strong spherical projection

Started 10 months ago | User reviews
chanaw
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strong spherical projection
10 months ago

I love this lens for being so small. Walking around, the people will not even notice when photographed. The bad side is the strong spherical projection. Sometimes it does not matter, however, for landscape and buildings with a more flat appearance this lens delivers pictures not so good as should be.

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4.0
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4.5
Leandros S
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your copy may not be typical
In reply to chanaw, 10 months ago

Assuming that you're referring to barrel distortion, I suspect that your copy is not in spec - photozone review has this to say:

"exhibits only a minor degree of barrel distortion (~0.6%) which is usually not an issue"

Source: http://www.photozone.de/pentax/630-pentax40f28?start=1

If you're really noticing the distortion, there's probably something wrong with your copy.

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No amount of perceived entitlement can replace actual expertise.

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chanaw
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Re: your copy may not be typical
In reply to Leandros S, 10 months ago

I know what barrel distLeandros S wrote:

Assuming that you're referring to barrel distortion, I suspect that your copy is not in spec - photozone review has this to say:

"exhibits only a minor degree of barrel distortion (~0.6%) which is usually not an issue"

Source: http://www.photozone.de/pentax/630-pentax40f28?start=1

If you're really noticing the distortion, there's probably something wrong with your copy.

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No amount of perceived entitlement can replace actual expertise.

I know what barrel distortion is.

Thanks.

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Msroberts
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Re: your copy may not be typical
In reply to chanaw, 10 months ago

chanaw wrote:

I know what barrel distLeandros S wrote:

Assuming that you're referring to barrel distortion, I suspect that your copy is not in spec - photozone review has this to say:

"exhibits only a minor degree of barrel distortion (~0.6%) which is usually not an issue"

Source: http://www.photozone.de/pentax/630-pentax40f28?start=1

If you're really noticing the distortion, there's probably something wrong with your copy.

I know what barrel distortion is.

Are you saying the distortion you're seeing is not barrel distortion? If so could you please describe what you're seeing?

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chanaw
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Re: your copy may not be typical
In reply to Msroberts, 10 months ago

Msroberts wrote:

chanaw wrote:

I know what barrel distLeandros S wrote:

Assuming that you're referring to barrel distortion, I suspect that your copy is not in spec - photozone review has this to say:

"exhibits only a minor degree of barrel distortion (~0.6%) which is usually not an issue"

Source: http://www.photozone.de/pentax/630-pentax40f28?start=1

If you're really noticing the distortion, there's probably something wrong with your copy.

I know what barrel distortion is.

Are you saying the distortion you're seeing is not barrel distortion? If so could you please describe what you're seeing?

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It's simply spoken unsharp at the border where it should be sharp. It's very easy to see. The lens is sharp, but not in a flat plane, but strongly curved toward the camera. Sometimes it helps to get a real sharp picture from border to border, e.g., when photographing a scene where I stand in front of a building and at the border there are trees in the foreground. So I found out that the projection is a sphere rather than a flat plane.

I'm not the first person who makes this observation. For instance, go to the slrgear.com review and see the blur index. It starts with +1 from left to the center and goes up to +2 at the right border. They tell it so: "Our review sample of the 40mm ƒ/2.8 seemed to be slightly sharper on the left side than the right". In fact, it is perfectly sharp on the right side also, but you need to have some object in the foreground.

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Giklab
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Field curvature /nt
In reply to chanaw, 10 months ago

no text

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chanaw
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Re: Field curvature /nt
In reply to Giklab, 10 months ago

Giklab wrote:

no text

Yes, and it is very pronounced, so I'm wondering that so many people didn't notice. The effect worsens if you stop down. This is really strange, however, you can see it again at slrgear.com when you stick the slider to f/5.6. The curve starts at +1.5 at the left border, lowers down to +1 in the center and rises to just a bit under +3 at the right border.

If this is a bad copy, so I'm not the only one who got one of those.

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chanaw
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Re: strong spherical projection - Examples
In reply to chanaw, 8 months ago

I still owe the proof. Here is the very annoying picture.

Of course, you can have it sharp in the middle. This is not the problem with this lens. See this.

If you look through the branches you can see the center of the opposite shore is very sharp. On the border the opposite shore is out of focus, but the branches in the foreground are still sharp.
I've never seen such a pronounced field curvature elsewhere.

 chanaw's gear list:chanaw's gear list
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MightyMike
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Re: strong spherical projection - Examples
In reply to chanaw, 8 months ago

Why haven't you got it serviced yet? clearly you have a bad copy, stop complaining and get it serviced.

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Mike from Canada
"I am not a great photographer! God is a great creator! All I do is capture His creation with the tools He has provided me."
'I like to think so far outside the box that it would require a telephoto lens just to see the box!' ~ 'My Quote :)'
http://www.michaelfastphotography.com/galleries/VP-BDI_3a.jpg
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chanaw
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Re: strong spherical projection - Examples
In reply to MightyMike, 8 months ago

MightyMike wrote:

Why haven't you got it serviced yet? clearly you have a bad copy, stop complaining and get it serviced.

It's not a bug, it's a feature.

Since this lens is really sharp and I'm not sure what I will get back after "servicing" (what should they do?), I'm keeping this lens for special sceneries.
No one else will be in a position to control a certain situation when this particular property would be required.

Seriously, I guess, this is a standard error of the production line, because slrgear.com states the same.

In their blur index diagram of this lens the blur on the border starts moderately at f2.8 and increases surprisingly when stopped down. The maximum is at f5.6.

Really annoying is it only, when you expect to receive a lens with a behaviour "as usual".

Thank you and best regards!

 chanaw's gear list:chanaw's gear list
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Flex M
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Re: spherical like this?
In reply to chanaw, 8 months ago

Courtesy NASA/JPL-Caltech

http://kayakfari.wordpress.com/2014/01/01/happy-new-year/

Flex Maslan
www.kayakfari.com

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MightyMike
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Re: strong spherical projection - Examples
In reply to chanaw, 8 months ago

most issues like this get weaker as you stop down... perhaps its the aperture that is tilted.

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Mike from Canada
"I am not a great photographer! God is a great creator! All I do is capture His creation with the tools He has provided me."
'I like to think so far outside the box that it would require a telephoto lens just to see the box!' ~ 'My Quote :)'
http://www.michaelfastphotography.com/galleries/VP-BDI_3a.jpg
http://www.airliners.net/search/photo.search?sort_order=views%20DESC&first_this_page=0&page_limit=180&&emailsearch=mighty_mike88%40hotmail.com&thumbnails=

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chanaw
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Re: spherical like this?
In reply to Flex M, 8 months ago

Yes, exactly that's it!

In a special situation like this, the lens is wonderful.

All you need is the right scope of application.

Thank you and kind regards!

 chanaw's gear list:chanaw's gear list
Pentax K-3 Pentax smc DA* 200mm F2.8 ED (IF) SDM Pentax smc D-FA 100mm F2.8 Macro WR Pentax smc D-FA 50mm F2.8 Macro Canon PowerShot S100 +8 more
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chanaw
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Re: strong spherical projection - Examples
In reply to MightyMike, 8 months ago

MightyMike wrote:

most issues like this get weaker as you stop down... perhaps its the aperture that is tilted.

It gets better from f8...

Thank you for suggestion.

Although the effect is seen to the extreme left and right, it is not quite symmetrical. The pictures explain exactly what slrgear.com has measured. They did not measure the field-curvature, but the blur caused by curvature. Maybe there are two bad copies?

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miles green
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Bad lens
In reply to MightyMike, 8 months ago

I'm with mike:

Based on the fiirst picture in particular, i think your lens needs repairs.

Infinity stop is off and field curvature is waaaay more than what's acceptable.

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Miles Green
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Corfu, Greece

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MightyMike
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Re: strong spherical projection - Examples
In reply to chanaw, 8 months ago

The tilt might change as the aperture rotates and of course most effects like this do vanish with higher DOFs

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Mike from Canada
"I am not a great photographer! God is a great creator! All I do is capture His creation with the tools He has provided me."
'I like to think so far outside the box that it would require a telephoto lens just to see the box!' ~ 'My Quote :)'
http://www.michaelfastphotography.com/galleries/VP-BDI_3a.jpg
http://www.airliners.net/search/photo.search?sort_order=views%20DESC&first_this_page=0&page_limit=180&&emailsearch=mighty_mike88%40hotmail.com&thumbnails=

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rogerstpierre
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Re: strong spherical projection
In reply to chanaw, 8 months ago

Interesting observation. I must admit, field curvature is one thing I never noticed on my DA40 and in any cases, strong is certainly not how I would describe it on mine.

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Roger

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andrew britten
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Re: strong spherical projection - Examples
In reply to chanaw, 8 months ago

chanaw wrote:

MightyMike wrote:

most issues like this get weaker as you stop down... perhaps its the aperture that is tilted.

It gets better from f8...

Thank you for suggestion.

Although the effect is seen to the extreme left and right, it is not quite symmetrical. The pictures explain exactly what slrgear.com has measured. They did not measure the field-curvature, but the blur caused by curvature. Maybe there are two bad copies?

This lens has long been well regarded for its sharpness, corner to corner, regardless of aperture.

You've got a bad, maybe dropped, copy - simple as that.

AB

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chanaw
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Re: strong spherical projection
In reply to rogerstpierre, 8 months ago

rogerstpierre wrote:

Interesting observation. I must admit, field curvature is one thing I never noticed on my DA40 and in any cases, strong is certainly not how I would describe it on mine.

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Roger

Thank you!

Maybe that even a bad copy could produce an image like this. Or, would you regard this as the result of a bad copy?

My attention was aroused when I saw the review of Klaus Schroiff at photozone. He did a valuable remark when he tested this lens on a K-5: "You may also spot a slight focus shift towards the background when stopping down ("residual spherical aberrations") - if you observe the "17" at the various aperture settings in the chart below you will notice that it doesn't get any sharper and the focus hotspot moves towards the background."

Moreover, if you look carefully you can see that in his demonstration the lines which are about in the middle of DOF at f2.8 actually walk out of the field regarded as sharp at f5.6. In other words, if the camera focusses a special spot at f2.8 exactly, this spot may be OOF when stopped down. I have not only one picture showing this behaviour. This effect may be independent of field curvature.

However, I must admit that in most cases DOF helps very much with this short focus length. And in many pictures the extreme borders do not count. So, I'm quite happy with this lens also. I do not play football with my lenses.

Some people already mentioned that this pancake because of it's extraordinary smallness has to face some compromise in IQ.

So, I believe that it is not evil to deliver some examples for the "bad" side also. We have not always fair weather.

Kind regards.

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JeffAHayes
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Re: strong spherical projection
In reply to chanaw, 8 months ago

What IS that in your next-to-last picture, Chanaw -- the Leaning Tower of Piza??? Take that lens back for an EXCHANGE -- like YESTERDAY!!!!!

Jeff

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A word is worth 1/1000th of a picture... Maybe that's why I use so many words!

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