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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 986
Loc: Oman
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Quote:
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!
Ummmm. Dual chip is actually quite a lot more inconvenient than off-axis guiding. You see, in OAG you can independently rotate your guide chip to find a bright-enough guidestar and normally the OAG guidechip is before any filter you may be using, so the stars look much brighter to it. With a dual-chip, when you rotate to search for a guidestar you are also rotating your carefully-framed composition on your imaging chip. People have also tried to work around the filter business by having filters that are smaller and more rectangular that they do not cover the guidechip, but with most dual chips you end up covering the guidechip simultaneously. There is always some fly in the ointment. That's why my huge preference is no guiding at all. The mount is where most $ should be spent.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 986
Loc: Oman
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Quote:
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.
Basically if the seeing is 2 arc-sec per pixel (and that is quite rare!) then the max useful image scale is around 1 arc-sec per pixel. People who are chasing the ultimate resolution go for a factor one-third instead of one-half. But frankly anything finer than 1.5arc-sec per pixel is most likely to be futile for most of us at average locations. A C14 Hyperstar delivers 1.4arc-sec per pixel on a Canon 500D, close to perfection. 30sec sub-exposures and no autoguiding is required.
The reason why I use a lower ISO at light-polluted sites is mainly because I want to keep the total number of subs under, say, 100. At a light-polluted site you need to increase the integration time (same factor as the skyfog is brighter). Also you end up eating up the dynamic range available in each sub if the skyfog hump is way up on the histogram. Between ISO 1600 and ISO 200 the Read Noise in Canon DSLRs does increase, but not exponentially. Eg there is little difference between 1600 and 800, so you do not do much harm in using 800 (or even 400) when the skyfog is brighter. At my home there is so much light pollution that with ISO 1600 my subs using a C14 Hyperstar are total wash-outs with 10sec exposures! To get 5 hours' integration time (quite reasonable but not very deep for the amount of skyfog) I'll have to shoot several thousand subs each 10sec long! Indeed no autoguiding required but just the logistics of processing that lot...
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Bored? Peruse my website:
http://www.samirkharusi.net/
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freestar8n
sage
Reged: 10/12/07
Posts: 299
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Quote:
Basically if the seeing is 2 arc-sec per pixel (and that is quite rare!) then the max useful image scale is around 1 arc-sec per pixel. People who are chasing the ultimate resolution go for a factor one-third instead of one-half. But frankly anything finer than 1.5arc-sec per pixel is most likely to be futile for most of us at average locations. A C14 Hyperstar delivers 1.4arc-sec per pixel on a Canon 500D, close to perfection. 30sec sub-exposures and no autoguiding is required.
Many of us are guiding SCT's on mid-range mounts with 0.5-0.8" per pixel and getting 2" fwhm under non-exceptional skies. With OAG and good guiding technique you can make a mid-range mount yield results comparable to a much more expensive setup. It is easier to use short focal length and not guide at all - but with proper technique and software, high resolution results are obtainable with minimal effort and expense.
My examples, with C11 and CGE totalling $4k combined, which is much less than a high end mount alone, can be seen here.
Some of the images have details related to my OAG setup and its use with a field of view indicator (FOVI).
Frank
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Quote:
Ummmm. Dual chip is actually quite a lot more inconvenient than off-axis guiding. You see, in OAG you can independently rotate your guide chip to find a bright-enough guidestar and normally the OAG guidechip is before any filter you may be using, so the stars look much brighter to it.
Ahh - and again my inexperience shows itself. I was unaware you could rotate the OAG to find your guidestar. Obvious once pointed out though! Does make me wonder about an OAG option for something like that f/4 newt. Lightweight compared to something like a ST80 and higher resolution then a 50mm finder, and given that the newt is an f/4 it is more likely to be able to find a guidestar then something like an f/10 SCT. I wonder if the newt would have issues coming to focus with an OAG in the path....
Quote:
The reason why I use a lower ISO at light-polluted sites is mainly because I want to keep the total number of subs under, say, 100.... ......At my home there is so much light pollution that with ISO 1600 my subs using a C14 Hyperstar are total wash-outs with 10sec exposures!
Yikes - 10-seconds only! From my local (and my lack of a C14/hyperstar!  ) I suspect I will not be bumping below iso800 often. Certainly iso1600 seems to be the way to go with the 300mm camera lens. Then again... the sky was REALLY REALLY bright with that full moon out!
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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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adamsp123
sage
Reged: 11/20/08
Posts: 444
Loc: welshpool mid wales UK
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Quote:
Adamsp123: so you are using something similar to the KWIQ Guider setup? That does look appealing, especially considering weight issues since I have a CG-5 mount.
JUst like that but self assembled from a spare finder and QHY5 link
http://stargazerslounge.com/diy-astronomer/84726-diy-finder-guider.html
It works with no weight adder to the system and I can get nice round stars at 8 mins on my F/4 8" Newt+MPCC. BTW having a fast scope makes life so much easier.
The only major problem I had was an inbalance I had managed to induce in the DEC axis by the position of the camera on the Newt, took a long time to suss but rotating the scope in the rings fixed it 100%.
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SkyWatcher 120ED PRO, GSO 200mm F4 Astrograph, Meade 10" SNT, WO 72ED & 66ED
Vixen Sphinx and Vixen Atlux with starbook,
QHY5 guider, Modded Canon 1000D, Baader MPCC.
WO Flattener III
Don't you wish there were a knob on the TV to turn up the intelligence? There's one marked 'Brightness,' but it doesn't work."
TV is called a "medium" because it is neither rare nor well done.
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freestar8n
sage
Reged: 10/12/07
Posts: 299
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Hi-
Newtonians are not as easily adapted to OAG because of limited backfocus. But for that matter, they may also have trouble focusing on a DSLR. Some Newtonians, like the Vixen and the Tak 180, have imaging in mind, so they have lots of backfocus.
So - for your particular OTA, OAG may not be an option with your DSLR and you may need to use a guidescope. If you do, be prepared for signs of flexure in long exposures, and beware that flexure can happen not only in the guidescope but within the OTA itself at the mirrors, which is harder to fix.
Since you are working on a budget, it may make most sense to make your own small guidescope with available components and mount it tightly. If flexure dominates, then the guidescope quality doesn't matter much - but if you don't have much flexure and you want small stars in the image, you may need a higher quality guidescope.
Frank
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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Quote:
The only major problem I had was an inbalance I had managed to induce in the DEC axis by the position of the camera on the Newt, took a long time to suss but rotating the scope in the rings fixed it 100%.
I am guessing that you rotated the tube so the camera is above the tube rather then to one side or the other - is that correct?
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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:
Newtonians are not as easily adapted to OAG because of limited backfocus. But for that matter, they may also have trouble focusing on a DSLR.
The 8" f/4 I was looking at is the new Orion Imaging Newt - so it is set up with imaging in mind. Looks to be the same sort of setup as the Astrotech AT8IN. Still unknown just how much extra back focus there is though.
You are right that on my 4.5" f/8 scope there *ARE* backfocus issues getting the camera to focus, let alone with an OAG inline. I am going to experiment with the f/8 newt anyway, I got a cheap 1.25" focuser that I will try and modify till I get enough backfocus to bring my DSLR or a webcam into focus. If that does not work there is no real loss other then the plastic focuser I "modified" (I have the original 0.965 focuser stored away so I can restore the scope to original specs very easy).
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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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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 986
Loc: Oman
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Quote:
Quote:
Basically if the seeing is 2 arc-sec per pixel (and that is quite rare!) then the max useful image scale is around 1 arc-sec per pixel. People who are chasing the ultimate resolution go for a factor one-third instead of one-half. But frankly anything finer than 1.5arc-sec per pixel is most likely to be futile for most of us at average locations. A C14 Hyperstar delivers 1.4arc-sec per pixel on a Canon 500D, close to perfection. 30sec sub-exposures and no autoguiding is required.
Many of us are guiding SCT's on mid-range mounts with 0.5-0.8" per pixel and getting 2" fwhm under non-exceptional skies. With OAG and good guiding technique you can make a mid-range mount yield results comparable to a much more expensive setup. It is easier to use short focal length and not guide at all - but with proper technique and software, high resolution results are obtainable with minimal effort and expense.
My examples, with C11 and CGE totalling $4k combined, which is much less than a high end mount alone, can be seen here.
Some of the images have details related to my OAG setup and its use with a field of view indicator (FOVI).
Frank
I suppose your non-exceptional skies have better seeing than my non-exceptional skies  Basically the message I was trying to put across is that very long focal lengths require rather heroic efforts at guiding, and are unlikely to yield a commensurate response for the amount of diligence. Of course, e.g. your Bubble does show very nice detail and looks well worthy of the level of effort you seem to be putting into it. For my highest resolution attempts I just go for ultra short subs and ultra bright targets (star clusters), like 4 to 15 seconds for which guiding is often superfluous, even at 4000mm focal length. Of course one runs into a whole slew of other problems, like even after mirror pre-release I still get shutter shudder for exposures between 1/30th sec and 1 sec. Anyway this below is the highest res DSO image I managed to get so far, the Trapezium, but only 20sec integration time. One night in the indefinite future I may yet try for more, if and when the seeing ever cooperates:
That H pair of stars are only 1.6 arc-sec apart. Autoguiding longer exposures may work (OAG) but then the seeing is unlikely to cooperate for several minutes per sub. Ah well, I suppose we all agree that OAG is the superior method  but nothing beats unguided for sheer simplicity...
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Bored? Peruse my website:
http://www.samirkharusi.net/
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adamsp123
sage
Reged: 11/20/08
Posts: 444
Loc: welshpool mid wales UK
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Quote:
Quote:
The only major problem I had was an inbalance I had managed to induce in the DEC axis by the position of the camera on the Newt, took a long time to suss but rotating the scope in the rings fixed it 100%.
I am guessing that you rotated the tube so the camera is above the tube rather then to one side or the other - is that correct?
I had the camera to "one side causing a strong DEC inbalance - top heavy, so I rotated the scope/camera in the rings so the CofG of the camera and finderguider were opposite the counter weight no DEC inbalance and CW sorts out the RA balance.
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SkyWatcher 120ED PRO, GSO 200mm F4 Astrograph, Meade 10" SNT, WO 72ED & 66ED
Vixen Sphinx and Vixen Atlux with starbook,
QHY5 guider, Modded Canon 1000D, Baader MPCC.
WO Flattener III
Don't you wish there were a knob on the TV to turn up the intelligence? There's one marked 'Brightness,' but it doesn't work."
TV is called a "medium" because it is neither rare nor well done.
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adamsp123
sage
Reged: 11/20/08
Posts: 444
Loc: welshpool mid wales UK
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Quote:
Quote:
Newtonians are not as easily adapted to OAG because of limited backfocus. But for that matter, they may also have trouble focusing on a DSLR.
The 8" f/4 I was looking at is the new Orion Imaging Newt - so it is set up with imaging in mind. Looks to be the same sort of setup as the Astrotech AT8IN. Still unknown just how much extra back focus there is though.
You are right that on my 4.5" f/8 scope there *ARE* backfocus issues getting the camera to focus, let alone with an OAG inline. I am going to experiment with the f/8 newt anyway, I got a cheap 1.25" focuser that I will try and modify till I get enough backfocus to bring my DSLR or a webcam into focus. If that does not work there is no real loss other then the plastic focuser I "modified" (I have the original 0.965 focuser stored away so I can restore the scope to original specs very easy).
The GSO F/4 I have has an 2" extension piece as standard on the focuser, you need it for EPs normally and remove it for the Camera, with no problems focusing the camera, a 1000D with MPCC attached. The secondary is the large size for imaging and I am pleased with the scope indeed.
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SkyWatcher 120ED PRO, GSO 200mm F4 Astrograph, Meade 10" SNT, WO 72ED & 66ED
Vixen Sphinx and Vixen Atlux with starbook,
QHY5 guider, Modded Canon 1000D, Baader MPCC.
WO Flattener III
Don't you wish there were a knob on the TV to turn up the intelligence? There's one marked 'Brightness,' but it doesn't work."
TV is called a "medium" because it is neither rare nor well done.
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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adamsp123: where did you pick up your GSO newt in the UK? I have been trying to find a source for them in the US or Canada but not found any yet....
The GSO scope *looks* rather like it may be the source for the AT8IN and Orion 8" f/4 imaging scope - would be interesting to see how they compare in price.
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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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adamsp123
sage
Reged: 11/20/08
Posts: 444
Loc: welshpool mid wales UK
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Quote:
adamsp123: where did you pick up your GSO newt in the UK? I have been trying to find a source for them in the US or Canada but not found any yet....
The GSO scope *looks* rather like it may be the source for the AT8IN and Orion 8" f/4 imaging scope - would be interesting to see how they compare in price.
Yes got mine from Modernastronomy UK also Telescope-service.com - Germany do them (I think they are the main european suppliers). I believe the AT version has the same optics but longer tube, I just added a home made dew/light shield made out of a camping mat, dead cheap and lightweight.....works to!
link for Teleservice http://www.teleskop-express.de/shop/product_info.php/info/p52_GSO-Newtonian-200-800mm---2--Crayford-Focuser---optical-tube.html
Pete
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SkyWatcher 120ED PRO, GSO 200mm F4 Astrograph, Meade 10" SNT, WO 72ED & 66ED
Vixen Sphinx and Vixen Atlux with starbook,
QHY5 guider, Modded Canon 1000D, Baader MPCC.
WO Flattener III
Don't you wish there were a knob on the TV to turn up the intelligence? There's one marked 'Brightness,' but it doesn't work."
TV is called a "medium" because it is neither rare nor well done.
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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*nod* that longer tube & internal baffles on the AT8IN do seem to be the only difference. The Orion version just like it is just a black painted version of the GSO original. Since the GSO at those shops is 449 pounds or 478eur ($755.77cdn) vs $449usd ($477.74cdn) for the Orion and AT versions there does not seem to be much point in going for the GSO version from my location. Odd that the standard telescope carriers here do not sell the GSO brand directly. *shrug*
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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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This is an interesting product for low-backfocus OAG:
http://www.teleskop-express.de/shop/product_info.php/info/p1188_Off-Axis-Guider---only-9mm-length---w--Canon-EOS-adaptation.html
Costs more then the SSAG, nearly as much as the scope itself, but it DOES look like the right tool for the job!
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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: 53
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wonder if any north american retailers have anything like that?
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guyroch
sage
Reged: 01/22/08
Posts: 255
Loc: Ottawa, Canada
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Quote:
Quote:
Quote:
The only major problem I had was an inbalance I had managed to induce in the DEC axis by the position of the camera on the Newt, took a long time to suss but rotating the scope in the rings fixed it 100%.
I am guessing that you rotated the tube so the camera is above the tube rather then to one side or the other - is that correct?
I had the camera to "one side causing a strong DEC inbalance - top heavy, so I rotated the scope/camera in the rings so the CofG of the camera and finderguider were opposite the counter weight no DEC inbalance and CW sorts out the RA balance.
But wouldn't this setup create an obstructed view for you guide scope which is aiming dead smack in between your camera and finder scope? Is there enough clearance? I don't think there is enough for my setup. Furthermore, this would make my finder scope almost useless as the guide scope would be in _my_ way for when I would try to peek in the finder scope. I am reading this correctly?
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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:
But wouldn't this setup create an obstructed view for you guide scope which is aiming dead smack in between your camera and finder scope? Is there enough clearance? I don't think there is enough for my setup. Furthermore, this would make my finder scope almost useless as the guide scope would be in _my_ way for when I would try to peek in the finder scope. I am reading this correctly?
I am guessing that his guide scope is installed in the finder bracket attached to the tube rather then attached to the top of the rings.... In that configuration you would not be using a visual finder, but rather just watching the output of the guidecam to act as your finder.
That is how I get on target when using the camera & standard lens, use the Frame and Focus mode (keeps taking shots as fast as possible) in nebulosity to find my location on the sky as looking through the camera is useless and there is no finder scope at all.
Pete - any chance you could post a picture of the configuration you are talking about?
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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: 299
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Quote:
I suppose your non-exceptional skies have better seeing than my non-exceptional skies
Hi Samir-
It's true I don't know much about the skies in Oman - but your trapezium image does look like it can be pretty steady. My skies in the northeast U.S. seem pretty well correlated with the jet stream. I don't know if you have other people in your area doing high res. imaging with OAG on good mounts, but that is one way to know what is possible. It's not clear to me you have tried it, so it may be possible at your site to get good results at long focal length and long exposure.
Here is an image of NGC 6946, and beneath it is the luminance version, plus a close up of a single 10m exposure with no processing showing how small the stars are on the scale of the 0.8" pixels. The seeing was pretty good that night, but such nights do happen, and with OAG and rapid corrections I don't find it too difficult to get results like these regularly at long exposure with a relatively humble CGE.
There is no question that unguided imaging is easier, but high res. work with mid-range equipment can be very rewarding without too much effort.
Frank
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adamsp123
sage
Reged: 11/20/08
Posts: 444
Loc: welshpool mid wales UK
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I will try to post a pic of my setup, but Falcon you are right, the finderguider swaps with the finder and simply goes into the standard finder shoe. Once I am on target I don't need the std finder and if I want to change to a different target off goes the finderguider on goes the finder, takes but a few seconds each swap. The one thing I do have is a dew strap on the finderguider as they will dew up at a drop of the hat!
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SkyWatcher 120ED PRO, GSO 200mm F4 Astrograph, Meade 10" SNT, WO 72ED & 66ED
Vixen Sphinx and Vixen Atlux with starbook,
QHY5 guider, Modded Canon 1000D, Baader MPCC.
WO Flattener III
Don't you wish there were a knob on the TV to turn up the intelligence? There's one marked 'Brightness,' but it doesn't work."
TV is called a "medium" because it is neither rare nor well done.
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