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5 or 30 minute exposures for narrowband?

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#226 freestar8n

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Posted 05 February 2013 - 03:51 AM

With regard to running unregulated - if you have a camera with pattern noise then you want to take a perfect image of the dark current pattern so it will subtract away. Since the pattern noise depends on temperature, you need the darks and lights to be at exactly the same temperature so the pattern noise matches and will subtract away.

But if your camera doesn't have pattern noise and it only has dark current Poisson noise (plus some hot pixels) then there is no need to subtract the master dark - and therefore no need to run it at a fixed temperature. You just want the lights to have as little dark current noise as possible - and that means running them as cold as possible even if it varies a bit due to changing ambient or something.

This is the principle anyway - but if you end up cooking your camera then it is not a good idea. And other bad things may happen also. But in terms of the noise model - if you aren't subtracting a master dark, then you just want each light as cold as possible.

Frank

#227 freestar8n

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Posted 05 February 2013 - 04:06 AM

Hi-

Here is what I get for your system. Again, not a huge win going from 15m to 30m - and dominated by sky more than read noise.

I guess I should relabel the "sky" signal since it also includes some amount of dark current - but yours is so cold that I guess it is more negligible.

Frank

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#228 Inverted

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Posted 05 February 2013 - 08:28 AM

Skimming through The info on Wikipedia about the HST deep field, it sound like 11.5 days of 20min exposures. At this point, I'd just settle for a full cloud free night, an hour or so of integrate ion per night just isn't cutting it for NB :foreheadslap:

#229 CCDMan

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Posted 03 March 2013 - 11:52 AM

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#230 Inverted

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Posted 03 March 2013 - 01:32 PM

I wish we could get Adam Block to dispel all the science fact from science fiction on here. He is a true wiz at this (just watch one of his tutorials). I think the average beginner to intermediate user is now totally confused with all the "theory" being spread here. David has the perfect solution attend AIC and listen to the John Smith and go tell him he doesn't know what he's talking about! Hey let's call the Myth Busters!


Well, all I can say is that I tend to pay much less attention to posts from people who are all theory with no links to actual images they have done. They may be right or they may be wrong but a post from someone who has links to actual images that they have taken with their own equipment and processed themselves (like Adam Block) carry much more weight in my mind than posts from someone, however well informed, that does not have the available online results of their efforts. Not to say they are wrong, they may be quite correct, but I don't know anything about them or their expertise if the evidence of that is not available to me. Anyone who does imaging (and I have done it for 20 years now) knows that the science is critical to the effort but is not, by itself, enough. Experience and creativity are also essential to produce a great image. I try to find the people that have all three and emulate them.

Yes, going to AIC is a great idea, I have been there a few times and gave a short talk myself once in the early years. Most of the bright lights of imaging can be found there at one time or another and it is a great place to bankrupt ones self on equipment! <g>



Well, I'm certainly no expert, so, I am not saying anything, just asking questions to understand better. What I would say is the people posting scientific info have posted info and links. This to me, is useful. The ones who are just name dropping have not (or when they have the links don't appear to support what they are claiming). This is not useful. So, far, all the name dropping stuff is hearsay as far as I can tell, i have no way of knowing if those being quoted are being quoted correctly in the correct context. Why would anyone go to AIC and tell John Smith he doesn't know what he's talking about, based on what someone posting info on the web says he said? There is no evidence that I can tell, that John Smith necessarily disagrees with what is being said here, there is only someone claiming to speak for him, saying so. How on earth can someone speak for someone else? If you have evidence that someone disagrees with something being said post a link or Something. Scientists produce scientifically accurate images, and much of the stuff being quoted appears to come from scientific resources. I want to produce accurate images, so, these are the resources that are important to me. If they are being misinterpreted, don't tell me "so and so told me X" so Y is wrong because so and so told me and he produces better images". That is not useful information unless it comes from the hoursess mouth and we are given the opportunity to ask questions and understand the context better. Perhaps being new I've just missed past discussions and don't have the full context, but, at least in that context, a lot of the commentary just sound ridiculous to me and to be honest, sounds more along the lines of trolling than anything else.

#231 freestar8n

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Posted 03 March 2013 - 01:40 PM

Not to say they are wrong, they may be quite correct, but I don't know anything about them or their expertise if the evidence of that is not available to me.



Not sure who you are referring to - but I like to go by results that show minimal processing - including raw subexposures and gray scale. Some of my images are on the MetaGuide site - and include raw subexposures, with fwhm's in arc-seconds - etc. They are all captured with relatively humble equipment - c11 with reducer on cge/cge pro and small sx camera in light polluted, sea level skies - at fairly high resolution of around 0.8" per pixel.

So - yes - I also like to see results that people achieve with their equipment. In my case, I offer such results - along with the software that I wrote to achieve those results - free of charge.

I don't put my site in a signature because it may appear promotional - even though it is free - but people who follow my posts are aware of my site and results I have posted, and I occasionally refer to the site and particular images when it is relevant to the thread.

But if you have specific concerns about the plots I made and the conclusions I draw from them - they are based on the same noise model everyone is using, including users of the HST in the paper I cited. If you see an error or specific reason for disagreement - I welcome any corrections - either theoretical or based on raw images you have captured that indicate a failure of the underlying noise model on which the plots are based.

Frank

#232 Mike7Mak

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Posted 03 March 2013 - 02:12 PM

[Anyone who does imaging (and I have done it for 20 years now) knows that the science is critical to the effort but is not, by itself, enough.

In a discussion of the science it is most certainly enough. I don't need a picture to grasp 2+2=4.

The lack of a link to a couple pretty pictures does not disprove anything. Nor does it justify peanut gallery heckling (which is what you quoted, btw).

'That's not what so-and-so says' isn't a valid rebuttal in and of itself.

#233 vpcirc

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Posted 03 March 2013 - 03:05 PM

I think most amateur imagers could care less about all the theory, links and long drawn out arguments that never end on on this subject and those who troll the posts looking for a chance to write a thesis. They just want the best advice. The "name dropping" is quoted only to show what the best are saying, and sharing from my own learning. Their statements are neither made up nor exaggerated. People can take their advice and learn what works best or do whatever they please. If you're happy with the results shooting 5 min subs that's all that really matters, not what anyone else thinks. Maybe they should start a new category "scientific discussions", then those who want discuss the measurement of noise can provide all those great resources. In the meantime I'm going to continue to learn, listen and emulate those whom are producing what I want to produce. So far it's brought me a long way in 3 years.

#234 shams42

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Posted 03 March 2013 - 04:10 PM

Well, all I can say is that I tend to pay much less attention to posts from people who are all theory with no links to actual images they have done.



I'd be more sympathetic to this view if the quality of one's images only depended on one's knowledge. Regardless of how much you know, the fact is that the highest quality work requires the highest quality equipment, optimal seeing, and dark skies. Just because someone may not own a $60k rig at New Mexico Skies does not mean that they don't know what they are talking about.

#235 vpcirc

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Posted 03 March 2013 - 04:22 PM

Well, all I can say is that I tend to pay much less attention to posts from people who are all theory with no links to actual images they have done.



I'd be more sympathetic to this view if the quality of one's images only depended on one's knowledge. Regardless of how much you know, the fact is that the highest quality work requires the highest quality equipment, optimal seeing, and dark skies. Just because someone may not own a $60k rig at New Mexico Skies does not mean that they don't know what they are talking about.


You are 100% correct. Most of the people giving me the best advice are not remote. You can have the best equipment in the world, but if you don't understand how to get the most out of it what good is it? I've seen plenty of guys on here that can take modest equipment in their back yard and produce wonders. Sal Grasso is a perfect example, Bill Synder is another. BTW, I only have $22k invested and I still produce a lot of garbage, which is why I must learn from the best imagers if I ever want to hope to come close to what they do.

#236 Inverted

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Posted 03 March 2013 - 05:22 PM

I think most amateur imagers could care less about all the theory


I have no idea. I've never done a poll. It is a pretty technical, scientific type hobby though, so, I would assume it attracts some that are interested in such. I am to an extent, although honestly I have a pretty technical job, so when I get home I usually don't actually want to think about that stuff too much. Once and a while when it is cloudy maybe. I am to an extent more interested in accurate images than "pretty pictures" though. That is just a personal preference. for me though, I'd rather understand the technology rather than just listen to someone who has great equipment, and/or is good at photoshop. There is something to understanding the equipment and how it works, and knowing that a faint background nebula is really nebula and not just smoothed out pattern noise for example. Perhapse it is not necessary to discuss such things on these threads, but some of us do appreciate the time others take to explain the stuff nevertheless.

#237 cn register 5

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Posted 03 March 2013 - 06:02 PM

Why is there such hostility to science?

Anyone can get good images by throwing money, exposure and dark skies at the problem. You don't need to understand anything if you have those advantages.

But this is of absolutely no use at all for those who don't have those advantages. Should we just give up because we don't have the resources to have a top of the line imaging system at somewhere like New Mexico Skies?

I think not. I think we should do what we can and take every advantage of our understanding of the science of image acquisition to extract the best we can from our limited resources.

If Cloudy Nights is not the place to exchange the sort of information that's useful in astro imaging - and from what I see it isn't - then can people suggest a better forum for discussing the technical aspects of Astro imaging

I'm not belittling the good work done by the technical people here but I'm fed up with the arguments from authority and ad hominem attacks.

Chris

#238 vpcirc

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Posted 03 March 2013 - 06:16 PM

Why is there such hostility to science?

Anyone can get good images by throwing money, exposure and dark skies at the problem. You don't need to understand anything if you have those advantages.

But this is of absolutely no use at all for those who don't have those advantages. Should we just give up because we don't have the resources to have a top of the line imaging system at somewhere like New Mexico Skies?

I think not. I think we should do what we can and take every advantage of our understanding of the science of image acquisition to extract the best we can from our limited resources.

If Cloudy Nights is not the place to exchange the sort of information that's useful in astro imaging - and from what I see it isn't - then can people suggest a better forum for discussing the technical aspects of Astro imaging

I'm not belittling the good work done by the technical people here but I'm fed up with the arguments from authority and ad hominem attacks.

Chris


Chris you are dead wrong there. It takes a lot more than equipment and skies to make a good image. You can have the fastest car on the track and still finish last if you don't know how to race. If it was so easy I wouldn't have to ask the teachers what I'm doing wrong. Learning from those with far more wisdom and experience than I seems like a pretty smart thing to do.

#239 korborh

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Posted 03 March 2013 - 06:57 PM


I'm fed up with the arguments from authority and ad hominem attacks.

Chris


They all come from just one CN member; just ignore these and continue this productive discussion.

#240 Konihlav

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Posted 04 March 2013 - 02:47 AM

Hi, "nice" thread of 12 pages. I haven't read any post except of the first one.

My answer is simple - for NB work, go as deep as you can go (10, 15, 20, ... 30?). The only exception is - extremely adverse conditions (full moon, snow all around reflecting light, SQM like 16 mag skies) AND/OR you are a owner of say Atik 460EXM or 314L+ (these cameras I thorougly tested and used and these two (or other with ICX674, ICX694, ICX285, ICX445 etc.) are really different beasts for NB work apart from the rest that I find useless for NB ;D but I am extreme guy wanting only the best for the particular task). In that case, you are OK with 10minutes no matter if you use 12nm wide or 3nm narrow filters. Period. No more important stuff to add on this one.

hope I was helpful for at least someone :)






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