Questions about the tutorials on shift lenses, filters and aperture limit.

[dimitr]

Hello all,

after not doing much photography in perhaps 15 years, I recently felt motivated to explore this world again.
I do remember some of my experience with analogue cameras, but am trying the switch to a DSLR & bought a used Canon D30 for this purpose.

Foremost I would like to thank the author(s) of the tutorials on this website-- they have been the best resource I have found on refreshing the concepts & learning a lot of new things. Will certainly pass the URL to friends.

I do have a few (very basic) questions, though. Not sure if I should start a new thread for each one, so I'll just list them here:

• On shift lenses, the tutorial suggests cropping as an alternative:

  One way would be to use a wider angle lens and then only make a print of a cropped portion of this, [...]

  But: the wider the lens you use, the more distortion you have, and hence the more you have to crop. So it seems to me, that unless you can get further away, cropping of the image won't really produce the desired result.
• On filters: Just to make sure I understand right... are filters inconsistently named? I.e., UV- & polarized light filters filter UV & polarized light, respectively, while e.g. green & infrared filters actually pass those colors?
• On diffraction limited aperture: Can setting my camera to a lower resolution actually help with this phenomenon? Or is it inherent to the physical size of the photosites?

Again, thanks a lot for the great tutorials.

[Paw Paw Bill]

Hello all,

• On shift lenses, the tutorial suggests cropping as an alternative:
  But: the wider the lens you use, the more distortion you have, and hence the more you have to crop. So it seems to me, that unless you can get further away, cropping of the image won't really produce the desired result.
• On filters: Just to make sure I understand right... are filters inconsistently named? I.e., UV- & polarized light filters filter UV & polarized light, respectively, while e.g. green & infrared filters actually pass those colors?
• On diffraction limited aperture: Can setting my camera to a lower resolution actually help with this phenomenon? Or is it inherent to the physical size of the photosites?

Again, thanks a lot for the great tutorials.

To answer a couple of your concerns:

Yes, UV will block ultravoilet light, Polarized filters will pass light waves polarized in one direction and block the light waves polarized at 90 degrees to the passed light. Colored filters pass the color that they are named for and block other color frequencies.

Changing resolution on the camera won't alter aperture defraction. The sensor gets the same image without respect to output resolution. The camera's software reduces the pixel count for reduced size by averaging a number of pixels into one. This results in a multi-meg image with some percentage of distortion and produces a lesser-meg picture with the same percentage of distortion.

On shift lenses, you can get an approximation by cropping, but perspectives won't work out properly because of the plane of the image sensor in respect to the plane of the subject. Distance from the subject won't change this angular difference by a great deal, but the subject size in relation to the distance from the camera will improve the result, but only marginally. Post processing can simulate some shift lens aspects, but again, even that has its faults and problems.

[Colin Southern]

Couple of quick notes ...

Diffraction is a very real, but IMO, is insignificant in real world photography and (a) as images that are going to be displayed on the internet need to be down-sampled (or they'd be too big), and the down-sampling also down-samples the diffraction (so you can't see it), or (b) in images that are going to be printed, the diffraction is too small for the human eye to resolve in a small photo. So in reality, about the only time you'll ever be able to really see it's effect is when looking at the image at full resolution / high magnifications on screen, or when producing an exceptionally large print and examining it up close. In reality, correct sharpening is far more important (also, limiting the F-Stop you use so as to limit diffraction will probably damage your image more due to lack of depth of field than it will through diffraction).

With regards to TS lenses ... distortion comes from not having the sensor parallel to whatever you want to photograph eg you want to photograph a tall building, but you need to "point the camera up to get it all in". With a TS lens you'd keep the sensor parallel to the building (to stop converging lines) and then use the shift function to shift the view upwards. The alternative as Sean explains in the tutorial is to use a WA lens (so you can get the field of view that you want) - keep the sensor plane parallel to the object (to again stop converging lines), and then crop out the excess below what you're photographing.

Hope this helps

[dimitr]

Wow. That was quick!

Thanks a lot, Bill & Colin, very clarifying answers.

[Inkanyezi]

Shifting a lens is essentially exactly the same as using a wide angle lens cropped, as the shift lens is indeed a wide angle lens, that covers a substantially larger image circle than the format diagonal. Wide angle lenses of good quality should not distort the image, but having the image plane at an angle to the structure that you photograph will give a perspective effect called keystone.

With software, the keystone effect may be corrected completely; thus there is actually no need for shifting the lens, unless you want to use the entire sensor area for the final image. You lose some resolution and image area when you correct for keystone. If you instead shift the lens, you may use a larger part of the sensor area for registering the image. For practical purposes, this is insignificant, but when you have a shift lens, the image requires less post processing and may be inspected directly on the screen.

When shooting a building upwards, accepting the keystone effect, depth of field may be a limiting factor, but With a tilt lens the image plane of the lens may be altered by tilting, so that the entire building becomes sharp. Thus tilt is perhaps a more important feature than shift. There is however a caveat. Modern DSLR cameras are often unsuitable for this technique, as focus cannot be checked critically over the entire viewfinder area; mirrorless cameras with EVF are better in this respect, and live view on the screen also solves this problem.

[Colin Southern]

Modern DSLR cameras are often unsuitable for this technique, as focus cannot be checked critically over the entire viewfinder area; mirrorless cameras with EVF are better in this respect, and live view on the screen also solves this problem.

Excellent summary

Possibly just worth mentioning that although there's no such thing as auto-focus with tilt-shift lenses, the focus confirmation light still works - so although one can't check the focus over the entire image area, at least one can get a bit of an idea by selecting different AF points.

[Dave Humphries]

On shift lenses, the tutorial suggests cropping as an alternative:

One way would be to use a wider angle lens and then only make a print of a cropped portion of this, [...]

But: the wider the lens you use, the more distortion you have, and hence the more you have to crop. So it seems to me, that unless you can get further away, cropping of the image won't really produce the desired result.

This may not need saying, but ...
Indeed it was implicit that you would stand further away and/or use a wider angle lens in order to keep the sensor plane parallel to the building - in extreme cases; this can effectively waste almost half the sensor area.

It is how I tend to shoot large buildings, but I do keep recognisable shapes away from the corners to avoid distortion effects c

Cheers,

[Glenn NK]

I had invested in a 5DII to get increased pixel count and more coverage than I got with my 30D. To shoot buildings I could waste one half (or more) of the image by keeping the sensor plane parallel to the building face (and crop like crazy). Or I could angle the camera up a bit and live with converging lines (which could be fixed in PP with an attendant loss in pixels - required when the image is stretched at the top).

To take advantage of the new camera, the obvious solution was to acquire a TS lens. They are expensive, but all other options impose a penalty on image quality (the goal of better image quality was the prime consideration when acquiring the 5DII in the first place.) This is likely why a TSE is in so many bags and why it's in mine - in spite of the cost.

The most difficult question one faces is which focal length? The choice depends on many things - there is never a simple one-size-fits-all solution.

It is a difficult lens to use, let alone master, but I would not want to use one without live view.

Glenn

[dimitr]

Thanks a lot for all the responses. This has been very clarifying.

BTW, it's only been a few days with the Canon 30D (not D30 as I wrote above), and I have been quite happy. There are some digital-specific stuff I still have to explore a lot more (and controls witch need getting used to, e.g. having the aperture on the body instead of the lens), but overall it isn't that different than shooting with a regular SLR.

The kit lens included has a very narrow focusing ring, and it is IMO opinion way too close to the glass (always risking getting finger grease on it), also, the action isn't quite as smooth as I remember from my analogue SLR.

Is this because it is a kit (read beginner) lens? Or are all lenses nowadays designed towards AF? I am more comfortable with MF, given that it is the only mode I knew... also, AF feels like driving an automatic transmission, can help but think I am missing out on half the fun and control possibilities. What do you use for everyday shooting?

[Dave Humphries]

The kit lens included has a very narrow focusing ring, and it is IMO opinion way too close to the glass (always risking getting finger grease on it), also, the action isn't quite as smooth as I remember from my analogue SLR.

Is this because it is a kit (read beginner) lens? Or are all lenses nowadays designed towards AF?

Yes, undoubtedly - they are built down to a price and no-one expects the focus ring to get much use!

Use of a lens hood would avoid the 'finger contact' problem

I am more comfortable with MF, given that it is the only mode I knew... also, AF feels like driving an automatic transmission, can help but think I am missing out on half the fun and control possibilities. What do you use for everyday shooting?

I love AF, but then I also drive an automatic transmission car.
It is true I sometimes yearn for a gear stick and clutch (and more hp) to demonstrate my skill at smoothly engaging the correct gear, as I get if I drive say, the kids cars - but do I get the same feeling of satisfaction and control from manual focussing? - no way. MF is a drag and one I can do without thank you. The AF always does it better and quicker than I can, but then my eyes are worse than my driving skills and I don't have the benefit in the digital camera of the split prism focus aid and surrounding faceted ring.

I suspect the use of AF will 'grow on you' over time

Cheers,

[Inkanyezi]

/.../ The most difficult question one faces is which focal length? /.../

Considering the cost, you would hardly try your way through all focal lengths, but I have found my preferences, and I think they might be if not universal, at least a good starting point.

I use a tilt adaptor that has no shift for a µ4/3 camera, so in my case tilt is the only option and I can use it with many different focal lengths. My adapter takes M42 lenses and I have various focal lengths, the shortest 24 mm and then upward to ridiculous focal lengths.

Of course it depends on how you actually plan to use the lens, but so far, I haven't had much success with any long focal length. I have tried it with 50 mm, and it can be used in a rather limited way. It works best with shorter lenses; those that I use are a 29 mm Pentacon and a 24 mm Tamron. The quirk is that I want it for focusing from very close to infinity, and the shorter the lens, the closer I can get. A too long lens does not give the angle of view I want for most shots. So I am looking for a reasonable cheap Tamron 17 mm.

Tilting is not impressive with long lenses or at short distance with medium long ones. It changes sharpness to a different angle, but only slightly. So if you are thinking of getting a tilt or tilt-shift, I'd suggest that you go for a short one, not longer than a normal lens for the sensor size you are using. For the APS-n formats that will fall in the region of 25 to 35 mm, and probably an even shorter lens will be more useful. Those TS lenses that are available are mostly made for FF.

Presently it seems as all lenses that fit APS.n Cameras are made for full frame. If I had a crop camera from Canon I'd first think of the 24 mm lens, which is a good compromise for focal length that will also serve very well after an upgrade. The 17 mm might be considered too wide, but is the one that is most flexible of all. There is a Hartblei 35 mm as well, which can be used for crop cameras too, although personally, I'd prefer a shorter focal length.

If you intend to use one for architectural shots, you can try your focal length preference with the kit zoom. Tilt the camera for the shots and use keystone correction with your software to see what focal length you might need, before investing in something as expensive as tilt-shift.

[Glenn NK]

Thanks a lot for all the responses. This has been very clarifying.

BTW, it's only been a few days with the Canon 30D (not D30 as I wrote above), and I have been quite happy. There are some digital-specific stuff I still have to explore a lot more (and controls witch need getting used to, e.g. having the aperture on the body instead of the lens), but overall it isn't that different than shooting with a regular SLR.

The kit lens included has a very narrow focusing ring, and it is IMO opinion way too close to the glass (always risking getting finger grease on it), also, the action isn't quite as smooth as I remember from my analogue SLR.

Is this because it is a kit (read beginner) lens? Or are all lenses nowadays designed towards AF? I am more comfortable with MF, given that it is the only mode I knew... also, AF feels like driving an automatic transmission, can help but think I am missing out on half the fun and control possibilities. What do you use for everyday shooting?

A few comments:

1) I have a 30D and a 5DII - I prefer the 30D for closeup work with flowers, and in fact it's just as good because with my 100mm macro I don't have to get as close or don't have to crop the image.

2) Dave's comments about "quality" of the kit lens are accurate - as is his suggestion to use a hood.

3) I spent far more time with an SLR than I have with a DSLR so am still comfortable with MF. Of course the TSE lens is not AF so it's a good thing I didn't forget how.

4) There was an interesting post somewhere else about quality control and variation but it also gets into the accuracy of AF.
http://www.dpreview.com/articles/733...-and-fallacies

Glenn

[Colin Southern]

I am more comfortable with MF, given that it is the only mode I knew... also, AF feels like driving an automatic transmission, can help but think I am missing out on half the fun and control possibilities. What do you use for everyday shooting?

To be honest, I've always felt that manually focusing an AF lens is a bit like buying a new car and then pushing it

Why not just use and enjoy the automation? (same goes for metering etc). Sure, there are times then AF doesn't work well, but for the majority of the time, where's the fun in making things harder?

[nikko]

RE PURCHASING LENS FILTERS - UV, POLARIZERS ETC. I can't find any critical references/reviews of filter glass quality when purchasing same. Any ideas where we can get some test reviews? Thanks.