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Converters Apertures and DOF

vic cross

Link Posted 22/01/2008 - 20:33
Iv'e tried to get an answer to this question for years. When a smaller aperture/higher F No. is used then the DOF increases. When a converter is used, for instance a (2X) then you lose two stops. Hence F5.6 becomes F11. Does this mean that the DOF would increase as it would without the converter if F11 was used or does it remain the same as it would without the converter at 5.6? CHEERS Vic
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.


Link Posted 22/01/2008 - 21:31
There's one way to find out...

I think f11 will be f11 in every respect, but I hadn't really thought about that one before.

However, seriously, the answer can be found simply enough by trying it out and seeing what happens.

Any volunteers?

Best regards, John


Link Posted 22/01/2008 - 22:54
I could be wrong, but normally: The longer the lens, the smaller the DOF given the same aperture. So, for example take a 2.8/300 mm at 5.6.
After using a 2x converter it becomes a 5.6/600 mm. I would think DOF decreases. But again......... I am not sure
Best regards,


Curious about my photography?? Just Follow the Light.

MX veteran

Link Posted 23/01/2008 - 00:51
With a 2x f8 becomes f16 and the depth of field is halved approx, the amount varies with the focal length.
K100D Super, 18-55, 50-200, Sigma 10-20, Sigma 70mm macro and lots of old lenses


Link Posted 23/01/2008 - 13:15
Try out the figures:
(For gallery, tips and links)

vic cross

Link Posted 23/01/2008 - 19:36
To John. Your right I should just experiment and will try it on a 50mm lens when my wife lets me off the extended major redecoration project.(I must do as I'm told)

To Martin. You are right the longer the lens the less the DOF however with a 2X converter a 300mm F5.6 would not be a 600mm F5.6 but it a 600mm F11.

To MX Veteran.With any length of lens going from F8 to F16 increases the DOF however increasing the focal length decreases the DOF hence my question in the first place which has the most effect.

To MattMatic. I've been to the DOFmaster site and even have it in my favorites. It states that it takes the field of view crop into the calculations for the camera used and also adjusts for any focal length multiplier (2X converter) but I can't figure out how it does this as there is no way of putting in this information.

CHEERS to all Vic
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.

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