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You guys have to get a Mallincam...I see serious color (like hubble color) on a lot of objects in near real time even with my AP 180mm.

Visually I see color with my 20 inch Obsession on the Orion nebula and the Dumbell and a few other larger objects. ...Not neon, but not usually just one color either... There are numerous small blue or green planetaries especially in the summer.

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Yes, but a Mallincam is astrophotography and not visual observing. It is possible to see color in brighter emission and planetary nebulae, although again, the colors are somewhat subdued and red will be the most difficult color to discern. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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Maybe, if the observer's eye was sensitive enough (otherwise, probably not). I have only seen the typical bluish-green color in my 10 inch (but 36 inches is a lot of aperture).

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The maps of OIII and Ha emissions shows that the ratio Ha/OIII is greater at the centre than in the outer shell. The fringe is greener than the centre. So: if one sees geen the centre it must cannot see the fringe reddish regardless how much sensitive he is to red (the first red he should see should be at the centre).

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It depends on the spectral sensitivity of the observer. Most of the observations I have read on NGC 1535 do not mention red at all (bluish, bluish-green, or even gray). One mentions that the outer edge looks a bit "coppery" in color.

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The theory that observed colors are necessarily real is dead.

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Well, it is dead to you, but not to those who have observed the reds. There is no definitive proof that these colors are illusionary despite all you have provided.

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This, besides the ears of M27, is a proof of false color percetion at a relatively high brightness.

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No, again, this is not "proof". You have misread a number of the postings here and distorted what was said.

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What hiopes remain? IC418 is much redder, so if real red is see that should happen there. Let us see if it is visible in Halpha. As for M42, the brightness levels where red is seen are similar to those of rthe above false colors. Unfortunately those regions are red so we cannot discriminate between false color perception and real perception based on the perceived color. But we only have to wait the ha test.

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There is no need to "hope". IC 418 *does* appear red on the edges, and this is well documented as you have been told more than once by a number of people. Also, the "H-alpha test" was done for you by me (and others) using a variety of filter combinations to rule out a contrast effect. Red was seen in parts of M42 when a narrowband filter with H-alpha and OIII/H-Beta passband was used and was not seen when a filter that had only the OIII/H-Beta passband was used. Red was seen when an H-Beta line filter with a high red transmission secondary passband was used on M42 but not when an OIII filter *without* any red transmission was used. This is clear evidence that the red is not a contrast effect, as the red vanished when the filters without any red transmission were used. Why can't you understand this? Although it can be difficult to do, it is definitely *possible* to see reddish hues in M42, M8, IC 418, and Campbell's Hydrogen Star. It is your contention that it is not possible which is "dead".

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Also, the "H-alpha test" was done for you by me (and others) using a variety of filter combinations to rule out a contrast effect. Red was seen in parts of M42 when a narrowband filter with H-alpha and OIII/H-Beta passband was used and was not seen when a filter that had only the OIII/H-Beta passband was used. Red was seen when an H-Beta line filter with a high red transmission secondary passband was used on M42 but not when an OIII filter *without* any red transmission was used. This is clear evidence that the red is not a contrast effect, as the red vanished when the filters without any red transmission were used. Why can't you understand this? Although it can be difficult to do, it is definitely *possible* to see reddish hues in M42, M8, IC 418, and Campbell's Hydrogen Star. It is your contention that it is not possible which is "dead".

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The test must be made with a Ha alpha filter. It might be that the OIII with read leak passes the star field lights in a different way that without the leak (thus color constancy effects work differently). Given the examples that one can see red through a OIII filter without the red leak, who can say what happens in those critical condition.
You are so convinced that "every color must be real" that you prefer to question the colors of a photo (nor you point any other photo). But, let us suppose that the real red is really seen in some parts of M42 and IC418. Can we say that "every reported color is real" where there is the evidence that starting at 17-18 there are false color perception in *perfect* agreement with the experiments by Pokorny et al? How many real reds are there? I said I think zero, but if it turns out they are 2-4 is that very different?. If you clearly state that except for those few cases red is not seen then we will focus on those four candidates and see if they survive the Ha filter test. To see red, red must be not only above L-cones threhold (which happens in the hygenian region for example) but also *a lot lot lot* stronger than OIII to prevail on it.

As for what concerns the red in the outer fringe of NGC1353, I am afraid but the central part is brighter an richer of Ha (comapred to OIII which still is dominat). Thus there are two unbeatable points against your theory that someone very sensitivy to red might have perceived it:

1) in order to perceive red which is fainter than OIII one should have a sensitivity to Ha *greater* than *his owns sensitivity* to OIII. People sensitivity to Ha is 10% than that to OIII. You imagine somebody who has 200% sensitivity to Ha compared to *his own* OIII (a completely reversed perception of colors!)

2) If somebody would be really able to sense the red in the fringe he *should* also see the brightness and richer in red centre as red too. Not green.

There are serius experiments that fit very well the reports. Why not at least reading and evaluating them? Why ignoring them? How can one say they are not valid without even having read?

PS I google many NGC1535 oics: none shows any trace of red at all. Note that the following picture shows the centre less blue than the outer fring (in agreement withn the fact that the centre has *more* red than the fringe, so why the fringe is seen red and the centre green?).



Do you think that all the pictures are wrong? You probably will rebut the pictures (all?!?) because they do not represent the real perceived colors. The point is however that pictures are more sensitive to red than the eye.

Edited by Mauro Da Lio (12/12/07 04:28 PM)

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The test must be made with a Ha alpha filter. It might be that the OIII with read leak passes the star field lights in a different way that without the leak (thus color constancy effects work differently). Given the examples that one can see red through a OIII filter without the red leak, who can say what happens in those critical condition.

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You are so convinced that "every color must be real" that you prefer to question the colors of a photo (nor you point any other photo).

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I hope to get a chance to view the area with an Ha filter in January. I got "skunked" by the weather this month. I'm not certain that will prove anything, because if the image is faint enough, my brain might be filling in the deep red colors instead of their being really transmitted by the Ha filter.

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The only difference between the OIII with the red passband and the one without *is the existance of that red passband*.

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As for M27, I have never seen any red it it, but the aqua (bluish-green) coloration is quite prominent, especially at lower powers or in large apertures. This is a "balanced" image of M27 taken by Richard Johnson of rural Park Rapids, Minnesota using a 14 inch SCT. He has balanced the color so that an early G-class star like our sun would appear essentially white.

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Balancing the RGB channels to match G stars as white is not enugh if line spectra are involved. See here an explanation.
http://www.astrodon.com/oldsite/ColorExposure.html
For color realism ith line spectra one needs to reproduce the photopic sensitivity. The passband of the red channel in photos is often a square window, not wheighting the different wavelenghts according to photopic sensitivity. Note how the Ha line is wheighted the same than OIII in the below example set. (cameras not for astronomical use include a filter to reduce sensitivity to red to match eye photopic curve).

All reds in the red passband wheight the same. This is not much of a problem for broadband sources, but it definitely is for line spectra: a line at 565 nm and a line at 656 have the same importance for the digital image but (see below) the latter is 10 times fainter to the eye.
By comparison this is the photopic sensitivity: to the eye Ha it looks 10 times, 2.5 magnitudes, fainter than peak sensitivity of cones, and 1200 times fainter than rods (in mesopic conditions rods sense OIII and cones Ha).



Thus pictures capture Ha stronger than the eye unless a proper wheighting is done *before* the wavelengths passed by red filter are lumped into a "R" overall intensity (or, if R comes only from Ha, a proper reduction factor must be applied to reflect the eye sensitivity to that line http://heritage.stsci.edu/2000/25/ngc7078supp.html). See the link of the hubble realistic color rendering. To see real red you need something really brighter in Ha than in OIII.

Edited by Mauro Da Lio (12/13/07 06:43 PM)

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If one looks through OIII filter without the red leak keeping the filter close enough to the eye so that no stray light is seen, one will see something like this:

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Suppose one sees: 1) red with the OIII with red leak, 2) not red with the OIII without the leak and 3) you do not see anything at all with Ha; what would be the conclusions?

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I have looked at M42 using my "Mars" filter (a Wratten #23a equivalent red filter), and while the image was somewhat dim, what I saw was *red* in the nebulosity with *no* other colors present. The brightest red was in the Huygenian region, but the color did extend to some degree away from that area. The filter is not as light efficient as a dedicated H-alpha interference filter, but it does let through H-alpha and did allow me to see clear red coloration in the nebula.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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No, I see a bluish-green coloration to *everything* when using my OIII that only has the 110 nm FWHM OIII passband.

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... The brightest red was in the Huygenian region, but the color did extend to some degree away from that area.

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... the parts of M42 which show reddish colors to me tend to be well *away* from central Huygenian region and the Trapezium rather than adjacent to them

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No, I see a bluish-green coloration to *everything* when using my OIII that only has the 110 nm FWHM OIII passband.

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1. How do you explain the second photo? (the filer must be kept somewhat away as in the photo). There are colors through the filter in the photo (also original reds and black look the same color!). The same happens to the eye (do not tilt the filter, we are not changing the band pass).

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I don't have to explain the photo! It does *not* represent the situation where you are viewing a nebula with a filter. End of story.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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... The brightest red was in the Huygenian region, but the color did extend to some degree away from that area.

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and here is a quote from another post of yours #2005477

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... the parts of M42 which show reddish colors to me tend to be well *away* from central Huygenian region and the Trapezium rather than adjacent to them

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From these descriptions I understand that the parts that really stimulates the cones (first quotation) are not the same that show reddish color (the second quotation). I mean that I understand that "some degree away" il less away that "well *away*".
So, are you meaning the same regions? And which exactly are these regions?

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These are two COMPLETELY DIFFERENT OBSERVATIONS! One was with a red filter, and the other was with a different filter like the NPB or the dual passband OIII. You are comparing apples and oranges. With a red filter, *all* the visible nebulosity was red: PERIOD.

With the dual passband filter, the red was primarily not in the inner Huygenian region but in the area around it and in spots well away from the Huygenian region, like patches in the "wings" of the nebula or the area south of the inner Huygenian region. The inner Huygenian region appears a greenish-blue color in the NPB filter. In the H-beta filter (which also has a red passband), the Huygenian region appears more bluish but the area around it appears more reddish than in the NPB filter, as the H-Beta contribution is weaker than the H-alpha line.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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I don't have to explain the photo! It does *not* represent the situation where you are viewing a nebula with a filter. End of story.

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As for what concerns the views with different filters, the point is that if real red exists in one spot, it must be seen with both methods. I understand that red was seen in spots far away from the huygenian region with the red-leaking filters, the same spots were not visible at all in the red filter (red seen in the huygenian region and somewhat away it). Am I wrong?

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Yes, you are wrong. With the single-passband red filter (Wratten 23a), red was seen in the Huygenian region *and* the area around it (as well as in the parts of the inner "wing" sections of M42 that are fairly bright) . With the dual passband filters (NPB narrowband, red-leak OIII and red-leak H-Beta), extensive red was not seen in the Huygenian region itself, as most of that appeared a greenish-blue color. However, reds *were* seen in various parts a little outside the Huygenian region, as well as in sections of the "wings" and in some other parts nearer to the outer boundary of the nebula. With the *single* passband OIII line filter or with my older Orion Ultrablock narrowband filter that has no red passband, no red was seen at all anywhere in the nebula (only bluish-green color).

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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1)...With the single-passband red filter (Wratten 23a), red was seen in the Huygenian region *and* the area around it (as well as in the parts of the inner "wing" sections of M42 that are fairly bright).

2)...With the dual passband filters (NPB narrowband, red-leak OIII and red-leak H-Beta), ... reds *were* seen in various parts a little outside the Huygenian region,

3)..as well as in sections of the "wings" and in some other parts nearer to the outer boundary of the nebula.

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Unfortunately, due to work, I will not be able to do this test until the new moon period in January.

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I understand that regions listed in point 2 are appering red also in test 1.
I understand that regions listed in point 3 are the so called "well away" spots which are not seen in test 1.

Thus, at least for the latter, they are seen red in the red-leaking filter but are not visible in the W23A.

My point is not whether the regions seen red in W23A turns green in OIII+Ha (that is obviuos if they emit enough OIII). My point is about spots seen red in OIII+Ha which are far away from the immediate surroundings of the Hygenian regions and are not seen in the W23A. How can be possible that a red spot is no longer seen in a red filter?

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You still aren't reading what I am saying! The red filter I have does *pass* H-alpha, but is *not* an H-alpha interference filter! It is a simple dye glass color filter with some of the characteristics of the Kodak Wratten #23a light red filter, and is intended *only* for viewing lunar and planetary detail (such as the dark albedo markings on Mars). Its transmission at H-alpha is not very high (probably around 40% to maybe 60% at best), so while it does show the brighter H-alpha features, it cuts out enough light to hurt the view of the fainter ones. However, the red passband of a filter like the DGM Optics NPB is close to 90%, so there is little attenuation of H-alpha. This makes the somewhat fainter red features more easily visible. These fainter details were not seen in the simple red filter because the red filter does not have the transmission that the dual-band filters do.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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