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neptun2
sage
Reged: 03/04/07
Posts: 275
Loc: Bulgaria
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Hi all.I have read some older topics about the effect of aperture in astrophotography but there is still some questions which i can no answer myself so i am asking you for help. I understand that field of view and resolution per pixel are maybe most important but it depends on pixel size and focal length only so how can i be sure that the optical system is not limiting the ccd or dslr? Because i can have scope which is with 80mm aperture and 900mm f/l and also another one which is with 120mm aperture and same f/l. I think that if resolving power of the scope which depends on aperture only is better then arcsec/pixel ratio with given camera this means that optical system is not limiting. Is this so? I am asking because currently i have 200mm reflector which when used with paracorr is f5.75 (1150mm f/l). I wonder if there is any sense to buy for example skywatcher 120 equinox or black diamond for astrophotography only. I am shooting with nikon d5000 which has 23.6x15.8 mm sensor and 4288x2848 pixels resolution. So according to my calculations at 900mm f/l resolving power of the APO remains better then the arcsec/pixel resolution with this camera at this f/l. Is this correct? And also do you think that the 120mm APO will give me smaller stars and crisper picture then the 200mm newton with paracorr? Please help and thanks in advance to all who will respond.
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Skywatcher Explorer 200P 8" f5 newtonian reflector
HEQ5 Pro Synscan Equatorial mount
Nikon Action 12x50 , Nikon D5000
Nagler type 6 11mm , Pentax XW 7mm , Televue 2x barlow 1.25"
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adamsp123
sage
Reged: 11/20/08
Posts: 441
Loc: welshpool mid wales UK
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At home I image with a 200mm F/4 Newtonian with MPCC corrector and if I am away I image with a SW 120ED and with Flattener at F6.
I prefer the stars with spikes but the big advantage with the newtonian is it is photographically faster with slightly better resolution but the advantage with the refractor is the faster cooldown and no collimation worries.
The limiting factor with be the atmospheric conditions there are many extremely excellent pics taken with 80ED 72ED and 66ED scopes so I would not get to hung up on aperture but the 120ED is a darn fine scope for visual and imaging.
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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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neptun2
sage
Reged: 03/04/07
Posts: 275
Loc: Bulgaria
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Adam thank you for this information. You have both 200mm newtonian with paracorr and SW 120ED with flattener so i will ask a few more questiones. If you do not count that the newtonian is faster and compare both scopes only in term of resolution, aberrations and pinpoint of stars will you prefer the APO instead of newtonian? Did you try to take pictures of the same object with the APO and newtonian and if so can you post one or 2 so i can see the differences? What i am trying to figure is if there is any sense to buy SW 120ED and use it for photography instead of my current 8" f/5 newtonian with paracorr. I am asking mostly about image quality comparison. Thanks again.
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Skywatcher Explorer 200P 8" f5 newtonian reflector
HEQ5 Pro Synscan Equatorial mount
Nikon Action 12x50 , Nikon D5000
Nagler type 6 11mm , Pentax XW 7mm , Televue 2x barlow 1.25"
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adamsp123
sage
Reged: 11/20/08
Posts: 441
Loc: welshpool mid wales UK
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I do not have any comparison photos of the same subject but I have posted photos using both instruments on http://stargazerslounge.com/imaging-deep-sky/ as well as other pics by other people using similar scopes. Have a look because on that site the restrictions on photo size are not severe so the pics are of good resolution.
Of mine the ones with star spikes are done with the Newt and the stars without spikes were taken with the 120ED.
BTW I use the Baader MPCC not the Paracorr.
Hope that helps.
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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.
Edited by adamsp123 (11/08/09 03:08 AM)
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