So the extra detail you hoped to see gets lost in increased noise.there is an optimum point for best detail which is what you aim for when doing planetery.In an extensive technical blog, I put the Canon R6 mirrorless camera through its paces for the demands of astrophotography.Įvery major camera manufacturer, with the lone exception of stalwart Pentax, has moved from producing digital lens reflex (DSLR) cameras, to digital single lens mirrorless (DSLM) cameras. The light is spread out over several pixels which means that the signal-to-noise ratio is degraded for each pixel. You can get round it by using smaller pixels.but then the other point comes in. This is the normal situation for prime focus AP where you might be struggling to keep exposures times down of fitting an object to the sensor size. If the camera can't see all the details in the diffraction pattern because the whole pattern fits on a single pixel then there is not much point in worrying about the fine details of the diffraction pattern. A better mirror tidies things up a bit.it's a bit clearer.įrom the AP point of view there is a couple of extra considerations going on: It's an arbitrary definition of resolving power but it's stood the test of time for a century or more. Here you see a double start as two slightly overlapping central discs with figure-of-eight diffraction rings around the outside. To your other point, the standard Airy criterion for "good enough" is 1/4 wavelength in the focal plane. But sadly the micro-brewery at the Brandy Cask pup is gone. Thus leaving you a way out withminimal damage if it turns out not to be a good idea. Then, it might be possible just to drill a few extra holes in the tube 6" up and sit the mirror higher.
If you're going down this road I'd make sure the new mirror actually fits in the cell first, before cutting anything. I've seen 6" f/5 OTAs change hands on ABS for £50.and they come with a 2" focuser. Just my 2p.from a guy who's trashed a few scopes "improving" them. You might be quite happy with it as it is! The focuser will probably need a lot more attention than the mirror quality. Is the secondary large enough to illuminate your sensor without vignetting? This will get worse with a f/5 unless you change both mirrors together. Is it really worth hacking the tube of an otherwise nice scope for the mirror swap? The faster mirror has a wider convergence angle which makes the in-focus depth of focus smaller. The camera has to be exactly square to the focal plane which is harder to achieve. But the collimation is more critical, not just the general scope collimation. The faster speed of an f/5 mirror might well be an inprovement. And you know that if the system is not working properly, it's not the mirror at fault. Total hypocrisy in a way after my previous comments, but just occasionally the difference is worth it visually. But Synta or GSO aren't far behind and on an average night it's hard to tell the difference.
So what are my mirrors?.all 1/10 wave from OO, and the optical quality is indeed excellent on all of them. This sort of high quality mirror does have its place for visual use.once everything else in the optical chain is perfect. A GSO cheapie will do just fine.Ī very good mirror might be relevant for planetery photography by lucky imaging but even here I have my doubts.
Guiding errors, atmospheric distortion, poor mirror mounting, collimation errors, undersampling by the camera, will all add up making the use of a 1/10 wave mirror pretty much pointless. Is it even relevant? I doubt it if your aim is prime focus photography with exposures in terms of long seconds or low minutes. It's very hard to even test convincingly to that accuracy without very expensive test kit.
#BACKYARDEOS CLASSIC VS PREMIUM FULL#
I've got a shed full of "1/10wave" mirrors, some from very respected names, which test out on a Zygo as more like 1/4 wave in reality. If you really want 1/10 wave go to someone with the published means to test it, or a very good personal reputation. It's a complete minefield for the charlatan to exploit. 1/10 wave on the mirror surface or in the focal plane? RMS or peak-to-peak? What wavelength was the measurement made at?.
First, I'd be very, very skeptical of any old mirror that claims to be 1/10 wave.