Apertura 75Q User manual

75Q Quintuplet Refractor
User’s Manual
By Matthew M Paul & Edward Bevan
2023

Overview
The Apertura 75Q Quintuplet Refractor uses an FCD100 extra low dispersion element in its five
element Petzval design. It is of excellent quality and produces sharp, bright, high contrast
images for both visual and photographic use. The dual speed rack and pinion focuser has an
integrated rotator which is useful for imaging as well as quick positional adjustments during
visual observations.
SKU
APT-75Q-LTD
Model
75Q-LTD
Series
Apertura Refractors
Focal Ratio
f/5.4
Optical Design
Petzval Refractor
Aperture
75mm (2.95”)
Number of Refractor Elements
5 (Quintuplet)
Optical Glass Type
FCD100
Focal Length
405mm
Image Circle
44mm
Focuser Style
Dual Speed Rack & Pinion
Focuser Size
3”
OTA Weight
6lb 13oz with V style Bar
7lb 13oz with D style bar
Length (Dew Shield Extended)
467mm

Using The Telescope
Mounting
The Apertura 75Q comes from the factory with a 11.75” D series dovetail plate installed, which
can be attached to most telescope mounts on the market. An 11.25” V series dovetail has been
included in the box to allow for mounting in saddles of that style, or replacement of the top
handle if so desired. To replace the installed dovetail with the V series dovetail bar, use a 3/16”
or 5mm size hex head wrench to remove the four silver screws underneath the dovetail bar that
secure the rings to the D series dovetail. Then place the V series dovetail on the rings,
positioning as desired, and move it until the holes in the dovetail line up with the holes in the
telescope rings. Reinstall the four silver screws, tightening until these are just snug.
Utilizing the V series as a replacement for the handle allows accessories to be mounted on top
of the telescope with universal adapters that exist on the market. This allows for versatile
placement and quick removal of the supporting accessories, such as mini PCs, Wi-Fi camera
controllers, power distribution devices, or guide scopes. Please note that this requires removal
of the finder scope base to accommodate the V series bar, which can be done by unscrewing
the two silver screws with a 3/32” (2.5 mm). The handle can then be replaced by unscrewing the
two screws holding it to the rings with a 5/32” (4 mm) hex head wrench, and reusing these to
install the V series dovetail in the handle’s place.
Visual Use
1.25” Visual Adapter
This telescope comes with a 1.25” eyepiece
holder, for visual use. To attach this, first
lock the camera rotator with its thumb
screw. Then unthread the spacer for the
filter cell along with the cell itself, and thread
the visual adapter on in its place (pictured to
the right). The 75Q is now ready to accept a
1.25” diagonal!
The telescope is not compatible with 2” diagonals and visual acceslong perng 80 carbon
sories due to the available back focus of the system.
Focusing
With a 1.25” diagonal mirror, like the Apertura 1.25" Carbon Dielectric Mirror Diagonal
(APT-D1CF, sold separately), focus should be located around the 25mm mark on the focuser’s
drawtube. Though, this location will vary a little depending on the diagonal and eyepiece in use.

Photographic Use
(Shown with optional accessories and items not included with the Apertura APT-75Q-LTD telescope)
Back Focal Distance
“Back focus” is the term used to describe the distance between the metal back of the telescope
and the camera sensor. Meticulously spacing the camera out to this distance is typically critical
not only to ensure that it can reach focus, but also to obtain the sharpest, brightest, best
corrected image from the optics. Petzval optical designs are typically described as eliminating
the need to calculate and space the back focus distance, however this isn’t the whole story.
Scopes of this design still need the camera sensor positioned at a suitable location that allows
the camera to reach focus. What the Petzval design does eliminate is the need to exactly set
the spacing for great optical performance - so long as your camera is spaced out enough to
reach focus, the telescope will perform optimally.
The Apertura 75Q is designed to have a back focal distance around the industry standard 55
mm. This is the typical back focus of a DSLR with T-adapter, or cooled astronomy camera with
its included adapters.
The telescope offers optional M52 and M76 connections for flexibility in specialized applications,
should they be needed.

2” Filter Cell
The 75Q comes equipped with a built in threaded 2”
filter cell. To install a filter, first unthread the knurled
section at the very back of the telescope, the section
that the rear dust cap threads on to. Inside this section
are threads to hold a filter inside the telescope when
the cell is reinstalled. Simply thread a 2” filter into these
and thread the cell back into the telescope.
Focuser
The dual speed focuser comes from the factory with
two options to operate the focuser lock. The focuser
lock functions by holding the focuser draw tube in place, making accidental adjustments
impossible; useful when manually setting the focus point. A small thumb screw comes
preinstalled on the scope. Depending on the position of the dovetail plates and how the scope is
used, this thumb screw can be difficult to manipulate by hand. Inside the black cardboard
package that houses the V style dovetail bar there is a bag with a small set screw and a hex
key. By removing the telescope from the tube rings, the thumb screw can be replaced with this
set screw which allows the focus lock to be manipulated through the use of the hex key, though
the bottom of the dovetail bar.
When using an autofocuser it might be a good idea to replace the thumb screw with the lower
profile set screw. By doing so the hardware will not interfere with the auto focuser bracket.

Autofocuser Installation
Install the autofocuser on the coarse knob side of the telescope. Use the 2mm hex key that is
included with the telescope to loosen the set screw that holds the coarse focus knob in place.
Then, remove the coarse focus knob from the telescope.
The Apertura 75Q has a 6mm connection on the coarse adjustment shaft. This is the size
adapter or flex coupler that will need to be used when installing the auto focuser. There are
three possible M4 screw holes on the bottom of the focuser shaft housing that can be used to
mount the autofocuser bracket; these holes are shown in the image above. Below is an image
showing a common autofocuser installed on the 75Q.

Additional Technical Information

Warranty
The Apertura Absolute Warranty provides two years of coverage against product
defects. After the initial two-year warranty expires, this product qualifies for Apertura's
Three-Year Accident Replacement Program. In addition, the Apertura Absolute
Warranty is transferable! It is important to keep your original receipt and the product's
original boxes and packaging, should you need to make a claim.