DSLR Mods - Standardised naming?

[Merlin66]

There is much ambiguity in some of the references to the various mods which can be carried out to the DSLR - mainly Canons.
Is full spectrum the same as FULL spectrum?, when is a UV-IR replacement filter required? What about the clear filter replacement?
Can I work with all the filter elements removed??

The phrase "Astro modified" seems a very good choice to describe the removal of only the colour balance filter which enhances the response to the red region of the spectrum - including the Halpha.
To reduce star bloat it is usual to add back a UV-IR filter, or if you want to maintain auto focus with the standard camera lenses add a clear filter replacement.
For the mod which removes both filters (colour correction and the anti alias filters) and allows access to wavelengths from 360nm through to the NIR I think should be called a "FULL spectrum mod" Again the UV-IR or clear filters can be added back depending on the need.

What do you think?
Makes more sense?

[D4N]

I think one of the confusing points is that the canons have two filters inside, modification is normally done by remove the first one. However other brands may only have one. My Fuji only had one filter.

Removal of the first filter on a canon is not really a full spectrum mod even though it may get called this as the second filter is still blocking a lot of light. Removal of one filter on a Fuji is a full spectrum mod.

You can work with all the filters removed but a problem you can get is that any refracting elements in your optical train may cause dispersion of the incoming light. This will shift the focus apart making it impossible to achieve perfect focus on all wavelengths at the same time.

I notice this as red star bloat if I use my modded Fuji on my frac without a filter. It goes away if I use my UHC-S filter.

This isn't a problem with mirrors but you can still suffer from over exposure due to too much IR or UV hitting the sensor.

The mod sometimes includes adjustment of the sensor position as well, I moved my sensor closer to the shutter to account for the change in optical distance caused by the filter removal.

Oh and don't forget debayering is another mod altogether.

/Dan

Sent from my iPad using Tapatalk

[Astroboffin]

As far as I knew, if you removed both filters it was Called a full spectrum mod.....and if it just had the one filter removed, as I did, that is known as and Astro modified camera, or the hot mirror removal mod.

So am a bit confused....!

AB

[Merlin66]

AB,

I so wish that was the case!

Unfortunately there are many references to the removal of only the colour correction filter as being a "full spectrum" mod (especially when replaced with a UV-IR filter) when in fact the anti-alias filter (or the added filters) restricts the wavelength coverage.

(being active in spectroscopy I've been caught out before!!)

[Astroboffin]

AB,

I so wish that was the case!

Unfortunately there are many references to the removal of only the colour correction filter as being a "full spectrum" mod (especially when replaced with a UV-IR filter) when in fact the anti-alias filter (or the added filters) restricts the wavelength coverage.

(being active in spectroscopy I've been caught out before!!)

Ok fair enough, as I am fairly new to all this, and I knew the difference, I assumed most other people would

In that case I totally agree with you, as there is a big difference, I answer loads of posts with people asking about Canon mods and whether or not they will need an IR filter, and I tell them all the same, if you have the "Full spectrum mod" (both filters removed) then the answer is "Yes" if you just have the single filter removal then "No", as the filter that is left in the camera gives excellent IR cut and so a seperate IR filter is a waste of money.

Both filters have IR cut but the front one also cuts the Ha signal by around 60%, hence the removal of that one.

Maybe this could be explained by someone better than me, as English was not my best subject, and then pinned in the imaging section, for people to see.

AB

[sharkmelley]

I wouldn't rely on any consistent terminology.  Always ask the vendor exactly what the modification entails.

For the avoidance of doubt it is the rear filter of the two that filters out H-alpha.  The front filter (antialiasing and dust removal) does a good job of filtering out IR so it is often left in the camera.  If the front filter is also removed then an external IR filter is usually required during imaging to prevent out of focus IR wavelengths causing star bloat (single most equipment includes refractive elements).

Unfortunately the rear filter, the one that must be removed, is the thick one.  Once this thick filter is removed, it changes the optical path length and many standard lenses will no longer be able to focus at infinity.  It can also affect image quality on some scopes with correctors where that exact optical path length is critical. Therefore a piece of plain glass or Baader IR-UV filter or some other supplied filter  is often added back in to allow good focus for such lenses and good optical correction for such scopes.  When this is done, the front filter is usually removed.

So given there are so many combinations, don't expect any consistent terminology anytime soon!

Mark

[Merlin66]

Yes, I've added a Astronomik clear clip-in filter to allow the use of standard camera lenses for spectroscopy to my FULL spectrum modded 1000D.

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[sharkmelley]

Yes, I've added a Astronomik clear clip-in filter to allow the use of standard camera lenses for spectroscopy to my FULL spectrum modded 1000D.

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A nice idea!

Mark