Opinions?

So what is everyone's opinion here, is it better to observe galaxies (not find them but actually observe them) with a low power, wide field or is it better to bump up the power?

I've heard both ways on this but I'm curious what everyone else thinks.

Cheers

David Brokofsky said:

So what is everyone's opinion here, is it better to observe galaxies (not find them but actually observe them) with a low power, wide field or is it better to bump up the power?

I've heard both ways on this but I'm curious what everyone else thinks.

Cheers

The answer is, "It Depends on the Size of the Galaxy."

It's always helpful to bump up the power if the skies are not perfect (darkens the bright background) or the galaxy is a teeny tiny (pops out better).

OTOH, something like M101 needs plenty of sky background to frame it. Which is why M101 is so difficult from the city--though I could almost always see at least the core from my urban site with an 8-inch f/5 Synta when I was doing the observations for my last book.

OTOOH, do NOT eschew high power on any galaxy. At high power the huge M31 is a wonderland. So is M101. I've spent some remarkable evenings under the dark skies of French Camp, Mississippi counting HII regions in M101.

8)

As many other experts in the forum already have stated - the best magnification depends on which galaxy you observe.

Looking at photos of two different galaxies, e.g. M99 and M101 you could get the impression that they are similar in both size and appearance. However, M99 is tiny compared with M101. I would suggest a magnification around 100x for M101, but at least 170x for M99.

I don't say that M101 is an easy object to detect the spiral structure in. With my previous, high-end 8-inch Newtonian I could see the arms and the emission condensations in it only under very good sky conditions. Any scattered artificial light or auroral glow would make these details disappear. With 12.5 inches of aperture I observe them regularly. To me it is the most beautiful of the spirals.

Inge S

David Brokofsky said:

So what is everyone's opinion here, is it better to observe galaxies (not find them but actually observe them) with a low power, wide field or is it better to bump up the power?

I've heard both ways on this but I'm curious what everyone else thinks.

Cheers

OH OH...David knows what I'm going to say.

I think a lot depends on the object itself. Some galaxies just don't lend themselves well to higher power. However, INHO moving up the power range makes a difference in the amount of detail like dust lanes, etc you can see. They become dimmer, but I feel easier to make out.

With a relative handful of exceptions, the vast majority of galaxies visible in amateur telescopes are quite small in apparent size and I usually use exit pupils of 1.5 to 2.5mm when observing such objects. One of the telescopes that I've employed to view galaxies and other DSOs over the years is a 17" f/15 classical Cassegrain, which would be the very antithesis of a "deep-sky telescope" according to some. With this scope, I find magnifications of 162 to 259x very useful.

http://www.clarkvision.com/visastro/m51-mag/index.html

http://www.clarkvision.com/visastro/m51-apert/index.html

Dave Mitsky

Attached Image:

Unless you're looking at large galaxies - like M31 - try using a 2mm exit pupil. That's the conventional wisdom and it seems to work. I notice much more detail when doing so on galaxies, whether I'm using my 11" of 16" dobs.

It can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope. More simply, it is the diameter of the objective lens divided by the magnification.

See

http://www.saguaroastro.org/content/EYEPIECE.htm

http://www.skyandtelescope.com/howto/basics/3304201.html

http://www.astromart.com/articles/article.asp?article_id=30




K. Michael M.