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Imaging plant specimens in museums

camera settings

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7 replies to this topic

#1
Denis McMillian

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We are imaging many many 1000's of botanical specimens in botanical institutions in different countries. These are pressed plants mounted on flat usually white, rectangular, thin card - somewhat larger than A4. I have a tripod and 3 way head. A Nikon  D750 with a Nikor 50 mm lens. I have good LED lighting. The camera is mounted on tripod facing down and had a release cable.

 

The plant specimens range from very flat to a little bulky max depth of a woody specimen may be 1.5 cm.

 

So our objective is to have sharp as possibleimages to put online. As a non-photographer, I want to get the best out of this excellent camera and with no movement and plenty of light, I guess it's possible to get top top results.

 

Im looking at what settings to choose for best results. Sharp and light images.

 

As an example, my ISO is set to 100; F16; Shutter speed I have at 1/5 second

 

1. I have read that for 50 mm lens, the speed should be faster? Should I up the ISO? I want all to be in focus hence F16.

 

2. I have it set to manual and use the green square in the centre of the specimen. Can I use the D750 to focus on multiple areas rather than just one green rectange area?

 

3. And would there be a way to adjust the light balance as a lot of the specimen is white card.

 

Much appreciate a few pointers, Denis

 

 



#2
Jerry_

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Welcome to the forum.

You can use the 50mm lens with a 1/5 exposure time when mounted on a tripod (as you do) but shorter exposure times will avoid you to have minor camera movements (f.i. From the mirror movement) to blur the picture.

While the D750 allows for higher ISO, to gain in speed, considering that your subject is always flat and basically never exceeds a thickness of 1.5cm, you can securely select a wider aperture. F.i. At 1m distance a 50mm opened to f10 on a full frame camera gives you a depth of 23cm. For selecting the good settings for your composition you might want to give the following site a visit:

Online Depth of Field Calculator

Also, while you can select multiple focus points, the used focus distance will be the best average amongst them, as the taken picture has a single focus pane. With the particular type of subject that you have, there should be little difference in the result if you select a single or multiple focus points if the used aperture is not to wide open.

#3
Ron

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If I were going to do thousands of botanical specimens, I would definitely consider purchasing or borrowing a copy stand and a micro Nikkor lens. 

 

Ideally, you would want two lights...  I use flash but continuous light is far easier to work with. The lights should be adjustable so as to allow you to dial one side up or down for a slight 3D effect (assuming this is desirable). The extra light will also help with obtaining good exposure.

 

Exposure would be trial and error (unless you have a hand held incident light meter) but since you can immediately view your results, not a large problem. I would probably want to start with an exposure somewhere around 1/100s @ about f/11. I use f/16 and higher all the time but, in my experience, diffraction starts to rear it's ugly head above f/11 for most Nikkor lenses. This results in an ever so slight loss of image quality. Depending on your subject, this may or may not be a problem. For me, usually the increase in depth of field makes up for the IQ loss due to diffraction. Since you will be shooting mostly flat subjects that require very little depth of field, you probably won't need to worry much about that. So, if possible, I would try to aim for exposures centered around f/11.

 

You will also want to purchase a cable release because even the act of pushing the shutter button can introduce camera shake. If the rear LCD on your camera moves enough to allow comfortable viewing at your normal work position, I would consider using Live View in conjunction with the aforementioned cable release. This will raise the camera's mirror eliminating the possibility of camera movement due to mirror slap as well as allowing you to focus far more critically (using the magnification buttons on the back of the camera). You can also set the camera to go from 0 magnification to 100% with a single press of the magnification button. A real time saver. 

 

If white balance is critical, then you need to think about moving away from auto and either purchasing a color checker kit or using a white card to set white balance.

 

Can't think of anything else at the moment. Hopefully, Peter will jump in. I believe he has far more experience with this stuff than I.

 

--Ron



#4
ScottinPollock

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I doubt that any lens will be at its sharpest at f16. Consider stopping down 2-3 stops from wide open and use focus stacking to increase deep of field if need be.



#5
Merco_61

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As a starting point, I would stay away from the Nikkor 50-s as they all have a marked field curvature. I would much rather go with one of the 55 mm manual focus MicroNikkors as they are made for repro use. A copy stand will make your life much easier, as will using a colorchecker and shooting tethered. Twin light sources make getting the light even much easier, but one light and a reflector screen can work if you are careful. Take control over all aspects of the exposure you can as you will want consistent captures of all the specimens. This means manual aperture, shutter speed, ISO and white balance. To get things critically sharp, focus manually using either liveview or the computer monitor to check focus.

 

The 55-s (all versions) have the highest contrast and are free from vignetting @f/8. You can use the grey-card that is part of a colorchecker passport to measure your exposure with the camera's meter. If you need more DOF than the lens gives, focus stacking is a much better choice than stopping down.

 

If you don't want to shoot tethered, use Liveview and a cable release to minimize camera shake.



#6
Ron

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I completely forgot about shooting tethered. That's a very good idea, especially considering that a camera positioned to shoot down... be it on a tripod or copy stand will be difficult to manage. Shooting tethered eliminates a number of problems including the need for a separate cable release. 

 

With thousands of individual specimens to photograph focus stacking would add significant time and effort to the project.  And, because botanical specimens are usually fairly flat to begin with I'm not sure focus stacking would be necessary to overcome a lack of depth of field. But then I don't know what the depth of field for a micro Nikkor 55mm would be at f/8 or f/11.

 

--Ron 



#7
Merco_61

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Stacking will probably not be needed if you shoot the full specimen cards with a 55 as the distance will be somewhere around 60 cm, the reproduction ratio ~1:8.9 and the DOF around 40 mm @f/8. 


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#8
Marcus Rowland

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The first thought I had on this was that you might get better results on the flatter specimens by scanning them. But I suppose it would slightly increase the chances of damaging them.