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10-27-2009, 08:46 AM   #16
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QuoteOriginally posted by wildlifephotog Quote
Super shot there Nick.
I used something similiar years ago.

It is a telescope for a lens. The diopter goes at the business end. And the teleconverter at the camera end. One paper tube fits inside the other for a slide focus adjustment.
You can build a pretty fair telescope from a +1 diopter and eyepiece from a binocular or reading glass.
Nick's idea to use a teleconverter to couple the objective lens to the camera is a good one.

These, plus bellows + suitable black tube should be an easy way to construct long telephoto lenses. I assume that achromatic close-up lenses should be used.

How is the image edge quality & distortion in such a setup?

Dave in Iowa

10-27-2009, 09:00 AM   #17
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Usually very good. You are basicly making a telesope with a 2X barlow attached. The better the glass, the better the end result.
A +2 diopter has a focal length of .5 meter, or 19.6850 inches. The longer, the better CA control you'll have.
10-27-2009, 10:47 AM   #18
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QuoteOriginally posted by wildlifephotog Quote
Usually very good. You are basicly making a telesope with a 2X barlow attached. The better the glass, the better the end result.
A +2 diopter has a focal length of .5 meter, or 19.6850 inches. The longer, the better CA control you'll have.
sorry if i'm being obtuse but i dont know much on the technical side of lenses but does that mean when assembling a DIY lens/telescope that you need the the teleconverter 0.5 from the objective lens?
10-27-2009, 12:17 PM   #19
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Due to manufacturing tolerances, I'd start a little further away and adjust the focus tiil it is perfect. The 19.6850" is the nominal distance.

10-27-2009, 01:20 PM   #20
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Here is what's left of the lens.



It was made as an experiment, not for serious use. I will probably build a better one later from something more solid than construction paper. The moon picture was not taken with the K1000 is this picture, but with my K2000. I removed the macro lens to use for macros, but it used to be taped the the front.

The close-up lens used was a 52mm +2 diopter "Sigma achromatic macro lens".

With a 30mm diameter aperture stuck to the front the lens was at f33. The aperture didn't really make any difference in image quality. It was just as good wide open at f20.

The formula for calculating focal length is:

1000 _____ = focal length
# of diopters

The formula for calculating the f stop is:
focal length (mm) = f stop
aperture diameter


I was really surprised at how good homemade lenses can be.

The contrast of this lens was pretty bad probably because the long tube of paper wasn't completely black. Foccussing was also very difficult because of how long the tube was.
10-27-2009, 02:01 PM   #21
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QuoteQuote:
The close-up lens used was a 52mm +2 diopter "Sigma achromatic macro lens".
I think maybe that's a 1.6 diopter lens (but I haven't measured it.)
10-27-2009, 02:10 PM   #22
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QuoteOriginally posted by nick c Quote
Here is what's left of the lens.



It was made as an experiment, not for serious use. I will probably build a better one later from something more solid than construction paper. The moon picture was not taken with the K1000 is this picture, but with my K2000. I removed the macro lens to use for macros, but it used to be taped the the front.

The close-up lens used was a 52mm +2 diopter "Sigma achromatic macro lens".

With a 30mm diameter aperture stuck to the front the lens was at f33. The aperture didn't really make any difference in image quality. It was just as good wide open at f20.

The formula for calculating focal length is:

1000 _____ = focal length
# of diopters

The formula for calculating the f stop is:
focal length (mm) = f stop
aperture diameter


I was really surprised at how good homemade lenses can be.

The contrast of this lens was pretty bad probably because the long tube of paper wasn't completely black. Foccussing was also very difficult because of how long the tube was.
PentaxForums and I are so grateful for your experiment. I am going to bug my good friend Dadipentax who may be interested in this 1000mm setup that cost like a coffee. I can ship him one of this and he can save the rest for his daughter's college fund. This will be LBA with a scientist twist. Love it! I am giving you a big Bravo.

Warmest,
Hin
10-27-2009, 02:25 PM   #23
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QuoteOriginally posted by newarts Quote
I think maybe that's a 1.6 diopter lens (but I haven't measured it.)
It may be. I just looked at it and it doesn't say how many diopters it is. I guess I just assumed that because when I foccussed it at infinity it was approximately 500mm away from the camera.

10-27-2009, 02:29 PM   #24
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QuoteOriginally posted by hinman Quote
PentaxForums and I are so grateful for your experiment. I am going to bug my good friend Dadipentax who may be interested in this 1000mm setup that cost like a coffee. I can ship him one of this and he can save the rest for his daughter's college fund.

Warmest,
Hin

I may never forgive you, Nick for giving Hin the chance to tweak me like that!

I wholeheartedly second the Bravo!
10-27-2009, 02:36 PM   #25
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QuoteOriginally posted by newarts Quote

How is the image edge quality & distortion in such a setup?

Dave in Iowa
Distortion was hard to measure since it was a 1000mm lens. However, there wasn't very much, definitely not enough to be noticable. Edge quality was about the same as in the middle (not that great, but for a close-up filter as a lens its not bad)
The main issues with image quality were getting the picture in focus (because the lens was so long) and lack of contrast (probably because my paper wasn't completely black).
10-27-2009, 02:37 PM   #26
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Iím officially impressed. Great shot and great work
10-27-2009, 02:40 PM   #27
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Very nice!, I need to rethink my approach for moon shots.

Cheers. Mike.
10-27-2009, 03:02 PM   #28
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QuoteOriginally posted by nick c Quote
It may be. I just looked at it and it doesn't say how many diopters it is. I guess I just assumed that because when I foccussed it at infinity it was approximately 500mm away from the camera.
I've seen it specified at 1.6. It is a pretty good lens I think.

Do you have any tricks for blackening optics tubes? a candle maybe?
10-27-2009, 03:13 PM   #29
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You just make mirror lenses obsolete for moon shots for the cost of a cup of coffee.
10-27-2009, 03:21 PM   #30
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Nick, you obviously don't understand that the whole point of this photography thing is to spend hundreds, if not thousands, of your local money-units to produce such images! This frontal attack on the world economy may not go unpunished if you persist in this rebellious manner.

Well done, sir!

H2
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