How do I interpret Takahashi diagrams?

[John]

It would be interesting to know if something like the TSA 102 could properly split the close pair of the Tegmine (Zeta Cancri) triple star. My data shows the separation at 1.1 arc seconds which is a touch tighter than the Dawes limit for 102mm aperture of 1.14 arc seconds.

 

[mikeDnight]

I like the colours!  Other than that, for a purely visual observer such as myself, the graphs don't really tell me much. Neither the two TSA's, one FC100DC, two  DL's or one DZ that I've observed with showed any hint of visible CA. 

[JeremyS]

12 minutes ago, John said:

It would be interesting to know if something like the TSA 102 could properly split the close pair of the Tegmine (Zeta Cancri) triple star. My data shows the separation at 1.1 arc seconds which is a touch tighter than the Dawes limit for 102mm aperture of 1.14 arc seconds.

 

Interesting, John. There are a few owners of TSA 102’s on here that could try. 

[dweller25]

Joking aside - It makes we wonder about all these optical diagrams because when I compare the TSA102 with the FC100DZ I see no difference in planetary detail and there is no CA in either scope. Whilst Takahashi do state that the TSA has 1/3rd the CA of fluorite lenses (the FS range at the time) I suspect the real world difference at the eyepiece at focus is minute.

Either side of focus my FS128 shows CA but at focus there is no visual CA - and that’s where the focuser is set when I observe 🙂

The only difference I see at focus is tonal with Jupiter in particular looking whiter and colder in the TSA.

To me the big advantage fluorite brings is it’s ability to deliver great views with just two lenses which keeps the weight of the scope down, which has allowed me - with an ever worsening back - to go out and observe more since I bought the DZ last year.

 

Edited February 15, 2021 by dweller25

[andrew s]

@dweller25 I think you are right, we are into counting angles on the head of a pin.

Tonal colour is most likely due to different absorption in the glass and the anti-reflection coatings.

Regards Andrew 

[John]

I think the main purpose of these charts and diagrams is to fuel discussion on forums

 

 

 

 

[andrew s]

12 minutes ago, John said:

I think the main purpose of these charts and diagrams is to fuel discussion on forums

 

 

 

 

It will never work. Regards Andrew 

[JeremyS]

1 hour ago, dweller25 said:

Whilst Takahashi do state that the TSA has 1/3rd the CA of fluorite lenses (the FS range at the time) I suspect the real world difference at the eyepiece at focus is minute.

 

 

Indeed, one-third of not very much is hardly anything at all 🤣

[mikeDnight]

2 hours ago, JeremyS said:

Indeed, one-third of not very much is hardly anything at all 🤣

Wow - I'm in awe of your Vulcan logic Jeremy.  No wonder you're a doctor!    

[dweller25]

1 hour ago, mikeDnight said:

Wow - I'm in awe of your Vulcan logic Jeremy.  No wonder you're a doctor!    

Witch kind of a doctor ? 🤣🤣

[jetstream]

7 hours ago, dweller25 said:

The only difference I see at focus is tonal with Jupiter in particular looking whiter and colder in the TSA.

Have you tried them both on Saturn when the planet is high up? I'm curious about the tonal difference and which scope you prefer. And after that Ill make an offer to purchase on the TSA102 😀 but I know it wont be for sale

Edited February 15, 2021 by jetstream

[dweller25]

24 minutes ago, jetstream said:

Have you tried them both on Saturn when the planet is high up? I'm curious about the tonal difference and which scope you prefer. And after that Ill make an offer to purchase on the TSA102 😀 but I know it wont be for sale

Hello Gerry,

Sadly not - Saturn was very low last year, will try this year - but Saturn will still be low 🙁

Results were very similar with Mars last year.

But you have the TSA120 so a 100DZ would bring rapid cool down grab and go to the party.

[Ken82]

I know what you mean....

 

[KP82]

On 15/02/2021 at 08:11, dweller25 said:

Joking aside - It makes we wonder about all these optical diagrams because when I compare the TSA102 with the FC100DZ I see no difference in planetary detail and there is no CA in either scope. Whilst Takahashi do state that the TSA has 1/3rd the CA of fluorite lenses (the FS range at the time) I suspect the real world difference at the eyepiece at focus is minute.

Either side of focus my FS128 shows CA but at focus there is no visual CA - and that’s where the focuser is set when I observe 🙂

The only difference I see at focus is tonal with Jupiter in particular looking whiter and colder in the TSA.

To me the big advantage fluorite brings is it’s ability to deliver great views with just two lenses which keeps the weight of the scope down, which has allowed me - with an ever worsening back - to go out and observe more since I bought the DZ last year.

 

APO triplets are meant to produce CA free views either side of focus, not just in focus. But as you've said for visual users, it's only the in-focus view that counts. In this case, these fluorite doublets are pretty much on par with the triplets.

Even if Tak have been telling the truth that CA of a TSA (e.g. TSA102) is only a 1/3rd of a fluorite doublet (e.g. FS102), visual users won't be able to tell the difference because the measurements are in micrometres.

[jetstream]

Ok I'm going to break down and buy a doublet Tak, but there's different versions?...doesn't much matter I guess- they're all out of stock.

[JeremyS]

45 minutes ago, jetstream said:

Ok I'm going to break down and buy a doublet Tak, but there's different versions?...doesn't much matter I guess- they're all out of stock.

Now the fun begins 👍🏻
Are you thinking FC 100?

[jetstream]

42 minutes ago, JeremyS said:

Now the fun begins 👍🏻
Are you thinking FC 100?

Yes, I just set the TSA120 up on the AZEQ6 and would like a lighter, faster to set up 100mm. Question is DC,DZ,DF... I actually know little about these scopes. A mount /tripod recommendation would be good as well. Up on the hill the trees obscure the south view but down by the carport I can see longer, a bit worse local seeing down here though. The fast to cool FC100 should be perfect I think.

Edited February 16, 2021 by jetstream

[Deadlake]

19 minutes ago, jetstream said:

Yes, I just set the TSA120 up on the AZEQ6 and would like a lighter, faster to set up 100mm. Question is DC,DZ,DF... I actually know little about these scopes. A mount /tripod recommendation would be good as well. Up on the hill the trees obscure the view but down by the carport I can see longer, a bit worse local seeing down here though. The fast to cool FC100 should be perfect I think.

Seeing as cool down is not an issue (left in a case outside) and your a thinking about NV, maybe some F6 triplet would be good. Your dob would show you a lot of structure in various targets, however a smaller scope would let you frame larger objects. By the way what are you doing with your 90mm, presume that’s staying put. The TSA is not that heavy maybe just a light mount, too heavy for a ScopeTech what about a discmount?

Edited February 16, 2021 by Deadlake

[jetstream]

Just now, Deadlake said:

Seeing as cool down is not an issue and your a thinking about NV, maybe something F6 triplet would be good. Your dob would show you a lot of structure in various targets, however a smaller scope would let you frame larger objects. By the way what are you doing with your 90mm, presume that’s staying put. By the way the TSA is not that heavy maybe just a light mount, to heavy for a ScopeTech what about a discmount?

I just have a weakness for good glass!

I'm attached to my Raptor, it was a very good dark site adventure buddy. Many trips on the snowmobile/atv etc. Its the length of the 120's thats the issue. Yes Im looking at a Diskmount but no way to get it over here atm, everythings being brokered by the shippers and they are charging a lot. I do have a Stellarvue M2 that works with the Raptor but a step up might be nice.

One of those Berlebach crank up tripods would be good with an AYO... no idea if they are still available. I'd like to put encoders on the mount for my SkyCommader box, it is deadly accurate.

[Deadlake]

1 minute ago, jetstream said:

I just have a weakness for good glass!

I'm attached to my Raptor, it was a very good dark site adventure buddy. Many trips on the snowmobile/atv etc. Its the length of the 120's thats the issue. Yes Im looking at a Diskmount but no way to get it over here atm, everythings being brokered by the shippers and they are charging a lot. I do have a Stellarvue M2 that works with the Raptor but a step up might be nice.

One of those Berlebach crank up tripods would be good with an AYO... no idea if they are still available. I'd like to put encoders on the mount for my SkyCommader box, it is deadly accurate.

I was going to suggest at az100, which are still turning up in the US. However it’s 10 kg, which might be too heavy. However the encoders are built in for push too. Other advantage is you could put an APO and a Newt on it at the same time. Wide field and narrow field for fine structure at the same time. 
Some people have gone and bought FSQ’s (even the 130) to get the fast enough speed for NV, I thing that’s a little overkill...

[jetstream]

1 minute ago, Deadlake said:

Some people have gone and bought FSQ’s (even the 130) to get the fast enough speed for NV,

I think that f6 or 7 with the 50mm ?plossl with be fine for f3 or 4 equivalent.  I look forward to showing people the views with one- theres no chance a first time observer will see Barnards Loop without it for example.

There is the Losmandy AZ mount too, but it looks very precisely made with slow mo controls- guaranteed not to work in the cold.Even the diag holder threads tighten up too much, some wont work.

[JeremyS]

30 minutes ago, jetstream said:

Yes, I just set the TSA120 up on the AZEQ6 and would like a lighter, faster to set up 100mm. Question is DC,DZ,DF... I actually know little about these scopes. A mount /tripod recommendation would be good as well. Up on the hill the trees obscure the south view but down by the carport I can see longer, a bit worse local seeing down here though. The fast to cool FC100 should be perfect I think.

Of those 3, I’d go for the FC 100 DZ. that’s what I did in the end.

Not sure about lightweight mount. The ScopeTech on Berlebach Report is very light, but the DZ is on the high side for it.

Deadlake mentions a lighter mount for the TSA120. I sometimes put mine on a WO EZTouch (no longer made) on Berlebach Planet. The mount and tripod are grab and go: UNI 28 would be more so. 

[JeremyS]

18 minutes ago, jetstream said:

I just have a weakness for good glass!

I'm attached to my Raptor, it was a very good dark site adventure buddy. Many trips on the snowmobile/atv etc. Its the length of the 120's thats the issue. Yes Im looking at a Diskmount but no way to get it over here atm, everythings being brokered by the shippers and they are charging a lot. I do have a Stellarvue M2 that works with the Raptor but a step up might be nice.

One of those Berlebach crank up tripods would be good with an AYO... no idea if they are still available. I'd like to put encoders on the mount for my SkyCommader box, it is deadly accurate.

Good glass. What about the FOA 60Q, Tak’s finest? Maybe a bit small, but having just spent an hour with my FS 60Q, there’s lots of fun to be had.

I must admit to being tempted by the FOA in the quality stakes.

Here the FS 60 Q grab and go

[jetstream]

7 minutes ago, JeremyS said:

I sometimes put mine on a WO EZTouch (no longer made) on Berlebach Planet

I just looked up the WO mount- it looks very good. The Planet is THE tripod to have for stability I hear. Settling times?

Being able to raise  and lower the scope's tripod is a vg feature that I think I'd like to try... The DZ is a very highly recommended telescope.

Edited February 16, 2021 by jetstream

[jetstream]

3 minutes ago, JeremyS said:

I must admit to being tempted by the FOA in the quality stakes.

The scopes look so good, the quality is superb across the line up. So many choices...The 90mm Raptor will be retired, unless more of those sled trips happen and I was thinking of a 100mm to replace it. This summer I'll pour concrete in the carport and sheath part of it in for scope storage down here. It will only be 10 steps out to observe.

The rest of the equipment will be up in the seacan on the ridge.