conrad2k

I just got a 27" 5K 4.0GHz iMac - and it absolutely flies.  Worth considering now while you can still upgrade the memory yourself, as it seems Apple are removing the possibility for users to upgrade their own memory in newer models.  I put 24GB in it for just £64.  The 21" 4K has pre-configured memory, so you'll end up paying Apple a lot of money for 16GB of RAM.  It also can't be spec'd up as high as the 27".
 
Also - if you are looking for a new machine and a 27" 5K display - this is a no brainer.  There is no display better than this for the money.

When cropping a panorama, there's the option to inpaint 'Missing' areas. Please could you build this into the straighten tool too?

Conrad2k, your question caused me to experiment a while. A very general answer is: there is no optimum. An optimum assumes that there is a number of photos from which on the result gets worse. This is not the case. Every additional photo improves the noise reduction. But the contribution per photo gets smaller and smaller, and the calculation time gets higher and higher.
 
While adding pictures to the stack, my observations are (observed with 100%zoom):
- the first 4 pictures significantly contribute to the noise reduction improvement, wow!
- the 5.-8. picture can be considered as polishment, they raise the noise reduction of the picture to 90% of the overall  result. 
- the 9. and 10. picture only slightly contribute to improvements, i guess it is now about 98% of what you can reach.
- the 11. and 12. picture brings quite invisible improvements, its more the light than the noise that changes slightly
- the 13. and 14. picture are the last pictures where I remark any visible changes at all at 100% zoom
 
For more pictures, I have to zoom in:
- the 15.-18. picture bring, visible with 170% zoom, still slight improvements on pixel level 
 
Finally it is a trade of between quality, computational power, hard disk space and time. If you want maximum quality and you have a zoom of 150%, you see still noticeable noise reduction improvements between 14  and 18 pictures. 
 
Another perspective: 
- at the zoom level "overall picture" (cmd 0): the 11.-18. pictures do not bring remarkable improvements
- at the zoom level "100%": the 14.-18. pictures do not bring remarkable improvements
 
As you see,
- 10 pictures provide super results for the overall picture zoom,
- 14 pictures provides super results even for 100% zoom, and
- 18 pictures are for purists. 
 
Here the examples for 1, 4, 10, 14 and 18 pictures. Click on them to see them full size (each ca. 220kb)
    
 
In any case, thanks to the Affinity Photo development team for this powerful feature. The noise reduction is impressive.
 
Best regards
BlauerClaus

How conrad2k
 
Most people use 10 images when stacking images for Noise Reduction. The image attached was achieved by stacking 10 images :)
 
 

Hi talkgtr,
Welcome to Affinity Forums :)
Affinity extensions were revamped in the latest update (v1.4) last week. It now includes 6 new extensions for Apple Photos. Check this video tutorial for more info.