6" or 8", what's the difference?

[Cjg]

And before someone posts 2":), I mean in practical use when viewing.

Am talking about a Dobsonian scope, I don't have a lot of spare space, so was poised to go for a 6", but will the 8" be massively better - I mean it's only 2" right? Does that extra light gathering make a practicable difference when viewing under dark skies??

Thanks,

Chris

[swamp thing]

Hi Chris

Whilst the 8" is a more powerful scope, a 6" Is still a great tool for observing with.

TBH there is not much difference size wise as their focal lengths are similar on most commercial models.

The 6" are normally f/8 whilst the 8" are usually f/6 so they are both around 4' (1200mm) long.

It's just down to base size (which I can't help with sorry).

Either way you can't go wrong they're both great scopes.

Regards Steve

[ronin]

You will gather about 75% more light, 77% is the ratio but the secondary of the 8" may be slightly bigger so lets approzmate to 75% more.

So you will see a bit more, but the eye response is not linear, so the additional objects is not as greatly increased as you may think.

It will enable a fair bit more then the 6" to be seen. That 75% is a decent increase.

It will be heavier, close to twice I would suspect. It will be a bit less easy to haul out and set up, bigger and longer.

You will I suspect be happier with the 8" and you will not need to consider an aperture increase, well not for some time.

If anything bigger is your intention at some time, 10" or 12", then perhaps the smaller one if the price difference makes it sensible to keep the difference and put towards the later bigger option.

Problem is that the scope is the start, you will also soon be looking at additional eyepieces and a collimator at least, say another £100 for these. Factor these into the cost and perhaps the 6" allows for these as well.

[Bazzaar]

Its because the light gathered is proportional to the area of the mirror which involves squaring the mirror size(radius actually) times pi.

That results in a more appreciable difference.

6 squared = 36

8 squared = 64

Regards

Barry

[Beulah]

I have owned both scopes and yes, the 8" outperforms the 6" by quite a bit.

Sorry, that was a rather vague answer. Try the nebula in Orion, for example (M42) it looks pretty staggering and textured with a bright core in the 8", whilst the 6" shows a more uniform, contained "flower" shape to the nebula.

[PRICEMAN]

I've got the 8 inch. Fits quite easily in the corner of any room and easy enough to move about by yourself. It ain't one of the best selling scopes in the uk for no reason. Worth the extra money if you ask me.

Leigh.

[Cjg]

Thank you very much for the input everyone, very helpful

[wayneh]

Have to say i have just got the 8".. and iam very happy with :-)

[dweller25]

I have had a 6" F/8, a 8" F/6 and a 10" F/4.7

The 10" gave the best planetary views but was heavy.

The 8" was only slightly bigger/heavier than the 6" but gave better planetary views.

For me the 8" F/6 was the best compromise and was easy to collimate too.

[Demonperformer]

The increase in light grasp equates roughly to 0.6 magnitudes (according to the table in Burnham)