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02-18-2019, 12:07 PM - 1 Like   #31
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This might help with the light loss & DoF discussion. Same light on the ruler, 1:1 mag in each shot. DFA100mm@2.8 on bellows in the top photo. DFA100mm & DCR250 in the bottom two, f/5.6 in the middle, f/2.8 in the bottom (apologies as it appears I bumped the ruler and slightly increased the angle, but it is still very representative of the DoF).




QuoteOriginally posted by photoptimist Quote
Actually, BrianR is right and it is the laws of optics and physics that creates the differences between tubes and close up lenses.
My own photography education is pretty random, some of it having been scrawled on the sides of cereal boxes or bathroom stalls. I try to keep an open mind that I could be utterly wrong about pretty much everything, so I always take it as a good sign when you agree with me, or what you say jibes with what I think I know

02-18-2019, 12:18 PM   #32
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QuoteOriginally posted by UncleVanya Quote
You can add a macro add on lens like the raynox dcr-250 or 150. The extreme back site memtioned earlier can roughly indicate the final ratio.
Huh. The Raynox suddenly becomes more interesting to me. I've always assumed it would degrade the 100WR's images. Apparently it does not.
02-18-2019, 12:26 PM - 3 Likes   #33
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QuoteOriginally posted by gatorguy Quote
Huh. The Raynox suddenly becomes more interesting to me. I've always assumed it would degrade the 100WR's images. Apparently it does not.
Doundounba is a master of this combo, if you haven't already trawled his flickr stream go back to his post in this thread. Raynox should probably give him a commission

For reference, I made a little chart showing the magnification & working distance of the dcr250 when coupled with the dfa100mm you might find useful. Calculators are handy but do make assumptions about simplified lens constructions, this is based on practical tests:

Magnification of DFA100mm + Raynox 250 - PentaxForums.com
02-18-2019, 01:39 PM   #34
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Big thumbs up Brian!

02-18-2019, 02:54 PM   #35
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Very interesting. We still do not agree so I have to perform some extra tests. (I suppose that some glow-worms were hidden in my extension tubes and skewed my measures, I'll have to clean them).
02-18-2019, 03:27 PM - 1 Like   #36
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QuoteOriginally posted by tryphon4 Quote
Very interesting. We still do not agree so I have to perform some extra tests. (I suppose that some glow-worms were hidden in my extension tubes and skewed my measures, I'll have to clean them).
Nothing I said disagrees with your extension tube tests, just how you've said close-up filters affect things. Throw your Raynox into the mix, and try it out. Be clear in the settings of your macro lens + Raynox and what magnification you're getting, metered light reading, etc.
02-20-2019, 10:33 AM   #37
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I performed a quick test yesterday: Tamron 90mm F/2.8 macro (272E) + DCR-250 versus Tamron 90mm F/2.8 macro (272E) + extension tube, in the same conditions (same magnification, same light, same aperture, same ISO setting).
The shutter speed, in the first configuration, is about 2x the second one. So the extension tubes really eat half of the light.

This result questions my previous tests, I'll have to perform a new batch of test to compare close-up to extension rings with different lenses.

By the way, at the maximum magnification with the DCR-250, the working distance is shallow. With a 50mm I wonder whether a DCR-250 will be useable or not.
As I do not own a 50mm macro, the question remains open.
In general, it is preferable to use extension tubes with short focal length lenses and close-up with long focal lenth lenses, for 2 good reasons:

- a close-up, like a reversed lens, decreases the focal length of resulting setup.
- the mecanic register (provided by extension tubes, bellows etc.) increases the magnification, but this increase is inversely proportional to the focal length.

Last edited by tryphon4; 02-20-2019 at 10:44 AM.
02-20-2019, 11:08 AM - 1 Like   #38
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QuoteOriginally posted by tryphon4 Quote
By the way, at the maximum magnification with the DCR-250, the working distance is shallow. With a 50mm I wonder whether a DCR-250 will be useable or not.
As I do not own a 50mm macro, the question remains open.
It's been on my to-do list, so I figured I'd check it off. Detailed results are here: Magnification of DFA100mm + Raynox 250 - PentaxForums.com

At min. focus distance, the dfa50mm&DCR250 will give 1.32X magnification and a working distance of about 25mm. At infinity focus, it's 0.42x mag. and 111mm working distance (measurements are approximate!).

It's not a combo I'd ever go out of my way to use. As you say, closeup filters are better suited on longer focal length lenses, and the dfa100mm being the size it is, I'll virtually always have it with me.

02-21-2019, 07:22 AM   #39
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A big thank you to BrianR, tryphon4 and photoptimist for the enlightening discussion on the relative effects of tubes vrs diopters with respect to magnification, light and aperture! One of the nicest, most informative discussions I've read on PF!

This is stuff I did not know explicitly, but totally corresponds with the intuitive knowledge of the Raynox I had developed. Meaning that it's bright as hell, but you need to stop down like crazy. I totally did not know that the Raynox reduces the effective aperture. The upside is that you need very low flash power at a given magnification, which helps the flash keep up when shooting focus stacks at 8.3fps... I guess the downside is that if you were using tubes, you might not need to stack at all for some shots. This is super useful to understand! I just might actually try tubes again for some frontal portraits...

QuoteOriginally posted by BrianR Quote
Doundounba is a master of this combo, if you haven't already trawled his flickr stream go back to his post in this thread. Raynox should probably give him a commission
Haha! Thanks!! Sometimes I dream that they would license some of my images for their publicity and I would at least recoup the (very minimal) cost of the Raynox. On the other hand, of everything I've purchased in photography equipment, it's definitely the item that has given me the most bang for the buck...

Last edited by Doundounba; 02-21-2019 at 07:47 AM.
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