Canon 1100D modded sesnor spacers

[Stub Mandrel]

I've got and 1100D, astromodded, that I use for wide angle imaging, meteor hunting etc.

I dind't do the mod myself and like the 450D I did do, it hasn't had a spacer or extra filter put in.

I fancy using it for some ordinary photography as well, so I'd like to add the sensor spacers or an aftermarket filter to restore autofocus

Can anyone recommend a filter that fits over the sensor that won't ruin the Ha response and/or tell me the thickness of spacer I need to add?

[michael8554]

Restoring Autofocus involves reducing the spacing between the sensor and the lens, not adding more.

Or adding a Baader BCF Filter to replace the removed LPF#2 Filter.

Some say that a Clip-In filter compensates.

Michael

[Stub Mandrel]

7 hours ago, michael8554 said:

Restoring Autofocus involves reducing the spacing between the sensor and the lens, not adding more.

Good point... it need to be a=bout 1/3 of the filter thickness, can anyone tell me what that is?

7 hours ago, michael8554 said:

Some say that a Clip-In filter compensates.

I doubt it as it would be in front of the mirror and affect the autofocus as well. It needs to be behind the mirror.

Hmm.. problem with a filter is that for another £20-30 I could get an unmodified one..

[michael8554]

9 hours ago, Stub Mandrel said:

it would be in front of the mirror and affect the autofocus as well

Isn't that the objective...... ?

Michael

[Stub Mandrel]

26 minutes ago, michael8554 said:

Isn't that the objective...... ?

Michael

No... the autofocus isn't affected by removing the sensor glass as it uses the image reflected up to the pentaprism.

If you use a clip filter the focus point will change to compensate so the sensor image will still be out, compensating glass needs to be behind the mirror.

[Merlin66]

To maintain autofocus either the original sensor filter needs to be replaced with a similar clear or UV/IR filter, or the position of the sensor needs to be chnaged.

Adding a clip in filter allows standard EF lenses to be focused. I use an Astronomik CLS clip in filter on my FULL modded (both filters removed) 1000D to allow me to use standard lenses for spectroscopy.

 

[michael8554]

2 hours ago, Stub Mandrel said:

No... the autofocus isn't affected by removing the sensor glass as it uses the image reflected up to the pentaprism.

Wrong I'm afraid.

Autofocus becomes incorrect once the #LPF2 filter is removed.

Autofocus assumes the sensor is in the factory position, but removing the #LPF2 filter has the same effect as if the sensor was moved further from the lens.

Autofocus is corrected by removing shims to move the sensor closer to the lens.

Or screwing in the Torx screws on newer Floating Sensor models.

As I thought, Merlin has managed to correct with a Clip-In filter.

Michael

 

[Merlin66]

Michael,

Not really. The clip in filter allows manual focusing of EF lenses, the autofocus is still out of focus.

 

[michael8554]

44 minutes ago, Merlin66 said:

Not really. The clip in filter allows manual focusing of EF lenses, the autofocus is still out of focus.

Ah yes, not quite the same !

Does that give correct focus through the viewfinder, or only with LiveView ?

Michael

 

Edited July 22, 2020 by michael8554

[Merlin66]

Michael,

Manually focused using either the Viewfinder or the Live view screen. Is only the auto focus feature which doesn't work.

 

[Stub Mandrel]

17 hours ago, michael8554 said:

Wrong I'm afraid.

Autofocus becomes incorrect once the #LPF2 filter is removed.

Autofocus assumes the sensor is in the factory position, but removing the #LPF2 filter has the same effect as if the sensor was moved further from the lens.

Autofocus is corrected by removing shims to move the sensor closer to the lens.

Or screwing in the Torx screws on newer Floating Sensor models.

As I thought, Merlin has managed to correct with a Clip-In filter.

Michael

 

Sorry Michael,

The autofocus mechanism is all before the mirror; removing the internal filter does not affect the autofocus mechanism. This is the fundamental reason why you need to make a correction.

You said a clip filter could work - it most definitely won't help with autofocus.

I've found the Baader filters and they are too costly given the risk of breaking the camera.

My main question stands... what distance do I need to reduce the shims by - not having the original filter I can't estimate it and the only figure I could find assumed a thinner filter was used to replace it..

 

... but I've been given an idea by this discussion: slightly reduce the height of the mounting pillars, insert a rubber grommet, and treat as a 'floating' sensor adjusted by trial and error.

[michael8554]

4 hours ago, Stub Mandrel said:

The autofocus mechanism is all before the mirror; removing the internal filter does not affect the autofocus mechanism.

You're absolutely right, the autofocus mechanism is before the mirror and its working is not affected by the mod.

Nowhere have I said the autofocus mechanism is affected by the removal of the filter.

Quite the reverse, because it isn't affected it can't compensate for the new back-focus which is now about 0.20mm shorter.

Here's what one of the professional modifiers says, it includes why the Clip-in filter doesn't work, because it is before the Autofocus mechanism, not after.

A little about the workings of Auto-Focus

The below diagram shows the light path in a dSLR during auto focus

The auto focus is achieved by two crossed lines of pixels in the top of the camera which the light is reflected on to by the mirror. Anything in the optical path at this point is compensated for - i.e., using a filter behind the lens will not effect the operation of the auto focus.

This means that the presence of the eos clip filter is compensated for by the auto focus which remains sharp and accurate. When the mirror is raised, if both sensor filters are still in place, focus will still be accurate. If you then remove the rear of the two filters the focus is still effected - the removal of 0.8mm of glass still impacts on the focus of the resultant image in *exactly the same way* as it would whether the clip filter is there or not, as the clip filter has been compensated for by the auto focus.

The best way to ensure a tight focus in a modified camera is to accurately reposition the sensor.

[Stub Mandrel]

I think I'll have a go at my unconventional 'floating mod'... kill or cure!