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Lens hood. Tulip. And flats.

astrophotography
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#1 Geordie Stew

Geordie Stew

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Posted 25 January 2021 - 02:53 PM

Evening all (UK)

I'm using a Sony 20mm f/1.8 lens. It has a tulip shaped lens hood (not fully round).

Should I be shooting with the hood on or not?
What's the best way to take flats with such an odd shaped hood? I've seen talk of building a rectangular shaped box to sit over the hood.

Thanks in advance


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#2 Jim Waters

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Posted 25 January 2021 - 04:02 PM

I point the lens at a computer monitor screen that's all white.  Make sure the two are parallel to each other.



#3 StarBurger

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Posted 25 January 2021 - 04:33 PM

Lens hood use is only a method of keeping direct sunlight form impacting the front lens/filter and causing flares in terrestrial daylight imaging.

At night the moon or lighting from directly visible sources may cause similar effects.

Obviously it is desirable to eliminate this. The impact will depend on the dimensions, shape and position of the hood especially at wide angle 20 mm. 

A test would be to image a blue sky or white screen with the hood on and stretch the result to see if any vignetting happens or at least see any difference between hood or no hood.

If you are lucky enough to work under a dark site without any light directly impacting the lens then forget about the hood.

Taking flats with such a setup could be problematic, as at such a wide angle sky gradients will be more severe, something that flats will not correct.


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