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Information on the Optec Filter Slider
The Optec filter slider is an attachment of exceedingly high quality that holds and automatically places filters in the optical path for imaging or photography of almost any sort. It can also be used to hold filters for viewing. I am very happy with this attachment for a number of reasons which will become apparent in the following discussion. Thus I have stated my prejudice and my biases will follow.
The biases are basically as follows. I believe the filter should be a large distance from the imaging surface, whether it is film or a CCD chip, so that any defects or dust are well out of focus. I also feel that the filter should be large enough so that there is no possibility of vignetting on a full 35 mm format or when focal reducers are used with CCD imagers. It is also desirable to have easy exchange of filters and use of filters which are standard size so that a great variety of filters can be used. Finally, the operation of the filter slider should be fully automated for use with standard CCD imagers.
Here the Optec filter slider is shown on the back of a 10" LX200 with
the JMI focuser including the DRO. Details of the adapters are shown
in the following discussion.
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The Optec filter slider adds only 25.9 mm to the back focus requirements.
It mounts on an adapter ring of its own and has the correct sized ring
on the back to take the JMI directly. This arrangement insures full
2" clear openings internally. The top view shown here demonstrates
the small thickness of the combination. It is very strong mechanically
as well.
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Here are shown the Optec filter slider and the Optec adapter tube along
with the JMI adapter tube. The Optec tube is 60.5 mm outside diameter
and 53.1 inside diameter and screws directly on the back of the 10 or 12"
LX200. The JMI adapter is 55.8 mm outside diameter and 51.2
inside diameter. It is no longer used with the Optec filter slider
in place. The back side of the filter slider has a 55.8 mm outside
diameter tube which takes the JMI directly as seen in the photos above.
This makes for a very strong mechanical connection and gives a full 2"
clear internal opening. The actual opening is 50.5 mm. While giving
statistics, the JMI weighs 1 1/4 pounds and the Optec 1 3/4 pounds.
This weight is of course very close to the declination axis and easy to
balance. In fact, if you use the Meade dew hood, as I do, you need
all of this and more to balance the hood. The small motor drives
the filters with great positional accuracy to the three positions.
The system is fully automated and compatible with the SBIG imager filter
commands. One slight disadvantage is that there is no clear filter
position to facilitate focusing.
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Another view of the Optec filter slider shows the filter tray that in
this case is provided with a three color filter set for CCD color imaging.
The Optec filters are all exactly the same thickness so focus is maintained
when changing filters. Separate blank trays can be had into which
any color filter set desired can be mounted. The openings in the
trays are 50 mm with a 47 mm shoulder and thick enough to take standard
48 mm filters. For example, I have a tray loaded with filters for
use with monochrome imaging. Additional trays can be set up
with viewing filter sets or with color filter sets that have different
densities and pass bands. See a discussion of filters for use in
color imaging elsewhere on this web site. (Attachments/Filters/Three
Color Filters) The little door on the end allows for quick
interchange of filter sets. (it takes less than a minute to do this
operation)
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The filter slider comes with a control box and cable with manual selection
buttons. There is an eject button for changing filter trays on the
end of the tray structure itself. The entire Optec filter setup is
well build and works as advertised. It is not inexpensive but it
provides versatility that is hard to find elsewhere. For example,
it can be used for 35 mm film photography when filtering is desired and
for direct viewing when band pass filters are desirable and need to be
exchanged quickly.
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