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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.
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.
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.
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)
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
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