8" vs 10" Dobsonian

[Ricochet]

I am looking to invest in my first "proper" scope and based on my interests and budget I'm thinking that a Dobsonian from the Skywatcher Skyliner range is probably my best bet but my question is; 8" or 10"? Aside from cost and weight is there any advantage to buying the smaller scope or would doing so just leave me wishing I'd gone for the bigger one a few months down the line?

Also, what is the quality of the supplied eyepieces like? Should I be looking at supplementing or replacing them and what with? I've seen some recommendations for BST's but is there anything else in a similar(ish) price range that would perform better? (X-Cel LX perhaps?)

It's also worth noting that I live in an area with quite a lot of light pollution so each observing session will require either dealing with that or transporting the scope to another location.

Thanks in advance.

[laudropb]

I had the same thoughts when I purchased my Dob. I decided on the 200 mm mainly because of its longer Focal ratio, f5.9. The f4.7 of the 250mm makes it a bit more difficult keep collimation and it will be a bit harder on eyepieces. I have not regretted this decision. It is a very nice scope. As for eyepieces supplied, they are usable, especially the 25mm and I used them for a month or so as I learned how to use my scope. I did replace them with better eps once I knew what I was looking for.

[spike95609]

I had the same dilemma, and somewhere on this forum are a couple of posts revealing all the agonising that went on in my head. In the end I went for the 10" and am delighted that I did. The problem was, because I'd never owned a scope before and had no personal experience to relate to, all of my worries were based on what I thought might happen as opposed to what would happen. I'd got it into my head that the 10" would be difficult to collimate and would require constant maintenance. Not true at all. It took me just an hour to collimate it, only 15 minutes of which actually involved turning screws, the rest was me reading instructions, taking my time and thinking. Well I've had it for 11 months now and haven't had to adjust it once.

The 10" is F4.7 so will put a strain on eyepieces, but again I think far too much is made of this. I remember being very surprised when I used the 10mm and 25mm eyepieces (they retail at £15) that came with the scope and found that the view was surprisingly clear. I'd expected it to look like a badly tuned analogue TV, yet weirdly everything was sharp. Okay the 10mm does suffer a bit, around the edges the quality dips off quite a lot, but it's still perfectly usable if you're only looking at what's in the centre. I got very fine views of Jupiter, M2 and M42 with it. I upgraded after a few months to the TV plossls and Vixen SLV you can see below, which are certainly an improvement but in all honesty I think you can get away with much less and be very happy. BSTs are pretty cheap and well liked by many a 10" user.

I don't think the 10" will provide a radically superior view over the 8", but there will be an improvement, and if like me you're interested in DSOs then every extra inch of aperture will help. The only questions that remain are how much you can lift and what you can afford.

[Gazabone]

I went for a 10" and really enjoy using it. It does need collimating every now and again but I use a cheap laser collimator and it's usually done inside 2 mins now. I did have a look at a friends 8" and the mechanism looks a bit different so, although the collomation was a bit out, I didn't touch it.

Personally, I would say provided you can physically manhandle the 10" that's the one to go for.

Happy viewing.

[Moonshane]

What can you afford once you have spent £100 on a red dot finder ) tetrad recommended) and a right angle corrected image finder?

Considering the above buy the one that fits your budget. The 8 is great but aperture more often than not gives you more. These scopes are about the same size.

[Ricochet]

Thanks everyone for the replies. How much difference does a  RACI finder make? I've got a standard straight finder on an existing scope and I haven't had much of an issue with it other than it being a dew magnet.

[Piero]

Thanks everyone for the replies. How much difference does a  RACI finder make? I've got a standard straight finder on an existing scope and I haven't had much of an issue with it other than it being a dew magnet.

Both Raci and straight finders are prone to dew. For limiting this you could put the cups on when you don't use it, or build a dew shield. As far as I know the only ways to remove the problem is to get an electric strip or using a hair drier. 

The benefit from using a RACI compared to a straight finder is for your neck, particularly if you are star-hopping difficult targets.

A RACI finder allows you to hold your head straight instead of assuming weird positions which can be very uncomfortable especially when you are pointing at the zenith. On the other hand a RACI is not very suited for getting close to the area before star-hopping. Therefore, many folks use a telrad or a zero-magnification pointer (which are straight) to first locate the area of interest and then locate the target precisely with the RACI. Of course a telrad is not required for a straight finder as you already know where you are pointing because it is straight. 

As a RACI has a 90 deg diagonal like a little refractor, the view is correct UP and DOWN, but reversed LEFT and RIGHT. Therefore, when you use an atlas, you need to mentally reverse the image LEFT-RIGHT. This is not too difficult though.

Apart from these differences, the two finders work in the same way, they are essentially small achromatic refractors. If you are used to a straight finder and comfort hasn't ever been an issue for you, possibly you don't need a RACI. I cannot answer this question for you though. If you can try the two combinations, it would be better. 

Cheers, Piero

[Moonshane]

A raci finder has a view which is the same as your map not right left inverted. That's what the corrected bit or the c means. Some right angled finders do have a left right inversion though but i avoid these as they do my head in.

[Piero]

A raci finder has a view which is the same as your map not right left inverted. That's what the corrected bit or the c means. Some right angled finders do have a left right inversion though but i avoid these as they do my head in.

Thanks for the correction!

Always new things to learn!

[Dave In Vermont]

You've answered one of your questions yourself: 8" or 10" - if you're even asking after realizing that you might feel pangs of remorse if you got the 8", of course you would! Yep - go for the 10" one. Don't let the dreaded word "collimation" deter you. The horror of collimation is only present the first time you do it. And you'd have to do it with either scope a first time. We have quite a few people here who will gladly help you find your way and de-mystify this for you. After that, you'll wonder what the fuss was about. Some of us actually find we enjoy collimating our scopes! Egads! Call the men-in-white-coats to come with their nets!

Or not.

Yes an RACI. Less expensive than taking Yoga-Lessons to limber up enough for using the straight-thru variety on a Dob. Speaking of men in white-coats, who was the genius who thought to put a straight-thru finder on a Dob in the first place? Not being a fan of red-dot finders regardless, I have no opinion on which is who. Sounds like Moonshane has you well-advised there.

Eyepieces should not be planned for until you've used the scope and it's included pair for long enough to know what you like viewing. Some are perfect for planets and terrible for nebulae. And the reverse is true as well. Give yourself some time.

Clear skies,

Dave

[baggywrinkle]

I agree with LGM, 10'' with a RACI, Telrad or similar for a finder. I had a staright through on my 12'' dob and it is a pain...everywhere. A Telrad is easier to look through but the RACI wins hands down.

Once I had done a first collimation I owndered what all the fuss was about.

[Ricochet]

Eyepieces should not be planned for until you've used the scope and it's included pair for long enough to know what you like viewing. Some are perfect for planets and terrible for nebulae. And the reverse is true as well. Give yourself some time.

Thanks. I guess the real reason that I was asking is that I've seen a  few second hand and refurbed units being advertised as without eyepieces. In that scenario knowing if the price being asked for is reasonable depends on the value/usefulness of the eyepieces included with a new scope. For example, if the general concensus is that the supplied eyepieces need replacing with BST's then a "good as new" scope for £300 plus £100 on a pair of eyepieces is a better deal than paying £400 for a new scope with eyepieces that are not up to the task. On the othhr hand, if the supplied eyepieces only need supplimenting at a future stage then the warranty and support of a specialist supplier makes the new telescope the better choice.

[Matt Scunthorpe]

You'll be amazed at how much money you can spend on EPs. I paid £79 each for Celestron Xcels, and I bought 4.

I would go for the 10, just because of what Dave mentioned before. if you get the 8, you'll keep thinking/wishing that you got the 10. In real terms, theres probably very little difference between them, and as you've not used either before (I assume) you wouldn't know what the other is like anyway to compare it anyway!

Keep us posted on what you decide to buy

Matt.

[Ceramus]

I've just ordered a Skywatcher 300p goto and am concerned about the weight as it's quite a big scope. I'll have to move it from the house across the terrace to a dark part of the yard. I'm building a platform on 4 rubber 75mm rubber castors but I understand the mounting needs to be level for accurate alignment. Any ideas?

Clear skies!

[Ricochet]

I would go for the 10, just because of what Dave mentioned before. if you get the 8, you'll keep thinking/wishing that you got the 10. In real terms, theres probably very little difference between them, and as you've not used either before (I assume) you wouldn't know what the other is like anyway to compare it anyway!

There is actually a shop reasonably close to me that rents them out but the current weather forecast makes any comparison at this time purely theoretical.

[Matt Scunthorpe]

That is ideal then if you can get your hands on them. Have you considered finding a local astro club near you? They're will be a lot of scopes there for you to look at, not just dobs, for a few more ideas. but then again you might end up with more questions than before!

Matt.

[Ricochet]

If by considered you mean "googled" then yes I have, but I've not got any further than that. It looks like there are three in Hertfordshire so I guess it's a case of cross checking thier meeting dates with the weather forecast to try to go along on  a night when there is a chance of getting to look through some?

[Andyb90]

I've just bought the 10 inch Skyliner and its a great scope. I started with the 6 inch Skyliner and decided I wanted more aperture quite quickly.

I can say from the few observing sessions I've had so far there is definitely a big difference in the view between the 6 and 10 inch scopes.

The 10 inch scope is fairly hefty to move, but I can manage carryng it a short distance from the house to the back garden or into and out of the car for the dark site.

I have a 25mm X-Cel eyepiece which is okay with the scope and a Vixen SLV 12mm eyepiece on order.

Andy.

[Ricochet]

Anyone know anything about the Bresser Messier 8" Dob or Bresser optical quality vs Skywatcher?