Takahashi v APM optical quality

[DRT]

At some point in the not too distant future I plan to buy a high quality refractor for visual use. I have been researching the pros and cons of the various Tak OTAs and came across a post on CN which alerted me to the fact that APM sell their objective lenses and cells to allow them to be used in DIY scopes. 

If I buy a Tak it is likely to be the TSA120 with the FT focuser, which is knocking on the door of £5k. However, if I fitted the APM Doublet ED Apo 152 f/7.9 Lens Cell to my SW Evostar 150 it would cost around £2k. I already have a Moonlight focuser that could be fitted to the SW OTA so that would give me a pretty awesome ED scope.

The question is, are the optics in a Tak materially better than the APM?

 

[Timebandit]

 

Hi . what about an Esprit 120.

By all accounts these are supposed to be extremely good. And at around 2k new could be well Worth considering

Or even the Esprit 150 , these are around 4k new . So still well below the  5k Tak TSA120

 

 

.

 

[John]

13 minutes ago, DRT said:

The question is, are the optics in a Tak materially better than the APM?

 

From the optical tests I've seen of the APM's I'd say that they are good but not quite as good as Taks. I'm generalising but I reckon the average APM 150 F/7.9 would have strehl ratio of around 0.93 to 0.95 or something like that wheras Tak TSA120 examples has been measured at around 0.97 to 0.98 or even better.

Now whether these figures matter to you is another question ......

 

[DRT]

3 minutes ago, Timebandit said:

Hi . what about an Esprit 120.

By all accounts these are supposed to be extremely good. And at around 2k new could be well Worth considering

Or even the Esprit 150 , these are around 4k new . So still well below the  5k Tak TSA120

Oh dear, what have I done?...

 

[DRT]

3 minutes ago, John said:

From the optical tests I've seen of the APM's I'd say that they are good but not quite as good as Taks. I'm generalising but I reckon the average APM 150 F/7.9 would have strehl ratio of around 0.93 to 0.95 or something like that wheras Tak TSA120 examples has been measured at around 0.97 to 0.98 or even better.

Now whether these figures matter to you is another question ......

 

Good to know, John, thank you.

Are those figures for the APM based on their standard ED doublet or the LZOS triplet?

[John]

1 minute ago, DRT said:

Good to know, John, thank you.

Are those figures for the APM based on their standard ED doublet or the LZOS triplet?

Thats the standard APM ED doublet. The LZOS lensed scopes are definitely in the Tak league and with prices to match

[DRT]

I've just noticed this in the APM sale: https://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/apm-doublet-ed-apo-152-f-7.9-ota

?

[DRT]

6 minutes ago, John said:

Thats the standard APM ED doublet. The LZOS lensed scopes are definitely in the Tak league and with prices to match

Thanks. Do you know what the strehl range would be for a typical Chinese ED refractor such as the SW ED120 (or forthcoming ED150)?

 

[John]

You can get the APM 152 ED doublets for around £2K pre-owned or even a touch less. The early ones had some issues with objective cell design though, which ahve been rectified with the more recent ones I understand. I've considered a few used ones but the prospects of a troublesome objective cell put me off I have to say. 

 

[John]

1 minute ago, DRT said:

Thanks. Do you know what the sterol range would be for a typical Chinese ED refractor such as the SW ED120 (or forthcoming ED150)?

 

I've seen ED120's tested varying between 0.94 and 0.96 strehl and even as good as 0.98 and 0.99 strehl.

I've no idea about the forthcoming ED150 of course but Synta know that it can't be a dud.

 

 

 

 

[DRT]

12 minutes ago, John said:

I've seen ED120's tested varying between 0.94 and 0.96 strehl and even as good as 0.98 and 0.99 strehl.

I've no idea about the forthcoming ED150 of course but Synta know that it can't be a dud.

That is pretty amazing about the ED120 given the range you quoted for an APM equivalent that costs 3x the price!

I must confess I am an aperture freak so in the end I might spend my money on a SW ED150 plus a smaller second hand Tak ? 

[John]

3 minutes ago, DRT said:

That is pretty amazing about the ED120 given the range you quoted for an APM equivalent that costs 3x the price!

I must confess I am an aperture freak so in the end I might spend my money on a SW ED150 plus a smaller second hand Tak ? 

The difference between, say 0.93 an 0.98 strehl are probably more or less undetectable to most observers I reckon Derek so the APM 152 doublets are pretty good scopes considering their cost.

When I want aperture I have my 12" dob. It outperforms all my refractors when the conditions are decent and cost considerably less than they did !

I still might be tempted by a 6" frac again at some stage but then again, maybe not

 

[25585]

If buying a suitable mount for one was not an added expense, the 150 would appeal to me. But buying yet another mount, almost doubling expenditure was the big deterrent.

 

[DRT]

8 minutes ago, John said:

When I want aperture I have my 12" dob. It outperforms all my refractors when the conditions are decent and cost considerably less than they did !

My problem is that the high fences trees and and bushes that surround my garden mean that my VX12 F4 Dob can only be pointed at anything higher than about 50 degrees above the horizon. My fracs can reach much lower objects and I have come to prefer using them rather than reflectors. 

The truth is, I’m just confused ? 

[DRT]

2 minutes ago, 25585 said:

If buying a suitable mount for one was not an added expense, the 150 would appeal to me. But buying yet another mount, almost doubling expenditure was the big deterrent.

 

My mount already handles two 150s side by side, so that’s not an issue. My dilemma is what to look through ?

[Stu]

As John says Derek, LZOS and Tak are similar, nowt to choose between them really.

To confuse matters, how about a used TEC140 for a similar money?

I think that in similar circumstances I would want an LZOS 130mm like John’s, having used the Tak 100, I do think top quality optics really deliver, particularly at higher mags with good seeing.

Having said all that, the Esprit 150 is pretty tempting for that price.

No wonder you are confused!  

[Louis D]

I've often wondered if AP's scopes are in the same league as Taks and worth the long wait times.

[Uplooker]

6 minutes ago, Louis D said:

I've often wondered if AP's scopes are in the same league as Taks and worth the long wait times.

They do come up 2nd hand quite regularly, not like buses though.

[Stu]

10 minutes ago, Louis D said:

I've often wondered if AP's scopes are in the same league as Taks and worth the long wait times.

I reckon they are Louis, I would have a 130mm Gran Turismo anytime I could afford it!

[DRT]

Are AP and APM the same thing?

comments elsewhere suggest not!

[Stu]

10 minutes ago, DRT said:

Are AP and APM the same thing?

comments elsewhere suggest not!

No, very different.

AP is AstroPhysics, US company founded by Roland Chretien.

http://www.company7.com/astrophy/index.html

APM is a German company founded by Marcus Ludes

http://www.apm-telescopes.co.uk/apm-history.html

[DRT]

1 minute ago, Stu said:

No, very different.

AP is AstroPhysics, US company founded by Roland Chretien.

http://www.company7.com/astrophy/index.html

APM is a German company founded by Marcus Ludes

http://www.apm-telescopes.co.uk/apm-history.html

That's what I thought. I was just a bit confused by @Louis D's comments regarding waiting times as I thought he might be referring to APM.

[Stu]

Just now, DRT said:

That's what I thought. I was just a bit confused by @Louis D's comments regarding waiting times as I thought he might be referring to APM.

Ah yes, I see that now!

[John]

One APM branded scope that has long intrigued me is the 140mm F/7 doublet. It uses an FPL-53 element in the objective:

http://www.peak2valleyinstruments.co.uk/page_3615969.html

 

[JeremyS]

4 minutes ago, John said:

One APM branded scope that has long intrigued me is the 140mm F/7 doublet. It uses an FPL-53 element in the objective:

P2V has has an ex-demo one of these on offer for a while, but now sold.

Wasn't you was it John?