limit. I've only tested that personally from 30sec to 120sec subs. And I'm sure its a whole different game when you switch over to CCD from DSLR. I know with my dslr at 2min subs I found 8hrs to be about the limit. Now whether more subs will help bring down the noise even if you aren't increasing the data....I'm not sure. With a dslr I would think there's a limit on that as well just because of the fact the dslr are very noisy. I do plan on doing some of my own tests on this to find out once the weather allows me to go out...which will probably be another month at least till it starts getting cold enough.

Thanks for that, i do understand there has to be a limit i guess, i'll just keep collecting more data for now.

Or just get a dustbin to hide it in, bring it out a few months later and use the excuse of 'oh, this old thing?' 'that's always been there!' :D.

I had a vision of James in the garden late at night with 2 dustbins upto his eye's saying ' oh no love i've always had these binos......don't you remember' :-)

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Great capture Ewan!

I've been trying to get this the last couple of times out but haven't managed to even find it yet! Doing a mosaic of my scanning images trying to find M27 I found that at one point I was less than 1/8th of a frame to the east of the nebula! I was using a DSLR mounted straight onto my CG-5 GT and I hadn't done any star alignment and I haven't got a finder scope for my camera yet.

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I had a vision of James in the garden late at night with 2 dustbins upto his eye's saying ' oh no love i've always had these binos......don't you remember' :-)

Good job she doesn't read SGL or I'd have to find some other way to disguise them now...

James

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Great capture Ewan!

I've been trying to get this the last couple of times out but haven't managed to even find it yet! Doing a mosaic of my scanning images trying to find M27 I found that at one point I was less than 1/8th of a frame to the east of the nebula! I was using a DSLR mounted straight onto my CG-5 GT and I hadn't done any star alignment and I haven't got a finder scope for my camera yet.

Thanks Bryan, the Polar alignment i follow always allows me to slew to a target now & its in the EP view, i can pm you if you like as we have the same setup ?

With good PA you should still get 60-90 secs & don't use a focal reducer like i did the other night, got some good shots but at f6.3 & i don't know if i can resize them to overlay or stack with the F10's.

Using PHD2 my Polar align error is avg 0.23, to be honest i do not know if this is good or bad but it did allow me to capture the above.

I hope you do grab it Bryan, i know it's pretty small but it's quite amazing

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  • 5 months later...

Woo Hoo, well done! The very small just got a bit bigger. Super stuff.

The F10 thing needs to be in context. For most of us, inlcuding 20 inch RC owners, this object is going to struggle to fill the chip. This means that F ratio isn't the issue. If it fills your chip (unlikely around here!) it is aperture which matters.

Olly

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Wow thanks for all the replies, thought this thread was well and tuly archived :-).

Having tested the NB / RGB water now with the Atik i will give it another shot, just checked the fov if i go with the 314 + C8 which should give a good compromise between object & starfield.

I appreciate this topic 'resurfacing' as, even only after a year, i reflect back at what i was achieving & how i have progressed, a lot of it is down to constructive tips on SGL.

Woo Hoo, well done! The very small just got a bit bigger. Super stuff.

The F10 thing needs to be in context. For most of us, inlcuding 20 inch RC owners, this object is going to struggle to fill the chip. This means that F ratio isn't the issue. If it fills your chip (unlikely around here!) it is aperture which matters.

Olly

Cheers Olly, i must admit soon after i bought the C8 i did read it can be a nightmare guiding at that FL but to be honest it kind of 'made me learn', i am quite happy to use SCT on any target now, i have grown to enjoy it more the more it get's used.

Great for those small clusters but also for my Horsehead project which i am really really trying to capture (weather is terrible) honest !!!.

I love the widefield shots i see on SGL but i won't name name's as it will take too long, but i also enjoy finding detail in those widefields & thinking i will try just that small bit with the big scope.

BTW very nice M45 in AN this month, one day Olly one day :grin:

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Thanks everyone, i did shoot this 3 days ago but i had my reducer on while i was testing phd2 as i thought the lower fl might make things a bit easier but im very happy finally getting some longish subs at f10.

Longer focal length does help but it is do able on lower.

I have seen a couple of shots of this done with the DMK & the image lookex considerably bigger so that's one thing im looking at trying with rgb, anyone know rough settings for doinv long exp using the DMK or have tried simlar ?

I will add some more to this but i must reach a 'data' limit using a dslr ?

Excellent work Ewan - a terrific capture.

The DMK image scale thing is a bit of a red herring.  It's only the pixel (photosite) size that matters it's just that the chip on the DMK is so small compared to the chip on your DSLR.  Assuming the same size pixels you would get exactly the same result by cropping your image.

As for "data limit" there is a limit to the length of your individual exposures which is largely dependent on your light pollution.  Aside from that, for shot noise the signal to noise ratio goes with the square root of the exposure.  To double your signal to noise ratio you need 4 exposures, to improve it four fold you need 16 exposures,  to improve it by a factor of 8 you need 64 exposures so you can see that there is a diminishing return but the signal to noise ratio of your image will continue to improve with every additional exposure (just by less and less the more you add). 

I can recommend a great book that explains all this much better than I have!

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Thanks Ian, the diminishing returns argument is one where i guess you decide when to draw the line & call it a day.

Glad you liked the shot though & i will add the Deep-sky Imaging Primer to my goodies to buy, i did get a nice edition of The 100 Best Astrophotography Targets, it basically gives you an example finished shot of the target, most suitable ways of aquasition, filters to use & processing, very very useful, what i found most exciting was that most of the images in the book are comprised of just 300 sec subs.

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