Author Topic: Fast Telescope  (Read 993 times)

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Carole

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Fast Telescope
« on: Jul 03, 2020, 10:31:50 »
Using the Samyang lens has really spoilt me, and I am now looking for a fast refractor and possibly a triplet as I never seem to get the nice sharp stars others get.

Takahashi's are cost prohibitive, but I have found this scope this morning and apart from the fact that I can't see anywhere to mount my finder guider, it looks ideal.  (I have shot off a few questions to them).

It says you can capture the same data in half the time and I have indeed had to lower the LRGB times (when I have used them on the Samyang lens) otherwise I get a completely white and blown out sensor.

Just wondered whether you guys had any thoughts or opinions on this before I press the buy button:
https://www.teleskop-express.de/shop/product_info.php/info/p7224_TS-Optics-Imaging-Star-80-mm-f-4-4---6-element-Flatfield-APO-Telescope.html

TS-Optics Imaging Star 80 mm f/4.4 - 6-element Flatfield APO Telescope



Carole   

RobertM

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Re: Fast Telescope
« Reply #1 on: Jul 03, 2020, 11:52:08 »
You need to think about focal length with your sensor first to get the field of view you want.  Once that’s decided then the choice is on...

Personally I have not been over enamoured with SW scopes but the Esprit 150 has made me rethink that.  If I was looking right now it would be between the Esprit 80 (f/5) and 100mm (f/5.5) scopes and then get a decent reducer like the Apex to increase the field of view.  With the Imaging Star I’m sure you will be limited to 360mm focal length... worth thinking about if you want to cover different objects.

Robert

Carole

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Re: Fast Telescope
« Reply #2 on: Jul 03, 2020, 16:11:58 »
Thanks Robert, I did look at the Esprit scopes first. 

I am thinking of keeping roughly to the 80mm aperture, but might consider the 100mm but would like to see the latter first as if it is too long I don't want to end up with pier/tripod clash like I get with my ED120.  Or maybe I can find out the length.

The Esprit 80 doesn't come with tube rings so i can mount a 2nd scope piggy back (dual rig), and both come with a soppy little foot so you'd have to add a longer dovetail to get balance, and apparently fitting another dovetail is not simple (so i have read) something about having to get one specially made),

The Esprit 100 is a better design, it has the tube rings I would want,  but comes with a Losmandy dovetail plate also a stupidly short length - I need Vixen.

I am not all that handy with adapting things, so really need to get the features that I need. 

I haven't ruled them out though, but might need to actually see them, chat with vendor.

I have also posted up this same question on SGL and one imager posted up a rather problematic report on the scope I first mentioned.  So may have to re-think anyway.

Many thanks for your reply and I will certainly give it some thought and maybe see what First light optics can come up with as regards measurements and perhaps changing the dovetail for me on those Esprits.

Carole

« Last Edit: Jul 03, 2020, 19:30:39 by Carole »

NoelC

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Re: Fast Telescope
« Reply #3 on: Jul 04, 2020, 11:46:09 »
Carole
Why are you looking at f4.4 when you have been working at f 2.4?
Would have thought you wanted something a little faster; noticed this yesterday:-
https://astronomynow.com/2020/05/27/sharpstar-d-150mm-f-2-8-hnt-an-imaging-telescope-with-sharp-vision/
Comes with a vixen style shoe for your guidescope.
The spot diagrams look impressive (if I'm reading them correctly), maximum spot of 25µm v the SED-80 at 42µm at 15mm diameter)http://www.sharpstar-optics.com/index.php/en/150F28/240.html
Any use?

Doesn't Duncan use a TS apo?

Noel
« Last Edit: Jul 04, 2020, 13:14:00 by NoelC »
Synta mount, a bunch of telescopes and a shed (on wheels).

Carole

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Re: Fast Telescope
« Reply #4 on: Jul 04, 2020, 20:13:20 »
Hi Noel,

I was not expecting to get anything like f2.8, but thought I would like to at least get something halfway between my current f7.5 and f2.8.  Trying to get something around f4.4 ish which has to be better than what I already have.

Also asking around, some of the fast scopes can be a bit risky as to their efficiency which is why I am getting opinions. 

Thanks for the suggestion, but I am not looking for a Newtonian, been there and done that and I know that lower focal ratios are even more demanding.

So basically it's a compromise.

I haven't made a final decision yet but I have today borrowed a TS80 Photo Line (to try out) from a guy who also has an Esprit 100, and judging from what he has said and my investigations, I think I am leaning towards the Esprit 100.  Plus it seems to be highly recommended.   I have shot some questions off to a retailer. 

However I will try out the TS scope first before I make a decision.

Carole

The Thing

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Re: Fast Telescope
« Reply #5 on: Jul 05, 2020, 19:20:38 »
Hi Carole, trying to bring even more bad weather to Blighty?🔭✨🙂

I'm very happy with my Sharpstar 61efph which is 275mm f4.5 with the flattener. I think they want to clone Takahashi's looking at their lineup.
We're all guinea pigs in the laboratory of life. Better a fluffy guinea pig than a lab rat!
¯\_(ツ)_/¯ (Gallic shrug :))

Carole

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Re: Fast Telescope
« Reply #6 on: Jul 06, 2020, 00:08:30 »
Quote
I'm very happy with my Sharpstar 61efph which is 275mm f4.5 with the flattener. I think they want to clone Takahashi's looking at their lineup.

Wow, that is a really good price for a Triplet, and thanks for that.  I will certainly keep a note of it should I want to replace my WOZS71, but am currently looking for something with a longer focal length such as 80 - 100mm

Carole


The Thing

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Re: Fast Telescope
« Reply #7 on: Jul 06, 2020, 07:41:32 »
Hi Carole, Sharpstar do a whole range of refractors. I got mine from 365astronomy


https://www.365astronomy.com/ASTRONOMICAL-TELESCOPES/?keep_https=yes#rfplist
We're all guinea pigs in the laboratory of life. Better a fluffy guinea pig than a lab rat!
¯\_(ツ)_/¯ (Gallic shrug :))

Carole

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Re: Fast Telescope
« Reply #8 on: Jul 06, 2020, 09:39:33 »
Thanks Duncan I took a quick look, his website is a bit messy, and the names are half covered up by the photo. 

As a general comment, I can't believe the soppy short foot these manufacturers put onto these expensive imaging scopes, how on Earth do they expect you to be able to balance the kit.

I found the same thing when I bought my WOZS71, and had to mount the foot on another longer dovetail. 

They put all this effort into producing great optics and then make it impossible for you to image without further adaptation.  I know others have complained of this too.

Carole
« Last Edit: Jul 06, 2020, 10:30:06 by Carole »

The Thing

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Re: Fast Telescope
« Reply #9 on: Jul 06, 2020, 09:58:42 »
I'm having the same problem, wasn't really an issue with the eq mounts but the StarAdventurer needs very good balance. I'm away from home and have had to lash up a solution. Thank the Lord for Swiss army knives! If there was a tripod bush hole in the focuser that would have sorted it but the holes available are metric.
We're all guinea pigs in the laboratory of life. Better a fluffy guinea pig than a lab rat!
¯\_(ツ)_/¯ (Gallic shrug :))

Carole

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Re: Fast Telescope
« Reply #10 on: Jul 06, 2020, 10:40:15 »
I have another issue because I like to run a dual rig, so I also need a scope that has decent mounting rings so I can sit another scope on top, plus somewhere to add a finderguider.

Never had any of these problems with my Skywatcher ED80 and ED120. 

I borrowed over the weekend from a chap called Ray from SGL a TS 80 Photo Line, which is a triplet.  I like the focusser screw attachment but it comes with a flattener and not a focal reducer, so I don't think I am going to see the benefit of the fast optics with it at F6.  There is no finderfoot on it.  That's OK I said to Ray I have a spare finderfoot at home.

Yippee the bolt holes are the same distance apart, so I remove the hex bolts on the scope.....

Errr, hmmm, right angled guiding - lol



In the past I had the finderfoot mounted onto a mounting ring I had made for my very first imaging scope, the Megrez 72 APO, and luckily it fits the TS80, so hopefully I will be able to get it working.



Carole

« Last Edit: Jul 06, 2020, 11:03:15 by Carole »

Carole

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Re: Fast Telescope
« Reply #11 on: Jul 07, 2020, 12:47:54 »
Thanks for the advice every-one (Robert) , I have ordered an Esprit 100
https://www.rothervalleyoptics.co.uk/skywatcher-esprit-100-ed-f55-super-apo-triplet-refractor-ota.html

They will bench test it before sending.

I need to change the Losmandy dovetail as I use Vixen and the supplied one is too short anyway. 

I am going to use the TS x 0.79 focal reducer with it which although not made for it, several people are using it with this scope and say it works well (will need a thread adapter apparently). 

Scope = f5.5 and the x 0.79 will bring it down to f4.34.

Won't be available until September but have the loaned TS80 photo line I can use in the meantime. 

Thanks Duncan regarding the Sharpstar scope as well, which I will bear in mind if I later decide to replace the WOZS71.

Carole