New APO - TEC 140 possibly ?

[DaveS]

Hi Will

I think there's been a misapprehension on the Astrograph site, as Lanthanum Oxide is a component of the glass, or at least one of the glasses, rather than a coating. Generally the addition of Lanthanum Oxide can give the glass useful optical properties, whether used in crown or flint type compositions. Though of course the whole triplet has to be designed as a whole balancingncing the glass types, and FPL 53 isn't a magic bullet guaranteeing optical perfection. I think there's a blog on the Altair Astro site on the subject of triplets.

I only gave the Tecnosky as one example (Though one I've been looking at myself), there are others including the Altair Astro and TS options. APM also do one, though we're back near TEC prices.

[cs1cjc]

On 23/04/2016 at 21:25, DaveS said:

Hi Will

I think there's been a misapprehension on the Astrograph site, as Lanthanum Oxide is a component of the glass, or at least one of the glasses, rather than a coating. Generally the addition of Lanthanum Oxide can give the glass useful optical properties, whether used in crown or flint type compositions.

This is a common error which seems to come from machine translators.  The german for crown (glass) is being translated to coated.

[NickK]

On 21 April 2016 at 12:52, Retro Gear said:

Sorry to be a bit dim but is the Petsval design optics an inherent part of the Esprit scope or is it associated with the field flatteners ?

I have a Pentax SDP - it has doublet and then a rear doublet in a Petsval (persval?) design. The design itself is a field flattened design but a rear mounted flattener/televue/barlow etc would have the same issue.

For Solar if you have rear glass elements in the scope then the concentration of light onto the rear elements can cause thermal shock.

It IS possible to use these types of scope and rear glass however you need to reduce the amount of light incoming to safe levels first - so in my case I use solar foil for white light. However you'd need a energy rejection filter ahead of the objective.

Hope that helps

[DaveS]

4 hours ago, cs1cjc said:

This is a common error which seems to come from machine translators.  The german for crown (glass) is being translated to coated.

Thanks for that, something I hadn't realised. Which suggests that it uses a Lanthanum Crown element, something like this perhaps?

http://refractiveindex.info/?shelf=glass&book=SCHOTT-LaK&page=N-LAK7

[Retro Gear]

Thanks DaveS for clarification on the Lanthanum – I looked on Wikipedia and found “La₂O₃ is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness” - confirming what you said

Will

[Retro Gear]

NickK – thanks for clearing that up – apparently it's Petzval (according to Wiki – been reading stuff there to help get to grips with terms I'm coming across on posts etc.). Yep – I now see how that would impact on solar if it's a part of the scope architecture. I hope once I have the wherewithal to start with solar to use a front ERF and blocking filter at the rear – I assume with that arrangement the inclusion of a Petzval design in the scope is irrelevant with regard to heat issues. Thanks again

Will

[DaveS]

A google search on "Cooke Photovisual Triplet" turned up this interesting read on various Apo Triplets down the years, including a couple of oil- spaced designs which look similar to the TEC objective

    http://rohr.aiax.de/HP/Chapter%204b.htm

[Peter Drew]

I don't think a front mounted ERF is sufficient to avoid potential problems with Petzval designs. The main attenuation is in respect of UV and IR radiation, there is still enough heat at the eyepiece end to burn your hand!

[Retro Gear]

DaveS – thanks for the link – a good read indeed and will be undertaken tonight whilst taking in a bit of liquid refreshment  ! I've been reading many posts by SGL members regarding help choosing proposed new scopes and this has set me on a bit of a new track – going to post a bit later on with some thoughts – hope you might have a look then and give me your opinion.

Will

[Retro Gear]

Peter – Yikes! – That may scupper a few plans I had . So is a scope incorporating a Petzval design ruled out from solar observation (narrow band) entirely or are there specific filters appropriate for such designs of scope. Sorry if I've misunderstood what you are saying.

Will

[Davey-T]

Two folks on the solar imaging forum, Dazzaa1966 uses an Esprit 120 for solar and I think Montana uses a Tec140.

Dave

[Retro Gear]

Well I've been reading many threads covering the theme of “advice on a new refractor” and learned a great deal. Depending on the candidate scope being discussed, it seemed to me that often a Takahashi, in one form or another (with the possible exception of the Sky 90), was used as a sort of benchmark instrument to relate the candidate with (I may be wrong about that but Taks always seemed to appear somewhere in the thread). I hadn't considered one of these fine instruments initially since I had set my sights on a 150mm APO and Taks of that calibre were way out of my original budget (£4000). But, having been really tempted by the TEC 140 – I extended the budget to about £6000 but as time went by realised I'm going to need a pile of “extras” (filters/good eye pieces/a ccd at some point … the list goes on doesn't it!) and potentially two scopes instead of one as mentioned earlier in the topic.

So to get to the point – I've decided to get a quality 130mm APO and looked again at Taks. I could afford to get a TOA 130S (£4299 Harrison Telescopes) – (a scope mentioned by Mike further back in the topic) and have cash available for extras (or even the second scope for imaging at some point). What do you think? This would be my visual scope (mainly) and since I really like planets/moon/sun this should be a cracker. I know I'm losing about an inch of aperture with the Tak compared with 150mm options like the Esprit etc. but the excellent Tak optics would more than compensate (I would think). I have read that “old eyes” like mine benefit from greater aperture but reliable quality (I'm guessing quality control at Takahashi is likely to be similar to that of TEC – I'm probably going to get a broadside about that ) must count for a great deal.

Thanks for your help and encouragement with this – I feel I'm getting somewhere now .

Will

[william123]

Will:

Have you considered the new Astro-Tech 130 EDT f/7 triplet, sold by Astronomics in the USA?  See www.astronomics.com.  This telescope is getting rave reviews on Cloudy Nights, for both visual and imaging.  The scope costs only $1800 USD and it may take a few months to get one.

Bill  

[DaveS]

That looks similar to several 130 f/7 'scopes over here, eg from Altair-Astro and Tecnosky / TS, and by the time you've added shipping and 20% VAT it's in the same price range, even allowing for exchange rates.

[swag72]

There's a couple of nice scopes on ABS at the moment - A Tak TOA130 and a TOA150....... 

http://www.astrobuysell.com/uk/propview.php?view=111920 and http://www.astrobuysell.com/uk/propview.php?view=111920

[ollypenrice]

The link to the 6 inch Tak should be this one: http://www.astrobuysell.com/uk/propview.php?view=111923

Very tempting stuff in both cases.

Olly

[Retro Gear]

Bill – as DaveS has said it might work out relatively expensive with the various tax's involved - but thank you for the information – I'm still looking.

Will

[Retro Gear]

Oh my hat – the Tak 150 on ABS sound remarkable – in fact at that price it would be a real bargain (it's only £1500 more than the 130 being sold). That said I am very reluctant to buy second hand since I simply would not know what to look for in a used piece of equipment. Experienced users would spot potential problems. I think at my level of experience buying new and getting some good support from the supplier – whilst obviously more costly – might be the sensible option for me. I have to think a bit more about this – but quickly since I imagine the 150 is going to go fast.

Thank you for the that Sara & Olly

Will

[cs1cjc]

On 25/04/2016 at 12:25, Retro Gear said:

Thanks DaveS for clarification on the Lanthanum – I looked on Wikipedia and found “La₂O₃ is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness” - confirming what you said

Will

This relatively short thread contains information on the design of the APM 140/7 FPL53 doublet http://www.cloudynights.com/topic/514293-apm-140mm-f7-doublet-test-data/.

The optical design is by Gerd Düring  a German amateur astronomer who also designed the APM/Lunt 152/8 and the APM coma corrected Barlow.  The design was checked by 2 different designers (one from Germany, one from USA) and the factory designer and all are agreement that it is good.  It is manufactured by Kunming United Optics.  It is a doublet with S-FPL53 and a a matching lanthanum crown glass, H-LAK7A from CDGM, a Chinese company.  The secondary spectrum is corrected to the level of 1/13200 of the focal length (for C/e/F) and the design polystrehl is 91.7 %, though in the case of my particular lens the secondary spectrum was not evenly split between C and F.

If you have time then this thread gives more information about visual ED refractor than most mortals need: http://www.cloudynights.com/topic/488766-apm-announces-140-mm-fpl-53-doublet/!

My and others experience of the scope appears here: http://www.cloudynights.com/topic/520337-apm-140mm-f7-is-on-its-way/.  There are a number of other thread on Cloudy Nightd with more discussion.

 

 

[ollypenrice]

5 hours ago, Retro Gear said:

Oh my hat – the Tak 150 on ABS sound remarkable – in fact at that price it would be a real bargain (it's only £1500 more than the 130 being sold). That said I am very reluctant to buy second hand since I simply would not know what to look for in a used piece of equipment. Experienced users would spot potential problems. I think at my level of experience buying new and getting some good support from the supplier – whilst obviously more costly – might be the sensible option for me. I have to think a bit more about this – but quickly since I imagine the 150 is going to go fast.

Thank you for the that Sara & Olly

Will

I would take an artificial star and an eyepiece and star test the scope. If it gives nice round diffraction circles just inside and outside focus and is OK from a 'wear and tear' point of view, with nothing nasty growing on the lenses and a sound focuser, I'd be in there!

Olly

[swag72]

5 hours ago, Retro Gear said:

Oh my hat – the Tak 150 on ABS sound remarkable – in fact at that price it would be a real bargain (it's only £1500 more than the 130 being sold). That said I am very reluctant to buy second hand since I simply would not know what to look for in a used piece of equipment. Experienced users would spot potential problems. I think at my level of experience buying new and getting some good support from the supplier – whilst obviously more costly – might be the sensible option for me. I have to think a bit more about this – but quickly since I imagine the 150 is going to go fast.

Thank you for the that Sara & Olly

Will

Someone who has that type of scope is going to look after it. If you check out the seller, Phil has sold many, many things on ABS and so would be considered to be one of the genuine sellers on there in my opinion.

At that price I would snap that up in a heartbeat if I was in a position to do so

[Retro Gear]

I don't normally drink in the afternoon but feel the need at the moment . I've just spotted another scope on UK ABS http://www.astrobuysell.com/uk/propview.php?view=111945 from a dealer in Birmingham (ENS Optical – not come across them before). What is going on – is this the way of things with second hand equipment (like buses - you never see one for ages then then three turn up at once).

Thank you Sara for the insight into the seller – do you know if he is a “dealer” or just someone with a taste for changing his equipment regularly ?

Olly – I would have to get my act together quickly and get the necessary test kit (that shouldn't be a problem – it would be more down to me to correctly do the testing – I'm still a real novice at this in spite of having a scope for a while).

Thinking hard guys – get back to you – and thanks again.

Will

[Retro Gear]

Chris C – thank you for the information – I'm looking at the threads now – the 140 looks a great scope – I'm assuming it's this one http://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/apm-doublet-ed-apo-140-f-7-fpl53-ota.html and very affordable. I'm tempted by the sudden occurrence of the various Tek & APM scopes on UK ABS – although my initial thought was to stick with a new one with warranty etc. and supplier support – having to rethink – thanks again.

 

Will

[cs1cjc]

1 hour ago, Retro Gear said:

Chris C – thank you for the information – I'm looking at the threads now – the 140 looks a great scope – I'm assuming it's this one http://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/apm-doublet-ed-apo-140-f-7-fpl53-ota.html and very affordable. I'm tempted by the sudden occurrence of the various Tek & APM scopes on UK ABS – although my initial thought was to stick with a new one with warranty etc. and supplier support – having to rethink – thanks again.

 

Will

Indeed, and also at: http://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AG140APO

[ollypenrice]

2 hours ago, Retro Gear said:

Chris C – thank you for the information – I'm looking at the threads now – the 140 looks a great scope – I'm assuming it's this one http://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/apm-doublet-ed-apo-140-f-7-fpl53-ota.html and very affordable. I'm tempted by the sudden occurrence of the various Tek & APM scopes on UK ABS – although my initial thought was to stick with a new one with warranty etc. and supplier support – having to rethink – thanks again.

 

Will

 

57 minutes ago, cs1cjc said:

Indeed, and also at: http://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AG140APO

I would, and without a nanosecond of hesitation, look at the ABS offerings first. But that's just me.

Olly