Astronomy Equipment Compatibility / no guesswork hidden

Build a rig that adds up.

Check spacing, thread handoffs, sensor coverage, image scale, and field of view before ordering another adapter.

No sign-inLocal calculationsEditable assumptionsSource-linked methodology

Illustrative starting inputs. Replace them with your own measurements and evidence.

01 / Set your assumptions

Make it your own.

Every input stays visible and editable.

Telescope focal length mm

Reducer / Barlow factor ×

Pixel size µm

Sensor width mm

Sensor height mm

Published image circle mm

Required sensor distance mm

Spacing tolerance mm

Apply filter-path correctionDo not apply again if already included in the manufacturer specification.

Filter glass thickness mm

Glass refractive index

3 records

Optical train components

Illustrative lengths only. Include the camera flange-to-sensor distance. Thread syntax: M42x0.75 male or M42x0.75 female. Unknown labels stay unresolved.

Import CSV

Edit records Review every assumption

Component	Optical length mm	Input thread	Output thread	Specification
Component, row 1	Optical length, row 1 mm	Input thread, row 1	Output thread, row 1	Specification, row 1
Component, row 2	Optical length, row 2 mm	Input thread, row 2	Output thread, row 2	Specification, row 2
Component, row 3	Optical length, row 3 mm	Input thread, row 3	Output thread, row 3	Specification, row 3

Your working plan

One train. Every connection visible.

Computed locally

Your optical train needs review

1 spacing, connection, coverage, or missing-component checks need attention.

Spacing to add / remove+0.67 mmTarget 55.67 mm; entered 55 mm

Field of view2.1° × 1.41°Rectangular sensor at the effective focal length

Image scale1.21″/pxAngular sampling, not a seeing forecast

Sensor diagonal28.26 mmInside the entered image circle

Optical order: telescope side → sensor

Ordered train

1Spacer16.5 mm · M48x0.75 female → M42x0.75 male
2Filter drawer21 mm · M42x0.75 female → M42x0.75 male
3Camera flange to sensor17.5 mm · M42x0.75 female → Sensor

Before you act

Use matching diameter, pitch, gender, and flange-reference conventions. Nominal thread labels do not verify engagement depth or clearance.
Verify the reducer-specific working distance and filter correction with the manufacturer. A larger image circle does not guarantee good corner stars.

Rig bill of materials


Spacer	16.5	M48x0.75 female	M42x0.75 male	User-entered; verify
Filter drawer	21	M42x0.75 female	M42x0.75 male	User-entered; verify
Camera flange to sensor	17.5	M42x0.75 female	Sensor	User-entered; verify

Calculation notes & limitations

Effective focal length = telescope focal length × reducer or Barlow factor. Pixel scale = 206.265 × pixel size in micrometers ÷ focal length in millimeters.

Optional plane-parallel glass correction adds thickness × (1 − 1/refractive index) to the physical backfocus target. Apply only when the manufacturer reference excludes this correction.

Field angle = 2 × arctan(sensor dimension ÷ (2 × focal length)). Mechanical lengths are summed once; include the camera sensor flange distance as a train component.

Plan name

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02 / Look under the hood

The method is part of the tool.

Enter the exact focal length, reducer factor, sensor dimensions, and published sensor working distance for your equipment.

List the optical train in physical order, including every spacer and the camera sensor flange distance. Match thread pitch and gender, not just nominal diameter.

Compare summed mechanical distance with the target, apply any documented filter correction once, and report field of view and angular sampling separately.

Read the full methodology

03 / Know the boundaries

Evidence before certainty.

Spacing and nominal thread agreement do not guarantee physical clearance, engagement depth, sensor illumination, or optical quality. Verify each manufacturer reference.

These are reference sources, not evidence that example records have been verified. Imported records retain the source links you provide.

ZWO product manuals and documentation

Field notes / Optical Train