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  #21  
Old 10-09-2015, 07:59 PM
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........ (unfortunately, my 3D printer is not capable of producing threads with such a small pitch (0.75mm.. or is it?) .. ......
Well, I tried to make the thread 42x0.75mm.. and guess what, it worked
It doesn't look perfect, but it can be screwed in and tightened enough to support the camera weight.

Last edited by bojan; 10-09-2015 at 08:32 PM.
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  #22  
Old 10-09-2015, 10:36 PM
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Yep, only one..
BTW, for 2 surfaces the attenuation is 11.64%.. or transmission is 100% - 6% = 94%, and minus additional 6% of 94%, total is 88.36%..
11.64% in total
that depends solely upon the refractive index, but that is what i said!
the higher the refractive index the more light lost due to reflection, but also the better the multicoat works!
i have seen enough and worked on many spectacle refractive indices when i was hoya lens optical technician and an uncoated THI 1.8n lens looks like a mirror!
pat
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  #23  
Old 15-09-2015, 02:41 PM
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I've just received the message from Stefan that my lens is ready for me to pick it up

Now I have to finish the mechanical aspect of this adventure, over the next weekend.
And then, it will probably rain every night here in Melbourne, for the whole month

Last edited by bojan; 15-09-2015 at 02:57 PM.
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  #24  
Old 20-09-2015, 07:49 AM
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Ready for star test tonight, weather permitting.

I couldn't dismantle the front group yet, so a bit of fungus is still there, but I am not worried about it right now.
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  #25  
Old 20-09-2015, 08:53 AM
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That looks the business mate. I'll post a pic shortly of my backyard engineering project involving an old manual focus 300/2.8. I've hobbled together an arduino/easy driver stepper focuser to the rig as well as working on implementing temp compensation. I've found through testing that the focus shifts by enough to ruin images with every degree of temperature change. I am considering two options. Temp compensation in the focuser but this will require a lot of coding that im not too sure on how I would implement and a very accurate thermal probe, or alternatively I am considering using heater bands at the front and back of the lens with a thermal probe and a PID maintaining the lens temperature at say 17 degrees all night, thus negating focus shift.

Seems there is far more involved in using a camera lens for imaging than I thought.
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  #26  
Old 20-09-2015, 08:56 AM
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Oh, and yes. Since having mine mechanically ready and only needing a clear night to test it's been beautiful sunshine all day with afternoon storms and cloudy nights for 7 days.
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  #27  
Old 20-09-2015, 06:19 PM
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First test..
Just a hint of CA, when slightly out of focus.

I think the lens is as good as new , thanks to Stefan.
This is a crop from 200%, taken at full aperture.
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Last edited by bojan; 20-09-2015 at 07:48 PM.
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  #28  
Old 20-09-2015, 06:22 PM
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brilliant outcome!
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  #29  
Old 20-09-2015, 06:57 PM
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Sensational outcome to be sure. Looks to be a cracker of a lens
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  #30  
Old 20-09-2015, 07:56 PM
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It seems it suffers from slight astigmatism, but I didn't expect a perfect performance at F2.8 anyway. So, with external aperture set at 3..3.5 it will be much better.

This crop is form 100% size, one frame straight out of camera (Canon 60D, full resolution).
In corners - the same.. it's as flat as pancake
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  #31  
Old 20-09-2015, 08:58 PM
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hi bojan i hope it all worked out.
what are the details of stefans operation on the lens may i ask?
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  #32  
Old 20-09-2015, 09:08 PM
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He removed couple of 1/100'ds mm of glass from the damaged surface, polished and applied antireflective coating, so the lens element looked like new after that.

Last edited by bojan; 20-09-2015 at 09:30 PM.
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  #33  
Old 20-09-2015, 09:56 PM
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Stefan just jumped to the top of the 10 most helpful people list I guess. Haha
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  #34  
Old 21-09-2015, 10:35 AM
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Bojan,

That's a great outcome. I'm really happy for you! Great work, Stefan.

Would you mind posting a sample image once it's stopped down to f/3.5, please?

H
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  #35  
Old 21-09-2015, 10:38 AM
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Bojan,

That's a great outcome. I'm really happy for you! Great work, Stefan.

Would you mind posting a sample image once it's stopped down to f/3.5, please?

H
H,
You will have a full report.. I only need a bit of clear skies to do tests.
Probably by this weekend.
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  #36  
Old 21-09-2015, 11:03 AM
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Awesome, cheers.

H
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  #37  
Old 22-09-2015, 09:32 PM
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Comparison between F/2.8, F/3.5, f/4
Since I removed internal iris, the aperture is external (black plastic folder).
Exposure times were 5sec, 7sec 10sec, single frames, straight out of camera.
Stacks look much better - see Catalina (crop from full resolution stack 16x10sec, ISO1600 @f/4)

The difference between full aperture (143mm) and f/3.5 is drastic.. but 3.5 and 4 are almost the same (in terms of diameter, this is 114 and 100mm).

So, it seems 110mm will be just right.
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  #38  
Old 23-09-2015, 07:48 AM
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This morning I did some processing of the frames from previous post, taken last night.

Those processed images below are crops (100% size) from the middle and all four corners of the full resolution stack (Canon 60D) 17x10sec, ISO1600, @F/4 (external aperture).
I am pretty happy with the results.

Stefan, I wish to thank you here again for your help, in my opinion this Canon monster is fully restored.
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Last edited by bojan; 23-09-2015 at 03:05 PM.
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  #39  
Old 23-09-2015, 08:12 AM
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For comparison, below are crops from 100% sized stacks (16x) taken with f/2.8, f/3.5, f/4

Drastic difference between f2.8 and 3.5.
F/3.5 was taken with 50% increase (7sec) in exposure time.
F/4 was taken with 10sec exposure time.
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  #40  
Old 23-09-2015, 09:05 AM
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just a thought, but some optics designs use the aperture placement to help control aberrations in addition to limiting the amount of light (eg a MN uses the aperture placement to control coma). I have no idea if it makes sense with your lens, but it might be just be possible that it would work better at f2.8 if a full open aperture stop was placed where the original one was.
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