How to focus manually a lens for which it was not designed.

[xilman]

Originally Posted by xilman

You might like to look at this version of DSC_0617.NEF --- it's a quick hack and I'm sure I can do much better. Gently raising the gamma will bring out more detail but raising it to more than 1.2 or so will show the artefacts which a slow hack would try to avoid. Nonetheless it's a marked improvement on the original IMAO

I believe the faint patch at (1066,360) is NGC 604, a H-II region in the M33 galaxy. It's catalogued as being mag 12.0 which seems rather faint to me. Perhaps your camera is particularly sensitive to H-alpha.

It will be interesting to stack these images carefully and then process the hell out of them to see whether other H-II regions show up.

[Spherical Cow]

Originally Posted by xilman

I believe the faint patch at (1066,360) is NGC 604, a H-II region in the M33 galaxy. It's catalogued as being mag 12.0 which seems rather faint to me. Perhaps your camera is particularly sensitive to H-alpha.

It will be interesting to stack these images carefully and then process the hell out of them to see whether other H-II regions show up.

It certainly does looks like NGC 604, when you align star patterns to the image of M33 on this Astronomy Picture of the Day image: http://apod.nasa.gov/apod/ap121220.html

Thanks for mentioning the ImageMagick program. I've downloaded that and am starting to learn it. Looks to be substantially more useful than what I use (Paint.Net), although even the brute force type processing of Paint.Net brings out the spiral structure in these images. Hopefully I'm not intruding, but have learned a bunch in this thread.

Norm

[xilman]

Originally Posted by Spherical Cow

It certainly does looks like NGC 604, when you align star patterns to the image of M33 on this Astronomy Picture of the Day image: http://apod.nasa.gov/apod/ap121220.html

Thanks for mentioning the ImageMagick program. I've downloaded that and am starting to learn it. Looks to be substantially more useful than what I use (Paint.Net), although even the brute force type processing of Paint.Net brings out the spiral structure in these images. Hopefully I'm not intruding, but have learned a bunch in this thread.

Norm

You're not intruding at all, as far as I am concerned. Quite the opposite, I was beginning to think I was the only person interested in this material. Anything you can contribute will be most welcome.

I'm also a novice at this sort of stuff and have learned quite a bit since starting. Earlier today, for instance, I've learned how to do least squares fitting to convert pixel (x,y) into (RA, Dec) given the identification of particular pixels with stars of known position on the sky.

[fivemack]

Trying to estimate limiting magnitudes by correlating positions of barely-visible stars with the SIMBAD database is a really good way to see exactly how much dust there was on my monitor.

I suspect that (882,485) is TYC 2293-1006-1 of V-magnitude 12.0

I think the almost invisible star at (898,527) is 2MASS J01341095+3024547 of V-magnitude 12.6 and that the slightly brighter one at (876,541) is 2MASS J01340151+3021151 of V ~ 11.8 ; I guess I should be pleased rather than annoyed that I've fallen off the bottom of the Tycho catalogue. Querying Gaia is harder work, and it's annoying that http://gea.esac.esa.int/archive/ doesn't give you persistent URLs!

So being able just barely to see a V=12.0 object is entirely credible. I don't think the camera is especially sensitive to H-alpha, though M42 does look a very pleasing shade of pink.

I too am very glad that other people are reading and enjoying this discussion!

My stretch goal would be to have a detection of the brightest globular cluster of M33, which is at 01 34 49.6 +30 21 57, but it's certainly not visible in a single frame and I think I need to gather many more photons before starting.

The brightest globular cluster of M31, at 00 32 46 +39 34 40, is V=+13.8 and might be tractable with enough stacking.

[fivemack]

Originally Posted by xilman

I'm getting interested in discovering the limiting magnitude of your set up. The canonical area for determining such things is the North Polar Sequence. I don't know if the north celestial pole is visible from your location (it might be behind a building or be excessively light polluted for instance) but you might want to consider taking a few images around there.

The North Celestial Pole is visible from my location; there is a slight issue in that, for the 200mm lens, I usually mount the camera on a small tracking mount (http://www.skyatnightmagazine.com/re...r-camera-mount) which cannot point within thirty degrees of the pole because the camera back bumps into the mount. But I can easily use the fancier mount with it, assuming I have a free night with a clear sky any time soon ... the rest of this week looks either cloudy or foggy, and clear nights are distressingly correlated with date nights with my uninterested-in-astronomy girlfriend.

[VBCurtis]

Originally Posted by fivemack

I too am very glad that other people are reading and enjoying this discussion!

The brightest globular cluster of M31, at 00 32 46 +39 34 40, is V=+13.8 and might be tractable with enough stacking.

Definitely enjoying the discussion, nearly tempted into trying to learn the image-processing tools myself so that I might play along. I appreciate that you two discuss such things in public!

[fivemack]

I'm having considerable trouble getting rid of the background without getting rid of the spiral arms, but attached is the result of a stack in Photoshop of all the M33 images with no attempt at background removal; NGC604 is definitely non-stellar, the faint star at [128,797] next to the brighter binary is recorded by SIMBAD as magnitude 13.8; the blobs at [412,393] [492,437] [587,426] definitely correspond to big nebulae in the AladinLite view (NGC595, NGC592, NGC588).

The star at [215, 732] is I think 2MASS J01343393+3022233 with V=15.1

[xilman]

Originally Posted by fivemack

I'm having considerable trouble getting rid of the background without getting rid of the spiral arms, but attached is the result of a stack in Photoshop of all the M33 images with no attempt at background removal; NGC604 is definitely non-stellar, the faint star at [128,797] next to the brighter binary is recorded by SIMBAD as magnitude 13.8; the blobs at [412,393] [492,437] [587,426] definitely correspond to big nebulae in the AladinLite view (NGC595, 'the B69 nebula', NGC588).

The star at [215, 732] is I think 2MASS J01343393+3022233 with V=15.1

Here's a quick hack (made while the morning coffee is brewing) with background removal, conversion to grey scale (the background removal turned the stars cyan) and mild gamma adjustment.

[Spherical Cow]

Originally Posted by xilman

Here's a quick hack (made while the morning coffee is brewing) with background removal, conversion to grey scale (the background removal turned the stars cyan) and mild gamma adjustment.

And this is the one-button, brute force "auto-level" from Paintnet. What that involves isn't well-explained in the documentation, and I'm trying to use ImageMagick to duplicate and understand it. The general lightening on the lower left of the image has a yellowish-greenish tinge in the auto-level, so I've also converted to black-and-white.

Norm

[xilman]

Originally Posted by Spherical Cow

And this is the one-button, brute force "auto-level" from Paintnet. What that involves isn't well-explained in the documentation, and I'm trying to use ImageMagick to duplicate and understand it. The general lightening on the lower left of the image has a yellowish-greenish tinge in the auto-level, so I've also converted to black-and-white.

Norm

The difference between the two is rather interesting. Mine is noisier but has a flatter background. I think yours is the more visually pleasing, largely because of the reduced noise.

My "quick hack" is really very simple. Blur the hell out of the image (the most recent used a Gaussian blur with 100-pixel radius) and subtract the result from the original. The blur removes all the high frequency detail and what is left is a fair approximation to the background. That should be enough of a clue for you to work out what needs to be done with ImageMagick.

[xilman]

This is turning out to be a rather educational project. For years I've thought that I really ought to know how to drive R, even if very crudely, but never managed to dispel enough apathy.

So a few days ago I installed R and began what was for me a very steep learning curve. The taks I set myself was to convert pixel coordinates to RA and Dec coordinates by fitting an affine transformation to star locations in each coordinate frame. The catalogue positions are converted to radians in the usual manner: by dividing by 180/pi) for Declination and by first dividing by 12/pi then multiplying by cos(Dec) to give Right Ascension. The coordinate transformation is then (RA, Dec) = (ax+by+c, ax-by+d) where (x,y) are the image coordinates and [a,b,c,d] are fitted coefficients.

A very slapdash measurement of a portion of the Capella image led R to report

Residuals:
       Min         1Q     Median         3Q        Max 
-0.0049740 -0.0019603 -0.0003176  0.0022869  0.0061191 

Coefficients:
     Estimate Std. Error t value Pr(>|t|)    
V1 -2.303e-05  5.965e-06  -3.862 0.000972 ***
V2 -6.539e-05  5.965e-06 -10.963  6.6e-10 ***
V3  8.429e-01  2.457e-03 343.089  < 2e-16 ***
V4  2.030e+00  2.457e-03 826.383  < 2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.003202 on 20 degrees of freedom
Multiple R-squared:      1,	Adjusted R-squared:      1 
F-statistic: 1.377e+06 on 4 and 20 DF,  p-value: < 2.2e-16

2mrad corresponds to 7'52". Not wonderful astrometrical accuracy but this was a learning exercise, not a research project. The star positions were measured only to a pixel or two and I already have ideas on how to improve that significantly.