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9.25 inch refractor project

Started by jimegger , Jan 16 2013 07:49 PM
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407 replies to this topic

#201 Mike I. Jones

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Posted 05 April 2013 - 11:42 PM

Here's the OSLO file that includes the wedged airspace, in case you wanted to doodle with it.

Jim, that's one fine lookin' refractor image. Let's see some Moon shots as soon as you are able to!

It was an honor to work with you on this project. You're an A+ optical worker for sure.

Mike

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#202 jimegger

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Posted 05 April 2013 - 11:44 PM

I did see that Mike in the star images during star testing.

This is your design Mike, come to fruition. As soon as the moon comes into view again I'll get some shots of it, maybe even Jupiter. After a week of sunny clear weather we have gone into the usual Alaskan cloudy stuff with snow on the way. We only have until April 24rth at the latest for night skies then it is just too light except for the moon and bright planets. By this coming fall I should have the scope mounted up and ready for some real use as well as imaging.

Here are a few of the scopes I have available to me along with the 127 APO, a six inch refractor I made and the 9.25 inch refractor. The blue scope is my 12.5 inch reflector which has awesome optics and is equipped with a 5 inch Surplus Shed refractor, a 90 mm refractor and a 50 mm finder. It takes excellent images and is easy to set up for imaging. I am really spoiled here ! The 26 inch reflector is in the background and also has excellent optics which produce great images when the atmosphere allows it. I made all of the 26 inch components except for the diagonal mirror as well as all of the 12.5 inch components except for the lenses and the diagonal. There is something about working with glass that I just really enjoy.

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  • 5780977-IMG_5128 - Copy.JPG

#203 Mark Harry

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Posted 06 April 2013 - 05:17 AM

Jim, what a difference in the last 2 mountain pics!!!
I'm impressed!!! Nice work.
(quite a stable of scopes there, too.
M.

#204 Mike I. Jones

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Posted 06 April 2013 - 07:49 AM

Man, lookit them polar axis angles almost pointin' straight up! You could almost just put a rock under the south side of a Dobson and be equatorial!
Mike

#205 Old Will

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Posted 06 April 2013 - 06:16 PM

I weighed my 9,5" achromat blank set ,, it is 12.6 lbs
The set is SK18A & SF5 11/16" thick. When I make it I am thinking of f/20 = 180". I am going to tri-fold it down to a 60" OTA. First though I am going to use my other achromat sets, a 6" & an 8" to gain experience. I'm also wanting to avoid excessive moment arm torque,, cheers. Will

#206 Old Will

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Posted 06 April 2013 - 06:19 PM

Mike can you give me the radii multipliers for 4" achromat using SK51 & DF2 ,, is DF2 different than F2? I have three sets, they were gifts

#207 jimegger

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Posted 09 April 2013 - 01:25 AM

I weighed the objective in its cell and it came to 15 lbs.

#208 Herr Ointment

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Posted 09 April 2013 - 09:53 AM

Dude, you deserve some kind of an award!

Incredible!

#209 Mark Harry

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Posted 10 April 2013 - 05:42 AM

Jim, how long has this project taken?
2 years?
M.

#210 jimegger

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Posted 10 April 2013 - 04:02 PM

Mark, it took a year and a half. A lot of that was time off from it though and I had a couple of glitches with chipping blanks etc. Actual labor time in the glass itself is about 90 hours. It was well worth it !

#211 Mike I. Jones

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Posted 10 April 2013 - 04:51 PM

You mean, so far, or are you DONE??!!

#212 jimegger

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Posted 10 April 2013 - 09:36 PM

Mike , I may be done after this next test but it is so close that it is not going to be much longer. It is giving nearly identical star test images inside and outside focus. Star images are very tight to where it easily splits Castor and has improved even more with the last test. I am still awaiting clear skies to evaluate the last 15 minute correction session.

#213 MKV

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Posted 11 April 2013 - 06:01 AM

I may be done after this next test but it is so close that it is not going to be much longer. It is giving nearly identical star test images inside and outside focus. Star images are very tight to where it easily splits Castor and has improved even more with the last test. I am still awaiting clear skies to evaluate the last 15 minute correction session.

Jim, Castor is a whopping 5 arc seconds apart these days -- hardly a "test" for a 9.25 inch aperture. If you're testing the theoretical limit of your 9.25 inch objective, then the distance ten times smaller (i.e. 0.5 arc seconds) may present a real challenege. Find a 0.5 arc second double in the Almanac and, on a good night, see how close the scope comes to its theoretical limit.

One thins is certain: your objective should be able to cleanly separate 1 arc second doubles, i.e. stars five times closer than Castor on any average night.

Even way back in the 1960s and 1970s, Castor was a tighter pair, separated by 1.8 arc seconds, which was a good test for a 3-inch objective, but certainly never for a 9.25
inch lens!

Reagrds,
Mladen

#214 kfrederick

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Posted 11 April 2013 - 06:51 AM

http://www.windows2u...oons_table.html Jim you might be able to see some of Jupiter other moons . Congrats

#215 Mark Harry

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Posted 11 April 2013 - 07:54 AM

Finding atmospheric conditions where .5 arc second rez is possible, is ludicrous where there's a lot of weather related changes- my 2 cents.
M.

#216 jimegger

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Posted 11 April 2013 - 11:14 AM

When I mentioned Castor as being EASILY separated with this objective , it was done with not the best seeing. It was done with the objective still in the process of being figured which it still is but indicates it is going in the right direction. Once I get to where the star is a point with 2 or so diffraction rings around that point like in my six inch will I consider it done. It is still inching towards that moment - more work to be done ! The weather up here is the clincher as it generally is bad seeing.

#217 saemark30

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Posted 11 April 2013 - 11:15 AM

Did you start with pregenerated curves on the blanks Jim?
I gather you did all the grinding and figuring by hand.
If so, you deserve an extra round of applause.

#218 jimegger

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Posted 11 April 2013 - 11:19 AM

I tried generating curves myself with a diamond tool but chipped the blank (crown) so I ended up doing it all by hand. I would certainly recommend getting the supplier to generate curves as it will save a ton of time grinding. If you are using glass tooling then you need them made with matching curves as well of course.

#219 jimegger

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Posted 17 April 2013 - 12:27 AM

Okay Mike, here's your lunar limb shot taken with a hand held Canon digital camera through a Meade 50 mm wide angle 2 inch eyepiece when the sky is still somewhat light in the evening.

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  • 5803838-Moon.jpg

#220 Mark Harry

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Posted 17 April 2013 - 06:07 AM

I'd say that's pretty darn good!!! Moon's so bright there should be a bit of color anyhow. Doesn't look objectionable, and usually a small camera's shot misses a lot of what can actually be seen.
(My 2 cents)
M.

#221 mikey cee

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Posted 17 April 2013 - 09:27 AM

Nice job Jim. Even my large objective shows a scosh of yellowish green along the limb....plus a tad of purple but that is only around 410 and above. :waytogo: :waytogo: :waytogo: Mike

#222 jimegger

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Posted 17 April 2013 - 01:12 PM

If i move my eye around the eyepiece the color on the limb goes from purple to greenish but is not hugely so on either account. I have noticed the eyepiece itself has some small color issues when used on my reflectors so that may account for some of the color as well. This objective is still a work in progress as the figuring is progressing toward the goal of diffraction limited performance. It is very close now. After doing star testing and getting it in the ball park I used the first surface mirror I was suspicious of to check the objective and it seems to be okay since it gave the same basic shape on the objective as the star tests showed. Now I am going for the DPAC straight Ronchi lines and Foucault cutoff. It is very close according to that test. Visually the moon was showing very nice detail and the stars at 200 X were tight diffraction patterns but too many bright rings yet and the bad seeing wasn't helping. Baby steps..... baby steps...

#223 mikey cee

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Posted 17 April 2013 - 01:49 PM

Jim you've done a bang up job there. I still can't get my head around the fact you can turn clear blanks into frosted glass and back into crystal clear and highly polished "paper weights"! That's exactly what I would call them after I got done that's for **** sure! :foreheadslap: Still can't believe my eyes! Super job! :bow: Mike

#224 saemark30

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Posted 17 April 2013 - 02:19 PM

Could you take an image of Polaris (as it doesn't move much) showing the bright rings?

#225 Mike I. Jones

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Posted 17 April 2013 - 02:53 PM

Jim, that looks pretty good, but it's hard to tell with all the extra optics (eyepiece, camera lens) in the path, and the relatively low image contrast. Do you have a DSLR that you could just plug directly in and take photos, directly onto the focal plane? That will be the true telling of performance. Also, the Polaris idea is good.
Mike
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