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Photographing coins with your phone and add-on lenses


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On 13/11/2022 at 13:23, Charliemouse said:

Hi

This topic was inspired by comments from @theman73 and @Silverlocks.

To summarise: trying to use a close-focusing telephoto lens to photograph coins.

I have no idea how much you know about photography, so I will try to stay fairly basic.  Some of what I say will not be 100% correct, as I may miss out scenarios and exceptions to rules.  I welcome people correcting / augmenting my description in the comments.  This topic is not meant to be a general tutorial on how to take photos of coins.

Definitions

(Feel free to skip if you are familiar with the terms.)

Basically, aperture is how wide open the lens is.  It is controlled by a diaphragm inside the lens that blocks the light.  Sometimes this is fixed (most mobile phones), but sometimes it can vary.  Confusingly, the wider the aperture, the smaller the f-stop number.  f/1 is wide and lets in a lot of light, f32 is narrow and lets in a tiny amount of light.

Put simply, depth of field is how much of a scene is in focus.  A wide depth of field means both close and distant things are in focus.  This is what most 'snappy' cameras and mobile phones want to achieve most of the time, because it's easy - when photographing groups of people, buildings and landscapes, you want everything in focus.  A narrow depth of field means only a small 'range of distances' is in focus.  This is useful for isolating subjects, like in portrait photography. 

Optically, depth of field is relative to the f-stop when the photo is taken, and that is determined by the ratio of aperture diameter (how wide open the lens is) to focal length (how long the lens is).

The problem

Mobile phone cameras have a relatively small diameter and therefore aperture.  Normally, because the focal length is also pretty small, this leads to a kind of average f-stop of f/5.6 to f/11.  This is a really useful range of apertures, and means that for most photography, most subjects are in focus and most backgrounds are pleasantly blurred.

However, strapping a great big telephoto lens on the front means a small aperture coupled with a long focal length, which gives you a very small (high number) f-stop, say f/22 to f/32.  So, you are not getting much light onto the sensor.  To compensate for that, the phone will either decrease the shutter speed or increase the ISO (sensitivity), or both.  Decreasing shutter speed leads to camera shake and motion blur, unless you are using a tripod.  Increasing ISO leads to noisy photos and loss of detail.  Also, having such a small f-stop has its own problems, as your lens starts to act as a diffraction grating, and you get blur.

With such a small aperture, you would think that your depth of field would be pretty good.  However, at macro sizes, your depth of field will still, at best, be a couple of millimetres.  And that is only if you can get the phone to accurately focus with a third-party lens strapped to it.

Put simply, there is no way a phone with a telephoto lens is going to match even the cheapest DSLR or Mirrorless camera with a macro lens.  Physics just gets in the way at every turn.  A lens and sensor that is 3mm across vs a lens that's ~60mm and sensor that's 35mm - no competition.

What I would do

Honestly, if your phone has a half decent camera on it with a high enough pixel count and good macro focusing (ultrasonic), take the lens off, hold the camera about 6-12 inches away from the coin, and take a photo.  Even better, use a tripod, use manual settings to control the shutter speed and ISO, and that should sort out the camera shake issue too.  Your coin will look tiny in the photo, but then crop it down - you have the megapixels to do it.

How could it work?

If you are thinking of buying a macro or close-focus lens for your phone, think long and hard.  If you must, buy one from an established lens manufacturer, not a cheap plastic thing from Amazon.  Optical quality makes a difference, and the example photos on Amazon are almost certainly fake.

With or without a third-party lens, here are some tips:

  • Use a modern phone.  Something at the top of the range from the last 5 years or from a mid-range in the last 2 years.  You need a high pixel count if you want to crop photos, and you need reliable focusing.
  • Use a tripod.  You can get pretty cheap mobile phone tripods.  Get a metal one, not plastic, from a good tripod make.  Plastic ones will be useless, and a waste of money.
  • Use manual photo mode on the phone.  Keep the shutter speed above 200 for hand-held.  Let the ISO go wild - see post-processing.  Take lots of photos and see what works - digital photos are free.
  • Control the lighting.  Precious metals reflect everything.  If you can, build or buy a lightbox - a box about 1-2 feet on every side, with one side open for you, and drape some black cloth over the front to avoid light coming in.  Use a flash or torch or some kind of light you can position.  Lighting is a huge topic on its own.
  • Learn how to do basic post-processing of photos.  Find software that will remove noise from high ISO photos, and can crop and straighten images.  I recommend G.I.M.P. which is free and has a lot of open-source community support.

Yes, very good content.

I have now put dozens of photos onto TSF over the years, initially with a Canon using the macro facility, but now all I use as a camera is my iPhone 11.  It seems to do the job very well. Getting the light right can be tricky with coin reflections, especially when close to the coin, when the phone itself casts a shadow. I find by raising the phone ‘til you have the nice gold or cameo affect you want, the zoom can finish the job.

I prefer using natural light so the image looks like that seen by the eye. Many pro pics whilst showing great detail with heavy editing seem to produce a flat and artificial image. For me a quick tidy up on the iPad (mostly cropping) and it’s finished!

The most difficult aspect IMO is getting the colour right. Even the Royal Mint struggles with its overly ‘PINK’ sovereigns!


So it’s all down to the iPhone really, which has got millions of people into photography.🙂

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1 hour ago, Britannia47 said:

The most difficult aspect IMO is getting the colour right. Even the Royal Mint struggles with its overly ‘PINK’ sovereigns!

Thanks for the comments.

I find the white balance* to be the biggest problem here.  Most phones (and cameras for that matter) on automatic, are pretty good at guessing white balance for your average scene, because they have been programmed to look for clues in the average scene.  For macro shots, they don't know what to look at.  Often, they will look at a gold coin, assume that's meant to be 'white' and map all the colours accordingly.  So, you get washed-out 'silver' gold coins.

Because the camera can't guess what colour light you are using, you need to tell it.  Usually, phones and cameras have an option to change from 'Auto' white balance to a specific light source: incandescent, fluorescent, cloudy, sunny, etc.  Try them all, and see which one matches your light.

Best of all, shoot raw!  Again, this is a big topic, but one of the advantages of raw is that it just records the data from the sensor.  It doesn't apply a white balance filter.  So, you can apply one later.  This avoids trying to fix the wrong white balance further down the line, which can get messy.

Finally, I use a light panel** that allows me to set the colour temperature precisely.  I set it to the typical daylight value of 5,600K.  When I'm processing my photos, I tell the software that the colour temperature is 5,600K.  Gets it right every time.

 

* White Balance is the actual colour, or temperature, of the 'white' light in a scene.  The light from an old-fashioned light bulb is a very different colour to the light from an LED, and very different again from the Sun.  Colour temperature is measured in Kelvin, and can realistically be anything from about 2,000K to about 10,000K.  This is a huge subject, and entire books have been written on colour temperature alone.  Your eyes (and brain) automatically adjust, so you don't usually perceive the difference.

** The one I own is an IVISII G2 Pocket RGB Video Light, which I highly recommend.  Others are available.

Edited by Charliemouse

12 Beginner Tips for Better Coin Photos

Everything you need to take great coin photos

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  • 3 weeks later...

I won't win any prizes for my photos but my kit is simple, convenient and cheap, and the results show the condition of the coin. Yes, I could get better photos with a DSLR, a dedicated lighting kit, tripod and macro lens, but the inconvenience and cost would vastly outweigh the minor benefits.

I use my Samsung S10 phone which has a telephoto camera with 2x optical zoom and is f/2.4 so no need for bright lighting or slow shutter speeds. Yes, narrow depth of field but not excessively so and rarely a concern for photographing coins. Need to bear in mind that depth of field is also linked to sensor size, and the microscopic sensors on mobiles lead to comparitively large depths of fields.

When photographing small things and wanting to maintain high quality rather than digital cropping I prefer to magnify using an add on lens.  I use this clip on which cost me £20 or so. Seems very high quality. 

20221205_152833.thumb.jpg.af899c9af4977de7dd633a3bfbf8bbea.jpg

 

Here is a 1g coin with the native 2x camera on the phone at minimum focus distance

20221205_152803.thumb.jpg.7cb8b8456f0217d95407ce4ed38e63f9.jpg

 

And magnified with the clip on macro lens at minimum focus distance

20221205_153052.thumb.jpg.bc39f231fd56f2fc82d9aa2542c2187c.jpg

 

Yes, a little depth of field issue due to tilting the phone due to letting in some side light being in so close, but hoping to remedy this with a photo box from @DrDave , and will have to see how close this allows me to get. In daylight this would be no issue but being up here in Aberdeen we are basically now in permanent night until March. 

Note nice gold colour. This is due to Tungsten lighting and the white balance recognising the colour of the subject must be gold. This is using all auto settings but if needed I can adjust the WB in pro mode. 

I find the S10 to have one of the best cameras of any phone I've tried and they are now cheap as chips.

 

 

Edited by arphethean
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4 minutes ago, arphethean said:

I won't win any prizes for my photos but my kit is simple, convenient and cheap, and the results show the condition of the coin. Yes, I could get better photos with a DSLR, a dedicated lighting kit, tripod and macro lens, but the inconvenience and cost would vastly outweigh the minor benefits.

I use my Samsung S10 phone which has a telephoto camera with 2x optical zoom and is f/2.4 so no need for bright lighting or slow shutter speeds. Yes, narrow depth of field but not excessively so and rarely a concern for photographing coins. Need to bear in mind that depth of field is also linked to sensor size, and the microscopic sensors on mobiles lead to comparitively large depths of fields.

When photographing small things and wanting to maintain high quality rather than digital cropping I prefer to magnify using an add on lens.  I use this clip on which cost me £20 or so. Seems very high quality. 

20221205_152833.thumb.jpg.af899c9af4977de7dd633a3bfbf8bbea.jpg

 

Here is a 1g coin with the native 2x camera on the phone at minimum focus distance

20221205_152803.thumb.jpg.7cb8b8456f0217d95407ce4ed38e63f9.jpg

 

And magnified with the clip on macro lens at minimum focus distance

20221205_153052.thumb.jpg.bc39f231fd56f2fc82d9aa2542c2187c.jpg

 

Yes, a little depth of field issue due to tilting the phone due to letting in some side light being in so close, but hoping to remedy this with a photo box from @DrDave , and will have to see how close this allows me to get. In daylight this would be no issue but being up here in Aberdeen we are basically now in permanent night until March. 

Note nice gold colour. This is due to Tungsten lighting and the white balance recognising the colour of the subject must be gold. This is using all auto settings but if needed I can adjust the WB in pro mode. 

I find the S10 to have one of the best cameras of any phone I've tried and they are now cheap as chips.

 

 

Great photo! Did the Ebay seller send all the Maples together special delivery? Or did he risk it with signed? haha

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