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Can I Still Download Aperture

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  Can I Still Download Aperture Angeles Bartholomew <bartholomewangeles@gmail.com> - 2024-01-06 01:24 -0800

#86443 — Can I Still Download Aperture

There will eventually be a 'it's small enough aperture that the view visibly deteriorates' threshold given the Dawes Limit / Rayleigh Criteria. But that's going to be rather small aperture for casual visual observation of the disc of the Sun.



can i still download aperture

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Maybe somewhere around 60mm aperture? Where the resolution is heading for 2 arc seconds or worse, perhaps? I have heard that the 40mm aperture of the Coronado PST is a limiting factor in its performance.


But the basic answer to your question is that there's extremely little benefit -- if any -- to using an aperture bigger than 60 mm for viewing the Sun at 30X. That's true for the Moon as well, by the way, though 30X seems pretty low for the Moon even if you're not trying to zero in on specific features.


This is the way it works: If you use a 5mm exit pupil on a 4" scope and a 5mm exit pupil on an 8" scope, your subject will be just as bright in each scope. The sky will also be just as bright in each scope as well. This means that the contrast between the object and the sky does not really change. What you get from using the larger aperture is that you see the object at twice the scale. Twice the scale is very important for things like the Ring Nebula, because the better contrast of the larger nebula will show more structure in the larger aperture and this structure will be easier to see.


Then there is contrast transfer. On the surface of a planet, the moon, or the sun, the larger aperture will often (but not always) produce more contrast transfer. In other words, if a faint detail on the sun has a contrast of 20%, it might only be seen with a contrast of 10% in the larger scope, and only 5% in the smaller scope, once again, making it hard to see.






As for the sun, an 80mm aperture is about the largest you can use during the day that will give a good view when used visually. This is because daytime "seeing" is often poor, meaning that the light get aberrated by the currents of air in the atmosphere, breaking them up. This causes the loss of contrast as well. The larger the aperture, the more affected it is by seeing. I have used solar scopes of 40mm, 60mm, and 80mm, and the 80mm has given the best view but even at 80mm, during a typical session, the scope will only work at its full contrast potential for some of the time most of the days, though in just about every session, there are usually several minutes where the air is steady enough for the telescope to work at its best. This will be true for the moon and planets when using large scopes at night, and this means that sometimes a smaller scope like a refractor, can produce better planetary views than a larger scope like an SCT can.


As for the sun, an 80mm aperture is about the largest you can use during the day that will give a good view when used visually. This is because daytime "seeing" is often poor, meaning that the light get aberrated by the currents of air in the atmosphere, breaking them up. This causes the loss of contrast as well. The larger the aperture, the more affected it is by seeing. I have used solar scopes of 40mm, 60mm, and 80mm, and the 80mm has given the best view but even at 80mm, during a typical session, the scope will only work at its full contrast potential for some of the time most of the days, though in just about every session, there are usually several minutes where the air is steady


I have a different experience, Two years ago my club had solar outreach party near the summer solstice. There was a dozen scopes set up all of them were 80 - 100 long focus refractors except mine. One was an 100mm f/9 ED. All had white light filtrration with either baader astro film or glass filters. I brought an 8 inch dob with an astro-film full aperture filter. It was approximately 6:00PM The sun around 30 degrees above the horizon, intermittent wind and in the upper 80 degree temps. The dob was easily the best view for sun spot detail. It wasn't a contest. Both amature and experienced club members agreed. It should be noted that I could not crank the power on the dob without the image going mushy. All scopes were running about 100x. Was this increased resolution? increased exit pupil? Another benefit was that due to the wind, the dob was much more stable than a tripod mounted refractor. It takes a very sturdy mount to hold a long refractor steady in the breeze.


If the above advantages didn't exist, there would still be little justification, especially if one has the choice between those two telescopes, in going with the larger telescope. This, due to typical daytime seeing effects that typically place greater limitations on resolution -- something that your low magnifications would also limit. The typical advantages of using larger apertures vanish, as a general rule -- under the circumstances you've specified.


Among those who know what they're doing (and have similar telescope choices as you), more people choose to use telescopes in the neighborhood of 4-inch apertures than telescopes in the neighborhood of 8-inch apertures for observing solar eclipses.


It does matter which telescope you bring for your specified purpose -- and it's the smaller (4-inch) aperture telescope that would be the better (and likely safer) choice for that purpose -- in my opinion.


Alright. I get it. The OP's post was pretty much answered so I just took the heart of the original post to the extreme. My point was why set some hard limit on aperture for the eclipse? Why go minimal? For most this is a once in a lifetime event. Take advantage if you can.


As with any photography, the correct lighting is key to beautiful still life images. That means paying close attention to the exposure triangle and adjusting as needed until you get the desired effect. When readying your camera, consider these tips as starting points:


Once you feel comfortable with your camera settings, the sky's the limit when it comes to your creativity. Take your still life photography to the next level by adding more objects and textures, experimenting with new techniques, or even incorporating visual storytelling elements.


Shutter speed is the amount of time the shutter is open to allow light to hit the sensor. Beyond controlling the amount of light, the shutter speed also has a profound effect on the perceived motion in your photos. A slow shutter speed is open for a longer time, allowing anything within the frame that is moving to blur. Conversely, a very short shutter speed freezes the motion of even a quickly moving subject. The creative choice of shutter speed in nature photography depends on whether you want to show motion with some degree of blur or whether you want the moving subject to be sharp and still in the frame. Thus, the choice of shutter speed when there is movement is a creative decision.


The following photo from the Smoky Mountains demonstrates this perfectly. I chose a rather slow shutter speed to allow the water flowing over the rock to blur a bit, thus enhancing the sense of motion in the image. Had I chosen a fast shutter speed, the water would have appeared frozen and would have had no feeling of movement. In a nature photos like this, I choose the shutter speed first, then balance the aperture and ISO to get a proper exposure.


In contrast, the following image of a loon during a preening wing flap was captured at a shutter speed of 1/1600 of a second. I had observed the loons over several days and could anticipate when they would rise out of the water and spin their heads around. I wanted to capture the water droplets flying off of their feathers. After a few missed shots with slower shutter speeds, I determined that I needed 1/1600 to freeze the water droplets. I balanced the aperture and ISO to get a good exposure as always. Because of the shutter speed I chose, the resulting photograph tells exactly the story that I wanted to tell.


These two nature photography examples demonstrate a critical concept about using shutter speed creatively in your work. You must first determine what you want to say with your image and then decide what shutter speed is required to tell that story. You still must be mindful of balancing your shutter speed with aperture and ISO for proper exposure.


Just as shutter speed has a dual personality controlling exposure and perceived motion, aperture also has two sides to its coin. We know that aperture is the size of the opening in the lens that allows light to enter and hit the sensor. Obviously, a larger opening (smaller f-stop number) lets in more light.


But, in addition to having an effect on the exposure, the choice of aperture has a profound effect on the depth of field and how much of your image is in focus. A tiny aperture (larger f=stop number like f16) produces a large depth of field; you can have everything in focus from fairly close to your camera all the way to infinity. In contrast, a large aperture (small number like f2.8) results in a shallow depth of field. Depending on where you focus, a large part of your image may be out of focus.


So, depending on the story you want to tell, the choice of aperture is critical for nature photography. In fact, in my work, my decision about aperture is usually the first choice I make when determining a proper exposure.


When I am taking wide angle nature photos, I usually want everything to be in focus. This is particularly true when I have a strong foreground element. It is important that the foreground element be critically sharp and the distant background be acceptably sharp. I achieve this by using a wide-angle lens, a relatively small aperture, and focus just past the foreground element. I choose my aperture first, then balance shutter speed and ISO for exposure.


The following image from the Oregon Coast is a good example of this. I needed the foreground rock to be in focus as well as the distant sea stacks. Choosing an aperture of f14 gave me the depth of field that I needed and also allowed me to use a slightly slower shutter speed which helped to smooth out the reflection on the sand.

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