Loupe Shootout

[rmpsrpms]

LOUPE SHOOTOUT

There have been a number of discussions on this forum and others asking for recommendations on the best loupe to use for coins. Almost universally the Zeiss 3/6/9x and the Eschenbach 5x come up as most recommended. For the last couple years, I've been using enlarging lenses as loupes, so I usually chime in with the recommendation of a Nikon 50mm or 75mm, depending on the magnification needed. This recommendation usually falls on deaf ears, as most folks have no idea what to make of it. So, I decided to make a comparison among a few low to mid power (3-6x, with one 9x) loupes plus some enlarging lenses that can be used as loupes to show why I recommend them.

 

LIST OF THE CONTENDERS

 

Zeiss Aplanatic-Achromatic Doublet

This is an expensive (~$125) loupe that seems universally loved by those who own them

 

Lomo 6x Doublet

This is an inexpensive (I paid $10) loupe with decent performance

 

Eschenbach 5x Achromat

Another expensive (~$75) loupe with a strong following

 

Nikon 50mm f/4 EL-Nikkor

An inexpensive (~$25 used) enlarging lens. The aperture of f/4 gives a fairly narrow field of view when used as a loupe

 

Nikon 50mm f/2.8 EL-Nikkor

Another inexpensive (~$35 used) enlarging lens. The large f/2.8 aperture gives a wide field of view similar to the loupes in this shootout

 

Nikon 75mm f/4

A low-price (~$50 used) enlarging lens. The f/4 aperture gives a workable field of view due to the longer focal length

 

PHOTO OF THE CONTENDERS

 

SOME NOTES ON MAGNIFICATION

The shorter the focal length of a lens, the higher its ability to magnify an image but also the shorter its working distance. The Magnification Power of a lens of focal length FL is:

 

M = 250mm/FL +1

 

This formula assumes the lens is held close to the eye, which is pretty typical of how loupes are used to view coins.

 

So a 50mm enlarging lens, used as a loupe, has magnification of 250/50 + 1 = 6x. It will magnify like a 6x loupe. Similarly, a 75mm enlarging lens will magnify by 4.3x.

 

Some magnifiers are specified in Diopters rather than Focal Length or "Power". The Diopter rating of a lens is:

 

D = 1000mm/FL

 

So a 50mm enlarging lens is rated at 1000/50 = 20 Diopters. Given the Diopter rating, the Magnification is:

 

M = D/4 + 1

 

DETAILS OF THE SHOOTOUT

For the shootout, I used a 1956-D RPM#4 Cent as the test vehicle, centering the images around the Date and Mintmark area. The images were taken with a Canon XS camera using a Canon 18-55mm lens in manual mode. The test lenses were held at their normal working distance from the coin, and the camera height above the coin adjusted such that the view would be similar to what the eye would see in this configuration. Working Distances were:

 

Nikon 50mm f/4: 37mm

Nikon 50mm f/2.8: 30mm

Nikon 75mm f/4: 50mm

Zeiss 3/6/9x: 70/35/20mm

Eschenbach 5x: 45mm

Lomo 6x: 35mm

 

IMAGES TAKEN WITH THE LOUPES

Images are of the overall view seen by the lens, plus crops of the mintmark area.

 

ESCHENBACH 5X

 

LOMO 6X

 

ZEISS 3/6/9X AT 3X

 

ZEISS 3/6/9X AT 6X

 

ZEISS 3/6/9X AT 9X

 

NIKON 75mm f/4 EL-Nikkor

 

NIKON 50mm f/4 EL-Nikkor

 

NIKON 50mmmm f/2.8 EL-Nikkor

 

COMMENTARY

The images show that the simpler lenses are not as well-corrected as the more complex ones, with less sharp centers as well as less flatness across the field.

 

The Eschenbach 5X is a singlet lens, and it shows the weakest performance in this group.

 

The Lomo is a symmetrical doublet, with better correction and flatter performance to the edge.

 

The Zeiss is two singlets, though it is marketed as an achromat, so likely has more than one lens cemented together to form each singlet. It is a bit less sharp at the center than the Lomo, but is fairly flat to the edge. It is the best performer in the standard loupe category.

 

The Nikon 75mm f/4 is a 4-element Anastigmat/Anachromat, and is well-corrected for both color and field flatness. This shows up as both good sharpness in the center and edge.

 

The Nikon 50mm f/4 is another 4-element design, and is similar to the 75mm in sharpness. It has a smaller field of view but is still usable as a 6x loupe.

 

The Nikon 50mm f/2.8 is a 6-element, highly-corrected Anastigmat/Anachromat. It is the clear winner in this shootout for both center and edge sharpness.

 

While I did not attempt to photograph the effect of slightly tilting these lenses, you can probably imagine that if the edges of the field are starting to get blurry, any amount of tilt will result in more blurriness and distortion. This is the true test of field flatness and coverage. The enlarging lenses were designed for a wide field on both film and print planes, so can tolerate a lot of tilt before showing any unsharpness or distortion. None of the purpose-made loupes tested here can tolerate any tilt and must be held straight-on to the coin to achieve good sharpness.

[e1cnr]

They all look pretty nice to me (although some better than others)

 

How did you do the photos?

 

hold camera and loupe/magnifier?

autofocus on camera on/off?

[jpcienkus]

You had me at "hello"...

[DaveG]

Gee - no comparison with the B&L Packette 5x that many of us use?

[Nutmeg Coin]

Good topic, would like to see it address gold and silver coins instead of copper. Lighting issues remain even with the best loupes.

[rmpsrpms]

Gee - no comparison with the B&L Packette 5x that many of us use?

 

I'll include it in next go around. I should have included it this time.

[rmpsrpms]

They all look pretty nice to me (although some better than others)

 

How did you do the photos?

 

hold camera and loupe/magnifier?

autofocus on camera on/off?

 

The camera was on a copy stand, and loupes held up with proper height spacers. All done manual focus.

[rmpsrpms]

Gee - no comparison with the B&L Packette 5x that many of us use?

 

Here it is:

 

 

[mikew148]

You had me at "hello"...

 

+1 - I like it when when Ray tells me "what" is responsible for the equipments ability.

 

I love it when he tells me "why" it works the way it does!

 

I'm often baffled by the explanations given, the details and technical data are into the realm of the advanced professional photographer.

 

Thanks again Ray for your efforts in the field of Numismatic Photography - ever consider writing a book?

 

 

[michael]

thanks!! great thread

 

looks like zeiss 3x6x9 is the winner for me

[James_OldeTowne]

One thing I'll suggest, and it sounds utterly trivial at first... whatever swiveling loupe you get, make sure it is hinged with a screw, and not a rivet. They will eventually get annoyingly loose, and you can tighten the screw as required. The rivet... really can't be "fixed".

 

I always, always, always use an 8x 95% of the time. Higher power can be useful for checking on RPMs, die varieties, etc.

[Coindude]

James... a hammer can fix anything! But I agree with you, I have two 10x loupes that are riveted and over the years have become quite loose.

[rmpsrpms]

Or you could do away with the rivets and screws all together and use an enlarging lens...

[Kurtdog]

It looks like you've got one of the 56-D RPMs.

[rmpsrpms]

It looks like you've got one of the 56-D RPMs.

 

Yep, it's an RPM #4. It's one of the tougher ones to find, but I got lucky in a group of OBW rolls I bought and found a few in each roll.

 

I did a 3-D rendering of this coin a while back. Here it is again:

 

 

I should probably edit that pic to bring the images closer together so you don't have to cross your eyes so much. If it's hard to see, move a bit further from your monitor and it will get easier. It also works if you relax your eyes and look straight toward the images. Some folks find crossing easier, some find relaxing easier. Some can't do it at all! I find it all sort of gimmicky but it's fun anyway.

 

And here are some cool single-image perspective renderings as well:

 

 

 

 

[rmpsrpms]

Ended up hijacking my own thread. Anyway...

 

One subtlety in the loupe comparison is that viewing in-hand with a loupe is a bit different from photographing the view using a loupe. The reason is that our eyes can refocus quite quickly, and we also move the loupe to get the best overall focus on the subject. Taking a single photograph using a loupe can't take advantage of this effect. This skews the results somewhat. Loupes that are flat-field will photograph well with single images. Loupes that are not flat field, but don't distort at the edges, will show some focus problems at the edges in a single image as I've shown, but are compensated either by the user moving the lens to focus, or by the user's eye refocusing as it looks toward the edge of the field of view. Loupes that are not flat-field, and also show distortion at the edges, will appear to the user to be blurry at the edges no matter what.

 

The long-winded description above explains why some of the loupes, such as the Zeiss, don't photograph well, but are well-regarded by users. The lens is not flat-field, but does not distort at the edges, so the users eye can refocus as it moves around the field of view. I presume (but have not tested) that the Eschenbach 5x has a similar quality.

 

It may be that loupe manufacturers take advantage of the characteristic of our eyes being able to quickly refocus, and thus are able to make a lens that is not flat-field but still appears to be sharp from edge to edge.

 

This is the characteristic that is so interesting about enlarging lenses used as loupes...they are truly flat-field, so they eye has no need to refocus as the eye moves around within the field of view. The entire image area is in focus. It makes for a completely different viewing experience, perhaps even "boring", since you don't need to constantly refocus to compensate for the poor field flatness of the optic you're using.