My design complete, I take the prototype to the optics lab and test it out. Sure enough my tests show that .98 of the light ends up just where it should be and I go to market with my world beating design.

One of the best views I have ever seen of Saturn through any small amateur telescope were those produced by a humble 6” f/8 Newtonian. I have no idea what the Strehl ratio is or the wavefront error and nor do I care, because the views of Saturn on one night of perfect seeing will stay with me for a lifetime and that is what amateur astronomy is all about!

9mm hex allen wrenchautozone

Usually telescopes are rated for one color of light,  typically green.             The hard truth here, is that a triplet / quadruplet telescope that was designed for visual use at 450nm -680nm  maybe absolute garbage at 390nm.         (very important to solar observation)

If i am not mistaken ,  LZOS built  the best lens ever manufactured outside of a government agency.      I would love to see what adding LIDAR could do for a cnc milling/polishing process.    Probably would never need an interferometer report....

Conversely, for those of us that design and build telescopes, knowing we have a really fine piece of glass (of Strehl ration >0.8), it gives us something of a barometer for the success or failure of our design. If we can't see the Moon after hours of toil, we know we really screwed up something. If we've done due diligence in design and craftsmanship, we'll be assured of a great instrument.

It is in simple terms the ratio between the amount of light brought to focus at a specific point (the Airy disc) and what should be there in a theoretical perfect system. Therefore the best it can be is 1, which is sometimes expressed as 100.

Usually telescopes are rated for one color of light,  typically green.             The hard truth here, is that a triplet / quadruplet telescope that was designed for visual use at 450nm -680nm  maybe absolute garbage at 390nm.         (very important to solar observation)

9mm HexBit

Back in the real world, would a scope with a scope with a Strehl ratio of .92 be any better than the scope with a Strehl ratio of .85? The answer is potentially it could be, but equally it may not be…

Fascinating stuff! Not very practical though! In my new oldest book (270yrs!) the author uses a 126foot telescope of Huygens! I think it must be of similar design to your image. I’m wondering what S and N are in the image? Some sort of inertial dampers? Your scope looks amazing too!

Any optical system is only as good as the weakest link and not everything can be determined from the figures quoted in the advertisements. The best optics in the world placed in a poorly designed tube with a wobbly focuser will not make a great scope!

Well, for nighttime observing I've found that light shrouds are needed otherwise the wonderful optics show lowered contrast due to ambient light intrusion.

I believe a strehl of 0.8 is diffraction limited so any aberration error will be smaller than airy disk. And of course strehl plays no role in chromatic aberration!

Spectrally a little different for mirrors because they perform the most  amazing at blue light,   however spherochromatism is going to make or break your enjoyment with imaging and high magnification....

9mm hex allen wrenchhome depot

Well, for nighttime observing I've found that light shrouds are needed otherwise the wonderful optics show lowered contrast due to ambient light intrusion.

For the first image its a modified Lunt LS50C etalon that i put in a shroud for internal use. (normally is intended for external)

9mm AllenKey Socket

LZOS objectives often show as a touch better than the manufacturers supplied tests, when they are tested independently. The manufacturers test is just to demonstrate that they have met the minimum standards required I believe.

Allenkey sizes in mm

Spectrally a little different for mirrors because they perform the most  amazing at blue light,   however spherochromatism is going to make or break your enjoyment with imaging and high magnification....

First I pick the optics and let’s say TMB do a nice big lens with a Strehl ratio of 0.98 a nice big figure to go with my big lens.

The message is simple, look at the whole picture and if possible look through a sample of the scope - if you like what you see then these figures become irrelevant.

OK, so this is somewhat satirical and the big shiny telescope would never actually make it to the market. But it highlights the fact that you shouldn’t base your buying decision on such figures alone. In the example above a well-designed scope with a Strehl ratio .85 would actually perform considerably better.

That particular calcium filter is something that I developed and cannot be purchased (was my own development).    Its called a Skybender.

Here is my "big silver shiny zero baffle scope" that i point at the sun and get the images below.. .         250 years ago people literally mounted  huge optics to a roof, tied a string to it, and literally tied the eyepiece to a string dangling from said roof optic. and brought it to their eye.  No tube. No baffles. Nothing but 20 feet between them and the optic.     You would be pretty surprised how good a 4000mm focal length optic pointed at the moon looks through an eyepiece attached to a string......

One of the best views I have ever seen of Saturn through any small amateur telescope were those produced by a humble 6” f/8 Newtonian. I have no idea what the Strehl ratio is or the wavefront error and nor do I care, because the views of Saturn on one night of perfect seeing will stay with me for a lifetime and that is what amateur astronomy is all about!

9mm hex allen wrenchnearby

I believe a strehl of 0.8 is diffraction limited so any aberration error will be smaller than airy disk. And of course strehl plays no role in chromatic aberration!

9mm Allen wrenchequivalent

Next the tube, well I called it big and shiny so big and shiny it will be. So I have my tube chromed and polished to a highly reflective finish inside and out.

Finally my focuser, this will of course be big and shiny but I’ll make it in three segments so it will fold away neatly just like the sea captains scopes from the good old days.

Let me give you a telescope that will take the world by storm; I’ll call it the ‘big shiny one’, because it will be big and shiny.

Strehl ratio is becoming yet another one of those figures that is freely banded about in advertisements. But what does it really tell you?

I think you’re right Ags - N to balance the objective and s to balance the eye lens about the pivot Q. I think the little dog leg L on the end of the objective beam is to compensate for the string sag and keep the objective pointing down a little from the line of tension? And does it also keep the objective cell from tipping sideways in the neat looking ball joint M? Wonder why they used a ball joint though?

9mm hex allen wrench1 2

I love looking at old posts and reviving them!  Just seeing  the stargate telescopes by explore scientific really shows not much is needed other than the optics!

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Especially after the magic formula was cracked   How One Mathematician Solved a 2,000-Year-Old Camera Lens Problem (popularmechanics.com)

This is a great post! An excellent example of over-technical-izing the purchase of a telescope. It falls in the ralm of audiophiles searching for that extra 0.01% Total Harmonic Distortion they will never actually detect.