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A visual demo on the equivalence of small and large sensors
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Mon Sep 03, 2018 3:38 pm    Post subject: Reply with quote

Justwalking wrote:
rjlittlefield wrote:
Justwalking, I'm not sure I understand how you're thinking about this.
Up to now, I have been trying to get you to realize that at same DOF and same FOV, the number of Airy disk diameters across the frame will be the same for all format sizes.

Now, it sounds like you agree that the number of Airy disk diameters across the frame will be the same, but you're thinking that the small sensor will somehow see higher contrast than the larger sensor.

Is that what you're thinking?
If so, then what is your mathematical justification for that idea?
--Rik


This arithmetic method to count airy disks diameter across sides to find oiptimum pixels is useless for practice where we can't do anything with pixel pitch.
It simplified count that can't compute many other factors.


The highest spatial frequency a sensor can resolve is its Nyquist frequency, equal to 0.5/(pixel spacing). When a lens is stopped down so its Rayleigh limit is below the Nyquist frequency, the camera is limited by the lens rather than the sensor
For optimum quality (when extreme depth of field is not required), the aperture should be set at least one stop larger than the aperture where the Rayleigh limit equals the Nyquist frequency:
NR=N = 3.2 * pixel spacing (um).

http://www.normankoren.com/digital_cameras.html#Diffraction

For a pixel spacing of 1.4 microns, NR=N = 3.2 * 1.4 = f/4.48, so the aperture should be set at f/2.8-f/3.2 or larger.

With small sensor i can leave this "small" DoF as is and it will be not the extreme Dof for my sensor, so i can choose optimum quality for the Dof, but for the FF it is not so to achieve the same Dof.

Very small formats - for compact digital cameras with 11 mm diagonal or smaller sensors (1/4 the size of 35mm) are severely diffraction-limited at f/8, where DOF is equivalent to f/32 or more in 35mm.
But tiny digital cameras still produce very sharp images at f/4 and f/5.6 because their tiny pixels with no anti-aliasing filters — have far better lp/mm resolution than 35mm.
Amazing.

Once again, Justwalking has found a relevant formula, computed for one sensor, then stated an opinion without ever bothering to compute for the other sensor.

Apparently he has missed the concept that to use the math, you have to actually do the math.

Let us do the math for the FF sensor, as Justwalking did only for the 5.5 crop sensor.

At same MP, the FF pixels are 5.5 times larger, so 5.5 * 1.4 = 7.7 microns pixel spacing.

By normankoren's formula, NR=N = 3.2 * 7.7 = f/24.6, so the FF aperture should be set at f/17 or larger.

Then note that f/17 on FF is just 5.5 times larger than f/3.2 on crop 5.5 .

So, normankoren's formula recommends an aperture that is scaled exactly in proportion to the sensor size.

As we all agree now, that condition is exactly what's needed to make the DOF be the same.

In other words, normankoren's rule for optimal aperture on each sensor, also gives the same DOF on both sensors.

Earlier,
Justwalking wrote:
The Dof at crop 5.5 at m=0.5 at Feff=15 will be same as on FF but FF must be ... F'=82.5(!)
Do you think that they will be looks the same?

Yes.

Exactly as shown in my image pair at m=0.68 and f/8.5 on crop 5.5, versus m=3.74 and f/47 on FF. And as predicted by diffraction math, and as predicted by normankoren's formula.

Theory and experiment agree completely. At same FOV, same MP, and same rule for optimal aperture, the small sensor image and the large sensor image look the same.

--Rik
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Justwalking



Joined: 10 Jun 2018
Posts: 137
Location: Russia

PostPosted: Mon Sep 03, 2018 5:54 pm    Post subject: Reply with quote

rjlittlefield wrote:

Theory and experiment agree completely. At same FOV, same MP, and same rule for optimal aperture, the small sensor image and the large sensor image look the same.

Exactly as shown in my image pair at m=0.68 and f/8.5 on crop 5.5, versus m=3.74 and f/47 on FF. And as predicted by diffraction math, and as predicted by normankoren's formula.

In other words, normankoren's rule for optimal aperture on each sensor, also gives the same DOF on both sensors.

--Rik

Nope. The normankoren's rule is for optimal quality (when extreme depth of field is not required) not for the same Dof for both sensors.

For FF my "small" DoF optimal for the quality is "extreme" DoF.
F'/26 is not the "sweet spot" per FF compared with crop at F'/4.

You was trying to compare 8MP crop vs resized 36 MP FF and you even won't take same big Dof as mine 0.8X with your 1/2.5" sensor at less magnification.
Just i predicted before instead of real trying of correct comparision again
"it must be".

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rjlittlefield
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Joined: 01 Aug 2006
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PostPosted: Wed Sep 05, 2018 9:20 pm    Post subject: Reply with quote

Justwalking wrote:
Nope. The normankoren's rule is for optimal quality (when extreme depth of field is not required) not for the same Dof for both sensors.

Yes, I agree.

That's why I followed normankoren's rule, exactly as written.

Then I pointed out that applying the rule exactly as written also happens to give the same DOF on both sensors.

Let me repeat that. The rule was written to determine optimum aperture on each sensor, but it also happens to give same DOF on both sensors.

Same DOF falls out of the optimality condition, even though same DOF certainly was not an input for determining that condition.

Quote:
You was trying to compare 8MP crop vs resized 36 MP FF

Nope.

My normankoren computation was for same MP on both sensors.

The displayed images were for 7 MP small sensor versus 7 MP resized from FF. Sadly, I don't have a small sensor and FF sensor with same native MP, so resizing is the only way to do a same MP comparison.

--Rik
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rjlittlefield
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Joined: 01 Aug 2006
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PostPosted: Wed Sep 05, 2018 9:26 pm    Post subject: Reply with quote

@Justwalking,

Switching subjects, and putting on my moderator hat, I think you are missing an opportunity here at photomacrography.net.

So far, you've basically been trying to argue that your pictures are excellent because of the equipment that you're using.

That requires arguing that small sensors have some intrinsic advantage over large sensors regarding the DOF/diffraction tradeoff, and sorry, they just don't. The math of DOF and diffraction is quite clear on that point, as are head-to-head controlled tests. So in this forum, surrounded by people who have no trouble following the discussion, your current approach has no chance of working.

On the other hand, I think there is no debate that your images are excellent, independent of the equipment that you're using.

I have reviewed your work at https://www.coincommunity.com/forum/topic.asp?TOPIC_ID=280117, and I can easily see why Ray Parkhurst was motivated to invite you to post here at photomacrography.net . Your images of the Washington state quarter and your ball point pen are beautifully illuminated and are very sharp.

So, if you really want to make a positive contribution here at photomacrography.net, the best way for you to proceed is to stop praising your equipment and instead, take personal credit for the excellent appearance of your images.

Tell us how you control the lighting, and tell us the details of how you resize and sharpen for web presentation. These are things that would be valuable for us to learn.

I personally would also be very interested to hear more about your combination of "MORITEX industrial 0.8X HR lens with El-Nikkor in pair". From the coin image, it appears that you've managed to reduce the nominal 0.8X magnification to some much smaller value, and whatever technique you've used to do that could be helpful to other people also.

--Rik
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Justwalking



Joined: 10 Jun 2018
Posts: 137
Location: Russia

PostPosted: Thu Sep 06, 2018 6:00 am    Post subject: Reply with quote

rjlittlefield wrote:

My normankoren computation was for same MP on both sensors.

The displayed images were for 7 MP small sensor versus 7 MP resized from FF. Sadly, I don't have a small sensor and FF sensor with same native MP, so resizing is the only way to do a same MP comparison.

--Rik


Than your computation is not correlate to your pics wich you tried to compare.

7 MP resized fron 36MP means you have resized diffraction blur also and your pitch size is not the same as on 7MP FF sesor so this comparision is incorrect.
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Justwalking



Joined: 10 Jun 2018
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PostPosted: Thu Sep 06, 2018 6:41 am    Post subject: Reply with quote

rjlittlefield wrote:
@Justwalking,

That requires arguing that small sensors have some intrinsic advantage over large sensors regarding the DOF/diffraction tradeoff, and sorry, they just don't.
Washington state quarter[/url] and your ball point pen are beautifully illuminated and are very sharp.

So, if you really want to make a positive contribution here at photomacrography.net, the best way for you to proceed is to stop praising your equipment and instead, take personal credit for the excellent appearance of your images.

Tell us how you control the lighting, and tell us the details of how you resize and sharpen for web presentation. These are things that would be valuable for us to learn.

--Rik


Whithout understanding why they looks beautifully illuminated and are very sharp without stacking and why i need only 1-2 watts LED for ligtning of the object it is not any benefit for others.
Looks that nobody here have used small sensors prefer consumer FF camera instead, so my experience can't be helpful. You just can think that all is easy available regardless of sensor size.

Best wishes.
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rjlittlefield
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PostPosted: Thu Sep 06, 2018 9:12 am    Post subject: Reply with quote

Justwalking wrote:
7 MP resized fron 36MP means you have resized diffraction blur also and your pitch size is not the same as on 7MP FF sesor so this comparision is incorrect.

Once again, your flawed intuition and lack of experience has led you to an incorrect conclusion.

What determines how an image looks depends on the size of the diffraction blur compared to the subject area shown. That ratio is not affected by resampling to a different pixel count.

An equivalent interpretation is that the pitch of pixels in the FF image resampled to 7 MP is exactly the same as if the sensor had been physically 7 MP to start with. A moment of serious consideration, or evaluating the simple formula that pitch = sqrt(area/MP), should be enough to see this.

Quote:
Looks that nobody here have used small sensors prefer consumer FF camera instead, so my experience can't be helpful.

We would be very happy to hear about your experience with small sensor cameras.

But we definitely are not interested in continuing to hear scrambled theories about why a small sensor works well for you.

If you are not able to separate those two very different aspects, then I agree that photomacrography.net is not a good fit for you.

--Rik
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Justwalking



Joined: 10 Jun 2018
Posts: 137
Location: Russia

PostPosted: Thu Sep 06, 2018 1:07 pm    Post subject: Reply with quote

rjlittlefield wrote:

But we definitely are not interested in continuing to hear scrambled theories about why a small sensor works well for you.

If you are not able to separate those two very different aspects, then I agree that photomacrography.net is not a good fit for you.

--Rik


If the math looks just scrambled theory here then my experience can help only for more advanced knowledge.
https://www.olympus-lifescience.com/en/camera/color/sc180/
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JohnyM



Joined: 24 Dec 2013
Posts: 451

PostPosted: Thu Sep 06, 2018 1:16 pm    Post subject: Reply with quote

You work for Olympus now? I hope you're not an engineer? Or what does that link is supposed to prove?

Ok, here's my random link:
https://www.nikoninstruments.com/en_EU/Products/Cameras/Camera-Heads/DS-Ri2/Specifications
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Andy



Joined: 21 Sep 2018
Posts: 12
Location: Derby UK

PostPosted: Sun Oct 14, 2018 1:20 pm    Post subject: Reply with quote

Hello All,

My first post is intended to give further examples at the small and cheap end.

I am much encouraged by that Russian who specializes in Snowflakes using a point and shoot with a reversed Russian lens taped to a plank of wood. He exhibits ART in NYC!

Whilst I may not fully understand the maths in the spat I found the diagrams most interesting and informative. People starting out may want to drag out the old point and shoot whilst others may not like the bulk of some rigs.
An easy simple experiment can be undertaken to roughly quantify the DoF. If a rule (ruler) is placed in front of the camera at 60° to the lens axis the DoF is half of the “in focus” markings on the rule - cos60 = 0.5

I am having some difficulty with the SEARCH finding examples of NX-mini rigs - is there anyone out there using 1” sensor or less?

I am having adapters manufactured hence all pics taken without additional lens fixed, indeed lens resting on a couple of coins on the kitchen worktop!

Andy










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