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We make our Type D - DG Spectrum Filters to fit film cameras and camcorders with 28 mm threads all the way up to 72 mm threads.

Select Your Filter Size in mm 28 mm Filter 37 mm Filter 43 mm Filter 46 mm Filter 48 mm Filter 49 mm Filter 52 mm Filter 55 mm Filter 58 mm Filter 62 mm Filter 67 mm Filter 72 mm Filter Temporarily Out of Stock Type D1 - Patent Pending: $154.95

Select Your Filter Size in mm 28 mm Filter 37 mm Filter 43 mm Filter 46 mm Filter 48 mm Filter 49 mm Filter 52 mm Filter 55 mm Filter 58 mm Filter 62 mm Filter 67 mm Filter 72 mm Filter Temporarily Out of Stock Type D3 - Patent Pending: $144.95

We also make our Type D - DG Spectrum Filter in 48 mm (2" Telescope size).

These sizes are special orders and are generally shipped in two to four weeks depending on availability. There is a $20 sur-charge for Type D - DG Filters in a size other than 28.5 mm (1.25"). Generally the Type D1 - DG Filter works much better for longer distances from the image sensor (or focal plane) than does the D2 unit.

The D3 unit is a special effects DG Filter that produces multiple spectrums in four planes. The D3 grating has a very low dispersion so it produces spectrums that are shorter than those produced by our D1 units which makes the D3 unit a better choice for long mounting distances from the focal plane. The D3 unit is generally used as a special effects filter producing varied rainbow effects around the field of view.

These special sized Type D units are classified as Special Type D - DG Filters. The only difference between these and our standard Type D - DG Filters is that these units only have one protective cover glass and no PVC seals, while the standard Type D units have two, and these units have a transmission across the visible > 86% compared to our standard Type D units which only have a transmission > 78% across the visible. The Special Type D Filters are supplied with a Protective Glass Filter. When used with the protective glass filter the transmission decreases to the same as the standard Type D Filters of > 78%.

Colored glass filters may be used with most of our Types A to D - DG Filters.

Most of our DG Spectral Filters can be fitted with colored bandpass glass filters that reject light that falls outside of the bandpass of the selected glass filter. These glass filters are screwed on the back end of the DG Filter and can also serve as a cover protector, the same as used in DG Types C1/2, only here the cover glass is not clear.

Glass      Transmission  Bandpass (nm) #1    Bandpass (nm) #2
Filter      Visible (%)   Start  &  End      Start #2 & End #2    COMMENTS

#23A          29.5        560       900                           Cuts out Blues and Greens
#21           40.6        540       900                           Cuts out Blues and Greens
#15           50.2        510       900                           Cuts out Blues
#12           60.4        495       900                           Cuts out Reds and Blues
#11           30.4        415       900                           Cuts out Reds and Blues
#56           10.2        460       610          700      900     Cuts out Reds and Blues
#80A          23.2        360       800                           Cuts down Reds and Yellows

NOTE: Visible light falls between 400 nm and 700 nm, where 400 nm is Deep Blue and 700 nm is Deep Red.

When a color filter is used in combination with our DG Filters the resulting spectrum is restricted to the bandpass of the colored glass filter. For example: If you are using a Type B1 - DG Filter and screw a #23A (light red) filter to its filter threads the resulting compact image will contain a red image of the star and the Red and IR portions of its spectrum. Any reference calibration distances measured without using the colored filter will still be valid with the colored filter in place.

Select Your 1.25" Antares Glass Filter 1.25" Light Red #23A 1.25" Orange #21 1.25" Amber #15 1.25" Yellow #12 1.25" Yellow-Green #11 1.25" Green #56 1.25" Light Blue #80A Glass Filter $9.95

When more spacing is needed when using a B1/B2 DG Filter with a SBIG T-thread to Ring Adapter, or with some Starlight Express camera combinations, you can add an empty filter cell to the base of the DG Filter to increase the spacing so the DG Filter will have room to clear everything inside the lens well/holder (like an optical window placed in front of the CCD chip).

The Type B - DG Filter is screwed in one of these empty filter cells and the assmbly is screwed into the camera's 1.25" filter threads. These cells are 10.01 mm tall and are 8.03 mm high when measured from the top of the threaded portion to the top of the filter.

Using this empty filter cell will move the DG Filter 8 mm further out.

Type B - DG Spectrum Filter Dimensions:

The B1/B2-L Filters extend 21 mm past the bottom of the bottom of its holder (this is measured from the top of the threaded portion of the DG holder). The B1/B2-L Filters are 9/16" in Outside Diameter.

The B1/B2-S Filters extend 18 mm past the bottom of the bottom of its holder (this is measured from the top of the threaded portion of the DG holder). The B1/B2-S Filters are 17/32" in Outside Diameter.

Empty Filter Cell $9.45

If you ordered Several DG Filters on a Single Order and require more than the Single CD that was shipped with your order, you may order additional CDs up to the total number of DG Filters, that you have ordered, for an additional cost.

You will need to enter the Date of your Multiple DG Filter Purchase and the Name it was Shipped- To in the Shopping Cart's Comment Box. If we can't find this shippment in our data base we will refund your CD order amount and not ship you the additional CD.

There is nothing on the CD that requires it to be used at the location where the DG Filters are used. The files on the CD are generally DG Filter Manuals and Processing software which generally can't be used at the observing site. The information on the CD can be installed on a laptop and taken to the field or remote location if it is necessary but once this is done the actual CD is no longer necessary nor are additional CDs.

If you require several CDs with your purchase of Multiple DG Filters it is quicker and cheaper to place separate orders for the DG Filters with one DG Filter on each order.

Additional CD $7.95

This is a Variable Width Slit designed to be used with Type A, B and D - DG Filters. On Type B and D - DG Filters the Slit Cell screws on the back of the DG Filter. On Type A units the Slit Cell screws into the 1.25" filter threads of the camera.

The width varies from over 100 microns to under 10 microns. The width is Not manually adjustable. The width is widest at the top, near the center of the Slit Cell, and becomes narrower as you move away from the central area of the Slit Cell. The narrowing is uniform and linear.

The narrower the slit the dimmer the spectrum. An extended object is moved until it is centered over the desired width of the slit, then its spectrum will be visible. The Slit Cell needs to be rotated so that it is parallel to the Yellow or Red dot on the DG Filter then you will get the highest resolution.

This Slit Cell is only recommended for use with our Compact DG Filters as the object needs to be near the center of the monitor/chip. This positioning was necessary in order to accomodiate the various widths of CCD chips the DG Fiter is used with.

If the slit is rotated so that it is perpendicular to the grating grooves, 90 degrees from the Yellow or Red dot on the DG Filter, then it can be used as a cut off slit. Here, a large extended object is moved to the edge of the slit where its light will get blocked off by the slit's side edge. Then the spectrum formed will be for the portion of the object not eclipsed by the slit's edge.

There may Not be sufficient clearance to mount this Slit Cell on the back of a DG Filter if its being placed in a filter wheel. A Type D - DG Filter with a Slit Cell mounted on it will require 17 mm of clearance. The Slit Cell will reduce the transmission of the DG Filter by 84%.

When using a slit you need to focus on the slit not the spectrum or the object - refer to our FAQ.

This item is a special order and is generally shipped in two to four weeks depending on availability.

While the Variable Width Slit will work with most CCD cameras it is more efficient with cameras that have CCD chips that are 7 mm or more in width with Type 1 DG Filters (Compact version - 500 l/mm). The slit is NOT Recommended for the Type 2 DG Filters (High Resolution version - 1000 l/mm) as the dispersion is so wide that it requires a CCD chip 18 mm or more in width to see the spectrum - this is if the separation between the Type 2 grating and the CCD chip is 10 mm (greater separations would require a wider CCD chip in order to see the spectrum).

Variable Width Slit Temporarily Out of Stock $49.95

Most CCD cameras have an IR Blocking filter installed right in front of their CCD chip. This filter will cut the visible spectrum to well under 700 nm. If this filter is taken out the range can be extended well beyond 800 nm.

If the IR Blocking filter is removed then you may need to purchase an external screw-on IR Blocking filter for the times when you want/need an IR Blocking filter. However, some cameras have a removeable IR Blocking filter, in this case you don't need to purchase a screw-on one.

Meade's LPI Camera

The Meade LPI camera has the IR Blocking filter glued inside the camera body. To remove it is a bit involved, see our LPI tutorial page. Once removed you will need to replace the IR Filter with a cover glass to protect the CCD chip, and you should buy a screw-on IR Blocking filter for the times when you need it, like for photographing Jupiter.

Meade's DSI Camera

The Meade DSI camera has the IR Blocking filter located under the threaded lens barrel. To remove it you just unscrew the lens barrel and take out the large dark plastic washer with the small red glass in it. Then screw the lens barrel back in place.

Celestron's NexImage Camera

Celestron's NexImage camera has the IR Blocking filter made onto the top of the CCD chip. This one can't be removed easily without damaging the CCD chip.