OMG! You are killing me here. Now look what you have done. I have spent the last 15 years ignoring the previous 10 years of super deep imaging technology I was so involved in. Now your words have spurned a thousand scattered new scientific ideas I must now peruse. I am lucky that for the most part I hopped on this solar imaging scope because it was attractive and looked to produce good looking images. Now I am thinking that your personal solar scope is more along the lines of what I should go for. I only use dslr that I have because I have it and it produces good images I want. If I can adapt it to my solar setup and get nice captures that my eye can see I am fine. I can probably figure out a way to see with the same setup what my eye cannot. That is why I have the full spectrum modified A7R. I do know that those cmos sensors are less than ideal for collecting the images for truly quality astro and solar images, it would be nice to have the optics necessary and later assemble the proper sensor. Until then get by with the dslr.
So my first question is if I got an ED80(I do not know what that is) could I use it as a prime lens on my 60mp dslr and get satisfactory images(stars,birds)? Would it be as simple as adding SM60 etalons to get satisfactory images of the sun?
So all of my previous life as a photographic technologist consisted of being briefed by scientists and engineers on what needed to be imaged, what particular properties that system was expected to exhibit and the specific data needed to be gathered and the timescale involved in the entire process. I then determined all that it took to satisfy all of the required results. In this case I really don't know where to start. I have an old school Meade SCT on a LX80 mount I limp along with. In other words slightly <0 knowledge.
Do you have any suggestions? I personally don't know exactly where to start.
No worries, just trying to make sure you know what you're getting into and with what expectations. It's all too common to approach imaging with a dSLR/mSLR when one has a background of using them and not want to let go of using them. The sensors are actually very good, they're mostly Sony sensors without all the other complex stuff that goes into a "camera" for terrestrial use which is why the cost is so affordable for high efficiency, high quantum efficiency, fast FPS (fast data throughput), they're monochrome and are not plagued by an inefficient Bayer Matrix overlay, and are pretty good with noise. Some of the best solar images in the world by amateurs are done with almost laughably inexpensive cameras relative to the other equipment. But that said, none of it matters without excellent seeing conditions.
So, if you want to use you A7RIV, note you have 3.76um pixel pitch OSC pixels that will be less sensitive to Halpha wavelength (656nm). But, to image at the critical sample limit of your pixel size at that wavelength, you need to be operating around a focal-ratio of F14.1 (F14 rounded is good enough). Here's a calculator so you can calculate this yourself. Anything less than that is going to under-sample and literally lose data, low resolution, course image scale, no matter how many pixels are involved. So operating at F6.667 (which is what the SM3 actually is with its etalons, 400mm focal length, 60mm aperture, making F6.667, it's only F5.7 without the etalons using the 70mm aperture of the objective lens) is actually severely undersampling, so losing lots of data and not recording the resolution. So you use a 2x barlow, extender, powermate, etc, to bring your focal-ratio up to F13.3 (2 x 6.667). This is much closer to F14.1 that your 3.76um pixels need to critically sampling 656nm wavelength (Halpha). It's still only slightly under-sampling but it's close enough. And over that, it will over-sample, which gains zero resolution gain and instead just costs you light which requires more increase in ISO/Gain to be more sensitive to the signal and cost you noise and dynamic range. So your goal with your 3.76um pixels of your AR7IV is F14 approximately. F13~15 would be fine really but there's no reason to go higher than F14 at all, as there's no more resolution to gain and you're at the limit of the angular resolution of the aperture size at the airy disc at that point assuming perfect seeing conditions. Your sensor is much larger than the blocking filter. So no matter what, your imaging circle is the size of your blocking filter, so 10mm or 15mm depending on which blocking filter you get. So you will not be using very many of your pixels here at all (put a 10mm or 15mm diameter circle on the center of your 35mm sensor and that's all that is going to be used). To image, you will be using video. The faster the FPS the better. You have to freeze the seeing, so 10ms (1/100th) exposure time is likely as long as you want to go, shorter is better, to freeze seeing conditions. That limits you to 100 FPS possibly, if your system can handle that throughput of your sensor's data rate (knowing a lot of it is black space due to the blocking filter size), measuring several gigabytes in just a few seconds. You have to go shorter exposure to get faster FPS. You need fast FPS because that's how you get lots of frames to stack and align during brief moments of good seeing conditions, via lucky imaging. It looks like the A7RIV can go from 30 FPS to 120 FPS depending on different settings. If it can really do 100+ FPS that would be the one thing finally in its favor for this purpose. You will use as much ISO as needed to fill the histogram (which will be significant). Photographic speed is less important here (as in the focal-ratio number) because what really matters is the transmission of the filters (they will be very low, to be safe for human eyes).
It will work. But there's the information for you to start with.
The ED80 is an old workhorse telescope, nothing special, very inexpensive. It's an 80mm aperture, 600mm focal length ED FPL53 based doublet (F7.5). It has no CA during the day or at night in RGB. I use it for solar as well, because I like to get the most out of it as I have too many scopes and filters as it is (I use this at night for deep space imaging too, no false color at F7.5 with FPL53 glass at this aperture size). I use it because of the 600mm focal length and my 60mm etalon aperture produces F10 focal-ratio, which is critically sampled with my smaller 2.4um and 2.9um pixels of my cameras. There are many telescopes one could use out there for this purpose. But if you want to get the most out of it, it will be to choose one that has the resulting focal-ratio you need (with your etalon aperture size) to critical sample 656nm wavelength on a specific pixel size. So there's a lot of combinations to achieve this, and it's all completely calculable. It's generally much easier to just buy a pre-made dedicated solar scope (and cheaper). But most solar scopes are designed primarily for visual, and imaging is a second feature, so they almost always have less than optimal focal-ratios for the wavelength.
Anyhow, again, just more information so you can make the decisions on what to do best with your money and your expectations.
I highly recommend you take a look visually through a club or local scope to see what you can see with your eyes if you haven't already; and I really suggest a good solar handbook too, to learn the features you can see in different parts of the photosphere and chromosphere so you know what you're seeing and what you might image. It's a great thing, very dynamic, changes in minutes. And there's always something new to see in Halpha, every day!
Personally I'd say to skip the 70mm and try to go for a 90mm instead (even if its a single stack)!
Edited by MalVeauX, 22 May 2020 - 12:07 PM.