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Light & Short APO refractor for Star Adventurer


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Hi,

I've just spent yesterday evening doing some tests on my current setup, mainly my ASI1600mm (with RGB filters), and a 200mm Super Takumar, to verify how much chromatic aberration I've got for each stop.

The results were quite discouraging :(

I've always noticed in my shots a very bad halo, but I hoped that maybe closing it a little more it might have helped, but even at f/16 I got a very noticeable difference in star size between each channel.

 

So, long story short, I'm looking for a new scope for AP, I'd say an APO, with a short focal length, and lightweight (the star adventurer doesn't really like long focals, and heavyweight champions).

I couldn't find many scopes matching these requirements, but I've got my eyes on these three:

TS Photoline 70mm f/6 FPL53 Triplet Apo

Pros:

  • cheap
  • very lightweight (1.86 KG)

Cons:

  • Slightly too long (I planned to buy a focal reducer anyway, a 0.8 would put me at  336 mm)
  • No flat field (would be fixed by the reducer, but I'd need to buy another corrector if I'd ever want to use it at full focal length)
  • Slightly too slow (f/6)

TS-Optics Photoline 72 mm f/5,5 FPL53 Apo

Pros:

  • Faster (f/5.5)
  • Shorter focal length (400mm, 320 with the reducer)

Cons:

  • Slightly more expensive (not a big deal)
  • Doublet instead of triplet (could this be a problem?)
  • Slightly heavier
  • No flat field (see previous scope)

TS-Optics Imaging Star71

Pros:

  • Even shorter (347mm)
  • Fast (f/4.9)
  • Already corrected for flat field
  • Quadruplet, no ca and flat field advertised

Cons:

  • *a lot* more expensive
  • 347mm is still slighly too long. How could I reduce this even further? Most focal reducer are also corrector (which I don't want to). Could a cheap corrector like this do the job?

 

Just by reading the specs, I'd say the Imaging Star 71 should be the winner.

But the price is almost the double of the 72mm, and I'm wondering wether I'd really need the extra flat field correction (I'd be using it mainly with the focal reducer, to improve tracking with the Star Adventurer, and even with the native focal length, how much will the field curvature affect my image, given my sensor has a diagonal of only 21mm?)

 

The 72mm is a tempting alternative, particularly since with the reducer/corrector (0.79) I'd have a wonderful 316mm focal length and a fast f4.3 ratio.

The reducer/corrector surely is much more expensive than the plain reducer with no correction (but I'm still wondering if that one is a good choice, given the small price), but not as expensive as the Imaging Star 71mm. I'm just a bit worried about the "not triplet" point, and wondering if I'll ever use it without the reducer.

Basically, even buying the 72mm with both the reducer/corrector and the corrector alone, I'd still be cheaper than the 71mm.

Unfortunately I haven't been able to find many imges or reviews done with this scopes... this might help a lot, but no luck so far!

 

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Slight concern of the TS Imaging Star 71 is that it basically has to be a clone of the WO Star 71, and it is a copy of the original 5 element one which was gpod but the optical alignment/collimation of the many elements really needed to be done - FLO went to Ed Reid for this and that improved matters considerably. TS cannot do that. As it already has a reducer in place you will have to live with how it comes.

Don't know about the TS Photoline, they appear good however seems not many get mentioned as in use, probably worth asking in the Imaging specific section about either of these.

Why not f/6 out of interest. Fast causes other problems as the spherical surfaces are less ideal the faster the lens. Usually the faster the objective the greater the problems that get mentioned, both mirrors and lens.

There is the WO ZS1, that is £400 and the Flatenner another £150. Doublet only but reports appear good.

Edited by ronin
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I recently bough the William Optics Zenithstar 61 APO, and it's pretty good. As Ronin said, it's only a doublet, but from quick tests in a light-polluted area I am impressed enough with it.

It's 360mm in FL, and the flatener is a 1:1. It is also F/5.9, so maybe doesn't tick your boxes, but the build quality is pretty good.

Edit: At 1.45kg it is very light, which would be my primary concern on the SA.

Edited by agthomson
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3 minutes ago, ronin said:

Slight concern of the TS Imaging Star 71 is that it basically has to be a clone of the WO Star 71, and it is a copy of the original 5 element one which was gpod but the optical alignment/collimation of the many elements really needed to be done

@ronin the TS Imaging Star 71 is a four element scope, different design to the original 5 element.

http://www.teleskop-express.de/shop/product_info.php/info/p7085_TS-Optics-Imaging-Star71---71mm-f-4-9-Imaging-APO.html

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Thanks everyone. 

I was also considering the WO ZS61 and 71 (and similar from TS), but they're all FPL51 doublets, and I've read discordant reviews about them, some complain about residual CA.

All those I've linked are FPL53 doublets or triplets, which *should* (but not necessarily of course) limit a lot the amout of CA.

I was also considering a 60mm instead of a 70, but you know.. the bigger, the better :D

And same goes for f/6 vs f/5: if possible, I'd like to get the larger scope with the shorter focal length. I have doubts about how much my Star Adventurer can keep up with focal length over 300mm, particularly with slower f ratios (I'd need longer exposures, hence better tracking).

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@ziofrancotto ciao :)

That's another one I was evaluating. But the same applies: would I really need a field corrector with a small-ish diagonal of 21.5mm?

If so, I'd need to buy the scope itself, the reducer/corrector, and the separate corrector for the native focal length.

A 70mm is slightly more tempting, as I could go with further focal lengths (around 320 with reducers, and around 400 without), but again, with a shorter focal length range (320mm and 250mm) it might be easier on the star adventurer.

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2 hours ago, GuLinux said:

I was also considering the WO ZS61 and 71 (and similar from TS), but they're all FPL51 doublets

The WO61 is fpl53 synthetic fluorite. This would be my choice for the SA due to optical quality, weight, and focal length. The 71 is fpl51 so semi apo. 

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1 minute ago, Lockie said:

The WO61 is fpl53 synthetic fluorite. This would be my choice for the SA due to optical quality, weight, and focal length. The 71 is fpl51 so semi apo. 

Very interesting, didn't notice that... Thanks! It might be an eccellent player in the game :)

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I made up my mind: just bought the TS Photoline 60mm.

It was a really close match with the WO 60mm, but I'd rather stay safe with the lower focal length.. I already have enough trouble with polar alignment with my current 200mm!

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  • 6 months later...
On 9/22/2017 at 09:58, GuLinux said:

I made up my mind: just bought the TS Photoline 60mm.

It was a really close match with the WO 60mm, but I'd rather stay safe with the lower focal length.. I already have enough trouble with polar alignment with my current 200mm!

How's that 60mm working out?

 

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13 hours ago, View2 said:

How's that 60mm working out?

Unfortunately there's no setting on it to force a clear sky :(

I was able to do a couple of tests from the city, the best of which was this: https://www.astrobin.com/333208/?nc=user

Slightly overprocessed, and with a huge amount of light pollution, but gives an idea of stars size, residual CA, etc.

Overall, I think I can be very satisfied. Waiting for a real test though! :)

 

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  • 3 months later...

Hi,

I haven't really been really productive this year, mostly because of the weather, although I admit my laziness didn't really help as well ?

 

Tests were good though, I think this is the only one I've published so far: https://www.astrobin.com/333208/?nc=user kinda overexposed/overprocessed, but otherwise ok.

 

I'm using the scope unguided, with a 0.79 flattener/reducer (hence ~260mm focal length). This means you'd have to push towards shorter high gain exposures rather than longer subs. Also polar alignment is relatively painful and delicate, you really need to be as accurate as possible, and the Star Adventurer wedge is not that stable. Overall doable, though, with lots of care. I also bought one of these to help the process: https://www.amazon.co.uk/gp/product/B00KR5VSEA/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

 

If I get polar alignment good, and get to not shake the tripod too much after alignment (this one is the real challenge, as you of course will need to point the scope) I can get a 60sec exposure without any noticeable trail, maybe something more (90/120 secs).

I'm now mainly concentrating on the software setup, I've being developing this: https://github.com/GuLinux/StarQuew which is particularly suited if you want to run on a headless board (raspberry pi and similar) or a small laptop.

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Thanks for the reply! I know what you mean by weather and laziness.... when you do get a good night a lot time other things have come up right? 

It feels like it’s a bit of a pain in the ass the whole process.... Like said I was planning on getting the WO61 with my QHY8L on either this mount or the SkyGuider Pro and a 50mm guide scope, mainly for traveling purposes or when the big setup is making long exposures. But if it is that hard to get any good shots, it might not be worth the trouble.... 

 

keep us us posted if you make some more pics. The m42 looks cool!!

Edited by Obi Wan Ken00bi
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I've used a Sigma 70-300 DG Macro APO lens for Canon cameras. This lens is just about $150 and has 3 ED elements in it as part of the 13 elements. Absolutely no CA, no halos etc. I'd recommend that for a ASI1600 because of the image scale and compatibility with the SA. 

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9 hours ago, Obi Wan Ken00bi said:

Thanks for the reply! I know what you mean by weather and laziness.... when you do get a good night a lot time other things have come up right? 

It feels like it’s a bit of a pain in the ass the whole process.... Like said I was planning on getting the WO61 with my QHY8L on either this mount or the SkyGuider Pro and a 50mm guide scope, mainly for traveling purposes or when the big setup is making long exposures. But if it is that hard to get any good shots, it might not be worth the trouble.... 

 

keep us us posted if you make some more pics. The m42 looks cool!!

I wouldn't say it's too difficult... you just need to know that the higher the focal length, the more careful and precise you have to be.

The WO61 looks like a very nice scope, and I was undecided between the two. I opted for the TS because of the (slighly) lower focal length. But the difference is not too much, and by using a focal reducer you'll be fine.

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  • 6 months later...
On 24/07/2018 at 06:17, astrosathya said:

I've used a Sigma 70-300 DG Macro APO lens for Canon cameras. This lens is just about $150 and has 3 ED elements in it as part of the 13 elements. Absolutely no CA, no halos etc. I'd recommend that for a ASI1600 because of the image scale and compatibility with the SA. 

Last post awhile ago, but here goes.

Interested in your choice of lens to fit to the ASI1600. I have used the stock canon lens but these give me really bad stars away from the centre of the image, even when stopping down the lens. Presumably with the Sigma lens this works out fine? 

Any other views on the best Canon fitting lens to provide the best match for the ASI1600?

thanks

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43 minutes ago, alcol620 said:

Last post awhile ago, but here goes.

Interested in your choice of lens to fit to the ASI1600. I have used the stock canon lens but these give me really bad stars away from the centre of the image, even when stopping down the lens. Presumably with the Sigma lens this works out fine? 

Any other views on the best Canon fitting lens to provide the best match for the ASI1600?

thanks

Don't know about the best, but from what I've heard Samyang 135mm F/2 is held in high regard for wide field with ASI1600 (and other sensors).

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  • 1 year later...
On 08/04/2018 at 03:50, View2 said:

I just ordered the 72mm f/5.5 apo(doublet, we'll see....) along with the TS 0.79x ff/fr and appropriate spacers. ...... waiting for the weather.

Dear friend, 

May I ask you about the impressions from this scope? I am also interested in buying and though I searched in the internet, I haven't found much info. 

Are you satisfied with the performance of the telescope in photography and observation, as it is only a doublet ? Does it work well with the Star Adventurer or its too heavy? And I would like to ask you whether you have tried it with a binoviewer: in the TS site they mention that its possible to focus using a binoviewer and extension rings that are included in the box. 

Unfortunately I dont know the brand of this bino, as its a gift...

 

Many thanks! 

Aris

 

 

 

Edited by Aristeidis Bottas
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  • 2 weeks later...

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