Change of Plan...re. my 8'' Dob in France

[cybernautic]

Some of you might remember I started a thread a week or so ago about getting an 8'' Dob down in France. I decided on an Orion TX8 with a couple of lenses and a Telrad and RACI finder. You can guess what's coming...I put the order in and then changed my mind. By the time I'd ordered the extra bits I realised I could afford a 10'' scope instead, and that's when the doubts started creeping in about the 8''.

I live in a very dark sky site. The nearest small town is about 6 miles away. The nearest big city is over 35 minutes drive away. I couldn't help but think that I ought to take advantage of the viewing conditions by going with the largest aperture scope I could afford, even if it didn't come with the bells and whistle extras of the XT8. I imagined myself getting the 8'' and then thinking 'but I wonder what this would look like in a 10'''. I'm not massively fussed about doing a lot of plantetary viewing as I'm more interested in DSOs, and although I'm a little concerned about the increased weight of a 10'' scope I wouldn't be transporting it in a car, just into the back garden from the house.

The problem I have now is deciding on a 10'' scope.

I've tried to narrow it down to these two options:

GSOD880 Dobsonian 10'' Deluxe: 575 euros

http://www.teleskop-express.de/shop/product_info.php/info/p1192_GSO-Dobsonian-880---10----250-1250mm-Telescope---Deluxe.html

and

Skywatcher Skyliner 250PX: 559 euros (I can get it elsewhere for 499 euros)

http://www.teleskop-express.de/shop/product_info.php/info/p1994_Skywatcher-Skyliner-250PX---10--parabolic-Pyrex-Dobsonian.html

I know the Skyliner is popular, in both its 8'' and 10'' size. The GSO is more of an unknown quantity though. I think the Zhumell scopes are essentially the same and they seem to get quite good reviews. Does anyone have an opinion on things like the two-speed focuser, the general build/optical quality, the difference in mounts, etc.

If you were me, which 10'' would you buy in a similar price range?

Thanks for your time, and apologies to those who gave me such good advice on my previous thread.

Best wishes

Rich

[AlexB67]

Hello, welcome . I don't think there is much between the scopes from what I read overall, optical performance is similar, build quality also it seems. The GSO also has some nice little extras like compression rings on the focuser on that model, a 2 inch eyepiece thrown in to get you started, little bits an bobs, though it is a little more in the UK compared to the skyliner solid tube to buy new. 

If I had gone and buy a solid tube dob, I would be very tempted by the GSO I must admit. There have been some discussions on this forum about comparing  the two scopes and which one is best. There is one potential caveat with the GSO in some circles, not having owned the GSO but informed by a well respected member on this forum that owned two of them, he stated that the mirror coating degrade somewhat more quickly compared to the sky-watcher models.  Getting mirrors recoated is something that can be done in the end of the day, though there is a little hassle involved.

In the end of the day, both have positive reports in terms of you get what you pay for a mass produced scope, both are decent. 

Hope that helps a bit. Good luck with picking  

[cybernautic]

Hello, welcome . I don't think there is much between the scopes from what I read overall, optical performance is similar, build quality also it seems. The GSO also has some nice little extras like compression rings on the focuser on that model, a 2 inch eyepiece thrown in to get you started, little bits an bobs, though it is a little more in the UK compared to the skyliner solid tube to buy new. 

If I had gone and buy a solid tube dob, I would be very tempted by the GSO I must admit. There have been some discussions on this forum about comparing  the two scopes and which one is best. There is one potential caveat with the GSO in some circles, not having owned the GSO but informed by a well respected member on this forum that owned two of them, he stated that the mirror coating degrade somewhat more quickly compared to the sky-watcher models.  Getting mirrors recoated is something that can be done in the end of the day, though there is a little hassle involved.

In the end of the day, both have positive reports in terms of you get what you pay for a mass produced scope, both are decent. 

Hope that helps a bit. Good luck with picking  

Thanks for the reply, Alex

I'm in a real quandary at the moment and have been up until very late over the last few nights reading and reading stuff online about getting a Dob. I just don't know what to do and it's turning into a bit of a nightmare as this should be enjoyable!

Since posting this thread I have read some of the comments you referred to about the quality of the primary mirror coating on the GSOs. I do like the sound of the dual-speed focuser especially and the mount also seems to be very efficient too.

The problem is that I'm now starting to swing back to the idea of getting an 8'' instead of a 10''. I've had stuff piled on the bathroom scales in a pathetic attempt to try and get some idea about the weights involved. The fact that a 10'' is slightly faster than the 8'' and the effect it has on eyepieces is another issue, as is the need for a more accurate collimation of the mirror.

I've read so many threads on this forum and others from people trying to decide if they should get an 8'' or a 10'' and nothing I've read has made the decision any easier! I've realised that I'm not sure what SIZE scope to get, let alone what make.

I live miles from anywhere with a camera/astronomy shop or an astronomy group so I can't get up close to one before I buy it. My biggest worry is getting the 10'' and thinking 'wow, this is heavy and massive and too awkward to carry about', followed by the worry that if I get the 8'' I'll sit there thinking 'hmmm, but what would this cluster have looked like in that 10''...'

I've had two operations on my lower back so it's not the strongest of body parts for regular carting around of heavy things. As I said in the OP, the scope wouldn't ever have to travel to dark skies as I can get them from the yard in front of the house and storage area isn't an issue. It's just the weight that bothers me and whether I'd find the 10'' unwieldly, both to move and use.

I honestly don't know what to do and it's driving me nuts!

[brantuk]

There's a solution to everything. I sense that you are wanting the largest practical aperture for observing. Storage and portability aren't an issue cos it will be stored handy for your front or back yard, but lifting a large base and ota might be a problem for your back.

You can fit locking wheels and leveling feet to the base of your dob and roll it around on hard floor. Or if going over grass or rough terrain you can fit a removable pneumatic wheel barrow wheel and handles. These are common mods typically found on 16", 20", 25" and bigger dobs. So it would make a 10" dob virtually weightless to move around the garden and front yard. Hth

[Reeny]

UK Lidl stores will have £5 plant pot stands on sale next Monday.

I am getting one for inside the house, and a spare for the outside patio.

For longer trips I already have a fold up sack barrow.

 

I can't give you specific scope advice.

But I can tell you what I would do (i.e. just bought an 8" Dob).

After going around the houses, I went back to the 8" dob as my preferred option.

Skywatcher gives the best value for money at 8"

And I had already bought some decent plossls knowing that the SW freebies would be swapped out for something better.

Having the extra 10" apperture would be no good for my situation.

The negatives are:

- a base too big for the 50cm wide motorhome door for holidays

- £150 more cash, which could be better spend on extras

- Bulky and little bit heavier to move around as a truely "pick-up-and-go" portable scope.

If I was in your shoes I would find the extra money, extra storage space, and buy a trolley to move it around.

The Revelation 10" sold in the UK should be the same as the European GSO models.

If I was going for a 10" Dob, I would get the Revelation.

Partly due to customer brand loyalty after getting some optically perfect 15x70 binoculars.

And partly due to the extras which come as standard on the Rev 10"

The stuff I might like to buy for the Skywatcher 10" comes built into the 10" Revelation package already.

Only you can decide what you want out of the scope.

And which package does the job for you.

[haitch]

Not sure whereabouts you are in France but I've got a holiday home in a fairly remote part of the Limousin and, having used several scopes there from an 80mm refractor through an 8" SCT to my 14" pumpkin cannon of a dob (solid tube), I can categorically say it would be a crime not to go for the biggest you can afford if you've got good skies.

A 10" isn't huge by dob standards - remember you don't have to carry it all in one piece the tube comes off the base to move it.

Oh and collimation isn't really that scary and doesn't need to be mega precise to get an enjoyable view (speaking as the owner of a 14" f4.5)

Hth

[cybernautic]

I live about 5-10 miles from a very small town called Ruffec in the Charente department. Poitiers is 50+ minutes drive away to the north and Angouleme is 40+ minutes drive away to the south. Apart from that there's nothing. Just villages and hamlets. There's one nearby street light that goes off at 10.30pm in the winter and 11.30pm in the summer but even with it on I can see the Milky Way and M31 clearly from the garden which is sheltered from the glow of the street light. Having read other people's stories of light pollution it's made me realise how fortunate I am to have dark skies on my doorstep. I guess when the street light goes off it would rank around a 3 on the Bortle scale, and in the summer especially it's clear for weeks on end.

I like the idea of the wheels and carriers mentioned by Reeny and Brantuk up thread, so thanks for the suggestions! I can just about afford a 10'' but it would mean I'd be stuck with the eyepieces that came with the scope for a while as I'd not have much left over for replacements. I'd like to get the Skyliner 250PX although the GSO deluve 10'' comes with some decent accessories.

Also, as a beginner, would there be issues with the Skyliner having a focal ratio of f.4.7? I couldn't afford a coma corrector and if a higher focal ratio means complications then maybe the 200P would be better. One advantage of the GSO is that it's an f.5. Is there really such a big difference between an f4.7 and an f5?

[Bart]

I have the GSO deluxe. Love it. The alt/az motion is just beautiful. The focuser is used with heavy ES eyepieces. I have a bad back and wheel it all over the garden with a sack truck as a single unit. It's a dawdle to move around. Aperture wise, I get quite deep into the DSOs as I love galaxy hunting. Go for the 10", you won't regret it.

It's f5 so not too harsh on EPs. I have a coma corrector but rarely use it

Here's a pic of it sitting on the sack truck, beside its big brother!

Barry

[cybernautic]

Is there really such a big difference between an f4.7 and f5 in terms of things like coma and what EPs you can use?

[brantuk]

If you're only using it for observing (which you will with a dob) then the difference in focal ratios will make no noticeable difference in views. The f-ratios are more relevant to astro photography - a lower ratio means a camera can gather light quicker and save time on subs. As mentioned above - go for the largest aperture you're comfy with - that's what makes the difference when observing.

One other thing, at f-5 or less the views will generally be better with better quality eyepieces, whereas an f-10 scope copes reasonably well with the cheaper end of the eyepiece market.

[Charic]

Cybernautic......The Skyliner...........Pyrex glass means less warping of the mirror, but there`e got to be a lot of temperature variation i would imagine? Has a wider focal range 0f 4.8mm to 35mm, faster focal ratio, f/4.8 and cheaper at 559 Euro.
By comparison the GSO is plate glass, 5mm to 35mm f/5 and dearer by 20 Euro at 579 Euro. You may need to get 2" barrels for the 35mm or higher EP`s or opt to limit too about 25mm in the 1.25" barrel.

Regardless what you buy, you`ll still want to know what the next size up could produce. I love the 8" Skyliner. its about 27Kg fully laden, and I can carry that ok around my garden. If you get heavier, then your still going to have to lift it at some stage over, or onto something. I dont think the 10" is mighty heavier, but it has to be, because the mirrors bigger against the 8".

You probably wont notice the difference visually  between 4.8mm and 5mm. what you will notice is how much you saved by getting the skyliner, or save even more and get the 8" version. I know there`s better lenses, and Aperture being the most important, I know there`s bigger and better, but I`m happy here and now with the Skyliner 8"

I`m glad Im not the only one with `astronomitus`  keeps me awake all night with all this studying? take care

[cybernautic]

Cybernautic......The Skyliner...........Pyrex glass means less warping of the mirror, but there`e got to be a lot of temperature variation i would imagine? Has a wider focal range 0f 4.8mm to 35mm, faster focal ratio, f/4.8 and cheaper at 559 Euro.

By comparison the GSO is plate glass, 5mm to 35mm f/5 and dearer by 20 Euro at 579 Euro. You may need to get 2" barrels for the 35mm or higher EP`s or opt to limit too about 25mm in the 1.25" barrel.

Regardless what you buy, you`ll still want to know what the next size up could produce. I love the 8" Skyliner. its about 27Kg fully laden, and I can carry that ok around my garden. If you get heavier, then your still going to have to lift it at some stage over, or onto something. I dont think the 10" is mighty heavier, but it has to be, because the mirrors bigger against the 8".

You probably wont notice the difference visually  between 4.8mm and 5mm. what you will notice is how much you saved by getting the skyliner, or save even more and get the 8" version. I know there`s better lenses, and Aperture being the most important, I know there`s bigger and better, but I`m happy here and now with the Skyliner 8"

I`m glad Im not the only one with `astronomitus`  keeps me awake all night with all this studying? take care

For less than the price of the Skyliner 250PX on its own I can get the 200P plus an RACI finderscope, a Rigel Quikfinder (and extra battery), and a decent collimator. If I get a 10'' it'll have to be nothing but the bare bones and I'm not 100% sure when I'll be able to add things like another finder or even more EPs (especially if I'll have to buy more expensive ones for the f4.7 focal ratio). I can see the eventual cost climbing and climbing and climbing.

(This really is a dilemma! I wonder how many hundreds of other people have had the same conversation!)

As I'll be using it mostly for DSOs, will the 10'' show me appreciably more detailed views of things like the Whirlpool galaxy and is it worth the added expense?

[Charic]

cybernautic...........haitch hits it on the nail, re-read that message, Bigger Aperture =  better Light capture (wins Everytime) However, your lenses, RACI, Telrad will still cost  the same whichever size scope you purchase, their just after market issues. If you can afford the 10" then go for it, and it  will only take you  just a little longer to get the other bits. The straight 9x50 finder works well,  in addition the 25mm supplied  lens works ok, you only need to change the lowest focal length eyepiece to something like a 6mm and you`ll be setup for a good while yet, the supplied 25mm being a kellner/Modified is fine until you eventually want to upgrade from the K/M lens. With the  10" Focal ratio of f/4.7244???? you would need an eye piece of about the same size in mm. However with scope optical design, weather and everything else, the most you could be expected to get from your telescope is about 200x magnification! so a 6mm lens would  be a sound choice as your lowest focal length/ highest mag eyepiece. A simple rule to follow is this: The size of the aperture (254mm) is about the size of magnification to expect, so 254mm = 254x. (your highest magnification) but due to the constraints I mentioned, were now looking to keep within the 200x magnification mark (again,as a guide). Your lens is now  aquired from the focal ratio, at  1200/254= f/4.7244094. ( f/4.7  equates to a focal length of  about 4.7mm ?) That focal length   might be  too low  to start with, so  I suggest a 6mm lens.  Now divide the telescopes Focal length by the Eyepiece focal length  and you see,were back to 200x magnification? And I just picked this last tippet from the web. My 8" mirror has about 50 square inches of aperture, whereas the 10" has 78 square inches of aperture, again the math for better light capture?  And lastly, I have  the 8" Skyliner,  I would skip the 10" and go  to a 12" or higher next time, if i were needing to replace this one, or a  Catadioptric for Astro work. If I was starting  again from from scratch  choosing between the 10" vs. 8" Id still be stuck on here choosing, having the same dilema your having? Its all down to the final choice.......sweet dreams?

[Charic]

cybernautic.......Since my last  message. Ive spent a few hours in the back garden, as there were some breaks in the cloud. My 8mm BST picks out Jupiter at about 45 degrees up from the horizon (my mirror is still cooling) but can  just make out the cloud bands and four moons. Its so much  better to view when at its highest point in the sky. Now abeam my Zenith, its clearly visible using the 8mm (would it be any better on a 10" scope?) from my location, before it goes behind the gutter! ( I`m almost flat against the wall of my house so no Southerly views whatsoever, a little bit of sky to the North is visible, again shielded by trees, buildings and a street lighting, and a small gap to the East, again, blocked by the line of neighbours houses  and a tall tree line at about 300 feet away. Its so bright in the garden  here you can almost read a paper, I can clearly see all the details in the leaves on the tree directly North of me, just outside the fence illuminated by street lighting) so not the best viewing conditions. Basically I just follow Jupiter for a while, Then I try to get M31 Andromeda, invisible to my old naked eyes  but if I avert my gaze, I can locate it and it becomes visible through 7x50 binoculars. Better though, through the scope, but still no major detail, just a smudge really, and sat next to it I just make out M110 Galaxy. Then the clouds part again to my East (briefly) and I make out Planet Mars.  NO  real detail, about 1mm  - 1.5mm wide, just a small red  circle in my view. I tried the crappy 4mm lens from my Celestron, and the cheapo 3xBarlow, but no better. The 8mm gave me my best result, clearer,( would the 10" improve?) then I almost fell asleep in the cold cool night? I had a nice high backed comfortable chair and saw several meteors crossing the vicinity of Polaris, but was also chasing satelites all over the place with the binoculars, theres just so many up there, mind blowing! Even caught three last night as they came into view through the telescope. Its like a warp-factor streak through the star fields with the 8mm. But fun ( cant do that with an EQ). So two planets, two galaxies, tried to see other Galaxies aroung Ursa Major, but just to many clouds and light pollution. Maybe not enough aperture to see the other Galaxies from my garden. Ursa major is teaming with them! (would a 10" be better) I really must get away to a safe dark site, to see what, if anything, Im missing by viewing from the back yard in amongst all this glow! Only then will I really know how good the 8" is. The Skyliner is supposedly one of the best selling 8" scopes out there, not everyone can be wrong surely? so better conditions are required to make a more honest assesment. But seeing what I can already, Im still satisfied and happy with this setup, and  excited to try it at a darker site. I almost contemplated last night/ this morning the need to get a 2" 30-40mm wide angle. Nah! staying with the 1.25". Take care

[cybernautic]

Thanks for the replies, Charic

I think I've decided to stick with the Skyliner 200P. An 8'' Dob was my original plan (an Orion) and although my heart is telling me to get the Skyliner 250PX my head is telling me to get the 200P. I can just see it starting to get really expensive with an f4.7 scope when it comes to EPs and maybe a coma corrector, not to mention the other things I'd like to add like a Rigel/Telrad, a RACI finderscope, barlow lens, wide angle EP, nebula filter, etc. etc.

I can get the 8'' for 340 euros. The 10'' I can get for 499 euros. If the 10'' didn't require more expensive EPs then I might well have got the 10'' but I just can't justify spending £700-800 on a set-up, which it what I can see it costing eventually at least. Here in France there just doesn't seem to be the same second-hand market for optics that there is in the UK. In the UK I would've looked out for a second-hand scope anyway but here I have little option but to buy new. If I didn't have easy access to dark skies then I don't think I would've considered getting a 10'' but being down here in France seemed like too good an opportunity to miss.

I'm going to make my final decision tomorrow and definitely order something by the end of the day as I'm just going around in circles at the moment.

Best wishes

Rich

[Bart]

Whispering sound in the background..........."obey the aperture monster.....feed it, feed it!!!"

Barry

[cybernautic]

Whispering sound in the background..........."obey the aperture monster.....feed it, feed it!!!"

Barry

:grin:

Don't tempt me. Since posting my last response about buying the 8'' I've been online looking at the sort of EPs I can get away with in a 10''

[Charic]

cybernautic.....Keep running the circles, its a great exercise for the brain, and helps in your final decision. I say get the 8" but you may be saddened, because its not, in your opinion, as good as I describe ( remember Ive not had perfect conditions yet). You buy the 10" and think Wow! or maybe not, and think maybe the 12" could have been better? Its tough. I have what I have, and many others have the same setup. I wouldnt really worry about having to buy "expensive" lens because of the aperture. The lenses supplied with my scope are the same supplied with the 250PX so they will work just as well on either scope, its just that the 10" gathers more light, that gives a brighter image to the focal point (its still coming up a 2"- 1.25" draw tube to the eyepiece) but there are better designed lenses available, and dont neccessarily need to be"expensive". You will want to better the quality of the lenses one day, but its the 10mm that needs your attenntion first. There are lenses out there at over £500GBP but under my viewing conditions, thats a waste of money. Its the telescope that creates the image. you need an eyepiece to magnify and view that image. That £500 lens cant improve the original image, but will allow you to view it at its original best. The finderscope is 9x50. Ok for now. I want a Telrad!, love the idea, but its got to be mounted with sticky pads! needs batteries. All great fun and can be purchased at a later date. Choices? The 10" or the 8". You`ll not regret the purchase, but might regret the size? The two supplied lenses and the finderscope will work just fine, with improvements at a later date as required. Is this message too late now?

[cybernautic]

cybernautic.....Keep running the circles, its a great exercise for the brain, and helps in your final decision. I say get the 8" but you may be saddened, because its not, in your opinion, as good as I describe ( remember Ive not had perfect conditions yet). You buy the 10" and think Wow! or maybe not, and think maybe the 12" could have been better? Its tough. I have what I have, and many others have the same setup. I wouldnt really worry about having to buy "expensive" lens because of the aperture. The lenses supplied with my scope are the same supplied with the 250PX so they will work just as well on either scope, its just that the 10" gathers more light, that gives a brighter image to the focal point (its still coming up a 2"- 1.25" draw tube to the eyepiece) but there are better designed lenses available, and dont neccessarily need to be"expensive". You will want to better the quality of the lenses one day, but its the 10mm that needs your attenntion first. There are lenses out there at over £500GBP but under my viewing conditions, thats a waste of money. Its the telescope that creates the image. you need an eyepiece to magnify and view that image. That £500 lens cant improve the original image, but will allow you to view it at its original best. The finderscope is 9x50. Ok for now. I want a Telrad!, love the idea, but its got to be mounted with sticky pads! needs batteries. All great fun and can be purchased at a later date. Choices? The 10" or the 8". You`ll not regret the purchase, but might regret the size? The two supplied lenses and the finderscope will work just fine, with improvements at a later date as required. Is this message too late now?

No it's not too late

Still deliberating unfortunately

I agree that I won't regret the purchase but I might regret the size. I hope that a 10'' would be my maximum aperture! I don't think I'll be disappointed with the 8'' at all. It gets so many good reports. From having read around the subject, it seems there is no perfect telescope and everything comes with its own advantages and disadvantages. The 8'' is more portable, cheaper, easier to collimate, more forgiving of EPs and less prone to coma. The 10'' has over 50% more light-gathering ability but it's heavier, needs to be more precisely collimated, is more prone to coma, about 160 euros more expensive and less forgiving of EPs.

I'm still leaning towards the 200P at the moment. It just seems like a great all-rounder.

[Naemeth]

A 10" isn't that big. The tube is the same length as an 8" F/6, just a bit fatter. The OTA weighs 13kg and the base is 15kg - both very manageable for most people. I manage regularly to take it down 3 flights of stairs so I'd describe it as pretty portable (of course you can't cycle with it though!). Collimation is easy, and it seems mine holds collimation very well - sometimes I don't even check it as I use it for low power views most of the time.

HTH

[jetstream]

If I didn't have to transport my 10" to dark skies I would have at least a 12".Those truss SW Dobs look really nice....

[cybernautic]

Thank you to everyone who has contributed. I've gone round in a complete circle from an 8'' to a 10'' and now I'm back at an 8''. I'm pretty sure I'll order the Skywatcher Skyliner 200P Dobsonian. A bag of potatoes has convinced me. I got some today and it was a 10kg bag, the same weight as the OTA of the 8'' Dob. It felt comfortable to lift and I could imagine moving it down into the garden. I then put the spuds in another bag and added an extra 5kg, the same weight as the OTA of the 250PX. It might not sound much but I noticed a big difference. Yes, it was sort of manageable but it took more effort and it wasn't particularly comfortable. It even twinged my back a little! Having had back surgery in the past and a ruptured disc a few years ago I don't want anything that's going to aggravate a pre-existing issue. Yes, I can mount the scope on wheels or use a trolley but there are three steps up into the house and although there's an outbuilding I can keep it in, I'd rather store the scope downstairs in the utility room. Will I regret losing the 2'' of aperture? Probably, lol. But I'm also sure that the 200P will perform very well under the dark skies and, being easier to move, I think I'm much more likely to make use of it.

For others in the same situation of having to decide between an 8'' and a 10'' Dob, you have my sympathy!

[cybernautic]

Ordered the Skywatcher 250PX with Telrad in the end. I'll find a way of shifting it

I'll post an update when it turns up and I've got it assembled!

[bingevader]

Congratulations!

[AlexB67]

I am sure you'll like it, Have fun with it      Telrad is on my list when FLO get it in stock ( estimate 3 weeks ) , but I am kind of enjoying and try to live without one and getting used to the finder in a way and see how I get on with it, I am improving using it,  so it is not an immediate add on rush for me, though no doubt you'll not regret getting one straight away.