Is Infinity focus the same for one lens on different cameras??

I've got a Samyang 14 2.8 that I use for my (so far very limited) astrophotography. It is well known that the focus marks on the lens are far from perfect.

I want to make a mark on the lens that shows exactly where my lens is sharpest when focused on the stars. The recommended way to do this is to use Live View, and zoom in to 10x to set the focus. My problem is that I use the original 5d, which does not have Live View. I do have a recently purchased 7d, that DOES have Live View. If I were to use the 7d's live view to find the infinity focus, would it be exactly the same as on the 5d? Is the rear element and closer/further away on different cameras, or on full frame vs. crop?

Thanks!
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Heya,

The elements are a different distance, it may not be precisely the same. But I'm not certain. I'm interested to know this as well (I do a lot of astro).

Very best,

No difference. The tolerance of registration distance (from mount flange to sensor plane) is very fine.

No two cameras will be absolutely identical, but most DSLR bodies are close enough that you'd have a hard time measuring the difference.
Once you start mixing lens adapters, third-party manufacturers, etc, things can start to drift pretty quickly. The Blackmagic Cinema Camera was pretty far off, for example, especially for non-Canon lenses. The reason many lenses focus past infinity is to help compensate for missed manufacturing tolerances.

There will be a difference between different mounts however. Ie, a Samyang on a Nikon is not going to have the same infinity position.

JonKline wrote in post #16776674
The reason many lenses focus past infinity is to help compensate for missed manufacturing tolerances.

I'm fairly certain that is not the primary reason why autofocus lenses can be manually set beyond "infinity".

The main reason for the overtravel is so that when an autofocus lens is automatically driven to "infinity" that it will not be be hammering a solid end stop as it reaches the "infinity" position. If the lens were driven to a hard stop, it would easily damage the internal lens focus adjustment mechanism.

SkipD wrote in post #16776885
I'm fairly certain that is not the primary reason why autofocus lenses can be manually set beyond "infinity".

The main reason for the overtravel is so that when an autofocus lens is automatically driven to "infinity" that it will not be be hammering a solid end stop as it reaches the "infinity" position. If the lens were driven to a hard stop, it would easily damage the internal lens focus adjustment mechanism.

I thought there was a temperature variation that the extended infinity point allows for.

Foggiest wrote in post #16777209
I thought there was a temperature variation that the extended infinity point allows for.

That could be true, but the little bit of overtravel is critical for an automated motion system so the hardware does not have a tendency to crash.

SkipD wrote in post #16776885
I'm fairly certain that is not the primary reason why autofocus lenses can be manually set beyond "infinity".

The main reason for the overtravel is so that when an autofocus lens is automatically driven to "infinity" that it will not be be hammering a solid end stop as it reaches the "infinity" position. If the lens were driven to a hard stop, it would easily damage the internal lens focus adjustment mechanism.

How does this translate to minimum focus distance?

There isn't a buffer there and I would think folks hit MFD fairly often, I know I do.

hes gone wrote in post #16778259
=he's gone;16778259]How does this translate to minimum focus distance?

There isn't a buffer there and I would think folks hit MFD fairly often, I know I do.

If you're allowing the camera/lens system to frequently drive the focus mechanism to the minimum focus distance in a way that slams it against that travel end stop, I suggest that you change your technique. Going to manual focus would possibly be one good alternative.