Question about Sinar F2 DOF guage

[enivre]

Hi guys,

I was wondering why is there a 4x5 and a 6x9 range on the DOF gauge of my Sinar F2? Does this mean if I'm shooting my 6x7 I need to follow the 6x9 instead of the 4x5 readout from the guage?

Thanks!
Ervine

[blurblock]

Originally Posted by enivre Hi guys, I was wondering why is there a 4x5 and a 6x9 range on the DOF gauge of my Sinar F2? Does this mean if I'm shooting my 6x7 I need to follow the 6x9 instead of the 4x5 readout from the guage? Thanks! Ervine

I guess so ..... the DOF of 6x7 will be nearer to 6x9 then 4 x 5.....

[singscott]

Call me ma I will tell you I have the same camera. The bigger your film or sensor the less DOF you have in the same aperture and the same focus distance. It is call COC or Circle of Confusion. Really no joke.

[enivre]

Originally Posted by blurblock I guess so ..... the DOF of 6x7 will be nearer to 6x9 then 4 x 5.....

by nearer u mean shallower right? coz the guage for say f32 for 4x5, at 6x9 will be f40+ or something like that... which means 6x9 the DOF is shallower right?

Scott: Haha forgot your number liao leh... yeah I heard about the circle of confusion stuff

[blurblock]

Originally Posted by enivre by nearer u mean shallower right? coz the guage for say f32 for 4x5, at 6x9 will be f40+ or something like that... which means 6x9 the DOF is shallower right? Scott: Haha forgot your number liao leh... yeah I heard about the circle of confusion stuff

Actually, 4 x 5 = 4 inch by 5 inch, about 10 cm x 12.5cm sheet film.

6 x 9 = 6cm x 9 cm (can be sheet or roll film)

For CoC, like singscott said, 4 x 5 in will have bigger CoC, but depth of field wise, the larger camera will have greater depth of field if they are call calculated based on the same focal length.

For a similar 210mm lens with same f/22 and focusing at 7 meters (for example),

A 4 x 5 will have a DOF of approx 5.2m to 10.7m as it's CoC is 0.10mm (Total DOF = Approx 5.5m)

A 6 x 9 will have a DOF of approx 5.6m to 9.3m as the CoC is 0.07mm (Total DOF = Approx 3.7m)

A 6 x 7 will have a DOF of approx 5.8 to 8.9m as the CoC is 0.06m ( Total DOF = Approx 3.1m)

(Based of Approx Calculation error rate +-10cm)

For 6 x 7 film to achieve a DOF similar to a 4 x 5, you will require the Aperture to be at about f/36 (If there is even a f/36 :P, For 6 x 9 film to achieve a DOF similar to a 4 x 5 you will require the Aperture to be at about f/32)

(For your analogy of f/32 at 4 x 5, you will require approx f/46 at 6 x 9 to achieve similar DOF. At 6 x 7 you will require approx f/53 to achieve similar DOF)

Thus it is nearer to 6 x 9 then 4 x 5.

(

* P.S. I think, if I am not wrong, Singscott's idea of "The bigger your film or sensor the less DOF you have in the same aperture and the same focus distance." is not wrong, he is relating it to the same angle of view as well.

For example an AOV for 210mm at 6 x 7 is about 350mm at 4 x 5.

At 350mm, a 4 x 5 view the same aperture and focusing distance will give you about a total of 1.8m DOF in relative to 3.1m at 6 x 7
)

[enivre]

thanks for the maths bro!

Okay I got it!! Hope to run a 2nd roll of film to test things out, ruined my 1st roll already...

[kex]

i think it is the other way round..

the bigger the film/sensor area,the less DOF,thats y some digicam only have aperture up to F8 becoz of the small sensor and some aperture value can go up to 128 in large format.

[blurblock]

Originally Posted by kex i think it is the other way round.. the bigger the film/sensor area,the less DOF,thats y some digicam only have aperture up to F8 becoz of the small sensor and some aperture value can go up to 128 in large format.

Actually, that is more like because if the size of the glass . A Small digicam can goes up to only f/8 is because a 50mm equalivent (50mm Angle of View in 35mm) in a digicam may only be in actual fact a 15mm lens. At f/8, a 50mm lens in 35mm camera will need a aperture size of 6.25mm. The same f/8 on the digicam at a 15mm lens size, the aperture size would be 1.8mm. Imagine you try to get it to f/32 like a Marco Lens. It would be 1.56mm (Dia) Aperture on a 35mm lens while a Digicam with similar fstop would required a 0.47mm aperture.

Hence that is why some digicam can only goes up to f8.

[enivre]

Ok now I'm confused again...

I also thought that the larger the format the shallower the DOF... the thing is what happens when you have a larger format that's shooting on a smaller format film?

In this case a 4x5 shooting 6x7 instead?

[kex]

just shoot a ruler with a 200mm/210mm lens at F11 with a 35mm and 4x5 camera and compare the DOF.

[enivre]

Originally Posted by kex just shoot a ruler with a 200mm/210mm lens at F11 with a 35mm and 4x5 camera and compare the DOF.

but that's not the same as shooting 35mm on a LF camera right?

[enivre]

here are a few photos I did with the 4x5 but shot on 120 film at 6x7...





I based the aperture on the 6x9 DOF gauge on the rear standard of my Sinar F2, not sure if I got it right or not though, coz there were times when the gauge showed I was supposed to shoot at f64...

[blurblock]

Originally Posted by enivre Ok now I'm confused again... I also thought that the larger the format the shallower the DOF... the thing is what happens when you have a larger format that's shooting on a smaller format film? In this case a 4x5 shooting 6x7 instead?

In the same Angle of View, a 4 x 5 will have shallower DOF, due to extended focal length. If you are comparing same focal length instead of same Angle of view, then the large format camera will have better depth of field, due to larger CoC.

[blurblock]

Originally Posted by enivre but that's not the same as shooting 35mm on a LF camera right?

The Theory is the same. At 210mm on 4 x 5 Large Format camera, it is a mild telephoto lens, akin to 60mm on 35mm camera (Meaning the Angle of view is similar to a 60mm on 35mm camera). What you can do is to get a 210mm Lens on a LF camera and 35mm Camera, then focus at 7 meters away at f/16 to shoot.


Have three objects. The one that you want to focus at 7 meters, then put one object at 8 meter and another one at 6 meter. At 210mm f/16, on Large format, you should see all three relatively sharp. The 35mm, however, only the focused object will be sharp.

[enivre]

Okie I think I get it... I understand the angle of view VS focal length bit when comparing 35mm to 4x5 or 6x7 when shot with different cameras, but what happens when you take a 4x5 but shoot in 6x7?

The angle of view becomes smaller due to the cropping from 4x5 to 6x7. Focal length remains the same, so DOF changes because the angle of view changes??

[blurblock]

Originally Posted by enivre Okie I think I get it... I understand the angle of view VS focal length bit when comparing 35mm to 4x5 or 6x7 when shot with different cameras, but what happens when you take a 4x5 but shoot in 6x7? The angle of view becomes smaller due to the cropping from 4x5 to 6x7. Focal length remains the same, so DOF changes because the angle of view changes??

Yes.

It is the same as using the same lens on a "Full Frame" 35mm camera and a APS sized digital camera, the DOF will be slight different.

[enivre]

Originally Posted by blurblock Yes. It is the same as using the same lens on a "Full Frame" 35mm camera and a APS sized digital camera, the DOF will be slight different.

I see i see... okay I think i more or less got it, but this means that shooting 120mm film on LF cameras will demand large aperture values in order to get the required DOF right?

[singscott]

In fact all are right. Blurblock is very detail and he right. COC circle of confusion. The circle here mean image circle. So it the DOF that releted to the lens image circle. If this lens is design for a 4X5 camera compare it a medium format camera lens of the same focal length the 4X5 will have less DOF. But use the same lens on different format the DOF will change again as you are not using the entire image circle. So the DOF in case will be less on 4x5 film but will be slight more DOF on 6x9 film use on the same 4X5 camera and same lens. Then compare DOF to a medium format camera which will have even more because the lens on the medium format have smaller image circle.