markse68

9 minutes ago, saac said:

I doubt very much that it is a "cheat" rather a well documented affect.  Our ability to see colour and shade is very much influence by the surrounding colour and shade.  Take for example the "black" pixels projected onto a screen by a projector - exactly how does a beam of light produce black.  It is the surrounding pixels which make it appear black to our eyes/brain. 

Jim 

 

 

Yes I understand that and indeed if i download the image and put it into gimp using ink dropper tool the shades are identical. But why when i take a photo with my phone of the pc screen and do the same thing in gimp are the shades not the same at all? 🤷‍♂️

On 19/08/2020 at 19:15, saac said:

. In the image above the two squares A, and B are actually the same shade; something is clearly happening in the brain!

I think that is a cheat- this is the one from Wikipedia page and they are different shades!

Or can it be possible that the optical illusion not only fools our brains but my iphone camera too? They are quite different shades in the photo I took of the illusion on my PC screen!

1 hour ago, Sunshine said:

Nice report! and, a great little scope the 150P is. You mentioned Zeta Herc, after trying for weeks, almost nightly, i finally had a clean split on this most challenging target. It took around 260X, i was so stoked to notice the second blob like star, hovering at the 3 O'clock position and, a gap between them.

Good stuff Sunshine- feels great to finally split a tricky one like Zeta Herc that you’ve been trying for ages! Have you tried Tau Cyg? I think it’s supposed to be a similar separation but for some reason I find it more difficult- guess it must be a bit tighter as I needed crazy mag to get a clean split

10 minutes ago, Captain Magenta said:

If the secondary’s edge, from your eye’s place at the focal point, sits on the edge of a cone (centered on the focal axis) emanating from your eye, then and only then should it appear perfectly circular. Assuming it is a “root-two” ellipse and the “bounce” is 45degs.

Subsequently, if the edge of the primary is concentric to that, you’ve “coincided” the primary cone with your “eye-emanating” cone.

That circularity and concentricity are beautifully convenient optical tricks making Newtonian collimation so much easier.

I think I understand the geometry it just seems odd to me to stress getting the outline of the secondary perfectly circular when that seems a very imprecise thing to try to attain? What's important surely is that the secondary is positioned so that its opposite edges are symmetrically spaced within the focuser tube circular outline- that is that the minor axis is central and the major axis too, getting it roughly circular, then the precise alignment happens when you tilt it around the minor axis to see the primary evenly spaced within its outline. Isn't that far more sensitive than trying to eyeball the perfect roundness of the secondary? Getting the secondary roughly circular and therefore roughly to 45deg helps to judge the centrality of the secondary though, barring offsets

11 minutes ago, JeremyS said:

This plot shows how significant the longitudinal drift of GRS is.

Help me understand what i’m looking at there Jeremy- is it the wobbles in the plot or the overall slope? If the latter, what are they using as a datum to measure drift from?

Does Jupiter count as a minor body? 😳

edit- didn’t make a difference to displayed position on my phone either

PS I thought you were talking about our longitude- doh 🤦‍♂️😂

18 minutes ago, JeremyS said:

Thanks Mark. As far as I can see the S&T App is spot on regarding moons and shadows etc, too. It's just the GRS that's a problem. Which makes me think some of these programs don't use its correct longitude.

Interesting observation Jeremy. Here’s a thought- what with it being a huge vortex storm in a really huge ball of gas could it be moving about a bit of its own accord? Like our own weather does? It’s never going to be as predictable as a crater or mountain on a rocky planet? The image/model they’ve used in SS looks like it could be quite out of date as GRS looks smaller now through my scope, and redder/orangier

3 minutes ago, JeremyS said:

So it does, Mark! Turning Light time off makes it appear that the GRS has rotated further across the disc. So I need light time "on", which is how I have used it. But I'm pretty sure it still shows the GRS has rotated further than what reality tells me it has 🤔

It's also curious (and not helpful) that it doesn't change the predicted transit time in the events list 

I’ll have to check again next time we get a clear patch but I’ve always found it pretty accurate esp with moon transits

Mark

2 hours ago, Knighty2112 said:

Nice shots. Well done!  
 

I was out this morning from 1am to 2:30am. Using my Mars filter on my Omni 120 ‘frac I could see the south polar cap very easily, along with some subtle details on the surface when the seeing clicked in with.

Trying to decide if i like my Mars B filter or not. It does increase contrast so subtle dark features are a bit easier to make out and it does make mars look very red! but theres more colour variation without and the detail’s still there without- just needs a bit more time to visually integrate it. Mars was stunning last night at 2am from here in London either way.

6 minutes ago, JeremyS said:

Thanks Mark. However, I find the same predicted GRS time whether "Light Time" is On or Off in Sky Safari

It still happens at the same “time” but the display does change- on mine anyway. First pic is with it on, second with it off for same time

9 minutes ago, Stu said:

@Captain Magenta light time seems to be 36 mins currently. I recall one of the apps, possibly JupiterMoons or was it Stellarium, there was a tick box to say allow for light travel time which then showed it correctly as seen on earth

SS seems to have it too

On 10/08/2020 at 00:19, AstroTim said:

Looks like SkySafari might be on offer at the moment too. £19.99 for the pro version, which is listed at $39.99 full price on their web site (unless it’s one of those permanent price reductions)

Not permanent but fairly frequent I think- that’s how i got mine and as i use it every time i take my scope out, well worth it i think  

I can usually tell Ganymede as it’s obviously bigger but the other 3 seem much of a muchness so far- need to hone my disk sizing skills 

not a big fan of the clicky centre punches as they have a tendency to jump off the mark in my hands so much prefer the simple type like recommended ^ 

On 25/01/2016 at 17:39, vlaiv said:

 

 

love this animation Vlav!

I’m pretty new to this but since becoming obsessed i’d say yes definitely- i live in a bortle 8-9 region so any opportunity for darker skies is welcome and actually a good justification to take a holiday.

Thanks for doing this btw- it looks like quite a lot of effort! If the outcome is an effort to reduce light pollution then i think that benefits everyone really so thank you 

3 hours ago, John said:

There is a slight irony that it takes until the latter part of ones life to be able to afford excellent optics which you might be better able to exploit more with younger eyes and younger energy levels.

You maybe get more patience though to partially compensate? 

17 minutes ago, WJC said:

You have done your homework. I think the tracking mount and holder for the binos are a boon for this method. However, this provides conditional alignment only. If the error is small and the bino is going to be used at, or near, one IPD it may be all that is required. Even so, without knowing the doctrine, the screw tweaking CAN (in some cases) damage the instrument and almost always takes it farther from the 3-axis collimation used in most factories.

 

 

 

Bill

Hi Bill, thanks for your comments. Yes you’re right about it only being conditional on my ipd. I have thought about making some differently spaced targets and “v” block holders but i’m not sure i have the patience to go through the whole process and i’m intending on making them right for me.

I have been thinking about some way to ensure perfect alignment of the mechanics of the bino- the hinge- as if that were possible I think a single alignment ought to be all that was needed?

Interesting remark about the screws- are you referring to prism tilt screws? I haven’t got any binos with that method- mine afaik all have eccentric adjusters but good advice for others contemplating diy collimation. 

25 minutes ago, mikeDnight said:

The Pentax 3.5mm XW is a pretty awesome eyepiece worthy of consideration.

Interesting that in this test chart posted on another thread the 5 and 7 XWs got an (!)  for “centre sharpness”. Not as good as others at the edge but exceptional in the centre where you’re actually looking- or that’s how I interpreted it anyway  None of the HRs or TOEs in there though but i’m sure they’d have an exclamation mark too. Also interesting that the only ortho in there didn’t. That was in longer fl scopes though- not so great in faster scopes

http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p41976

That’s a really beautiful image Alan! 

11 minutes ago, DaveL59 said:

Reading so many reports on how good ortho's are I figured at that price let's take a look.

Enjoy the orthos Dave- love mine  

6 minutes ago, JeremyS said:

Looks great Mark.

Impressive case too! Is that a custom job on the insert that the eyepieces fit into?

Thanks Jeremy- yes it’s a simple design using a couple of cut sheets of hdpe and hex spacers- you can see the construction here 

it makes for pretty hassle-free ep swapping 

family portrait just for @JeremyS

hoping the scurvy and rickets will pass now i can abandon the lentil and 99p lidl pizza diet i’ve been on for the past several months saving to complete the set  Such extravagance! But they are a joy to use and that’s what matters

Mark

ps noticed I need to recharge the desiccant urgently!

Came up with an adjustable support that holds the binos pretty solidly now. Double V’s for the eyepiece end set at my ipd allow binos to be squeezed in to set correct ipd, and adjustable wedges at the objective end allow levelling of the entrance optical axis for different models whilst preventing lateral motion. Works surprisingly well for a few bits of flimsy plastic sheet!

24 minutes ago, JeremyS said:

Did I miss the family portrait pic, Mark?

🙂

PS it's only😂 money 

 

You didn’t Jeremy- I’ll have to take one later