NIRISS Focus Template Parameters

JWST's NIRISS Focus Engineering template, available in the Astronomer’s Proposal Tool (APT), is used for calibration observations for the NIRISS instrument. 


Purple text indicates the parameter is Limited Access.

Boldface italics type indicates the name of an APT parameter or a value for a parameter.

(warning)Red text indicates restrictions on a parameter.

(red star) Black text indicates an important note.

Brown text indicates notes for the developers.

Green text indicates the name of the parameter used by Commanding.

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

These parameters are required to obtain Focus observations. Note that this type of observation cannot be obtained as a parallel to normal science observations.

The focusing mechanism will be scanned through the specified number of relative positions centered on the current best focus, and then returned to the starting position.  At each point in the focus sweep, an image will be obtained for analysis. If only one position is specified, the focus mechanism is moved to the specified position (i.e., the best focus position is reset).

The NIRISS Focus template consists of the following parameters:

FieldDetailsValues Notes
General Information   
 Observation Numberassign observation number


Observation Label provide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Special Requirementsspecify special requirementschoose from listif needed
Template Specific Information   

Target Name

select target name

choose from list

 Filter select filter namechoose from list 
Readout Patternselect readout patternNIS, NISRAPID
Number of Groups/Integrationspecify number of groups per integrationnumber 
Number of Integrations/Exposurespecify number of integrations per exposurenumber
Relative Positionspecify array of positionsarray of 1-20 positions 

General Information 

The following parameters are generic to all templates, and are not discussed in this article: Observation Number, Observation Label, Observations Comments, Target Name  , and Special Requirements.

Target Name

Select the TARGET NAME [TBD] from the list of targets previously entered; see list of targets


FILTER [FILTER] = F090W, F115W, F140M, F150W, F158M, F200W, F277W, F356W, F380M, F430M, F444W, F480M

This parameter specifies the filter to be used for the exposure.

Exposure Specification


Readout Pattern


This field specifies the readout pattern to be used to obtain the science data. NIS is used for faint targets, while NISRAPID is used for bright targets or scenes with high backgrounds.

Number of Groups/Integration

NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration. (warning)For readout pattern NIS, the range is 1-200, while for NISRAPID the range is 1-30.

Number of Integrations/Exposure

NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated. (warning)The range is 1-10.

Relative Position

The RELATIVE POSITION [DELTARRAY] parameter specifies an array of 1 to 20 positions that the focus is to be moved to; note that each position must be unique (i.e., a given value can only appear once in the list). The positions are given in millimeters (range -9.0 to +9.0) in the OTE frame, and are offsets from the current position. The exact order in which the positions will be executed will be determined by the onboard scripts. There are 3 unique cases:

  1. to perform a focus sweep (returning to the original focus), enter from 2 to 20 positions
  2. to reset the focus, specify only 1 position
  3. to use the default scan (10 steps of -0.4mm from -2.0 to +2.0), select the checkbox

Note for developers: when the checkbox for default scan is selected, the Relative Position input area should be inactive.

Change log

The initial version of this chapter was provided by Lily Liu. 

Version 3 (April 18, 2019)

  1. Editorial change (moved change log to main article)

Version 2 (September 18, 2017)

  1. PR 87895 - updated Exposure field labels to Groups/Integration and Integrations/Exposure

Version 1 (October 26, 2016)

This is the converted Word file from Chapter 49.