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Surplus Shed Special on 6.1" Triplet F/1.25

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#26 btieman

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Posted 28 June 2013 - 07:07 AM

Btieman are you any other lens or just prime
Focus. ?

I did this awhile. Back lots of sa


Prime focus.

What was the nature of your sa? I'm only using about 1/3 of the exit pupil so the effects may be minimal...

#27 Chuck Hards

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Posted 28 June 2013 - 09:30 AM

Your results are similar to mine. I posted a terrestrial shot through the lens last year and thought it showed promise (can't seem to find the thread now). It was also hard for me to achieve a precise focus due to the "rigged" nature of the test setup.

#28 highfnum

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Posted 29 June 2013 - 04:23 AM

OK no more pictures of cars, trees, vents , air conditioners
here is a star shot - with 72mm corrective lens set
its my best so far - 15 sec - there still is a fair amount of coma - but star test is the best

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#29 highfnum

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Posted 29 June 2013 - 04:26 AM

just to show what a pain in the buttskie it been with this lens here is shot with 90mm corrective lens set

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#30 highfnum

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Posted 29 June 2013 - 04:29 AM

above shot was 25 sec - you can see north American nebula
but it looks like Scottie put us in warp drive!

#31 mikey cee

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Posted 29 June 2013 - 09:24 AM

Wow! :shocked:Looks like it's back to ant burner city!! :grin:

#32 Mike I. Jones

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Posted 29 June 2013 - 01:57 PM

Actually, it could be a low-f/# long-range objective lens for a night vision system. Any military designations or codes on it? If so, its color correction is likely optimized for Class B filtering, from 0.64-0.9 microns. It might just make a dandy H-alpha nebula lens, if you can get a 3-5nm passband H-alpha filter in the path ahead of the camera.

On the other hand, night vision systems didn't have to be super-corrected. Resolution of 20 lp/mm would be a superbly sharp lens for a fiber faceplate photomultiplier objective. But, them stars do look pretty sharp!

Mike


#33 highfnum

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Posted 29 June 2013 - 03:43 PM

that was my idea use it for h-alpha only
the first star shot ain't perfect bad not that either

#34 Chuck Hards

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Posted 29 June 2013 - 04:12 PM

I wonder if it was originally used with a curved film-holder, somewhat like a Schmidt camera?

#35 btieman

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Posted 29 June 2013 - 05:22 PM

highfnum (which is a kinda humorous moniker playing with this lens!) what is the chip size in your star image with the high coma? And what is the focal length of the 90mm secondary? Is it the 90mm that's supposed to go with this primary? Something else? If it has a positive focal length, it's probably making coma worse?? If it's a negative lens, it's not looking good :(

Still, my hope is photometry and not pretty pictures. Coma is more difficult to deal with, but not impossible and I've written my own photometry software so adding a way to deal with different apertures for different stars is doable.

#36 btieman

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Posted 29 June 2013 - 05:23 PM

I wonder if it was originally used with a curved film-holder, somewhat like a Schmidt camera?


I can't find it again now, but there was another thread here on CN from several years ago where someone had the entire lens set. As I recall, it was the 155mm by 195mm focal length primary, a 90mm by -78mm secondary, then two 30mm lenses for transfer optics--I think 75mm and -75mm focal lengths or thereabouts. Between the transfer optics was a beamsplitter to a secondary port...wish I could find the thread again!

Mine's now buttoned up a bit better and mounted on my son's CGEM. Looks a bit ridiculous up there :) Not looking good to get it under stars tonight, looking more and more like rain. But hopefully soon!

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#37 kw6562

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Posted 29 June 2013 - 10:21 PM

This is the "big" thread on that lens - 6" triplet --Keith

#38 btieman

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Posted 30 June 2013 - 01:51 AM

OK no more pictures of cars, trees, vents , air conditioners


Agreed! I outlasted the clouds and got the setup pictures above out under the stars for a few hours...

Below is my rendition of the North American Nebula using this lens.

This is full aperture, no-additional optics. Using The Sky, this calculates to something like 3.46 degrees across the width of the image. Certainly some coma, but does it seem as bad as highfnum got in his shot?? Maybe...

There are still other optical issues to sort out though. The rectangular blob with halo in the left is puzzling me. It's not astigmatism as it changes orientation with the camera and thus seems independent from the lens. I thought for a bit that it was the long adapter plate that sticks out in front of the lens in the picture of it mounted on the scope above. Problem is it moves with the camera and its bi-symmetric whereas the plate should only be on one side. The tube is flocked with felt paper, and I think the camera is mounted pretty tightly to the housing but the PVC blank the camera is mounted to is not flocked and there are some metal bits holding the camera in place so maybe it's reflections off that off the primary again? Hard to say, but baffling may be next on my todo list.

Image is a single 30s exposure on the North American Nebula.

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#39 GlennLeDrew

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Posted 30 June 2013 - 02:07 AM

Btieman,
All stars above a certain brightness have that vertically oriented 'bow tie' flaring. I wonder if it has anything to do with the very fast light cone's interaction with the pixels???

#40 btieman

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Posted 30 June 2013 - 02:37 AM

Btieman,
All stars above a certain brightness have that vertically oriented 'bow tie' flaring. I wonder if it has anything to do with the very fast light cone's interaction with the pixels???


It could be I guess? I don't see anything similar when I saturate bright stars at f/7 with my 11" on the same camera. I thought the butterfly effect and square stars were due to microlenses. No microlenses on this camera and front side illuminated...should be no surface structure on this CCD to delineate pixels...just a hunk of Si.

I find it suspicious that the effect has a clear circular boundary which you can see around the brightest star. And the star is off center in the circle. I know the cutout the camera mounts to is canted (cut with a hacksaw by hand) so the chip isn't square to the lens so a reflection off the lens back surface makes some sense...except doesn't explain the wings. There is some metal holding the CCD in place, but it's got four fold symmetry--not two. The metal mounting is 45 degrees to the chip but I can't see where the light/dark pattern would arise.

Ack...getting too tired! I think I'll flock the back and think about some baffling then give it another go some other night!

#41 btieman

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Posted 30 June 2013 - 02:39 AM

Kieth, thanks for linking the "big" thread! That is the one I was thinking about that discusses the full lens system this primary came from.

#42 highfnum

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Posted 30 June 2013 - 08:09 AM

btieman - that (your star shot) also show halo from not all color in focus
I had a similar results - GlenDrew expressed valid critic of a similar going raw shot.

#43 highfnum

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Posted 30 June 2013 - 08:13 AM

well I tried again
1) I added red filter to control color
2) went black and white
3) 2- 35 second shots
4) full and cropped
5) its best so far - but lots of coma
6) btieman yes im using positive lens - I ordered a negative to see if I can correct

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#44 highfnum

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Posted 30 June 2013 - 08:14 AM

sweet section

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#45 highfnum

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Posted 30 June 2013 - 08:15 AM

just one more set for the hell of it

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#46 highfnum

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Posted 30 June 2013 - 08:17 AM

cropped - note - I stretched first crop shot

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#47 highfnum

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Posted 30 June 2013 - 08:23 AM

as a reference I too this shot with computer lens and same camera - 200 sec so now you know area

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#48 highfnum

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Posted 30 June 2013 - 09:49 AM

by the way makes a great low power monocular
human eye adapts to curve
saw nB visually

#49 Chuck Hards

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Posted 30 June 2013 - 10:08 AM

At what size exit pupil?

#50 btieman

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Posted 30 June 2013 - 10:13 AM

btieman - that (your star shot) also show halo from not all color in focus
I had a similar results - GlenDrew expressed valid critic of a similar going raw shot.


That may be. There's clearly something making the stars rectangular and adding the wings. I doubt that's color and until it's figured out, I'll withhold judgement on how color corrected these lenses are.

In the end, I don't much care about color as I intend to always use it filtered. Depending on how the final detector mounting goes, I can get a filter up right close to the CCD where it won't vignette.






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