Sharpest f-stop?

[bob_camarena]

I have a Busch Pressman 2 1/4 x 3 1/4 camera with a 101mm f4.5 Graflex Optar

lens. I've just had the shutter cleaned and am ready to start shooting with it.

Other than some initial tests to see if it was functional and worth having the

shutter cleaned, I haven't used it and am new to larger format cameras.

 

I was wondering what f-stop would be the sharpest for landscapes. I know that

my 35mm lenses are best when stopped down a couple of stops but not at f16 or

f22 but I read somewhere that larger format lenses were different and were best

at smaller f-stops. I know that I should probably run my own tests, but I'd

appreciate any advice you might have on what to expect.

[mharris]

I might be wrong but each lens has a sweet spot. You should probably test a few apertures to see which is best for you. I have seen some articles in which people have done some of the testing but I don't remember where.

[sattler123]

Don't worry about diffraction with LF lenses - you will need the small apertures to get everything into focus, despite the diffraction issue.

[brian_ellis19]

"Sharpest f stop" is a relevant concept for lens testing purposes on an optical bench. In real life landscape photography use the f stop that provides the necessary depth of field for the photograph you want to make. Loss of sharpness due to inadequate depth of field will be far more noticeable than any loss of sharpness due to diffraction with 4x5 negatives. However, if depth of field is irrelevant, e.g. if you're photographing a wall or painting, then the "2-3 stops from wide open" rule of thumb is probably as good as anything else.

[michael_briggs2]

The typical f-stop scales with the format, so while f22 might seem an extreme aperture for 35 mm, its quite normal in LF.

 

You are correct that the best thing to do is to experiment. I agree with Brian that depth of field will usually be the most important consideration. If you have to stop down past the optimum sharpness of the lens to get the depth of field that is appropriate for your photo, the viewer of the print probably won't know, because they won't have anything to compare to. But if you didn't stop down far enough, they will notice because they will have references within the print.

 

I experimented with two 4x5 lenses and found the best overall performance to be from f16 to f32. This was to obtain full coverage to support movements. If you just look at the center, excellent performance might be obtained sooner.

[Troll]

Go with f:11 or f:16, for the "best" combination of depth of field and sharpness for a 101mm lens.

[justinblack]

The answer is f/16.3. Anything else is rubbish. Just kidding. The real answer is to forget

the optimum aperture nonsense and focus on practicality. In other words, you'll have a

good working aperture range from f/16 to f/32 (or possibly f/45) for landscape work

depending on the composition in question. If you need f/45 and a third to get the depth of

field you need after making the appropriate tilts and swings to optimize the plane of

focus, then by all means use it. If you can get by at f/22, then sharpness might be a bit

better. The kind of image you are trying to make will dictate the aperture you need to use.

Good apparent sharpness due to adequate depth of field will often serve the image better

than inadequate depth of field in exchange for optimum sharpness at the focal plane.

[nbg90455]

Well, Bob has a 2x3 camera, so really not a LF camera ;-)

 

The concept "sharpest" is a bit tricky, since it is not uni-dimensional -- do you mean sharpest in the middle of the photo or sharpest across the whole photo? In theory, the best trade-off between refraction and defraction for LF lenses is typical 2 stops from maximum aperture (unless you have a wide-angle lens, in which case you should use 3 stops).

 

In practice -- and for your lens/camera combination -- I'd close it down a little more. These Optar lenses aren't the greatest, so I'd go down to f16 (rather than f9-ish = f4.5 + 2 stops), in general, to get good overall sharpness. I have a Crown Graphic 23 with a 101 Ektar (IMHO, a better lens) and that's what I do.

As pointed out elsewhere, if you need the extra DOF -- by all means -- close it down more...

 

Mike

[michael_briggs2]

Some previous discussions:

 

"Beginner, Optimum Aperture" at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004NpY

 

"Clarification on f11 sweet-spot" at

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004Olk

 

and "Is f/22 the Sweet Spot for 4x5?" at

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004lAf

[frank_menesdorfer]

I have wrote on this subject here once but again according to the lens manufacturers such as Schneider or Nikon that any lens gives it's best and absolute performance on f stops which is stated on the lens technical description.

 

Modern large format lenses actually works best on f22 but older lenses best works on f11 or on f16.

 

Now, you shouldn't use the smallest aperture as the final resolution. Restitute (camera movements=restitution) and just use the necessarily f stop which is enough to or needed to get your image sharp. If you just for example taking pictures of flat things such as a wall so most of the time it's enough with two stops. We actually saying that one stop for the negative and the rest is for sharpness. If you are out and taking picture of landscape it works a same way.

 

In my schooldays (long time ago) actually I made a picture on a soccer plane. I place one ball on the middle of the plane and than one on each meter from me toward the end of the plane. I have used some movement on my front of the camera and stopped down only one f stop and get everything sharp. So that's how it works.

 

Good luck to you!

[mike_earussi1]

An Optar lens is a Tessar 4 element design. This means that though they are very sharp in the center, the corners do not even start to become sharp until f11, and probably peak out around f16. Naturally, as you stop down the lens to increase corner sharpness defraction effects will lower the lens resolution in the center. So it becomes something of a tradeoff, as for each shot you have to decide what's more important to you, maximum center or edge sharpness (defraction also lowers the contrast). Of course, if your final enlargment is 4x or less (10x14 full frame) it's unlikely you'll see any defraction caused difference at all, even at f22. But the higher your final print magnification the more critical absolute sharpness becomes. Plus each individual lens will be slightly different due to manufacturing variations and just general wear and tear such as whether the lens has been dropped or repaired or cleaned poorly over the years. So it is still necessary to test the lens over a range of f stops and then compare the results with a good 8x loupe or a microscope at low power (10-20x).

 

As for comparison between 35mm and MF a (very) general rule of thumb in comparing resolutions, as determined by defraction between each format, is to double the f stop with each increase in format. For instance, free air resolution at f5.6 at 35mm will approximately equal f11 in 6x7 format, f11 1/2-f16 in 6x9 and f22 in 4x5. Though in the real world f22 in 4x5 will look much better than f5.6 in 35mm due to film grain limitations.

 

Another limitation in shooting much wider than f11 is how flat the film is being held in your roll film holder. Usually you have to shoot at least at f11 to have enough depth of focus at the film plane to compensate for film curl. But, of course, this depends on the quality of your film holders. I'm not familiar with the ones used on the Pressman but the original older ones for the Graphlex are quite poor in this regard requiring around f16. The later Graphic ones as well as the Mamiya and Horsemen backs are good (especially the Horseman) and hold the film very flat. The fastest way to check is to sacrifice a few frames by loading film in your holder and then, in the light, open the dark slide and observe how much the film buckles, if virtually none you have a good back, if a lot then you need to stop down to f16-f22.

 

Hope this helps. Mike Earussi

[mike_earussi1]

One further comment, if you do decide that what you are really wanting is to maximumize sharpness then you need to switch to a better lens, such as a 6 element symmetrical design like a Symmar, whose corners are sharp at f8 plus has enough coverage for some camera movements and, being symmetrical, can double as a very good close up/macro lens as well. A 100mm symmar usually runs in the $100-$200 range depending on condition, shutter and who you buy it from.

[dan_fromm2]

Bob, if you can find your way to http://groups.google.com/advanced_search?q=& , do a search on raptar with author Richard Knoppow.

 

Richard, who knows whereof he speaks, reports that there's a design problem common to all tessar type Raptars; your Optar is a Raptar rebadged for Graflex, Inc. He says that they all suffer severe coma. Coma is an off-axis aberration that is controlled a little by stopping down.

 

According to Richard, all tessar type Raptars must be stopped down to at least f/22 to get barely adequate sharpness in the corners. He also says that in this respect tessar type Ektars (for 2x3 Graphics, 101/4.5 Ektar) are all much better.

 

So, if you want good sharpness in the corners, stop way down. Otherwise let the, um, needs of the image dictate.

[bob_camarena]

Wow, what an amazing group of answers! Thanks for the information except now you have me thinking about a new lens as well. I'm sure it can wait a while since, even with the one I have, I know that the results are going to be impressive compared to what I'm used to from my 35mm (my initial test shots were). I doubt that I'm going to be making anything larger than 11 x 14 prints anyway.

 

Unfortunately, at least for now, I don't have the ability to take advantage of my camera's movements since it has a Graflex back on it and no ground glass. Whether or not I work on that as a next step remains to be seen.

 

By the way, I posted my question on this forum instead of medium format since I figured that my camera and lens had more in common with large format cameras than the typical MF cameras.

[pico]

That lens has rather poor image contrast and is susceptible to flare so don't be terribly

disappointed.

[frank r]

Bob: You should consider making a simple ground glass for your camera. Being able to focus on an actual ground glass is invaluable.

 

A cheap one can be made by using the glass from a picture frame from the dollar store. If necessary, cut it down to fit the space for a film holder. Place strips of frosted scotch tape across the surface.

 

The thickness of the glass should be very close to the dimension from the frame of your film holder to the film plane inside. You may need to start with a slightly thinner piece of glass and shim under it with taped on cardboard strips. See this link for an example.

 

http://www.rolandandcaroline.co.uk/homemade4x5/homemade4x5.html

 

Email me if you have any questions.

[bob_camarena]

My main roadblock isn't the ground glass itself, it's devising a mechanism that would make the Graflex back easy to remove for composition and focusing and to replace for shooting. I have a dark slide for it, but it's currently attached to the camera with two metal brackets and screws.

[michael_gilday]

Don't be too quick to discount the humble Optar. In particular, shoot a number of shots yourself, under different conditions, before believing the 'severe defect' story. I have two 101 Optars, and one each 101/4.5 Raptar and 101/4.5 Velostigmat, and they're all perfectly good lenses, though they offer very little movement on the full 2-1/4x3-1/4 format; I usually use them with a 6x6 back with movements, or a 6x7 back, without. Yes, the lens is around fifty years old, and nowhere near the same level as a modern Nikkor or Schneider lens... but nowhere near the cost, either. I have faster lenses, and longer lenses, and lenses with more elements, and lenses frequently considered far better than the Optar (like the 105/3.7 Ektar), but I still shoot regularly with the Optars, Raptar, and Velostigmat, anywhere from f/16 to wide-open, because I like the look. They're all about equally sharp; the biggest differences seem to be propensity to flare, amount of contrast, and bokeh. The Optars don't necessarily excel in these areas, but they're uniformly decent across the board, unlike a few other lenses I have for the format.

[discpad]

Just as a side note, when you're shooting with a lens stopped down in the f/16 range or thinner, keep an eye on exposure times, compensating for exposure times due to reciprocity.

 

If you're shooting B&W film and you underexpose (or more accurately, underdevelop for the exposure index you assume), it's not *too* bad.

 

On the other hand, with C-41 film (and you send it out for processing), if you underexpose you'll have other problems besides sharpness.

 

>>> Don't get me wrong: Keep the lens stopped down into the f/16 to f/22 range to keep your sharpness; but just increase your exposure times if your shutter speed gets down below 1/10 second when shooting color negative film.

[jeff bishop]

Hi Bob, Everyone has their own ideas and opinions; myself included. What's important is how the lens performs for your type and style of photography. You will have to come to your own conclusion.

 

Bear in mind that your question presents the opportunity for a certain amount of 'poison' too. For instance, arriving at the idea that you might need to add another lens before you give this one a thorough test. I wouldn't lower your opinon or expectations on this lens until you see how it will perform.

 

I have a 2x3 Crown Graphic with this same Optar lens. I also had a 2x3 Mini Speed Graphic with the 101 Ektar. While I liked that lens a lot I still let it go in favor for the Optar. Why? Because I needed the shutter to have flash sync, and only the Optar filled that need.

 

I suggest you shoot some rolls or sheets of transparency film, put it under the glass and see what you think. Just be sure to keep complete notes for a reference. I suspect that your little Optar may surprise you.

[murrayatuptowngallery]

While talking about Optars, Raptars & Velostigmats are they same, similar or different?

 

I think the Velostigmat is pre-WWII )?(, don't know about the others.

 

Murray

[dan_fromm2]

Murray, Raptar and Velostigmat are Wollensak trade names. Optar is a Graflex trade name.

 

Most Raptars are tessar types, BUT there are others.

 

Some Raptars were rebadged for Graflex and sold as Optars. Most of these are tessar types, but again there are others. And after Wollensak stopped supplying lenses to Graflex, Graflex sold at least one tessar type Rodenstock lens as an Optar.

 

Wollensak changed their trade names in 1946, relabeled Velostigmats as Raptars.