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So I have been really contemplating pulling the trigger on a brand new 160ED. I want to use it at a remote hosting site and this will be my first remote setup. I was planning to pair it with the ZWO AM5 on a pier, and either a 2600mm pro or 6200mm pro (have not decided on on that yet), and with an Opetec leo focuser / wanderer astro flat panel. The only thing that kept me from going immediately for it is it felt that the focal length at 530mm would lose some detail and maybe a waste for a remote setup, but the 1.5x extender for it caught my attention. It will turn the telescope to f/5 and extend the focal length to 795mm. That seems more appealing to get access to smaller targets, it also would relax the sensitivity on tilt and other issues. Also since it will be a remote site with B1 skies, f/5 seems plenty fast. Does the extender ACTUALLY have better details (Lower FWHM in arc seconds, better resolution, etc) on a 3.76um camera like the 2600mm or the 6200mm pro, or is it about the same? How well does it perform on a full frame sensor? |
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IMHO: 1) There are three reasons to go remote... a) Clearer weather b) Darker skies c) Better seeing "a" is not relevant to focal length and speed but the other two are. "b" argues for a faster system to get the faint stuff. "c" argues for a longer focal length to get better detail. Unless you want to spend a huge amount of money (think PW Delta Rho), you are not going to get both in pone scope so you have to choose. The ideal system therefore is two scopes, one short and fast and the other longer and slower. Just how long depends on the seeing at the site. Not all dark sites have great seeing so you need a realistic evaluation of that (preferably another user, not the owner). If you are under (about) 2 arcsec seeing you will want something 1.5 meters and up. The 160 with extender will not do that. So I would go with the speed w/o the reducer. In fact, I plan to replace one of my two scopes at a remote site in June with a 130D because the present refractor is too slow (f 5.8). I do have two scopes there, the other being a CDK 14 - so high res is already covered. |
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Bill McLaughlin: Thanks bill. So I am primarily going to a remote hosting site for darker skies, and maybe slightly better weather. But I am confused by your point. Why would being under darker skies encourage you to get a faster system? 1 hour of data from a Bortle 1 is equivalent to 21 hours under Bortl 7 for the same system. Shouldn't that mean that being under darker skies means sacrificing some speed for more focal length is less of an issue?  I was hoping to get even slightly more details while sacrficing some speed. What I am trying to decide is if that is a good tradeoff or not in case of the E160ED. |
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Bill McLaughlin: If you are at 2" seeing and have a 3,76um sensor you are already sampling at 0,52"/px (at 1500mm focal lenght). Even including the effect of square pixels and convolution I still dont see any benefit it it. You will be seeing limited anyways. Personally I usually shoot with 2" seeing and I am already seeing limited at 550mm, let alone 1500mm. |
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Luka Poropat:Bill McLaughlin: I don't have a direct way of measuring my seeing conditions but I did find a significant improvement in FWHM values when I went from 900mm 5 inch refractor to an 11 inch SCT. I don't know how accurate this site is, or if I am misinterpreting what they are saying, but supposadly my seeing condtions from my backyard are well below 2". https://www.meteoblue.com/en/weather/outdoorsports/seeing/victoria_united-states_4739157 |
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Luka Poropat:Bill McLaughlin: The reason is that in my experience in the era of Blur Exterminator, being oversampled (by conventional standards) is a good thing. |
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Bill, did you notice your FWHM values in arc seconds are lower with the extender, compared to the native corrector, or were they the same? Also how well did it perform on your full frame sensor? |
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Ashraf AbuSara: The average FWHM (in ") from your single subs IS your seeing. The MeteoBlue stuff is rubbish. |
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andrea tasselli:Ashraf AbuSara: ... assuming you are not undersampled, and everything from focus, to tracking to optics to collimation is perfect and seeing is your only limitation. What do you think of the extender idea Andrea? Yay or nay? |
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Yay, go for it. Instrumental seeing, as specified by me, is your actual seeing and includes all the various potential snags. |
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I have one of the 160ED extenders, but I rarely use it. But I image mostly from my home in Bortle6/7. If I recall, it did help with corner illumination on the full frame a bit, but not a ton. The 160ed still drops to about 65% in the corners of the full frame. With the extender it was a little less exaggerated. (there's a whole post on full-frame imaging with the 160ed you should check on) In terms of image detail, I couldn't tell the difference in sharpness. If you are really going to use the AM5, I think you'd want to keep your focal length at the F3.3 and instead do shorter exposures. What sort of performance are you expecting to get on the AM5? Why not something equitorial if portability isn't a factor? In the end, I think it's just preference. If you go with the asi2600 at F3.3, you can invest that extra 3k into the mount. Just an idea |
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Nick Grundy: Thanks for the feedback Nick. Seems like the extender won't be that helpful, especially if it won't improve image detail at the cost of speed. I have been reading that post you referred to and it is a great wealth of information. As to the AM5, the Epsilon 160ED will be a piece of cake for it at f/5 or f/3.3. I have used my C11 at f/7 on the AM5 (focal length 2065mm) and it worked just fine with proper settings and setup. Just a couple of examples (and many more on my page) of what I could do with it combined with the C11 here: https://www.astrobin.com/yyqx04/C/ https://www.astrobin.com/5a5d7v/C/ I haven't been using my AM5 lately which is why I wanted to send it. My AM5, 2600mm, set of chroma filters and opetec leo focuser have all been gathering dust and I am trying to utilize them for this new remote setup without getting new stuff apart from an OTA. Unfortunately my Chroma narrowband 36mm filters are 3nm so I may have to get a new set that can work at f/3.3. |
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Ashraf AbuSara: Ahhh! that makes a lot more sense then. I thought you were buying all equipment new. I've actually been considering my epsilon for moving remote and the filters are something I may want to adjust if I do. (they are Baader Highspeed, 3.5/4nm versions) I bought that mono duo camera asi just released. hopeful the guiding will be fine and I can stop with the guidescope on the epsilon. But might have to move to wider bandpass if I do. |
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Ashraf AbuSara: You should try the 3nm filters first. I used 3nm filters for years with my E-210 f/3 and never had issues with them. |
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Bob Lockwood:Ashraf AbuSara: Thanks I will give it a shot. I just wonder realistically how much signal is lost due to band shift at that focal ratio. |
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I use the e160 at f5 and f3.3. My usual HFR at f3.3 is 1.5-1.65. With the extender my typical numbers are 1.6-1.8. Dan |
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Dan Brown: Thanks Dan. I am presuming that HFR is in pixels? If it is in pixels that extender must be getting you slightly more details because the image scale would be about 30% smaller. |
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I can’t speak for the E160 but the extender for the E130 has proven useful. There’s a clear gain in detail vs the stock corrector. Do keep in mind you’re going to have to be even more diligent with collimation though. |
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Dan: Interesting thanks for the feedback. I would have thought the slower focal ratio of the extender would have made collimation/ tilt less critical. Is it because of an improvement in spot sizes? |
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Ashraf AbuSara:Dan: Yes, smaller stars so a more pressing need to ensure they are round. At f3.3 imperfections in center stars aren’t as obvious but at f5 they are. |
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I’m a little bit confused by some of the advice in this discussion. The ɛ160D with 1.5x extender would be on paper is advertised at 792mm f/4.95, which at 3.76μm pixels would sample at 0.98"/pixel. Which isn’t demanding exceptional skies for sampling. Recently I picked up (ah, financial indiscretion) an ɛ180D with the 1.5x extender, and it has been an absolute delight to use in both configurations, and my time so far with the has not left me dissatisfied with the sampling of my results. Say nothing for using a tool like BlurX and latitude afforded with some drizzle upsampling (which, for me so far, has been beneficial even in terms of sampling thanks to the generally moderately stable atmosphere where I image). The performance of the extender is exceptional. At a remote imaging dark site, I would personally be more concerned with having something set up to run at the field of view I was interested in than having it be as fast as possible—at least in this case where both fall in sampling ranges that allow for benefit. Presumably the purpose of setting up at a remote site includes not just the dark skies, but also a cozy quantity of good imaging nights across the year, so plenty of time to work on projects. Especially at this rather fast focal ratio. To my ears, the option of using an extender makes sense. Although either configuration sounds delightful. If I had this set up at a remote site I might run natively for a part of the year and with the extender for the remainder of the year. |
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| Honestly, I think it'd go well either way. Based on my own usage, I would go for the 160 native for a year, then think about adding that extender. (for the 1100 it costs). In terms of image sharpness, I didn't feel like it was any sharper than at native, but that can misleading given the FL change and such |
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James Peirce: That's exactly the kind of information I was trying to contend with and gather from this post. The extender is not exactly cheap at $1100. What I am trying to determine, assuming we are not limited by seeing, is if the extender will indeed result in improved resolution in the smaller targets that maybe imaged with this configuration that it is worth the investment upfront. It's also not just added cost, but also lost speed and FOV. So the question is does it actually resolve better details to be worth those tradeoffs? Having a smaller theoretical image scale does not always translate to a better real life improvement in resolution, especially when we are talking about the same aperture. But it seems to me from your description that you have found the extender, combined with drizzle 2x and deconvolution, to improve the resolution of your images compared to say the native corrector with similar drizzle deconvolution? Any objective measures in your experience comparing the extender vs the native corrector that perhaps can answer that question? Maybe the FWHM results you are getting compared in your subs and final raw stacks? |
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Ashraf AbuSara:Dan Brown: Pixels and arcseconds ;) My last three images uploaded were taken with the 1.5 extender. Dan |
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Dan Brown:Ashraf AbuSara:Dan Brown: Sorry Dan I didn't understand. Your HFR is 1.5-1.65" with the native corrector, and 1.6-1.8" with the extender? Btw great images  |
