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10-15-2010, 11:25 PM   #16
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QuoteOriginally posted by yeatzee Quote
Or take a lot of thinking and DIY work
Exactly! Even the pop up flash with a home made diffuser (made from house hold items) could work wonders.

10-15-2010, 11:25 PM   #17
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QuoteOriginally posted by tomwil Quote
I had recently purchased a Sigma 50mm macro, and am also interested in increasing its working distance at 1:1. I will probably have to eventually upgrade to the Tamron 90mm.

Hmmm...that lens, watch, lens case, place mats, and table look familiar! Why indeed! It is my table, my place mats, my lens case, my watch, my lens, and MY PHOTO!


Steve
10-15-2010, 11:32 PM   #18
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To the OP...

A couple of suggestions...
  • Raynox on a tele zoom
  • M42 tele prime on bellows or extension tube

Or simply crop the hell of of something taken with your FA 77/1.8 (See below)


Taken with FA 77/1.8, no bellows, no tubes, no attachments


Steve
10-16-2010, 01:33 AM   #19
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A note to those suggesting lens-reversal setups:

OP wants "greater working distance" and the only way to achieve that with lens reversal is to use a long-register lens. Some Bronica & Mamiya MF lenses have registers in the 100-110mm range, but I don't think those are readily available cheap. Lens reversal with common SLR glass, on extension or stacked, gives a working distance under two (2) inches. That's great if you want to work that close, not so great if you don't.

And that's why I recommend extension (tubes and bellows), and enlarger lenses in the 80-140mm range. Such a setup can do general (non-macro) work, and can give 1:1 or greater magnification from 3-5 inches distance. And a good setup with several lenses can be assembled for well under US$100. The only trick is lighting without aperture automation. If OP has a controlled-light studio setup, that's no problem.

10-16-2010, 03:14 AM   #20
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thanks so much guys. it's been a great help!! time to start trolling ebay for tele-primes, enlarger lenses and bellows

What's the image circle like on enlarger lenses? If i can find bellows with rise/fall or shift movements and use an enlarger lens how much can i move before running into the edge of the image circle?

thanks!!
10-16-2010, 05:12 AM   #21
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QuoteOriginally posted by scathontiphat Quote
thanks so much guys. it's been a great help!! time to start trolling ebay for tele-primes, enlarger lenses and bellows

What's the image circle like on enlarger lenses? If i can find bellows with rise/fall or shift movements and use an enlarger lens how much can i move before running into the edge of the image circle?

thanks!!
For a simple lens, the image circle depends only on how far the lens is from the image plane and for macros with long lenses, this is quite far.

Natural vignetting limits the image circle of a simple lens to about:

image-circle-diameter=focal_length(1+magnification)

This is based on light intensity at the edge of the image circle being down about 1/3.

I think your idea of getting a tilt capable bellows & enlarger lens is a good one, but such bellows are costly and hard to find (a Nikon PB-4 might be adapted easily.) I added a tilt adapter to my bellows instead.

Dave

Last edited by newarts; 10-16-2010 at 05:23 AM.
10-16-2010, 05:29 AM   #22
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QuoteOriginally posted by stevebrot Quote
Hmmm...that lens, watch, lens case, place mats, and table look familiar! Why indeed! It is my table, my place mats, my lens case, my watch, my lens, and MY PHOTO!
Steve, thanks for the use of the photo. It showed exactly what I was experiencing.

Unfortunately, the forum doesn't let me link to each individual review (which had your photo), so I could only link to the review page, which is where you go if you click on the photo.

Sorry! In hindsight, should have given credit in my original post.
10-16-2010, 10:48 PM   #23
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QuoteOriginally posted by scathontiphat Quote
thanks so much guys. it's been a great help!! time to start trolling ebay for tele-primes, enlarger lenses and bellows
Heh heh, another successful case of LBA infection! Good work, comrades! Our masters at KEH will be pleased!

QuoteQuote:
What's the image circle like on enlarger lenses? If i can find bellows with rise/fall or shift movements and use an enlarger lens how much can i move before running into the edge of the image circle?
Different EL's have different image circles. Typically, shorter focal length EL's were/are used with smaller negatives, longer EL's with larger negatives. I recall printing from 6x6 negs with a 75mm and 135's with a 50mm. I mention this because usable neg size indicates the image circle size. I just now roughly tested a 50, 90, and 160, and they seem to have image circles about 3/4 of their focal lengths, but that may or may not be a coincidence.

In earlier days, kits were sold as dual-purpose cameras and enlargers. Print with the same gear you shot with! Such were rough because the lenses typically were NOT the edge-to-edge sharp flatfield glass we expect in EL's. But the principle holds.

Remember that EL's longer than 75mm can focus to infinity on bellows. But also remember that T&S works best with shorter lenses. A 35mm EL meant for 135 frames (on a small enlarger) might work on a T&S bellows if not extended too far, but it'll never reach infinity. For your purposes that may be irrelevant. But I'm afraid that if small-scale T&S work was easy, we'd all be doing it.

10-16-2010, 10:52 PM   #24
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QuoteOriginally posted by tomwil Quote
Sorry! In hindsight, should have given credit in my original post.
No problem...penance done!


Steve
10-17-2010, 02:58 AM   #25
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QuoteOriginally posted by RioRico:
...I just now roughly tested a 50, 90, and 160, and they seem to have image circles about 3/4 of their focal lengths, but that may or may not be a coincidence....
No coincidence. As I said in the posting above, for infinity focus and 2/3 relative brightness at the edge,

image-circle-diameter=focal_length

For an image circle defined by a relative edge brightness of 3/4, the relationship is:

image-circle-diameter~(3/4)focal_length as you observed.

Your observation is an easy one to remember, the brightness of the image is 3/4 at a diameter of 3/4 the focal length (actually distance from the lens rather than focal length).

This is a result of simple geometric "natural vignetting" in which off-axis brightness falls as the fourth power of the cosine of ray angle.

I believe it is an important reason why "normal lenses" are such that the focal length is close to the sensor diagonal (image circle):
1) if focal length is much smaller than sensor diagonal (sensor diagonal > image circle), sensor area is wasted (sensor edges aren't illuminated.)
2) if focal length is much larger than sensor diagonal (sensor diagonal < image circle), information at the scene edge is lost (predators creeping in are missed.)

Other kinds of vignetting can be a problem too, like the lens tube being too small in diameter, hence interfering with the cone of light coming from the lens ("mechanical vignetting").

Dave

PS I'll bet that a "normal lens" for a raptor differs from that for a rodent because a raptor needs to identify prey far away,while a rodent needs to watch for threats from any direction.

Here's a quote from http://www.raptorrecoverynebr.org/whatrap.htm

"The structure of a hawk's eye is very unique in that each eye functions like a telescope. The lens is flattened and placed farther from the retina, giving it a long "focal length" which produces a large image."

Last edited by newarts; 10-17-2010 at 07:09 AM.
10-17-2010, 11:09 AM   #26
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QuoteOriginally posted by newarts Quote
No coincidence. As I said in the posting above, for infinity focus and 2/3 relative brightness at the edge,

image-circle-diameter=focal_length
I was going to object, noting that my 10-17 and 16/2.8 and 21/3.8 lenses produce image circles rather greater than their FL's, else they couldn't fill HF frames let alone FF. Then [lightbulb goes off inside head!] I realized: retrofocus groups! The RF elements spread the image to project it onto the required frame. And EL's don't have RF groups, so the IC:FL relationship holds for such simpler lenses.

Out of curiosity, where do you derive that relationship? I've just scanned a pile of optics PDFs and the term "image circle" is hard to find. My rough gargling for IMAGE.CIRCLE FOCAL.LENGTH hasn't turned up anything. Can you point me to a reference?
10-17-2010, 12:06 PM   #27
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QuoteOriginally posted by RioRico Quote
I was going to object, noting that my 10-17 and 16/2.8 and 21/3.8 lenses produce image circles rather greater than their FL's, else they couldn't fill HF frames let alone FF. Then [lightbulb goes off inside head!] I realized: retrofocus groups! The RF elements spread the image to project it onto the required frame. And EL's don't have RF groups, so the IC:FL relationship holds for such simpler lenses.

Out of curiosity, where do you derive that relationship? I've just scanned a pile of optics PDFs and the term "image circle" is hard to find. My rough gargling for IMAGE.CIRCLE FOCAL.LENGTH hasn't turned up anything. Can you point me to a reference?
Look for "natural vignetting", like at Vignetting or Testing Camera Lenses - Vignetting - Bob Atkins Photography I can't recall ever having seen "Natural Vignetting" and "Image Circle"explicitly related! nb..Here's one! http://books.google.com/books?id=cuzYl4hx-B8C&pg=PA134&lpg=PA134&dq=natural+...circle&f=false

It is geometric optics.
1) Light intensity falls with the inverse square of distance from a source, and the inverse distance from the aperture to the sensor changes as cos_squared(angle from optic axis).
2) If you look at an aperture from an angle , the apparent area of the aperture falls as cos(angle from normal =angle from optic axis)
3) If light strikes a sensor plane at an angle, the intensity is reduced by cos(angle from from normal = angle from optic axis)

Putting these factors together yields the "Natural Vignetting" equation:

Relative_Intensity = Cos_fourth_power(angle from optic axis)

The angle from the optic axis can be expressed in terms of image circle diameter and distance from the aperture as:

Angle_from_optic _axis = arctan(Image_circle_diameter/2focal_distance)

I think Natural vignetting is basically why the registration distance for most all cameras is similar to the image plane diagonal (image plane diagonal=image circle diameter). (nb RioRico points out that this is incorrect - SLR's registration distance is large to allow for mirror motion.)

I think a good way to understand RetroFocus groups is that they serve to move the aperture away from the image plane specifically to avoid natural vignetting. It contributes to the cost of wide angle lenses.

Dave

PS I think this simple, physical phenomenon explains a lot about why optics systems are the way they are in both natural and technological worlds.

here's some numbers for illustration:
at image_diameter=focal_distance, angle from optic axis = arctan(1/2)=26.56 degrees.
at 26.56 degrees, relative brightness=cos^4(26.56)=0.64 ie, about 2/3

at image_diameter=3/4 focal distance, angle from optic axs = arctan(3/8)=20.56 degrees.
at 20.56 degrees, relative brightness=cos^4(20.56)=0.77 ie, about 3/4

Last edited by newarts; 10-18-2010 at 05:50 AM.
10-17-2010, 04:23 PM   #28
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I wonder if a Sigma 180/5.6 macro would work for you. I think it only goes to 1:2 but a short extension tube would fix that aspect. Working distance is decent compared to other options mentioned. No idea how much one would cost in your part of the world. I bought one for $200AUD recently and our lenses are always higher priced than anywhere else.
10-17-2010, 05:00 PM   #29
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A Raynox 150 on your DA 77 will yield about 0.56x at a working distance of about 208mm.

A Raynox 250 on your DA 77 will yield about 0.84x at a working distance of about 125mm.

I recommend trying the $50 Raynox 150: a display enlargement of 1.78x should give good image quality at the 1:1 magnification you seek. All the automatic functions of your lens will continue to work including p-ttl flash. The working distance will be a little more than the 200mm for a 100mm macro lens at 1:1.

It will be as easy to use and challenge the image quality and ease of use of a fully automatic 100mm macro lens (except for autofocus which is of little use at these magnifications).

Dave

PS see the Raynox Macro Club on this forum for examples of image quality: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/74221-raynox-macro-club.html

Last edited by newarts; 10-18-2010 at 05:37 AM. Reason: typo in writing Raynox magnificatons 1.56->0.56 etc.
10-17-2010, 07:57 PM   #30
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QuoteOriginally posted by newarts Quote
No coincidence. As I said in the posting above, for infinity focus and 2/3 relative brightness at the edge,

image-circle-diameter=focal_length

For an image circle defined by a relative edge brightness of 3/4, the relationship is:

image-circle-diameter~(3/4)focal_length as you observed.
This is quite the thread hijack, but you have got me confused here. I own two large format camera lenses, a 90mm and a 150mm. The 90mm has an advertised image circle of 221mm (102 degrees) at f/22 and the 150mm has an advertised image circle of 231mm (75 degrees). Neither lens has significant light fall-off at those distances, though it does fall off quickly beyond those numbers. Neither of these lenses are telephoto (in the proper sense of the term) and I don't think that they employ retrofocus groups though they may.


Steve

Last edited by stevebrot; 10-17-2010 at 08:02 PM.
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