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Any point in changing f numbers???? (1 Viewer)

kevindurose

kevindurose

Well-known member
From what I understand there is no point in choosing higher f numbers while digiscoping even if good light allows this. There is no extra depth of field, as this is dictated by the focal length of the scope. Can any anyone confirm if this is true?

I have always undertood this to be the case so I have always used the lowest f number to get the fastest shutter speed. Just that there are people advising people on bird forum to choose higher f numbers presumably for increased depth of field.
 
Malc,

Great detective work and well tested. I never bothered to test this myself, largely because I was told this by a professional photographer who began as a digiscoper.

That has added a new complication to my digiscoping.

Kev

Kev
 
Feathered one said:
It is not true.
There is more depth of field with higher f numbers.
Click to expand...

In most cases, yes - BUT if you eg. have a small scope & high powered eyepieces (= small exit pupil), the scope may become the aperture limiting component and in this case you may have to stop down the camera a lot before you see any effect.

Having said that, I always recommend the use of large scopes, low powers AND if possible stopping down the camera - unfortunately we just often have to use the largest aperture (and a shallow DOF).

Ilkka
 
Ilkka

Thanks for information on depth of field with a small scope.

I had looked on the forum to see what scope Kev uses, a kowa 823 +32wa, and thought it would be about the equivalent to the Nikon ED82 and 30x DS I use.

Anyway a good point explained thanks Illka

Malc
 
iporali said:
In most cases, yes - BUT if you eg. have a small scope & high powered eyepieces (= small exit pupil), the scope may become the aperture limiting component and in this case you may have to stop down the camera a lot before you see any effect.

Having said that, I always recommend the use of large scopes, low powers AND if possible stopping down the camera - unfortunately we just often have to use the largest aperture (and a shallow DOF).

Ilkka
Click to expand...

Ilkka is correct here, I have had a scope setup where if you stop down below about f6 vignetting started to appear. So advise given to me along the way is, make your own tests with the gear you have, don't rely so much on what you read, use them as a starting point by all means. Ernie
 
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