20 replies to this topic

[TheLightCollector]

So I'm planning on buying my first 8 inch dobsonian soon, and I'm torn between two scopes.The ones I have it narrowed down to are the Firstlight 8" dob from Explore Scientific, or the Skywatcher Classic 200P 8inch dob.They are pretty much the exact same price,and I'm not too worried about the accessories, because I already have some decent eyepieces & barlows. Although,I do want a decent finder,and the ES comes with a red dot ,while the Skywatcher comes with a more traditional straight-through finder scope.The big advantage of the ES is that it comes with rings & a dovetail,which is a good option should I ever decide to run it on an EQ mount.Also I already own a little 90mm/500mm doublet from Explore Scientifics firstlight series ,and I really like it.So I guess I'm kinda leaning towards the ES,but I was curious to hear some opinions,and experiences you all may have with these two scopes to aid in my decision.

[havasman]

The alt bearings are the difference maker for me - go with the ES. I've manipulated Wyatt's 10" and it's pretty sweet.

Edited by havasman, 06 July 2019 - 02:42 PM.

[Sam M]

Not to muddy the waters, but...

The AD8 costs more, but has a RACI finder, useful altitude clutches, a fan for the mirror, two speed focuser, and a laser for collimation (if you need it).

[dfie515024]

Just to at least see a possible scope you could order, check out the DobStuff 8" or 10" light-weight model made by Dennis Steele who is exceptionally pleasant to work with and does wonderful work, both with the woodwork and the light path equipment.

The reason I suggest taking a look is that I not long ago I was struggling with similar choices as you are now and someone on here suggested DobStuff. And WOW! But it costs more than the 2 you are comparing.

[Asbytec]

The alt bearings are the difference maker for me - go with the ES. I've manipulated Wyatt's 10" and it's pretty sweet.

I agree...my ES 8 stays put when changing eyepieces and can carry a range of heavy stuff up top without uncommanded slewing toward the zenith or the horizon. That's the main reason I sold off my previous Dob. In my view, all Dobs need to be made like the ES (Dobstuff and Discovery, among a few others).  

 

Not to muddy the waters, but...

The AD8 costs more, but has a RACI finder, useful altitude clutches, a fan for the mirror, two speed focuser, and a laser for collimation (if you need it).

That's also true. The Firstlight is not really a beginner's scope as the name may seem to imply, but it is a descent bare bones scope. You'll need to add a fan, probably a descent finder, and a collimation tool plus any other bells and whistles you may want such as a dual speed focuser.

 

In my personal experience, YMMV, I have never had much luck with clutches on the alt axis. They were either too loose or too tight and sticky depending on the balance load. In my view, the alt bearings (on my previous Dob) were too smooth for their own good. Even with a counterweight and applying tension to various loads, I could never find Nirvana and became wary of changing an eyepiece. I could get it to hold, but then movement was sticky. Just frustrating and not something I experienced on my previous homemade Dobs. Again, others seem to have some success with it, not me. Got tired of fooling with it. 

 

IMO, the cost of adding a few accessories far outweighed the frustration of finding good balance, even with a counter weight. Now, I do counterweight my ES, too, but I do it so the tube can ride a little higher in the saddle. A simple solution is to strap one a USB power banks weighting, about a half kilo or more, to the bottom of the tube to run a USB fan. Nirvana at last. 

 

Another problem with my previous Dob was the secondary holding collimation with changes in altitude. I could see the laser dot move on the mirror with changes in altitude. The ES spider is much more sturdy and holds perfectly still. It's a bit larger, but it seems to have plenty of back focus for a fully illuminated field all the way to maximum focuser travel. When fully extended, I can still see the entire primary mirror. I suspect they have plenty of in or back focus for bino viewing. It requires the supplied 3" extension to achieve focus with eyepieces, so removing it gives you plenty of in focus for whatever application, too. 

 

After my experience with my previous Dob, I am glad I got the ES this time. 

[Sol Robbins]

I had the same choices you have and I went with the E.S. 8. There's a thread I started here when I took delivery.

 

Some things you might consider are:

 

The scope needs some adjusting, 

The E.S. mirror is really an ~8.375" diameter while the GSO is at ~7.9".

The tube's inside diameter is 9 9/16", so the scope looks and is a little oversized.

The E.S. secondary minor axis is at 2.24" while the circular hub that the spider vanes attach to is at 2.6" diameter. That means the central obstruction is at 33% even though the secondary mirror is smaller.

The red dot finder is useless and you might need an Explore Scientific to Synta conversion shoe if you if not using an Explore Scientific/Meade finder.

The Explore Scientific cell has an 80 mm. hole in it. I use a Thermaltake 80 mm. fan that has a USB connector with retracting power cord and built in variable speed knob. I attached with double sided foam tape and requires a rechargeable 5 volt USB battery. 

The included 20 mm eyepiece is low quality.

 

That said, it really is a good scope optically. No regrets after 8 months of using it and I've been using telescopes for over 40 years.

Edited by Sol Robbins, 06 July 2019 - 08:22 PM.

[TheLightCollector]

First off thank you all for the feedback.It sounds like the majority of you guys prefer the ES.As I said I was kinda leaning that way anyway.I'm also planning on using it in conjunction with the ES firstlight 90mm doublet that I metioned earlier,so it's kinda cool that the color schemes will match when I have them setup together.

[TheLightCollector]

So heres a pic of my short tube refractor. Notice the color scheme is the same as the 8" dob.I think they will make a good looking pair.

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[TheLightCollector]

I'll probably upgrade the ST refractor too eventually for an APO, but for now I actually really enjoy that little scope.

[TheLightCollector]

I've seen two different looking versions of the Skywatcher 8inch dob on different websites. They seem to be the exact same features & price.I was just wondering if anyone knew if there are any differences?

[TheLightCollector]

Here are pics of both variations 

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[Asbytec]

Sol, that the primary is 8.38" in diameter is a revelation. I assumed it was the standard 7.9". When I stow it away for the monsoon, I need to measure it. That's kind of cool, but definitely non standard for a Newt, yea? I wonder if they are using 8" SCT blanks that are (supposed to be) a little bit 'over sized'. Just curious. 

 

When I do the math for a 2.6mm diagonal support, I get 2.6/8.38 = 31% obstruction. Not a ton of difference, but comforting to some. My MCT has a 30% +/- obstruction and offers no ill feelings. The images are nice. It should have the contrast of a 8.38 - 2.6 = 5.8" refractor, and you do not hear folks complaining about those views. It still puts ~90% of the maximum light into the Airy disc compared to a perfect 5.8" APO. It's right at the diffraction limit with a descent (not premium) mirror. 

Edited by Asbytec, 06 July 2019 - 08:30 PM.

[Sol Robbins]

Actually I took lots of measurements regarding the E.S. 8, and measured many times. Not because I was obsessively compelled to, but I had an opportunity to acquire another 8" mirror with a "pedigree". So I needed to know if I would be able to use the E.S with little if any modification for an actual 8" diameter with a traditional 1.4" thickness to work.

 

To the original O.P. the stock E.S. primary is also 7/8" thick so the 6 point floating cell is just another little plus for the E.S. over the GSO or Synta. 

 

With the stock E.S. 8 that's well collimated and cooled Jupiter showed a bit better than TEC140 with really good, (8P) seeing. On D.S.O. no contest.

Edited by Sol Robbins, 06 July 2019 - 08:50 PM.

[TheLightCollector]

Thanks for the info Sol.I have decided on the ES ,thanks to your input ,and the feedback of everyone else on this post.
Now I just gotta' wait for my next paycheck , so I can scrape the cash together!

[TheLightCollector]

Also thinking maybe getting a nice raci finder as the first upgrade.

[25585]

I have a 10" version of the ES and its mount is the deal maker. My astro soc has the 10" SW version, and there is nothing optically between them, but the ES mount is superior though I like the SW round base.

[castorpolu11]

I love that I can shorten my ES FL 8" focus tube and binoview!

 

I too did the simple fan installation and it helps with balance since my old battery pack rides on the low end of the tube. I keep it in place with a big rubber band. I also use an orion magnetic counter weight when the focuser is loaded. I'm currently using it with an adapter liberated from a Celestron StarSense Explorer scope giving me plate solving based push-to on the ES FL. It's nice

Edited by castorpolu11, 10 February 2021 - 09:32 PM.

[WillR]

, 

The E.S. mirror is really an ~8.375" diameter while the GSO is at ~7.9".

 

ES website gives the mirror's spec as 203mm. Is this something you directly measured? It's hard to believe they would not describe this as a 213mm mirror since that would be a selling point.

Edited by WillR, 04 October 2021 - 10:54 AM.

[Sol Robbins]

See post #13.

[sixela]

ES website gives the mirror's spec as 203mm. Is this something you directly measured? It's hard to believe they would not describe this as a 213mm mirror since that would be a selling point.

What I've sene with GSOs in the past as well is that some batches of mirrors can be larger than others (they possibly don't evne come from the same source?) So that they're 213mm now doesn't mean they'll always be, so the marketing literature might want to reveal the minimum size.

[Sol Robbins]

What I've sene with GSOs in the past as well is that some batches of mirrors can be larger than others (they possibly don't evne come from the same source?) So that they're 213mm now doesn't mean they'll always be, so the marketing literature might want to reveal the minimum size.

This may be true, but the mirror cell is designed for the 213 mm mirror diameter.