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8" Dob or 10" Dob?

Hootsitabernacle

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Hootsitabernacle

Hootsitabernacle

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so im def getting a Dob in a couple of weeks...the question is what size? aperture is king so i have read on this here forum but i have also read that if i get the bigger dob then i need to get more expensive ep's? would this be the case? a wee bit of advice on this would be most helpful..thank you please :grin:

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Stargazer_00

Stargazer_00

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The 8" is an F6 and the 10" is an F4.7

It's this speed difference which troubles an eyepiece. The faster the scope (newtonian) the more the eyepiece has to work to mitigate the coma introduced by the speed. Coma is a stretching of the stars at the edge of the field of view into tear shapes.

Obviously a 10" will give better views visually in terms of detail and resolution simply because its hoovering up more photons but it comes at the expense of the coma. You can buy very expensive eyepieces to 100% mitigate against this, or buy cheap eyepieces and care less about it., or buy a coma corrector... many choices. Eyepieces will work in both scopes, just the visual defects are slightly more visible in the faster scopes due to the speed. It comes down to your personal tolerance of the effects. Any eyepiece you buy isnt going to look worse than those supplied with the scope, in my opinion.

The good news is that optics in eyepieces are becoming more and more affordable at higher and higher qualities and in truth you can get very good performing eyepieces at a very moderate price these days (between £100-£200 each as opposed to £500+ each)

As they dont wear out or degrade you can collect them over time and ultimately the 10" scope would become the better option. It does depend how much you want to invest into the hobby though.

The 8" is a very good platform from which to jump into this hobby, make no mistake. It is the single most recommended starter scope on this forum.

I faced this same dilemma and went with the 10", and now want a 12" :)

hope that helps

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JamesF

JamesF

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Yup, the 10" Skywatcher dob is f/4.7 which is fairly demanding of eyepieces. My BGOs work fine in mine and based on John's review of the BCOs I imagine they would as well, but their field of view is quite restrictive and I personally find them hard work to use in a manual dob. My 32mm GSO/Revelation plossl that gets used very heavily in all my other scopes just won't play nicely in the 10" scope. There are more visual faults than I could count. I've posted already this week that owning the 10" dob doesn't mean you have to go out and buy a full set of Naglers, but you will have to make eyepiece choices carefully. You can't just go out and buy, say, a BST and expect it to work (I've no idea if they do or not off the top of my head). If you can live without wide field views then the Tele Vue plossls might be a good combination and they do come up reasonably regularly second hand at affordable prices. You should be able to be reasonably confident that the expensive end of the eyepiece market will work ok with the scope, but as you get to the cheaper end there are fewer choices.

I don't think the issue should stop you buying the 10" dob if that's what you'd really like, but you should be aware of the compromises you might have to make if you decide you need to expand your eyepiece collection to get the best use from it.

James

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swamp thing

swamp thing

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If its your first scope, I would go with the 8" simply because, you're probably going to want to upgrade no matter which one you get. The logical upgrade from an 8" is a 12", the logical upgrade from a 10" is a 16" monster :eek:

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knobby

knobby

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All very good points made above , also as a beginner I found it much harder and critical of collimation when I went from 6" to 10" I guess this would be the same of the 8" vs 10".

Either one will be a great scope so good luck with your choice :D

----edit----

Also, have you felt the weight of these scopes?

maybe try an club to try lifting one.

I found the 6" harder to lift than the 10".

I know that sounds stupid but because I could lift the 6 while on its mount , I struggled with it as none lump.

With the 10, I can't so i carry it as 2 lumps which is actually easier than struggling with the 6.

Good luck!

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Stargazer_00

Stargazer_00

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My rationale for 10" to 12" was to get a slightly slower scope and a little more aperture. On pure aperture alone it probably isnt worth it but a 12" is slower than a 10" and a 14" - 16" is typically slightly faster than a 10" at F4.5 and F4.4

Oh and that a 14" + would require some sort of ladder to view zenith (i believe?)

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swamp thing

swamp thing

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IMO the jump from 10" to 12" just isn't worth it as an upgrade. It's fine as a finishing point where you are just fine tuning. If you accept the views aren't going to be knockout better, just a small improvement. Then yeah it's okay, but if your expecting a decent sized jump in the view then I think 14" is minimum 16" is better.

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Stargazer_00

Stargazer_00

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Can a 14" skywatcher flex be viewed at zenith standing? I'm 6 foot exactly and its a 1600mm focal length. Assuming the primary mirror is 250-300mm off the floor like my 10" and that a portion of that focal length is from the secondary to the eyepiece I'd say the EP height at zenith of the scope would be about 1700mm off the floor. Think thats an inch or two above my eyeline.

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swamp thing

swamp thing

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Yes. I could pretty much do all my observing without going on tip toes through a 16" f/4.5.

edit: Hang about, Skywatcher have a habit of putting the focuser on at a stupid angle. I remember this from their 16" version that I had a look through. That needed steps because of where they put the focuser. Stupid design.

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blueroom

blueroom

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My first scope was a 130p Heritage, I then upgraded to the 8" and I'm very happy with it. I got the 8" cos I wasn't sure if I could handle the 10" plus I read somewhere that the 8" is more forgiving when it comes to collimating.

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Stargazer_00

Stargazer_00

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8" is a more forgiving scope than a 10" in a lot of ways. If you are not sure exactly what you're getting in to (not just scope but whole hobby) then an 8" is a good way to go. They have good resale value as many people desire them for a first scope so if you want to upgrade it'll shift in no time.

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Bart

Bart

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I think we've just spent your money on a 16 inch dob...... sorry :p

I upgraded from a 6inch to a 16 inch in january and have never looked back.

Happy shopping :smiley:

My God, you must have seen some difference!!!

Barry

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twotter

twotter

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They do say that the best telescope is the one you use the most.

I looked at both the 10" and 8" Skywatcher dobs for my first telescope in my local astronomy shop and on the face of it wanted the larger aperture. But, I have a back problem, and found the 10" was too much for me, but I could manage the 8". After buying a Skyliner 200P I found that it also has the advantages of holding collimation well and being tolerant of cheaper eyepieces.

I like it a lot and it's shown me some wonderful views of the night sky :)

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Hzadbhat

Hzadbhat

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I've got an 8 and a 10.

I believe the difference is definately noticable.

The first scope is always going to be a difficult choice though. Portability issues with the bigger scope can be a pain in the neck for a lot of people, but i've got a large 4wd.

That's the main reason I went for a collapsible. I'm already noticing that I will need better quality ep's though.

Either way, you will have a great time. Join a local club and read stuff here regularly to help you learn more.

My advice is bigger is better (if you can get around the weight and the fact that as you get bigger scopes, you need better ep's).

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