how a doubler affects my aperature

[george_spiteri]

I have a Minolta XG 9 and just got a doubler for it. I am using it

with my 50mm lense and the question I have is when I use a flash,

how do I compensate for the doubler.

[h._shafi]

Assuming I understood the question correctly, if you bought a 2x teleconverter then your effective aperture is 2x what the lens setting says. Regarding flash compensation, you've effectively cut its range in half for a given lens aperture setting.

 

I hope this helps.

 

-Haz

[anupam]

2 stops.

[peterblaise]

.

 

FYI For Your Information, here's a table of teleconverter "X" values and the resulting f/stop reduction, in case someone else wants to know what other teleconverter values equal, or what combinations equal, or how to calculate the results:

 

Column #1 = TC Teleconverter focal length and f/stop multiplication factor:

 

Column #2 = f/stop reduction factor: log(TC,base2^.5)

 

1.00 x 0.00

 

1.04 x 0.10

 

1.07 x 0.20

 

1.11 x 0.30

 

1.15 x 0.40

 

1.19 x 0.50

 

1.23 x 0.60

 

1.27 x 0.70

 

1.32 x 0.80

 

1.37 x 0.90

 

1.41 x 1.00

 

1.46 x 1.10

 

1.52 x 1.20

 

1.57 x 1.30

 

1.62 x 1.40

 

1.68 x 1.50

 

1.74 x 1.60

 

1.80 x 1.70

 

1.87 x 1.80

 

1.93 x 1.90

 

2.00 x 2.00

 

2.07 x 2.10

 

2.14 x 2.20

 

2.22 x 2.30

 

2.30 x 2.40

 

2.38 x 2.50

 

2.46 x 2.60

 

2.55 x 2.70

 

2.64 x 2.80

 

2.73 x 2.90

 

2.83 x 3.00

 

2.93 x 3.10

 

3.03 x 3.20

 

3.14 x 3.30

 

3.25 x 3.40

 

3.36 x 3.50

 

3.48 x 3.60

 

3.61 x 3.70

 

3.73 x 3.80

 

3.86 x 3.90

 

4.00 x 4.00

 

4.14 x 4.10

 

4.29 x 4.20

 

4.44 x 4.30

 

4.59 x 4.40

 

4.76 x 4.50

 

4.92 x 4.60

 

5.10 x 4.70

 

5.28 x 4.80

 

5.46 x 4.90

 

5.66 x 5.00

 

5.86 x 5.10

 

6.06 x 5.20

 

6.28 x 5.30

 

6.50 x 5.40

 

6.73 x 5.50

 

6.96 x 5.60

 

7.21 x 5.70

 

7.46 x 5.80

 

7.73 x 5.90

 

8.00 x 6.00

 

8.28 x 6.10

 

8.57 x 6.20

 

8.88 x 6.30

 

9.19 x 6.40

 

9.51 x 6.50

 

9.85 x 6.60

 

10.20 x 6.70

 

10.56 x 6.80

 

10.93 x 6.90

 

11.31 x 7.00

 

11.71 x 7.10

 

12.13 x 7.20

 

12.55 x 7.30

 

13.00 x 7.40

 

13.45 x 7.50

 

13.93 x 7.60

 

14.42 x 7.70

 

14.93 x 7.80

 

15.45 x 7.90

 

16.00 x 8.00

 

You can build your own spreadsheet from there.

 

16x combination of teleconverters, eh? Yeah, I tried that. Good for reducing the pain when shooting directly into the sun - NOT! =8^o Actaully, with a camera pointing straight ahead, the stack of teleconverters equaling 16x sags into an arc and the lens on the front of the setup is pointing pretty much straight down! ;-)

 

Click!

 

Love and hugs,

 

Pete Blaise peterblaise@yahoo.com http://www.peterblaisephotography.com/

[hakon_soreide]

If it sags down, do you get a tilt effect from it as well?

[ilkka]

It may help to understand the basic principles at work.

 

You have a 50 mm lens, let us say you set an aperture of F/4 on it. The actual aperture within the lens is 50mm / 4 = 12.5mm.

 

When you attach the doubler, it multiplies the focal length by 2, so the combination now becomes a 100 mm lens. But the actual aperture within the lens does not change (the doubler does not increase the size of the front element and the aperture blades inside). It is still 12.5mm. So the new F number is 100mm /12.5mm = 8. So two stops smaller than before.