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@Clarkey Could you please do me a quick favour and measure the distance from the back of your RC8 to the back of your astrocamera? I'm trying to work out if I'd need an extension pier to stop the camera-end of the telescope thwacking into my pier... Thanks!

🥴 So am I looking at a reduction in integration time of three or four times..? (Although in reality I'll probably just stick with imaging a target for weeks at a time).

Ok, does this mean that five hours with RC8 and binx3 is equivalent to 20 hours with FRA400 and binx1 (factor of four); or 15 hours (factor of three)? Totally, this was my (mis)understanding until you talked me through it.

Thanks, those are some good images! I wonder, can you use the top Vixen dovetail as a carrying handle? It's hard to tell from the pictures if you could fit your fingers underneath it to get a good grip. Maybe with some risers? The collimation does sound like a pain, but it holds well once done?

OK thanks, makes sense. Four times faster, I think? RC8 binx3 = 84600; FRA400 binx1 = 19510. OK, let me write my understanding of this binning malarkey and let's see if I've got it: If I were to use my 2600MC with no binning (i.e. binx1) with an RC8, I'd get an image with a resolution of 6248 x 4176. However, I wouldn't actually be getting useful data across all those pixels because seeing conditions and mount limitations combine to, in effect, "blur" the view. When processing the data, I could binx3. This would make a square of nine pixels into one super-pixel. The plus points of this are that it would increase my SNR by a factor of around four. What takes me 20 hours with my current set-up would instead take five. Or, I could image for 20 hours and get a SNR equivalent to 80 hours with my current set-up. It would also decrease processing time due to the smaller file sizes. The downside is that the image's resolution would only be 2082 x 1392. This isn't that bad though, because the "lost" resolution wasn't useful data. I wouldn't be able to crop in very much with this lower-resolution image, but the RC8's focal length of 1600mm gets me very close in anyway, so that's not a big issue. If I need a wider FoV I could mosaic. Is that accurate? The lower final resolution still makes me itch a bit because I'm used to dealing with very high res images (both in astrophotography and regular photography) but I understand that with the proposed set-up it's not really a fair comparison. If I need a higher resolution image, e.g. for printing, I guess I could always use Photoshop's Enhance feature, or Topaz GigaPixel AI, to artificially bump up the pixel count. I just did an experiment doing that with some of my existing data, and it looks quite good to my eye. Enough to somewhat allay my fears about low-res images anyway. Thanks vlaiv, I definitely owe you a pint! 🍻

Thanks, I'd be interested to hear more about how you go about collimating it. I read some threads here on SGL and it seems rather tricky. Any and all other thoughts on the telescope would be most welcome too!

Thanks vlaiv, an 8" RC is a definite possibility, and FLO have them in stock. Your options are sufficiently cheaper than what I was considering that I may be able to get an EQ6-R PRO too, which would make something heavier, like a Sky-Watcher 190MN an option too. I've been reading up on binning, and think I'm starting to get my head around it, but am coming stuck with a comment you made earlier in this thread: "RC has 1600mm. Bin your pixels x3 and you have effective focal length of about 500mm (which is increase over your current 400m)." How is it that binning reduces effective focal length? I'm imagining that a binx3 image would have the same field of view as a binx1, but a much lower resolution -- but I'm pretty sure that analysis is wrong!

Thanks vlaiv and raadoo, you're both legends and are being very generous with your time in helping me. I'm going to digest all your comments, and read up more on binning. This is also what ONIKKINEN suggested earlier in this thread. Well it's not that I definitely want something speedier, more that I'm a bit reticent to get something much slower 😁

Thanks vlaiv, that's a really useful example. I'm understanding that perhaps I should bite the bullet and get a new mount to improve guiding and allow more options for an OTA. An EQ6-R PRO should fit my DIY pier and so be a relatively straight-forward upgrade. It's been mentioned before that with my current mount and sky conditions, a FL of 700mm is likely a realistic limit. I wonder, how is this worked out? What would be a realistic FL limit on an EQ6-R PRO? And how much better would this new mount be compared to my Orion Sirius EQ-G? The EQ-G's manual says that its resolution is "0.144 arc sec (or 9,024,000 steps/rev)", while the EQ6-R PRO is "9216000 Counts/Rev., approx. 0.14 arc-second". Sounds basically the same..? Something else I've learned from this thread is about the "speed" of an imaging system. I just want to check I'm getting this right... If I calculate aperture squared multiplied by image scale squared for the FRA400, I get 19,510. For a much bigger telescope -- the Askar 130 PHQ -- the result is 10,177, i.e. 52% of the FRA400's speed. In real terms, would that mean that I'd need twice the integration time from the Askar 130 to get a comparable SNR from the FRA400? It's hard to get my head around, considering the slower telescope has a significantly larger aperture. Thanks again to everyone helping with all these questions!

Blimey, this is intense! So, the PHQ107 would get me sharper views, but not "closer"; and would be about 0.6x the speed of the Askar FRA400 (calculated earlier in this thread) thereby necessitating longer total integration times? That doesn't sound like a great deal for a £2500 'scope, compared to the Askar FRA400's ~£1000 price tag... It does seem weird that increasing the aperture by such a large amount doesn't really yield much in the way of any benefits, and it's actually down to the quality of the optics that there would be an improvement 🤯 And is it the case, flagged earlier, that ~700mm is an effective limit on focal length for any system if I stick with my current mount?

Thanks vlaiv for the thorough answer, as always. I appreciate your efforts to "summarise!" Here's the spot diagram for the PHQ107. Does it help with the comparison with the FRA400? You say that to take advantage of a large aperture telescope, I need a good mount and good skies. Well, I'm stuck with the skies I've got. But I could consider a mount with a higher tracking accuracy and larger weight capacity. (Not sure which one, exactly..!) The FWHM percentage improvements you calculated don't seem that significant, so should I conclude that if I want something that will be a decent step up, I should be getting a new mount *and* a large aperture telescope? Thanks again...

Thanks! Re: speed, earlier in this thread it was said that "You can work out a measure of the “speed” of your current system- it’s aperture squared multiplied by image scale squared." FRA400 = 72^2 * 1.94^2 = 19,510 107PHQ = 107^2 * 1.035^2 = 12,264 Given that method, the 107PHQ is 0.63 (let's say 2/3) the speed of the FRA400. But you're saying that the 107PHQ would be a bit faster. So there's something I'm missing, or not understanding. For clarity, and I think this is what you're saying, the subframes would be slower, but the total integration time would be a bit faster?

Aaaah, the plot thickens. That's odd. I use an ASIAIR Plus for my imaging, and the FL there is correctly stated as 400mm (or 402mm or something, from memory). It uses this info to plate solve correctly. I've no idea where 749mm comes from -- unless it's a sign from above that I should get the 107PHQ, which has a FL of 749mm 😝 I've got a fair few telescope options to choose from. I appreciate the benefits of going for something like a 6" reflector, but fear it would be a bit fiddly and, for me, not as fun to use. The MN152 looks appealing, but hard to get hold of now. As for refractors, I'm still drawn to the 107PHQ (FL 749mm, f/7). I haven't quite got my head around speed and binning and the like. So, with that telescope in mind, would you be so kind as to summarise the differences I'd get between it and my current FRA400 f5.6? I *think* I'd get "closer" views, would see more detail (e.g. separating close stars), but would need longer integration times to reach my desired SNR. Or maybe longer subframe lengths and the same total integration... I'm getting in a muddle and am not sure of anything 🤣🥴 Thanks vlaiv!

Good shout, the 115 looks pretty tasty.

Totally agree, 100%! (Although I'm very grateful to the experts here on SGL who assist with my understanding of the technical aspects!)

This is a brilliant list, thanks! I've spent some time this morning looking through them all. I think the two that appeal to me most are: ES102CF. This has a good specification, and a like how light it is. Would it need a flattener though? It sounds like it can take a ZWO EAF but longer bolts are needed. Askar 107PHQ. This was my original thought for an upgrade and it's hard to shift it out of my head. I hear you about the quality control issues, but FLO bench test all their Askars, which means they should pick up on any lemons. And the ES MN152 is an interesting proposition that may be the best of all worlds. Maybe hard to get hold of though! Have you been following the other posts in this thread? It's interesting to hear about the limits of sky conditions and the like, and vlaiv's comments around how there may not be much gained by having a new telescope rather than just cropping in on the images we're taking already. (Although you and I are using different cameras).

Thanks, this is very helpful. It does sound like around 700mm is my limit; maybe a bit more on very steady nights. The MN190 and TS 130/910 are a bit heavy for my mount, I fear. An Epsilon 130d with 1.5 extender is an interesting proposition, and not something I'd considered. Do you know if it would fit a ZWO EAF? I'm not so keen on diffraction spikes, but could be persuaded if all my other boxes are ticked. Given that I image a single target over many weeks, would I need to consider the OTA's orientation to keep the diffraction spikes in the same positions? (If that question makes sense).

Ok, thanks. So what if I didn't bin (i.e. BINx1) with the PHQ107? Better resolution but slower speed (0.6x my current?)

It is a tempting option. But annoying if they've just been discontinued though! Do you know if they fit a ZWO EAF? And does it come with a camera rotator?

Arc seconds, I think... Attached is a FITS file if you'd be so kind as to check! NGC_3372_Light_600_secs_2022-03-24T21-00-32_001.fits Thanks, I never noticed. Something for me to investigate further!

Here's a FWHM analysis of the subframes that went into my latest image:

That could work, similar to the Askar 107PHQ I'm pondering.

Hi vlaiv, thanks for your input -- invaluable as always! I guess in non-technical terms, I want to take "closer up" images of DSOs, primarily but not exclusively nebulae. With my current wide-field set-up I can get a large nebula in a single field of view, which is good, but I find I'm wanting to zoom into specific areas more. I can crop in, but then the image resolution and quality go down. If that makes sense? Perhaps I've been thinking about it too simply, but my logic was "get a telescope with a longer focal length to get closer in, but also a larger aperture so it doesn't take months to gather enough light to make a decent image." It would also be good to get sufficient signal-to-noise ratio faster than I'm able to currently, but that's secondary. I'm quite patient 😁

This is so so helpful, I can't thank you enough! So, going through those calculations I come up with the speed of three options: Askar FRA400 (as a baseline): 19,510 Askar PHQ107: 12,264 (0.63x the speed of the Askar FRA400) Explore Scientific MN152: 26,008 (1.3x the speed of the Askar FRA400) That's a point in the MN152's favour. I thought that the focal ratio was an important factor in the speed of a system though, have I just had the wrong end of the stick all this time?

Yes ok, that's a good point. The Explore Scientific MN152 does seem like it could be a good option. And no backfocus issues you say..?