LensRentals.com

The Most Honored Photograph

Posted by

Photograph in public domain, this copy from Naval Aviation Museum

 

Doesn’t look like much, does it? But, depending upon your definition, this photograph, a team effort by 9 men, is the most honored picture in U. S. History. If you want to find out about it, read on. It’s an interesting tale about how people sometimes rise beyond all expectations. It takes place in the early days of World War II, in the South Pacific, and if you’re a World War II history buff, you may already know about it. Continue reading

The First Annual Photogeek Geek Photo Contest

Posted by

I’ve been writing a lot of geeky testing stuff for the last couple of weeks, most of which can be summed up as ‘take some pictures; if they look good everything is fine.’ So last weekend, I went out and took some pictures. It was pretty fun. So much fun that I thought maybe I could have a photo contest just to entice some of my fellow geeky types to go out while there is still some sunshine to take a few pictures.

Don’t worry, my pixel-peeping photogeek friends, I know that your usual images of ISO 12233 charts, backfocus targets, dog and cat fur don’t lend themselves well to the various photo competitions out there. I know that a beautiful picture of a cloudy sunset doesn’t give you the opportunity to evaluate corner resolution, and that it’s impossible to assess for spherical aberration in an artfully shadowed nude. Yes, we could enter an superbly sharp brick wall in the architectural category of a normal photo contest, or a 100% crop of our cat’s whiskers in the wildlife section, but we know those ‘artsy’ photo judges never have proper appreciation for that kind of work. Continue reading

Bad Times with Bad Filters

Posted by

A long time ago I wrote a blog post called Good Times with Bad Filters about how cheap UV protective filters are different from good ones. It was mostly in fun.

Today I’ve got a post about how cheap UV filters may hurt your lens. It’s not in fun.

Here at Lensrentals we see lenses come back with scratched front elements every so often. Not a big deal, it happens. But since the Canon 24-70 f/2.8 Mk II lens came out we’ve seen a whole lot of them come back with scratched front elements. The weird thing was it was always in the center of the lens and often circular in pattern like the one below. (Ignore the dust, this front element had been taken out for replacement and sat on my desk for an hour before we took the picture.)

 At first I thought maybe there was a problem with the new coating Canon was using, but it seemed a coating issue wouldn’t occur just in the center.

It turns out that the combination of the slightly bulging front element of this lens and a ‘less than best quality’ thin or ultra-thin filter is the culprit. Let me make this point first, though: The vast majority of filters do NOT touch the front element of this lens. I went through a number of filters before I found one that did. But it can happen and that’s worth knowing.

This 24-70 had a front element that was about to be replaced because of some scratches near one edge (which is why I didn’t mind putting filter after filter on it to see if any caused a problem), but the center was absolutely clear.

 I went through 8 filters with absolutely no issues. The 9th filter, though, seemed to come in contact with the front element. It’s hard to be certain about that by just looking and feeling. So I dusted on the back side of the filter with a little carbon black. Notice I covered a fairly large area of the filter with it.

 

Then I put the filter on the lens, took it back off the lens, and took a picture of the front of the lens. Notice the circular pattern of the carbon,which is fairly clingy. Other than a few specs, it doesn’t come off the filter except where there was glass-to-glass contact. This is a much smaller area than the large smear of carbon I put on the filter.

And when we blew the carbon off the lens, there were a couple of scratches that hadn’t been there before.

READ THIS PART

This is a good demonstration about what MIGHT happen. I will add that I’ve put another dozen brand name filters (Heliopan, B&W, etc.) on this lens with absolutely no problem and no sign of glass-to-glass contact. It seems that you need the proper combination of a thin-line filter with glass close to the back of the filter, and a lens with a slightly bulging front element (this lens has one, but so do lots of others) to even worry about it. I would also think that wider front elements (this is 82mm) might allow more play or sag in the center making this more likely.

For those of you who can’t wait to go post something about how the Canon 24-70 f/2.8 II has a problem, let me assure you that’s not the case. I had to try a number of filters and the one that I used in the demonstration is a ‘discount’ filter that someone sent back to us in place of the name-brand filter we sent them. The other name-brand filters I tried were all fine.

I’ve also seen this ‘center circular’ scratch pattern on a few other lenses and we’ll start watching for it now that we know what it is. But I don’t have enough records to go back and figure out which of the numerous front element scratches we’ve seen were of this type.

My suggestion, though, is that you stay away from ultra-thin filters on these lenses, especially discount ultra-thin filters. If you look across the front of your lens from the side, you can get an idea how far up the center of the lens bulges. Then look at the back side of your filter and see how far the glass is from the bottom of the threads. If those two distances seem similar – well, be careful!

Roger Cicala

Lensrentals.com

October, 2013

There Is No Perfect Lens Test, Either

Posted by

In my last article, I wrote about the fact that every copy of a given lens has some bit of sample variation. This affects lens reviews, whether lab-based or photography-based, because the copy they tested will be just a bit different from the copy you buy. I suggested, that if you want to get a feel for what the lens you purchase is likely to be like, you had best compare several different reviews. That should give you an idea of the variation that exists.

Photographs are really the best way to evaluate a lens’ performance, but you have to look at a few dozen, minimum to do it. That takes a lot of time and a fair amount of bandwidth. Looking at online size jpgs is worthless unless all you do with your images is post online-size jpgs. You need to download at least full-size jpgs (preferably RAW files) and look at them at 50% magnification to get a good idea about a lens’ performance.

Lab testing, with its numbers, gives us nice, quick overviews of lens performance. It’s useful for lens reviews so that you can compare one lens to another. It’s useful for people like me who have to test lenses to make sure the optics are OK, since it eliminates some of the human variability that comes with looking at images of a test chart.

But each type of lab test has its own strengths and weaknesses that nobody ever talks about. This is important if we’re going to compare several different reviews of a lens, because we should have some idea of what the reviewers are actually analyzing. Like every scientific test, if you don’t have a grasp of the testing methods being used, you can’t possibly understand the results. Continue reading

There Is No Free Lunch, Episode 763: Lens Adapters

Posted by

Lens adapters can be useful things sometimes, letting you mount one brand of lens on another brand of camera.

One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces. When you look at the thick metal pieces on the front of the camera and the back of the lens, and then consider that they have to be lined up exactly parallel to the image sensor, it’s kind of amazing it works. Continue reading

There is No Perfect Lens

Posted by

The Three Questions

I get asked a couple of questions every time I publish a graph showing Imatest results for multiple copies of lenses like the one below. Most people understand that some copy-to-copy variation is inevitable in the manufacturing process. Most are surprised, though, at how large the sample variation seems to be. Heck, I was surprised at how large the sample variation was when I started doing this kind of testing.

The three questions I get asked over and over are the same questions I asked myself when I first started seeing these results:

  1. Are you sure the variation is that great?
  2. Can you really see the difference in a photograph?
  3. Can optical adjustment make the copies with the worst results better? Continue reading

Lensrentals is Coming to Nashville!

Posted by

We are happy to announce the opening of our satellite location in the Nashville area. Our Nashville office will serve as a pick-up center beginning on September 12th. There is no charge to pick-up from the Nashville location. Initially, all Nashville orders will be available the next day, although we hope to soon offer same-day pickup for our most popular items. Continue reading

What’s All This RAW Hack Business?

Posted by

You’ve more than likely heard about the Canon 5D Mk III RAW Hack. We too have been keeping a close eye on the Magic Lantern (ML) team as of late. In the last 4 months they’ve enjoyed their greatest triumphs since initially cracking the 5D Mark II’s code almost 4 years ago. It’s been a wild ride, and even though it’s far from over, we’re ready to join in. The LensRentals crew has been independently testing the various new firmware builds all summer long and we feel it’s now safe to recommend them to our customers.

Fig. 1: Artist rendering of what the Magic Lantern team might look like. Continue reading

Fun with Color Vision

Posted by

I’ve been doing a lot of technical things lately, writing up our repair data and investigating methods of reducing optical variation in lenses. So I thought I’d take a bit of a break and write a post about something fun. Human vision is always fun to me, since it’s an area where I can apply both my photography and medical experience.

Most of you probably know some of these things, but I bet most of you don’t know all of them. So I would recommend skimming along this rather long post to find the topics that interest you. Since it covers (among other things) carrots, advertising, Impressionist painting, evolution, optical illusions, and warship camouflage, there ought to be something of interest somewhere. Continue reading

Lensrentals Repair Data: 2012-2013

Posted by

Correction: Lenses called “Rokinon” in the “Weeks to Failure” rate incorrectly included Bower & Samyang branded products. Because of this error, data for lenses called “Rokinon” lenses has been removed. We apologize for this inaccuracy, and any confusion that may have resulted therefrom.

What Is This?

We have a unique opportunity: We own a very large number of lenses and cameras subjected to rather harsh conditions. Basically, we have a laboratory set up to stress test photography equipment and we share those results with you.

Our numbers reflect heavy and hard use. Your personal equipment shouldn’t fail nearly as often; it isn’t subjected to rental conditions. But this does provide some comparison about how fragile various pieces of equipment are.

It’s not completely scientific, but with data on over 12,000 copies resulting in over 2,000 repairs it’s a bit more useful than posts on a forum going back and forth between “mine’s great” and “mine sucked.”

This list is not a comment about how good a lens is. It’s simply data about how often it breaks under harsh conditions. Some of my favorite lenses and cameras are rather fragile. Continue reading