Comments for coinimaging.com Blog

Comment on 22: The numerical aperture. by Vijayakumar

Vijayakumar — Fri, 20 May 2011 08:50:05 +0000

This is very useful. I had the same question in mind why we take sine of the angle instead of tangent. Well explained. I searched for half a day and found this. Lot of thanks.

Comment on 5: Lens focusing by Administrator

Administrator — Fri, 22 Apr 2011 00:36:09 +0000

Lenses focus by setting the distance from the lens to the detector. At a given focal length, every individual distance from the lens to the camera detector will correspond to a specific focus distance out in front of the lens. when the lens is one focal length from the detector, the focus distance is at infinity. As the lens moves farther away from the detector, the focus distance will get closer and closer.

There are two principle ways to change the focus on a lens – move the lens as a unit, change the focal length of the lens. Moving the lens as a unit is called “block focusing.” these lenses will lengthen as the focus plane is moved closer to the camera. Changing the focal length, “internal focusing,” can be accomplished by moving groups of lenses in relation to each other inside of the lens housing. This will allow focusing without changing the physical length of the lens.

As an example, if you have a 70 mm lens and it is focused at infinity. Now you move the internal elements of the lens around and change to focal length to 35 mm. If the distance from the lens hasn’t changed (a bit of a simplification), the focus will now be in the macro range at 1:1 magnification. since the change from 70 mm to 35 mm is gradual, you can also focus anywhere in between. Many modern and high-quality lenses will use internal focus as the primary focusing method.

Comment on 5: Lens focusing by Jesse Toula

Jesse Toula — Thu, 07 Apr 2011 02:04:54 +0000

Hi, I’ve been doing a lot of research on lenses recently and this is the first place that seems to be filled with information that is actually correct. I am having trouble understanding what exactly changing the focus of a lens is doing. How is it that higher quality lenses are able to change focus with out any apparent change in focal length?

Comment on The book has finally arrived! by Rob Larick

Rob Larick — Mon, 08 Nov 2010 06:06:51 +0000

This is a great book and time saver to learning how to shoot coins! Very helpful!

Comment on Update on the timing of the book. by Rob Larick

Rob Larick — Mon, 08 Nov 2010 06:04:59 +0000

I have been reading for hours and came to this page and the realization that I have your book! Initially, it was very helpful. I bought some $10 extension tubes, a copy stand, lights/bulbs, diffusion etc etc then after some disappointing results with a 35-105 Canon lens I tried an old 35 – 70mm Nikor adapted and extended to my Canon 40d and viola! http://www.pcgs.com/setregistry/MemberImageGallery.aspx?m=27235

Should you ever do a revision to your book. having camera set-ups pictured and examples from those set ups would have been really helpful. Ideal Picture information in your book might have included:

Camera
Lens
Extension & other info like reversed lens etc
Approx Distance of coin to lens
Lighting type and angle

Then all the other stuff
Auto/Manual
f stop
shutter speed
etc

Something from my perspective that I have learned and is now crucial to any coin images I take is, Live view and remote shutter release. Viewing from a computer has allowed me to create nearly perfect color and luster duplication from coin to computer image. Also, a copy stand that allows for micro adjustment by way of crank or dial has also been a huge time saver. I can roughly set the lens to fill the frame with the coin through the viewfinder, then use micro adjustment to bring the coin into focus on the computer. Having live view on the computer also allows for swinging lights around to different positions for the most desirable images.

Warmest Regards!
Rob

Comment on A small error in my book. by Administrator

Administrator — Sat, 16 Jan 2010 19:11:55 +0000

As the magnification rises, the depth of field becomes more equally distributed front to back. The general rule is that the distribution is equal front to back for macro and for all practical purposes that statement is true. In reality, there is always slightly more DOF away from the focus plane compared to closer, however minimal that may be.

Comment on A small error in my book. by Chris Lilley

Chris Lilley — Sat, 16 Jan 2010 18:47:15 +0000

It is correct that at high magnifications the DOF is much more on the camera side. The equations do need to cope with macro distances though – ones aimed at normal photography typically drop this complexity as a simplifying assumption.

(P.S. I just ordered your book, second edition).

Comment on Update on the timing of the book. by Administrator

Administrator — Sun, 25 Jan 2009 16:10:46 +0000

You can purchase all of the products on the back cover from various camera suppliers. I like B&H Photo.

Copystand: Bencher Copymate II
Lights: Kaiser RB300
Camera: Nikon D200
Lens: Nikon 85 mm PC micro

Comment on Update on the timing of the book. by Î¤heodore G Vogiatzoglou

Î¤heodore G Vogiatzoglou — Sun, 25 Jan 2009 14:38:57 +0000

Dear friend.
I would like to know if this photography kit (backside of the book)exist and how could i buy it.
Cheers Theodore

Comment on The book has finally arrived! by Bob Perrin

Bob Perrin — Fri, 08 Aug 2008 00:46:43 +0000

I bought my copy from Amazon. Will probably buy a couple more copies as gifts for friends. The book explains the concepts and practices of numismatic photography in an easy to understand fashion. This book is a wonderful addition to any numismatic library.