Hickson 68 - 10 inch v 16 inch

[mdstuart]

On forums people often ask is it worth upgrading from a x inch to a y inch.

So is it worth upgrading from a 10 inch to a 16 inch?

Well lets take Hickson 68 in CVn as our test object. Its a group of galaxies 100 million light years away in a strand of galaxies which stretches from the Virgo to the Coma cluster..apparently.

2011 - 10 inch

Back on 10th April 2011 at 10.30pm I looked at this group of galaxies with my 10 inch Skywatcher. I could see the pair NGC 5353/4 (both mag 12) but I noted they were faint and I could only hold NGC 5353 with direct vision and NGC 5354 required averted vision. I did manage to spot NGC 5350 (mag 11 but lower surface brightness) but noted it was very tough and I only got occasional glimpses from time to time.

2015 - 16 inch

So four years on almost exactly, at 10.20pm , two nights ago I looked at this group again with my 16 inch. WHAT A DIFFERENCE.

I recorded NGC 5353/4 both as bright and easy with direct vision. 2* on my observability scale. NGC 5350 was fainter but I could still hold it with direct vision.

But wait, there is now more.

NGC 5355 - mag 13 but small was now visible with averted vision

NGC 5358 - mag 13.6 was also just visible as a small slither next to a fine double star.

So as they say with Porsche. "there is no substitute" get a big dob!

Here is the best image I can find of this group ( until the imagers on here get going) on the internet for your enjoyment.

See how many of these little fuzzies you can see.

Mark

[cotterless45]

That's impressive, just wondering if you suffer light pollution sufficient to make galaxies difficult in an 8" , would aperture rule ?

Nick.

[mdstuart]

My thoughts would be that if your background sky glow was say mag 12 then no scope no matter how large will show a mag 13 galaxy...

[YKSE]

Mark,

Nice picture and observation descriptions

Your observation with 10" is about the same as my experience with my C8 in my dark site.

You have 5.5 NELM sky IIRC, and my dark site is around 6.0, this 0.5 mag difference corresponds to 2.51^0.5=1.58 times of light grasp capacity, and a 10"  has (10/8)^2=1.56 times light grasp capacity over an 8", also the constrast in better darker sky because of less sky glow, I'd say my 8" in my dark site should perform better than a 10" in your sky with same observer.

[estwing]

Mark I now find this Galaxy hunting to be the sport of big dob owners!...thanks for sharing

[John]

Mark,

I've been having a look at Hickson 68 with my 12" dob just now.

NGC 5353 and 5354 are fairly easy with direct vision. NGC 5350 is on the edge of direct and averted vison, clearer with the latter of course.

Then I switched from a 21mm (76x) to an 8mm (199x) eyepiece and NGC 5355 became visible on the direct / averted vision boundary. NGC 3550 now visible with direct vision. Some more dark adaptation and scrutiny with averted vision showed NGC 3358 intermittently, nextdoor, as you say to that nice double. 

The last one was hard work and difficult to hold even at 199x more than fleetingly.

Interestingly the 8mm Ethos eyepiece was showing a chunk of sky very similar in extent to the area covered by the above image.

Thanks for the "heads up". I've enjoyed Hickson 68 - I'll visit again I'm sure

[mdstuart]

Well done John...The optics on your 12 inch make it a match for my 16!

[John]

Well done John...The optics on your 12 inch make it a match for my 16!

I'll bet the galaxies were not as clear with my scope though. NGC 3358 was only visible when I pressed on the power and then only intermittently.

[DeepSkyBagger]

Hi Mark,

I made an observation of this field back in March last year. My telescope is a 12" Newtonian, but my skies are a bigger limit, NELM 4.8 on a really good night. It wasn't that good on the night that I made these observations.

24/03/2014

5350 - Larger than either of the other two galaxies in the field. Elongated. Dim and of uniform brightness.

5353 - Small, bright and elongated. No nucleus seen. 

5354 -  Very small, faint and round with no structure seen.

I didn't see 5355 or 5358.

A dark sky makes a huge difference. I have a series of observations of galaxies in Leo and Virgo made many years ago with a 4.5" Newtonian under 6.0 skies. They compare very favourably with my more recent observations of the same galaxies with a 12" under 4.5 skies.

Good post. Cheers.

Patrick

[John]

Nice report Patrick

Do you recall how much magnification you were using when you observed this group ?

I found that it was only when I pushed the power up to 199x that 5355 and 5358 became fainly visible with my 12" dob. Very faintly in the case of the latter !

[DeepSkyBagger]

Hi John,

I was using a 10mm Plossl eyepiece for the observation, which gives me x150.  I find that contrary to the advice given to new Deep-Sky observers, for most (nearly all) DSOs, higher power is better. I very often cannot see a dim galaxy using my finder eyepiece ](x81), but it's quite visible at x150.

Here's the actual observation.

Cheers,

Patrick

[pyrasanth]

I admire your resolve to see these objects visually but I still prefer a camera but I agree that rising to the challenge is most of the fun. Clear skies to you all.