Daylight tryout - funny phenomena?

[turboscrew]

To get to know my tube better, I did some practice in bright daylight. I noticed two phenomena.
The bigger magnification, the thicker "milky fog". Where does that come from? With 300x it was very hard to focus.
The other was when I attached my Canon PowerShot A590 to it (Yes, I did get a projection adapter. Shame on me.) Very blurry image (and the camera did play games with me when I tried to adjust - low batteries, maybe). I guess the bad image was due to bright daylight. I think that was because the day light was too bright, and if I adjusted the aperture, I got secondary mirror shadow.
What causes the first phenomenon (milky fog), and am I right about the second (secondary mirror shadow)?

[SkyHiker]

The magnification limit by Dawes' criterion limits the magnification to roughly the objective diameter, or better half of it, in mm, which 300x for your 12" mirror. Your secondary will give a further contrast limitation though, and a diameter of anything above 8" will suffer disproportionally from turbulence. So really from a resolution perspective your scope is really 8" or 200x, with further deteriorating factors (more turbulence in the daytime probably).

The shadow is caused by your daytime pupil being smaller so the light hole caused by the secondary can cover your entire pupil. At night this is effect is also present except the pupil is much larger so it does not get noticed. See Al Nagler's article in S&T, https://skyandtelescope.org/astronomy-e ... ce-primer/

I just went to Nagler's articles at TeleView and they are very worth while reading: http://www.televue.com/engine/TV3b_page.asp?id=154

He also has an article that calls the magnification rule that I just used a myth, check it out: http://www.televue.com/engine/TV3b_page ... vice&id=86

[Lowjiber]

What SkyHiker said.

[turboscrew]

The magnification limit by Dawes' criterion limits the magnification to roughly the objective diameter, or better half of it, in mm, which 300x for your 12" mirror. Your secondary will give a further contrast limitation though, and a diameter of anything above 8" will suffer disproportionally from turbulence. So really from a resolution perspective your scope is really 8" or 200x, with further deteriorating factors (more turbulence in the daytime probably).

The shadow is caused by your daytime pupil being smaller so the light hole caused by the secondary can cover your entire pupil. At night this is effect is also present except the pupil is much larger so it does not get noticed. See Al Nagler's article in S&T, https://skyandtelescope.org/astronomy-e ... ce-primer/

I just went to Nagler's articles at TeleView and they are very worth while reading: http://www.televue.com/engine/TV3b_page.asp?id=154

He also has an article that calls the magnification rule that I just used a myth, check it out: http://www.televue.com/engine/TV3b_page ... vice&id=86

I'm still wondering about the "milky haze". And the latter was not about eye, but a camera, but I assumed the effect of reduced aperture is similar.
BTW, I apperciate your feedback, SkyHiker,: a tech guy to another. I guess I understand what you say.

[John Baars]

About the Milky haze.
( given a perfect mirror, without aberrations like a.o spherical abberation)
Three things at work here:
1- The higher the magnification, the lower the contrast. As magnification goes up by say 2X, the image will become 4X dimmer. At a certain level details will dive under the threshold of the human eye is capable of. Details will be blurred.
2- As the magnification goes over the resolution limit of the telescope, a black line will not be imaged as a black line, but is grayed.
3- The better the optics are polished, the less light scattering occurs. ( I.e. less micro-surface-ripples) That is why handpolished Zambuto mirrors have that high quality. Machine-polished mirrors work OK at lower- midrange magnifications. At highest magnifications ( 2XD - 3XD) it becomes more and more obvious as a mist/ haze hanging around the highly magnified star. The better the optics, the less the haze.

Nr 1 is due to the human eye. Nr 2 is an optics-rule, nr 3 is due to polishing quality.

[turboscrew]

About the Milky haze.
( given a perfect mirror, without aberrations like a.o spherical abberation)
Three things at work here:
1- The higher the magnification, the lower the contrast. As magnification goes up by say 2X, the image will become 4X dimmer. At a certain level details will dive under the threshold of the human eye is capable of. Details will be blurred.
2- As the magnification goes over the resolution limit of the telescope, a black line will not be imaged as a black line, but is grayed.
3- The better the optics are polished, the less light scattering occurs. ( I.e. less micro-surface-ripples) That is why handpolished Zambuto mirrors have that high quality. Machine-polished mirrors work OK at lower- midrange magnifications. At highest magnifications ( 2XD - 3XD) it becomes more and more obvious as a mist/ haze hanging around the highly magnified star. The better the optics, the less the haze.

Nr 1 is due to the human eye. Nr 2 is an optics-rule, nr 3 is due to polishing quality.

The view was not blurred, but just misty - even foggy, and that was 333x with a 300 mm primary mirror.
And in broad daylight, in the middle of a sunny day.
I tried to focus to a spruce cone.

[John Baars]

The view was not blurred, but just misty - even foggy, and that was 333x with a 300 mm primary mirror.
And in broad daylight, in the middle of a sunny day.
I tried to focus to a spruce cone.

Foggy even at 1.1XD ?
That is serious. It rules out the minor Seidel aberrations like Field curvature, minor Coma, Distortion.
Astigmatism but above all severe Spherical aberration could be a cause of it. Zones are candidates too. But I haven't heard you complain about fat stars at night.


Daytime:
Don't rule out extraneus lights, like the brilliance of low angle scattered light even in a blackened tube, especially during daytime. It can be really really horrifying during the day but hardly visible under dark skies while examining DSO's. Flocking your tube might help.

Two pictures of a telescope directed at clouds, as seen from the eyepiece.
Not- flocked and flocked. Look at all the extraneus light that reaches the eyepiece.

Last thing I can think of is that the edges of the mirror are not well polished at all. Nr. 3 in the former post. Zambuto makes his mirror surfaces smooth, but that is not the only thing. If there are lots of little scratches and digs remaining from the coarser grinding process, especially at the edges, it leads to a mistier image. Everybody looks at the middle of a mirror, but that is the least important place. The edges are more important. You can examine that yourself with a very strong magnifying glass.

[turboscrew]

The view was not blurred, but just misty - even foggy, and that was 333x with a 300 mm primary mirror.
And in broad daylight, in the middle of a sunny day.
I tried to focus to a spruce cone.

Foggy even at 1.1XD ?
That is serious. It rules out the minor Seidel aberrations like Field curvature, minor Coma, Distortion.
Astigmatism but above all severe Spherical aberration could be a cause of it. Zones are candidates too. But I have't heard you complain about fat stars at night.

Fat stars? Well, if I don't know what they are, I've probably not seen them?

Daytime:
Don't rule out extraneus lights, like the brilliance of low angle scattered light even in a blackened tube, especially during daytime. It can be really really horrifying during the day but hardly visible under dark skies while examining DSO's. Flocking your tube might help.

I guess that's possible. It was a pretty bright and sunny day.

Two pictures of a telescope directed at clouds, as seen from the eyepiece.
Flocked and not-flocked. Look at all the extraneus light that reaches the eyepiece.




Last thing I can think of is that the edges of the mirror are not well polished at all. Nr. 3 in the former post. Zambuto makes his mirror surfaces smooth, but that is not the only thing. If there are lots of little scratches and digs remaining from the coarser grinding process, especially at the edges, it leads to a mistier image. Everybody looks at the middle of a mirror, but that is the least important place. The edges are more important. You can examine that yourself with a very strong magnifying glass.

I'll check that. It's the OrionOptics VX12 with the 1/10 pv mirror.