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06-24-2016, 02:18 AM   #46
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QuoteOriginally posted by ScooterMaxi Jim Quote
Hate to have to correct Bob Atkins, who really does know his photo stuff overall, but he isn't an optical engineer by any means! As for Clackers' background in physics, it is a very broad area of science, and unless you were teaching a section on optical engineering - it really doesn't indicate an in-depth understanding.
I regret looking at this thread again, Jim ... very disturbing!

If the top of the pencil in your reference website's diagram lies between the blue and red lines in Bob Atkins' diagram, light will fall on the lens but *never* on the cropped sensor.

If you don't believe me, and drawing helps, you can prove it yourself:

Cyberphysics - Rules for drawing ray diagrams


Last edited by clackers; 06-24-2016 at 03:41 AM.
06-24-2016, 02:22 AM   #47
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QuoteOriginally posted by GUB Quote
Chinon 50mm1.4 @ 1.4. A 25mm velcro dot on a 29mm rear lens. I think it is pretty clear a crop sensor uses all the glass that a FF does. What say you Clackers?
Firstly, I love your special bokeh, GUB ... a lotta fun, like the paper valentines you can cut out and put on the front. The dog photo is especially enjoyable.

Secondly, it's terrible logic. Put a Velcro spot on the edge of the *outer* element of a FF lens and see what happens!

You will not see it on the APS-C sensor.

Last edited by clackers; 06-24-2016 at 03:47 AM.
06-24-2016, 03:51 AM   #48
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Gotta agree with this Clackers -- I learnt these as a 16 year old too -- I am now 60 and my learning curve hasn't been totally flat!!
EDIT: Clackers has edited post 46 after I uploaded this post. He was referring to the fact his 16 yr old students had no trouble understanding his link)

QuoteOriginally posted by clackers Quote
Firstly, I love your special bokeh, GUB ... a lotta fun, like the paper valentines you can cut out and put on the front.

Secondly, it's terrible logic. Put a Velcro spot on the edge of the *outer* element of a FF lens and see what happens!

You will not see it on the APS-C sensor.
And totally agree here too clackers. Of course I wouldn't see it on an apsc sensor --- I sat it smack in the middle and I couldn't see it. The same would apply to a FF sensor. The point of the image was despite covering almost all of the centre of the lens there was an image still. It can have only come from the periphial of the rear lens which means the apsc is receiving light from the outer edge.

"You're not using any of the glass that's outside the sensor, GUB. ☺"

Where else am I supposed to be looking for this glass unused by the crop sensor?

Last edited by GUB; 06-24-2016 at 02:28 PM.
06-24-2016, 04:45 AM   #49
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QuoteOriginally posted by GUB Quote
and its own special bokeh!!
I like it too. What brand of Velcro dot did you use?

06-24-2016, 05:11 AM   #50
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QuoteOriginally posted by bxf Quote
I like it too. What brand of Velcro dot did you use?
A very sticky one. Which limited lens are you proposing to use.
Perhaps I should put a disclaimer here ---- Kids don't try this at home.
If you are wanting to recreate the effect it was a 25mm felt one from a plain pack. If I was going shopping for it I think a larger sticky paper dot like the one I used earlier is available and would be better.
06-24-2016, 05:42 AM - 3 Likes   #51
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Some more
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06-24-2016, 06:11 AM   #52
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This is one of the most interesting things I've read in a long time. I still don't quite understand, but it's fascinating.

06-24-2016, 06:37 AM   #53
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Here is a rear view of the Schneider Super-Angulon 65mm f/5.6
It is for the format 6x9 with AOV of 105 degrees,
and has an image circle of 170mm at f/16 to allow for movements.

This photo shows that the distance of the rear cell to the film plane and and the larger diameter of the rear cell
The aperture is set to f/16 with shutter open to illustrate the angle required for the corner rays.
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06-24-2016, 09:02 AM   #54
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Speaking of Confused about FoV, how exactly did we get here?

Not that I haven't contributed mightily to the totally out-of-view direction of the thread, but I'm surprised we haven't been shut down!
06-24-2016, 02:19 PM   #55
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Sorry guys ,I should have started a new post when I uploaded that chart.
06-24-2016, 11:56 PM   #56
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QuoteOriginally posted by ScooterMaxi Jim Quote
Speaking of Confused about FoV, how exactly did we get here?

Not that I haven't contributed mightily to the totally out-of-view direction of the thread, but I'm surprised we haven't been shut down!
No this is far to interesting to be shut down.
06-25-2016, 04:22 AM   #57
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Fascinating discussion. Interesting bokeh effect. Going to try it.
06-25-2016, 04:37 AM - 1 Like   #58
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QuoteOriginally posted by k22 Quote
Fascinating discussion. Interesting bokeh effect. Going to try it.
The lens (M50mm f2) from the earlier experiment with the 14mm black dot makes a softer bokeh;
Just don't expect to get anything totally sharp.
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06-25-2016, 05:18 AM   #59
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So, let's relate all of this to dust, haze, and damage. A solid dust particle won't actually be seen on the image but will affect image quality (and bokeh) since it disrupts light that contributes to the image. Correct? Likewise with a scratch or other damage, but the translucent nature of these things needs to be taken into account. What about haze? Can haze be thought of as an infinite collection of somewhat translucent dust particles?

(edit: Going off topic)

Last edited by k22; 06-25-2016 at 05:28 AM.
06-25-2016, 05:36 AM   #60
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Minor haze or fungus will be seen mostly as lower contrast throughout the image, but will also lower resolution. As multi-coating has improved, you really notice the increased contrast making a lens - such as the DA 50 - appear somewhat sharper and more saturated than the earlier versions with other coatings. Actual resolution is generally no higher, though. The better coatings also allow more light transmission - so T-rating is closer to stated aperture.
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