Meade's LPI IR Blocking Filter Page

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Meade's LPI IR/Pink Image Problem:

I had been noticing pickish images with some of the LPI pictures that I took. I decided to see what was the cause. I first called Meade and asked them. Their customer service representative said that he had never heard of this problem. He put me on hold and asked around and when he came back on the line he said that they didn't know of anything that could cause this.

I took my LPI camera apart looking for the problem and then I decided to carefully remove the IR Blocking filter that Meade, or their Chinese manufacturer, glued into the front of the LPI camera to see if that was causing the problem. This filter was about 12mm square and was held in by a small dab of Silicone glue on each corner of the filter.

To keep dirt out of the camera I glued a small 12.5mm dia. optical window in place where Meade's IR Blocking filter had been. Then I proceeded to test their filter. The following details my findings.

The IR Blocking filter that Meade uses in their LPI camera is designed to stop all light above a certain wavelength from illuminating the CCD chip. This is because the CMOS CCD chip has greater sensitivity in the red part of the spectrum then does our eyes. If this wasn't corrected then the pictures taken with the LPI camera would not show the object as we see it through the telescope.

Putting IR Blocking filters in CCD cameras has been going on for years by all of the manufacturers so it isn't something new. What is new is the filter that Meade uses. Their filter has a sharp cutoff at 659 nm and allows only 65% of the light below this wavelength to get to the CCD chip.

The H-alpha emission line of nebulas is at 656 nm and the Meade filter attenuates this wavelength to less than 30% of the original. I assume that as Meade doesn't consider this camera a deep space camera that it doesn't matter if it attenuates H-alpha light or not. LPI stands for Lunar, Planetary Imager. They figured it would only be used to take pictures of the Moon and the Planets (and possibly a few terrestrial objects). As I wanted to photograph the spectrum of the planets I was very concerned about this loss of light. I also purchased a deep IR Blocking filter for times when I needed one.

Now, I had Meade's IR Blocking filter out of my LPI camera and I had several other different IR Blocking filters I decided to run a test to see how they all perform. To keep Meade in the picture I mounted their old LPI filter in an old 1.25" filter ring. This way I could just screw in a filter and take a picture and screw in another and take a picture and so on.

I ran the tests on the planets Jupiter and Saturn. The results of the photographs taken are shown below:

Filter          Trans.  Cut Off    Saturn     Saturn       Jupiter      Jupiter
Manufacturer     (%)      (nm)     Color     PhotoShop      Color      PhotoShop

Meade (LPI)       65      659      Natural    Natural      Washed Out   Natural
China Import      77      680      Pinkish    Natural      Natural      Natural
Edmund Optics     83      710      Pink       Pinkish      Light Pink   Natural
None             100      890      Very Pink  Pinkish      Pink         Pinkish


Natural   = means the raw image looks the same color as seen in the telescope
None      = means no IR Block filter was used
PhotoShop = means the images were processed in PhotoShop and then compared

NOTES: These were all color images; the 890 nm cut off for None means the camera is limited by the IR transmission characteristics of all the optical components in front of the LPI CCD chip (the cover plate and the optical window in front of the chip)

The results were that about any IR Blocking filter will work for Jupiter, after the image is processed. The raw images of Jupiter looked best when using an IR Blocking filter with a cutoff above 680 nm.

Saturn was a different story. Its raw images looked best using the Meade IR Block filter, and the processed images looked best with an IR Blocking filter with a cutoff above 660 nm.

If you are interested in photographing the H-alpha line you will need to remove the Meade IR filter but you could use any IR Blocking filter with a cutoff above 660 nm.

Faster Exposures:

Exposures with the Meade IR filter were running about 0.354 seconds (using a 2X Barlow). While the exposures with No IR filter (None) were running about 0.044 seconds (using a 2X Barlow). The increased amount of light getting to the CCD chip was very noticeable over the Meade filter.

While color photography of the planets may require an IR Blocking filter to make them look like you would see them in a telescope, black/white photography is a completely different matter.

In B/W mode (mono on the LPI control panel) there is no pinkish color to contend with. If you are taking pictures in B/W mode you can get the job done much faster by removing the IR Blocking filter. Remember that taking faster pictures reduces the atmospheric effects.

Modifying the LPI Camera:

Before you start I would recommend that you purchase an IR Blocking filter and a small optical window to cover the place where the Meade filter will be removed from.

First you need to take the back case off of the LPI camera. There are just two small Phillips screws (#0) that hold the back side case to the front side of the case. These two screws are located on the front side. One in the upper right corner (when looking at the front of the camera), and the other is in the bottom left corner of the case.

Next, remove the printed circuit board. There are two small Phillips screws in the corners of the circuit board. This will allow you to remove the circuit board and expose the CCD chip and the IR filter. When you are finished the bottom of the circuit board and the IR filter assembly will look like the picture to the right.

Then you will need to carefully remove Meade's IR Blocking filter. I would suggest that you use thin latex/rubber gloves so you don't inadvertently get your finger oil on anything. Its much easier to keep the oil off in the first place but a real problem to clean off after the fact. The filter is held in place with Silicone glue. You can use a small exacto knife or razor blade to cut it free. Silicone glue does not get hard so its like cutting a small piece of soft rubber.

After you have removed the old filter you are ready to put in the new optical window. DO NOT HANDLE the Optical Window before you put it in unless you have rubber gloves on...

Clean off the old glue and blow the area clean (but move it off the working area to blow the old glue out so you don't get any dirt on the CCD chip).

Place the new Optical Window in the IR well. Put a few dabs of glue on its edges. About any kind of glue will work even Rubber Cement. I would not use Crazy Glue. I used Duco cement on mine, and I got it from a hobby store for $1.49.

Now, you are ready to assemble everything but first you need to be sure that the inside of the Optical Window and the Face Place of the CCD chip are COMPLETELY free of dirt and dust... I can't emphasize this point enough.

You need to very carefully inspect the front plate of the CCD chip under a strong light, BEFORE you attach the circuit board back, to be sure that nothing got on the face plate. If you can see anything no matter how small then it needs to be cleaned off prior to reassembly. DO NOT Use cleaning fluids or Windex. Do not touch the face plate with your finger!. Do not use kleenex (they have oil in them to keep them soft). Use a new small very soft artist paint brush - one that you have not touched the bristles with your fingers (you can get them at a hobby shop for a dollar).

Any dirt that sticks to the CCD's face plate is so small that it clings due to molecular attraction - it is generally not charged. A soft paint brush will wipe it off but don't use a lot of pressure when you wipe the face plate. I generally use a jewelers loop (that little black thing that goes over your eye) to check for very small dirt particles. I got mine from American Science & Surplus for $3.50 + S/H (2005 price) and mine has a head band to hold it on which frees up both of my hands.

That's it. You are finished except for reassembling the camera. I would let the glue dry for several hours before reassemblying the LPI camera. During this time I would keep the circuit board in a plastic baggie so nothing gets on it.

The LPI camera reassembly is just the reverse of the disassembly. There are two small Phillips screws that hold the circuit board to the front side case, and two small screws that hold the rear section of the case to the front side of the case.

Now, when you want to take fast pictures don't use any IR filter for B/W, use an IR Blocking filter for color. If you want you can mount the old Meade filter in an old 1.25" filter ring (you will need to cut a plastic disk the size of the filter glass, 27 mm, and make a small hole 0.3" in the center to mount the filter - see my photo above) and use their filter sparingly.

Pink Image Problem:

It may seem that this has cured the Pink Image problem I started out with. As a matter of fact it did not. However, I finally found out what was causing the Pink Image problem. It was caused by the LPI control panel software. I was using version 3.16a at the time. What I found was that sometimes, very infrequently, when I would start up the LPI Imaging module (from within Autostar Suite) the image on the monitor would have a pronounced pink color to it. All you need to do is to shut down the LPI module and then reopen it.

I have since updated to Autostar Suite version 3.18 and I haven't see the problem again. But I am not sure it has gone away as Meade didn't seem to know anything about the problem. So in case you see all pink images as soon as the monitor image comes up, just close it down and restart it.

Taking Pictures of Spectrums:

If your interested in taking pictures of spectrums the you really need to get rid of the Meade IR Blocking filter as it cuts out a lot of the upper part of the spectrum. But don't take my word for it, just compare the two full image spectrums of Jupiter here. The image on the left is with no IR Blocking filter at all, while the image on the right was taken using the Meade LPI IR Blocking filter in place. These pictures were taken through a 90 mm Apogee refractor using a modified (as set out on this page) Meade LPI camera and a 906 l/mm DG Filter.

Disclaimer:

This modification is for Meade's LPI CCD Camera ONLY!. These modifications are not intended to be used with other cameras, although other cameras may also suffer from the same problem.

We/I will not be responsible for any problems that arise from anyone using the information provided herein. While we have taken great care to ensure that everything set out here is accurate, we will not share in any responsibility for any damage(s) that may result if this information is used in any way.