topic Re: 50mm f1.8 on 7D in EF & RF Lenses

50mm f1.8 on 7D

sloansmom — Tue, 02 May 2017 00:18:13 GMT

Using my Canon 50mm f1.8 on 7D body.

This was shot AV -- f1.8, ISO 800, shutter 1/100.

Any idea why I keep getting that offset duplication of the candle flames? This has happened a number of times in the past.

Can't seem to figure out what's going on.

Re: 50mm f1.8 on 7D

ScottyP — Tue, 02 May 2017 01:08:51 GMT

The nifty fifty does not have a lot of fancy anti-glare lens coatings. It has to be some kind of a reflection coming off of one lens element and then reflecting back off of another lens element in there somewhere. Still a good deal for $100 bucks.

A lens hood might help. That is exactly what they are for really.

Re: 50mm f1.8 on 7D

sloansmom — Tue, 02 May 2017 01:32:45 GMT

Thanks!!!!! I actually had the hood on. It's the strangest thing.

Re: 50mm f1.8 on 7D

jrhoffman75 — Tue, 02 May 2017 10:27:13 GMT

The reflection is upside down and backwards.

I think it is reflecting off the sensor, onto the rear element of the lens and then back to the sensor.

Known phenomenon, which is why newer lenses designed for digital have special design rear elements.

https://photo.stackexchange.com/questions/53787/is-there-a-real-difference-between-digital-and-film-lenses

Re: 50mm f1.8 on 7D

Waddizzle — Tue, 02 May 2017 11:15:22 GMT

A cheap filter can cause it, too, but I suspect that in this case it is purely internal. Which is strange, because I have use the EF 50mm f/1.8 STM, and have never experienced this issue.

Are you using the "STM" version, or the older EF 50mm f/1.8 II, the one with the plastic mount?

Re: 50mm f1.8 on 7D

ebiggs1 — Tue, 02 May 2017 14:23:22 GMT

Whatever the cause Lightroom can fix it easily. Simple mouse click.

Also will correct the WB.

Re: 50mm f1.8 on 7D

TCampbell — Tue, 02 May 2017 15:30:04 GMT

Remove the filter from the front of your lens (you likely have a UV filter on the lens).

With cheap UV filter on the lens:

Same shot - but with no filter on the lens:

All glass creates reflections. Some better filters have good anti-reflective coatings to reduce this and make the issue less noticeable, but if you want to be sure... just remove the filter completely.

Re: 50mm f1.8 on 7D

TTMartin — Tue, 02 May 2017 16:08:23 GMT

@jrhoffman75 wrote:
The reflection is upside down and backwards.

I think it is reflecting off the sensor, onto the rear element of the lens and then back to the sensor.

Known phenomenon, which is why newer lenses designed for digital have special design rear elements.

https://photo.stackexchange.com/questions/53787/is-there-a-real-difference-between-digital-and-film-lenses

I agree, get the new EF 50mm f/1.8 STM lens. It has the anti-glare coatings needed for a digital camera. In addition it has a metal mount and more precise autofocus, well worth the money to upgrade as it is still only about $100.

edit: If you already have the STM version of the lens, do as Tim says and remove the filter.

Re: 50mm f1.8 on 7D

TCampbell — Tue, 02 May 2017 16:00:33 GMT

@jrhoffman75 wrote:
The reflection is upside down and backwards.

I think it is reflecting off the sensor, onto the rear element of the lens and then back to the sensor.

Known phenomenon, which is why newer lenses designed for digital have special design rear elements.

https://photo.stackexchange.com/questions/53787/is-there-a-real-difference-between-digital-and-film-lenses

Unlikely -- due to the focus. The reflected candles aren't very far out of focus. If the reflection was coming off the imaging sensor then the light would have to travel forward a didstance close to 50mm (Canon's distance from the mounting flange to the focal plane is 44mm), reflect off the lens, and then travel back that same distance again. This would mean the light has to travel an extra 90 to 100mm beyond the focal plane to hit the image sensor a second time. What you'd end up with would have very strong out-of-focus bur.

In the post you linked, I suspect such a reflection would be so heavily blurred that it wouldn't be very well-defined but enough light (even strongly out of focus) could result in a loss of contrast.

You can test any lens for this. Just put the camera on a tripod, point it at an off-center light source, and then _heavily_ over-expose that image by a good 10 stops or so... and check the results.

But I have seen this happen with many UV filters threaded onto the front of the lens where the distance from the front lens element to the filter is much closer.