Best super zoom camera for bird shots? (1 Viewer)

RJM · Apr 26, 2009

Hey, I am always willing to be schooled by those who can teach. You failed to give me a valid test to consider in support of your theory.

FWIW, I understand camera lens aperture is determined by the diaphram opening at the REAR of the lens assembly, not the size of the objective. In the case of the FX28 the diaphram opening will never be larger than 20mm (fl86.4mm/F4.4= 19.6) at the telephoto end (and always less than 2mm at the wide end!).

There can be many optical reasons why the TCON is big, but I don't think "passing more light" to compensate for a 1.7x increase in focal length is one of them.

Rick

tjsimonsen · Apr 26, 2009

All TCs do "steal" light.
I don't know exactly how much the super zoom dedicated TCs take, but you will need longer exposure time compared to the camera without TC. However, that is NOT the reason why the camera (or more correctly the producer) wants you to report the TC to the camera. As far as I know all modern cameras use TTL metering, so the camera will set the exposure according to the light that comes through the lens (and the TC if it is attached). This is also the reason why you can tape pins on a dSLR TC to get AF (sort of anyways) and still get the correct exposure. There might be other reasons why the camera producer doesn't want you to use a TC combined with certain settings: it might not work well with the macro mode, there might be vignetting at the wider end, and so on. Sometimes producers seem to feel that users hardly know which way to point the camera, and STILL blame the producers when their pictures turn out to be not exactly award winners. By restricting the number of mistakes the users can make, they probably limit the number of complaints they'll get themselves.
I haven't used TC with PS since is I briefly used one with my Nikon Coolpix 4500. Then I simply got around the restrictions by using program mode and not telling the camera that the TC was attached. I had to check that there wasn't too much vignetting, yes. But AF and exposure worked automatically (and perfect).

Thomas

RJM · Apr 26, 2009

tjsimonsen said:
...As far as I know all modern cameras use TTL metering, so the camera will set the exposure according to the light that comes through the lens (and the TC if it is attached). This is also the reason why you can tape pins on a dSLR TC to get AF (sort of anyways) and still get the correct exposure. There might be other reasons why the camera producer doesn't want you to use a TC combined with certain settings: it might not work well with the macro mode, there might be vignetting at the wider end, and so on....

That's right. I use the taped contact trick with my Sigma 150-500mm and Sigma 1.4x TC to get AF functionality. However, the lens' TC-modified focal length and aperture is no longer correctly reported in the Exif data when I do this. While we can hope the TTL metering system is working 100% perfectly without the correct lens information, I also think we can never be 100% sure. Heck, the camera metering is not always right even with it! Isn't that why we have Exposure Compensation?

Anyway, if someone actually did the 3-pic test with the FZ28 and TCON it could give a hint as to what the FZ28 Menu setting is or is not doing. Knowing so would not make a bit difference in the nice pics folks are taking with this setup, but at least the results will can be understood by the optical facts.

cheers,
Rick

hollis_f · Apr 27, 2009

RJM said:
There can be many optical reasons why the TCON is big, but I don't think "passing more light" to compensate for a 1.7x increase in focal length is one of them.

Sorry, I have to disagree. Here's a sketch I did that I hope can help demonstrate my reasoning...

The upper diagram shows an unconverted lens projecting an image circle onto the sensor. There are two obvious things that affect the amount of light hitting the sensor - The width of the front opening of the lens (the bigger this is, the more light hits the sensor) and the size of the image circle (the bigger this is the less light hits the sensor). There are other factors (e.g. how much light gets absorbed by the glass) but they're fairly minor.

On a dSLR a TC sits between the lens and the sensor. It doesn't change the size of the front of the lens, but it does change the size of the image circle. That results is a larger, dimmer, image.

With a P&S you can't put anything between the lens and sensor, so you can't change the size of the image circle. But you can put an extra element in front of the lens. This can do two things - 1. magnify the image and project that magnified image onto the lens proper; 2. Because the front of the TC can be larger than the lens it gathers more light than the lens alone.

In that final situation the brightness of the light hitting the sensor my be brighter, darker or the same as the light without a TC, depending on the magnification factor and the size of the front element of the TC.

hollis_f · Apr 27, 2009

RJM said:
FWIW, I understand camera lens aperture is determined by the diaphram opening at the REAR of the lens assembly, not the size of the objective.

If only that were the case, then my 300 f2.8 wouldn't need such a huge mass of glass. They could use the same lenses as my old 75-300 (f5.6 @ 300mm) and just put a larger opening at the rear of the lens.

hollis_f · Apr 27, 2009

A Test

Wow! Amazing the sort of stuff one leaves lying around on the interweb. Back in March 2005 I had just bought a TCON-17 for use with my Nikon 8800. Attached are two images, the first is the lens alone at 350mm equiv, the second is with the TC at 595mm equiv. Both were done in AV, f 5.2 The first image had a shutter speed of 1/100, the second (with TC) was 1/125.

Now a 1.7 TC on a dSLR would mean a drop in light of one-and-a-bit stops. This is obviously nowhere near that, in fact this and my experience with the TC is what led me to be fairly sure that this TC on that camera didn't reduce the light hitting the sensor.

RJM · Apr 27, 2009

Frank I wrote the message below as you were posting your pics. Unfortunately, the exif data has been stripped from them so I am going bet that camera's ISO increasing is why the shutter speed did not by at least 1 stop.
---------------------

Hi Frank,

Thanks for taking the time to make the sketch. But it seems you are reasoning a camera lens like a refracting telescope. A camera lens doesn't really work like that, especially a zoom lens. Camera lens aperture and thus the amount of light leaving the lens is determined entirely by the iris-like diaphram behind the lens group opening and closing.

With a prime lens, the iris-aperture opening will be largest when the lens is "wide open." But with a long focal length zoom, the iris-aperture physical opening is actually smaller with the lens zoomed out (WIDE) than it is zoomed in (TELEPHOTO). I know it seems counter-intuative, but watch what happens to the iris of your superzoom camera when it zooms in-out. Zoomed out, the iris is a pinhole. Zoomed in, it will be about the size of your thumb.

This is because lens aperture is the key metric for a refracting telescope whereas focal length is the key metric for a camera lens. All calculations flow from it.

Anyway, if you increase the focal length of a lens but are physically unable to increase its aperture size by the same proportion, and don't change the sensitivity (ISO) of the sensor, the shutter speed has to "give" in order to get the same amount of light hitting the sensor, aka exposure.

Rick

hollis_f · Apr 27, 2009

RJM said:
Frank I wrote the message below as you were posting your pics. Unfortunately, the exif data has been stripped from them so I am going bet that camera's ISO increasing is why the shutter speed did not.

Both at ISO 50 (wow! Did I really have to shoot that low just a mere 4 years ago?).

Full Exif is available by clicking on the thumbnails here.

hollis_f · Apr 27, 2009

RJM said:
Thanks for taking the time to make the sketch. But it seems you are reasoning a camera lens like a refracting telescope. A camera lens doesn't really work like that, especially a zoom lens. Camera lens aperture and thus the amount of light leaving the lens is determined entirely by the iris-like diaphram behind the lens group opening and closing.

Let's stick with primes to make it simpler. Are you saying that the reason a 300mm f2.8 produces a brighter image than a 300 f4 is because the size of the hole at the rear of the lens is bigger? It seems obvious to me that the extra light is because the hole at the front is bigger.

RJM · Apr 27, 2009

Basically, yes. If your lens has an aperture collar look through the rear of the lens as you turn it to F4. The "hole" in the iris-diaphragm gets smaller. The size of the front lens is almost irrelevant in standard photography. Heck a pinhole camera doesn't even need one! The lenses are just there to bring the light cone to focus over the infinite number of distances to the subject. Of course, in order to do this within the physical limits of the focal length/aperture limits of the design, the lens must meet a minimum diameter. The upper limit is bounded by other design criteria. This diaphragm controlling aperture is really a basic camera system concept in photography.

I took a look at the exif data in your pics. First pic was shot in Program Auto with a wonky shutter speed of 10/1021sec. The second pic was shot in Shutter Priority at 1/125sec. Because of the different Exposure Programs, especially the Shutter Priority shot, I feel the test shots are inconclusive.

Rick

hollis_f · Apr 27, 2009

RJM said:
I took a look at the exif data in your pics. First pic was shot in Program Auto with a wonky shutter speed of 10/1021sec. The second pic was shot in Shutter Priority at 1/125sec. Because of the different Exposure Programs, especially the Shutter Priority shot, I feel the test shots are inconclusive.

Rick

They're at the same aperture, same ISO and near-identical shutter speed (1/102.1 vs 1/125 - blame Nikon for wonkiness in the Exif). Different exposure programs (hey, it was 4 years ago, I forgot) makes not a hoot of a difference. They are the same exposure values and they both produced fairly correct exposures of a similar scene.

This, and several other tests I did at the time, were enough to convince me

Review of TCON-17

The effective aperture of the lens/attachment combination stays unaffected

Another BF thread where TCON-17 users state it can be used with no light-loss, and an explanation as to why.

Even used with a dSLR -

I've placed the Olympus TCON-17 on my Nikkor 50mm f/1.4, with
no change in the aperture, ISO or shutter speed, and the exposure of the
photo looked the same as without. The extra light gathering of the very
large front optic seems to almost completely offset the exposure reduction
one would expect by the increase of the focal length.

RJM · Apr 30, 2009

Frank, if you can't understand that it is the opening/closing of the iris-like diaphragm behind the lens group that controls the amount light hitting the sensor/film in photography, and not the size of the front-most lens then we will never reach a consensus.

As for the FZ28 Menu setting, I have determined from other sources it one affect seems to prevent the camera lens from fully zooming out to prevent vignetting.

cheers,
Rick

hollis_f · Apr 30, 2009

RJM said:
Frank, if you can't understand that it is the opening/closing of the iris-like diaphragm behind the lens group that controls the amount light hitting the sensor/film in photography, and not the size of the front-most lens then we will never reach a consensus.

You're right - and wrong.

For any single lens you can change the aperture by opening and closing the diaphragm. That's where you're correct.

But when comparing the maximum aperture of different lenses the size of the hole at the front is what matters. Again, I'll use 300mm primes as an example. The f4 has a diameter of 90mm. That gives an area of 25442 sq mm. The f2.8 has a diameter of 128mm and an area of 51462 sq mm. Oh look, that's exactly twice the light-gathering area - which is why it's a stop faster - because twice the area gathers twice the light.

Anyway, I'm off for a long weekend now. So I'm going to unsubscribe from this thread and stop banging my head against a brick wall. One thing I learned from 13 years of teaching is when to give up.

RJM · Apr 30, 2009

By different lenses, you must mean different focal lengths in order for your theory to hold. But if the focal lengths are equal, and the F2.8 lens with its larger front element has been stopped down to the same F4 of the smaller lens, it will pass exactly the same amount of light to the sensor.

To sum up: an F2.8/300mm lens stopped down to F4 EQUALS a F4/300mm lens wide open.

Rick

hollis_f · Apr 30, 2009

RJM said:
By different lenses, you must mean different focal lengths in order for your theory to hold. But if the focal lengths are equal, and the F2.8 lens with its larger front element has been stopped down to the same F4 of the smaller lens, it will pass exactly the same amount of light to the sensor.

To sum up: an F2.8/300mm lens stopped down to F4 EQUALS a F4/300mm lens wide open.

Rick

Well, duh!

Now please tell us what makes an f2.8/300mm lens capable of being used at f2.8 whereas an f4/300mm lens cannot. Is it the size of the front element being twice as large (what I think) or is it the size of the hole in the diaphragm being twice as large (what you think)?

RJM · Apr 30, 2009

We're going circles!!

Of course a F2.8/300mm lens will pass twice the light as an F4/300mm lens when both are wide open! And for the record, the actual aperture at the diaphram is 300/2.8=~107mm vs, 300/4=75mm.

But I think you just agreed that any two lenses at the same focal length opened up to the same F stop will pass the same amount of light??? So why continue to be fixated on the size of the front lens? It is obvious the iris diaphram opening is the only aperture that matters!

Do you actually think the light coming from the outer 19mm of the F2.8/300 zigzags its way around the 75mm opening of the diaphragm as it intrudes into the light cone at F4!!!? I hope not!!

When your F2.8/300mm lens is stopped down to F4 it only "see" light coming from the centermost area of the 128mm lens, not the periphery. That is one of the reasons most lens get sharper when stopped down. They use the "best part" of the glass. Get it?

If not, then lets end this.
Rick

Ultra Lite · May 1, 2009

Hollis and Rick,

I've read and re-read your posts. For the life of me I can't see any disagreement. It seems like you are both talking past each other.

What, succinctly, do you two believe is in dispute?

Henry B · May 1, 2009

So , what is the best super zoom camera for bird shots.

twolf · May 1, 2009

Not a scientific test by any means, but here are two shots taken with Panasonic FZ-50 at my bird feeder back in November.

The first is with the bare lens, second with TCON17 attached.

Both shot in manual mode at the same settings (ISO100, 1/160, wide open). They're less than a minute apart. EXIF should be available.

Tele-adapters are built quite differently from TCs for DSLR (which act like a standalone straight telephoto group).
These ones loose very little light if any, insignificant to the exposure value.

RAH · May 1, 2009

Ultra Lite said:
Hollis and Rick,

I've read and re-read your posts. For the life of me I can't see any disagreement. It seems like you are both talking past each other.

What, succinctly, do you two believe is in dispute?

Well, the disagreement started when RJM said that the TCON-17 cut down on the light. I disagreed and said that the TCON-17 does not cut down on the light. Hollis agrees with me (as does Olympus literature). The rest of their discussion kind of flowed from that basic question - does the TCON-17 cut down on the light or not?

Best super zoom camera for bird shots? (1 Viewer)

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