99.7% Moon, binoviewing with a Telementor

[Stu]

Prompted by @vineyard’s lovely report on his Telementor, I had a nice little lunar session last night using my little Telementor II. I had been clearing out my garage and found my old Unitron 114 AltAz mount which I hadn’t used for a while. This mount has very good slow motion controls on it, although because the weight of the scope is above the alt axis, it does need some careful balancing when looking at higher altitudes. Particularly when using binoviewers as I was last night, I need to dig out my front counterweight to help keep things in balance. I did push the scope as far forward in its rings as possible which was workable.

I can thank @F15Rules for the idea of binoviewing with this scope, so this was the first time I had properly attempted it.  I managed to get it to focus very well using a T2 Zeiss prism, with the barlow element of an AP Barcon fitted to the front in place of a normal barrel, and the Mark IVs mounted straight to the prism to save optical path length. I also got a slightly higher power using a x2.6 GPC so will continue experimenting to see which works best. I could likely get to higher powers as this scope has proved it will take up to x280 using a Nag Zoom, so I look forward to achieving this with the binoviewers. Last night I was still getting the full disk visible with a reasonable amount of sky around it which was a great view.

Despite the Moon being almost full (99.7%), there was plenty to see, including a tiny sliver of terminator which proved fun to try to identify what was there. I used the MoonGlobeHD app on my phone to help, and picked out a few highlights.

First off were craters Atlas and Hercules, towards the top limb. Atlas caught my eye with a small dark circular mark in the bottom left (refractor view), presumably a crater in shadow but it looked quite unusual. Beyond these two was Endymion, and right on the top limb was Mare Humboldtianum, quite distinct right on the limb.

Moving anti-clockwise, I found Gauss, Kästner then Ansgarius, on my way to Humboldt showing a couple of peaks beyond the limb. Petavius, a little further onto the disk was clear despite not being highlighted with shadow. Forming a nice little sequence running in from Ansgarius were la Pérouse, Kapteyn and Barkla.

Other highlights for me? The rays around Copernicus looked amazing, Aristarchus was bright and I love being able to spot the little pair Messier and Messier A with their ray trace heading away from A. The different contrasting shades across the disk were wonderful as usual, washed out a little by the thin cloud scudding across the sky but it was very nice to be out there still.

This scope does show CA on the limb of the Moon (most of which I have processed out in these images), but otherwise is very sharp and shows lovely contrast and variation of shading on the different areas of the Moon. This turned out to be a bit of a Zeiss fest; Zeiss Telementor, Baader Zeiss T2 Prism, Baader Zeiss Mark IV binoviewers and Zeiss converted microscope 25mm eyepieces! Just the AP Barcon breaking the chain but that’s hardly roughing it I guess 😉.

Pictures below of the scope in action, and a couple of handheld smartphone shots, tweaked a little in PS Express.

[F15Rules]

Great report Stu, and beautiful images👏👏👏!

So glad that you can get focus with the T2 system too.

That's a cracking little scope!.

..teaser..I've pulled the trigger on a mint Carton Japan 60mm F12 with equatorial mount and all accessories..watch this space😁👍

Dave

[Nik271]

Lovely report! I looked at the Moon last night and focused on the limb only. The other areas were so bright they were blinding. A situation where aperture does not always win  This gives me an idea to investigate binoviewers, half the light in each eye seems a good plan for Moon watching!

[John]

I find the moon OK with my 12 inch scope but I do tend to observe at high magnifications which dim the surface and make it quite comfortable to observe.

With my smaller aperture scopes, at the sort of magnifications that I like to use to tease out the finer lunar details (250x plus), I sometimes find the surface a little dimmer than I would like.

 

 

[Alan White]

30 minutes ago, F15Rules said:

teaser.. I've pulled the trigger on a mint Carton Japan 60mm F12 with equatorial mount and all accessories..watch this space😁👍

Dave

Aha, that's what your up to Dave, I await more news.

Sorry @Stu, sideways direction on your thread, very nice to see the Telmentor on Lunar.
Are these longer f ratio scopes with smaller aperture comparable or better than a shorter f ratio larger aperture, such as a 4" f8 or similar??

[vineyard]

That's a lovely report @Stu& what a Zeiss-geist!  I cannot get my hands on a T2 prism for love nor money but apparently they should be available from mid-Feb?  Of course there's always the Zeiss Baader T2 prism for about a GBP 100 more 🤨 ...must be patient.

That full disk of the moon is superb for all the 'tendrils' it shows.  Didn't have a chance to set up last night, but busy trying to get some solar in now.  If it stays clear tonight, I'm definitely on to Luna again.

Cheers!

[Stu]

28 minutes ago, vineyard said:

That full disk of the moon is superb for all the 'tendrils' it shows.

Great, aren’t they? Here’s an over boosted version to show them better. Probably looks rubbish on a PC but ok on my phone.

[Stu]

42 minutes ago, Alan White said:

Are these longer f ratio scopes with smaller aperture comparable or better than a shorter f ratio larger aperture, such as a 4" f8 or similar??

I am sure a 4”f8 scope would give better views; better resolution and larger exit pupil for equivalent magnification, so a brighter view.

I guess the benefit of the smaller aperture and longer focal length is reduced CA vs larger/faster scopes.

Ultimately I just enjoy seeing what these little scopes are capable of but remain realistic about their capabilities.

[vlaiv]

1 hour ago, Alan White said:

Are these longer f ratio scopes with smaller aperture comparable or better than a shorter f ratio larger aperture, such as a 4" f8 or similar??

When you have such scope - you can have the best of both worlds. For DSOs and resolution when larger aperture is a bonus - use scope at full aperture.

Want to have the same color correction as Telementor - use aperture mask and stop down lens to 60mm - you'll get equivalent aperture and F/ratio and hence color correction.

For example, I can easily stop down my 4" F/10 to 66mm and F/15, to get specs for "classic" achromatic refractor.

I did this on my short focal length refractor. Want to see color free images of planets (up to x80-x100)? - use 2" opening on lens cap. With my StarTravel 102 F/5 that gave me 2" (50.4mm) F/10 scope. That is Conrady standard - CA ratio of 5 or more.

[vineyard]

2 hours ago, Stu said:

Great, aren’t they? Here’s an over boosted version to show them better. Probably looks rubbish on a PC but ok on my phone.

 

I'm not sure what it looks like on a phone but on a laptop it looks like an oil painting - pretty good!

[vineyard]

1 hour ago, vlaiv said:

When you have such scope - you can have the best of both worlds. For DSOs and resolution when larger aperture is a bonus - use scope at full aperture.

Want to have the same color correction as Telementor - use aperture mask and stop down lens to 60mm - you'll get equivalent aperture and F/ratio and hence color correction.

For example, I can easily stop down my 4" F/10 to 66mm and F/15, to get specs for "classic" achromatic refractor.

I did this on my short focal length refractor. Want to see color free images of planets (up to x80-x100)? - use 2" opening on lens cap. With my StarTravel 102 F/5 that gave me 2" (50.4mm) F/10 scope. That is Conrady standard - CA ratio of 5 or more.

I'm going to try that w the Vixen 102M - there's a removable smaller lens cap which I guess makes it around 50mm aperture which would then be f20 - will report back when I can do a side-by-side - cheers!

[vlaiv]

1 minute ago, vineyard said:

I'm going to try that w the Vixen 102M - there's a removable smaller lens cap which I guess makes it around 50mm aperture which would then be f20 - will report back when I can do a side-by-side - cheers!

In case you have access to 3D printer - simple lens cap with hole of wanted diameter should be fairly easy to print.

When I had ST102 and was experimenting with aperture masks, I found that 4" PVC pipe plug is perfect as a base for making aperture masks.

A bit of flocking self adhesive material makes it fit dew shield perfectly. Problem is of course cutting appropriate opening - it took quite a bit of elbow grease to cut and sand it down to shape.

[John]

I could stop down my 130mm triplet refractor to 50mm and have an F/24 triplet apo. The 130mm is already classed as a super apochromat so I guess it would be a 50mm super, duper, apochromat

Bit of a bulky 2 inch refractor though ......

Edited December 1, 2020 by John

[vlaiv]

49 minutes ago, John said:

I could stop down my 130mm triplet refractor to 50mm and have an F/24 triplet apo. The 130mm is already classed as a super apochromat so I guess it would be a 50mm super, duper, apochromat

Bit of a bulky 2 inch refractor though ......

Well you can - but it will still cost as much as it does and it will still have the same color correction

[John]

7 minutes ago, vlaiv said:

Well you can - but it will still cost as much as it does and it will still have the same color correction

Not that I'm going to do it but I'm curious, would a 50mm F/24 triplet not show even less CA than a 130mm F/9.2 ?

 

Edited December 1, 2020 by John

[vlaiv]

Just now, John said:

Not that I'm going to do it but I'm curious, would a 50mm F/25 triplet not show even less CA than a 130mm F/9.2 ?

 

I think it certainly would. There are few other benefits as well - those wide field Erfles are going to be razor sharp to the edge

Downside is that 130mm F/9.2 still can't be mounted on that tall and slim EQ mount - to give you impression of that slow but razor sharp achromat from 60's, and of course resolution will suffer.

[John]

12 minutes ago, vlaiv said:

I think it certainly would. There are few other benefits as well - those wide field Erfles are going to be razor sharp to the edge

Downside is that 130mm F/9.2 still can't be mounted on that tall and slim EQ mount - to give you impression of that slow but razor sharp achromat from 60's, and of course resolution will suffer.

Good points of course !.

Fortunately I have an F/13.3 60mm achromat from the 60's so I don't need to stop anything down.

Just need to get it on a steady mount and equip it with a 1.25 inch diagonal.

Reading threads like this provides an incentive to do that

 

Edited December 1, 2020 by John

[vlaiv]

22 minutes ago, John said:

Good points of course !.

Fortunately I have an F/13.3 60mm achromat from the 60's so I don't need to stop anything down.

Just need to get it on a steady mount and equip it with a 1.25 inch diagonal.

Reading threads like this provides an incentive to do that

 

It would be a good comparo though - scope like that and 4" F/10 mass produced Chinese glass stopped down to something like 66mm F/15.

[John]

22 minutes ago, vlaiv said:

It would be a good comparo though - scope like that and 4" F/10 mass produced Chinese glass stopped down to something like 66mm F/15.

I have a F/11.1 90mm chinese achromat (Synta ?) that I can easily stop down to 60mm / F16.6. That would be interesting to compare with the Japan made 1960's 60mm F/13.3. The latter is circle T so Towa I think ?

A project for the Winter 

 

[Ships and Stars]

I was showing the moon photos above to my four year old, and she said was he on the moon when he took those? I said no, no and pointed to the photo of the telescope. She exclaimed 'whoa, that's a good one!'

I'd love to have a nice Telementor, I've a soft spot for vintage things that are functional. 

 

[John]

I'd like to get hold of something that has a similar spec and performance to the scopes that Galileo used. It would be fun to see what he had to work with (albeit under darker skies I guess) and see what can actually be seen today with such an instrument.

 

[johninderby]

Have look at Thomas Harriots  lunar maps. Amazong detail given the primitive telescope he was using. And oh yes he was observing the moon through a telescope before Galileo and made far more detailed observations.

https://academic.oup.com/astrogeo/article/50/1/1.27/201448

Edited December 1, 2020 by johninderby

[Stu]

13 minutes ago, John said:

I'd like to get hold of something that has a similar spec and performance to the scopes that Galileo used. It would be fun to see what he had to work with (albeit under darker skies I guess) and see what can actually be seen today with such an instrument.

 

DIY project for you John....

https://www.popsci.com/build-diy-replica-galileos-telescope/

[Stu]

On 01/12/2020 at 19:04, Ships and Stars said:

I was showing the moon photos above to my four year old, and she said was he on the moon when he took those? I said no, no and pointed to the photo of the telescope. She exclaimed 'whoa, that's a good one!'

I'd love to have a nice Telementor, I've a soft spot for vintage things that are functional. 

 

Lovely stuff. I very much enjoy vintage scopes too. I now have a Televue Genesis, Vixen FL102S fluorite, a TAL 100r and the Telementor. Need to get more use out of the TAL to see how it performs. I suspect that one will find a new home in future but the other three will definitely stay.

[johninderby]

One of these days I will have to build this Japanese telescope kit. 🤔

 

 

Edited December 1, 2020 by johninderby