165mm Ilex Caltar 1:6.3 Arrived, Aperture Question

[David]

My 165mm Ilex Caltar in the Seikosha shutter arrived yesterday. It had minor dust, but that cleaned right out with some air puffs and now it looks like it just came out of the box.

In checking the aperture tonight, I noticed that it stops down WAY past the f45 mark. f45 is about 3.5mm (which jives with that calulation being that on a 165mm lens f45 should be 3.667mm.) The minor difference can be chalked up to my plastic caliper. It stops down way past f45, though, to a hole which is slightly smaller than 1mm. So... f165 or smaller.

Is this uncommon for an LF lens?
Is that even practical on 4X5?
Are LF films susceptible to diffraction IQ loss like small format?

I'll be picking up a lens board for this during the week and making a mount this weekend, I hope, so I should be able to test it next week after my cast comes off.

[Mos6502]

It's not uncommon at all. Since the same shutter and diaphragm mech would be used to hold many different types of lenses, there are going to be instances where the diaphragm can be stopped down much further than the marked apertures.

As for diffraction, it will be the same regardless of negative size. However, because the negative is larger and doesn't have to be blown up as much, the effects of diffraction are less noticeable when working with large formats.

[David]

That makes sense about the shutters. So if there's a larger lens, they'd swap out the number plate on the aperture scale to match it. Thank you!

[luisalegria]

Thats right.

Most LF shutters were made in standard sizes to which all sorts of lenses could be fitted. Few lenses were offered with custom-sized shutters.

Its also common to see non-factory custom-engraved aperture scales, where a lens was upgraded from one shutter to another, or remounted from a barrel.

I have even had a couple of Wollensak LF wide angles where the shutter aperture opened WIDER than the maximum marked aperture.
Same reason.

[SXR_Mark]

Don't forget that the f-number is determined by apparent the size of the aperture i.e the size as viewed through the front of the lens and not the physical size of the aperture. So, unless the aperture is in front of the lens, the f-number calculated by measuring the physical aperture size will be incorrect.

Mark

[hifisapi]

Its very common for large format shutters to stop down way past f45. some to f128 or so. Diffraction doesnt hurt as much with large format because there is less enlargement in a final print compared to the negative. Those small f settings come in handy in increasing the depth of field because there isnt much with large formats. You might even want to try f64 and f90 sometime.

[David]

Thank you, everyone! I can't wait to try it. First I need to make a lens board. The 33mm opening the Seikosha needs isn't a standard Copal size, I don't think. The lens board is easy, though.