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Calling all owners of larger scopes

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Hi All

I have a couple of scopes at the moment and will be selling one to part finance a new mirror set.

However I have a couple of questions in my mind:

1/ Is the jump from 16" to 20" large enough that a real difference is evident, or will I need to go bigger (22")?

2/Is there enough difference between a 20" and a 22" to justify the extra cost, The 22" is another £1000?

Any replies gratefully received.

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I have no experience in 16" vs 20", but 8" vs 14" vs 20". It is much depending on how dark skies you have. On 5 mag skies a 20" cant benefit it's huge light gathering power and an 14" is sufficient. On 4.5 mag skies an 14" vs 8" gives a real improvement. You need rally dark skies to benefit an 20". There the 20" will go deeper than an 16".

Cheers Martin

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If light grasp is the improvement that you are looking for, the ratios for 16", 20" and 22" are 64, 100 and 121 respectively, so there is quite a jump from 16" to 20" but not so much to 22". One of the biggest difference (apart from cost) is the manageability, I have a 30" F4.1 that is awaiting a rebuild and installation in an observatory as it is rarely calm enough to use it in the open air. :rolleyes:.

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Always tough to give advice. My club owned scope is a 16" Dob, and a member has a 20" Dob. I would say that there is a noticable difference on deep sky. However the 16 does not need a ladder, the 20 does, and is much less portable.

Given the choice between 20 & 22, I would choose the one with the better mirror, good construction and smooth movements, and forget the difference in light grasp.

Good luck in your choice, Ed.

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If you halve them the comparison is roughly the same.

So a 16" to a 20" is like the jump from 8" to 10" which is easily noticeable.

The jump from 20" to a 22" is like the difference of a 10" to an 11" not very noticeable.

Obviously the jump from 16" to 22" is better but for the extra cost against how many nights a year you can get the most out of this aperture, I think that 20" is probably as big as one would need go, in this country.

If you are in a foreign country with better skies then ignore me. I am sure some of the peeps abroad can help.

20" is the size that I will be going to next after very long deliberation.

Regards Steve

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