guyroch
sage
Reged: 01/22/08
Posts: 255
Loc: Ottawa, Canada
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It's a basic SkyWatcher 6" reflector at f/5.
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Skywatcher 750mm 6" Reflector f/5
Celestron CG5-GT mount
Orion ST80 + SSAG autoguider + PHD
Canon 40D (unmod) + TC-80N3 remote timer
Astronomik CLS clip filter
Orion SkyGlow light polution filter
Orion AccuFocus + homemade Bahtinov mask
Bushnell 8x42 h2o® Waterproof Binoculars
Sky Atlas 2000.0 Field Version (Laminated)
Plenty of patience and a wife that doesn’t quite understand my love for clear skies, but let’s me go out anyway ~ thanks honey bunny 
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Quote:
did you notice that orion has come out with its own 8" f/4 newt as well? they list theirs at 16lbs. its the exact same as the astro tech so i dont know how that is or who is right.
Well that is new! I am sure it *is* made by the same factory as the AT8IN. I had been warned away from the AT8IN because of the extra weight for the CG-5 mount - 50% rule and all that. The Orion 8" is 2lb lighter then the AT, probably because the AT model has the extended tube and internal baffles... So that leaves me with 1.5 lb for the DSLR and guidecam (SSAG?) if I use a 50mm finder as the guidescope. Kinda tight, but perhaps if I made it a 55% rule.... 
I *really* want to think this will be a good setup, it does exactly what I want (f/4, but a nice 800mm focal length). With the 300mm lens as the "wide" OTA as the alternative scope it SOUDNS just about right for my CG-5! Anything more and *certainly* a larger mount would be needed.
Quote:
ive seen some great pics from people using similar loads
A similar load on CG-5 mounts?
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Quote:
It's a basic SkyWatcher 6" reflector at f/5.
Ok, so in exactly the same range as I am going to try for then!
So I have to ask - how *IS* your experience imaging with a guided newt on a CG-5? I had been warned a newt would be harder to guide to do it's longer moment-arm compared to a similar-weight refractor or SCT so hearing real-world experience would be good!
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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waassaabee
Carpal Tunnel
Reged: 11/26/07
Posts: 2710
Loc: Central California Coast
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My CG5 was pretty good to me. I used a William Optics Megrez 90FD (621mm @ f6.9 and with a TV .8x FR/FF, 500mm f5.5) and @ 2 minutes unguided, could keep 70% no problem. I added a miniBorg 50 w/Qguider (predecessor to the SSAG) and could go 10 minutes if I wanted to, but now had 80-90% at my target 3-5 minute exposures.
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Gary
34N 120W
-My kingdom for blue squares!-
WO Megrez 90FD/TV 0.8x FR/FF
AT8RC
mini Borg 50/Q-Guide/PHD
CGEM
Canon 350D Hap Griffin Baader mod - o.o
My Friend Flickr
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Waassaabee - thanks, looks like you have about 1/2 the weight I am looking at, but very encouraging you are able to get 10-minutes exposures! Now if a 6 or 8" newt can just get that 70% at 5 minutes....
Would be nice to have one of those miniBorgs!
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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bardo
member
Reged: 09/13/09
Posts: 54
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Quote:
A similar load on CG-5 mounts?
yes. just from clicking on everyone personal sites i seen some really great shots coming from cg-5's/lxd's/GP[D] with 8" f/5 newts, 8" sct's, etc. probablly more of an exception though.
for instance
http://www.saratogaskies.com/category.pl?c=equip&sub=Scope1
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waassaabee
Carpal Tunnel
Reged: 11/26/07
Posts: 2710
Loc: Central California Coast
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I'm looking at your location... How much wind do you get? An open tube and wind make for frustrating adventures. The CG5's have known slop in the gears, and when I used to view with my 5" Newt it was very noticeable on windy nights.
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Gary
34N 120W
-My kingdom for blue squares!-
WO Megrez 90FD/TV 0.8x FR/FF
AT8RC
mini Borg 50/Q-Guide/PHD
CGEM
Canon 350D Hap Griffin Baader mod - o.o
My Friend Flickr
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Where I am tends to be quite calm, unless there is a storm blowing in from the south. Durring the summer it is common to have thermals blowing throughout the day, but they die down quick come dusk, and during the winter there is almost ALWAYS a north wind blowout down the sound (a local condition known as the Squamish winds). The Squamishs will be blowing 10-25 knots much of the fall/winter/spring, but where *I* am on the south end of Gambier is sheltered from them unless it is blowing in the 35knot range (not too often thankfully as those winds also strand me on the island - too rough to cross!).
So to sum up the overly complicated answer, wind is not often an issue on nights where imaging is possible.
I have much more of a problem with those pesky clouds...... 
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Quote:
for instance
http://www.saratogaskies.com/category.pl?c=equip&sub=Scope1
Quite a productive imager! With 8-minute exposures no less! The C8-N + CG5 combo on celestron's site is listed at 67lb... take away 11 for the extra counterweight, and 42 more for the mount itself and you are left with 14lb. slightly lighter, but at 37" MUCH longer then the 16lb 27" Orion 8" f/4 newt. Encouraging indeed!
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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waassaabee
Carpal Tunnel
Reged: 11/26/07
Posts: 2710
Loc: Central California Coast
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Then if you like diffraction spikes (and I do...), then the 6" or 8" would be great! And instead of the miniBorg, look at some of the threads on modifying a 50mm finder scope.
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Gary
34N 120W
-My kingdom for blue squares!-
WO Megrez 90FD/TV 0.8x FR/FF
AT8RC
mini Borg 50/Q-Guide/PHD
CGEM
Canon 350D Hap Griffin Baader mod - o.o
My Friend Flickr
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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I also like the spikes Ya, the modified 50mm finder is my current plan for my finder - or it is now after getting this far into this thread! A 50mm finder based one also works perfect given the 8" comes with one!
But, you know, if I won the lottery or something, a miniBorg WOULD be nice to have even if I did not use it for a finder! :P
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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guyroch
sage
Reged: 01/22/08
Posts: 255
Loc: Ottawa, Canada
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Quote:
Quote:
It's a basic SkyWatcher 6" reflector at f/5.
Ok, so in exactly the same range as I am going to try for then! So I have to ask - how *IS* your experience imaging with a guided newt on a CG-5? I had been warned a newt would be harder to guide to do it's longer moment-arm compared to a similar-weight refractor or SCT so hearing real-world experience would be good!
I bought my SSAG and Orion ST80 in September 2009 and only had a few clear nights so far. I was able to get 5 and 6 minutes shot with pin point stars right from the get go with my setup. I was also successful with a few test shots at 10 minutes with pin point stars. But I was not able to get consistent shots in different parts of the sky. However, my setup was a tab bit off balance as I did not have enough counter weight to offset the guide scope. I have since bought additional counter weight but the clouds are not cooperating but my guess is that I will be successful with 6 minutes exposures 80% to 90% of the time. If not, I see an NEQ6 Pro mount and a 120mm EQUINOX APO in the crystal ball.
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Skywatcher 750mm 6" Reflector f/5
Celestron CG5-GT mount
Orion ST80 + SSAG autoguider + PHD
Canon 40D (unmod) + TC-80N3 remote timer
Astronomik CLS clip filter
Orion SkyGlow light polution filter
Orion AccuFocus + homemade Bahtinov mask
Bushnell 8x42 h2o® Waterproof Binoculars
Sky Atlas 2000.0 Field Version (Laminated)
Plenty of patience and a wife that doesn’t quite understand my love for clear skies, but let’s me go out anyway ~ thanks honey bunny
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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I think your conclusions are fine. These days I do not even bother to re-think all this stuff each time. For white light I use 1 minute subs at f2.8, 2min at f4, 4min at f5.6, etc. Triple length for narrowband. ISO 1600 at a dark site, lower ISO if there is appreciable light pollution. I suspect too many people have not yet caught onto the fantastic ease of everything when using a fast focal ratio OTA. The mentioned Orion 8" f4 Newt sounds intriguing! If one can find a suitable flattener for it (Parracor?).
Another thing that changes all the parameters fundamentally is that the new Canon DSLRs have such tiny pixels; eg the 500d (T1i) has a 4.7 micron pixel pitch. People used to be very happy to have a large, super-priced APO ($10,000+) and a $10,000 35mm format astroCCD to image at 1.5 to 2 arc-sec per pixel, to end up with a decent A3 sized print. Well, with the 500D you can do similarly with a focal length of only 500mm to 650mm. Basically, for average seeing (around 3 arc-sec) you never need a focal length longer than 650mm to shoot DSOs with the 500D. This reduces the cost of the OTAs tremendously, and you often end up with a faster focal ratio. The OTA being much lighter also enables the use of less expensive mounts. Of course, because of the fine image scale, guiding may still be necessary. You cannot have high resolution without paying a price somewhere  But the total package price is much, much lower. The prices in these things go up exponentially, so they have now also come down exponentially. If only people took the time to comprehend what impacts their budgets and how.
Camera? Tiny pixels, modded. OTA? Fast focal ratio, max focal length of 650mm. Mount: best you can afford for the load. Autoguiding? Depends on previous selections.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Interesting that you do not think going past 650mm is needed... It does indeed makes sense to match your pixel-resolution to seeing-limited resolution. If 3 arc-sec is "average" seeing then that 8" newt will be seeing limited unless I get an exceptional night! With an XT or 20D I would have 1.65 arc-sec/per pixel.
Looks like someone needs to make us a 6.5" f/4 660mm schmidt-newtonian imager!  That should hit the spot! Or while I am dreaming of the impossible an 8" f/3.25 650mm or 9.25" f/2.8 658mm would do quite nicely. Oh, and $99 is an excellent price BTW.... 
Back to the real world... You mention using a lower ISO in light-poluted areas, what is the reasoning behind this? So far I have been shooting basically all ISO-1600 here.
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Small bit of extra info - from watching ClearSkyChart's graphs of seeing for my area and looking at what Environment Canada's definitions are for those levels I generally have seeing in the ~1.0-2.0 arc-sec range, so with the XT and the 8" newt it seems I SHOULD be in about the right resolution to be at the seeing limit, but not beyond, on most nights.
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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freestar8n
sage
Reged: 10/12/07
Posts: 301
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I will summarize my take on this issue, which is very different from what is found on the web. The claim that guiders are now very accurate because they do sub-pixel centroid calculations is based on assumed precision in the centroid estimation, and not the actual accuracy. There are many ccd imperfections that cause a small star spot to have a poorly defined centroid, so I claim that as long as the star is bright enough, you want to make the focal length as long as possible so these pixel-scale artifacts have less impact.
A key measure is the actual fwhm of the guidestars on your guide camera. You may have 2" per pixel on the guide camera, but with a short refractor the actual stars may be bloated to 12" fwhm, which makes it hard to get 2" fwhm stars on the image. It is like an archer not wearing glasses - they can still see the target and estimate its center, but the actual aim will improve with a clearer view.
This is why I promote OAG and dual-chip guiding wherever possible. If you want to do long exposures (you mentioned narrow band) with a reflector, it will result in much tighter stars and more consistently due to flexure and centroid inaccuracy. It is how most high-end images at long focal length are taken.
On the other hand, if you are just getting into imaging and want to keep it simple - the best way may be to guide a short refractor with a short guidescope. This will be much more forgiving, and the lack of mirrors will reduce the impact of internal flexure.
Finally - I recommend examining the results and techniques of other people with similar equipment to what you plan to use. The best practice with your mount may be very different from what works on another mount.
I aim for small, round stars in the 2" fwhm realm with a C11 on CGE guided with OAG and MetaGuide. Some of my images are here.
If you want to work with your Newtonian, it may be possible to do short exposures with a guidescope, but narrow band may be too difficult. Some people do well with Vixen R200ss with a guidescope, so if your OTA is similarly tight, you may be able to get good results.
Frank
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bardo
member
Reged: 09/13/09
Posts: 54
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a tad off topic here as well but has anyone seen orions new adaptive optics that works with dslrs? its pretty pricey but i wonder how well it will work.
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Frank
Interesting - this was a bit closer to my assumption beforehand, that long focal length is good. (though high f/ratio is bad). What exactly do you mean by dual-chip guiding?
As for narrowband - I do not have plans to do narrowband myself at this time, Samir was just pointing out the extra exposure times required if I ever did.
Bardo: pricy indeed! Looks sorta like IS for terrestrial photography built into an off-axis guider adaptor.
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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bardo
member
Reged: 09/13/09
Posts: 54
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sbig, starlightxpress, etc ccd cameras use two chips in one unit. or one chip where a portion is allocated to guiding.
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Ahh - interesting, I was unaware of those type of cameras! Starting with a DSLR as part of my equipment blinded me a bit to that aspect of potential gear. Ya, I can see why having a guide cam integrated into the main cam would be nice - quite a bit nicer then off-axis guiding I would imagine!
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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