Sunspots 24 Aug 2011

[PhilB]

This afternoons sunspot offering:



Details are:
Telescope is Stellavue AT1010 f6.1, fitted with Baader Solar Safety film and stopped down to 60mm
Main image is with an InageSource DFK fitted with X2 Barlow. Gain set to 300 at 1/92 sec
Inserted image is the same ImageSource DFK this time fitted with 0.5 focal reducer. Gain set to 300 at 1/2500 sec
Main image is 100 best frames stacked in Registax 6 and final processing in CS2
Inserted image is 65 best frames stacked in Registax 6 and final processed in CS2
Both images have the yellow channel bosted to increase contrast

[The Thing]

That's really nice Phil.

[Fay]

You are really good at this Phil

[mickw]

Nice work Phil

But I have a question  

At 1/92 sec with x2 barlow, 1/184 sec should give the same result without a barlow.
Sooooooo, with a 0.5 FR would 1/368 be more appropriate ?

I have been wrong before (once or twice  )
Just curious

[PhilB]

Thanks guys.

But I have a question:

At 1/92 sec with x2 barlow, 1/184 sec should give the same result without a barlow.
Sooooooo, with a 0.5 FR would 1/368 be more appropriate ?

That's a very good question, Mick.. Not sure I have an equally good answer 

Here goes:

With the 2X Barlow the effective aperture is f12.2. This drops to f3.05 with the focal reducer. So, on the face of it your figures are reasonable. However, the inserted full disc image is cropped much more severely than the Barlowed shot of the sunspots. To put it crudely, there was a large amount of sky in the full disc shot, considerably more than in the sunspot shot which is hardly cropped at all. This resulted in the sunspot image being very much brighter than the full disc image. Hence the seeming mismatch in the exposures.