[K David]

I have three versions of the 50mm f/1.4 in K (plus the M42.) I have and have used the K, SMC-M, and SMC-A. I've used the M the most and it's the best 50mm lens I've ever used. I tried out my A for the first time a few weeks ago and noticed it was hot spotting in the center, greenish, and chalked it up to bad flash placement. It then did the same thing in daylight, indoor light, and low-light in subsequent shoots.

I've heard of hot spotting before but thought it only affected lenses when they were pushed beyond their normal operating range (for instance in macros). Does anyone have experience with this version of the 50mm f/1.4 hot spotting or know what the cause or solution might be?

I've only used it on digital so far.

[monochrome]

Could it be sensor reflections/ghosting? (Mine doesn't do this).

[Wheatfield]

I have three versions of the 50mm f/1.4 in K (plus the M42.) I have and have used the K, SMC-M, and SMC-A. I've used the M the most and it's the best 50mm lens I've ever used. I tried out my A for the first time a few weeks ago and noticed it was hot spotting in the center, greenish, and chalked it up to bad flash placement. It then did the same thing in daylight, indoor light, and low-light in subsequent shoots.

I've heard of hot spotting before but thought it only affected lenses when they were pushed beyond their normal operating range (for instance in macros). Does anyone have experience with this version of the 50mm f/1.4 hot spotting or know what the cause or solution might be?

I've only used it on digital so far.

Do you have a filter on the lens?

[stevebrot]

I've heard of hot spotting before but thought it only affected lenses when they were pushed beyond their normal operating range (for instance in macros). Does anyone have experience with this version of the 50mm f/1.4 hot spotting or know what the cause or solution might be?

Yes, it does happen in general use with some lenses,* but I have never heard of any problems with an Asahi or Pentax-brand 50/1.4. As with Wheatfield, I wonder if maybe a filter might be to blame.


Steve

* My Auto Rikenon 55/1.4 hot-spots due to its wide, flat rear element that readily reflects back onto the sensor in some lighting conditions.

[kiwi_jono]

Likewise, I don't have this issue with my A50 f1.4
As an aside, while I love the build of my M50 f1.4, I have noticed my copy of the A50 f1.4 is just a bit sharper (especially near wide open) and I understand they did tweak the optical formula slightly for A (and same formula for the following F and FA variants).

[Quartermaster James]

Isn't there one version of this lens that has delamination problems? Could that cause this?

[Not a Number]

No such problems with my copy, with or without a filter.

Post an example image.

[K David]

Do you have a filter on the lens?

No filters.

Could that cause this?

Optics are spectacular

Post an example image.

I have two from some eBay shots I took. The others I deleted as they weren't usable.





The hot spot changes size and shape with the aperture setting, too.

Could it be sensor reflections/ghosting

I like this as a candidate but I'm not sure. I should give this lens a go on film under the same conditions as the DSLR and see if it repeats.

[Not a Number]

I think @monochrome called it and you're getting reflection off the rear element. On mine the coatings look similar in color.

Well after all film era lenses are not optimized for digital cameras and this is one of the problems that can happen.

https://www.pentaxforums.com/forums/173-general-photography/331960-old-film-l...d-digital.html

[bassek]

Likely the white background with bright lighting makes reflections more prone on the dark objects in the center of the shot.
Anyone agree or disagree?

Seb

[Ontarian50]

Back awhile, Tamron updated some of their film era lenses (including the excellent 90mm macro) and re-badged them "Di" for digitally integrated. While this was the time when everything photographic was getting a "digital" tag grafted onto it (digital tripods, anyone?) Tamron pointed out that what they had done was upgrade/change the coatings on the rear lens elements.

Again, this was to suppress reflections off the shiny sensor from bouncing back off a shiny rear element - something that didn't really happen when the destination was a matte-surfaced piece of film. The problem seems to be worse with large flat rear elements

This is a similar problem to ghosting off the rear surfaces of filters, especially noticeable with bright points of light at nighttime (which has been discussed here before).

As for the aperture shaped reflection (yup, I've seen my ghosts clearly hexagonal in shape) I've sometimes gone so far as to select the offending area in Photoshop and desaturate the offending colour cast. It can work surprisingly well.

[ScooterMaxi Jim]

David, there is no doubt that you have a significant hot-spot there, just as originally indicated.

I know for certain that the f/1.4 lens was redesigned between the m-series and the A-series. I own the m-series and haven't seen the problem even when mounted on a Q body (this would be the ultimate torture test). I'd be curious to know if the rear element is flatter on the A-series.

By the way, you haven't mentioned which body you are using - and that can have some impact. My guess is its on a K-3.

[K David]

My guess is its on a K-3.

You are correct.

Anyone agree or disagree?

Agree

I think @monochrome called it and you're getting reflection off the rear element

It dawned on me last night that it might be off an internal element in front of the aperture. Since the hot spot changes size and shape based on the aperture, it can't be reflected just off the rear element. That would explain the blue margin: diffraction.

But it looks like it's a characteristic of this copy of the lens, unfortunately.

[Wheatfield]

No filters.



Optics are spectacular


I have two from some eBay shots I took. The others I deleted as they weren't usable.





The hot spot changes size and shape with the aperture setting, too.


I like this as a candidate but I'm not sure. I should give this lens a go on film under the same conditions as the DSLR and see if it repeats.

I have the same problem with my A100 f/2.8 macro. It's a flare caused by the white background. I had thought it was limited to FREE designed lenses, but apparently not. What you are seeing is a sensor reflection off one of the lens elements. Unfortunately, the only way I have found to eliminate them with lenses that are prone to it is to discontinue the use of high key backgrounds.

[altis]

I've noticed it too with the F 50/2.8 macro. Happens when I try to get a bright white background with flash.

Here's how I fixed it - well sort of. It doesn't make it all go away but at least it's not so offensive:
Correcting SMC-F 50/2.8 macro hot spot: Pentax SLR Talk Forum: Digital Photography Review