8" or 10" Dobsonian

[Farnsworth]

Hello everyone,

I recently sold my 8" f/6 and now I'm racking my brain over whether I should replaced it again with an 8" f/6 Dob or a 10" f/5 Dob.

Don't get me wrong, I don't regret selling my old scope, since regardless of whether my new scope will be 8 or 10 inches its mirror will be better than my old one's. Not that its mirror was awfully bad, but I'd like to have something really good with min. 0.95 Strehl ratio and quartz substrate.

Surprisingly the overall price difference between 8 and 10 inch would only be around 100€ (8"~750€, 10"~850€), which kind of screams for the 10".

However, I'm still not sure what to take... In many comparisons of 8" and 10" Newtonians I read that there is only a minor difference in brightness and that you don't gain any noticeable details at DSO. I should mention that I use the scope mainly for Deep Sky observing.

On the other hand the 10" also has drawbacks: it's obviously heavier and larger (still manageable though) and it shows more coma - I have no idea to what extent it impairs the view though.

In terms of eyepieces most of mine should work at f/5, I only had to replace the lowest power eyepiece.

All in all my question is whether you think that the larger aperture of the 10" f/5 is worth the drawback of coma and that it demands better eyepieces. It surely is a thing of personal preference afterall, but I'd like to know your opinion. Has anyone maybe ever done a side by side comparison?

CS

Yasin

[Charic]

I would like to see what  a 12" offers first, then see if a 10" would  suffice ( based  purely for visual use) Buying another 8" is not really an upgrade.

If I can use my BSTs on an f/5 I`d be happy, as I track/view on axis.

The  larger aperture would give more brightness,  more sharpness resulting in  better / larger image at the focal plane.

[nicoscy]

If you can stomach that there may be delays and that they are not the most responsive / offer the best customer care, I would wholeheartedly recommend a 12" from Orion Optics UK. Sufficient jump in aperture and very lightweight for the aperture. I have problems with my lower back and this telescope is a breeze to move and set up.

You are right regarding the difference in views from 8" to 10". Yes, there will be some difference and a bit of a further reach for DSO, but you really need to jump from 8 to 12 and then to 16 to see significant differences.

[sbooder]

I would go the 10", it will give you better views of DSOs than the 8" and if you are going OO then you will not be disappointed.  A 12" would in my view be a bit heavy for some but if you can afford it and weight is not a problem then as the others say a 12" will blow your mind compared to an 8".

[Luke]

I would go for the 10 inch, significantly more light gathering power, a step up from an 8 inch scope under my okay skies. I have a 10 inch GSO and I like that it's pretty easy to move around. I had a 12 inch Skywatcher, which had better optics in my view, but I put the 10 out more because it's that bit lighter/easier to move around. For me the temptation would be a short 12 inch dob that is similar weight to my 10 inch GSO and with good optics (the F4 12 inch Orion Optics looks perfect on paper, will be demanding on eyepieces but I have a Paracorr and Delos eyepieces so should be fine).

[nicoscy]

Luke, that's my scope and in real life it actually feels much lighter than it looks. Also very easy to carry due to the rings.

[estwing]

The 10" is the way to go. The 12" dob is a mighty thing to move about on your own and DSO's will be nice in that size app

[mapstar]

Always a trade off between views and portability 10" would be better though

[John]

The 12" Orion Optcs dobsonian weighs the same as a 10" Skywatcher or GSO / Revelation dobsonian

Mine is really very easy to move around in 2 sections and I can even move it a short distance in one piece. I'd not want to do stairs with it in one piece though.

[faulksy]

bigger is better go to 12" if you can, 8" is fine but never go backwards

[estwing]

The 12" Orion Optcs dobsonian weighs the same as a 10" Skywatcher or GSO / Revelation dobsonian

Mine is really very easy to move around in 2 sections and I can even move it a short distance in one piece. I'd not want to do stairs with it in one piece though.

didnt know that John...go for the 12"!!!

[swamp thing]

Go for the biggest you can handle. Coma can be cured with correctors.........aperture fever can't

Joking aside. be realistic on what you can handle. You want it collecting photons, not dust.

[Farnsworth]

Thanks for your replies. I should've mentioned that I can't carry 12 inch, there simply isn't enough space in my car. I'd rather have an 8 or 10 inch which I can take to a dark site...

CS

Yasin

[nicoscy]

Thanks for your replies. I should've mentioned that I can't carry 12 inch, there simply isn't enough space in my car. I'd rather have an 8 or 10 inch which I can take to a dark site...

CS

Yasin

Ah, but the 12" f4 Orion Optics UK Dob is the same lenght as your average 10" dob 

[nicoscy]

Check the f4 model.

[Farnsworth]

Oh nice, thought it was f/5. However, with this Scope price becomes an issue, with a dobsonian mount it's more than 1600€, way more than I intended to spend.

I guess I will just get the 10" and if coma bothers me too much, I'd buy a coma corrector.

Is coma actually very distinct at f/5?

[jabeoo1]

10 inch = perfect !

Note:  I have no outside storage for it and it needs taking upstairs.

For me any bigger would remain very underused, however the 10inch remains well used and guilt free.  It is doable for a short 1 hour session.  Also with a bit of brawn it can single handedly be taken off to a dark sky in a small car without threat of back injury.

Thats just my pennies worth.  

[nicoscy]

No paracorr needed at f5. It is nice to have but far from essential.

[Charic]

Remember the simplicity and ease of use the 8" gave you. The 10" has the same complexity only with a bit more power. Tell us when you order it?

I wouldn't go flex-tube route either, needs  a jacket  to hide stray light and collimation checks possibly every use? Get a 10" solid tube

Edit:....just realised, you may not have had a Skyliner. The 10" Skyliner is f/4.7 ( my reason for the 12" Skywatcher at f/5 ) would need precise collimation and possibly better EPs than you had before?......Nothings so straightforward is it 

[russ.will]

I had an 8" SW and then want to a 12" SW. The difference was not small in visual terms.

I sold it and then picked up a 1/10 wave OOUK 8" F6, reasoning in my head that the superior optics would help bridge the aperture deficit. It lasted about three months before I realised that what I needed was another 12" Dob, but in a more manageable form factor.

I don't know what level either of the the mirrors in my 12" Dobs rate, but for visual, they spank the 8" 1/10.

Both of the 12" were/are F4.9. I had a coma corrector in the first one, but haven't bothered thus far in the ES. Yes, you can see it, but I'd spend the money on better EPs first, as that results in a greater increase in viewing quality. At higher magnifications, I honestly thought it was beneficial to remove the extra glass from the light path, coma being a non-issue (for me) above 150x.

Russell

[Astro Imp]

A very interesting and informative thread as I am trying to decide just this question.