smaller sensor to use lower mag objectives?

[nielsgeode]

In the process of getting to a setup I can use to stack both the best quality possible and to do quick stacks at a lower quality (mainly for selling mineral specimens) I'm thinking about getting the new 12 MP high-res Pi camera. I have a Raspberry Pi 4B already so I would need only the camera.

Specs are as follows: Sensor 6.29mm x 4.71 mm, pixel pitch 1.55 microns.
My current camera is a Sony A7r iii with a 36 x 24 mm sensor, pixel pitch 4.51 microns.

Main purpose are Dimage 5400 scanner lens (2x) / Nikon 4x NA 0.10 and Mitty 5x objectives. The tiny FOV and increased pixel count with this sensor is appealing. Cropping a 42MP pixel to the FOV of the Pi camera would give only 1.4 MP, which is a bit low-resolution, even for eBay etc.

The big question is: will it help, or will the diffraction-limit with the lenses mentioned here render this idea useless?

[chris_ma]

Not sure I understand this correctly... do you want to keep the same FoV as with your FF sensor or the same as the FF cropped?

Because for the former you‘d need lenses with different magnification, for the latter your idea could work, but the Pi camera might not have terribly good dynamic range nor colors.

Then again if the camera is fairly cheap it might be fun to try and see if you like the results.

[nielsgeode]

Not sure I understand this correctly... do you want to keep the same FoV as with your FF sensor or the same as the FF cropped?

Because for the former you‘d need lenses with different magnification, for the latter your idea could work, but the Pi camera might not have terribly good dynamic range nor colors.

Then again if the camera is fairly cheap it might be fun to try and see if you like the results.

Yes, same FoV, so I can use smaller magnification lenses (or a trade-off: a smaller magnification lens but not small enough to compensate for 100% so the FoV could go from 5mm to 4mm for example).

[chris_ma]

Well, if the sensor is 5 to 6 times smaller then you‘d need lower mag lenses, like 0.3x to 1x if I understood things properly.

So the M5400 lens reversed should be truly excellent and resolve a lot of detail even on small pixels.

[Scarodactyl]

Changing sensor size is not the right solution for changing FoV. If you need higher magnification you will get better results using lenses that are meant to perform at that magnification. The rapsberry pi camera looks really cool but would ideally be used with reducing optics for lenses with wider field coverage.

[rjlittlefield]

One problem with small pixels is that they need wide apertures to avoid too much diffraction.

Nikon's rule, for matching pixel density to microscope images, is 2 pixels/cycle at the diffraction limited cutoff frequency, for lambda = 550 nm green light.

Following that rule with pixels of size 1.55 microns implies that your optics would have to be running at effective f/5.6 or wider.

It's not clear to me that any of your current lenses will do that.

Scarodactyl's suggestiion of reducing optics also gives smaller f-number (wider aperture), in proportion to the reduction factor, so that would certainly help.

--Rik

[clarnibass]

Yes, same FoV, so I can use smaller magnification lenses (or a trade-off: a smaller magnification lens but not small enough to compensate for 100% so the FoV could go from 5mm to 4mm for example).

In that case...

Cropping a 42MP pixel to the FOV of the Pi camera would give only 1.4 MP, which is a bit low-resolution, even for eBay etc.

I'm not sure about this comparison. This is only relevant if you're using the x0.3 to x1 magnification on the Sony instead. You can use whatever is enough magnification for the purpose.
Or did you mean you already need to crop and often left with about 1.4MP from the Sony at the x5 magnification?

A lot depends on the actual size and how you plan/think/guess others will view it. Between using (e.g.) x5 on the Sony and x1 on the smaller sensor (guesstimating... let's say it's approx the same FOV) I can only guess that for ebay, assuming about full screen in FHD, the 12MP from that camera (or any half decent camera) is probably going to be more than good enough. If they view them on a very good 4K screen... probably ok. If they want the absolute largest photos to magnify on their screen... who knows.

It's maybe partly a marketing question rather than a photography question

[nielsgeode]

Yes, same FoV, so I can use smaller magnification lenses (or a trade-off: a smaller magnification lens but not small enough to compensate for 100% so the FoV could go from 5mm to 4mm for example).

In that case...

Cropping a 42MP pixel to the FOV of the Pi camera would give only 1.4 MP, which is a bit low-resolution, even for eBay etc.

I'm not sure about this comparison. This is only relevant if you're using the x0.3 to x1 magnification on the Sony instead. You can use whatever is enough magnification for the purpose.
Or did you mean you already need to crop and often left with about 1.4MP from the Sony at the x5 magnification?

A lot depends on the actual size and how you plan/think/guess others will view it. Between using (e.g.) x5 on the Sony and x1 on the smaller sensor (guesstimating... let's say it's approx the same FOV) I can only guess that for ebay, assuming about full screen in FHD, the 12MP from that camera (or any half decent camera) is probably going to be more than good enough. If they view them on a very good 4K screen... probably ok. If they want the absolute largest photos to magnify on their screen... who knows.

It's maybe partly a marketing question rather than a photography question

Let's say my crystal is 0.8 mm in height (shot in landscape mode) and I need a descent eBay pic. With a 42MP FF and 10x Mitty the crystal fills a 3rd of the frame height so cropping half the height (to leave some space) gives 42 * 0.5 * 0.5 = 10.5MP
The Pi-cam sensor height is 4.71mm and with a 4x objective the vertical FOV is 1.18mm, which means I don't have to crop at all and can use a 4x lens instead of a 10x lens.

The advantage is that stacking with a 4x is much quicker compared to stacking with a 10x. So it's a matter of convenience of lower magnification. The real advantage is in crystals smaller than 1 mm where I no longer need 10x or 20x objectives to do a quick pic. If a crystal is a few mm I can also quickly shoot with my MP-E65 on FF at 2-3x and then crop a bit.

The question is: does it work or will my 4x NA 0.1 pics look significantly worse than my 10x NA 0.28 pics (due to diffraction)?

[rjlittlefield]

The question is: does it work or will my 4x NA 0.1 pics look significantly worse than my 10x NA 0.28 pics (due to diffraction)?

Resolution on subject is proportional to the NA. So, your NA 0.1 pics will show almost 3X less detail on each axis.

If you need only the detail of NA 0.1, and stack depth is a problem, then I suggest to add an aperture behind your Mitty to stop it down to NA 0.1 also.

The required aperture diameter would be 4 mm.

Of course you can also use intermediate aperture sizes to get just the resolution you need.

When stack depth is important, you should experiment to determine how large a step size you can get away with. The standard formula that DOF = 0.00055/(NA*NA) is only a guideline.

--Rik