KAF-8300 Horizontal Blooming?

[CraigT82]

I've been getting some funny star shapes over the last couple of nights when running my 383L binned 2x2 which I initially thought was either terrible guiding or pinched optics, but having a look at them closely I think it might be horizontal blooming as only the brightest stars are affected, which from googling is apparently something that can affect the KAF8300.

Can anyone confirm if this is the case? Maybe you've seen it before?

If it is horizontal blooming then I think will just have to place an order for a 130pds and stick to unbinned imaging.

Image attached is a single 1200s sub (linear & uncalibrated). Star in the centre is mag 6.8. Star at upper left is mag 5.8.

Cheers

 

Edited March 8, 2021 by CraigT82

[tooth_dr]

18 minutes ago, CraigT82 said:

I've been getting some funny star shapes over the last couple of nights when running my 383L binned 2x2 which I initially thought was either terrible guiding or pinched optics, but having a look at them closely I think it might be horizontal blooming as only the brightest stars are affected, which from googling is apparently something that can affect the KAF8300.

Can anyone confirm if this is the case? Maybe you've seen it before?

If it is horizontal blooming then I think will just have to place an order for a 130pds and stick to unbinned imaging.

Image attached is a single 1200s sub (linear & uncalibrated). Star in the centre is mag 6.8. Star at upper left is mag 5.8.

Cheers

 

Hi Craig

I have imaged with this camera successfully binned 2x2 over 1200s, but I think the general consensus is that it prefers 1x1.   I would have imaged very faint stuff with no bright stars in the field though, and through narrowband filters.

[CraigT82]

Thanks Adam, I hope it is blooming actually as its the simplest to solve - buy a new scope (lol!) A 130pds was always my logical next step as the 200/1200 dob tube was just to get me going.  I will just need to get one sooner than planned and stick to fields with faint stars in the meantime. 

Certainly not a fault with the sensor, more of a quirk! 

[skybadger]

Full well is 26 K e and the anti blooming gate should catch most of that unless really bright. What is the guide axis ? Ide be  looking at PEC or tracking first. 

 

[CraigT82]

OK have been looking around on t'internet and have seen a lot of images showing the horizontal blooming of 8300 sensors and am now convinced that is the issue (with the bright stars at least). The dimmer stars are still not round but that is a different kind of 'not round', and is down to poor guiding the other night, so not overly concerned about that right now. Getting a 130pds should solve both issues 😂.

Apparently something to do with the shift register... lot's of info over on CN. 

 

[skybadger]

I'll take a look there. Ta. 

[CraigT82]

Here is a couple of threads with images of blooming....

https://www.cloudynights.com/topic/685884-blooming-with-kaf8300-sensor/

https://www.cloudynights.com/topic/486989-unusual-blooming/

The effect is much more noticeable un unstretched images and sort of gets lost in the glare during stretching, but is definitely still there. 

My plan going forward, is to shoot much shorter RGB frames and use the round, nicer coloured stars from those to replace the wonky stars in the long exposure narrowband stacks.  Not sure if this will work or not, not even sure how to do it but there's bound to be a tutorial somewhere. 

Edited March 10, 2021 by CraigT82