Varifocal vs. Fixed Lens Integrator PreferenceAuthor: Ethan Ace, Published on Dec 26, 2011
When selecting lenses for surveillance cameras, there are two fundamental options: varifocal and fixed focal length. Varifocal lenses allow the field of view to be adjusted within a range (e.g. 3-8mm, 9-20mm, etc.) after the camera is installed, without changing lenses. Fixed focal length lenses are just that, offering only one focal length. As part of our Fall 2011 integrator survey, we aimed to find out which of these two options integrators were most often installing.
We asked the following question of 84 integrators:
The vast majority of integrators (88%) preferred varifocal lenses to fixed focal length. Most commonly, flexibility and simplicity were cited as the reasons for this preference.
Flexibility of FOV
This was overwhelmingly cited as the number one reason for choosing varifocal lenses. Unlike fixed focal length lenses, varifocal lenses allow the field of view to be changed after the camera is installed, without changing the lens. This is often critical. If conditions on site differ even slightly from how they were when a pre-installation site survey was performed, it may affect lens selection drastically. Varifocal lenses allow fine-tuning to account for these differences, as well as customers simply changing their mind.
Here are some comments from integrators on the topic:
- "We prefer the varifocal lens b/c it allows our customers to 'change their minds' of what they want to look at vs. have them pre-determine their shot before we complete the install. This gives everybody more lee-way."
- "Allows flexibility to change view based on changes made at locations after the initial installation."
- "This type of lenses minimizes the time of site survey and also in the future we are able to change the camera view according to any modifications to the site or the request from the client."
- "Varifocal is easier to use as well as it doesn't lock you into a specific field of view. Customers change their mind and sales people don't always calculate the angles correctly."
- "Flexibility. If you can move a camera to another position when needed, that makes the equipment selection process less final. They know they can change their mind later, or respond to an unexpected situation."
Integrators also cited simplicity in ordering and stocking as a reason for choosing varifocal. Instead of stocking simply a 3-8mm varifocal lens, an integrator may instead need to stock 3mm, 4mm, 6mm, and 8mm fixed lenses. This is obviously more work in ordering and maintaining inventory. In the same amount of space, an integrator may stock one or two varifocal lenses which cover nearly all applications.
Integrators had the following to say:
- "Easier to use to get the field-of-view that the customer is expecting. It also reduces the complications associated with ordering cameras."
- "Gives our customers the option to zoom in or out after later without replacing lenses. Standardized purchase orders from manufacturers translates into less for work sales staff and less equipment on our shelves and vehicles."
Proponents of Fixed Lenses
Of the integrators who preferred fixed focal length lenses (12%), most commonly they cited better performance as their reason for selecting fixed lenses.
Integrators preferring fixed focal length lenses had the following to say:
- "It depends on the application. I prefer fixed lenses because they are less costly and usually optically better than vari focal. They also theoretically should take less time to adjust since there is no zoom adjustment to contecnd with. However, the vari focal option is very handy when a customer is indecisive about the scene they want to see or is prone to relocating cameras. WYSIWYG does not always sit well with customers when they are paying a premium for an IP system."
- "These are much easier to focus while using manual-focus cameras. Varifocal are only used when no one can make up their mind ahead of time as to where the cameras should be located or what they should see."
- "Fixed focal lenses offer a much clearer view and with HD cameras the limitations of vari-focal can show up"
In most cases, varifocal lenses are likely a better option. The flexibility and simplicity they offer will almost always outweigh the potential advantages of fixed focal length lenses. For one, few options exist for various focal lengths in fixed lenses, especially under 3MP. This greatly limits selection. Additionally, in preliminary tests of Tamron fixed and vari-focal lenses, we saw no clear optical advantages to using fixed focal length lenses.
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