Louis D

I can totally understand why fast Dobs have become so popular based the above cartoon.

That's a Webster 28" f/2.7.  Can you imagine putting that on an EQ mount, especially if it was f/8 like '50s era Newts?

14 minutes ago, Don Pensack said:

The same thing happened on a 10mm UFF several months later.

Which lens in the diagram was flipped?  It looks like only the negative lens in the lower barrel could be flipped and still get the whole thing to screw together.

I literally couldn't find any other M43x1 adapters or step rings anywhere on the internet.

On 17/03/2021 at 20:34, WJC said:

100% of the “collimation tips” on the Internet are WRONG!

I always thought that this site was fairly accurate, but if you say there are no correct internet discussions of collimation, I'll believe you.

Most Newtonians have such a large radius of curvature (equal to their focal length) that the field is very nearly flat for most eyepieces.  Refractors, especially short focal length ones, present a very curved field having a radius of curvature of about 1/3 the focal length.  Thus, the latter are far more demanding on eyepieces and the observer's accommodation.

14 hours ago, Spile said:

The first time I waved my hand in front of the aperture came as a bit of a shock when I was out of focus as above. 

What's also a revelation is to hold your hand in front of the scope in the winter after pulling a glove off.  The out of focus image shows the heat waves radiating off your hand.

14 hours ago, KP82 said:

I was referring to using the AZ5 with a 4" ED doublet. The Manfrotto 055 (I've got a 055CL myself) will be overloaded in this case.

Then pick up a second hand Manfrotto 3068.  They have a 40 pound capacity and have variable leg angles along with a geared center column.  I use mine with a DSV-2B mounting a 90mm triplet APO on one side and a 127 Mak on the other with no issues.

1 hour ago, Davey-T said:

Others use Nichrome wire heated with a battery I believe.

Most of those don't allow for plunge cuts, though.

I like the heated steak knife idea.  One could probably find a set for cheap at a thrift store to experiment with.  I'd probably learn the technique on discarded foam first, though.

Ever tried to look higher than 45 degrees in the sky with a 45 degree diagonal?  You either need to raise the telescope above eye level, crouch down low, or sit on the ground or close to it.

4 hours ago, Spile said:

I was impressed with the low tech approach of this...

 

https://www.instructables.com/Airline-portable-8-Dobsonian-telescope/

It amazes me there's no commercially made suitcase Dobs.  I think there are some bespoke makers in Europe, but at a very high price.  US bespoke Dob makers focus on large, high end stuff where profit margins are large.  It seems like Synta could make something compact and affordable, but they tend to focus on high volume, mass market Dobs.

6 hours ago, Deadlake said:

How do you determine the curvature of a scope?

Most amateur visual scopes have planes curving away from the eyepiece at the edges.

6 hours ago, wibblefish said:

@Louis D I am kind of loathe to buy something so expensive only to find it doesn't fit or won't achieve focus if it does  appreciate the assistance from @Waldemar and everyone else though and will report back if I find a different solution

Try removing the original visual back and just hold the T2 visual back up against the back of the bare tube to see if it will reach infinity focus with your eyepiece requiring the most in-focus.  Slowly pull the T2 VB away to see how much space you have for an adapter and can still reach focus.  This experiment won't cost anything.

I've found 60x on my ST80 is about the highest useful magnification due to my scope's spherical aberration and false color.  I can push my 72ED to over 100x by comparison thanks to the better color correction and lens figure.  Moving up from a fast achromat to at least to an FPL-51 doublet makes a huge difference in the purity of the views.  Moving up from that to an FPL-53 doublet or triplet is more of an incremental step in comparison.

Those old school AZ3 alt-az mounts are pretty horrible, but still better than the $15 photo tripod that came packaged with my ST80 20 years ago.  It is absolutely dreadful.  I now use it as a light stand for portraiture photography, and even then it's hard to set a fixed lighting angle.

4 hours ago, wibblefish said:

Well I have had a quick go, everything fits but with the additional piece I cannot attain focus. Pesky short tube refractors! I have a similar issue when I add additional filters onto my eye piece or try to use a camera on the visual back. Back to the drawing board! 

Definitely give that 3mm optical path length Baader adapter @Waldemar suggested above with the T2 threaded visual back attached to it.  It would replace the existing visual back and probably shorten the optical path length by 20mm to 25mm.

9 minutes ago, Thingo said:

Right now I'm thinking a pair of binos, possibly with the idea of the trekking pole monopod which could allow me to go for a pair of 15x70. Going with a pair of 10x50 wouldn't give me that much compared to my 10x26 for terrestrial - I presume. Back to my excel sheets for analysis!

15x70s are great for scanning the skies.  You will need to be seated and possibly reclined to use them effectively hand held.  8x42s are a great companion to them for wider views at about half the power.  Stick with porro prism designs to keep down the costs while maintaining good correction.  They will weigh a bit more than roof prism designs.

As Don suggests above, I use a TSFLAT2 attached in front of my GSO dielectric diagonal in place of the normal insertion tube.  For my 400m to 600mm focal length fracs, I find about 15mm of extension works well.  For your scope at about 800mm FL, you may want to dispense with any extension.  I use either the Blue Fireball M48 (2" Filter) Male Thread to SCT Male & M48 (2" Filter) Female Thread Adapter # C-05 with a 15mm extension or the Blue Fireball SCT Male Thread to 2" Nosepiece Adapter - Short # C-02 without any additional extension.  Either combination works really well to flatten the fracs' fields for my presbyopic eyes.

2 hours ago, Skygazerlass said:

Firstly I do not drive so getting someone to take me there for that length of time taking time out of their day is a big deal for me if I didn't I would have missed out on an amazing deal so I'm sorry it doesn't seem like a big deal to you but it was to me 🙂

Sorry, didn't mean to offend.  Pretty much everyone drives around here because mass transit sucks something fierce.  My daughter was a big proponent of mass transit during her college years until she got an internship downtown.  She tried the whole mass transit thing for a month and realized it was awful.  What should have taken 35 minutes to get there took over an hour if she caught the express bus.  However, it only ran every 30 minutes for 2 hours in the morning and evening.  If she missed one, she'd either have to sit and wait close to 30 minutes for the next one or take a local bus that takes 1.5 hours to get to downtown due to all the stops in between.  She ended up borrowing a family car for the summer or catching rides with friends and coworkers.  You can't live near work because decent houses in the city start at over $1 million.  Even dumps are over $500,000 now.  Apartments are over $1300/month, so you might as well put that money toward a house in the 'burbs.

You could try using an electric hot knife.  I'm sure there's a UK retailer of these things.

But it's getting more active now that we've passed solar minimum.

The Dob is much easier to set up and observe with while seated.  My refractors are nice for the purity of the star images, but can be a pain to use while seated as you said.  I can't stand and observe for more than a couple of minutes before fatigue sets in.

I use both just to change things up.

I would probably recommend a carbon fiber tripod to keep the weight down if traveling by plane.  That, and get a compact alt-az mount as some have suggested above.  A 72mm ED refractor would work well on camping trips, but it will be severely limited by its aperture for resolving smaller DSOs.  They are great for scanning the skies at low powers and for looking at midsize and large objects, though.

I put together a 127 Mak and 60mm finder scope combination on a DSV-1 mount with a Manfrotto 3068 tripod, all of it second hand, for my daughter's car camping trips.  It works well to provide wider field views through the finder along with higher power views through the Mak without taking up much space in the back of her mid-sized SUV.  The OTA and finder go in a gym bag, the tripod and mount in a long tripod bag, and the eyepieces in a pistol case.  I was able to cobble the whole thing together a couple of years ago for under $500.

On 14/03/2021 at 17:03, Pixies said:

I've never tried to work it out, but the TFOV appears to be the same as the outer ring of the Telrad - which is 6 degrees.

Telrad outer circle is 4 degrees.

I just double checked my cheap 45 and 90 degree Amici prism diagonals, and the OP is correct.  They are vastly stopped down.  I only use the 45 degree ones for terrestrial observing and the 90 degree one in a 60mm RACI finder, so the vignetting has never bothered me.

I've never experienced blackout with either, even with widest field eyepieces; but that was always with refractors.  Perhaps there is some interaction with the Mak's central obstruction going on as well here?

Another widest field option in a 1.25" barrel is the 24mm APM UFF.  It does quite well up to the last few degrees of field where it gets a bit indistinct.  The rest of the field is quite sharp.  I measured mine to have a 27.5mm effective field stop diameter, which probably accounts for the slight fuzziness at the edge since that is pushing what is possible in a 1.25" barrel.  By comparison, my 26mm Plossls have 22.3mm and 22.6mm field stop diameters.  I measured my 25mm AT Paradigm (BST Starguider) to have a 26.7mm field stop diameter, so it comes close to maxing out the available field of view in a 1.25" barrel.  The 24mm ES-68 at 27.2mm FS diameter has greater distortion to get to 68 degrees apparent field (AFOV), but not that much more true field (TFOV).  A 0.5mm difference in FS diameter isn't all that much.

If you already have 2" eyepieces and are comfortable with them, I would steer you toward the 22mm Omegon Redline (TS-Optics Expanse, Technosky Superwide HD, etc.).  They are better corrected than any of the above to the edge (just slightly behind the 22mm NT4), have excellent eye relief (once the eye cup is unscrewed) for eyeglass wearers, have a 28.4mm FS diameter (thus the 2" barrel), have a true 70 degree AFOV with very low distortion, and are lower priced than the APM or ES alternatives.