[ctron]

I currently use the K-x with an M42 200mm SMC Tak and a reversed Minolta MD 50mm 1:2 lens on front of the 200mm. This is what I had available and close at hand, but no cost because I already had them. Initial indoor shooting quickly showed that I was going to have to use flash, so I brought out some old Wein peanut slaves (which I still had in storage from my hummingbird days), and some Vivitar 283 flashes, also each equipped with a Wein peanut (the flashes are set at 1/16 power). Results so far have been ok, but lack contrast. About the only thing inside this time of year are the small, black house ants. With this set up, I am able to get about 3/4 of an ant across the field, but the result seems soft. I don't think it's a focus issue as I tried all sorts of manual micro adjusting of the subject/ lens-- more of a contrast issue I would guess. I have the lens aperture almost closed on the Minolta, which allows great DOF, but I just can't seem to get the sharpness I want and I would appreciate any suggestions. I can partially compensate for softness in Photoshop with unsharp masking, etc, but still not as sharp as I'd like. I do have a Raynox DCR-250 on the way as I write, but I'm not sure how much difference this will make in front of the 200mm lens versus the Minolta, or even across the front of the Minolta because if I'm already having softness in the system, all the '250 will do is amplify it. The goal is for greater than lifesize. In a small, black ant for example, I'd like to fill at least half the Pentax FOV with the head only.

Appreciate any help and advice.

Thanks,
C

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Last edited by photolady95; 01-28-2016 at 08:27 PM.

[WPRESTO]

You may find that the Raynox will give better IQ than the reversed Minolta, but no guarantee. Also, try stopping down the base lens (200mm) instead of the reversed lens. Sometimes this will impact IQ, sometimes it makes no difference.

[baro-nite]

A 50mm lens reversed onto a 200 gives you 4:1 magnification. Effective aperture depends on magnification; rule of thumb is to multiply the nominal aperture (setting of the aperture ring, in this case on the 50) by (m+1), in this case 5. So, if you have the 50 stopped down to f/22, you have an effective aperture of around f/110, and softening due to diffraction will be severe. You'd be as well off shooting at much lower magnification and cropping; as it is you are getting what is known as empty magnification -- larger image, but no extra detail.

Try some tests on a static subject, using different aperture settings. At 4:1 you'll probably find the best aperture range to be around f/5.6 or f/6.7. Yes, depth of field is miniscule. Hence the widespread use of focus-stacking software for extreme macro. You might still get acceptable results up to f/8 or so, but again, you are getting into empty magnification at this point.

It's hard to come up with a good test target for that much magnification, but lepidopteran wings are pretty good, in addition to being interesting macro subjects. Good because they are somewhat flat as well as having very fine structure.

[Edit]: Here's an example. Different setup, but similar subject size; this is a 1:1 shot on the Pentax Q, so it's similar to a 4:1 shot on APS-C. It's from a stack of 12 exposures. The nominal aperture is f/4. It's the wing of a tiger swallowtail.

[ctron]

Thanks, guys, I was going to start a new thread with a separate issue, but I'll try asking here first. After a lot of trial and error over the past week, I settled on trying to use the Pentax KX 18-55mm kit lens in reverse (at 18mm) on 2.25" of macro tube. When I measured this, I am getting roughly 7.5:1. However, the big problem I've been having is lack of contrast and some sort of flare that emanates from the center of the lens. It gets worse when I try and use flash (almost a must when photographing indoor macro subjects). I managed to negate most of the center contrast loss by making a small lens hood and then an internal cylinder of black paper between the camera and lens, the length of the macro tubes. However, a general contrast loss throughout the image is still present in each shot. If you look at a histrogram, the bulk of the x-axis lies well away from the shadows and well away from the top end. I've tried moving the flashes into all sorts of positions and adjusting flash power, different diffusion tactics, but the lack of contrast is still present. As you know, when the lens is used in reverse there's no way to adjust aperture, so I've been inserting small toothpics when I want to increase or decrease. The sweet spot of the lens seems to be when 2 toothpicks are inserted, not sure what f value this is, but sharper than either fully open or closed aperture. However, I can't get a very contrasty result. I'm beginning to think that since the lens lacks the same coatings on this side compared to when used normally, there are all sorts of reflections occuring and cutting contrast, but i'm out of ideas, so if anyone has tried this configuration, came up against this problem, and was able to solve it please share! One note, I AM able to get much better results with controlled studio lighting for macro instead of flash, but sharpness then suffers a bit and of course it's next to impossible to get a live image at 1/4 sec shutter speed. Thanks!

[WPRESTO]

Zoom lenses, reversed or not, are generally not very good for macro. The lack of contrast may in part be caused to the large number of elements in a zoom. The lens configuration in a zoom is also, I believe, not conducive to performing well in reverse position. I would predict much, MUCH better results with a plastic-fantastic 50mm f1.8, now going for about $80 new, combined with almost any close-up filter, and especially in reversed position.

Some SFL lenses were noted for performing very well in reversed position, perhaps the most notable being Tessar-formula lenses, so much so that there were macro-Tessars that came with an inverted sequence of elements.

[baro-nite]

With extreme macro I've found you just have to try things out, and some things won't work well. For example, the Pentax-A 50/2.8 macro lens I used for the above shot of a butterfly wing, when mounted normally on a 25mm extension tube suffers from low contrast just as you're describing. But reversing the lens onto a short extension tube gives the same 1:1 magnification and works great. There are many ways to achieve a given magnification, so rather than worrying about why one setup is poor, I just focus on finding setups that perform well.

7.5:1 on APS-C is extreme indeed. You need something around f/2 to avoid excessive diffraction softening at that magnification, and the only optics that perform well enough at that aperture are microscope objectives. Depth of field is measured in microns, so specialized hardware for focus stacking is practically necessary.

Check out photomacrography.net if you haven't already.

Here's 10:1, using a 10x microscope objective mounted in front of a 200mm lens as a "converging lens" (the microscope objective is of the "infinite" type, and requires a converging lens) on the Pentax K10D. It's a bluebird feather, based on a stack of 68 exposures:



I've used the same objective with a 150mm converging lens for 7.5/1, and with a 50mm converging lens for 2.5/1 on the Pentax Q. When I want magnification in the range of 4:1 to 6:1, I use

[TER-OR]

Remember when you're reversing lenses like that you're essentially making a microscope. You're going to need a LOT of light, you're focusing on a very small area. That will let you keep your ISO down.