Sensor and lens tilt and how to DIY adjust your equipment

Started Sep 19, 2020 | Discussions thread
Tristimulus Veteran Member • Posts: 8,536
Re: Sensor and lens tilt and how to DIY adjust your equipment

SamuelChia wrote:

It is difficult to determine which forum category is best for posting this thread since it is cross-disciplinary, discussing our discoveries and issues as it relates to astrophotography, though not necessarily limited to astro-work only, mainly using the Sony a7R II as an example, though the problem isn't Sony-specific. Perhaps it is best suited to live in the Sony E-mount forum since many of the examples are for the Sony system, but any enterprising photographer can easily adapt our methods to any other system.

Joseph Holmes and I have found our Sony a7R II (and my Canon 5D Mk II too) sensor to be crooked relative to its bayonet mount.

Seems more likely that field curvature (a lens issue) and slight deviations in sqaring on is the real issue here.

Image sensors and lens mounts are usually plane parallell to within tight specs.

My Sony A7III is deriver the same image quality over the entre field of view when used with my 106/530-5 astrograph (a high end flat field astrograph).

Not so when using ordinary lenses. Than field curvature and not perfectly squared on lens elements play a role. All within specification, but somewhat looser tolerances. That is real life in a not perfect word.

Flange distance to the image sensor is usually the least problem here.

A few years ago, such a claim would be considerably more aberrant. It is less so as sensors have gone way up in resolution and way small in pixel pitch, revealing tiny alignment errors better, and reader comments on Roger Cicala's recent flange distance articles and elsewhere on the web indicate that increasing numbers of photographers are concerned about such issues.

Only if over intepretating the results.

Need to know the specifications before complaining. After all Cameron and lenses are industrial products made within certaint tolerances (real life is a balance between price and cost). Only a fool would expect absolute perfection...

No one has yet proposed a simple and relatively cheap method that is also sufficiently precise for determining sensor tilt and my hope in publishing this information is to provide such a means to anyone interested.

Squaring on is well known within the astronomical community since the early days of telescopes. Lots of ingenious ideas even in the early litterature.

It should come as no surprise to most that lenses also have focus field tilt issues too, and on average the tilts seem to be more severe than sensors. Returning 'bad copies' which are decentered is fine, but returning them because they are tilted is a fool's errand since every single lens is tilted (according to Roger Cicala and also in our experience), unless one is so lucky to find one that matches the tilt of their camera. Marianne Oelund shared her method of adjusting field tilt using aluminium foil about three years ago. The ring shims Joseph and I found might be of interest. We think they are a more elegant way to shim the bayonet mount of our cameras and lenses. All the details are in my article.

Fair warning: the discourse is a very long one and covers a multitude of issues and discoveries, but I trust it would make a worthwhile read for anyone who cares.

View: original size

Samuel Chia

P.S. I posted this topic first on the Sony Full Frame E-mount forum a while back but it didn't seem to get any attention.

Most likely the real world results are good enough for 99.9 % of the users. This seems more like an issue, not to geeks, but to geeky geeks. I might be wrong, but then I am stuck in a real world life where nothing is perfect - most things are just good enough.

I thought perhaps since the content is quite astrophotography focussed, it might be useful to anyone who frequents this subforum category more. I hope it might help you.

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