incorrect APERTURE value in fits header

Stacking program, astrometric (plate) solver, fits file viewer

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incorrect APERTURE value in fits header

Forum: General discussions ASTAP

Creator: Axel Thomas

Created: 2026-06-14

Updated: 2026-06-15

Axel Thomas - 2026-06-14

Hi Han,
I noticed an APERTURE value of 2 in the fits header after calibrating NEF images with an EXIF FNumber of 2.8. Is this a known problem?

cs Axel

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han.k - 2026-06-15

The header aperture values are only for the record. They are not used unless you move in the viewer the mouse pointer around to measure individual stars.

Note that aperture value in the header is in pixels while in the photometry tab it is in HFD radius. So the difference is the arcsec/pixel factor.

So the values are not used in the photometry tab. When you use the photometry tab all stars are measured and calibrated against the database "on the spot" to provide the instrumental magnitudes in the list view. With comp star(s) as reference these values are shifted (a little) again to get the report values.

cs, Han

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Axel Thomas - 2026-06-15

Hi Han,
sorry, I explained the problem not precisely. I am talking about the lens aperture value: I have been using a 135 mm / f2.8 lens which is set correctly in the EXIF of the image but the fits image header in ASTAP records only 2.0 (see attachments). I can change the value manually with 'change header keyword' to 2.8 so it is not simply a problem of not showing the decimal value because it is zero.

cs Axel

astap1.PNG

astap2.PNG

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han.k - 2026-06-15

Sorry, I missed your remarks about the exif value. I was too much focused on other things.

Can you share one NEF file, so I can investigate why the value is rounded? It is not important but better to be fixed if possible.

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han.k - 2026-06-15

I see the same with other NEF files here. No need for you image. I will have a look.

Last edit: han.k 2026-06-15

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han.k - 2026-06-15

I found a fix. I will release next time an new version of the raw conversion utility.

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Axel Thomas - 2026-06-15

Thank you!

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han.k - 2026-06-15

You could download a new convertor program here:

Window:
https://github.com/han-k59/LibRaw-with-16-bit-FITS-support/blob/master/bin/unprocessed_raw%20win64.zip

Linux
https://github.com/han-k59/LibRaw-with-16-bit-FITS-support/blob/master/bin/unprocessed_raw%20linux%20amd64.tar.gz

Just unzip the unprocessed_raw executable and put it in the astap directory with overwrite.

cs, Han

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