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Old 12-07-2018, 11:31 AM
Startrek (Martin)
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Bintel 8” f5 OTA vs Skywatcher black diamond 8” f5 OTA

I welcome any advice from IIS members who have used or know anybody who have used either a recent Bintel 8” f5 OTA and/or a Skywatcher black diamond photo 8” f5 OTA so I can make some sort of comparison and decision later in the year to upgrade my astrophotography kit
I’m going for an 8” f5 newt on an NEQ6R mount

I currently have a Bintel 6” f6 OTA on a HEQ5 mount using a canon 600D DSLR which is used 80% for astrophotography and 20% Visual
This is a great little rig which I will eventually keep in Sydney and the 8” upgrade kit will find its home at my holiday house 220km away on the NSW south coast ( good dark sky site in my backyard) The 6” is great but has its limitations though.

I’m into light buckets not refractors for the moment ( that may change in the ensuing years when size and weight become a factor due to my age - I’m nearly 60 )

The Bintel 8” is about $160 cheaper than the Skywatcher but it is nearly 1kg heavier (fortunately cost is not a prime concern for me in my retirement)

Both scopes have dual Crayford focusers

Both scopes have 1000mm focal lengths

Both scopes have 200mm primary mirrors BK7 glass ?

The Bintel 8” has a 62mm secondary but I can’t find any data on the Skywatcher secondary

The Bintel GSO dovetail bar and tube rings on my existing 6” are poorly designed and manufactured. I have to guess when I assemble it if the tube rings are aligned , there are no locating seats or guides for you to tighten up on to. I don’t know whether the Bintel 8” is any better or the Skywatcher is manufactured with a good locating seat / purpose fit on the tube rings and dovetail bar.

Collimation on my Bintel 6” is a snack (takes me a couple of minutes )so I’m assuming both Bintel and Skywatcher f5 will be simple as well (I use a laser collimator )

The Bintel 8”comes in a semi gloss white finish but the Skywatcher comes in a black speckle fleck finish. I’m thinking if I set my scope up permanently for a couple of nights imaging, the Skywatcher will take a lot longer to cool down due to a higher ambient temperature absorbed throughout the day due to the black absorbing colour??

I don’t know which scope would be prone to flexure ( if any ) my 6” has a focal length of 900mm ( only 100mm less than the 8” ) and does not suffer from flexure. I have taken exposures of up to 80 seconds with just drift alignment, no guiding and no star trailing ( round stars to edge of field )

Any advice welcome in regard to choosing either the Bintel or Skywatcher 8” f5 OTA for 80% astrophotography and 20% visual

Thanks in advance
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Old 13-07-2018, 10:12 AM
Startrek (Martin)
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Any advice or comments from anyone ?
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Old 13-07-2018, 11:04 AM
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doppler (Rick)
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Hi Martin,

I think that Skywatchers mostly use Pyrex glass for their mirrors (more expensive but thermally more stable?), and skywatcher tubes are a bit thinner in diameter hence the lighter weight. I have GSO tube rings on my 10" skywatcher, so to make the rings more solid I screwed the dovetail bar to a heavier alloy bar and fitted the rings to that then added a alloy bar to the top.

Rick
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Old 13-07-2018, 11:49 AM
Startrek (Martin)
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Thanks Rick,

Appreciate your reply and advice, we’ll recieived

Any more advice and comments from the IIS community !!
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Old 13-07-2018, 02:25 PM
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ChrisV (Chris)
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I've got the GSO 8" F5 (same as Bintel?) and use it solely for AP. I like it, but I'm no expert. I can't comment on the skywatcher.

I took out the crappy secondary adjustment screws and replaced them with some I found on ebay with knurled plastic heads = poor man's Bob's knobs.

My main bugbear is that there's a bit of slop in the focuser which I've never really managed to get under control. Maybe someday I'll upgrade the focuser - unless anyone out there has any good ideas to fix it.
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Old 13-07-2018, 04:09 PM
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billdan (Bill)
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I have the Skywatcher 8in F5 and I went downstairs and measured the secondary for you, I was very surprised when it only measured 50mm minor axis.

Nevertheless it lights up an APS-c chip OK with very little vignetting. I have not had any issues with the focuser, but its not carrying much weight, Camera, OAG and MPCIII (about 1Kg tops).

EDIT: The black exterior is a dew magnet, not sure what a white GSO is like.
The inside of the OTA is more grey than black, so I painted mine with blackboard paint, while I was at it, I painted the back and sides of both mirrors as well (seemed like a good idea at the time).


Cheers
Bill

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Old 13-07-2018, 04:30 PM
Startrek (Martin)
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Thanks guys !

Bill,

How’s the quality of the tube rings and dovetail bar on the Skywatcher ?
Do they have locating pins , ridges or grooves to align the rings on to the bar, or is it guess work line of sight method ?

Also how’s the action of the dual speed focuser ? Is the main focus smooth ?

I find on my 6” Bintel GSO the main focus a bit rough, only the fine focus is really smooth

Thanks in advance
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Old 13-07-2018, 04:59 PM
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billdan (Bill)
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The scope rings are made out of thick aluminium and it seems mine came with two vixen dovetails (I don't remember buying a separate one).

There is no locating pin, just use the three rear holes to mount the rings, the central bolt holds it all together and the two outer hex key bolts are for adjusting the cone error.

My scope is 6 years old and it came with a single speed focuser, and I bolted a Skywatcher electric motor to it when I bought it. So I cant tell you how it feels, but its great with the motor.

Took a picture of the rings for you in the kitchen with no flash, so its a bit grainy.

Bill
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Old 27-07-2018, 06:33 AM
Paullus (Paul)
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Hi Martin,


As per the other thread I've opted for a 8" (over the 10"). I went with Skywatcher over the Bintel/GSO and have the following comments:
- from what I've skimmed from various forums and timelines over the past few days is that the GSO apparently is more prone to flex issues, not the other way around. This was from older posts, mainly relating to dobs so maybe it's not 100% correct now. Tube weights might have something to do with it, but I've seen some variance in the listed weights, some are OTA only, some are OTA + accessories (finder, tube rings etc). It's not always clarified on which weight is listed.

- SW have Pyrex glass while the GSO have the BK7 which seems to need recoating after a period of time. Again, sourced from old posts. Manufacturing may have improved. To the average amateur can they even tell when they need recoating or just a wash?

- Black vs white: while black surfaces do absorb more heat than whites, they also emit it better than white surfaces. I would have rather a white scope to match the mount

- The current SW f/5 8" is a 200P-DS (or P200-DS) which has an upgraded 58mm secondary from around 2012 or so (with the dual speed focuser). Again, found this information on one forum and one shop website but nowhere else. Will confirm when I unbox mine. I've been playing with some secondary calculators and while there is a slight dimming in magnitude near the edge of field it wasn't significant enough for me to jump to the 63mm (58mm is definitely better than the 52mm that the 200p used to come with). This larger secondary may only be to offset that the primary is further up the tube. I was only estimating a range of distances in the secondary calculator.

- The Bintel/GSO has the cooling fan and slightly larger secondary, but I've picked up the SW for $495 vs the Bintel unit for $479 + $50 shipping, so the cost of adding my own fan is offset by the cheaper purchase price.

Anyway that's a brain dump of what I've found over the last few days. As with anything, don't take it as gospel, YMMV etc etc, but hope it helps. I'm certainly no expert. I'm sure either unit will be fine to use .

Cheers
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Old 27-07-2018, 08:36 AM
Startrek (Martin)
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Hi Paul

Thanks for your brain dump very informative

Could you possibly post a brief report on how the Skywatcher 8” performs ?

Maybe some images as well ?

I’d be interested in how these perform as quite a few posts talk about the older models ( with the 52mm secondary )

Thanks
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Old 27-07-2018, 08:21 PM
Paullus (Paul)
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Yeah for sure. I've just unboxed and it's a schmick looking unit! I measured one of the floor models at the shop before I left and it is indeed a 58mm secondary.


I'll post up more after a few outings. Meanwhile I have to prep for tomorrow's lunar eclipse.
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