Nikon D90 -- removing the IR blocking filter and the mirror

[Star-Dust]

I want to remove the IR blocking filter and the mirror for deep sky objects

I have an old Nikon D90 with a busted shutter motor that I want to use for astrophotography.

I know what needs to be done, basically remove the mirror (Not necessary but gives better results than locking the mirror), secondly I need to remove the IR blocking filter.

Naturally, I will lose the autofocus, and I will have to use live view which is acceptable.

My question

do I need to add a clear glass in the place of the IR blocking filter on the sensor?

If the only reason to adding a clear glass piece is to allow autofocus, then I will not be needing that because I am also removing the mirror. So I will be doing manual focus using live view.

Or do you have another advice for me like buying a pre modified camera?

For landscape astrophotography , I have been using my Z9 but I also have a question there

Do the landscape astrophotography also require the camera IR blocking filter removed as in deep sky celestial objects?

The green comet taken with Z9

 

[andresch]

I do not know the D90 but i did the removal of the IR filter myself on a D5500. Two points you need to consider: The back focal distance will change slightly by removing the filter glass. Rule of thumb is 1/3 of the glass thickness. This may cause issues (deformed stars off axis). Secondly, you need some alternative IR filter, otherwise the IR wavelengths will bloat the stars. A typical astro UV-IR filter has a bandpass from 400 to 700nm. If you can find a replacement glass which filters also IR above 700nm, that would be the best.
I use my modded camera only on telescopes and i adjusted the sensor to compensate for the lost filter thickness. With telescopes, it is easy to add a filter somewhere in the imaging train, maybe not so with lenses.
On a further note, it is quite easy to introduce sensor tilt while removing the glass. Measure it carefully before and after the modification.
My personal view: for astro lanscapes and milkyway photography it is not necessary to have a Ha modded camera. Of course it adds some red "pop" but TBH i like the natural look more. It is different for DSO astrophotography with isolated emission nebulae, there you will catch way more signal.
Good luck!

 

[Star-Dust]

Very useful reply

thanks