Newbie Question - 150 Apo-Sironar-S on 4x5 cameras with Digital Backs

[AB14]

Dear All,

Have anyone use a 150 Apo-Sironar-S on 4x5 cameras with Digital Backs? Should I get the Sironar Digital Instead and which focal length would you recommend for universal use and which one for portraits?

I do not understand the image circle, angles, etc. I generally shoot 43mm, 80mm and 120 mm in medium format and 28mm to 560mm (w/2x converters) in 135 formats. My fav is 50mm in 135 format.

TIA

[Leigh]

The APO-Sironar-S is a beautiful lens. I use it on 4x5 frequently, shooting film.

I don't have a digital back for 4x5, so I've never used the digital version of that lens.

Image circle (IC) is a critical parameter when selecting a lens for use on any format.
The "cone of illumination" is exactly that, a cone with its base on the film plane and the apex in the lens.

IC is the diameter of the illuminated circle on the film plane when the lens is focused at infinity.
As you move the lens further from the film, to focus on closer subjects, the IC diameter increases.

Note that the IC diameter is usually given on the datasheet* for the lens stopped down to f/16 or so.
This IC diameter is larger than can be achieved when the lens is wide open.

As an example, the diagonal of 4x5 film is about 160mm.
If you get a lens with an IC listed as 165mm @ f/16, it will probably not cover 4x5 when wide open.

So the first step in determining which lens will work for your situation is to define the size of your sensor.

- Leigh

*Note: Some datasheets also include the IC diameter when wide open.

[Bob Salomon]

What size digital back? The 150 is a normal lens on 45 film. If your digital back has an image capture area smaller then this then the normal lens will be a different focal length for that back. With digital backs the common focal lengths range from 23mm to 180mm.

[AB14]

Thank you, Leigh

[AB14]

Hi Bob,

I am looking at the Leaf Aptus-II 40 Digital Back (Hasselblad V Series).

Thank you.

[Oren Grad]

I am looking at the Leaf Aptus-II 40 Digital Back (Hasselblad V Series).

The sensor in that back is 33x44mm. A normal lens for that sensor would be around 55mm. A 150 would be very long, roughly comparable to a 210 on 6x6cm or a 120 on 35mm.

[Otto Seaman]

The sensor isn't much larger than a 24x36mm full-frame or 35mm camera so figure on your 35mm focal lengths plus maybe a 1/3 more, just to ballpark.

The problem with using a lens intended for 4x5 is that all the extra image circle goes to waste and can even create a flaring, lower contrast situation. And while the Sironar-S is amongst the sharpest 4x5 lenses, a lens optimized for digital with a smaller image circle will still be noticeably sharper.

[AB14]

Thanks Oren and Otto.