Hejnar PHOTO F51 Dual Subtend QR Clamp Review

A year after the first release of the  Hejnar PHOTO F50 Dual Side Quick Release Clamp and a few months after I tested and reviewed its improved version, Chris Hejnar has released an alternative version of a Dual clamp with a different design approach.

Hejnar PHOTO F51 is a dual subtend clamp with two individually regulated opposing jaws, that promise compatibility with virtually any rail or plate combination clamped over and under.

The Clamp

Manufacturer Specification:
Model:	F51 Dual Subtend
Height:	23.6 mm (0.93")
Width w/ Screw Knobs:	97.7 mm (3.85")
Jaw Length:	60 mm (2.375")
Center Socket:	Countersunk on one side for 1/4" or M6 screw and threaded 3/8"-16
Safety Stop Relief Grooves:	Two on each side
Weight:	137 gr (4.83 oz)
Material:	6061-T6 Aluminium, Black hard coat anodized
Made in:	U.S.A.

The new Hejnar Photo Dual Subtend clamp follows the now recognizable Hejnar clamp design, with V shaped  safety stop relief grooves on both sides and a 3/8"-16 threaded center hole. The hole is counter sank on one side permitting the attachment of the clamp on a ball head with a 3/8"-16 stud or via an M6 or 1/4"-20 flat head screw. Both moving jaws have short, aluminium, black anodized knobs with a diamond pattern texture which makes them difficult to slip. The clamp itself has the same hard coat anodizing as all Hejnar clamps with a glossy finish.

A a stadard jaw height and a large jaw opening at both sides, make the F51 clamp virtually compatible with any Arca Swiss® type rail or base plate. However, this wide opening will take 8 rotations of the screw knob while it takes only half a rotation to release a rail for adjustment and 3 full rotations to release a standard 38mm (1.5") wide rail, for removal from the top.
An enlarged view of the above photo, shows better the moving jaw mechanism which utilizes tongues and grooves with rounded edges and hidden springs avoiding the accumulation of dust and dirt, ensuring smooth operation.

F51 drawing with detailed specs (courtesy of Hejnar PHOTO) (Click to enlarge).

Comparison with Hejnar F50 Dual Subtend Clamp.

A side by side view of the F50 and the F51 QR dual subtend clamps, reveals the difference between one dual moving jaw versus the two independently regulated jaws. F51 with a total height of 23,5 mm is by 3,5 mm taller than F50 's 21 mm due to the double moving mechanism. This difference in height is also reflected in the distance between the upper and lower clamping surfaces, which are 14,1 mm for the F51 and 11,4 mm for the F50.
Total weight is the same for both at 137gr despite the extra moving mechanism.

Used as a Long Lens Support Bracket lens foot regulator.

Combined with Hejnar PHOTO F60 QR Clamp, G16-80 5/8" rail and LSB-R2 bracket to form a very sturdy while versatile long lens support bracket.
The F51 QR clamp plays the role of the fore-aft regulator for the lens' collar foot equipped with a dovetail plate.

Compared to the  Hejnar PHOTO F50 Dual Side Quick Release Clamp reviewed some time ago, the F51 proves more compatible with any size of dovetail rail/plate and any difference in dovetail radius between upper and lower rails thanks to its dual and independent clamps.

In action with a Canon EF 100-400 L IS USM during a very windy day last August. More details may be found in the Create a Heavy Duty Long Lens Support Bracket article.

Arca-Swiss® Compatibility
The F51 Dual Subtend quick release clamp was tested with various camera plates and lens plates, as well as with multi purpose long rails of various thicknesses and widths. Plates / Rails tested were from Benro, Kiwi Fotos, Fotoporo, Marumi and Hejnar PHOTO, with excellent results.
For the readers that like numbers, I hereunder quote detailed measurements of the clamp Jaw dimensions, so as they can decide whether this clamp is compatible with the dimensions of their plates or rails.

Clamp Jaw dimensions	mm
Jaw Length	60.30
Steady Jaw Height	05.09
Moving Jaw Height	05.12
Min Jaw Lip Opening	32.64
Max Jaw Lip Opening	40.20
Min Base Opening	41.05
Max Base Opening	48.74

All dimensions fall within the average limits, consisting this clamp compatible with almost any Arca-Swiss® type plate and rail.

Pros
Very nice sturdy and dirt-proof design.
Very good machining, finishing and anodizing.
Excellent versatility with extra wide opening that can accommodate virtually any Arca Swiss® compatible rail or plate.
Excellent clamping strength with large clamping surfaces.
Very good value for money.

Cons
None until the time of this review.

Conclusion
A very strong and sturdy QR clamp, which resolves any clamping issues of its F50 rival.

I hope you found the review and ideas useful, thank you for viewing.
All Photos: © 2012 S.C.Vlachos

Note: The F51 clamp presented in this article is a prototype / first-production unit, kindly offered for evaluation and review by Chris Hejnar of Hejnar PHOTO. Therefore, there may be some small visual or functional differences from the final production units. For final products you may visit the "Special Clamps" section in the Hejnar PHOTO online store.

Price and Availability:
Current price for the F51 Dual Clamp is US$ 70.00 (+Shipping where applicable) and is available from Hejnar Photo online Store.
Check the Recommended Sellers page for a valid Hejnar Photo discount coupon.

Referenced Articles:
Hejnar PHOTO F50 Dual Side Quick Release Clamp Review
Hejnar PHOTO G15-80, G16-80 and G15-60 Multi Purpose Rails
Hejnar PHOTO F60 1" Quick Release clamp

Relevant Articles:
Ideas for a Long Lens Support Bracket (Part 1). (Part 2), (Part 3), (Part 4)
Create a Heavy Duty Long Lens Support Bracket