Difference between 12" and 16" Lightbridge

[prova]

just curious to know the 'real world' difference between these two on an overall performance comparison when observing the moon, planets and dso's

cheers

[astronut (John)]

Hi Prova,
Well the 16" has an 77% greater light grasp than the 12"
This of course doesn't mean that the 12" is shabby in it's performance.
The images the 12" shows in all areas is very detailed, the advantage the 16" has is greater detail still.
The "down" part of the 16" versus 12" is that the 16" is nearly double the weight and also the extra bulk of the base. Also to achieve the best images a Paracorr may be necessary (F4.5)
Depending on your height, it may be necessary to use a small step ladder for near zenith views.
The final difference is the price: 16" $2695, 12" $1499.
If the "negatives" don't bother you, go for the 16"
Either way take your time to way up the differences BEFORE you part with your money.

[janoskiss (Steve H)]

Have not used both scopes enough to comment on the optical quality but out-of-the-box the 16" is certainly more wobbly, less stable than the 12". I'm told that simple bracing of the rocker box with L brackets will considerably improve this.

[Kal (Andrew)]

I've looked through both (only at DSO's), and both gave fantastic views. The 16" will of course give better views of DSO's, but as John pointed out, it is at the expense of extra size and weight.

[janoskiss (Steve H)]

I would love to hear from someone who has done any serious high power planetary observing with a properly cooled and collimated 16" LB in good seeing. I am skeptical about a mass-produced fast 16" BK7 mirror delivering the goods in terms of resolution at high power but I'd love to see it or hear about it at least.

[citivolus (Ric)]

Bear in mind that a 12" dob with a quality mirror could provide better images than the 16" Lightbridge, if the mirror test results for a single sample over on cloudynights are accurate (1/3 wave, strehl 0.534).

The quality 12" would be more portable and not need a ladder to use, but would cost more.

[Kal (Andrew)]

Originally Posted by citivolus

Bear in mind that a 12" dob with a quality mirror could provide better images than the 16" Lightbridge, if the mirror test results for a single sample over on cloudynights are accurate (1/3 wave, strehl 0.534).

The quality 12" would be more portable and not need a ladder to use, but would cost more.

That 16" tested on cloudy night is 1/3.14 wavefront error, which is better than 1/6 wave peak to valley. To quote the tester: "The gentleman who tested the mirror was impressed by the test results given the fact it was a machine configured mirror. He also indicated it was the second best 16" mirror he has ever tested."

[Satchmo]

Originally Posted by Kal

To quote the tester: "The gentleman who tested the mirror was impressed by the test results given the fact it was a machine configured mirror. He also indicated it was the second best 16" mirror he has ever tested."

If a 0.536 Strehl Ratio 16" mirror was the second best he had ever tested, then hes definately living in the wrong country ... :-)

[iceman (Mike)]

I've only looked through a 16" LB a couple of times, but having seen them in the flesh, they are very large scopes.

The LB design is supposed to make them portable, but the base on those things is absolutely huge. It certainly would be very difficult to fit it in a regular car.
I don't even think they fit through a regular doorway!
Jakob has built a new, smaller base for his 16" LB so it can at least fit through doors!

I think John's (astronut) assessment is spot on.

[Kal (Andrew)]

Originally Posted by Satchmo

If a 0.536 Strehl Ratio 16" mirror was the second best he had ever tested, then hes definately living in the wrong country ... :-)

The central obstruction has no effect of the strehl ratio? I just assumed this was looking wierd because of the way they calculated it with the central obstruction.