badhex

Hello all, We've covering errors and uncertainties as part of the Astronomy course I'm doing. I'm comfortable calculating total error on, for example, colour index, where it's simply subtracting one value from another, meaning I would use the formula: But I'm completely lost with how to calculate error when distance modulus is involved. We have been told that the uncertainty on log10(d) is given by: So, I think, I need to plug in my distance (d) and (delta d), multiply that by 0.4343. Then I multiply that again by 5 because distance modulus is 5logd-5 Then I take that value and plug it into the first formula, for example as (delta x), where (delta y) would be the uncertainty on my apparent magnitude? So with an example: (delta y) = 0.165 d = 3930 (delta d) = 50 0.4343 * (50 / 3930) = 0.005525445293 0.005525445293 * 5 = 0.02762722646 SQRT((0.02762722646)^2)+(0.165^2)) To make matters worse, excel is giving me two different outcomes depending on whether I run the whole calculation as one or broken up! When I run it all as one calculation (I've checked the brackets, they are all in the right place) I get 0.1672969326 which seems to be likely to be the correct answer as the error on distance is very small, so should not modify the error on magnitude so much. When I break it up, I get 0.02817435337 which I'm sure cannot be correct, it's smaller than the original magnitude error. Am I as dense as a neutron star? Help!

You could use the losmandy but it will add quite a lot of weight as you said. If you have DIY skills all you actually need is a flat bar or plate which you can bolt to the holes at the top of the rings. It would need two holes for that, and a further two holes (ideally tapped) so you can bolt the small saddle you have onto that, then put your Skymax in that saddle. Depending on the measurements between the two holes on top of the rings, you could also use something like this photography cheese plate: Lightweight, fairly inexpensive (about £22) and plenty of holes to choose from.

That could also work if your tube rings will fit the 90. I guess the main downside to having the weight on the top vs the side is that your COG will be above the the alt axis centre, so it might make things a bit unstable and you'd have to be very careful with the AZ5 alt clutch (I think it has one?). You also might find eye placement when using the 90 a challenge depending on how you set up the diagonals etc. Obviously you have a similar issue with the COG out to the side but at least if the clutch is looser than expected it won't flop over.

Hi Lee, It might be pushing the limits of the AZ5 a bit but it's worth having a punt. Best configuration I can think of would be similar to your second picture. You can buy a short dovetail and bolt it to the top of the ST80 rings, and you'll need to remove the camera mount bolt with the black disc to do so. Then you can clamp your Skymax 90 on to the new dovetail using the saddle that you have in the third picture. This is a very rough drawing as viewed from the top: Ideally you'd want the heavier Skymax 90 on the inside, to bring the COG in, i.e. directly attached to the saddle, but without buying rings for it you have no way of attaching the ST80 in that case. Worth giving it a try with the kit you already have anyway!

With the barlow, I can recommend the GSO 2.5x Barlow which is very good quality and very reasonably priced. I also made this recommendation on another thread recently because I know it works well with the 10mm BCO. You'll effectively end up with a 4mm BCO with more eye relief than the 6mm, although admittedly 4mm might be pushing it a bit for average UK conditions. I can't seem to find it in stock anywhere, but I think TS-Optics have a rebadged version, otherwise have a dig about on the Internet for "GSO 2.5x Barlow", sometimes listed as ED or semi-apo. You could call a few suppliers to see if they can get hold of it, I got the below picture from 365astronomy.com who have it listed but not in stock.

BTW I should add that the 5mm BST is a great EP, and arguably more comfortable to use than the BCO (more ER) - but for planetary work the BCO is better.

Another vote here for the 10mm BCO, it's an excellent EP and barlows very well. I wrote a bit about the 10mm BCO and Barlow combo (in a 102mm ED doublet) last year, the first time I managed to spot Rhea, if you're interested:

Thanks Stephan. I'm not really a big fan of traditional binos for stargazing, so it will be very interesting to see how these pan out. The cost of the Vixens when bought in Europe has put me off in the past, considering they might be more of a novelty, so I never felt I had the right justification. The Docter 8x21 looks very interesting as well!

Thanks @Louis D it's good to hear that I'm not on my own! I also like the 5mm and would still use it had I not replaced it with a 4.5mm Morpheus. I also tend to find I don't need more than that on most nights.

Two additional points on this btw: One reason I mentioned the 5mm BST often being "the comfortable limit" is not because I think the scope can't handle higher magnification (it definitely can) but more because sky conditions are often the limiting factor. Second reason is that I've never got on with the BST 3.2mm in my two main use scopes (ZS73 F5.9 and TS102 F7) for some reason, but that's possibly just personal preference.

The Powermates are indeed excellent, but they are actually a slightly different design to a standard barlow, and would be less help here because they generally maintain the same eye relief of whatever EP you are using. A barlow will push the exit pupil further out towards your eye, meaning more eye relief which is helpful in this situation. TeleVue do a Barlow which is quite a bit less than the Powermates, but a more wallet friendly option would be the GSO 2.5x Barlow which is very good quality and very reasonably priced. I have used this very same barlow in combination with my BCO 10mm and ZS73 to good effect, and is definitely more comfortable than using the BCO 10mm + Powermate 2.5x + ZS73 The only problem is I can't see to find it in stock anywhere for you. I think TS-Optics have a rebadged version, otherwise have a dig about on the Internet for "GSO 2.5x Barlow", sometimes listed as ED or semi-apo. You could call a few suppliers to see if they can get hold of it, I got the below picture from 365astronomy.com who have it listed but not in stock.

I've heard about the DIY option in passing from the Actual Astronomy podcast but I think I might have missed the episode where they discussed how to actually make them! How do they perform?

From all the comments it seems more and more like I'm going to really enjoy them. I've been really enjoying widefield views of late so getting 25° in a Bortle 3 should hopefully be spectacular!

Interesting! Well, I will be in London area for a while after my trip and finally reunited with my all my other astro gear (so the stuff I had already in storage in London plus the stuff I built up in Berlin) so I imagine I'll be quite busy with all that lot, but the eventual plan is to move somewhere commutable but with darker skies, possibly Kent. Perhaps I can take them and an SQM with me when we go on field trips to figure out our final landing place!

Thanks Alan, have been a few times previously but never for so long. With the SGs I am lead to believe from the reviews I've read that the best results require you to get the eye lens quite close to the eye, so I'm not sure if glasses might mean you lost some of the field of view perhaps?

Great, this is exactly the thinking! The ultimate widefield travel kit perhaps!

Don't worry Jeremy! Plenty of photos to come. If anything I fear that your phone screen may wear out from all the licking 😂 Glad to hear you like the SGs. I figured they would not be something I'd get chance to use under normal conditions but I've liked the idea of them for a while and never really felt like I had a justifiable excuse - I think this counts! Everything I've read says a similar thing to you - not a conventional observing experience per se, more like super vision 🦸

Hello all, I have recently shipped all my astro stuff into storage for my upcoming move back to the UK, and have hit upon a quandary. We're visiting Japan for two months before we go back and mostly staying in large cities, so I reluctantly decided not to take any astro gear with me. For three weeks of that I'll only have a tiny backpack, so even binos were not really an option and I'm not really a fan for stargazing anyway, plus at the time we did not really know our itinerary. Now we have narrowed it down, and it turns out that we'll be doing a week of hiking and staying in several traditional Ryokan along the way, following one of the old Edo samurai postal routes. One of the Ryokan does a free stargazing/ observing evening at the top of a mountain, they provide the scope, and it's a Bortle 3! This has lead me to the idea of picking up a pair of the Vixen constellation binos to take advantage of the dark skies. As they are so small, I will be able to fit them into my backpack easily enough, plus they have Japanese made optics and are significantly cheaper there, so I'll likely pick them up in Japan. I'd love to hear any feedback or pointers from owners, and of course any reason why I *shouldn't* get them!

I an disinclined to believe you - you've been saying both of these for years 😂😂

From personal experience with a ZS73 F5.9, I found the 5mm BST to be around the comfortable limit a lot of the time. I never enjoyed using the 3.2mm with it. Although it doesn't really count as planetary for those looking for a 'pure' /limited glass experience, the Morpheus 4.5mm also works well with that scope. If you do want to go with minimal glass, BCO 6mm, or 10mm with a high quality barlow also works well as @jetstream says. In fact, the 10mm BCO plus barlow gives you additional ER which is helpful, as it can be very tight with orthos on a scope like that.

Good shout. I have a ZS73 and I will most likely get a 30mm UFF eventually for similar reasons, since the 24mm is so good.

Basically, what @Louis D said. I also have both the 35mm TS-Optics and 40mm Lacerta. The 40mm is better, so get that if you can. It also affords you approximately the largest FOV possible in a 2" barrel, and will give you a bit more of a difference to your 24mm. Only downside is that the larger exit pupil of the 40mm could be a bit of an issue in very fast scopes.

Am I right in thinking the other LVWs are 8 elements/5 groups?

Thanks Frank, glad to hear you've had good experiences with it, nice to hear some more in depth reports. It is a weird looking thing as you say! I'm not really in the market at the moment - I have a 24mm, 35mm 40mm and 41mm already 😂 but at the low price I was toying with the idea!

I'll almost certainly buy the 30mm UFF eventually because the 24mm is very nice - not that I'm particularly in the market for a 30mm EP and I'm also without scopes for the next few months! When I saw that these Vixens are currently on offer for half-ish the cost of the UFF I thought maybe I'd get one posted to family ahead of my return but I'll probably give it a miss for now.