90mm f8 vs f6.8 vs f5.6

[Brian Schall]

I have a SA 90mm f8. Using it in the bright New Mexico sun, I never really had a problem with focusing it. This weekend I was shooting in some darker wooded areas and the f8 just didn't make it. I was lucky to see enough to focus. I used my 150mm f5.6 for a shot and it seemed to jump into focus.

So I've decided to up grade the lens. I also have a little 65mm f8 Acugon I'd like to up grade but that one will definitely have to wait. (Then again, maybe I'd be better off dumping both the 90mm and the 65mm and getting a 75mm.)

How much of an improvement would the Rodenstock/Caltar 90mm f6.8 be over the f8? Or should I skip this lens (which is decently priced) and just go to a f5.6? Price is definitely a factor. The f6.8 I've seen at +/- $500, while the f5.6 runs $200 more.

I shoot mainly B&W with a Tachihara.

Brian

[Gene McCluney]

Do you use a good dark cloth? Can make a world of difference. The faster lenses are much larger and heavier, which may be an issue for location photography.

[Brian Ellis]

Forgive me if I'm pointing out the obvious but the difference between an f8 and f5.6 is one stop or a 100% difference in brightness (i.e. the f5.6 should give you twice the amount of light you now get with your f8, all other things being equal). How significant that is depends on the lighting conditions - if the light is real low even doubling the amount striking the viewing screen may not make any real difference -100% of zero is still zero to take an extreme case. Not only is price a factor but size and weight are as well - f5.6 lenses are going to be bigger and heavier than f8 lenses of the same design, though surprisingly to me there wasn't as big a difference between the 90mm Super Angulon f8 and f5.6 as I would have expected.

I'm sure you realize that the reason your f5.6 150mm lens seemed to jump into focus whereas your f8 90mm lens didn't wasn't solely because of the aperture difference. The longer the lens the easier it will be to compose and focus, all other things being equal, because a larger percentage of the light is striking the viewing screen from a shorter distance with a long lens than with a short one. So even if the two lenses had the same maximum aperture, the image on your viewing screen would be brighter with the 150 than with the 90, all other things being equal.

I had a 90mm Super Angulon and was considering adding a 75mm to get something wider. Instead I sold the 90mm, forgot about the 75mm, and bought the 80mm SS XL instead. I thought 80mm was close enough to the two focal lengths that substituting the one lens for two would work as well and saved a lot of weight and space. While the XL is expensive, I saved the cost of a 75mm and paid part of the cost with the proceeds from the 90mm so it wasn't too bad.

[Michael T. Murphy]

If size and weight are not a big concern, the Rodenstock/Caltar 90mm 4.5 is wonderful and quite bright!

I have the Rodenstock on a Toyo and the 90mm f/8.0 SA on a Cambo Wide. I just had to buy a Beattie Intenscreen for the Cambo, but it is still very hard to focus via the groundglass under darker conditions (which happens a lot more here in the midwest than in New Mexico )

I love the Rodenstock. I tolerate the SA because it is already mounted in a helical.

Best,
Michael

[Jack Flesher]

Way back when I was starting out in LF, the 90 I bought was the Nikkor f4.5 because everybody claimed it was a lot easier to focus than the f8 lenses... Not knowing any better, I blindly followed that advice. A year later I was schlepping it and my Technikardan up a mountain in Zion and came across another chap also shooting a TK. We chatted a bit and I noticed he had the f8 Nikkor mounted, so we did a comparison in the relatively low light under the wooded canopy. Bottom line was we could barely distinguish the brightness difference that supposed stop and a half should have been giving us -- yeah it was a little brighter, but no great shakes and certainly not worth the added weight, so I sold that particular beast and never looked back.

If you think your 90/8 is dim, view through any other lens that requires a center-filter mounted. (Some may disagree, but IMO the 80SSXL is such a lens and the main reason I don't like it...) If you do, I suspect you'll be a lot happier with what you already have.

My .02 and respect YMMV,

[Michael T. Murphy]

FWIW, there is a Rodenstock 90mm 4.5 on another board for $690. Looks like a "green stripe" version from the pics.

E-mail me for a link if you want. I am *not* selling it and don't know anything about the seller, but he does say he has Ebay & photo.net history.

[Bjorn Nilsson]

What really makes a difference is whether you use a fresnel screen or not. I've noticed that a fresnel is even more "active" with wide angle lenses than with normal or longer lenses.
The problem that the fresnel helps with is widening the very small "sweet spot" a wide angle lens gives on the ground glass.
The problem with the small sweet spot is inheritent to all wide angle lenses because of the combination of first the wide angle and second the short distance between the lens and the ground glass.
I read about similar concerns with e.g. the Fujinon A 240mm which have a f/9 opening, and also e.g. the Fujinon C 450 with a f/12.5 max opening. As both these lenses are longer focal lengths all of the light hits the ground glass at closer to an straight angle and there is less problem with the dimmer ground glass.
So IMHO, before shelling out lots of $$$ for a less portable lens, try with a fresnel.

[pierre salomon]

I had once a similar problem and quickly discovered that my lenses were fine, it was instead the post 50 syndrome when one day you can no longer have your eyes too close to the GG, the lenses become half bright and your focusing cloth seems suddenly too short. I bought myself a super screen from Bromwell Marketing and saved a few hundred $ from buying new lenses. I dont know how old you are but you can try a better GG. Just in case!
Pierre

[Emmanuel BIGLER]

I agree with Pierre Salomon.
In fact somebody who has a very fine eyesight will hardly notice anything when focusing a "slow" lens, say, a f/9 process lens..
If you are properly shielded from extraneous light, your pupil opens until the image is viewed comfortably. Then, the most important is that the lens is sharp. This is the case for modern process lenses.

People having a fine vision will see sharp even with their pupil wide open so whatever the actual max aperture of the lens, provided that the lens is sharp and the image well contrasted, like for all modern lenses.
Others like me suffering from various vision defects always prefer brighter images because the pupil will stop down and correct for some imperfections of the vision.
Personnaly I use the 6.8 grandagons, the 75 and the 90, I have never experienced any problem but most of the times I am using a bino reflex viewer.
In fact the problem is to be comfortable when you focus, so that you can focus quickly. If you spend too much time moving the standards back & forth, your eyes become strained and focusing might become erratic.
So if yo are more comfortable with a fast lens, you should go for it.
But if you test a good 6.8 and are comfortable with it, a faster lens will probably not bring much to you.

Incidentally it happens that I have a 2.8/100 mm planar (probably designed for the Baby Linhof 6x9) and I cannot complain about the comfort ;-) Imagine : 4 times brighter than a regular 5.6 lens ;-)

[Brian Schall]

Thanks for the input. As Pierre suggested, maybe it's my eyes. I'm 55 and wearing progressive bi-focals. If keep meaning to buy a +3 pair of reading glasses to use under the dark cloth; maybe that would help.