Astrophotographer contemplates extreme macro

[AtmosFearIC]

Until recently I've just been dabbling with macro with my Nikon D7200 and what is probably the first iteration of a Tamron 90mm macro F/2.8.

Being primarily in astrophotography (I love the technical aspect of both this and macro stacking) I started considering merging equipment from the two fields and delving into the world of extreme macro.
Until this weekend I had just been considering getting a Zeiss 100mm macro (only 1:2) and adding extension tubes. This weekend however it came to my attention (lots of research) that maybe a finite objective would be the way to go.

I am still yet to actually decide on the magnification I am interested in, will probably start with 5:1 I suppose and go from there. Equipment wise I have my Nikon D7200 (bought because it doesn't have an anti-aliasing filter) and a 16.3mp 3.8 micron monochrome sensor and the corresponding filters as it doesn't have a Bayer matrix.
I also have an electronic focuser that has 7,000 steps @ 1.27 micron steps. In a couple of weeks I'll be getting another one with 105,000 steps @ 0.085 microns/step. My current electronic focuser should be fine up to 20:1 macro while my next should be able to do the 100-200:1 with its fine step sizes.

So, now I am in need of some direction. Should I be getting a finite lens and just get adapters machined for correct back focus or go down the route of an infinite lens? I personally like the idea of a finite lens as I don't have to worry about getting a 100-200 lens to mount it to but it also comes down to which is sharper? Has better colour control?

Is there anything else that I should be considering?

Thanks in advance for any advice

[rjlittlefield]

AtmosFearIC, welcome aboard!

For microscope objectives, there are lots of feasible directions. Quick summary is that if budget permits, I suggest you will probably be most happy in the long term with the Mitutoyo M Plan Apo series, for example at https://www.edmundoptics.com/microscopy ... bjectives/.

The obvious place to start is with the Mitutoyo M Plan Apo 5X NA 0.14, which delivers that magnification in combination with a 200 mm tube lens.

However, on APS-C sensor, everything in this series can be either used at rated magnification on a 200 mm tube lens, or pushed down to lower magnification by using a shorter than 200 mm tube lens. For 5X, the sharpest lens in my arsenal is the Mitutoyo M Plan Apo 10X NA 0.28, pushed down with a 100 mm tube lens. That lens also gives a very nice 10X on 200 mm, although again it can be out-performed by a Mitutoyo M Plan Apo 20X NA 0.42 pushed down to 10X. Recent test results by another person indicate that the 7.5X NA 0.21 is extraordinarily tolerant of being pushed down.

One caveat on the concept of pushing down: you probably cannot do that by using a zoom lens on the rear. Zoom lenses are notoriously bad at vignetting when used at less than maximum length. Some of them don't work well even there.

You can also get excellent results using finite objectives, but there are some tradeoffs. First is that due to limitations of field size, most finite objectives do not push down nearly as well as the Mitutoyo M Plan Apo infinites. This is not anything fundamental with finite vs infinite, rather just a quirk of the Mitutoyo's. Second is that at higher magnifications, it does not work well to deviate from nominal tube length of a finite objective because that will introduce spherical aberration. There is quite a lot of flexibility at 5X and a fair bit at 10X, but at 20X deviations start becoming problematic and they get worse from there on out. In contrast I can easily push down a 50X infinite to give 25X, for example with the results shown at http://www.photomacrography.net/forum/v ... 825#103825.

A final point is that the Mitutoyo M Plan Apo's have very comfortable working distances, 20 mm at 20X and still 13 mm at 50X. Their combination of long working distance, good color correction, and large image fields is unmatched, as far as I know.

Switching subjects, I would be interested to hear about your electronic focusers. Can you tell us about those?

--Rik

[Chris S.]

Welcome to our rmacro community, AtmosFearIC! I'm delighted that you've joined us.

I suspect that astrophotography and photomacrography have considerable transfer, in that skills obtained in either field may provide a big head-start in the other.

Like Rik, I'd like to hear more about your electronic focusers, which sound interesting.

Equipment wise I have my Nikon D7200 (bought because it doesn't have an anti-aliasing filter) and a 16.3mp 3.8 micron monochrome sensor and the corresponding filters as it doesn't have a Bayer matrix.

This also sounds interesting. Did you have your Nikon D7200 converted to this monochrome sensor without Bayer matrix? Is your monochrome sensor in some other piece of hardware? Or is this a mode of the D7200 of which I’m not aware? (FYI, for studio macro I use Nikon D7100, which is similar to your Nikon D7200.)

. . .while my next should be able to do the 100-200:1 with its fine step sizes.

FYI, My sense is that that 100x probably represents the current practical maximum magnification for open macro setups. I regularly work at 100x magnification with a Mitutoyo 100x/0.70 objective. There are a handful of much more expensive objectives that might or might not perform a bit better for macro. (They cost vastly more, have much smaller working distance, and may not be apochromatic--so may well perform much more poorly; I'd love to test them if this could be done without sizeable fnancial risk) But to go significantly beyond 100x, without the result being empty magnification, seems to involve oil immersion objectives and very small working distances; this sort of work fits more neatly into traditional microscopy than work with "open" macro rigs (even if such rigs are, in essence, home-made microscopes).

Cheers,

--Chris S.

--edited typos

[ray_parkhurst]

AFIC...what do you plan to photograph? One thing I highly recommend is to gravitate toward objectives with long working distance. This allows more lighting flexibility.

[lonepal]

AtmosFearIC Wellcome!

Like Chris and Rik I am very interested on your electronic focuser.
Could you inform us a bit?
Thanks.

[AtmosFearIC]

Thanks for the thoughts and comments everyone. As it seems to be of biggest interest, I'll start with the electronic focusers.

At the moment I have a Precision Digital Focuser (PDF) made by Finger Lakes Instruments (FLI). I have been using this on a 677mm F/5.21 6 element lens which has a corrected imaging circle of 55mm (will take a 36x36mm sensor) but has a lose focus of something like 30m
I have a FLI Atlas arriving in a couple of weeks with a new telescope which is a 600mm F/3 catatropic. At this speed it has a critical focus zone of something like 3-5 microns so having smaller steps will really help.

Both focusers can be found at the link below.
http://www.flicamera.com/focusers/index.html

For connecting everything together I use Precise Parts, specialist company for making astro adapters (blackened and flocked). I can get them to fabricate lens adapters to the digital focuser.
http://www.preciseparts.com

It sounds like the infinite objectives are better performers than the finite ones, also sounds like this is mostly due to better infinite ones being made than the finite. Supply and demand perhaps?
In the telescope world, if you want an excellent 5" imaging telescope you have to get a refractor (lens). We also talk in aperture size as opposed to focal length so 5" (130mm). I have a 130mm F/5 that works at its best at F/5.21 (677mm).

In regards to the infinite objectives, you mention 200mm lens tube, I assume that this purely refers to using a lens with 200mm focal length?
Is the optical quality of the lens as important as the quality of the microscope objective?

The reason I ask is that I can get a second hand Nikkor AI-S 200mm F/4 for ~$250 which was built as a cheaper and lighter 180mm F/2.8 (this is what it seems to be recognised as). Alternatively I can spend a fair bit more and get a Nikkor 200mm F/4 Macro which is sharper and has better lateral colour correction but is also 8x the cost. Although arguably it can also be used around the garden as a long working distance macro lens too so it isn't all bad from that perspective.

As for my cameras. I bought my Nikon D7200 a couple of months back, it hasn't been modified at all though. Still have a Nikon D700 which I am still deciding whether or not I want to keep. Fantastic camera but with its anti-aliasing filter is quite soft. On the plus side with its 8.445 micron pixels, bayer matrix and anti-aliasing filter it requires a lens to be more or less damaged before it shows anything as being not "sharp" haha

The other camera I have is a QHY163M.
http://www.qhyccd.com/QHY163.html

To take colour images I screw it into a motorised colour filter wheel.
http://www.qhyccd.com/QHYCFW2-M.html

And have filled it with 7 Astrodon 36mm unmounted LRGB Ha OIII SII filters.
http://astrodon.com/store/p4/Astrodon_L ... lters.html

If you check out the spectral lines you'll notice there are gaps, these are mostly for light pollution (sodium/magnesium) emission lines. They're designed to the correctly colour calibrated for astrophotography so white balancing would be required for daylight photography.

As for what I actually want to photograph? No idea for the most part! Definitely do bugs (dead ones) and even more obscure things like carpet fibres, mould, fungi and wood. Why not through some cooking pans in the mix too

[Lou Jost]

Fascinating to learn of these focusers. There is no price information on the website, though. Are we talking $100s or $1000s of dollars?
[Edit- I found the prices, $1500-$2500.]

A 200mm f4 Nikon works as a very good tube lens.

I think we have much to learn from you!

[Lou Jost]

The automatic custom adapter generator you linked to is also amazing!

Edit-- it even can generate an adaptor for a Repro-Nikkor!

[Lou Jost]

It is interesting to realize that for subjects that don't move (like nearly all stacking subjects), we could double or quadruple the resolution of our pictures (!) by removing the Bayer filter from our sensors, and replacing it with mechanically-interchanged sequential RGB filters.

[ray_parkhurst]

It is interesting to realize that for subjects that don't move (like nearly all stacking subjects), we could double or quadruple the resolution of our pictures (!) by removing the Bayer filter from our sensors, and replacing it with mechanically-interchanged sequential RGB filters.

Now you're talking...

[AtmosFearIC]

Getting a camera without an anti-aliasing filter will have twice the resolution. Getting a monochrome camera will double the resolution again over that of a Bayer matrix. The benefit of an anti-aliasing filter is that it gives better and truer colour rendition due to the smudging and colour mixing.

A mono camera will give the highest resolution and best colour renditiom BUT it does involve taking three image stacks; one for each filter.

[Lou Jost]

I think that for objects that are primarily red or blue, taking out the Bayer filter would quadruple the resolution over a camera with a Bayer filter. For objects that are primarily green, the resolution doubles.

For our three-dimensional subjects, unlike stars, I think we would want to take three images (R,G,B) at each distance, combine them first into a full color image, and do just one stack with those. Otherwise, the stacks might be slightly different for different colors, just because of slightly different alignment cues from one color to the other.

Edit: Since most late-model cameras don't have anti-alias filters, I wasn't including the effect of taking out that filter.

[s58y]

I used to do astroimaging, but give it up due to advancing age (better to stop hauling around those heavy mounts, etc. before I hurt my back rather than right afterward). I never had electric focusers, large (130mm) refractors or fancy cooled astro-cameras, except for the autoguider. I mostly used modified DSLRs and telephoto lenses for wide-field imaging.

Currently I'm doing mostly closeup and macro photography (coins, etc.), but nothing extreme. 10X is my magnification limit, but most imaging is below 1x, not even in the macro range. For most photos, stacking is not required.

It's unclear how much skills transfer there was in my case, going from astro to macro. I do have a nice collection of 100mm to 200mm telephoto lenses that might work well as tube lenses, but I just use a 200mm Thorlabs ITL200 (older model) tube lens. Metal parts used to fasten the telephoto lenses and other items to the mount, along with stuff from my old barn-door tracker are now incorporated into my vertical macro setup. I have used some of the astro filters once to do a chromatic aberration test that someone asked for in another forum.

Anyway, it's nice not to have to worry about clouds, light pollution, seeing conditions, airplanes, satellites, fireflies, etc. anymore.

[AtmosFearIC]

Shooting RGB individually can also help with correcting for lateral colour shift as the entire channel may need 0.1-2 pixel correction (an issue for planetary imagers). One potential issue is however that unless your lens has very good correction, the RGB channels do not have exactly the same focus.

In astrophotography we deal with this by refocusing for each filter. What can be parfocal at F/10 may not be parfocal at F/5 or F/3 as the critical focus zone becomes smaller. Of course, all of this can be cast aside by just shooting black and white with the use of a luminance filter (UV/IR cut). It is a TRUE black and white.

You've also nailed the reason why I am thinking about macro, something to do when it's raining and cloudy outside for weeks on end

[lothman]

I think that for objects that are primarily red or blue, taking out the Bayer filter would quadruple the resolution over a camera with a Bayer filter. For objects that are primarily green, the resolution doubles.

Pentax K1 does this in camera and it has its effect, but doubling resolution? I don't think so. On static samples it's quite good, see the samples on dpreview:
https://www.dpreview.com/reviews/pentax-k-1/9