Canon LTM lens hood question

Canon M39 M39 screw mount bodies/lenses
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while searching for a hood for the soon to arrive 35/2.8, i noticed that canon has round hoods for most of it's 35mm lenses but it also has a square hood for one it's 35's ---

now, wouldn't the angle of view be pretty close for any 35mm lens?
so, why would the shape of the hood be so different?

what am i missing here?

joe
 
round v. square hoods, what's the reason?

so, does anyone have an answer?

is this a basic thing that i have missed in my photo training?

joe
 
Joe, I guess the rationale is following: lens hood should provide maximum protection from off-axis light (outside of actual frame captured) without actually obstructing the image forming on the frame (vignetting).
Since the camera frame is rectangular, it is logical that, to achieve the above, the shade should be rectangular. Circular shades provide more protection (shut out exraneous light) only in the corners, with wide areas in top and bottom (for 35mm format, but on all sides in 6x6 format) being more "exposed".
It's the test you do if you want to see whether a lens shade will vignette: put the shade on, open the back of the camera, put the shutter on "B", press shutter, and with the curtains open, look into the lens, with the back aimed at a bright background (white piece of paper will do). Slowly point the lens upwards, and you'll see the back "opening" (black frame) coming down from the top through the lens. If that black frame comes to the edge of the lens before the shade obstructs the view, the shade won't vignette. Ideal lens shade would be the one where both lines (shade and back frame) meet at the same point, at the edge of the lens. It's kind of complicated to explain, but if you do it, you'll see what I mean.
Obviously, having in mind all of the above, and if we assume that the function of a lens shade is indeed to shut out all extraneous light outside of frame, the logical conclusion is that the lens shade should be of the same format as the negative frame - i.e. for 6x6 medium format (like Rolleiflex), the shade has to be square, with all sides the same. For 35mm ("Leica") format, the shade should have the same proportions as the 35mm frame - i.e. 36 x 24 mm, i.e. 36/24 = 1.5 = meaning that the longer (top and bottom) sides should be 1.5 times longer than the shorther (left and right) sides of the "perfect" shade.

At least that's how I understand this, and I think the above explanation should clear some issues.

BTW, the circular shades are easier to manufacture (cheaper), and another very important point is that they do not vignette, regardless of how you screw them in. With rectangular shades, the shade has to be aligned properly with the negative "opening", i.e. the frame, to avoid vignetting - which usually means you need some kind of bayonet to affix the shade - making it (and the lens) more expensive/complicated to manufacture. If you ever handled a Roleliflex or another TLR camera, you have probably noticed that it's almost impossible to "mount" the shade incorrectly - once you "lock" it in position, it's aligned perfectly. If it's askew, it means it's not locked.

Hope this helps,

Denis
 
thanks denis.
it seems so obvious now, that the shape should mirror the film opening, but i guess i must be too used to the round shape of most hoods to have given it much thought.

i am now more curious to see how this squared off hood will do with my rectangular opening.
curiously, this hood is actually made for a different 35 mm lens but it has the same filter size so i bought it.

i hope to get the 'proper' shade someday but this will do (i hope).

joe
 
Shouldn't flower-shaped lens hood give better shading than rectangular one?

The shortest distance will be from the center of the frame to the top/bottom of the frame and the distance from the center to the corner of the frame is the longest. Flower-shaped hood has the largest petal on top and bottom and cut on the corners so that it does not cause vignetting.

Also, eventhough two lenses have the same focal length, it doesn't mean they can use the same lens hood. One lens may have deeply recessed front element (like 50/2.5 Compact Macro) and the other doesn't, etc.
 
Thanks for the excellent explanation.

Another reason for manufacturers to favor circular hoods is that w/many lenses, including most Zeiss glass for the Contax RF & many Canon RF lenses like the 100/2, the entire lens front rotates during focusing, making it difficult to keep a rectangular hood aligned.

denishr said:
. . .

BTW, the circular shades are easier to manufacture (cheaper), and another very important point is that they do not vignette, regardless of how you screw them in. With rectangular shades, the shade has to be aligned properly with the negative "opening", i.e. the frame, to avoid vignetting - which usually means you need some kind of bayonet to affix the shade - making it (and the lens) more expensive/complicated to manufacture. If you ever handled a Roleliflex or another TLR camera, you have probably noticed that it's almost impossible to "mount" the shade incorrectly - once you "lock" it in position, it's aligned perfectly. If it's askew, it means it's not locked.

Hope this helps,

Denis
Click to expand...
 
Kris said:
Shouldn't flower-shaped lens hood give better shading than rectangular one?
...
Also, eventhough two lenses have the same focal length, it doesn't mean they can use the same lens hood. One lens may have deeply recessed front element (like 50/2.5 Compact Macro) and the other doesn't, etc.
Click to expand...

Kris, I'm really not an expert on shades :)

All of the above was actually the stuff I read elsewhere, and some of the tests I did myself (shade vignetting test).

As for "tulip" or "flower-shaped" hoods, I know I usually see them for wider lenses. I bet you'll never see one used by a professional cameraman (cinematographer) :)
If in doubt about which are the best lens shades, check out what the pros use - I mean professional cameramen - you'll almost always see collapsible bellows shades. Those are used for different lenses, and since the film format is always the same, only the distance to the front element is adjusted, depending on the focal length of the lens.
I mean, those guys shoot some very expensive film, and the footage they make usually costs a fortune to redo/reshoot. Ergo, they usually use fool-proof equipment. I admit I have not seen that many cameramen at work, but those I did see (either in person, in various documentaries on TV or on photos) inevitably used rectangular bellows hoods. Not ONE of them ever had a circular (round) hood, and I've never seen a tulip-shaped shade on a professional (movie) camera.

As for the remark on different hoods for same focal length, you are right - but the hood vignetting test I mentioned should provide you with the answer.
Too bad you can't do that when buying from ebay :(
All that said, I must admit that I use mostly circular hoods on my lenses - those were the only ones I could find, most are not originals, and were bought second-hand.
However, even a substitute, circular, lens hood is better than no hood at all.

Denis
 
Joe:
Yikes! $37 (US!). I have two of these and rarely use either. I also have a round Canon shade, marked for 50/1.8, 35/2.8, 35/3.2. With the 35/1.8 on a P, it blocks the corner of the finder. It extends in to the 100 frame lines. The 2.8 lens is much flatter, but the hood will still stick into the finder quite far. I think these hoods were meant for use on the bottom loaders with an auxiliary finder. Before you look on ebay, you should ask if anyone here has what you want/need.
 
i know, i know!
that hood was at 13 bucks till the end and then i got caught up in the competition and lost it. kevencameras even has one for 35 dollars. it was a dumb move.
however, i still want one made for that 35/2.8 and since you have one...would you like to sell it to me?

joe
 
Sell it? OK. It's in good shape-round as the day it left the factory-but it has some bright marks. I don't know what it's worth; I bought it over a year ago to hold Series VI filters on the 35/1.8, but then bought a set of 40mm Walz filters a week or two later.
 
well, considering you were kinda making fun of me for spending 37 bucks, my manly pride dictates that it has to be under 37 bucks.
just take what you paid for it and then discount that figure about 60% ;)

but seriously, i have paid as low as 4 bucks and as high as 37 for a canon hood.
i want it for sure, you have me at your mercy...name a price (gulp).

joe
 
I don't remember what I paid for it. How about $20 CDN, including postage from Toronto to Edmonton? If I could figure out how to attach an image to this reply, you'd be able to see the hood.
 
done deal!

i will send a crisp 20 dollar bill tomorrow, provided the postal outlet is doing business.

don't need a pic, i trust ya! even if you come from taranta...
maybe p.m. me with your info and i'll reply with mine.

joe
 
btw, for future reference...

for posting a pic from your hard drive go to
'post reply' at bottom of post
under the messege box you will see (i think) 'attachments' hit that, go to your pic & click.

joe
 
very nice and it's silver to boot, great!

that's a very nice looking p you have there.
i take it you are a canon user then?
what else ya got?
if i'm not being too forward..

joe
 
denishr said:
Joe, I guess the rationale is following: lens hood should provide maximum protection from off-axis light (outside of actual frame captured) without actually obstructing the image forming on the frame (vignetting).
Since the camera frame is rectangular, it is logical that, to achieve the above, the shade should be rectangular. Circular shades provide more protection (shut out exraneous light) only in the corners, with wide areas in top and bottom (for 35mm format, but on all sides in 6x6 format) being more "exposed".
It's the test you do if you want to see whether a lens shade will vignette: put the shade on, open the back of the camera, put the shutter on "B", press shutter, and with the curtains open, look into the lens, with the back aimed at a bright background (white piece of paper will do). Slowly point the lens upwards, and you'll see the back "opening" (black frame) coming down from the top through the lens. If that black frame comes to the edge of the lens before the shade obstructs the view, the shade won't vignette. Ideal lens shade would be the one where both lines (shade and back frame) meet at the same point, at the edge of the lens. It's kind of complicated to explain, but if you do it, you'll see what I mean.
Obviously, having in mind all of the above, and if we assume that the function of a lens shade is indeed to shut out all extraneous light outside of frame, the logical conclusion is that the lens shade should be of the same format as the negative frame - i.e. for 6x6 medium format (like Rolleiflex), the shade has to be square, with all sides the same. For 35mm ("Leica") format, the shade should have the same proportions as the 35mm frame - i.e. 36 x 24 mm, i.e. 36/24 = 1.5 = meaning that the longer (top and bottom) sides should be 1.5 times longer than the shorther (left and right) sides of the "perfect" shade.

At least that's how I understand this, and I think the above explanation should clear some issues.

BTW, the circular shades are easier to manufacture (cheaper), and another very important point is that they do not vignette, regardless of how you screw them in. With rectangular shades, the shade has to be aligned properly with the negative "opening", i.e. the frame, to avoid vignetting - which usually means you need some kind of bayonet to affix the shade - making it (and the lens) more expensive/complicated to manufacture. If you ever handled a Roleliflex or another TLR camera, you have probably noticed that it's almost impossible to "mount" the shade incorrectly - once you "lock" it in position, it's aligned perfectly. If it's askew, it means it's not locked.

Hope this helps,

Denis
Click to expand...

Denis

Thanks for the explanation. I was waiting and hoping that someone else would answer this question. I was trying to avoid the lengthy explanation. You saved me from typing HELL!

Thanks
Russ
 
Joe,
That Canon P is kind of a sad story...pretty good deal from ebay... then a CLA...I really like it for 50mm lenses...I buy a Canon 50/1.4 to use...then last winter the camera slid off a cafe seat and hit the table leg...no damage except the front glass of the finder is cracked.

I actually prefer the bottom loaders for their small size, but sold a nice IV in the mid-70's. Fifteen years later I bought a Serenar 50/3.5 from Downtown Camera. The SAME Serenar that was on the IV! It's now on my Leica IIIF. I've always bought Canon or Nikon lenses for the IIIf because I couldn't afford Leitz lenses. Now I prefer the Japanese lenses. They're simply better than German lenses of the same vintage.
 
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