Webcam IR filter question

[Skipper Billy]

I am about to covert a MS webcam for astro use and all the websites I have found make it clear to remove the IR filter from the front of the chip as well as the lens etc.

They also almost all suggest using an IR filter in front of the camera screwed onto the end of the tube that goes into the eye piece holder.

I dont get that - why not just leave the IR filter on the front of the chip ???

Or is it me misunderstanding ???

[jonnopfc]

Hi Skipper, from what i can understand it is because the ir filter that comes with the webcam is not of shall we say a very good standard. Whereas the one you buy to replace it with is of a better quality and more appropriate for astrophotography.

Jon

[Kropster]

It confuses me too.

Removing the IR filter made my webcam a lot more sensitive.

I suppose if you are using a reflector the IR and visible light will come to the same focus, but with a refractor probably not.

So, maybe use a filter with refractors but not necessarily with reflectors?

[Skipper Billy]

Well I am glad its not just me that's confused!!  ;-)

[jambouk]

I think IR is more than just chromatic aberration; structures which are visible only in the IR may not be visible in the visible light range, but they may both stimulate the pixels, so you could potentially lose detail of visible structures. I'm not sure how important this is, but would imagine it would become more apparent the greater the aperture and resolving power of the kit.

My first webcam had no IR cut filter and i had no obvious problems, but i was only using a small aperture scope. I'm still waiting to see a side by side comparison of some stacked images from a C14 say with and without IR cut filter of Jupiter to see the difference.

Jd

[todd8137]

Wether it be a 6" pr 14" scope it would make no diference remove in the ir filter lets the max amount of light through ,For astronomy use, you may need to fit an I.R. stop filter somewhere in the optical path. This is more likely to be needed with refractors because the lens will not focus I.R. at the same point as visible light, leading to fuzzy CCD images. Reflectors are less of a problem because mirrors focus all wavelengths at the same point.

Pat

[Oddsocks]

The standard factory-fitted IR blocking filter supplied with a non-astro webcam has quite a broad cutoff range and if you leave the standard filter fitted then you lose quite bit of the red spectrum, especially around the important Ha emission line.

The add-on IR or IR-UV blocking filters designed for astrophotography have a narrower cut-off range that blocks the far IR only and allows part of the near IR, including the Ha emission line to pass through unattenuated.

I don't know how much difference leaving the original IR filter in situ, compared to an add-on IR filter, would make to planetary imaging but would expect a big loss of image data when using modified webcams in LX mode for deep space imaging.

[Mr TamiyaCowboy]

Webcams have a small ALL IN ONE lens and filter. now the problem is getting this filter OUT

with out Breaking it, and trust me it is hard. the glass is very thin even a pin tip trying to pry it of shatters it.

here we just throw away the problem, ie the tiny allinone filter/lens and replace it with something that has a 

a better filtering in place, ( cheap all in one filter and lens units are cheap things ) 

The reason is the Sensor itself does not have a filter system, all it has is a clear glass protector cover.

the filter is glued into the lens unit ( usually a small disc) and is the pain to remove without it breaking apart.

i have tried lots of times and failed with these micro lens units.

then you have the problem of making a small round filter into a big square filter and somehow

fitting it to the sensor protector without harming the optical quality of the glass protector.

a normal camera will have a thickish IR filter and this acts as a Sensor protector, some fit in a rubber bellows system to hold them inplace

some are glued in place, you would normally remove this and replace with an aftermarket Astro breed IR filter/protector. 

Difference there is one : 

i had the webcam in use before astro conversion, image was 100% RGB and pure. 

After the astro conversion and purchasing a £21 IR filter, the same camera using a telescope

now gives a slight red/IR hue, so much so i turn down saturation to zero and run B&W on it.

this is a microsoft HD5000 (true hd720p 30fps ). focus always seems off due to the IR being focused to a differnet point

the difference is in FILTER choice, £21 sounds expensive so should have done the job

BUT the filter does not it is not cutting all IR light , a pink moon is not ideal even when running

an IR filter inline. so also take into account the cheaper the filter the less well made it is

and the lower quality coating it shall have

[JamesF]

If you want to leave the standard IR filter in place then you could use it like that.  I'd recommend a separate filter personally because they're made to a much higher standard.  They should have a well-defined pass-band and be optically flat.

If there's any glass anywhere in the optical train you probably want an IR filter of some sort.  A newt may use mirrors, but put a barlow in it and you then potentially have to deal with IR and visible light not coming to focus at the same point.  I'm not sure that even apo barlows guarantee to focus IR at the same place as visible light.

CCD and CMOS sensors are often very sensitive to IR, so failing to block it can cause overexposure, colour balance problems or bloating in the image.

James

[spaceboy]

For what it is worth.......... I found my Baader Neodymium Filter I/R cut showed improvement visually compared to unfiltered views and as a result purchased the Baader fringe killer I/R cut for my refractor and found that also made to my eyes a noticeable improvement. I'm sure if there are benefits when using them visually there has to be benefits when using them imaging but other factors have to be taken in to account when using high magnifications on planets like barlow quality, is the scope ambient to it's surrounding, collimation, focusing and seeing conditions. For example when I visually observe planets I find that over a few minutes I have to refocus a couple of times.

[Mr TamiyaCowboy]

it is slightly different for me,

i own a IR 720nm camera filter system. ( very dark black/red filter )

to take a picture in focus, i have to first focus camera with lens, then without

loosing focus, attach the filtering system. now i am ready.

my system blocks all white light and only allows wavelengths at 720nm in the IR band.

to remove the pink hue, i first take a shot of some nice GREEN grass. i then use this image as a

custom whitebalance, it remove the pink hue. 

for astronomy i had to swap the red and blue channels in editing software to give the false color effect.