Bigger Image Circle Nearly Always Better ???

[scott_fleming1]

Ok I'm planning my lense outfit. What would be the advisability of

going for lenses with image circles for at least 5x7 even though I'm

using a 4x5 camera? Not considering cost here. I won't be needing

extreme movements but it would be nice to know I was covered. Then

there is the 'sweet spot' consideration ..... or is there?

 

While I've got you here I have questions about tele lenses too.

Occaisonally I might wish to use the tele effect of compressing

landscape features. Rodenstock says their new lenses obviate the

need for tele lenses and their 'disadvantages'. Assuming I have a

camera with 500mm of bellows ext and I can wedge an Apo Ronar 480 in

there ... will I get the same sort of tele compression ..... or not?

(I know this is only equivalent to 200+ 35 mm)

 

And oh yeah, what is back focal lenght anyway and what is it good

for?

 

Thanks.

[scott_fleming1]

What do you all think of the Nikon convertable teles?

[dick roadnight cotswolds]

If a lens is optimised to cover a small format, the resolution will be better than for a lens which has to cover a larger format, and you would also get less flare.

 

So I will keep my 47 and only use the 47XL (for 612) when I need the coverage... or I will try bot to see if there is any difference.

[robert_a._zeichner1]

Many popular lenses for the 4x5 format do cover 5x7 with limited movements.

 

The compression effect you speak of is strictly determined by focal length and not lens type. A 500mm telephoto formula will "compress" identically to a lens of conventional design and of the same 500mm focal length. The compression effect is really a phenomenon that is a result of the great distance between object and lens. As others have pointed out, if you were to make negatives from the same vantage point with both a long and short lens and then enlarge a section of the negative made with the short lens the most distant subjects would have the identical compressed effect as with the long lens.

 

Telephoto lenses, as a rule do not typically feature large image circles. Their advatage in the world of LF is that they require less bellows draw. For example, if you were to mount a 300mm Fujinon T to a camera like a Horseman 45FA, which only has around 240mm of draw, you would still be able to focus at infinity because the 300mm Telephoto lens has a flange focal depth of around 180mm. This is the distance between the mounting flange of the lens and the plane of focus, when the lens is focused on an object at infinty. Telephotos work like this because their optical center is virutal and lies outside of the body of the lens. This is done in the non-LF world to keep lens weight and physical length to a minimum.

 

You'll also notice that telephoto lenses for hand cameras typically don't focus very close. This is because telephoto lenses require compensation for the exit pupil factor. Simply stated, if the size of the image on film gets to be larger than 1/10th of the actual size of the object, exposure compensation is required to counter the effects of exit pupil size. The same rule holds true when they are used on LF cameras.

 

Another peculiarity of telephoto designs on view cameras is that because the optical center of the lens is actually in front of the lens, when you attempt to do tilts and swings at the front of the camera (and your ability to do so will be very limited by the smaller image circle) the adjustment by way of observation on the ground glass will be trickier. This, because the central nodal point of the lens is not where you think it is. Then again, you'll probably not be needing to do too much of this with such a long lens.

 

My vote is for a long focal length lens of standard design. If necessary (and if your camera can stand the weight), you can make an extension lens board to hold the lens a couple of inches further out than normal. How far you can take this depends on the aperture size of the front standard. I recently acquired an Apo-Ronar 14" graphic arts lens that I had Steve Grimes mount for me in a real clean Ilex 4 shutter. It's one of the sharpest lenses I currently own and one of the least expensive as well. Steves's fee was very reasonable considering the great quality of his work, but was more than I paid for both of the components combined! I use this lens, by the way, on both 4x5 & 5x7 and have oodles of movement.

[david_goldfarb]

Robert's offered some good advice. I would only add one other issue, which is that more bellows extension on a windy day means less stability. What you lose in sharpness due to the optical design of a telephoto lens, you may gain back by having a more solid camera.

 

A 480mm conventional lens on a 500mm bellows is cutting it really close. Depending on how generous your bellows design is (some are actually a bit longer than the maximum extension of the rail, leaving room for movements at maximum extension), it might be stretched to the point at which no movements are possible for many shots. Normally one wants about 25% more bellows than focal length.

[jerry2]

I refused to buy teles for years as I was nervous over the loosing resolution. Then when I moved up to 800 and 1200mm, I had no choice but use teles. Some of my 1200 shots are the sharpest shots I ever made, and this includes stiff competition from my other lenses, such as the Fuji 240A, 110 & 150 Super Symar Xl's. I can't speak for all tele lenses, but I have great luck with the 800 and 1200 Nikors.

[ilkka]

As I see it, the disadvantages of too much coverage are:

 

1-Lens is bigger and heavier, especially for the same maximum aperture

 

2-Additional coverage may cause internal reflections within the bellows

 

3-Price, but that was not a concern to you.