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Old 13-09-2016, 10:05 AM
glend (Glen)
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One Scope to Rule Them All

Here is the question: i need to find one scope for my declining years that works well for imaging and deliveres outstanding performance within the constraints outlined below. The plan is to reduce my present scope collection to One.
  • Must be a very capable as an astrograph, as 95%+ use will be imaging due to reducing vision capability.
    Must weigh no more than 12kg for easy of carry and low stress guiding when image train equipped on NEQ6. Note i had considered replacing the mount but decided to spend the money on a scope that works within the mounts restrictions.
    Mid-range focal length, say 600-1000mm,
    Fast if possible, no slower than f6-7.
    True colour rendition, with no fringing or bloating, i don't have a design preference other than no RCs (ie, refractor, newt, etc.).
    Aperture, bigger is always better.
    Must be both narrowband and broadband performer, thus no achros (i already have one of those).
    Must be cost effective, not interested in paying a premium for a collectable brand name, function and performance for the $.
    Budget, would like to stay under $3000 total spend, and if flatteners, etc are required they must fit with budget, and happy to source from anywhere.

I have a short list of possibles but i want other opinions.
Let the suggestions flow. Thanks for looking.
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Old 13-09-2016, 10:22 AM
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Shiraz (Ray)
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Quote:
Originally Posted by glend View Post
Here is the question: i need to find one scope for my declining years that works well for imaging and deliveres outstanding performance within the constraints outlined below. The plan is to reduce my present scope collection to One.
  • Must be a very capable as an astrograph, as 95%+ use will be imaging due to reducing vision capability.
    Must weigh no more than 12kg for easy of carry and low stress guiding when image train equipped on NEQ6. Note i had considered replacing the mount but decided to spend the money on a scope that works within the mounts restrictions.
    Mid-range focal length, say 600-1000mm,
    Fast if possible, no slower than f6-7.
    True colour rendition, with no fringing or bloating, i don't have a design preference other than no RCs (ie, refractor, newt, etc.).
    Aperture, bigger is always better.
    Must be both narrowband and broadband performer, thus no achros (i already have one of those).
    Must be cost effective, not interested in paying a premium for a collectable brand name, function and performance for the $.
    Budget, would like to stay under $3000 total spend, and if flatteners, etc are required they must fit with budget, and happy to source from anywhere.

I have a short list of possibles but i want other opinions.
Let the suggestions flow. Thanks for looking.
guessing the MN is too heavy?

Suggest a Skywatcher CF F4 200mm with a Paracorr and a Moonlite focuser. Use your 1600 camera so that you can guide with a guidescope and take short subs - would be a killer system. Oh, and cover that black CF dew magnet OTA with reflective tape to remove dew issues - won't be pretty, just effective.
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  #3  
Old 13-09-2016, 10:25 AM
rally
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FSQ106N 2nd hand
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Old 13-09-2016, 10:33 AM
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Glen , the Skywatcher 190m F5.3 Mak-Newt is 11kg and would tick all the boxes. Didn't you allready own one?
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  #5  
Old 13-09-2016, 11:05 AM
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Merlin66 (Ken)
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Glenn,
I've been at this game for over fifty years.....
My "declining years" telescope for performance and portability will definitely be the original Genesis 4" f5. (Serial 1007)
I haven't found anything to beat it over years.
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Old 13-09-2016, 11:18 AM
glend (Glen)
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Yes Mark, and Ray, i do have a very nice MN190 that i have just improved by installing a Moonlight focuser. Skywatcher lists the tube weight as 12.5kg on their website but it feels heavier to me, ha ha. My wish list does read as if i am describing it doesn't it. One of my options is to just rationalise to the MN190. I wish it was just a kilo or so lighter, a carbon fibre tube version would be a dream, and hard to do with all the baffling.
I did not mention it purposely, as i was after greenfield options.
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Old 13-09-2016, 11:26 AM
glend (Glen)
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Originally Posted by Merlin66 View Post
Glenn,
I've been at this game for over fifty years.....
My "declining years" telescope for performance and portability will definitely be the original Genesis 4" f5. (Serial 1007)
I haven't found anything to beat it over years.
Ken according to my research the TV Genisis 4" f5 is in fact an achro doublet design, albeit with a rear Petzval corrector. Yes it may have nice glass up front but it will still have colour issues. I have been using a Bresser 152mm f5 with a Petzval corrector in the rear, for narrowband imaging but it is unsuitable for broadband.
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Old 13-09-2016, 11:34 AM
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Originally Posted by glend View Post
I wish it was just a kilo or so lighter, a carbon fibre tube version would be a dream, and hard to do with all the baffling.
I did not mention it purposely, as i was after greenfield options.
I know a very skilled sheet metal worker who could replace the steel tube with aluminium and do all the internal baffles too and put reinforcing plate under the focuser. That might be an option if weight is the only factor. You won't get so many boxes ticked for that money in the Apo department .
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  #9  
Old 13-09-2016, 11:36 AM
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dannat (Daniel)
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I wasn't blown away by a genesis -heavy for a 4" too I thought -much more than a skywatcher 100 f9

intes mn someone has already upgraded the focuser for you, weight just below 10kg I think
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Old 13-09-2016, 11:40 AM
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Atmos (Colin)
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I agree with Ray, a good 8" F/4 Newt with coma corrector would be a great place to look.
As rally suggests, a second hand FSQ 106 is also a good option but you're not likely to find one around the $3,000 in good condition.

Out of those two I'd gravitate towards the Newt given your requirements.
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  #11  
Old 13-09-2016, 12:25 PM
glend (Glen)
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Quote:
Originally Posted by Satchmo View Post
I know a very skilled sheet metal worker who could replace the steel tube with aluminium and do all the internal baffles too and put reinforcing plate under the focuser. That might be an option if weight is the only factor. You won't get so many boxes ticked for that money in the Apo department .
Mark, i will consider that. Doesn't aluminium flex more than steel when used in that sort of construction or does it have to be build thicker to compensate? What about thermal expansion?

I have emailed Teleskop-Express to see if they can provide a carbon tube for the MN190. The stock MN190 tube appears to be the same basic steel tube as the 8" Skywatcher f5 newt but with the baffling added. TS already provide a Skywatcher 8" f5 newt carbon tube at a reasonable price of about 400 euro. If i could get a MN190 carbon tube, with baffles, with focuser bore positioning correct, it seems ideal. Lighter in weight, more thermal stability, stiffer, etc
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Old 13-09-2016, 12:40 PM
glend (Glen)
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Originally Posted by Atmos View Post
I agree with Ray, a good 8" F/4 Newt with coma corrector would be a great place to look.
As rally suggests, a second hand FSQ 106 is also a good option but you're not likely to find one around the $3,000 in good condition.

Out of those two I'd gravitate towards the Newt given your requirements.
Colin, thanks, i would probably prefer an f5, simply for ease of collimation and longer focal length of 1000mm. The concerns i have with newts (in their pure form) are: diffraction spikes, the mandatory secondary heater, focuser/camera positioning, but i lived with those issues with my 10" f5 newt. The good thing about newt choice is that i can get carbon tubes for most of the popular imaging versions, which might allow greater aperture for the weight limit. I already have a Baader MPCC and spacers for my camera.
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Old 13-09-2016, 12:46 PM
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Slawomir (Suavi)
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Hi Glen,

If you are going to use this telescope primarily for deep space astrophotography, then given that it will sit on EQ6 and that your camera has 3.8 micron pixels, I would personally not venture over 500mm fl, unless you like babysitting your mount and tweaking guiding settings during most sessions, if of course you aim for the best possible data. At 500mm fl your camera will give you a comfortable 1.57" per pixel, and honestly, I would probably even aim towards around 2" per pixel with EQ6 for enjoyable astrophotography and use drizzle in my workflow.

A second hand FSQ85 would tick all boxes for me with this mount and this camera.

Just my five cents.
Suavi
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Old 13-09-2016, 02:23 PM
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Originally Posted by glend View Post
Mark, i will consider that. Doesn't aluminium flex more than steel when used in that sort of construction or does it have to be build thicker to compensate? What about thermal expansion?

I have emailed Teleskop-Express to see if they can provide a carbon tube for the MN190. The stock MN190 tube appears to be the same basic steel tube as the 8" Skywatcher f5 newt but with the baffling added. TS already provide a Skywatcher 8" f5 newt carbon tube at a reasonable price of about 400 euro. If i could get a MN190 carbon tube, with baffles, with focuser bore positioning correct, it seems ideal. Lighter in weight, more thermal stability, stiffer, etc
Its worth asking but I have never heard of a carbon fibre version of the MN190 and those prices only come through economies of scale . Its not hard to make an aluminium tube as stiff - just a small increase in thickness as stiffness goes up by the cube root. Also the internal baffle rings that Gary makes are like sleeves with a 90 degree bend - they add a lot of stifness.

I dont think these days that an aluminium tube is much of a hindrance as subs are usually 5 minutes or less and you can check focus every so often . Anyways I don't think baffles do anything at all in a Newtonian type design - I think they are really there to appeal to the retractor community .Flocking is all that is really necessary . The primary mirror and secondary already give you a massive amount of baffling .

Still if you can get a carbon fibre mod it would be ideal .
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Old 13-09-2016, 02:29 PM
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Colin, thanks, i would probably prefer an f5, simply for ease of collimation and longer focal length of 1000mm. The concerns i have with newts (in their pure form) are: diffraction spikes, the mandatory secondary heater, focuser/camera positioning, but i lived with those issues with my 10" f5 newt. The good thing about newt choice is that i can get carbon tubes for most of the popular imaging versions, which might allow greater aperture for the weight limit. I already have a Baader MPCC and spacers for my camera.
You've just named every single reason why I went with a refractor over a newt or a MN190 Not a fan of diffraction spikes and I don't like the focuser position.

I tend to agree with Suavi, the closer you are to 500mm the better. At 400-800mm you are at a nice pixel scale where you can drizzle every bit of good seeing out of your data but not be as restricted on nights of less than perfect seeing.

As you say however Glenn, F/5 is a LOT easier to deal with in the way of collimation and sensor orthogonality.
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Old 13-09-2016, 03:02 PM
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You've just named every single reason why I went with a refractor over a newt or a MN190 Not a fan of diffraction spikes and I don't like the focuser position.
While theres nothing to be done about focusser position other than some classy after-market ball bearing rotating mount rings for ergonomics , there are certainly no diffraction spikes other than any mirror clips in a Mak-Newt and the central obstruction is relatively modest on an F5.3 .

With good native off axis spot performance they should be optically superior to any 8" apo provided you are not going for a really large diameter focal plane - not that there are many 8" APOs in the world as the cost of the glass is prohibitive for even the keenest retractor buffs !
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Old 13-09-2016, 03:08 PM
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What about some of those Stellarvue scopes? The 70T in Andy's hands is producing some fine images. William Optics 110mm may be another 2nd hand with reducer.

Try the Teleskop Services website. They have some imaging Newts. A 110mm APO William Optics would be very nice. Stellarvue have some as well. Not sure if new is in your price bracket but 2nd hand some would come up.

Greg.
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Old 13-09-2016, 03:14 PM
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Originally Posted by Satchmo View Post
While theres nothing to be done about focusser position other than some classy after-market ball bearing rotating mount rings for ergonomics , there are certainly no diffraction spikes other than any mirror clips in a Mak-Newt and the central obstruction is relatively modest on an F5.3 .

With good native off axis spot performance they should be optically superior to any 8" apo provided you are not going for a really large diameter focal plane - not that there are many 8" APOs in the world as the cost of the glass is prohibitive for even the keenest retractor buffs !
No diffraction spikes on the MN190 but I do like the simplicity of the straight through focusing position on a refractor or SCT/CDK ect. Makes balancing in all three axis a lot easier
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Old 13-09-2016, 03:51 PM
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Rationalised it myself fairly recently and chose a Tak Sky 90. Superb performer, flat and fast with reducer (f4.2) . Very short and very light. cools much faster than an fsq85 and is just as good a performer.

Cost me $1600 and truly very happy. Yes you need to check collimation occasionally (the second generation versions don't have an issue with this) but well worth it. The FSQ85 ranks in my top 3 of all the scopes I have owned but good luck getting a 2nd hanf one under 3000.

Or consider an Esprit 100 second hand if you can find one. Astromart will be your friend
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  #20  
Old 13-09-2016, 04:05 PM
Ken
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The MN190 has a Aluminium tube or at least the Orion version does, just checked mine with a magnet.
Clear skies Ken.
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