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Imitating What you see visually

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#1 Madratter

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Posted 15 January 2013 - 07:03 PM

I have been kicking around this idea in my head for a while. I understand the desire to get the best possible image of an object for yourself and I have tried a little bit of that myself. But then I am competing with people who do amazing work along with the big telescopes/hubble etc.

But what I have never seen is someone intentionally trying to take photographs that mimic what is seen visually through a scope, or at least visually through some scope (since the first may be impossible).

Now certainly it is possible to take a picture and limit the exposure time so you only get the stars down to whatever magnitude a telescope could see visually. That works for star clusters. But it does not work at all for things like galaxies. Now how deep the stars go is dependent in large part upon size of the objective and the exposure time. How deep extended objects goes depends largely on exposure time and f/ratio. And I think you would need a very fast f/ratio scope with a relatively small objective to imitate well what we see visually.

So here is the question. Say you wanted to imitate what can be seen visually through an 8" SCT working at f/10.

What scope would you need to do that and what kind of exposure times would be involved?

Thanks!

#2 Alex McConahay

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Posted 15 January 2013 - 08:31 PM

You know, you could probably use any scope/camera, etc.....the key is in the processing.

Alex

#3 jgraham

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Posted 15 January 2013 - 09:31 PM

I've been using my cameras as a companion for my visual observing for many years. The key to mimicking the visual appearance is to go easy on the processing. Make adjustments to brightness (levels) only. No non-linear processes at all; no contrast adjustments, curves, midtones, or gamma. If you adjust the brightness carefully you can use just about any exposure, but generally I've found exposures in the 10-20 second range work very well. This can be a lot of fun and unprocessed source images make the absolute best finder charts. :)

#4 David Ault

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Posted 15 January 2013 - 10:08 PM

I tried this with my last attempt at M42. This would be about the equivalent view through an 8" SCT with a 16mm eyepiece. I took the image with a 65mm refractor and did a very mild stretch (the data was a combination of several exposure lengths). I tried to make it match what I saw the last time I looked through the scope. I've got a monochrome ccd so I gave it a slight blue hue to match my perception.

Regards,
David

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#5 Erskin71

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Posted 15 January 2013 - 10:10 PM

A few summers ago I tried that. I placed my visual nebula filter on my scope and imaged M8. Came out pretty close I thought.

I may have used my C8 if I remember..then again maybe not. Who knows. Like I said it was a few summers ago :-)

#6 Madratter

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Posted 15 January 2013 - 10:58 PM

I've been using my cameras as a companion for my visual observing for many years. The key to mimicking the visual appearance is to go easy on the processing. Make adjustments to brightness (levels) only. No non-linear processes at all; no contrast adjustments, curves, midtones, or gamma. If you adjust the brightness carefully you can use just about any exposure, but generally I've found exposures in the 10-20 second range work very well. This can be a lot of fun and unprocessed source images make the absolute best finder charts. :)


I decided to try your advice on a picture I took of the Pleiades. I did both visual and more normally processed versions of it. For the visual, I tried to imitate roughly what can be seen in an 8" scope.

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#7 Madratter

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Posted 15 January 2013 - 11:01 PM

Here is the more processed version. Exposure time was 266 seconds at f/5.6 and 420mm, ISO 400.

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#8 Madratter

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Posted 15 January 2013 - 11:04 PM

Very nice. That is exactly the sort of thing I am looking for. And being in monochrome is perfect for this sort of thing.

#9 David Ault

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Posted 15 January 2013 - 11:18 PM

Those are nice Madratter. Your first version looks a little closer to what I remember seeing through a small refractor at a star party. I've heard people say that you can see some of the nebulosity through a large enough scope at a dark site, but I've never seen it.

Regards,
David

#10 Madratter

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Posted 15 January 2013 - 11:35 PM

Here is a try at doing this with the Flame Nebula, NGC 2024. Again, trying to get somewhat close to the view through an 8". Exposure was 255 seconds at f/5.6 and 420mm, ISO 400.

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#11 NeilMac

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Posted 16 January 2013 - 12:34 PM

Nice !!

#12 rigel123

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Posted 16 January 2013 - 02:57 PM

I tried this with my last attempt at M42. This would be about the equivalent view through an 8" SCT with a 16mm eyepiece. I took the image with a 65mm refractor and did a very mild stretch (the data was a combination of several exposure lengths). I tried to make it match what I saw the last time I looked through the scope. I've got a monochrome ccd so I gave it a slight blue hue to match my perception.

Regards,
David


That is about dead on! I see more green than blue when I view it but maybe that's my eyes! :cool:

#13 David Ault

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Posted 16 January 2013 - 04:21 PM

Warren, that's really interesting. I was at a fairly light polluted area last time I viewed M42 and I wonder if that has an effect on how I perceived the color, or if it is something biological. I'm partially red/green color blind (it's not severe enough to legally prevent me from driving), I wonder if there is something going on there.

Regards,
David

#14 rigel123

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Posted 16 January 2013 - 05:56 PM

Warren, that's really interesting. I was at a fairly light polluted area last time I viewed M42 and I wonder if that has an effect on how I perceived the color, or if it is something biological. I'm partially red/green color blind (it's not severe enough to legally prevent me from driving), I wonder if there is something going on there.

Regards,
David


When you are looking at grayish/green/blue objects I think it is all subjective! :grin:

#15 Madratter

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Posted 16 January 2013 - 10:20 PM

Warren, that's really interesting. I was at a fairly light polluted area last time I viewed M42 and I wonder if that has an effect on how I perceived the color, or if it is something biological. I'm partially red/green color blind (it's not severe enough to legally prevent me from driving), I wonder if there is something going on there.

Regards,
David


When you are looking at grayish/green/blue objects I think it is all subjective! :grin:


My wife and I rarely agree on whether blueish-green is green or blue. And neither of us is color blind.






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