183 replies to this topic

[Mr. Bill]

Well, I "pulled the trigger" on two 127mm f/5.5 Istar achromats in collimatable lens cells to build binoculars using 3.1 inch secondary mirrors relaying lightcone to 2 inch diagonals in low profile helical focusers which relays to 1 1/4 inch diagonal.

Raytrace shows full illumination over 27mm lightcone at fieldstop of 19mm and 24mm Panoptic eps.

This will be a fun project that may be my ultimate Milky Way sweeper.

CAD drawing shows layout for 6 inch f/5...this will be same design for 5 inch f/5.5.

Attached Thumbnails

• 

[Mark9473]

One of my cherished memories is a view, some 22 years ago, of the Great Orion Nebula through a 5" f/5 scope under mag 7 skies. I can only dream of getting that with two eyes.

[GlennLeDrew]

Bill,
If you wish full illumination across a 27mm field stop (or whatever the desired circle), your mirrors must be large enough to field the full envelope of light contributing to image formation. In your drawing here, the mirrors have been undersized (or located too near the objective), and in the case of the first mirror may result in *reduced* aperture.

What are the 'strange' rays emanating from the ~3/4 radius on the objective. They serve no useful purpose for ray tracing. Indeed, it seems they've led you astray. Get rid of them, and consider only the outermost pair of rays, which accurately represent the light bundle for 100% illumination to the field edge.

[Mr. Bill]

Glenn

I show the drawing (not mine) only to give general layout of my design, not dimensions. It is obvious that there it considerable vignetting as drawn.

If you take this and scale it for 5 inches instead of 6, and adjust the light cone for f/5.5 instead of 5, you will see there is no vignetting.

The raytrace I did on paper shows full illumination over 27mm which is the fieldstop of the 24mm Panoptic.

[Mr. Bill]

Just got back from observing trip in central Nevada and found box from Istar waiting.

Coatings are almost invisible on these....reminds me of the coatings on my Fuji 25x100s. Definitely different coatings than on my Istar 6 inch f/5 lens cell.

Interferograms show RMS on both 0.020 and P-V 0.215 and 0.229 which bodes well, certainly for the low magnification views which these are intended.

Be interesting to build box to test monocularly with high power.

Note consecutive serial numbers.

Attached Thumbnails

• 

[Rich V.]

Now the fun begins......

Rich

[GlennLeDrew]

Bill,
With good figures such as these lenses posses, you'll be good to 150X. The 5" f/5 bino I built for a friend has objectives having about 1/3 wavefront errors, and we've used Nagler 4.8mm eyepieces for about 130X to quite good effect. Exciting times ahead for you!

[Mr. Bill]

Am building box next week to test out monocular.

[Mr. Bill]

Bill,
With good figures such as these lenses posses, you'll be good to 150X. The 5" f/5 bino I built for a friend has objectives having about 1/3 wavefront errors, and we've used Nagler 4.8mm eyepieces for about 130X to quite good effect. Exciting times ahead for you!

Glenn

Did you use 3 mirror design in my above CAD drawing?

[Mr. Bill]

If my calculation is correct, with RMS 0.020, the Strehl ratio is 96.8%.

If that is the correct RMS value as shown on the report, that's much better than the 88% minimum promised.

[Rich V.]

That's a pleasant surprise, Bill. It really could make a killer binoscope with good high magnification capabilities as well as your intended WF application.

Rich

[Unknownastron]

Oh how I wish I lived near you and could see this creation take shape. Much work and much tweaking ahead but the result will be an instrument for life. Keep us posted.
Clear skies and clean glass,
Mike

[GlennLeDrew]

That 5" f/5 I built did indeed use a 3-mirror system. The first mirror is a 2.14" m.a., and the other two are 1.52" m.a., arranged to direct the light inward and then upward to the eyepieces. In spite of the somewhat smaller-than-46mm field stop on widest field 2" eyepieces, the 1.52" mirrors cause no discernible edge-of-field darkening. All mirrors were purchased from Lumicon, and have enhanced aluminum coatings.

[Mr. Bill]

Looks like total cost of components is about $2K (not including eps)....certainly reasonable when you consider what a similiar product would cost if available.

The only other similiar (5 inch) binoscope I know about that can be ordered now is the Vixen which is $4K for the OTA.

This will "blow the doors" off the Vixen (or Garrett's 6 inch for that matter)... I am willing to bet a C note on that.

[GlennLeDrew]

It most definitely will blow the doors off the current crop of Chinese-made offerings. I'd also choose it over the vaunted Fuji 150mm models in a heartbeat!

[Mr. Bill]

I'd also choose it over the vaunted Fuji 150mm models in a heartbeat!

Been there, done that...time to move on.

[Mr. Bill]

Just ordered 99% 1 1/4 and 2 inch pairs of diagonals from Stellervue.

Ordered the other 3.1 from Discovery.

Could have this together in time for the GSSP SP next month!

[Mr. Bill]

Given some thought to both inter and intra barrel collimation...

Current idea is to build separate barrel boxes so that each can be collimated individually, attach boxes so that they can be pivoted (pitch) for altitude collimation correction and shimmed to correct for azimuth correction.

[GlennLeDrew]

That'll add mass and needless complexity. One rigid body is best. You can carefully align and then lock down five of the six mirrors, leaving just the one to do the tiny tweaks occasionally necessary.

In the 'big box' 5" f/5 bino I built, the larger, first mirrors are tilt adjustable. The other, smaller ones are mounted via RTV to pieces of square aluminum tubing cut at 45 degree angles, and act just like small periscopes. The mutually parallel sides to which the mirrors' back surface are RTV'd make alignment of these two pairs of mirrors absolutely reliable. The beauty of this system is that the 45 degree cuts need not be to micrometric precision--errors can be as large as a couple of degrees. Why? Because the light exiting will be parallel to that entering, even with considerable rotation of the unit.

[Mr. Bill]

OK...so first mirror (3.1) would be adjustable.

So one of these could have rotation in the azimuth and could be shimmed to create altitude.

Does that sound right?

[Wes James]

Would love to see some drawings/pictures of some of this... for us "visual" learners!

[Mr. Bill]

Would love to see some drawings/pictures of some of this... for us "visual" learners!

Will start a thread on ATM forum and post link on this thread.

Still waiting on parts and finalizing construction details.

[GlennLeDrew]

One would be tiltable in the fore-aft direction, which would cause the image to move up-down. The other would rotate about the optical axis (as coming from the objective, not that as reflected), which would cause the image to move L-R. As long as reasonable care has been exercised in the dimensioning of components and their placement, the rotation of the one mirror in order to effect collimation will be so slight that image rotation will not be an issue.

When I first assembled the 5" f/5, I had adjusted the tiltable mirrors on the rear assembly merely by eye. When I attached this unit to the body, the bino was not far from collimation, only small adjustments being required. I say this to assure you that as long as you observe (my version) of the carpenter's dictum which states, "measure thrice, cut once", your bino will come together nicely and perform splendidly.

[Mr. Bill]

Glenn

Just ordered 2 of these....using 1 box design and collimate with secondary holders.

http://www.astrosyst...biz/sechold.htm

[Mr. Bill]

Looks like all the bits and pieces will show up by end of week.

Soon as I verify a few measurements (like back focus through diagonals), I can draw up the dimensions and start cutting box pieces.