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03-26-2012, 03:53 PM   #1
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Stepdown ring as lens hood for Sigma 30?

Hi All,

Is it possible to use a stepdown ring as a lens hood for a larger diameter lens like the Sigma 30mm 1.4 (62mm filter)? (cheapo DA40 Ltd style)

I know this works well for smaller diameter lenses like the DA40, F28 and the FA43, I use a 49->28mm stepdown as a great stealth low profile hood for those.

Is a 62mm thread just too large for something like this to be effective? Or is it just a matter of getting the right diameter stepdown and it should work?

Any ideas on what would be required to be effective without a vingette? 62mm->?

Thanks for your help

(SOldbear's image from another thread, stepdown ring hoods shown here with smaller lenses)



Last edited by Deimos; 03-26-2012 at 04:00 PM.
03-27-2012, 06:57 AM   #2
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I guess nobody is enough of an "optical engineer" to know this?
03-27-2012, 05:15 PM   #3
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This approach may make sense if you use the hood to protect the lens mechanically.

The 30/1.4 should support this method because it is a full frame lens and you use it on APSC. As a guideline, draw a line from the border of the front lens lement at an angle which is half the field of view angle. Note that vignetting isn't visible to the naked eye if it isn't pronounced. Of course, you can use smaller diameters if you use the lens stopped down only or if you are ready to accept additional vignetting.

However ...

Lens hoods have a function. They are made to protect the lens from stray light. Such as direct sun light which isn't in the frame. Or light sources at night or indoor.

Your step down rings don't cast a shadow onto the front lens element. A hood works more efficiently if its diameter is small compared to its length. It's simple geometry. The angles to a point on the hood edge for opposite sides of the front lens shall be as equal as possible. They become equal for an infinite length hood. Your step ring approach is the other extreme.

So, the larger the lens diameter, the longer the hood needs to be. The lens diameter is focal length/F-Stop. The length should probably be about 1-2x this value. Which is about 30mm for the 30/1.4.

Of course, some lenses are more susceptible to stray light than others. So, your YMMV.

If you want to follow your approach, the Sigma 30/1.4 has a 62mm filter size and 22mm aperture diameter. The half angle of view is 23 (15 for APSC). From an image, the front lens seems to be 48mm and 13mm recessed. So, for APSC, the step down ring shouldn't be smaller than 55mm (58mm for FF). Assuming it is flush with the lens' front edge.

However, the function then is nil and the mechanical protection is minimal.

DISCLAIMER:

All statements made above are probably wrong. Don't blame me if it doesn't work out this way. You'll have to try first.
03-27-2012, 05:40 PM   #4
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QuoteOriginally posted by falconeye Quote
the Sigma 30/1.4 has a 62mm filter size and 22mm aperture diameter. The half angle of view is 23 (15 for APSC). From an image, the front lens seems to be 48mm and 13mm recessed. So, for APSC, the step down ring shouldn't be smaller than 55mm (58mm for FF).
Your calculation is very very good. I did try the step-down adapter ring approach with my copy of the Sigma 30mm F/1.4. I don't remember the exact details, but I think the best I could do without vignetting was either 62-55 or 62-58, and I concluded that it was not worth the effort.

If I have time, I'll try it again tonight.

Update: Test result: 62-49 does not vignette at F/22, but severely at F/1.4. I can't find my 62-52. But even if 62-52 works, it's not worth it.


Last edited by SOldBear; 03-27-2012 at 10:21 PM.
03-27-2012, 07:07 PM   #5
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QuoteOriginally posted by Deimos Quote
Is it possible to use a stepdown ring as a lens hood for a larger diameter lens like the Sigma 30mm 1.4 (62mm filter)?
For APS-C, I use Bower 72-58mm and 58-49mm step-down rings on a ZK85/1.4,
along with a 49mm rubber hood and 49mm Pentax lens cap.

It's more compact, and quicker on the draw,
than the original Zeiss hood designed for FF.
03-27-2012, 09:52 PM   #6
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QuoteOriginally posted by falconeye Quote
The 30/1.4 should support this method because it is a full frame lens
I think the 30/1.4 is APS-C only. I recall seeing images of it on a full frame camera and the edges were black.

I think the fact that it's not a full frame lens would leave you with very little room to play with. (ie. See SOldBear's experience that he shared a couple posts above.)

EDIT: Found the site with the 30mm full frame images here: Samples of Sigma 30mm f1.4 lens on Canon 5D full frame DSLR Photo Gallery by Charles Durrant at pbase.com
03-28-2012, 12:54 AM   #7
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QuoteOriginally posted by Arrvon Quote
I think the 30/1.4 is APS-C only.
You are right, it is a DC, not a DG.
I wouldn't have thought so with the Nikkor 24/1.4 and Pentax 31/1.8 both being full frame.
03-28-2012, 06:05 AM   #8
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Thanks for the response Falk and everyone else.

So, from what I am reading there are a number of issues with this type of hood in general (potential minimal flare protection) and given that this lens is not FF, there is very little chance to utilize this kind of hood on this size lens with any real benefits.

I guess the lens engineers know what they are doing when they design their hoods

That said does this mean that using these stepdown ring hoods even on smaller lenses like the FA43/F28/DA40 (or on any lenses I guess) offers minimal flare protection? Would the film-age designed hood of say the FA43 do better even on digital? I believe I have read that there is a difference between film and digital as far as hoods go unless the difference is between APS-C and FF...

03-28-2012, 06:57 AM   #9
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Would this effect the bokeh?
If so i would love to see the DA*55 test with it. =]
03-28-2012, 08:01 AM   #10
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Why use just a ring on the lens? I can guess some reasons:

1) It's possible.
2) It's compact.
3) It looks kewl.

But as mentioned, it doesn't work. A hood does provide mechanical protection, but its main purpose is to prevent incident light from reaching the lens. A ring is insufficient; a deeper inset is needed for that. But if one *must* take this approach, try this: Buy a mount-reversal adapter and a cheap set of PK macro tubes. Put the adapter on the lens and a tube section on the adapter. Voila! Instant rugged hood! And it's ugly! Ultra-kewl!

Last edited by RioRico; 03-28-2012 at 08:07 AM.
03-28-2012, 08:32 AM   #11
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QuoteOriginally posted by RioRico Quote
Why use just a ring on the lens? I can guess some reasons:

1) It's possible.
2) It's compact.
3) It looks kewl.

But as mentioned, it doesn't work. A hood does provide mechanical protection, but its main purpose is to prevent incident light from reaching the lens. A ring is insufficient; a deeper inset is needed for that. But if one *must* take this approach, try this: Buy a mount-reversal adapter and a cheap set of PK macro tubes. Put the adapter on the lens and a tube section on the adapter. Voila! Instant rugged hood! And it's ugly! Ultra-kewl!
Here a read about lens hoods.
Lens hoods
03-28-2012, 09:19 AM   #12
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I mounted a rubber lens hood on my DA 40mm and tried to compare the amount of shade it provided vs. the factory metal "hood". I couldn't see any significant difference. IMO if a step-down ring is tight to the image circle, it will shade the front element effectively.
03-28-2012, 09:29 AM   #13
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A rubber lens hood also helps to keep dust away from the lens,
and provides some cushioning against lighter impacts,
as well as stopping incident rays that might get reflected off the inside of the ring.
03-28-2012, 09:33 AM   #14
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I use a combination of empty filter rings for the depth and then step down rings to make all my lenses fit either 30.5mm or 49mm lens caps.
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