Refractor for imaging with full-frame sensor

[Max N]

I currently have a Celestron Edge 800 on an AVX mount which I use mainly for imaging. It was a bit of a steep learning curve but I'm getting some reasonable results now.

I want to buy another scope for bigger targets. Playing around with FOV simulation tools, I think that I need a focal length of about 600mm to frame most of the bigger targets nicely with my full-frame sensor. At the moment I'm only looking at refractors. I would prefer a scope with integral flattener, so that spacing isn't an issue. So I have come up with the following parameters for my new scope:

• 600mm focal length give or take a bit
• Fully illuminate a full-frame sensor
• Integrated flattener
• Decent focuser that won't need upgrading
• OK on an AVX mount

Although it seemed at first like there were loads of refractors out there, once I applied all of the above the choice narrowed dramatically. In the end I could only find two candidates:

• TS-optics Imaging Star 100 (aka TSAPO100Q)
• Takahashi FSQ106 family

Both of these are more money than I originally planned to spend, but if necessary I will just have to save my pennies. The Tak would definitely need to be secondhand. I would be grateful for any advice/input from anyone who has gone down this route before.

Are there any other choices I should consider?

If I went for the TS-otics scope, where would be the best place to buy it from? I'm in the UK. Am I better off buying from a UK dealer, or direct from Teleskop-Express? Most users of this scope are very happy and there are some excellent images online taken with this scope, but there is always the risk of getting a less-than perfect example. Ideally I would like a pre-inspection report and/or tune-up, but I'm not sure if that is available anywhere with this scope.

Thanks for any input

 

 

[Tim]

Get a Skywatcher Esprit?

[Max N]

9 hours ago, Tim said:

Get a Skywatcher Esprit?

Hi Tim. Yep, I had a good look at the Esprit 100, but the image circle is only 40mm, and it doesn't have an integral flattener. It does have a very good reputation, and I like the fact that FLO and a few other places offer the pre-inspection. The others in the range are not the right focal length.

In the end I may have to compromise somewhere, but the TSAPO100Q does tick all the boxes - at a cost...

[RayD]

9 hours ago, Tim said:

Get a Skywatcher Esprit?

That's funny as that was my thought earlier, but I thought I'd better not suggest it as people will begin to think I'm on a commission with them 

With the dedicated flattener spaced at 55mm I get perfect corner stars on my 16200 (APS-H) chip on my 100.  Don't forget you'll need 2" fillers. 

[Tim]

Always remember it is very difficult to manufacture a four or five lens telescope which maintains a flat field over a range of temperatures.

Those that work are worth the money.

Did you consider the Vixen VSD100?

http://www.skyatnightmagazine.com/review/telescopes/vixen-vsd-100-f38-astrograph

Whether it is suitable will depend on your camera, colour or mono. It yields a very very flat image, but do read Steve's review.

[Max N]

12 hours ago, Tim said:

Always remember it is very difficult to manufacture a four or five lens telescope which maintains a flat field over a range of temperatures.

Those that work are worth the money.

Did you consider the Vixen VSD100?

http://www.skyatnightmagazine.com/review/telescopes/vixen-vsd-100-f38-astrograph

Whether it is suitable will depend on your camera, colour or mono. It yields a very very flat image, but do read Steve's review.

Yes, I looked at the Vixen. Tring Astro had one on clearance a few weeks ago, which was tempting. But in the end I decided the focal length was just too short. 600 would be ideal, I might come down to 500, but 380 is too much of a compromise.

[Tim]

Did you know they do a X1.58 tele extender for it? That would give you 600mm, not sure what it would do to the image circle though.

It must sound like I am trying to talk you out of the TS scope, which I am not

[Max N]

No worries Tim, its always good to get some input. Tbh, there's no way I could afford the Vixen anyway, and the tele would probably add on best part of £1000 on top :-)

It is looking like a choice between the TS and a secondhand Tak...

 

[ollypenrice]

We use a pair of Tak FSQ106Ns here, with 530mm focal length. These are the older models with the 'F' standing for fluorite. These don't take the focal reducer but don't suffer the extreme focus-temperature drift of the later models and, being unfashionable, they are remarkably affordable. From memory the pair we have here came in at about £2000 and £2500, one of them being newer. Their performance is identical - and excellent. They have no trouble covering the full frame CCDs we use, though even 2 inch unmounted filters vignette. Flats easily correct this, though. If I had to choose a pair of scopes to do the same job I would simply choose the FSQ106N again. They just work. (Minor miracle in this game!)

Olly

 

[Uranium235]

I know it goes against the OP, but wouldnt it make more sense to upgrade the mount before putting an expensive telescope on it? An AVX might be fine for planetary, but with a heavy load it may not be suitable for exposures of 15min+. I cant see the TS or Tak being what I would call "light", well... not light enough to get a 100% hit rate from an AVX (especially when loaded up with a guidescope and camera etc...).... just my 2p worth

I used to own the previous model to the AVX (the CG5), and although it has been improved - I cant see it moving on that much to make it comparible to an HEQ5 or 6... not unless theyve done some serious upgrades (I think it still runs on servo motors though). With my old mount, about 5kg was the limit to get a good enough hit rate (ie: amount of useable subs).

 

[Max N]

12 hours ago, ollypenrice said:

We use a pair of Tak FSQ106Ns here, with 530mm focal length. These are the older models with the 'F' standing for fluorite. These don't take the focal reducer but don't suffer the extreme focus-temperature drift of the later models and, being unfashionable, they are remarkably affordable. From memory the pair we have here came in at about £2000 and £2500, one of them being newer. Their performance is identical - and excellent. They have no trouble covering the full frame CCDs we use, though even 2 inch unmounted filters vignette. Flats easily correct this, though. If I had to choose a pair of scopes to do the same job I would simply choose the FSQ106N again. They just work. (Minor miracle in this game!)

Olly

 

Thanks Olly, that’s good to know. I will look out for a Tak FSQ106N. Although your recommendation may make them a bit more fashionable/pricey :-)

[Max N]

11 hours ago, Uranium235 said:

I know it goes against the OP, but wouldnt it make more sense to upgrade the mount before putting an expensive telescope on it? An AVX might be fine for planetary, but with a heavy load it may not be suitable for exposures of 15min+. I cant see the TS or Tak being what I would call "light", well... not light enough to get a 100% hit rate from an AVX (especially when loaded up with a guidescope and camera etc...).... just my 2p worth

I used to own the previous model to the AVX (the CG5), and although it has been improved - I cant see it moving on that much to make it comparible to an HEQ5 or 6... not unless theyve done some serious upgrades (I think it still runs on servo motors though). With my old mount, about 5kg was the limit to get a good enough hit rate (ie: amount of useable subs).

 

Good points. I was initially worried about the weight of these scopes on my AVX, but have convinced myself it is worth trying, for the following reasons:

• My AVX is giving me acceptable (to me) results at 2032mm focal length, although definitely not 100% hit rate at 15min+. This is on deep sky targets, not planetary. I figured that at 600mm things would get easier.
• My imaging gear is very light, just a Sony a7s plus whatever spacers/adapters I’d need. No filter wheels, OAGs or anything. So the all-up weight shouldn’t be too bad.
• I have seen some very nice images taken with the TSAPO100Q on an AVX, so I know that the combination can work.

[Tim]

Ah, the Vixen perhaps wouldn't serve you well anyway with a colour camera, at least not the one that Steve and I tested, it was a smidge off being truly apochromatic.

The Tak sounds like the perfect solution

[newbie alert]

A avx has a very similar payload to a heq5 and more than happy with a 600fl ed80 on mine..it tracks very nicely..whether it changes much with a 4 inch scope with a bit more weight on it I don't know but it be very similar to a eq5 payload wise..

[kirkster501]

On 10/6/2017 at 19:48, ollypenrice said:

We use a pair of Tak FSQ106Ns here, with 530mm focal length. These are the older models with the 'F' standing for fluorite. These don't take the focal reducer but don't suffer the extreme focus-temperature drift of the later models and, being unfashionable, they are remarkably affordable. From memory the pair we have here came in at about £2000 and £2500, one of them being newer. Their performance is identical - and excellent. They have no trouble covering the full frame CCDs we use, though even 2 inch unmounted filters vignette. Flats easily correct this, though. If I had to choose a pair of scopes to do the same job I would simply choose the FSQ106N again. They just work. (Minor miracle in this game!)

Olly

 

I am on the lookout for one of those 106's for the larger imaging circle.  They are not cheap and do not come up used very often.  You need to be on ABS regularly and get in there early.  I recently missed out on one....

[Wiu-Wiu]

On 6 oktober 2017 at 23:01, Uranium235 said:

I know it goes against the OP, but wouldnt it make more sense to upgrade the mount before putting an expensive telescope on it? An AVX might be fine for planetary, but with a heavy load it may not be suitable for exposures of 15min+. I cant see the TS or Tak being what I would call "light", well... not light enough to get a 100% hit rate from an AVX (especially when loaded up with a guidescope and camera etc...).... just my 2p worth

I used to own the previous model to the AVX (the CG5), and although it has been improved - I cant see it moving on that much to make it comparible to an HEQ5 or 6... not unless theyve done some serious upgrades (I think it still runs on servo motors though). With my old mount, about 5kg was the limit to get a good enough hit rate (ie: amount of useable subs).

 

As for maximum load for an AVX: I have mine bearing a 5" apo triplet (the maxvision series), with upgraded moonlite focusser, and an Orion shorttube guidescope, and although I have reached the limits of my mount (I had to get a second counterweight to balance it off), I get better guiding results than with a lighter telescope. They are not 100% though, and I only make 5 minute subs. I usually have to get rid of about 1 sub per hour worth of lights.

if I get another mount, it will be because of sturdiness or even more precision, not because it fails me (probably because I wanted a bigger scope)

 

Most people who have this scope have upgraded the focuser already, so it is full frame ready. No flattener included though. I'm looking into that for when I'm ready to go full frame myself.

but I bet this is a good value scope and if you can find one second hand, it will fit quite a bit of your demands.

 

good luck!

[Uranium235]

42 minutes ago, Wiu-Wiu said:

As for maximum load for an AVX: I have mine bearing a 5" apo triplet (the maxvision series), with upgraded moonlite focusser, and an Orion shorttube guidescope, and although I have reached the limits of my mount (I had to get a second counterweight to balance it off), I get better guiding results than with a lighter telescope. They are not 100% though, and I only make 5 minute subs. I usually have to get rid of about 1 sub per hour worth of lights.

if I get another mount, it will be because of sturdiness or even more precision, not because it fails me (probably because I wanted a bigger scope)

 

Most people who have this scope have upgraded the focuser already, so it is full frame ready. No flattener included though. I'm looking into that for when I'm ready to go full frame myself.

but I bet this is a good value scope and if you can find one second hand, it will fit quite a bit of your demands.

 

good luck!

At payload of ~5 or 6kg with the CG5 I was regularly doing 10 or 15min subs, and when it behaved it could do a whole night without dropping a sub. Apart from the meridian flip - as the CG5 didnt much like guiding through it (though I believe that has been fixed with the AVX). Having said that, I did strip mine down and tweak it a bit.

Its worth getting a bigger mount becuase then you can go for 100% all night, every night the only thing that stops it is cloud (and perhaps the odd gale or two!). Plus a heavier mount will be more of a "setup and walk away" affair, without you having to constantly watch a PHD graph for backlash.

[Wiu-Wiu]

True. When portability is not much of an issue (or money  ). I think the AVX is a good deal, maybe I am Lucky with mine, but I have to say that since I curbed PHD and switched to MGEN my guiding has been WAY better.

I have chosen to invest my budget to upgrade my scope, when I have enough experience I might consider an upgrade for my mount. it is as you say: setup and walk away... apart for the occasional check of cables and focus, I can pretty much leave it and do other things.

After that.. I might get an acute case of Aperture Fever.

[Max N]

I have just spotted the TSAPO85Q on the teleskop-express site. Is this a new scope? The focal length is slightly shorter than I wanted but it ticks all the other boxes. I think this might be the one for me!