Un-aberrated coverage for larger camera sensors?

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RichA
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Joined: Wed Mar 06, 2019 1:04 am

Un-aberrated coverage for larger camera sensors?

Post by RichA »

Most full-frame shot microscope images I've seen (m4/3rds to 35mm) are significantly aberrated (colour error, distortion, field curvature) and only provide decent images when heavily cropped. I'm using a Nikon microscope and plan achro objectives. What kind of relay optics (eyepiece/relay lenses) would be good to minimize this problem, or should I start with replacing the objectives with Plan-apos/plan-fluors?
Thanks!

enricosavazzi
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Re: Un-aberrated coverage for larger camera sensors?

Post by enricosavazzi »

RichA wrote:Most full-frame shot microscope images I've seen (m4/3rds to 35mm) are significantly aberrated (colour error, distortion, field curvature) and only provide decent images when heavily cropped. I'm using a Nikon microscope and plan achro objectives. What kind of relay optics (eyepiece/relay lenses) would be good to minimize this problem, or should I start with replacing the objectives with Plan-apos/plan-fluors?
Thanks!
In general, plan apo objectives are the best to avoid chromatic aberrations, followed by plan fluor. Plan achro are generally a cheaper series that gives a lower performance, and meant for applications like medical diagnostics where image quality, especially at the edges of the image circle, is not essential.

Then you must make sure you are using the tube lens (if your system is infinity corrected), photo eyepiece/"relay lens" and eyepieces designed for use with the objectives of your microscope.

Coverage of a large-size sensor is another topic. It requires a photo eyepiece with a higher magnification (which usually also gives a wider FOV). 1x-1.2x photo eyepieces (or a photo tube without optics) are usually adequate for Micro 4/3. 1.5-2x is generally recommended for APS-C, and 2-3x for full frame. This also depends on the size of the image circle of the objectives and the diameter of the field stop of the photo eyepiece.

For example, Olympus UIS objectives and eyepieces provide an image circle and field stop of at least 22 mm, and UIS2 objectives a higher image circle of 26.5mm. This is enough to cover Micro 4/3 sensors in direct projection (i.e. without a photo eyepiece), and for UIS2 often also an APS-C sensor in direct projection (possibly with minor cropping). 160 mm tube length finite Zeiss and Zeiss Jena objectives only cover about 18-20 mm, which is not enough for direct projection on Micro 4/3 (and in any case a photo objective is required by design to correct some of the residual aberrations of the objectives).

If you are using modern CFI infinity corrected Nikon objectives with the correct tube lens, then you can in principle use direct projection.

Then one further consideration when assembling a photomicroscopy system is that a sensor larger than Micro 4/3 and about 16-20 Mpixel is not really necessary to record all information provided by the microscope optics at magnifications about 20x and higher. There is nothing to win in terms of image quality by using a physically larger sensor or a larger pixel count. The only reason to do so is when you already have a camera with a larger sensor/resolution and want to use it also for photomicrography.
--ES

Ichthyophthirius
Posts: 1100
Joined: Thu Mar 07, 2013 5:24 am

Re: Un-aberrated coverage for larger camera sensors?

Post by Ichthyophthirius »

RichA wrote:I'm using a Nikon microscope and plan achro objectives.
Hi Rick,

What microscope and objectives exactly? Does the microscope have any intermediate tubes (1.25x)?

From the CF optics onwards, they should cover field of at least FN 26.5. Conservatively, you can use the central 22 mm diagonale (FN 22) for photography, that's not heavily cropped. For biological objects there shouldn't be any problems at FN 22.

Regards, Ichty

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