Sensor Sensibilities

[JohnDownie]

Hello,

I am a newcomer to the 1X+ world and have been going through the gear gears, as it were. I am honing in on my target lenses, but wondered about sensor choices.

In the past few months we have seen two new additions to the interchangeable lens game - the Pentax Q, with a 6.17 x 4.55 mm sensor and the Nikon 1 cameras, with 8.8 x 13.2 mm sensors. The Nikons have completely electronic shutters (with a mechanical option on the upper model), which presumably would be a life-prolonging feature in the shutter-intensive world of stacking.

So...just wondering about the pros and cons of the smaller sensor, assuming low noise at base ISO.

TIA

John

[rjlittlefield]

Sensor size does not change the fundamental relationship between DOF and diffraction blur. When you end up framing the same size subject in the same size final image with the same DOF, then you also get the same diffraction blur. So, for single frame photography where you're trying to maximize DOF by adjusting f-stop, sensor size doesn't matter. Stacking changes the rules by removing single-frame DOF as an issue. In that case, the smaller sensor may also reduce the total amount of detail you can pack into an image. However, this is mainly an issue at lower magnifications (more precisely larger subject sizes), where small effective f-numbers can be achieved and the lenses can over-resolve the sensor.

The main effect of the smaller sensor is that it may be harder or easier to get the right optics for whatever subject you want to shoot.

For use with a microscope objective, an 8.8 x 13.2 mm sensor (15.9 mm diagonal) would be just about ideal for direct projection by a finite objective, and this arrangement would be very simple if you can get the right mechanical adapters. On the other hand, the trick of using a telephoto in combination with an infinity objective might not work so well because of issues with mismatching aperture sizes. Looking in the Nikon Store, I'm only seeing 3 lenses, and none of them inspires confidence for this use. If adapters are available for legacy mount lenses, then the whole picture changes.

For use with say an enlarger lens reversed, I think the main issue would be mechanics -- just a matter of getting the right mount. This presumes that the camera will work properly without its own dedicated lenses. That is NOT a slam-dunk assumption and you would want to check that aspect very carefully.

The issue of shutter life with conventional DSLRs seems to be more scary in concept than in practice. Typical shutter lives are in the vicinity of 100,000 exposures, more if you buy a better camera. To replace one costs a couple of hundred bucks. So if you're shooting 100-frame stacks, you can expect to get say 1000 stacks per shutter, at a cost of 20 cents per stack. It's a small component of the total system costs in most cases. Mechanical shutter life could be really important if you were planning to crank out a long series of spherical object stacks, say one stack every 5 degrees with 50 frames per stack, but is that what you plan to do? Run the numbers for your own case.

One last caution: be careful to compare apples and apples, not apples and cranberries. The same 10 mm subject field is 3.6X on full-frame, 2.3X on APS, 1.6X on a Nikon 1, but only 0.6X on a Pentax Q. I mention this because you've described your interest as being "1X+", and I wanted to point out that 1X means different things in different places.

Is this helping?

--Rik

[JohnDownie]

Thanks Rik,

That is about what I figured. I am putting together a spreadsheet that will summarize the available sensor sizes, and resolutions, show the optical magnification required to print to 8 x 10 @ 288 dpi as well as the largest print available at that level of print detail.

As you point out, legacy adapters are key here - both Pentax and Nikon have announced these products.

I suppose another slight advantage of a purely electronic shutter is completely silent/movement free operation.

John

[Oskar O]

One problem with smaller sensors is that they need larger apertures to reach similar level of resolution than larger sensors do and at some point it becomes hard to find fast enough lenses. This problem is alleviated in macro though, since less magnification is needed with a smaller sensor to cover a subject of the same size, thus the effective aperture will be large if the nominal aperture is the same. But I haven't really done the maths of where the cutoff in terms of quality is, simply because larger sensors practically always have better signal to noise ratios and many advantages for non-macro work, which makes them preferably purely from an image quality perspective.

It's worth to note also that when dealing with magnifications that do not require microscope objectives, there are plenty of lenses which will cover a large sensor, thus giving the larger sensor an edge.

An obvious advantage for smaller sensor is that a more compact and portable setup can be made. I have had good results with a small bellows and a micro 4/3 camera, a quite flexible setup that is easy to carry in the field can be assembled.

[JohnDownie]

Thanks Oskar - I may just bite the bullet on a Canon T3i, so I only have to deal with one set of adapters, etc., and take advantage of the larger, higher-resolution sensor.

John

[rjlittlefield]

I have an older T1i, and I'm quite fond of it. Be sure to take advantage of the electronic first shutter curtain provided in Live View.

--Rik