SL filter Factor?

Good morning world,

I recently got my A36 UV or SL filter for my uncoated Summar. I

also got one of those fancy movable lens hoods 50-135.

I took out this last weekend I found that the lens hood set on

50mm vingettes my corners. so I guess I can push it in to the

bottom to rectify that .

My film came out thin. Could this be me F&*^in' up my metering

or Is there a factor for SL filter?

Thank you

Skinny

Stacking that hood on the filter "zoomed" it telephoto. So you need to pull the hood back in 4 millimeters or so. Plus, the front element of a Summar is larger than the Elmar that hood is designed for, so you need to zoom it wide.

A protective filter on a Summar is just going to make the flare tendendcies even worse. It's a Hobbesian tradeoff, the front element of the Summar and Summitar is soft as hell, so you want to protect it, but both lenses are going to work noticeably worse with a filter on. (The other approach is to be extremely careful in how you clean these lenses.)

There's no filter factor (well, 1X) for a UV, SL, or H filter.

If the front lens cell is not completely firmly screwed into the Summar, the aperture index mark will not be in the right place. If yours is the version with the two lugs behind the aperture ring, the index mark should be in the same place as the center of the upper lug.

Also, just eyeball the iris. You should not be able to see the blades at all at f/2.

Also, there certainly could be a stop of haze in the interior of the lens, if it hasn't been cleaned.

Enjoy your "variable contrast" lens. I need to play with my new one more, I've just done the most perfunctory tests on mine after cleaning up the front lens cell.

There is a filter factor for any filter, since even a plain piece of glass will reflect, absorb, and scatter a little bit of light. B+W engraves a factor on their UVa filters, of "1x" which is to say, the factor is so slight as to be not be worth considering. The same company marks its skylight filters "1.1x" which I assume means ten percent of the light is absorbed by the filter. That will affect the exposure the same as if the shutter speed is ten percent too fast. Well, ten percent is within the tolerance for pretty much any shutter. The effect will be a slight intensification of colors, perhaps not unwelcome; or with black & white, a slight loss in density, detectable with a densitometer, but not by the eye.

But then, what happens when the ten percent loss in the filter, is combined with a shutter error in the same direction? And there is always the possibility of a ten percent (or greater) metering error. Now we have a 30% underexposure. Also, some lenses (like the 21mm SA, IMO) don't transmit as much light as the marked f-number implies. That would increase the error. Oh, and a given batch of film could be ten percent off. Now we are getting up to around a half to two-thirds of a stop.

Normally these errors could be expected to randomize out, i.e., some of them ought to be in the opposite direction--unless we are unlucky. But there is always a possibility they could add in the same direction.

When I use a UVa or SL without using a through-the lens exposure reading, I seldom bother to apply any filter factor; and I'm seldom aware of any resulting underexposure.

So my answer is that a skylight filter factor by itself means little, but could become significant in combination with other errors.