Instagram does not offer an app with native support for the iPad, and blowing up the iPhone app on an iPad is not ideal unless you enjoy blurry, pixelated images. There are a number of free apps -- InstaFlow, Padgram, Pictacular -- that let you view your Instagram feed on the iPad, so why would you spend $1.99 on Iris? I can't quite recommend you do so, but it is the most polished of the group I looked at this week.
Before I get into Iris, I must first offer the standard Instagram-on-the-iPad disclaimer: Instagram does not let you post photos via a third-party app. Thus, no third-party app offers full Instagram functionality. An app such as Iris, however, lets you view crisp, clear, and large Instagram photos on an iPad, along with a variety of fun and useful features, from commenting on and liking photos to sharing via Twitter and browsing photos by location on a map.
When you first launch the app, the welcome screen will ask you to sign into your Instagram account. After a brief, three-slide tutorial, you will be dumped into your Instagram feed. Unlike other Instagram viewers that cram in small thumbnails, Iris features only two columns of photos. Each photo has a Polaroid-like border that displays the name and profile picture of its author along with the number of likes and comments.
Tap on a photo to expand it. You won't see any additional information in the expanded view except for a comment if the author included one. You can double-tap the photo to like it (you can also do this when browsing smaller images). Tap on the like or comment icon and a panel slides out to show you either the likes or comments. From the comments panel, you can add your own comment if you have something to say. There is a third icon in the expanded view that when tapped shows you where the photo was taken on a map.
Along the left side of the screen are five icons to see your various Instagram feeds: your feed, popular, your profile, search (by tag or user), and your likes. You'll notice that the popular feed displays four columns of smaller thumbnails, while your profile (along with profiles of other users) gives you a choice between two columns or four (but not three). When viewing a profile, you can toggle a small switch in the lower-left corner to switch between the two views. Why this switch isn't offered on the main feed I do not know.
No matter which feed you are currently viewing, you'll see a pull-down switch in the lower-right corner to refresh the feed. (You can also just tap the arrow icon below the switch to refresh.)
To share a photo, tap on an expanded photo and three icons appear. They let you share via Twitter, copy the link for the photo to your clipboard, or open the photo in Safari.
From your profile, you can access lists of your followers and those whom you follow. To follow or unfollow someone, however, you will need to open their profile instead of simply being able to toggle that setting from either list. Also from your profile (and on other user profiles), there is a button to see the location of photos on a map.
In the upper-right corner is a settings button. The only setting offered is the capability to turn the sound on or off; Iris makes a pleasant click sound when you tap certain buttons.
The biggest omission from the otherwise well-designed Iris app, and the one that prevents me from suggesting you plunk down $2 for it is the inability to swipe from one large photo to the next. Instead of leisurely browsing through a feed of expanded photos, you must tap to close an expanded photo, return to the thumbnail view, and then expand another photo from the grid. Free apps such as InstaFlow and Pictacular provide such functionality, which I think is key for viewing Instagram on the iPad.