markse68

I caught the ISS pass earlier this evening with the telementor. Then my boss walked out and of course wanted a look (it’s currently my work scope and I’m always there late- don’t ask lol) But with the reversed image and him not being used to it of course he struggled to keep it in view. But it’s got a sort of rifle sight on it so I stood behind the scope (lucky I had the diagonal in) and kept it on target so he got a good long look- he seemed quite happy 

Nice project! The base plate looks awful thin n flexible for 3D print?

28 minutes ago, DaveL59 said:

haven't had a chance to test it properly so far other than q quick play when I took the pics, gave myself a touch of food poisoning so pretty out of action this past couple days  I've a feeling it might reduce the FoV  a little on the finder but the image is clear and sharp. 

Sorry to hear that Dave- hope you’re on the mend

17 hours ago, DaveL59 said:

this arrived this evening, the bay via hermes, quite surprised they were out delivering on a bank holiday. A pentax angle finder 1:1 in original box and case.

Figuring to adapt it for the polarscope on the EQ5 and to make the TAL finder into a right-angle one too without having to hack the finder and fit a diagonal. With that in mind a quick check with an eyecup off a scrap DCF type bino:

 

and it fits, not ideal but will do for testing

Need to figure something else for the polarscope and more secure for the finder, but nice and clear view through the combo so a nice cheap mod  

Do you lose any fov using it like that Dave? I did purchase an old slr amgke Dundee for just this purpose but abandoned idea as it had a much smaller afov but maybe the one you got is better

40 minutes ago, Chriske said:

My point is : I like to try different methods. It's easy indeed to copy what your 'neighbour' did or what you found on the net, but I myself like to explore other possibilities that works as well(at least) as the classic methods.

Chris

 

I love your attitude Chris I really do- it’s totally in the spirit of John Dobson too 👍 I’m too far into this now-I  just want a “traditional” design that’s better than what I have inherited and using now and to get it as close to right as possible first time

1 hour ago, andrew s said:

I don't  think it would impact the diffraction directly. However the vains and mirror support will add to the seeing within the tube. Only the upper and lower parts of the vains "see" the sky (lower via the main mirror) the rest face the walls. As the heat loss depends on the temperature gradient as well as the surface emissivity the main heat loss and source of seeing is, I suspect, the main mirror.

Regards Andrew 

PS  if you provide a link I will look at what they say.

There's some discussion in several threads but here's one which links to a 1949 piece by Andre Couder

https://www.cloudynights.com/topic/545953-are-curved-spider-vanes-better-and-if-so-why-are-they-not-standard-equipment/page-3

https://translate.google.co.uk/translate?sl=fr&tl=en&u=http%3A%2F%2Fwww.astrosurf.com%2Faltaz%2Feffetthermique_e.htm

On 25/05/2020 at 09:02, Chriske said:

I opened the link and closed it immediately, sorry..
There's nothing to calculate at all.

.....The movement of alt-bearing should 'feel' the same as my az-bearing.

 

But I don't have your years of experience though

Are you saying the calculator will not give accurate results? If it does then surely it's a pretty useful tool for someone with less experience who doesn't want to build multiple dob bases trying to get the right feel?

I like your method for reducing the AZ bearing friction but in my case (8" dob) the problem I think I'm going to have using that calculator is having too little friction! I could use nylon instead of PTFE but then the friction goes up too much. Based on the results of the calculator I'm thinking I might have to increase the ALT bearing support angle to try to increase the ALT friction to match the AZ friction but then I'm going to use Tufnol for my ALT bearing rings and the COF is a bit of an unknown... AND they're both coming out a bit low and I don't want to increase my AZ bearing diameter too much more

Mark

ps Mel sent me a link to improved calculator  it has choice of units 👍

my calculated values seem rather low 😬

Edit it I forgot the link 🤦‍♂️

http://bbastrodesigns.com/NewtDesigner.html#movementFriction

8 hours ago, andrew s said:

Yes it would. It is the fact the vanes block the light that cause the diffraction  pattern. 

Regards Andrew 

There's a thread over on CN that advocates leaving spider vanes polished metal- the theory being that black body radiation can actually lead the blades to cool to below ambient temp causing a thermal gradient and increasing diffraction! Does that sound likely to you Andrew?

1 hour ago, faulksy said:

when you read my build, didnt you see it 😝

4 years ago and coating is still fine and its used a lot, did use the hammerite special surface primer as well. seriously its ace. well tidy

 

I have to confess to only flitting through your build thread- it’s quite long 😉 I’ll sit down and go through it more thoroughly I promise 😂 What I saw looked really great though 👍

I never would have believed that paint would stand up to that much use but I guess it goes to show how low friction ptfe really is! (And how tough hammerite  is!)

20 minutes ago, faulksy said:

i didnt use formica for any of my bearig surfaces on my dob build. i used hammerite paint on my ground board and alt bearings. makes the motion lovely and smooth and consistant 😀

Interesting- has it lasted? Wouldn’t have thought it’d be as durable as Formica but I guess when it’s fully cured it’s pretty tough stuff

51 minutes ago, rl said:

The three front eyepieces are Ramsdens bought from Fullerscopes in 1974. I had just built my first "proper" telescope at the tender age of 16; an 8" f/8 long focus Newtonian  funded by a 50 pound legacy from an old aunt. 

The eyepieces were a subsequent birthday present. They are RAS thread, 1", 1/2" and 1/4 ", all without coatings (dust doesn't count!). Not so long ago I compared then to my ethos collection on Jupiter and I was amazed that they gave up very little in the amount of detail seen. The presentation in the ethoses was of course a zillion light years better with the vast field and sharp field stop, and lack of reflections, but in terms of what you could actually draw on paper there wasn't that much in it.  I think they were 4 pounds each which I thought was expensive at the time!

The 4.8mm Nagler has already featured in this thread. Mine was purchased for the 1988 Mars opposition, for use with a 5" f/10 refractor. At the time it was a big disappointment because Mars was low and the eyepiece was a bit too much power for the conditions. It languished rather unloved for some years until I got into medium/ large fast reflectors, for which it proved to be a match made in heaven as a high power planetary eyepiece. In a 12" f/4 or an 8" f4/5 the views are actually very good conditions permitting. I still use it very regularly in spite of the fact I have a 4.7 ethos. It's small enough and light enough to use with any scope. 

Good to see another 4.8mm Nagler in this thread   I found it does have a couple of niggles- I guess the reason it’s not very popular now is the short eye relief but I find it no worse than my 6mm ortho and I’m ok with it though it takes getting used to the eye lash squishing. I used mine trying to split Sirius earlier in the year and when I finally got the conditions I could indeed see the pup with it but prior to that it exhibited a slight ghost image of the very bright Sirius which had me fooled at first till I realised it was moving the opposite direction to the star  ;). It’s been wonderful on the moon on nights of good seeing in my 8” f8 lately

Lovely moon pics- it was quite beautiful wasn’t it! I watched it setting beautifully framed by some construction cranes and stupidly ran off to get my phone and holder- it had disappeared by the time I got back 🤦‍♂️

21 hours ago, mikeDnight said:

I made a complete turn around a few years ago, and although I've had many years using expensive wide field eyepieces, I have none in my collection today. An experience with a 26mm pseudo Masuyama around five or six years ago was like a breath of fresh air. Today I only use pseudo Masuyama's of various brands, along with four Vixen high resolution, high power eyepieces. 

Hi Mike, how would you describe the view through a PM ep? As I understand it it’s like a plossl design with an extra correcting element thrown in. Plossl tend to get a bit soft at the edges and suffer pincushion distortion- is the PM simply a better corrected Plossl? Are the so called Super Plossl a similar design?

Mark

edit- did I look through one last night? 🤔 Is the parks 10mm here a PM design? That would be quite funny! It was perfectly sharp to the field stop and showed as much detail on Jupiter as the BCO maybe a little warmer  by comparison though. Then again the BCO has always struck me as being very cold- which is reality I don’t know...

Well that wasn’t very conclusive 😂 The little Lomo didn’t disgrace itself against the BCO or the others and the small field framed the planets nicely but a wider field makes life easier with the dob so this one will stay with the telementor I think. Jupiter had a very interesting moon pattern last night- 3 moons clinging tightly to its limbs and the fourth a long way off looking on

That’s very clever! So the inner pads take the load and generate the most friction force but have the longer lever to overcome it as they’re on the smaller diameter but then why is it recommended to use large diameter bearings for the alt axis?

i found this calculator for estimating the forces for given dimensions. I guess you have to enter them in inches and pounds as it’s American. I entered my new design values and they both by chance came out at 1.4kg friction force- within the authors ideal range. Handy tool for playing with dimensions and seeing how they’ll  affect real world results

https://www.bbastrodesigns.com/DobFriction.html

3 hours ago, Stu said:

Lovely wasn’t it Mark! Caught Venus, Mercury and the Moon in the Genesis and the Vixen side by side, widefield and higher power. Very nice.

Yes it was indeed Stu- quite different from last couple of evenings! Warm, little cloud and no wind- near perfect conditions for the great view

Yes they are John! The more modern Zeiss on the left isn’t an ortho though- in fact it doesn’t look to have much glass at all yet has a pretty wide field sharp almost to the field stop. It maybe a plossl 🤷‍♂️

I picked up this Lomo microscope ortho on eBay- incredibly cheap I think I paid £15 for a pair of them! And it’s a bit special! Well different at least  it’s a 12.5x which (250 /x) makes it a 20mm. It has a really small field stop- must be no more than 30 deg. It’s like looking through a McDonald’s straw but it’s oh so sharp and contrasty and completely free of any colour fringing or any detectable distortion or aberration! Earlier this evening it held its own against all the other eps giving lovely views of the moon and Venus in the Telementor. I don’t know if it’s actually sharper or if it’s an illusion brought on by the narrow fov but I keep going back to it. Daft huh! 

The plan is tonight to try it on Jupiter and Saturn with the 8” dob. I’ll compare it barlowed against some 10mm eps including the BCO, and unbarlowed against an 18mm ortho. What fun! 

Venus is amazingly crisp now it’s almost extinguished isn’t it! I barlowed the 6mm ortho that came with my telementor for a whopping 280x and apart from the crazy floaters there she was crisp and clear and shimmering in the atmospherics! No hint of CA or anything. Mercury was less distinct but it’s so tiny, but I could tell it had a phase- maybe 50%? The moon grew more and more beautiful as the detail rose out of the increasing contrast and looked amazing as it set behind criss-crossed cranes over in docklands. A lovely start to the evenings fun  This telementor really makes me smile- just dial in the coords from ss and swing it round and there Venus was- completely invisible to the eye at 8:30ish 

Oiii is astronomik, uhc Baader I think. The oiii is a ccd one but I don’t think that matters 🤷‍♂️

Well I’ve got uhc and oiii now this year with 8” dob- only tried the oiii the other night but couldn’t see anything- will try the uhc. Area is pretty bad- don’t suppose there’s many worse- SE London, though the skies have been a lot better lately due to covid 

Oops 😬

Augmented reality glasses (eg Epson) with a startracking sensor that can be linked to sky safari or similar to identify and give info on what you’re actually looking at. Maybe built into binoculars or a wa scope ep

On 23/05/2020 at 10:39, Dave1 said:

Well some more eyepieces arrived today, to add to my collection of 0.965" eyepieces. 

From left to right. Takahashi Ortho MC 7mm, Pentax Ortho 6mm, Takahashi Ortho MC 5mm.

Have to say they all look impressive build quality. And I can't wait to test them on Jupiter along side my CZJ O-10 which I haven't used yet.

David

Lovely collection right there! Where did you find them?

9 minutes ago, Stu said:

That’s how it came Mark, seems quite a good setup.

Nice! Now you’ve got it out I found on my one which is quite similar that adding half nuts gently tightened against the ends of the vanes dramatically stiffened the whole structure- not sure if it makes much difference in use and of course an additional obstruction/source of diffraction 🤔 but at edge and I’ve not noticed detrimental effect