markse68

Might be seeing condition related but high power on the planets doesn’t really work for me here. I’m finding on my 1625mm fl most pleasing views with a straight 15 or 18mm ep. 10 is ok but 5 (4.8) is an ill-defined mush. 5 on doubles last night seemed to work much better though with the clearer skies, and on moon was still quite pleasing

Me three- though for only 3 hrs 😉 Nice to think of us all out there separately looking up- connected in some way. Seeing is getting better and better- last night was the best session yet- found loads of new things including first look at Uranus! Gave up a bit frustrated not finding Hercules cluster but I couldn’t really make out the constellation so was just swinging the scope around in vain not really knowing what I was looking for. Sometimes it’s tempting after a few nights of clearish skies to think I’ll not bother- just more of the same, but persistence definitely paid off last night for me 😊

Past couple of nights the seeing has been much better hasn’t it- really sharp views of the gas giants despite haze and high altitude blanket. I really enjoyed Saturn too last night 😊 (and Jupiter with GRS)

Looks like it doesn’t it- it’s really an optical flat 😃- to check my secondary. I’m unnaturally happy about this... combination of nice tools and new hobby I guess 😉

this just arrived and it excites me way too much - a tub of Russian shaving cream!😳😉

Probably a consequence of @FLO price increases?

Well it seems improved but still there 😞 Artificial star is a light on a distant crane (a bit windy this evening!) 2F59A0E2-0CDA-43A6-9D2D-B7C737B667B7.MOV

I will try that next for sure but I think it will throw collimation too as the rim of the mirror isn’t perfectly parallel to the bottom surface. I actually taped it to prevent it rotating in case that happens

Hi Paul, no I don’t know that it’s not the primary but I’ll cry if it is. The secondary mount just seems to be the most likely culprit @Peter Drew I was told it was a Hysom primary but have no way of being certain- hope it is though. It’s not the best primary cell design by modern standard but I have freed up the mirror- removing the felt pads that jammed it in around its periphery and the 3 cork pads that supported its base. I replaced them with ptfe tape and the mirror can now slide around fairly freely in all dimensions. This is today’s bodge to hopefully see if it is the secondary mounting causing the issue. I removed the larger pads of UHB tape I’d previously used and instead used 4 small pads of pe foamed tape whose height equals its width. This makes them quite wobbly and should hopefully decouple the mirror from any bending of the support plate and it’s thermal movement. Not trusting the small area of double sided bonding I’ve reinforced it with thin strips of self adhesive aluminium tape doubled up. This should still allow the mirror some movement but hopefully stop it dropping on the primary! Fingers crossed . I think I will invest in a new mirror as this one doesn’t look great under a microscope. It has scratches and small chips in the glass and the backside actually seems better polished than the silvered side, though that might just be the coating. 83C17015-AA04-4B0B-9B76-7841828C07EF.MOV

Oh in case the primary does have a rolled edge (not sure that would cause such astigmatism though?) I made up a mask that shaves 3mm off the outside edge, still leaving 8.5” clear aperture as the mirror is closer to 8.75” actually.

I’ve had an issue with astigmatism with my scope since I got it and tried a few things but haven’t cured it yet. It shows as stars under high magnification blurring out linearly then perpendicular to that when racking focus back and forth. It’s making splitting doubles very hard and I feel the scope is capable of better.I think my collimation is ok and the primary is meant to be a Jim Hysom who apparently didn’t make bad mirrors. My suspicion is it’s caused by the secondary and more specifically the mount. I liked the mount at first- it separates tilt from rotate and height so nice and straight forward to dial in. But it’s design is I think flawed, inevitably imparting a bending moment on the mirror- especially the way the mirror is mounted to it with double sided foam tape. Differential thermal expansion could also be adding to it. I tried to remedy this by sticking it just at 2 places rather than over whole surface but it made no difference- possibly worsened it. The problem is to adjust the angle and lock it in place you must apply some torque to the 2 adjusting screws, pulling the mount and mirror against the fulcrum bar- not good. i like the look of the AstroSystems mounts- I think the way they support the mirror around it’s edge is probably ideal with no forces on the mirror other than gravity. So I may order one but am also toying with making my own mount- can’t be that hard can it? 🤔 Ive ordered a Russian optical flat to check the secondary flatness but it hasn’t arrived yet and I can’t wait... I might look to get a smaller secondary as I think this one’s a bit big (44mm) for an 8.5” f7.5 scope? Certainly the focal plane is quite a long 120mm out from the tube wall which seems a bit unnecessary- a smaller mirror further up the tube might be better. Need to play with the numbers in Newt. in the mean time I’m going to try another mirror mounting bodge with this mount to see if that helps and my theory is right...

There’s definitely something not right I think- have some ideas just need to experiment a bit

It’s amazing how addictive splitting double stars can be isn’t it? Never would have believed it! Thanks for adding another couple to my list of challenges Stu- it’s getting quite long now and without too much success so far. I’m struggling to optimise my scope- still suffering astigmatism which is killing high power star views 😞 But it’s ok- it’s actually a fun if frustrating part of the journey I think- cracking the scope mechanics to improve the view. I think it’s the secondary mount bending the mirror slightly- a flawed design and I’m umming and ahhing about whether to try to improve it or just replace it. Spent a few hours this week when weather permitted on Pi Aqu without success (I think I’m looking at the right star now 😉) and only managed one of the double double 😞 I think my 8.5” f7.5 should be doing better than this but seeing hasn’t been great either. Didn’t manage Antares yet either and unfortunately it’s getting too low too early now so will have to wait

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

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?