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Correction factor for Barlow / Reducer
Seeing areas FWHM
Focal length guidescope

Binning / Binning Guidecam
Pixel size Guidecam with / without binning

Focal length mm
Apparent field of view in degrees
Field stop in mm

Formula for vignetting


Telescope focal length
Aperture ratio
Aperture ratio without corrector

Camera number of pixels x / y
Pixel size x / y

True field of view in Arcmin
Exit pupil

Current filter distance to the chip
Filter diameter or bottleneck

Focal length
Aperture ratio with corrector

Nr. of Pixel
Pixel size after binning

min. sensible enlargement
max. sensible enlargement

Vignetting starts at mm chip diagonal
Vignetting in the corners in percent

Good focal length - ÖV - Barlow
for planetary shots

Image Scale range in the above seeing
Sampling rating for current setupp

min. sens. wide-angle
max. sens. tele

Maximum distance of bottleneck to
avoid vignetting on the chip

Telescope aperture in inches
Telescope resolution in arcsec

Chip width mm
Chip height mm


FoV width in Arcmin
FoV height in arcmin

FoV diagonal in arcmin
ImageScale setup - Seeing / ImageScale (Px)

Visual limit size mag

Mega-Pixel (Binning)
Chip size in mm

Min. guiding focal length for telescope
opt. guide focal length for guidescope

Subpixel correction value


Implications of under-/over-sampling:

undersampling reduces the influence of guiding errors and improves signal to noise at the expense of finest detail

oversampling will require a good mount and careful guiding. OK for high magnification solar, lunar or planetary imaging. Might cause signal to noise issues with wide-field imaging

It is important to find a good balance between over- and undersampling. Namely so, that the camera still works as sensitive as possible, but the images are good shaded. The following figure illustrates graphically this relationship.


On the left the undersampling shows almost only square stars. On the right oversampling shows many shades of gray, but the light of the stars is smeared over many pixels.

Center of the picture is an example of good sampling. For deep sky imaging, the rule of thumb for the image scale is to achieve a value of about 1.5 arcsecs to 2 arcsecs per pixel. In this rule of thumb, the normal local seeing should be included. The seeing value is simply divided by 2.67 (low) or 2 (high) if you have local seeing on average of 4 arcseconds.

Blue rectangle = selected chip

Yellow line = image field diagonal

Red outline = Begin of vignetting on the chip through filter / bottleneck

Green outline = field of view for selected eyepiece on the telescope compared to the image field of the chip

Apply and save manually changed values in the white input fields.

Changes in the drop-down lists are automatically accepted and saved.

All values are stored as a cookie and are retained after the session ends.

Use this key to jump back to the last accessed page. Same effect like the Windows back button.

1 = FWHM 0-1 Wish dream
2 = FWHM 1-2 Perfekt
3 = FWHM 2-3 Very good
4 = FWHM 3-4 Good
5 = FWHM 4-5 Middle
6 = FWHM 5-6 Middle
7 = FWHM 6-7 Moderate
8 = FWHM 7-8 Bad
9 = FWHM 8-9 Very bad
10 = FWHM 9-10 Unusable

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