Have you thought of reflectivity of the mirror vs other mirrors or for that matter refractors? Mirrors are typically 92% and a refractor can be as high as 99%.
Aperture is king in visual astronomy. It also lets you gather enough light when running really high focal lengths to still get a clear image on slow (high F ratio) scopes. For astro-photography, your f ratio is a much more important number then aperture. Aperture only matters as it relates to a higher focal length while still keeping your f ratio reasonable. Higher focal length, smaller aperture=higher f ratio. Higher focal length, larger aperture=lower f ratio. All this means is, if using your telescope for photography, figure out how wide or narrow a field of view you want, then get the telescope with the lowest f ratio in that field of view. The actual size of the primary mirror or lens is irrelevant.
I know this is off topic for this video but I would like to know your opinion please. I was thinking of buying Celestron SkyPortal and auto focuser for my 8” AVX but after watching your ASIAIR tutorials I am thinking of going that route. Your thoughts please.
@@AstroBlender keep up your great work. Your explanations and examples clear up many questions I have as I move toward making a possible decision to move into astrophotography! Thanks.
I made a similar Excel spreadsheet when I was comparing telescopes. I think the question I've yet to see answered is, "so what does that mean?" What percentage difference is relevant? What is the practical difference of 3x more light gathered by the C14 over the C8, and at what point is that worth the cost difference, in both the telescope and the mount to hold it? I was debating an EdgeHD 11 and a RASA 11 over the EdgeHD 8 and RASA 8, but I couldn't tell, even after many days of looking through photos on Astrobin, that the difference between 8" and 11" was noticable.
@@AstroBlender I discovered Astrophotography about 2 months after I got my telescope and haven't touched an eyepiece since. With one exception, for Spring Break this past April we took a family trip to Flagstaff Arizona that included an hour one evening on a 24-inch Planewave CDK at the Lowell observatory, and that telescope was equipped with an eyepiece. We looked at about a dozen different galaxies, many of which I had imaged with my 8" EdgeHD. And the general consensus among my family was "meh" fun experience but they just looked like faint, fuzzy blobs, nothing like what I'd imaged with my much smaller telescope. So if the noticeable difference is for visual, then it sounds like my decision to stay with 8" for Astrophotography is a good one. Lighter weight and less expensive.
Very interesting for beginners! I think that times is actually a more useful figure than percentage. And in case it was not clear, 3 times more light means that 1 hour of integration with the bigger telescope would be equivalent to 3 hours with the smaller one.
Does it actually work out like that? I've been spending a lot of time on Astrobin, comparing similar targets between 8" and 11" scopes. While there is a lot of variability due to environmental conditions, other gear, processing, etc, I never found a situation where I could say "That right there is from an 11 while this one is from an 8" just by looking at the photo. In fact, some of the very best photos I found ended up being from 8" telescopes. It seems odd to me that there isn't more info on this topic.
@@JethroXP Yes, it works like that. I have a SkyWatcher 72ED and a RASA8 and both have almost the same focal length, around 400mm. Using the same camera, the difference in light gathering is astounding and is quite apparent just comparing raw shots. More generally, the direct comparison can only be done if the other variables involved don't change, like the sky quality, camera, etc. (An additional problem of using astrobin to do those comparisons is that images are post-processed, so it's hard to see whether differences are due to equipment or software).
@@vrruiz I think that comparison has more to do with f/ratio. The 72ED is an f/5.8 scope while the RASA 8 is an F/2. That means the RASA 8 is more than 8x faster than the 72ED. What I'm talking about is the difference between a RASA 8 and a RASA 11, where both are f/2. In that situation, how does the extra 3-inches of aperture manifest in measurable data or subjective quality?
@@JethroXP Just to be clear, because there's a lot of confusion around the f-ratio. To photographers is a useful tool because changing the f-ratio also changes the aperture of the lens, by closing the diaphragm. The know that closing the f-ratio an aperture stop is equivalent to reduce the exposure time by half or choose a lower ISO. But, we don't change the aperture of our telescopes, except when observing the sun. So: light gathering is only a function of the diameter of the telescope (minus central obstruction, if it exists). For point-like sources, like stars, that's the only thing that matters, the collecting area. In that regard, yes, the RASA8 has 8x the light gathering power of the SW 72ED, but the RASA11 is 2x more powerful than the RASA8 (1 full aperture stop, a photographer would say! :) With diffuse objects, like planets, nebulae and galaxies the issue is a bit more complicated, as the light is distributed in an area and the focal length (actually, the resolution per pixel) plays a role to consider. Also, large telescopes have more resolving power, although I don't see any advantage for that when working at a very short focal length.
Very Intresting Calculation!! I will definitely try This Out!! And Totally Agreed, Aperture is King, even For DSOs, I think Less Exposure time With More Aperture will give You good Signal To Noise Ratio!
Nice comparison with the pizzas! One thing to note is that the crust of pizzas usually has the same thickness regardless of the size of the pizza. This means that smaller pizzas may have less 'meat/filling' percentages compared to larger pizzas, which may be a good or bad thing depending on whether you like the crust :)
Use the function pi() vice 3.14 and do the radius conversion directly in the equation vice as an intermediate cell that you don't seem to need/use elsewhere. pi() * ( d/2 )^2
