Comments - A Direct Comparison Of 200mm f/4 and a 90mm f/7 Scopes - AstroGab2024-03-29T05:37:47Zhttp://astrogab.ning.com/profiles/comment/feed?attachedTo=6354305%3ABlogPost%3A56111&xn_auth=noI think you need to look ast…tag:astrogab.ning.com,2011-07-13:6354305:Comment:685022011-07-13T16:13:59.094ZRobert C. Millshttp://astrogab.ning.com/profile/RobertCMills
I think you need to look ast the actual spot size or spot diagrams of the 2 scopes. I have found that scopes with tighter /smaller spot diagrams produce better images regardless of some of the other factors. The R200SS has a central obstruction and collimation issues not found in refractors. For what it's worth.<br />
Bob
I think you need to look ast the actual spot size or spot diagrams of the 2 scopes. I have found that scopes with tighter /smaller spot diagrams produce better images regardless of some of the other factors. The R200SS has a central obstruction and collimation issues not found in refractors. For what it's worth.<br />
Bob Jules, the astrophotographer…tag:astrogab.ning.com,2011-06-16:6354305:Comment:603102011-06-16T11:23:09.885ZNeil Heacockhttp://astrogab.ning.com/profile/NeilHeacock
Jules, the astrophotographer in question is I, Neil Heacock, capturer of the dark dusty details in the Dark Horse nebula which was chosen as the Astronomy Magazine Picture Of The Day on January 10, 2010, and I can tell you that though the seeing conditions may have been different on the nights the various shots were taken, after a year or more with the R200SS and another year or more with the ED103S, in good nights and bad nights, dark sky and light polluted sky, the refractor outperforms the…
Jules, the astrophotographer in question is I, Neil Heacock, capturer of the dark dusty details in the Dark Horse nebula which was chosen as the Astronomy Magazine Picture Of The Day on January 10, 2010, and I can tell you that though the seeing conditions may have been different on the nights the various shots were taken, after a year or more with the R200SS and another year or more with the ED103S, in good nights and bad nights, dark sky and light polluted sky, the refractor outperforms the reflector every time. I always lets the reflector sit for an hour or two to acclimate to ambient temps before using it. Thats one of the reasons I don't like using it! I agree that the reflector will be more susceptible to scintillation, but there is another factor at play and that is the large secondary obstruction and particularly the large spider vains on that scope. That spider softens the image in that scope. The scope would perform better if a thinner spider was installed which some owners of the scope do. Clarification: Focal length i…tag:astrogab.ning.com,2011-06-02:6354305:Comment:553652011-06-02T15:39:44.155ZGreg Marshallhttp://astrogab.ning.com/profile/GregMarshall
Clarification: Focal length is the prime determinant of magnification, which, of course, does affect susceptibility to seeing. But focal length alone does not.
Clarification: Focal length is the prime determinant of magnification, which, of course, does affect susceptibility to seeing. But focal length alone does not. No, the larger aperture is "l…tag:astrogab.ning.com,2011-06-02:6354305:Comment:560412011-06-02T14:23:47.197ZGreg Marshallhttp://astrogab.ning.com/profile/GregMarshall
No, the larger aperture is "looking" through a wider column of air. This is true regardless of focal length or ratio - it's just aperture.
No, the larger aperture is "looking" through a wider column of air. This is true regardless of focal length or ratio - it's just aperture. Hmm... but if the two scopes…tag:astrogab.ning.com,2011-06-02:6354305:Comment:560322011-06-02T07:50:38.563ZNeil Heacockhttp://astrogab.ning.com/profile/NeilHeacock
Hmm... but if the two scopes have the same arc second per pixel I'd think they are equally susceptible to seeing issues. No?
Hmm... but if the two scopes have the same arc second per pixel I'd think they are equally susceptible to seeing issues. No? Here's another thought: Large…tag:astrogab.ning.com,2011-06-02:6354305:Comment:562012011-06-02T07:22:00.647ZGreg Marshallhttp://astrogab.ning.com/profile/GregMarshall
Here's another thought: Larger aperture scopes are more susceptible to seeing conditions, so you can't really compare compare scopes of different aperture unless seeing is perfect.<br />
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Nevertheless, I still think that the 200mm f/4 reflector is just not quite as good optically - maybe even without the obstruction.
Here's another thought: Larger aperture scopes are more susceptible to seeing conditions, so you can't really compare compare scopes of different aperture unless seeing is perfect.<br />
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Nevertheless, I still think that the 200mm f/4 reflector is just not quite as good optically - maybe even without the obstruction. Well done Neil. My instrument…tag:astrogab.ning.com,2011-06-01:6354305:Comment:561312011-06-01T23:02:28.981ZTrevor Woodrowhttp://astrogab.ning.com/profile/TrevorWoodrow
Well done Neil. My instruments are lower end versions of what you have here...I have an old SVD 200mm F4 and an Explore Scientific 102 F7 and I would even argue that if one had an edge over the other...I would say the 102 has produced the better images.
Well done Neil. My instruments are lower end versions of what you have here...I have an old SVD 200mm F4 and an Explore Scientific 102 F7 and I would even argue that if one had an edge over the other...I would say the 102 has produced the better images. Something I still wonder abou…tag:astrogab.ning.com,2011-06-01:6354305:Comment:561252011-06-01T22:36:45.547ZGreg Marshallhttp://astrogab.ning.com/profile/GregMarshall
Something I still wonder about is how much a star is different from other objects (things that aren't point sources) in terms of exposure.<br />
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As to whether f ratio matters, I've always felt that it does (and boldly said so!), but I've never done a careful measurement to test this theory. With my VC200L I use a reducer just because 1800mm focal length is just way too much magnification for the quality of guiding that I can achieve.
Something I still wonder about is how much a star is different from other objects (things that aren't point sources) in terms of exposure.<br />
<br />
As to whether f ratio matters, I've always felt that it does (and boldly said so!), but I've never done a careful measurement to test this theory. With my VC200L I use a reducer just because 1800mm focal length is just way too much magnification for the quality of guiding that I can achieve. Good point. Of course the cos…tag:astrogab.ning.com,2011-06-01:6354305:Comment:559262011-06-01T21:59:15.532ZRuss Ruggleshttp://astrogab.ning.com/profile/RussRuggles
Good point. Of course the cost of a RCOS three times the size of your scope will not be cheap.
Good point. Of course the cost of a RCOS three times the size of your scope will not be cheap. One of the things I didn't me…tag:astrogab.ning.com,2011-06-01:6354305:Comment:561212011-06-01T21:41:02.160ZNeil Heacockhttp://astrogab.ning.com/profile/NeilHeacock
One of the things I didn't mention is that when I got the R200SS I was upgrading from a William Optics MegRez 90 and I was looking forward to significant shorter exposures and detail increase... it never happened. I discovered right away that something isn't quite right with the theory on it. I don't know it or claim to understand it, but when I look at my images, I get better results with the smaller slower refractor so I'm staying here until I can really make a significant change in hardware.…
One of the things I didn't mention is that when I got the R200SS I was upgrading from a William Optics MegRez 90 and I was looking forward to significant shorter exposures and detail increase... it never happened. I discovered right away that something isn't quite right with the theory on it. I don't know it or claim to understand it, but when I look at my images, I get better results with the smaller slower refractor so I'm staying here until I can really make a significant change in hardware. Minimum of tripling the system in aperture and I don't really care about speed. I mean... even the high end RCOS scopes are f/8 and f/9 and I don't see the owners reducing them to f/5 or something.