Mod SLR

[jet486]

What is a Mod SLR camera? and how does it enhance night photography. Thanks

[[1ponders] (Paul)]

Hi Jet486

A modded DSLR is one that has had the IR blocking filter removed and either left as is or replaced with a clear glass or more selective filter.

The prob is the standard IR filter cuts too deeply into the red part of the spectrum and reduces the ability for Ha emissions to be recorded. Removing it let this most desirable part of the spectrum to be recorded with less exposure time. Its not all good news though. If a suitable IR filter isn't placed over the chip too much IR can cause colour balance problems and 'soft' images. Also if the filter is removed and not replaced with the correct thickness of glass/filter the camera with standard lenses won't come to focus using autofocus.

Typically an image from a modded camera has a much more red cast than a non modded camera. This can be alleviated for normal shots by shooting a suitable white background under good illumination and using this shot to set a custom white balance. It will only work though in the manual settings. Shooting in preset mode will usually end up having red images

HTH


Edit: I've attached a single unprocessed RAW image. Only been converted to jpeg

[wasyoungonce (Brendan)]

DSLRs have a front bandpass filter, a filter that allows a certain band of wavelenghts of light to pass thru to the sensor and block everything else.

This is because...the unwanted wavelengths..the wavelengths we cannot see ...still posses energy (even though we cannot see them) which will be registered (captured) but the camera sensor.

Thus the camera will be taking pics of wavelengths we cannot see converting them to images we can see. Thus the sensor will (can) "bloom" the image...that is become overwhelmed by the amount of energy reaching it making images "foggy/blurred".

Another consideration is that these unwanted wavelengths come to a differing focus wrt light we can see..thus the camera will convert this unfocussed energy to foggy images.

However...camera mfgrs are a little conservative when it comes to the band-pass filters they put on their DSLRs...so many do not capture some of the wavelengths we want....like Hydrogen Alpha and hydrogen beta. Which are abundant in the universe.

Thus users modify their DSLR to put in band-pass filter that allows these Ha/Hb wavelengths thru...or even leave out their filters to allow all wavelengths thru..like infra-red.

edit:

beaten!

[mswhin63 (Malcolm)]

I am looking at alternatives to modding my camera, still having difficulty deciding, but now considering clear glass then add Clip-in filter for majority of AP but also adding further filtering for more specific wavelength.

But still not sure of the best alternative and whether clear glass will come up with problems or multiple filters will cause another problem.

[jet486]

So correct me if I'm wrong by removing the IR filter in my Nikon SLR I am able to photography nebulas in a finner detail. I assume that the camera becomes useless for basic daytime photos unless I re-install the original glass filter. Is this easily done or do I have to take my camera to a specialist? Cheers

[mswhin63 (Malcolm)]

I believe there is another filter that can revert back to normal operation. The most affect is whitebalance so if you modify the camera the custom whitebalance has to be set.

[Bassnut (Fred)]

Originally Posted by jet486

So correct me if I'm wrong by removing the IR filter in my Nikon SLR I am able to photography nebulas in a finner detail. I assume that the camera becomes useless for basic daytime photos unless I re-install the original glass filter. Is this easily done or do I have to take my camera to a specialist? Cheers

Its not detail that is impoved, just shorter exposures in the near-infrared (eg Ha) frequencies which the internal filter cuts off.

You can get clip-in or screw on filters you easily fit for daytime photography to correct the colour balance properly again with the mod.

As mentioned, the original filter needs to be replaced with something, either clear glass or a higher freq cut off for auto focus to work for normal use.

The clip-in filter though, can get in the way for some stock lenses, so a screw on maybe the go..