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Using video for botanical close-up stacks
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gardenersassistant



Joined: 31 May 2009
Posts: 112
Location: North Somerset, England

PostPosted: Tue Jan 22, 2019 9:49 am    Post subject: Reply with quote

palea wrote:
gardenersassistant wrote:
I'm not impressed with any of them. They all get worse as the focal length increases.

Well, with the 45-175 at f/16 they're 2.2 MP effective and aren't going to pixel peep that happily. Downsizing to around 1700 x 1300 offers a more fair view in some ways and the histograms show the 202 is relatively overexposed, so it compares more favorably with the black point moved up as partial compensation. It also looks to me like the alignment tolerance is in the upper tens to a couple hundred of microns, which exceeds the depth of field and favors variable softness in the corners. I'm also unfamiliar with how wear smoothing's influenced the surface texture of the note. (There's also a potential confound if there's meaningful interimage variability in flash power.)

Within that, I believe this is the most controlled test of these combinations that's even been published. So that's very cool. It looks to me like 250 + reversed 250 might be better corrected for aberrations than 250 + 250 but have more field curvature.

gardenersassistant wrote:
I wonder how that would affect comparative sharpness between the two setups?

I think effective MP is most commonly calculated by dividing sensor area by Airy first null disk size at 520 nm. Probably the most important bit is this measure of the Airy disk width exceeds the 3.75 um pixel pitch of a 16 MP u43 sensor at f/5.9, which is equivalent to stating your G80 is diffraction limited for single shots or focus bracketing beyond f/6. At least when the optics deliver a spot size smaller than the Airy disk.

The math can be done a number of other ways depending on which Rayleigh, Strehl, or Airy criteria one likes with what colors of light and how one wishes to account for the Bayer pattern on the sensor.

It can be a helpful exercise to explore this in a spreadsheet, R, or whatever tool you like. I made a table comparing u43, APS-C, and 135 and end up going back to it every so often.

(4k post focus---and, to a lesser degree, 6k on the G9---are a bit more complicated to analyze due to video sampling and compression.)

gardenersassistant wrote:
(I've never found this documented anywhere but I have illustrated it in this video.)

Maybe try this thread. I'm not convinced the model described there is entirely correct but it at least captures some of the most significant factors. As a starting point, it's my understanding the Raynox 150 and 250 have a 37mm clear aperture, which makes them f/5.6 and f/3.4, respectively. 150+250 is f/2.1 and 250+250 is f/1.7. About a two stop advantage over most enlarging lenses and six stops compared to microscope objectives. I haven't seen a clear aperture for the 202 but my guess is 31mm, which makes f/1.3, though you can get a better number measuring yours.

The piece I suspect might missing be from Rik's model, as I understand it in the link, is calculation of the combined EFL of all of the lenses used and checking it doesn't produce some other limiting EA. This is unlikely to be significant at the >1x that discussion is concerned with but it might matter around 0.5x where's possible (though unlikely) to put f/2 or faster primes behind the f/2.8 or so provided by 150. It's also possible the model's entirely correct and it's just that the corner case is sufficiently obscure no one's ever noticed minor limiting incurred by the close up lens aperture.

I'd feel better about this if the model had more thorough discussion but, from what I can tell from what's currently available, it's only when maxing out the Raynox 202 that the EA of Raynox + 45-175 combinations might be limited by the close up lens rather than the 45-175. If it does happen the model predicts a 0.04 stop slowdown, so it'll be fussy to measure.


Thanks for furthering the conversation with these considerations. I will drop out of this part of the thread because I don't understand any of it, but I'm sure those who know more about these things may want to pursue some of this.
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palea



Joined: 17 Dec 2018
Posts: 21

PostPosted: Tue Jan 22, 2019 10:14 am    Post subject: Reply with quote

gardenersassistant wrote:
I will drop out of this part of the thread because I don't understand any of it

Well, I'm not sure about "any" but, yeah, there's an interaction between those particular learning curves and the questions you're asking about controlling image quality across sensor sizes and methods of obtaining magnification. Answers'll still be there if you want them later.
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gardenersassistant



Joined: 31 May 2009
Posts: 112
Location: North Somerset, England

PostPosted: Tue Jan 22, 2019 10:31 am    Post subject: Reply with quote

palea wrote:
gardenersassistant wrote:
I will drop out of this part of the thread because I don't understand any of it

Well, I'm not sure about "any" but, yeah, there's an interaction between those particular learning curves and the questions you're asking about controlling image quality across sensor sizes and methods of obtaining magnification. Answers'll still be there if you want them later.


Thanks.
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Nick

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Rework and reposts of my images posted in this forum are always welcome, especially if they come with an explanation of what you did and how you did it.
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ChrisR
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Joined: 14 Mar 2009
Posts: 8260
Location: Near London, UK

PostPosted: Wed Jan 23, 2019 3:20 am    Post subject: Reply with quote

Quote:
Quote:
I think you might be waiting a long time, cos the MP-E doesn't stop down far enough! (f/16).

But at 5:1 nominal f/16 is effective f/96, and with the MP-E on m43 it would be f/196 FF equivalent.

Sure, what I meant was, if you use an MP-E on full frame at near 1:1,
you can't get nearly as small an effective aperture as you can with what you have. So you'd not be able to get to the same DOF you're using eg in the wasp shots.
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gardenersassistant



Joined: 31 May 2009
Posts: 112
Location: North Somerset, England

PostPosted: Wed Jan 23, 2019 4:41 am    Post subject: Reply with quote

ChrisR wrote:
Quote:
Quote:
I think you might be waiting a long time, cos the MP-E doesn't stop down far enough! (f/16).

But at 5:1 nominal f/16 is effective f/96, and with the MP-E on m43 it would be f/196 FF equivalent.

Sure, what I meant was, if you use an MP-E on full frame at near 1:1,
you can't get nearly as small an effective aperture as you can with what you have. So you'd not be able to get to the same DOF you're using eg in the wasp shots.


Ah, understood. Yes indeed.
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