Piero

Indoor, I enjoy using Interstellarium and Bright Star Atlas 2000.0 . Outdoor, I generally use SkySafari Pro or Stellarium apps on a tablet. The only "paper" tool I use in the field are the Herschel 400 guides by Alvin Huey (see: http://www.faintfuzzies.com/DownloadableObservingGuides2.html, but a printed copy can be purchased and delivered at home) . When using these guides, I focus on one single constellation for the whole session. 

On 14/12/2020 at 09:06, CraigT82 said:

Have you got any pics with your Teeter shroud fitted?  I have just made my own from a big sheet of thick black lycra and it looks awful.

Sure and sorry for the delay

Heather Teeter's light shrouds are excellent in my opinion. Mine improved the telescope a lot!

On 14/12/2020 at 15:57, jetstream said:

Hi Mike, if astig is very bad it will look like ovals or oblongs that flip on either side of focus at lowish mag. Minor astig is harder to detect but does the same thing, seen at high mag. My 24" when its cranky will exhibit minor astig detectable at high mag. The big secondary caused astig before I repacked the holder for more even cushion and freedom.

Sling position can cause issues and I imagine a Whiffletree can too if the support roller distances are off or there is restraint in the cell system somewhere.

The main reason for detecting astigmatism at high magnification (e.g. <=1mm exit pupil) is because any potential astigmatism present in the eye is minimised or even absent. An observer's astigmatism must be really severe to show effects at high power. In general, most of the eye imperfections are off axis of the pupil. Reducing the exit pupil, reduces the use of that part of the pupil. On the other hand, any astigmatism in the telescope is still present, whether at high or low magnification. 

Of course, one could also discriminate eye astigmatism against telescope astigmatism at low magnification by rotating his/her head. Said this, it is difficult to quantify in this way because both astigmatism will still be overlapped somehow, meaning that the observer can see 4 spikes instead of two in / out focus.

Incorrect sling position can cause astigmatism. Mine did in the beginning when it was not at the COG.

Astigmatism is quite easy to detect and even to fix somehow, unless it is present in the optics. The reasons behind spherical abserration are trickier to analyse to me, instead. That is more noticeable at medium / high magnification, but there are some many factors which can play a role or mimic it (e.g. cooling/warming (dynamic), mirror support (static and / or dynamic), air turbulence (dynamic), surface roughness (, static, !=spherical aberration but the effect on the view is not so different), unbalanced temperature around the mirror (dynamic, causes astigmatism + spherical aberration), etc. 

In my opinion, a lot of people stating that only mags up to 200x can be used in the UK with their newtonian telescope, actually have issues with spherical aberration (and potentially astigmatism too)..

1 hour ago, faulksy said:

i made my own wiffle tree support mirror cell. look in my build thread

Yes, I remember your thread. It is among my browser bookmarks! 🙂

6 hours ago, jetstream said:

Totally agree and I find adjusting the truss shroud up a bit can improve things sometimes. Sometimes closed works, open a bit works... maybe interaction of scope to changing ground thermals? and or puffs of wind?

Getting truly high power views is a process IMHO.

Yup! Agreed 👍

On 07/12/2020 at 09:05, CraigT82 said:

I'm considering installing a glatter sling in my 12" f/6 dob.  Looking ta the actual Howie Glatter product it comes with two posts and sliders that the ends of the cable attached to, which I believe is to allow the cable to move with the mirror during collimation, so that the cable always stays perfectly parallel with the flat plane of the mirror as it tilts.

On my dob the posts for attaching the cable ends to could be attached to the base board of the cell, and the whole lot would move during collimation, hence negating the need for the sliders on the posts? Am I right in thinking that?

Yes, you can do that. You could install a metal bar on the that mirror wood panel to provide a support for the two shafts where the sling cable can be installed. On a 12" mirror, a 1/16" cable is fine. 

The difficulty is that you need to make sure that the height of the sling cable is at the COG of the mirror. 

The bearings in the Howie Glatter's design are there for this reason and because they are installed on the mirror cell of a Kriege's design, which is different from the David's design. 

Here is a tool for calculating the mirror COG: https://www.cruxis.com/scope/mirroredgecalculator.htm .

On 07/12/2020 at 09:40, markse68 said:

Hi Craig, I’d have thought it’d be better to put the posts on the main mirror box so it takes all the weight of the mirror. If you do it like you’re thinking all the weight of the mirror would cause a lateral force and bending moment on those collimation studs which could cause lateral movement of the mirror as the scope moves in alt axis.

Mark

That's a reason why I don't particularly like the collimation of the mirror panel, instead of the mirror itself. 

In any case the problem you mention is not caused by the sling. As it is right now, the problem is present. Said this, if the bolts are large enough and remain firm when threaded, it is fine. My dobson (another Lukehurst) is very similar and retains collimation well (tested this with Glatter's laser at 2x and Catseyes tools).

BTW, I now use this dobson with a TV paracorr2. Despite the fact that a few people suggest the requirement of a coma corrector on sub F4.5 Newtonians only, I can say that I do notice an improvement in the views of this F6 telescope.

Even more.. if one wants refractor-like views with a Newtonian telescope (AND I DO!), a coma corrector is needed, IMHO..!

On 23/04/2020 at 14:16, jetstream said:

You might find a bit more opening on the bottom to be a benefit...

Not necessarily. I've tested this quite a lot and I am more and more convinced that what really matters is the symmetry (or almost) of the air flow around the mirror. 

• In you astrosystems dobsons, there is a low opening on the bottom front and two circular openings at the bottom back. To me, the purpose of those two holes is to balance the air flow of the opening at the bottom front of the mirror box...
• In Kriege open design, the symmetry is present by definition
• John Dobson's design was fully closed, preserving the symmetry of the air flow.
• In David's design, this symmetry is not present instead. The flow is at the bottom front, but not balanced at the bottom back, causing unbalanced cooling. The problem is that David used that opening as a way for sliding the mirror cell in / out, whereas the real purpose of that opening (Kriege's design) is to decrease the height of the rocker box of 1-2 inches.... anyway.

It isn't just the air coming from the bottom... It is also the air coming into the tube from the UTA. If the design of the bottom of the mirror box allows a symmetric / balanced airflow, the mirror will be balanced in terms of temperature. In David's design the air flow can 1) go from the top UTA to the opening at the bottom front of the mirror box (therefore exiting) OR 2) hit the mirror and the wood behind the mirror, rotate and come up... 

In line with the points above, I found a significant improvement when the opening at the bottom of the mirror box is closed, basically replicating John Dobson's design. This guarantees a symmetry of the airflow. By significant improvement I mean that there is less turbulence in the tube, the mirror temperature is more stable and balanced across the body, and the views are better, noticeably better as I can reach 300-400x quite frequently without having bloated stars.

19 hours ago, CraigT82 said:

For anyone interested found some really good info on Howie Glatter slings in Piero's thread about his Lukehurst dob...

 

Just to clarify, David Lukehurst installed a sling cable which is not the Glatter's design. 

David's sling works ONLY IF it is installed on the same plane of the mirror and if the cable is mounted parallel to the COG of the mirror. If these conditions are not satisfied, astigmatism will be visible. 

In the telescope in that thread, the first condition was present, whereas the second was not (the cable was placed at half mirror height..). I reached the second condition by changing the back mirror supports, effectively raising the mirror height as much as necessary. The other issue that I found is that David installed 3 strong edge supports (unnecessary really as the sling is meant to be the mirror edge support). These additional edge supports tightened the mirror, causing astigmatism and spherical overcorrection as they also affected the way the mirror was supported by the triangles... The description and solution is in that thread. Thankfully it works well now.

I use 300-500x quite regularly after optimising my dobson and 150-370x with my refractor, so I cannot agree with the statements above.

To me most of the time, the "atmosphere" 1 inch on and above the mirror related to improper cooling, uneven mirror temperature in general, poor mechanics (e.g. mirror back and lateral support, the way the secondary mirror is mounted, the way the focuser drawtube moves, etc), often so and so optics, and poor collimation are at the basis of limited magnifications in larger telescopes, rather than the actual atmosphere.

To the OP. That's a great project. One warning though as you mentioned finances. Even if you make the whole thing, including the mirrors, the overall cost will still be noticeable.

I also have a TV-60 and think that it is a great little scope. 

I second the suggestion for: Panoptic 24mm, the Nagler 9mm and the 3-6mm Nagler zoom, which is what Al Nagler recommends on his website. The Vixen HRs are terrific eyepieces (have 3 of them) and to my eye they outperformed the Vixen SLVs and Delos eyepieces when barlowed with the superb Baader VIP barlow (which I consistently found to sharpen the views a bit). With a 6 and 5mm, the TV-60 does not deliver enough magnification power for planetary observations, therefore to me you will end up using the zoom at 4 and 3mm most of the time. As an alternative to the zoom, you could get the vixen HR 3.4mm and 2.4mm, delivering ~100x and 150x, both handy mags with the TV-60 for planetary, lunar and double star observing. 

One notice though, the Vixen HR have been discontinued. Apparently, here you can still find a 2.4mm: https://okularum.eu/Vixen/Vixen_HR_eyepiece_2-4mm . For the 3.4mm, you might have to research a bit, but I believe there is still some online shop in the UK / EU selling them.

Why didn't you attach the wheelbarrow handles to the rocker box directly, instead of using an intermediate structure? 

On 01/08/2020 at 14:02, mdstuart said:

Bearing creation with a borrowed router😀

Yeah, using a router for the first time is a kind of experience! Wood snow as you said and wild noise! 

38 minutes ago, bond19 said:

Thanks so much guys

Reassuring to know the set-up works. I'm going to give this some serious thought. You might have just convinced me on my next tripod!

No problem  

I checked Berlebach website. Mine is this one: 

https://www.berlebach.de/en/?bereich=details&id=242 

With the extras: 

* Double Cable Clamps UNI  (this is nice for extra safety, but I don't think it is needed - for my set up at least)

* colour: Natural (the nutwood brown looks lovely too.. )

* Thread: 3/8" but I asked them to make the bolt protruding 15mm (done free of charge)

* leg spread stop: Not the optional one, but I asked them to install this instead: https://www.berlebach.de/en/?bereich=details&id=170  

My tripod was ordered directly from them. They are nice guys, excellent customer service, and they accept customisation.

My UNI is rock solid with the Tak-100DF (which is a light refractor) but I don't think it would have any stability issue with 120mm diameter refractors. A guy on CloudyNights uses this same tripod with his TEC140 and he's happy with it. He also uses an AOK AYO II giro mount like mine. With that size, I think one is a bit in between this tripod and a Berlebach Planet.

TeleVue refractors can be a bit heavier than Tak ones. If I had a Tele Vue 102, I would go for a UNI for stability. Reports are nice and would do the job, although some vibration damping should be expected. All is a compromise really... less stiff => more vibration, but less stiff can also mean lighter, therefore more portable and ideal for quick observations. 

Yes, my berlebach UNI19 has an extension column and works really well.

In the UNI, the central column can be locked. 

I would also suggest to get the leg spreader (no innuendo was meant!). Berlebach can do it for you. They might install this slightly lower if you get a tripod with a central column, but this won't affect its stability. These are great tripods.

Also my telegizmo didn't cost anywhere near 200 pounds, but it is massive for your telescope...

In the end I decided to get plywood panels from https://www.slhardwoods.co.uk/ . Great customer service and very good sample.

For the time being, one B/BB board (12mm thickness, 9 plies) and one BB/BB board (15mm thickness, 11 plies). I will glue boards to get more thickness for the rocker box.

My order from Randy (Astrosystems) should arrive soon and truss attachments are already ready. So, it should not take me much time to make the UTA.

Thank you, everyone, for your advice

I've often wondered whether the hyperflex zoom is a clone of the Nikon zoom MC2.

I have the MC1 version, which is 21-9mm and unbarlowed, it performs slightly better than the Vixen SLV I had, which to my eye, were on par with TV Delos, apart from fov and colour tone. For the latter, I preferred the SLV.

A combo that I found to work really well is: low power / large fov ep, zoom, Barlow.

I regularly use two of these combos:

1) 2" combo: 30mm APM UFF, Zeiss zoom 20-75x, Baader VIP Barlow

2) 1.25" combo: 24mm TV panoptic, Nikon MC1 13-30x, Baader Barlow 2.25x

A good quality zoom can replace many eyepieces.

Sad news.

I have three of them and they are outstanding on both planets and double stars. They are also terrific for white light solar observing, although I do not remember the last time I observed a spot due to the low solar activity in these years.

It is also a shame that they did not make a 5mm model. As far as I read, the design cannot be scaled to that focal length. In a desperate need for a 5mm, some time ago I bought a Fujiyama 5mm HD ortho. Clearly not as comfortable as the Vixen HR, but to my surprise I do not have any issue with its rather tight eye relief (I observe without spectacles). I might have been very lucky with its optics because the eyepiece looks like on par with the HR trio I have, in terms of sharpness, snap focus, and neutral colour tone. It has been delivering some great views of Jupiter, despite the low altitude of this planet in these years. 

How many plies does your Marine and Birch plywood have?

Thank you all guys, really helpful feedback. 

I will check out Jewsons and Travis Perkins as you suggested, now that the mirror cell for this 16" dob is completed.

My plan is to have a wall thickness of 12mm or 15mm for both the UTA rings and mirror box.

For an f4, I could probably go for 18mm and make it hyper sturdy! Kriege advises 5/8”, which is almost 16mm anyway.

I'll check. Thanks for the info. 

I will need thicknesses of 1/2" and 1". 

So far, I found this source: https://www.slhardwoods.co.uk/

making a telescope, of course