Has anyone had any experience of this scope?

[RobertI]

I am talking about the TS-PHOTON 6" F6 Advanced Newtonian from Teleskop Express. At F6 it is different to the standard F5 and F8 of Skywatcher, and I have always thought that an 6" F6 Newt is the ideal size for me the following reasons:

• Size: short enough to fit onto a modest mount for quick setup, not too long to become a sail in the wind
• Focal ratio: F5 can produce distortions towards the edge of the field with many eyepieces, so F6 likely to be better in this respect
• Focal length: A bit easier to reach higher mags for lunar planetary than the F5

What do people think? Is my logic correct, and is this a decent scope?

Thanks

Rob

 

Edited December 24, 2019 by RobertI

[Chris]

[dannybgoode]

You’re certainly right about the advantages of a 6” newt. I have the f5 SW 150P and really like it. Large enough aperture to be useful, small enough to be manageable.  You’re also right about the potential issues of an f5 although I notice them more when I try to image with mine rather than visual. 
 

An f6 is indeed an interesting proposition. If you do bite the bullet let me know what it’s like. 

[John]

My first newtonian was a UK made Astro Systems 150mm F/6. great scope and very versatile.

The TS one is probably made by GSO:

https://agenaastro.com/gso-6in-f6-newtonian-reflector-ota.html

GSO make the Meade Lightbridge dobsonians and the Revelation dobsonians too.

 

[bottletopburly]

oh F6 misread lols

 

[vlaiv]

I think @iPeace used one for lunar and it was very good.

There is a thread about it, but I can't find it right now. Here are couple of threads of that scope being mentioned:

 

[RobertI]

Thanks or the comments everyone. @vlaiv the link you referenced was very informative, the user seems very happy with the scope.

Just for a bit of background, the reason I am looking at this is that, apart from the occasional EAA session, most of my observing at present is of the quick and casual type, where I need to get out and observing as quick as possible to make the most of the little time I might have (like many of us I guess!). So I need a scope which:

• Is capable enough to see a wide range of objects in varying conditions
• Doesn't need much cooling
• Easily carried and quick to set up
• Can be rock solid in breezy conitions on a modest mount (probably my Skytee 2)
• Of late I have been enjoying doubles so resolving ability and nice 'tight' stars would also be ideal.

The nearest I currently have to meeting the above are my Heritage 130P and my Tal 100R. Both great performers, but both also limited (the 130P's helical focuser, and the Tal being an achro). These scopes have re-affirmed that either a decent 6" Newt or a 4" ED frac would hit the sweet spot for me. Sadly the 4" ED frac is too expensive for me at the moment, leaving a 6" Newt. But what about F-ratio? I feel that my F5 130P does well, but there is some fall off of sharpness towards the edge of the FOV, and with doubles, works best when the in middle of the FOV and when my head is in the right position over the e/p - I am putting this down to the fact that it is F5 (and possibly my Hyperion eyepieces not liking this), so thinking that F6 might be better in this regard.

To complicate things further, the Skywatcher F5 130P is £20 - £30 cheaper than the TS F6 equivalent and has more accessories, so is the F6 improved performance noticable enough to be worth the extra money over the F5?

[iPeace]

As @vlaiv mentions above, I've acquired and used a couple of newts from TS. The white one shown above is a 6" f/6 branded TS, made by GSO, and doesn't seem to be offered by TS any more.

I am inclined to assume that the PHOTON is assembled by TS from quality (GSO) parts, as is the 8" f/6 I got from them:

https://www.teleskop-express.de/shop/product_info.php/info/p5052_TS-Optics-8--f-6-UNC-Planet---Newtonian---Fused-Quartz-Mirror---Carbon-Tube---made-in-Germany.html

As to the effectiveness of f/6, it does work very well, but I've never used a faster newt, so I can't really compare. My f/6 newts are easy to collimate.

I also own a 6" f/8 - which, of course, has the same tube length as the 8" f/6.

So...I suppose it would be helpful if I could tell you that the 6" f/6 works just as well as the 6" f/8 - and is easier to transport and mount...

Well, I hesitate here. I haven't mounted them up together to see which was best. I've used both (on separate occasions) to observe the Moon, and I didn't notice any real difference. I guess the theory is that the f/8 should be better than the f/6 on Moon and planets, but from my little bit of ocean floor (we're below sea level) it doesn't seem to matter.

Anyway, it's a bit moot for me, as I've got the carbon 8" f/6 and the other two newts get no more use (you'd be welcome to try them out, it's just that pesky North Sea that's so inconvenient).

I can confirm that the 6" f/6 works well on a Losmandy AZ8 mount, and fully expect it to do equally well on a SkyTee.

I've reported on how well it works on doubles.

Best of luck.

[RobertI]

Thanks @iPeace, appreciate the response, your topics were very informative. Its good to know the Skytee is up to the job. I would love to come and have a go with the scope, ironically you are prbably closer to me 'as the crow flies' than most of the rest of the UK! As you say, pesky North Sea.

It seems, then, that there is no clear evidence on the differences between F5/F6. I tend to think if Skywatcher deemed F5 a suitable for visual, then F6 won't be noticably better. Then again, TS say they offer an F6 Newt specifically for visual (they also offer F4, F5 and F8 in the same range), and implies its better than the F5 for visual with its narrower secondary (45mm compared to 63mm of the F5) and matches the performance of a 4.5" APO (conterversial!). Interestingly the tube lengths and weights of the F5 and F6 are the same. 

Perhaps I'll have a chat to TS in the new year and see what they can do........

Edited December 25, 2019 by RobertI

[rl]

A few years ago I was mulling over exactly the same arguments. F/5 too short optically, F/8 too long

OO-UK made me a VX 6" f/6 specially to order with a 1/10 ultra grade mirror and small secondary. It's very light, easily portable, with stonking optics that really deliver given the usual Newtonian caveats. You can get away without a coma corrector with a lot of eyepieces. It will handle *200 on moon/ planets given a good night with ease. 

[RobertI]

7 hours ago, rl said:

A few years ago I was mulling over exactly the same arguments. F/5 too short optically, F/8 too long

OO-UK made me a VX 6" f/6 specially to order with a 1/10 ultra grade mirror and small secondary. It's very light, easily portable, with stonking optics that really deliver given the usual Newtonian caveats. You can get away without a coma corrector with a lot of eyepieces. It will handle *200 on moon/ planets given a good night with ease. 

The OO scope looks really nice, thought the prices look reasonable too, until I saw that VAT is not included 😡

Also includes a fan which I’m not sure I’d ever use, but super optics and something a bit different. 

Edited December 25, 2019 by RobertI

[iPeace]

9 hours ago, RobertI said:

It seems, then, that there is no clear evidence on the differences between F5/F6. I tend to think if Skywatcher deemed F5 a suitable for visual, then F6 won't be noticably better. Then again, TS say they offer an F6 Newt specifically for visual (they also offer F4, F5 and F8 in the same range), and implies its better than the F5 for visual with its narrower secondary (45mm compared to 63mm of the F5) and matches the performance of a 4.5" APO (conterversial!).

I went through this myself, and though I'm not much wiser, I don't mind sharing...

I've come to the realization - and one's milage will vary - that it's all compromise. Always. Unrelentingly. It's never going to be perfect - whatever that looks like, anyway. But if you do your homework, it will always be good enough to make you happy, ecstatic, even.

You pick your premium. Whatever's important to you - size, weight, cost, light grasp, resolution, cooling, collimation, mounting, transport, etc. - a solution is available for your priorities, and you'll love it, exactly because it fits.

Plenty of folks fully enjoy their f/5 (or even faster) scopes for visual. They've often chosen eyepieces and other accessories to match.

You know what you really want. Go for it.

[Chris]

Happy xmas all Robert, I'd be surprised if there wasn't a noticeable difference between f5 and f6. There is a huge amount of coma and focus depth difference between f5 and f4 I found woth 8" Newts, and when I had my F8 6" Dob I ran alongside my f5 6". The f8 was clearly sharper in the centre and much sharper at the edge, plus showed better contrast. I maintain that an 6" f/8 is like a 5" Apo with diffraction spikes. The contrast is only a touch less as the central obstruction is so tiny (Around 1/4th the obstruction of an equivalent SCT). 

[RobertI]

Thanks both. I think I am confusing things in my own head with too many variables, my original thought was a 130PDS which I could use on my Sky Prodigy and also use for EAA. Then I thought I have been doing in a lot of quick ‘manual’ observing of late, particularly doubles, so perhaps a 150PDS or 150P might be better, then I thought well perhaps F6 would be better for visual and more apo like, but then not really useable for EAA anymore. Yes, I really need to decide what I want!  Chris, now you are making me want an F8! 😂

Right now I’m enjoying my new McLaren 675LT! 👍

 

 

[vlaiv]

1 minute ago, RobertI said:

well perhaps F6 would be better for visual and more apo like, but then not really useable for EAA anymore.

Hm, how do you do your EAA? What sensor size do you use?

Don't see why you could not do EAA/EEVA with F/6 scope, small sensor and x0.5 reducer. I've done it with 8" F/6 scope. FOV is small, but it worked:

In fact it worked so well at the time, that I decided to do some imaging in that configuration and ended up with these:

There are all taken with 8" F/6 scope and x0.5 reducer and QHY5IILc camera. Notice absence of coma because of small sensor and F/6 scope.

Lodestar which is mono and has 50% larger width and height and much larger pixels (at least x2 in both width and height) is going to be much better.

[RobertI]

Thanks @vlaiv very useful to know this. I use a Lodestar mono, I was thinking that the F6 might not have enough inward focus for imaging with a reducer (as it’s not optimised for AP) but looks like it would be ok? I currently use an RC6 with good results, but it seems overly complex for EAA and I can’t help thinking a newt would be easier and I can use it for visual too. 

Edited December 25, 2019 by RobertI

[vlaiv]

42 minutes ago, RobertI said:

Thanks @vlaiv very useful to know this. I use a Lodestar mono, I was thinking that the F6 might not have enough inward focus for imaging with a reducer (as it’s not optimised for AP) but looks like it would be ok? I currently use an RC6 with good results, but it seems overly complex for EAA and I can’t help thinking a newt would be easier and I can use it for visual too. 

Reducer that I used is this one:

https://www.teleskop-express.de/shop/product_info.php/info/p676_TS-Optics-Optics-TSRED051-Focal-reducer-0-5x---1-25-inch-filter-thread.html

It is 1.25" screw on reducer that can be easily sunken into focuser tube. I actually flipped lens on mine - it gave better stars in that configuration (I unscrewed retaining ring - took the lens out, reversed direction and returned it in the cell).

This reducer has focal length of about 101mm-103mm (source AgenaAstro website), which means that it should be placed at about 51mm away from sensor for x0.5 reduction (this is from lens itself - not from thread on cell).

When used like that, required inward focus travel is

50mm.

TS website says that focus position is approximately 50mm above 2" receptacle

I did not have issues with my 8" F/6 scope and focusing, but that might have been because camera at the time was 1.25" body type and could be sunken into 1.25" nosepiece adapter together with reducer.

[RobertI]

Thanks @vlaiv, I’ve never considered one of these, certainly more straight forward than any of the reducers I have, and solves any potential in focus issues, thanks for the heads up!