Re: [MaxImDL] Skyflat pluggin question for John Winfield


May 14, 2006

 


----------------------------

#24163 May 14, 2006

Hi,

What does the number reported by your magnitude calculator mean in

terms of Magnitude (mag 5 ect..)???

Brian



----------------------------

#24178 May 15, 2006

It returns a quantative figure for the sky brightness in units of

magnitude per square arcsec.



If you're asking how that corresponds to the naked-eye limiting visual

magnitude, that's a qualative figure which depends on the eyesight of

the observer and their ability to distinguish low contrast objects.



You could perform some experiments to see how your own eyesight

relates the sky brightness to your naked-eye limiting magnitude, but

it's likely to be different for different people.



Regards,



John



--- In MaxImDL@yahoogroups.com, "astroimage2002" brian@...> wrote:

>

> Hi,

> What does the number reported by your magnitude calculator mean in

> terms of Magnitude (mag 5 ect..)???

> Brian

>



----------------------------

#24184 May 15, 2006

John,



Thanks!



Brian

--- In MaxImDL@yahoogroups.com, "John Winfield" winfij@...> wrote:

>

> It returns a quantative figure for the sky brightness in units of

> magnitude per square arcsec.

>

> If you're asking how that corresponds to the naked-eye limiting

visual

> magnitude, that's a qualative figure which depends on the eyesight

of

> the observer and their ability to distinguish low contrast objects.

>

> You could perform some experiments to see how your own eyesight

> relates the sky brightness to your naked-eye limiting magnitude, but

> it's likely to be different for different people.

>

> Regards,

>

> John



----------------------------

#42321 Aug 20, 2010

John,



I have an update to my questions from my original email. The maximum value I was seeing was in the camera toggle window in Maxim and may not have been correct. As per my attached screenshot the value ranges are from 5396.1-8208.3 (tiny.cc/akxe6) (I have also posted in the files section titled Skyflat Screen shot). These values seem about right to me and I can also see the effects of vignetting.



You will also notice a double and almost triple spiked histogram. I suspect this is due to the IDAS P-2 filter I am using and as such it is blocking certain wavelengths of light. Does this make sense to you?



Thanks again in advance for your response.

Barry

> John,

>

> I have some questions for you regarding your Skyflats plugin for

> Maxim. I am currently using a light box so the levels should be

> quite consistent. I find however the error rate must be around

> 10% or it won't go through the process. Is this normal?

>

> I am also confused as to what the ADU value should be set at. My

> camera is a Canon 50D which is 14 bits and thus 16,383 ADU's for

> maximum saturation. In your program it states to enter a number

> around 30% of maximum saturation value, so I have entered 5461

> or 1/3. I am finding the max pixel in Maxim is reading only

> around 3000-3200 which is about 1/3 the value I entered in your

> program which again was 5461. Should I be entering the 16,383

> value in your program or leave the 5461 value I have already entered?

>

> Can you also comment on ISO? I have read it is best to keep the

> ISO value low around 200. Do you agree? I am shooting my light

> frames with ISO 800.

>

> I thank you in advance for your response and look forward to

> learning more about the proper use of your program.

>

> All the best,

> Barry



----------------------------

#42347 Aug 22, 2010

Hi Barry,



Sorry for the delay replying, I've been away at a wedding this week.



I'll try to respond to your questions one at a time:

>> I find however the error rate must be around

>> 10% or it won't go through the process. Is this normal?



You could try turning off the predictive algorithm - that works well with

sky flats and slow downloads, but isn't required with a light box.



>> Can you also comment on ISO? I have read it is best to keep the

>> ISO value low around 200. Do you agree? I am shooting my light

>> frames with ISO 800.



I'm afraid I don't have much experience using DSLR's - I use a dedicated CCD

camera which doesn't have a variable gain.

At a guess, I'd say you should keep the ISO the same as you use for the

lights, otherwise the gradient profile will not match.



> I have an update to my questions from my original email. The maximum value

I > was seeing was in the camera toggle window in Maxim and may not have been

> correct. As per my attached screenshot the value ranges are from

> 5396.1-8208.3. This seems about right to me and I can also see the effects

> of vignetting.



OK, sounds good. Switching to "area" view should show the same values the

app uses.



> You will also notice a double and almost triple spiked histogram. I

suspect > this is due to the IDAS P-2 filter I am using and as such it is blocking

> certain wavelengths of light. Does this make sense to you?



That's normal. There will be one peak per filter color, so the three peaks

will correspond to the RGB filtered pixels in some order, depending on your

light source.



Hope that helps,



John



On 20 August 2010 15:33, barry.schellenberg barryschellenberg@...>wrote:



>

>

>

> John,

>

> I have an update to my questions from my original email. The maximum value

> I was seeing was in the camera toggle window in Maxim and may not have been

> correct. As per my attached screenshot the value ranges are from

> 5396.1-8208.3 (tiny.cc/akxe6) (I have also posted in the files

> section titled Skyflat Screen shot). These values seem about right to me and

> I can also see the effects of vignetting.

>

> You will also notice a double and almost triple spiked histogram. I suspect

> this is due to the IDAS P-2 filter I am using and as such it is blocking

> certain wavelengths of light. Does this make sense to you?

>

> Thanks again in advance for your response.

> Barry

>

> > John,

> >

> > I have some questions for you regarding your Skyflats plugin for

> > Maxim. I am currently using a light box so the levels should be

> > quite consistent. I find however the error rate must be around

> > 10% or it won't go through the process. Is this normal?

> >

> > I am also confused as to what the ADU value should be set at. My

> > camera is a Canon 50D which is 14 bits and thus 16,383 ADU's for

> > maximum saturation. In your program it states to enter a number

> > around 30% of maximum saturation value, so I have entered 5461

> > or 1/3. I am finding the max pixel in Maxim is reading only

> > around 3000-3200 which is about 1/3 the value I entered in your

> > program which again was 5461. Should I be entering the 16,383

> > value in your program or leave the 5461 value I have already entered?

> >

> > Can you also comment on ISO? I have read it is best to keep the

> > ISO value low around 200. Do you agree? I am shooting my light

> > frames with ISO 800.

> >

> > I thank you in advance for your response and look forward to

> > learning more about the proper use of your program.

> >

> > All the best,

> > Barry

>

>

>





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