FS700 parfocal tests on three lenses

[Christopher Young]

Hi All ~

For anyone interested in finding parfocal zoom lenses suitable for an FS700, or FS100 for that matter, I have found some cost effective solutions out there.

The first cost effective lens I looked at was a modern one, the Alpha DT 2.8/16-50 SSM lens that is often the kit lens supplied with the 24 megapixel APSC Sony SLT A77 DLSR. On that 24 MP camera this lens delivers a surprisingly sharp clean image and best of all it’s a fixed aperture lens and is 100% parfocal. This lens was tested using an Alpha to NEX mount adapter bought off eBay. The adapter has an iris control ring that engages the lenses diaphragm pin on AF Alpha lenses. The lens itself is currently available from BHPhoto for around $750.00.

The second lens I looked at was a manual MD Rokkor lens from the eighties. Having used Minolta Rokkor lenses for many years and knowing what good performers they were I thought I would check out the highly regarded MD 35-70mm f1:3.5 Macro for use with the FS700. This is a fixed aperture parfocal lens that developed a very strong following amongst still shooters. Minolta's design on this lens was so good that it was approved and taken up by Leica in Germany. Subsequently Minolta built re-badged versions of this lens with Leica mounts and Leica marketed them under the name Leica Vario-Elmar. This lens has about a 100 degree focus throw. In all there were three versions of this lens. The first version had the narrow parallel zoom ring. The second version came with the familiar Leica style wider zoom ring but with the narrow cut-away section defined by the 35-70mm markings. The third version was exactly the same as the second version but with the addition of a macro function. Not a 100% true macro but very useful for close up work. All versions also had Minolta’s a distinctive and unusual concave front lens element which made them pretty flare resistant. This design helped in maintaining even contrast in most lighting situations and was one of the reasons this lens was much loved by those in the know. Back in the eighties regarding resolution this Minolta 35-70mm zoom was one of the few zooms available that could deliver close to prime lens performance. Good examples of these can be found on eBay for around the $65-80 mark although they are going up.

The third and last lens I looked at was a Minolta MD mount Angenieux designed lens built by Tokina. This lens is the Tokina AT-X 35-70mm f1:2.8 fixed aperture parfocal zoom. Not to be confused with the later AF AT-X Pro versions. This lens has a nice 170 degree focus throw and good wide focus and zoom rings. It’s a little bit more prone to flare than the Minolta but used wisely it is again a great value lens. Rarer than the Minolta Rokkor but in MD mount can be found for around the $80.00 – 90.00 mark on eBay
In summing up one can say that for under $200.00 you can pick up some great fixed aperture parfocal zoom lenses that work well with the FS700. Lenses that deliver great performance and that have virtually no CA or coma issues.
One thing I must point out though is that all the adapters I used to enable the use of these older manual lenses on the NEX e-mount have one major failing. From the $200 Novoflex to the $12 eBay cheapie they are all too short. Surprisingly some of the cheaper adapters were closer in spec and much better made on their MD mount release catches than some of the ‘name’ brand adapters. I can understand why these adapters are machined short because by supplying short adapters the manufactures of these adapters can guarantee infinity focus. With primes this is not such an issue but if you want to maintain focus throughout the zoom range of a parfocal zoom lens, especially the wider ones, it is critical that the back focus and the infinity end focus is spot on. ALL the adapters I tested needed shimming to achieve this end. Not a super scientific approach but for those interested in the parfocal test results and the shimming details the results can be viewed here:

Sony FS700 Parfocal lens tests x 3 with and without ' speed booster' - 1080-50p down to 720-25p 10.June.13 on Vimeo

Chris Young
CYV Productions
Sydney

[James Barbosa]

Good stuff, thanks a lot.