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Observing >> Deep Sky Observing

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GlennLeDrew
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Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5669112 - 02/08/13 01:52 PM

If the emphasis is on the observation of dimmer, low contrast, extended objects, a short f/ratio system is no impediment. The larger secondary will impart absolutely no detectable reduction in image contrast on galaxies and nebulae. Sure, the planets and crowded globular cluster cores will suffer some degradation, but in the regime of the faint, our eyes' resolving power is *very* much the weak link.

With this knowledge in mind, a squat system which keeps one's feet always on the ground is entirely justified. That's what I'd do. Indeed, an f/3 system is not at all off-putting, if it keeps me Earthbound.


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Dave MitskyModerator
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Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5669149 - 02/08/13 02:09 PM

I've used a couple of the new f/3.3 and f/3.6 Dobs and the views were excellent. That includes the planetary views. Being able to stand with two feet on the ground while looking through a 22" Newtonian is wonderful.

Dave Mitsky


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Jeff Morgan
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Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5669788 - 02/08/13 09:16 PM Attachment (23 downloads)

Quote:

Has anyone got dob parts suppliers for truss tubes, mirror cell, etc. I'm going with Novak for the diagonal.

Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.




Look at Aurora Precision for a mirror cell. I really like the design and construction on mine. Which BTW is a 16" f/7, Zambuto mirror. Here is a photo after daylight testing of the ServoCAT. Looking forward to First Light, weather is conspiring against me currently.


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Jeff Morgan
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Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5669793 - 02/08/13 09:21 PM Attachment (16 downloads)

Quote:

Consider one thing before you write off a longer 16" -- An orchard ladder. I use a six foot, three legged, aluminum with a flared base. It grabs onto any uneven terrain and is the most solid, stable thing I've ever climbed. It cost under $100, is excedingly light but very solid and if it didn't fit in my vehicle it rode the bike rack on the back.




For mine I'm going to use a rolling platform ladder. It has siderails, a large top platform, and it folds. It is surprisingly easy to handle, balances very nicely on the large wheels. Even on a reasonably uneven surface (that being, one level enough to set up a scope) there is zero - zero chance of a topple.


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Jeff Morgan
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Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5669795 - 02/08/13 09:23 PM Attachment (37 downloads)

This is what it looks like next to the scope. Suitable for scopes up to about 120" of focal length. And they make bigger - much bigger - models.

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azure1961p
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Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5669812 - 02/08/13 09:37 PM

Wow you fellas have some phenomenal sixteens - and a Zambuto!!! Yeah your going to have heavy cloud cover for six weeks.

It's interesting how there's both extremes here - the testimonials of fine f/3 and the proponents of the long focus designs. It is amazing too that with super huge aperture that despite the fast focal ratio the secondary can remain startelingly small .

I appreciate the points made in that with the eyes resolution of dim images the contrast boost of a small secondary is not realized . I think in stars it would be but not on objects like the Veil.

To keep costs down Im not going with a custom focal ratio but I understand the points made - and the agricultural ladder was well taken.

Thanks guys.

Pete


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azure1961p
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Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5669815 - 02/08/13 09:39 PM

Jeff,

That's amazing. You've got the whole thing worked out and in style. That is going to be a phenomenal performer. Please post your experiences. Even 5" planetaries are going to show well in that.

Pete


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IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5670952 - 02/09/13 03:57 PM

A real Serrurier, wow.

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Jeff Morgan
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Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5672091 - 02/10/13 10:19 AM

So a question to current 16 owners from a new 16 owner:

When hunting down "the faint ones" how close do you go to the theoretical limit for the aperture?

I realize this will be dependent on weather, dark site quality, and a few other things, but on a "typical" night from your best site was what I was thinking.

The reason for the question is that I am using Astroplanner to generate observing plans (by constellation) for SkySafari and there are a couple of issues here:

1) Sheer mass. Going from magnitude 14 to 15 (the limit of SkySafari Plus) about doubles the number of galaxies. Should I upgrade to Pro and go down an extra 0.7 magnitudes I would expect a similar increase, and;

2) Catalog issues. I was seeing some "drop out" of list targets when going from Astroplanner to SkySafari. Bill at Southern Stars was right on top of it, and said the source data can have some conflicts depending upon the measurements were done in. The difference could be a couple of full magnitudes in cases.

So my concern was that pressing to the theoretical limit could end up in a lot of time wasted chasing ghosts, and I'm curious what the experienced Galaxy Hounds do about it.

Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?


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azure1961p
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Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5672117 - 02/10/13 10:44 AM

In my 8" the faintest galaxies I could see with standard coatings was 13.5 under 6.2v sky's and stellar limit of 15. Moving to 16 I would think should add at least a full magnitude onto that and maybe 1.5v extra? I would also think the galaxies extended surface brightness would have a bigger improvement than the stellar. Seeing where I am is lousy often and the 8" with small CO produces some fine tight stars that larger apertures and COs tend to bloat and soften. Great seeing is another matter.

Ok that's my view from 8" anyway.

Pete


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Madratter
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Re: 12" versus 16" for galaxy structure [Re: Jeff Morgan]
      #5672601 - 02/10/13 04:03 PM

Quote:


Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?




I have a 20". The dimmest galaxy I have bothered to hunt down was listed at 16.0 (NGC 913). That was under good but not great skies (a little better than 6.0). I have bagged four others listed between 15-16. That said, a) I don't think the catalog values are all that accurate for visual work and b) personally, I don't go hunting for the really faint ones unless they are part of a group. They just aren't that interesting and there are plenty of brighter, more interesting ones that I still haven't seen.


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faackanders2
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Re: 12" versus 16" for galaxy structure new [Re: Madratter]
      #5672774 - 02/10/13 05:57 PM

Quote:

Quote:


Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?




I have a 20". The dimmest galaxy I have bothered to hunt down was listed at 16.0 (NGC 913). That was under good but not great skies (a little better than 6.0). I have bagged four others listed between 15-16. That said, a) I don't think the catalog values are all that accurate for visual work and b) personally, I don't go hunting for the really faint ones unless they are part of a group. They just aren't that interesting and there are plenty of brighter, more interesting ones that I still haven't seen.




+1


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IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5672984 - 02/10/13 08:17 PM

This is not exactly galaxy structure anymore but it seems that the original poster does not object, so... As far as deliberately going after faint galaxies, I usually stick to those plotted in Uranometria. This means to visual mag. 15.0 (that's what Uranometria says) and photographic just under 16 (my guess/generalization). The real limit (hitting the 0 probability of detection) for me with the 16" seems to be another half-magnitude fainter at around 16.5, although freaky exceptions even with normal morphology may go beyond 17.0 and still be visible. I don't mind wasting time

EDIT: I meant to say that my probability of detection at photographic mag. 16.0 is 50/50, and it is better than 50/50 for these faint, non-NGC galaxies in Uranometria that seem to concentrate in the photographic 15.5-16.0 range. Around photographic 15.5 the probability tends to 100% with my 16".

Edited by IVM (02/10/13 09:15 PM)


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george golitzin
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Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5673172 - 02/10/13 10:09 PM

The dimmest galaxies I found in a 16-inch were between mag 15.5 and 16, in the Corona Cluster--that was definitely pushing the envelope for that aperture. Like Madratter, I don't hunt these down unless part of a galaxy cluster: it's a particular sort of game.

You bring up a topic of interest with regards to charting. Once you step up to 16 or 18 inches, ordinary charts cannot really go deep enough for certain situations--Uranometria only goes so far (although it does contain deeper maps of specific regions), and so one must pick and choose magnitude limits for specific targets: one size no longer fits all. Last night I had several different charts with very different parameters--the deepest was the Perseus cluster, where I was able to identify 36 galaxies within a 1-degree field. For that chart I put no effective mag limit. For wider maps, that's usually not possible.

-geo


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HellsKitchen
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Reged: 09/05/08

Loc: Melbourne Australia
Re: 12" versus 16" for galaxy structure new [Re: george golitzin]
      #5673209 - 02/10/13 10:32 PM

I have a 12" Zambuto and where I live in the outer suburbs of a large metro area, the faintest galaxies I can detect are about V mag 14. The faintest stellar object I've seen is the Quasar HE 1015-1618 in Hydra which NED lists as V mag 15.7. My NELM is approx 5.5, I would say that at mag 13.5 for galaxies and mag 15 for stellar is where things start to get challenging.

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Jeff Morgan
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Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5673341 - 02/11/13 12:07 AM

Quote:

In my 8" the faintest galaxies I could see with standard coatings was 13.5 under 6.2v sky's and stellar limit of 15. Moving to 16 I would think should add at least a full magnitude onto that and maybe 1.5v extra? I would also think the galaxies extended surface brightness would have a bigger improvement than the stellar. Seeing where I am is lousy often and the 8" with small CO produces some fine tight stars that larger apertures and COs tend to bloat and soften. Great seeing is another matter.

Ok that's my view from 8" anyway.

Pete




The 15.7 magnitude value is what Astroplanner thinks the limit is on a 16" when you define your scope.

SkySafari Plus goes down to 15.0 so drops list components fainter. I'll probably be upgrading to Pro (which goes much fainter) when observing season gets rolling.

And it doesn't always seem to work "by the numbers". I've caught IC4617 near M13 with my 12.5" Royce - from the backyard no less! SkySafari lists it at magnitude 15.17, where Astroplanner doesn't provide a magnitude at all. I have yet to repeat that observation.

It should be interesting to track success rate vs. magnitude, but after awhile I could see myself putting a brighter limit on searches.


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Ed D
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Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5673728 - 02/11/13 10:02 AM Attachment (22 downloads)

Quote:

Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.

Normally I'm skittish about an f/4 or f/5 system as I never liked my ten, but here's no other way for me to comfortably use 16" in anything longer and it'd be a custom pricey order so the overwhelming light gathering advantage is swamping my resistance on several points.

Pete




Pete, I attached a picture of my friend's truss Dob he made using a 16" f/4.5 LightBridge mirror he picked up used for $150, not pristine or like new, but it does give great views. As you can see it's not all that tall, requiring using the first step of a folding step ladder only around zenith. He made it using the Kriege and Berry design. BTW, the mirror box weighs 50#.

Ed D


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IVM
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Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Ed D]
      #5674153 - 02/11/13 02:25 PM

I like how this 16" was apparently delivered to the site in the two-door car...

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Ed D
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Re: 12" versus 16" for galaxy structure new [Re: IVM]
      #5674931 - 02/11/13 10:37 PM

Didn't even occur to me to point it out, but that is the car it rode in. It breaks down very compactly and leaves enough room for all the other stuff. We each bring our own cars loaded with our scopes and other gear. The big Dob is actually easier to transport than my other friend's 8" GEM mounted Newt seen in the pic.

Ed D

Edited by Ed D (02/11/13 10:43 PM)


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ThreeD
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Reged: 12/23/08

Loc: Sacramento suburbs
Re: 12" versus 16" for galaxy structure new [Re: IVM]
      #5675016 - 02/11/13 11:55 PM

Quote:

I like how this 16" was apparently delivered to the site in the two-door car...


Since I built a new base for my LB16 easily fits in my Prius. I'm still using the original OTA too and that bottom tube is tall. Lots of room left in the car too...

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