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04-03-2012, 11:56 AM   #46
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QuoteOriginally posted by Philoslothical Quote
By far the easiest way to figure out this TC would be for Gibby to take a couple shots of the millimeter gradations on a measuring tape, or ruler.
Exactly what kind of process would you use to do this? I might do it if it isn't too much of a pain. :-)

04-03-2012, 12:13 PM   #47
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Not much of a process involved. Just lay out a tape measure flat, or a ruler, you want one with millimeters either way. Shoot it head on (I find straight down works well, like, with the tape on a tabletop) with the tape's edge on the horizontal axis of the frame. The shots don't need to be pretty, or perfect focus, you just need to be able to count how many millimeter marks are in the frame. If you see 24mm (technically, 23.6, I think) then you're shooting 1:1. If you see 12, then it's 2:1, 6mm visible would mean 4:1, etc.

Personally, I find it easier to do this, and then corroborate it with math, rather than just trust my math skills (Ha!) alone.
04-03-2012, 12:25 PM   #48
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Yep. I'll probably do that a bit later.
04-03-2012, 12:46 PM   #49
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QuoteOriginally posted by GibbyTheMole Quote
Yep. I'll probably do that a bit later.
If you do it please keep track of the working distance. Thanks, Dave.

04-03-2012, 02:05 PM   #50
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QuoteOriginally posted by GibbyTheMole Quote
Yep. I'll probably do that a bit later.
QuoteOriginally posted by newarts Quote
If you do it please keep track of the working distance.
Easy way to do this: Set a short (target) ruler against a book or something. Hold a longer ruler perpendicular to it, and hold the camera against the latter ruler. Switch LiveView on. Move the camera down the extended ruler; when the target ruler comes into focus, SNAP! and note the distance from the objective to the target. Count millimeters in the snapped shot and divide by 24. Now you have both the magnification and the actual working distance. For the frame-to-subject distance, measure back from the objective to the sensor frame. Piece of cake! Easy as pie!
04-03-2012, 03:07 PM   #51
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OK... Here's the data:

Pentax-A f1.7 50mm + 3x TC:
Working distance from subject to front of lens: 4 3/4"
17mm from left to right edges of photo
According to Philosothical's numbers (23.6 divided by mm from edge to edge), it figures out to be 1.38:1

Promaster 1:1 100mm macro lens

By itself:
Working distance from subject to front of lens: 4 3/4"
13mm from left to right edges of photo
According to Philosothical's numbers, it figures out to be 1.8:1

100mm macro lens with 3x TC:
Working distance from subject to front of lens: 5"
7.5 mm from left to right edges of photo
According to Philosothical's numbers, it figures out to be 3.14:1

The working distance stays roughly the same no matter what. (4 3/4" to 5" from ruler surface to front of lens.)

And I was wrong about the TC's focusing ring making a big difference. It doesn't make much difference at all whether it's set to infinity or 1:1.

And to be honest, the more I think about it, I'm thinking the shot of the flies was without the TC... Just the 100mm lens & flash. Otherwise, those would have been some extraordinarily tiny flies humping each other. That also would be a ridiculously sharp photo for a 3x TC... I'm thinking I shot it with just the bare lens. So I'm back to being undecided on what thing if any, to get. I might not even need that extreme degree of magnification. Plus, it's a real PITA to focus handheld with the TC on there.

Last edited by GibbyTheMole; 04-03-2012 at 03:39 PM.
04-03-2012, 04:52 PM   #52
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QuoteOriginally posted by GibbyTheMole Quote
Promaster 1:1 100mm macro lens

By itself:
Working distance from subject to front of lens: 4 3/4"
13mm from left to right edges of photo
According to Philosothical's numbers, it figures out to be 1.8:1
!!

That is... crazy for an off brand 100mm. How can that even be?

All interesting info, thanks for testing/sharing.
04-03-2012, 05:04 PM   #53
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QuoteOriginally posted by Philoslothical Quote
That is... crazy for an off brand 100mm. How can that even be?
It may be off-brand, (made by Cosina) but it's optically superb. I'm completely satisfied with the IQ. Here's a review of the optically identical AF version. The AF version has a lesser build quality, and I prefer MF for macro anyway.

It's a 1:1 macro lens on a film (or full frame) camera. I'm guessing the APS-C sensor's crop factor on the Pentax cameras probably accounts for the extra.

04-03-2012, 05:10 PM   #54
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QuoteOriginally posted by GibbyTheMole Quote
I'm guessing the APS-C sensor's crop factor on the Pentax cameras probably accounts for the extra.
No, magnification of a given lens doesn't change with sensor size. Your finding is most unexpected.

Edit: Then again, a 3x TC that increases magnification by less than 2x is also unexpected.

Last edited by baro-nite; 04-03-2012 at 05:15 PM. Reason: correction (deletion); addendum
04-03-2012, 05:14 PM   #55
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QuoteOriginally posted by GibbyTheMole Quote
It may be off-brand, (made by Cosina) but it's optically superb.
I didn't mean to disparage it, and didn't know it was re-branded Cosina either. In a few threads I've seen names like Promaster described as more budget/low end lenses, but it makes sense there would be exceptions. What did it cost, if you don't mind my asking?

QuoteOriginally posted by GibbyTheMole Quote
I'm guessing the APS-C sensor's crop factor on the Pentax cameras probably accounts for the extra.
Interesting, but I'm not sure it works. If I put a 50mm on 50mm of tubes, I should get 1:1 regardless of sensor size. The crop should be just that, chopping the border off and using the center portion of the lens more. I bet Rico can explain it, if it's something else.
04-03-2012, 05:14 PM   #56
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QuoteOriginally posted by baro-nite Quote
No, magnification of a given lens doesn't change with sensor size. Your finding is most unexpected.
So if I took the same shot on a FF camera, there would still be 13mm from edge to edge? Since the apparent image size increases 1.6x with any other lens, I would think the same would hold true for a macro lens. Am I missing something?
04-03-2012, 05:17 PM   #57
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QuoteOriginally posted by GibbyTheMole Quote
So if I took the same shot on a FF camera, there would still be 13mm from edge to edge?
Nope. It would be scaled up to maintain the same ratio for the full frame width.
04-03-2012, 05:22 PM   #58
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QuoteOriginally posted by Philoslothical Quote
I didn't mean to disparage it, and didn't know it was re-branded Cosina either. In a few threads I've seen names like Promaster described as more budget/low end lenses, but it makes sense there would be exceptions. What did it cost, if you don't mind my asking?
Oh, I know... Cosina makes the same line of lenses also branded as Promaster, Phoenix, Voigtlander, Vivitar, and in a few instances, Samyang. It is a budget lens, with a new price of about $135. I paid $60 for a pristine used copy a couple of weeks ago here on the forum. I've had a few of those Cosina/Promaster/whatever lenses. Some are sub-par, some are actually good performers, and in at least this case, at least one is outstanding.
04-03-2012, 05:23 PM   #59
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QuoteOriginally posted by Philoslothical Quote
Nope. It would be scaled up to maintain the same ratio for the full frame width.
Ah... I'm a newbie when it comes to the macro stuff. How bout I just take a shot with just the lens, upload it & let more knowledgeable heads figure it out? I'll do that now.
04-03-2012, 05:24 PM   #60
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QuoteOriginally posted by GibbyTheMole Quote
Since the apparent image size increases 1.6x with any other lens
Magnification refers to actual image size at the sensor. So, as Philoslothical says:

QuoteOriginally posted by Philoslothical Quote
Nope. It would be scaled up to maintain the same ratio for the full frame width.
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