Question about CV 15/4.5

Theo-Prof · 12-19-2005

A Question for other owners of the CV 15.4.5.

Several months back I bought a used 15/4.5 Heliar. A few weeks ago I noticed something and wonder whether it is normal for this lens. When I look throught the rear of the lens with the aperture wide open it looks as if the aperature is closed down slightly. Just to the rear of the aperature blades is an orifice that looks like a washer. This orifice is slightly larger than the aperture blades when they are set at f4.5. In all the other lenses I have owned I cannot see the aperture blades when the aperture ring is set to its largest aperture. I am wondering if this is normal for this lens.

Kevin

laptoprob · 12-19-2005

So right Kevin,
looks like the Heliar could have been a f/2. ;-)
Or not - Cosina is smart enough to make the most of it.

Answer: mine is the same. Must be normal.

cheers, Rob.

Theo-Prof · 12-19-2005

Thanks Rob. Since I bought it used I had no way of knowing if it had been dropped or tampered with. I love the shots I have taken with it but this question just kept nagging me. I would hate to use a handheld meter one day only to find out that the marked aperatures were way off.

Kevin

phototone · 12-19-2005

There are various lenses made over the history of optics and photography that have larger lens elements than their iris. This is not a flaw. It is just lens design. The maximum iris is the maximum iris that the lens design will deliver minimum stated results based on the lens design.

Fred · 12-19-2005

Kevin, don't worry. I've just checked mine and it's exactly the same, viewed from the rear you can see what looks like a washer outside of the iris. Looking through the lens the aperture looks roughly round though. I love this lens.

rich815 · 12-19-2005

Likely the performance below 4.5 is so bad (vignetting in particular) as to be unacceptable and therefore they limit it to that even if the lens design could in fact allow for a larger aperture.

peter_n · 12-19-2005

Mine is the same too and it works just fine. Great lens!

Theo-Prof · 12-20-2005

Thanks for all the responses. I had assumed that the lens was designed this way, but I just wanted to make sure. I'll be bringing my Bessa-R and 15/4.5 and 35/2.5 with me this Christmas for photos of family. Now if someone would just make a chromogenic 800 speed B&W film so I can use the 15/4.5 indoors under low light.

Kevin

Al Kaplan · 12-22-2005

It's designed that way to minimize vignetting. I find that because the image from an ultra-wide makes everything look so small I can often hand-hold at 1/15 second, even 1/8 or1/4 if I lean against something, brace my elbows tight against my body and breath slowly.

VinceC · 12-22-2005

>>Now if someone would just make a chromogenic 800 speed B&W film so I can use the 15/4.5 indoors under low light.<<

What Al said above is right. You can handhold a 15mm lens at 1/15th of a second no problem and should be able to get away with 1/8th too. I once held a 17mm SLR lens at 1/4 for an outdoor nighttime shot, and the resulting 8x10 print was sharp.

Also, chromogenic film has a lot of exposure latitude. Though labelled for 400 speed, they seem to have richer tones at 200, can be exposed at 100 and do quite well at 800 speed, but with more noticeable grain.