In betweener

[Mr Spock]

Another suggestion is a 6" CC. From what I've read the StellaLyra 6" f12 is quite good. No issues with CA there.

[jetstream]

3 hours ago, ollypenrice said:

TEC 140. Superbly built, wonderful views, corrected for visual (but a stunning imaging scope with the dedicated flattener.) A really great scope entirely free of Hospital Green and flashy red anodising!  (Yikes, I hope Jeremy doesn't read this...)

lly

My recent interest in DPAC has me reading tests already done. One test set in particular, from another site and from a few years ago showed a TEC 140FL with the fringes curved up in red and blue, green was ok. The TEC140ED tested was better corrected.

How can this be?

If that 140FL had been another brand the wolves would have been out, but because it was a TEC the comments were like " well its still a great scope" or "I'll take it off your hands lol" etc.

I dont believe in "mythical" scopes, just ones proven to give great views, and these ones will test well.

All this just an opinion.

[jetstream]

3 hours ago, Stu said:

Interesting. Matthew puts it at 30mins for the same scope from warm house to cool outside.

Great point and I must add a carbon fibre tube takes longer to acclimate.I chose CF for the 90mm because of all the abuse it would take on dark site trips and extreme temp differences. It has been "thrown" in the truck, no dents obviously and CF will not move around like an aluminum tube in wild temp swings.

A well designed aluminum tube and cell wont impact views in extreme temps ie the TSA120.

Its a crap shoot if the SW120ED will have a successful cooldown from 21c to -30c. The cell pinches more than 50% of the time, making it unuseable for a session then.

There is no question air spaced triplets take a fair bit of time to cooldown IMHO. Eventhough my TSA is stored in a seacan, I still give it time to settle down, maybe this is just me.

But the views speak for themselves..

[ollypenrice]

40 minutes ago, jetstream said:

My recent interest in DPAC has me reading tests already done. One test set in particular, from another site and from a few years ago showed a TEC 140FL with the fringes curved up in red and blue, green was ok. The TEC140ED tested was better corrected.

How can this be?

If that 140FL had been another brand the wolves would have been out, but because it was a TEC the comments were like " well its still a great scope" or "I'll take it off your hands lol" etc.

I dont believe in "mythical" scopes, just ones proven to give great views, and these ones will test well.

All this just an opinion.

I don't buy into mythical scopes either and my enthusiasm for the TEC predates its current perceived position as a full on premium apo. When it first appeared it was mostly remarkable for its price, offering good apo performance at well below the cost of the 6 inch AP or Tak, while having a lion's share of the aperture. Being oil-spaced and 140 rather than 150 gave it an enormous price advantage over Tak. I started using one myself a little over ten years ago, initially in visual and imaging but latterly only in imaging. I thought it was great visually and very good for imaging - though blue stars tended to bloat when very bright. I then started using the flattener and, although TEC insist that it doesn't, the flattener stopped the bloating in its tracks. The field illumination is also staggeringly even over a 35mm chip but it is designed for medium format, so no surprises. As an objective observation of its imaging prowess, a set of 10 minute luminace subs with Alnitak a little off-centre, a pure log stretch which brought the Horse and Flame into clear view, still saw Alnitak cleanly split as a double. This is extraordinary. My Tak FSQ106N gave Alnitak as a huge, sprawling blob needing differential processing to reveal it as a double - with difficulty.

Olly

[jetstream]

@ollypenrice  Your voice of experience is a much valued asset to us.

Ive heard about issues with the Tak FSQ which highlights the need not only to research the brand but also models within the brand- any brand. IMHO. I think I remember Tak having a coating issue years ago too.

My hat is off to you for reporting the FSQ issue you have, many if not most scope owners will not post about issues with their scopes as it can effect resale.

It sure helps people to know about the probability of getting a good telescope through these disclosures.

Gerry

 

[ollypenrice]

1 minute ago, jetstream said:

@ollypenrice  Your voice of experience is a much valued asset to us.

Ive heard about issues with the Tak FSQ which highlights the need not only to research the brand but also models within the brand- any brand. IMHO. I think I remember Tak having a coating issue years ago too.

My hat is off to you for reporting the FSQ issue you have, many if not most scope owners will not post about issues with their scopes as it can effect resale.

It sure helps people to know about the probability of getting a good telescope through these disclosures.

Gerry

 

I thought my Tak FSQ was a brilliant scope and probably the best 4 inch imaging refractor on the market. There is no other comparable scope I would buy (and I mean the old fluorite one, not the present one, which I would not buy.) It wasn't perfect, though. Bright stars would bloat slightly and many had a diffraction artifact in the form of two dark beams, possibly from pinching. When these were pointed out to me I would just say, 'Yes, I know. Now look at the picture!'

I make my living on reputation so gaining a few bob when selling on a bad used product would be idiotic on my part. It sits in my loft till someone who'd like it takes it away for free.

Olly

[Mr Spock]

Unfortunately some brands tend to attract a mythological status due to hype, cliquiness and false euphoria to the extent people wanting to buy such scopes almost cannot believe what they read. 

It would be nice if there were an unbiased and independent review source from which you could make an informed decision.

[jetstream]

6 minutes ago, Mr Spock said:

Unfortunately some brands tend to attract a mythological status due to hype, cliquiness and false euphoria to the extent people wanting to buy such scopes almost cannot believe what they read. 

It would be nice if there were an unbiased and independent review source from which you could make an informed decision.

Amen to that.

[jetstream]

9 minutes ago, ollypenrice said:

I make my living on reputation so gaining a few bob when selling on a bad used product would be idiotic on my part. It sits in my loft till someone who'd like it takes it away for free.

Kudos to you Olly👍

I respect your integrity. Gerry

[JeremyS]

31 minutes ago, Mr Spock said:

Unfortunately some brands tend to attract a mythological status due to hype, cliquiness and false euphoria to the extent people wanting to buy such scopes almost cannot believe what they read. 

It would be nice if there were an unbiased and independent review source from which you could make an informed decision.

It’s right here Michael:

🙂

[Stu]

3 hours ago, Deadlake said:

Doing a Google around this there is a huge range of cooling times for the same scopes, and even then if nighttime temperature is changing this has a large effect too. 
 

It’s just basic physics, start temp and outside temp, and whether that is stable or falling. 30 mins is probably about right, a doublet is faster.

[Deadlake]

3 hours ago, jetstream said:

Great point and I must add a carbon fibre tube takes longer to acclimate.I chose CF for the 90mm because of all the abuse it would take on dark site trips and extreme temp differences. It has been "thrown" in the truck, no dents obviously and CF will not move around like an aluminum tube in wild temp swings.

A well designed aluminum tube and cell wont impact views in extreme temps ie the TSA120.

Its a crap shoot if the SW120ED will have a successful cooldown from 21c to -30c. The cell pinches more than 50% of the time, making it unuseable for a session then.

There is no question air spaced triplets take a fair bit of time to cooldown IMHO. Eventhough my TSA is stored in a seacan, I still give it time to settle down, maybe this is just me.

But the views speak for themselves..

So far we've had three tubes types mentioned. aluminium, phenolic and Carbon.

Gerry do you know if carbon has tube currents like aluminium? 

Also we looked at lens being pinched, the LZOS is good to -30 oC so I imagine at more normal temperature it can compensate better then other designs.

[jetstream]

11 minutes ago, Deadlake said:

Gerry do you know if carbon has tube currents like aluminium? 

Any tube can have tube currents.  It is a function of the temperature difference between the lens assy and the tube itself, including the focuser etc or anything that could be a heat or cold sink.

Some SCT astronomers use reflective bubble wrap to "slow down" cooling of the tube to more closely match the cooling rate of the big corrector plate etc.

My truss dobs can have "tube currents" from the shroud closed and I adjust it for the most stable views, among other things done.

I hope the OP can garner some useful information from this thread in his future telescope choice.

[Deadlake]

1 hour ago, Stu said:

It’s just basic physics, start temp and outside temp, and whether that is stable or falling. 30 mins is probably about right, a doublet is faster.

I think there are many factors making up when a scope lens reaches null.

If you are really keeping track of it you would be testing the lens against green light, but how many of us do that?

The environment is not just temperature difference, it also includes cooling factors, change in pressure, how much latent heat is stored in the tote systems (lens tube, ground etc) from the day before all play a part.

How much the lens is over corrected to start with will be a factor of height and air pressure and hence how long to get to null.

Too much over correction at the start is a way to a decrease in contrast as the lens changes shape.

I think this conversation has been done to death on CN with the simple conclusion that to many factors to give a simple answer of it's 30 mins for this scope and 60 mins for another scope, etc..
 

[Deadlake]

54 minutes ago, jetstream said:

Any tube can have tube currents.  It is a function of the temperature difference between the lens assy and the tube itself, including the focuser etc or anything that could be a heat or cold sink.

True, but some tube materials will give less thermal currents than others. 

Polymers of most kinds are self-insulating, as is phenolic/paper, and so is fiberglass.

Carbon fiber tubes are not self-insulating.

All metal tubes need insulation of some kind.

Hence using a phenolic tube gives less chance of tube currents running the view.
 

56 minutes ago, jetstream said:

I hope the OP can garner some useful information from this thread in his future telescope choice.

Yes, there is no free lunch in hoping once scope will behave in a particular way, all a function of environment the scope is being used in...

[jetstream]

39 minutes ago, Deadlake said:

True, but some tube materials will give less thermal currents than others. 

Its the rate of cooling of the lens vs everything else that determines the currents. The slower cooling tubes degrade the image longer but this depends on the rate of cooling between the lens assy and everything else. IMHO.

There is no free lunch- unless the lens is equalized with everything the image is degraded IMHO.

[Stu]

1 hour ago, Deadlake said:

I think there are many factors making up when a scope lens reaches null.

If you are really keeping track of it you would be testing the lens against green light, but how many of us do that?

The environment is not just temperature difference, it also includes cooling factors, change in pressure, how much latent heat is stored in the tote systems (lens tube, ground etc) from the day before all play a part.

How much the lens is over corrected to start with will be a factor of height and air pressure and hence how long to get to null.

Too much over correction at the start is a way to a decrease in contrast as the lens changes shape.

I think this conversation has been done to death on CN with the simple conclusion that to many factors to give a simple answer of it's 30 mins for this scope and 60 mins for another scope, etc..
 

Very true, and without detracting from the thread any further, my simple point was that a fast air spaced triplet will not cool to ambient from a warm house/garage in five minutes. Can we leave it there please.

[Kobayashi Maru]

9 hours ago, ollypenrice said:

TEC 140. Superbly built, wonderful views, corrected for visual (but a stunning imaging scope with the dedicated flattener.) A really great scope entirely free of Hospital Green and flashy red anodising!  (Yikes, I hope Jeremy doesn't read this...)

lly

A second hand one is/was available on trademe here in NZ. $15k nzd. Ouch

[jetstream]

3 minutes ago, Kobayashi Maru said:

A second hand one is/was available on trademe here in NZ. $15k nzd. Ouch

If I were you Id be seeking a Tak .... your location helps... IMHO.

[Kobayashi Maru]

10 hours ago, Paz said:

One thing I notice is that as you allude to they are best when they are complimentary to each other.

I looked at length at 120-130mm refractors as I was aiming for downsizing to just 3 scopes, a 72mm refractor for travel so that had to be small, a 14" reflector for epic sessions, so that had to be epic(!) and being big/heavy didn't matter, and a third scope in between.

I looked at some 120-130mm refractors in the flesh and was worried about their size/weight and that I might need a more serious mount and that setting one up would be in the same league of challenge as the vx14 in which case the vx14 would probably get used and the big refractor would probably not. So I thought longer about the point of a 3rd scope. In the end I decided it had to be a general purpose great grab and go scope, I e. did not have to be small but did have to be fast and flexible and l easy to set up so it filled a gap that didn't compete with the 72mm or 14" and I ended up with a smaller 3rd scope than I initially wanted.

The above is just my own story and everyone would have different choicesabput a good mix of scopes that would work best,  but the thing that helped me was considering scope purpose again in detail and seeing if that helped to solidify a choice.

Regarding your starting point a challenge you have is that a 10" dobsoinian is a great visual scope and so anything else is going to have to have a specific advantage over that to make you motivated to use it once the novelty has worn off.

This seems a good approach to me. I’m in NZ , have fairy good seeing, and I’m not too far away (30mm) from pretty dark sky’s. I have a feeling a 100mm may make to to those dark sky’s more often

[Kobayashi Maru]

13 minutes ago, jetstream said:

If I were you Id be seeking a Tak .... your location helps... IMHO.

Yeah. There is also that matter of diminishing returns I suspect

[Kobayashi Maru]

Thanks for all the replies.

the mythic telescope idea is interesting. I’ve always wondered how much magical thinking there is in astronomy. Is it similar to hifi with their god speaker cables etc.

[Mr Spock]

14 minutes ago, Kobayashi Maru said:

Is it similar to hifi with their god speaker cables etc.

Not really. Difference in cable can be staggering and is easily demonstrated