Full Spectrum Modification and Auto Focus on DSLR

[Emilio]

Hello all,

I'm new to this forum and astrophotography, and observing for that matter!

I've been observing for a few weeks now, well, when the clouds allow, obviously! I thought I'd dip my toe in the water as far as imaging goes, but didn't want to go nuts in terms of budget. As luck would have it I managed to get hold of a Canon 1100D on eBay complete with full spectrum mod for £129, which seemed pretty reasonable to me given the cost of the modification on its own. The camera is in great condition and seems to work fine, however I have a couple of queries that I hope you more experienced peeps can help with.

Firstly I would like to get an OWB filter and wondered if anyone had an opinion on Optolong vs Astronomik? Astronomic are a lot more expensive so if the Optolong does a good job why spend extra?

Second, and more importantly, I have questions about auto focus. It seems that generally people say that if the IR/UV cut filter is completely removed then the camera will definitely lose the ability to auto focus (although some people say this isn't the case?). I checked with the eBay vendor and he confirmed that the in-built filter has been completely removed and no glass / filter replacement has been put back in place, which if my understanding is correct is what is required to retain auto focus. However, the camera seems to be auto focusing fine as far as I can tell.

How can this be?

Thanks.

[Emilio]

I think I may have answered part of my question. When using Live View the camera seems to auto focus correctly but when using the viewfinder it doesn't. Again though, not sure why this should be.

[michael8554]

Autofocus is calibrated to correctly focus on the factory position of the sensor.

Removing the #LPF1 and #LPF2 filters has the same effect as if the sensor had been moved away from the lens, so Autofocus is wrong, as is the viewfinder view.

Manual focusing with LiveView has to be correct because you are seeing the actual image the camera is producing.

Most "professional" mods reposition the sensor to restore Autofocus.

Michael