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Is there a camera that is correctly matched for sampling to the RC51? I can't find one. Most are under sampled and I find the smallest stars are blocks/squares rather than circles. I've used the tool at astronomy.tools to search for one and the best I can come up with is the ASI183. Even it is not ideally suited for 250mm focal length, although it does get it into the green area a little. Right now I'm stuck with the ASI294MC Pro and the ASI2600MC Pro. Neither even move it off the under sampled bottom. With what I have, the detail is almost non-existent and like I said, the small stars are square. I see many people posting pictures that are under sampled and they are OK. I'm looking for great.
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Why care about tiny stars being square? If you’re zooming in on the stars of a widefield image and criticizing it for square stars, you’re missing the point of widefield imaging.
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Dan H. M.: So under sampling is a myth when it comes to widefield? What about detail? Maybe I am missing the point. |
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DavesView:Dan H. M.: It’s not so much a myth as it is something not to be overly concerned about in certain situations. A redcat has a small aperture, so it won’t be able to capture many details anyway. Reaching 1” sampling won’t solve that. I would rather use its wide FOV to go after large objects and pair it with an APS-C camera. |
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I have paired my RedCat 51 with the ASI183 MC Pro and if my math is correct this combo yields 1.99 arcs/pixel.
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Michael Jarvis: That is correct, but the FOV is not really that great with the 183. I have access to one and it almost defeats the purpose of shooting widefield. Dan H. M.:DavesView:Dan H. M.: In thinking through this I find I was looking for the wrong answer. I expected more than there is. I'm nit picking. Agreed that widefield is somewhat less detailed, and in some of my images the detail is pretty good, but for other shots the detail is almost not there. The Rosette Nebula showed fairly good detail whereas Gamma Cygni showed little to none. I think my head is screwed on right now. Thanks! |
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DavesView:Michael Jarvis: Read noise, FWC, amp glow, and ease of processing are far more concerning than the amount of detail captured. Yes, it’s nice to be able to zoom in and see some detail rather than pure splotch. I’m not saying sampling is irrelevant, just that we have bigger fish to fry 🙂. |
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DavesView:Dan H. M.: The AstronomyTools CCD Suitability calculator is a useful tool, but it assumes you are always going to be limited by seeing rather than diffraction. This assumption only holds up for larger scopes. A 51mm refractor simply isn't designed to push against the limits of seeing. With a 51mm refractor, your Rayleigh Limit is 138/51 = 2.7" (assuming perfect optics). It doesn't make much sense to go finer than this with your sampling. Typical cameras with 3.76um pixels will give you a resolution of 3.1". This seems like a good match. With a RedCat, the main selling point is that it is a compact unit with a large corrected field for widefield imaging. To me, this advantage is wasted if opting for anything smaller than an APS-C sensor. I'd opt for an ASI2600MM and enjoy the wide field of view that results. |
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i’m putting at 6200mm on mine (v3). I will be experimenting with 2x drizzle and resample if i need to.
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Personally, I don't really see the undersampling and I think the ASI2600mc Pro produces great images with the Redcat. Here's one of my favorite images that I took with a similar setup (I have the redcat ii instead of your iii). https://www.astrobin.com/bnz7ae/ |
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DavesView: Whatabout a 294MM in bin1 mode (2.3µm pixels)? That gives you 1.90”/px with a bigger sensor than the 183 (19.1 x 13 mm vs 13.2 x 8.8 mm) (yes I realise this is mono and your original q was for OSC) |
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Hello, also consider that even you will get camera with tiny pixels to match at least 2arcsec/pix resolution you will have to do longer total integration for good S/N ration. Smaller the pixels, more time you need to get rid of noise. Those with smaller pixels are great for planetary imaging since there is enough light you can get in short time for …but for DSO I think something with pixel 3,76 as ASI2600 is plenty enough . I vote for ASI2600mono or OSC…FF sensor as ASI6200 does have will probably also work but it will take some time to deal with good corners (unless you pick up some ,,lemon,, regarding the RedCat…there is always a chance as ussually). Personally I did buy recently FRA 300 to match with my ASI2600MM Pro ..I know I will have to spent some more time to get reasonably S/N ratio as I´m getting with my f3 Newton 200/600 but that is still not a point. As said those are instruments for widefield imaging and you have to think about it so…images may not be so deep in detail, noise free, but you will get very wide FoV which is nice many time and worth to some sacrifice..and that is what it counts here I think. David |
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Hi Dave, personally I use a TS 71/350 scope. I used it for years now with the ASI183MM and it is a really nice combination. The RedCat is even shorter, but I guess you won't find a camera with smaller pixels. Zooming in to see the stars as pixel is way beyond what is useful to my eyes. Even if you have a 4k Monitor, the resolution of the image is much higher that that of your monitor. So when looking at the image on a computer screen, it is already interpolated and I assume, the stars will become only one pixel wide. When printing the image you have to do really large prints to see the "problem" on the tiniest stars. Such large print are usually viewed from a larger distance, which makes the "probem" negligiable again. If you collect much light, there may always be tiny stars somewhere. Oh, i just realized that if you own the 294MC, it has even smaller pixels (2.35 microns) unbinned than the 183 (2.4 microns). So this is even a better fit. If you are willing to live with even larger image resolutions, drizzling seems to be the solution. If I remember correctly, it was developed exact for this purpose. There are of course cameras with smaller pixels. But maybe not cooled ones. Look at the guide cameras for example. But these sensors have their own drawbacks. The sensor sizes becomes smaller, which will limit your FOV. I may say, that the RedCat is not meant to be used that way. If I do broadband imaging on a resolution of 20MPixels (ASI183) or even 45 MPixels (ASI294MM unbinned), the time to stack the images increases dramatically. Try to stack 500 images of 46 MPixels. You will wait a really long time to for the stacking process to finish. So usually I do increase the exposure to at least 3 minutes just to save time during the final processing. You already have really good images in your portfolio. I especially looked at two images. One was the veil nebula and the other one was M51. Both wre taken with the Flourostar 91. If you compare the stars in both of them, the stars in the veil image look super sharp. I assume you sharpened the image, because the stars around M51 are not that sharp at all. Maybe they are a bit overprocessed in the first image. Don't try that on a RedCat51 image  . On the other hand, your picture of IC410, taken with the RedCat 51, looks very natural to my eyes. I don't see any need to decrease the pixel size. That is my honest opinion.This comment will not be helpful to you in any way, I guess. But in my opinion, you already are on the right track…  CS Christian |
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Christian Großmann: I'm pretty certain this is the 294MM only in Bin1 mode. the OSC version stays in Bin2. |
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Dunk:Christian Großmann: Oh, yes it is. Sorry |
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Dunk:Christian Großmann: The 294MM and 294MC actually use entirely different sensors. The 294MM uses an IMX492, which has a native pixel size of 2.315 μm. The 294MC uses an IMX294, which has a native pixel size of 4.63 μm. For whatever reason, the astro camera makers decided to market the IMX492 as a mono version of the IMX294. It's apparent why, given the similarities in specs, but they are actually fundamentally different sensors. And now, to confuse matters further, Sony has released a colour version of the IMX492 sensor. |
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DavesView: I have the RC51 and the ZWO ASI 294MC. I really like the results. If you are using WBPP on Pixinsight activate drizzle. It will help to make the stars less squared. Just make sure that during the aquisition you are dithering. I do it every 5 frames. |
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Pixel size is only one thing, you also need an optics that is capable to provide spot sizes at that level (at short focal lengths the image scale is to your disadvantage). Most lenses/telescopes don't have spot sizes at the 2mu level, in particular not off axis, the simple reason being that this never was a design request (the specs still come from an epoch where 6-10mu pixels were the norm) . Even Takahashi recently had to update the optical design for some of their scopes considering that thanks to CMOS the typical pixel size nowadays is considerably smaller than in the past. |
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Dan had my question answered back at the beginning. I was looking at this wrong. I read about under sampling and decided, ooops… I'm under sampled. Being new at this and while I'm not easily misdirected, that sent me off on a mission to fix something that isn't broken. My solution is to put my ASI2600MC Pro on the RedCat51 and be happy. Lots of good discussion, though. Every little bit helps and I think I have a better understanding of it now.
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LookSpaceThings:DavesView: I also use that same combination and dither 1 pixel every 3 frames. I've tried drizzle and find that the detail suffers a little. Maybe it's me. I'll eventually settle on one or the other, but I'm thinking detail is more important than tiny square stars. |
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Aaron H.:DavesView:Dan H. M.: I did go for the ASI2600 MC Pro and will likely also get the 2600 MM Pro soon. This is a very versatile sensor. |
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DavesView:LookSpaceThings:DavesView: 1 pixel every 3 frames? that’s not enough dithering to do anything.. You should increase the dither to 3-6 pixels and more often. |
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Byron Miller: There are only two other choices in 'more often', every frame or every other frame. I'll give three pixels a shot and see, but I don't think I want to dither every frame, or do I? Seems like a lot of guiding recovery to me, although mine recovers pretty quickly, within a few seconds. Any other's opinions on that subject? |
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The redcat51, rokinon 135 among others are popular picks for widefield imaging. Surprisingly, the options for cameras with an ideal image scale are limited. I've seen amazing images produced regardless though. I would imagine astro camera designers and manufacturers are limited to what Sony and other sensor designers decide to produce. Most if not all dso camera manufacturers are using the same sensors from the same manufacturers. In the astro community there is certainly a market for a full frame sensor with a pixel size in the 2um range.
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