markse68

Doesn’t look like that through my scope but absolutely stunning image!

A block of alu arrived this morning so I’ve made a start on the 2” adapter. Decided not to add a field stop as there’s none on the prism assembly and when you position your eye right I don’t think it’ll be needed. Just need to add grub screws to lock it in place as no way was I going to succeed making a female thread for it, and paint the inside flat black. Oh and mount the focuser!

I picked up this military ep on eBay for very little money taking a chance it could be used in my scope. I think it’s from a tank or some other fighting vehicle and would have been part of a binocular pair. It came with very nice quality inverting prism assembly which I won’t use but the ep assembly just unscrewed from that. It’s quite a large chunk of glass with 32mm eye side aperture and 35mm entrance aperture though there’s no field stop as such and I’ll probably add one as it gets a bit distorted right at the edge. It has a nice wide afov as large as a Nagler but it’ll be smaller with field stop.

I have no idea what it’s focal length is though and no way to mount it yet so can’t calculate fl either so I came up with a method to estimate- does this make sense to you? I found 2 other lenses that focus approximately at the joint between body and 1.25” barrel and removed their barrels. These were a 25 and a 40mm plossl. Then I balanced each lens in turn on a ruler and looked through the ep so I could see the field stop and keeping other eye open sketched the ghost image of the width of magnified ruler on a piece of paper below the ruler. Dividing this magnified width by actual width I got magnification factors for the 3 lenses. It looks like the military ep is close to the 25mm plossl so I’m guesstimating it’s also 25mm or there abouts.

Next I rested the lenses on some graph paper illuminated from beneath by an iPad. The military lens has much lower rectilinear distortion than the plossls- better than the phone capture. If I spaced it to get perfect focus in centre of field then the edges started to defocus which isn’t great but if I moved my eye view to the edges they came back into focus. I think it might be quite a nice Widefield eyepiece.

Just need to make an adapter to 2” and get round to fitting a 2” focuser on my scope and will find out 😉

I saw this in the Deutsches Museum last week and it shocked me- I thought the idea of using bearings as anti-astigmatism edge support  (with whiffletrees) was a new discovery but looking at the fascinating cell design of this c1794 metal mirror by Johann Hieronymus Schroeter it seems not! Strange arrangement though with both lateral and vertical wheels kinda cancelling though I guess if they can move laterally on their shafts 🤔 Difficult to take pics but there were three sets of these around periphery of the cell

Thanks for the link- nice end caps and very interesting old thread 👍

Haha I can’t actually remember- think they were 20mm long the posts but probably could have been 15. Now of course the 32mm og eps don’t reach focus 😂 But all my 1.25” eps focus now.

What are these nitrile caps you speak of?

I did it a while back to mine- I used alu spacers so I could  reuse same springs though I swapped the screws for Allen heads to make it easier not to slip and scratch it up collimating

Saw a really beautiful early Tal-2m at the Deutsches Museum Munich last week- no plastic on it anywhere- even the OTA cover cap and finder dew shield were turned aluminium 😍 Most seem to have plastic parts that I’ve seen on eBay 

Thanks Stu- will give it another go this weekend hopefully 👍

As a noob with a bit of an eBay habit my eyepiece collection has grown a bit out of hand 😬 Initially happy with the 25mm/15mm/3x Barlow that came with the Tal-1 I first purchased, a bit of cut foam sufficed but now I have more and I absolutely need to take them all out with me just in case 🤦‍♂️ So I made this insert and am chuffed with it 😉 Will need another case soon for the couple of 2” wide angle eps I also bought though...

What time did GRS transit end? I went out about 10:30 but seeing wasn’t great and I couldn’t see GRS at all 😞 Saturn not much better and I still can’t find Pi Aquilae 

28 minutes ago, Northernlight said:

 

I guess the big attraction of friction drives is that they are supposed to be free of backlash, due to the lack of gears.  That said 10  micron manage perfectly well using conventional  gears / worms.

 

I wondered if that were the case but is the motor direct driving against the ring then with no additional gearing stage? I wondered if there was an advantage to being able to slip  the gearing like a clutch? I guess it’s a bit cheaper than cutting precision worm  gears also which almost inevitably have some run out and tight spots unless they’re supremely accurately made- or backlash to compensate. Does there exist harmonic drive mounts? 

What’s the deal with these new friction drive heads? What advantages do they have over traditional gearing? Are the motors geared before the final drive- would have thought they must be?

Anyone tried one of these? 

https://www.bw-optik.de/astro/astrookular-bertle-1-14/108/astrookular-bertle-1-1/4

I stumbled upon it on eBay and took a punt but not received it yet. I’ve read a couple of threads on other forums but nothing on here. Mixed reviews some very positive some not so mainly for yellow cast but if it’s anything like old Russian camera lenses there’s a simple trick that might help there.

for the price it seemed worth a shot and it will fit well in my growing collection of “interesting” eps

That’s better- liking it much more already 😉

Thank you for taking the time to pass on your experience Jetstream . I will definitely give it more time. I guess part of the problem is the seeing where I am (SE London) I think I really need to get out somewhere better as I’m pretty much stuck with moon and planets at the moment- I can only dream of high magnification like that but then my scope is only 8.5” so not sure it’s be physically possible anyway. But I don’t think conditions here allow really critical comparisons- it’s more about if conditions allow definition on Jupiter or it’s a mushy blur 😉

Apologies to SAW for derailing  this thread 😬

Ah I didn’t realise that was how it was meant to be used in an SCT. They do seem to only have .85 or .95” travel so I need to work out if all my eps will focus 😬

No I’m a complete noob- it is only personal “feeling” not even a proper opinion-  nothing more. Next time I get the chance I’ll spend some more time with it- I’m sure it’ll grow on me.

28 minutes ago, Stu said:

I sometimes Barlow my 12.5mm BGO rather than use the shorter focal lengths.

I would give your 10mm BCO a chance, they have an excellent reputation.

I will Stu. now the 12.5 BGO I’d love to get a hold of 😉

9 minutes ago, jetstream said:

Can I ask why?

Well it’s probably more a feel thing than its optical quality and I will spend more time with it but it just feels a bit cheap, I don’t really like the eyecup and when I have used it before it didn’t stay long in the focuser- unlike this barlowed combo that I couldn’t get enough of 🤷‍♂️

17 hours ago, Stu said:

If it is an ortho with tight eye relief then barlowing a longer focal length would be more comfortable.

Yes- the other barmy  warm  night I was out looking at the moon and think I found a new favourite - a recently acquired vintage Celestron 25mm ortho barlowed 2x gave beautiful contrast and tack sharp right to field stop image with decent eye relief. I don’t have a 12.5mm ortho to compare but I prefer this combo to the BCO 10mm I now kinda regret buying. 

I emailed Ron at Moonlite about their products as I’d like to use one of them on my planned dob build but see more of the SCT version come up second hand so wondered about fitting one of them instead of the newt version and I’ve seen many with the dual rate knob in mint condition for less than the single rate newt version is new 🤔

His response had me a bit confused though. He said that the CS version (SCT) is taller, the CR version (newt) lower profile and with much more travel.

I can understand wanting a low profile to bring focal plane closer to the tube to enable smallest possible secondary size if desired, but why would the newt need longer travel for the same eyepieces? Or is it more that you just can’t have long travel on an SCT? And why make the SCT version taller if it can be shorter like the newt version, though I guess if the bearings are wider apart it’ll handle heavier loads?

Mounting would be an issue but I was thinking of having printed a nylon adapter with the inverted conical part to mate with it giving the advantage it could be easily removed for transport or even rotated should that make for more comfortable focuser knob position.

Any reason not to do this if I can live with constraints?

1 hour ago, Jessun said:

It looked like this for a while too, when I moved to a different flat with no need for the overhang bit, so I chopped it off.

 

Awesome looking bit of kit- must have freaked out a few police helicopters though 😳😂

It does seem strange to me that it can vary so much- I guess they’re quite far apart in the sky. What sort of magnification are you able to use with the f8 Stu? I found around 160x (10mm ep) about the limit before image just degraded too much

Strange thing seems to happen here- some days Jupiter looks lousy but Saturn crisp, others like tonight Jupiter amazing and Saturn lousy- I don’t get it. Best most red grs Ive seen so far and hints of detail in the stripes. And I think I almost split Antares...

10 hours ago, Stu said:

Yep, tracked it most of the way across in the Telementor. Solar panels very clear.

You must have very steady hands Stu! I was too late for Io transit. But I did see the ISS - must have been  the next pass at around 11:30. First time I’ve knowingly seen it and I had no idea it moves so fast! And so very bright! I quickly put a 24mm in the 8” dob and managed to “track” it For a bit  past zenith to horizon but image was shakey obvs but yes I could make out a distinct H shape to it. Amazing!

Stayed up to see the moon and enjoyed a most pleasant summers evening under a nice clear sky.  Might well repeat tonight

On moon I’ve discovered that most of my plossls aren’t sharp all the way to the edge in this scope but orthos are- tack sharp.