How Much LP FILTERS ATTENUATE THE LIGHT

[lensman57]

HI,

I Still have my Canon 1000d with a Baader Mod. Tonight out of boredom I decided to measure the amount of light that is cut off from the sensor in general terms by various LP, UHC-S filters that I have by pointing the camera towards some quartz  living room lights. The Following is the result.

Camera : Baader Modded 1000d @iso 800, Canon EF 50 mm F1.4 lens @ F2.5 no filter meter reading: 1/800s Tungsten light balance setting.

Location : Sitting on my couch pointing the camera up.

Astronomik CLS CLIP FILTER   -1 2/3 F stop. ( slight blue cast )

OpticStar UHC-S ( Ha,Hb, Oii,Oii iand Sii)  - 21/3  F stop. ( strong cold blue cast with a hint of red at the top of the lamps )

Idas LPS-P2  -1 F stop. ( no colour cast at all, the most natural looking rendition )

SkyWatcher LP filter approx  -1 F stop. ( noticeable red - magenta cast )

The conclusion is that these lovelies just slow everything down to a halt, wether they will let enough of the remainder of the spectrum through to a lesser attenuation level needs a much more specific and accurate test. I guess the best filter is none at all if the skies were dark and none light polluted.

Regards,

A.G

[Sp@ce_d]

  you really are bored.. nice collection you have there though.

Of course they are all going to slow it down, they are designed to block the type of light pollution your ceiling is being illuminated with....   

I've got the SW & the Hutech. I used the SW for ages & the colour cast processed out ok. The best of the bunch I would say is the Hutech. However, it does depend on what type of LP you're trying to filter out as to which ones will be best at the job though. With the new LED types of lighting thats getting tougher.

[dph1nm]

It is an interesting question as to whether LP filters do more harm than good to imaging (and by that I mean does the signal-to-noise ratio become better or worse in the same exposure time).  This must depends on the amount/type of LP and the brightness/spectrum of your object, but it is not a straight forward calculation.

NigelM

[lensman57]

Hi,

Thanks for your comments, I did this just for fun  but also I thought that it may also be interesting for beginners in imaging as lloss of light through filtering is quite significant.

Regards,

A.G

[jgs001]

I have the CLS and had (I can't find it ) the SW LPR... I found that the CLS is best to about f/5 and beyond that the SW seems the best fit (for me at least). I tend to use 5 minute exposures with both. This gives the best balance between the skyglow (not too intrusive) and the detail I'm after as far as I can tell... I probably need to do somewhat more scientific testing, but that takes time... and when I have time, I don't want to be doing testing.