molson wrote:
I guess that's why the better lenses have those little sliding doors in the lens hoods... to let all the blurry air drain out.
an engineer would be capable of easily answering the last two/three questions put forth, no?
also why are there lens hoods with several, or more, permanent openings near the front element?
One of the first things I've done with my new long lenses (100-400mm, 75-300mm and 45-150mm) is to replace the factory lens hood with a one inch long screw-in hood. The short hood doesn't trap enough warm air to impact the images but still long enough to protect the front element from most bumps and scratches -- I don't fret much about flare because I seldom shoot toward the sun.
My vehicle is seldom heated to above 60-64 degrees in the winter and when shooting the first ting I do is open both front windows, shut off the heater fan and then the engine. By shooting in bursts some photos are sharp despite the escaping heat and the heat is soon dissipated anyway, even at zero (F) or below.
S-IS Off (Still-I.S. Off) Image stabilization disabled. Select this option when using a tripod.
S-IS Auto (Auto I.S.)
Image stabilization applies to motion on all axes. If panning motion is detected, the camera will
automatically suspend image stabilization on that axis.
S-IS1 (All Direction Shake I.S.) Image stabilization applies to motion on all axes.
S-IS2 (Vertical Shake I.S.) Image stabilization applies to vertical motion. Use when panning the camera horizontally.
S-IS3 (Horizontal Shake I.S.) Image stabilization applies to horizontal motion. Use when panning the camera vertically.
If you end up panning with SIS auto then the camera may think you are wanting to have a panned image, when in fact you don't want it, so perhaps putting it on SIS1 would be better in this case.
Paul_100A wrote:
an engineer would be capable of easily answering the last two/three questions put forth, no?
also why are there lens hoods with several, or more, permanent openings near the front element?
The two large permanent openings in the hood are to let light through to the front element so you can take a picture with the hood attached...
Lightweight metals like aluminum have a thermal coefficient a couple of orders of magnitude (i.e., more than 100x) greater than glass, so any heat trapped inside the lens will be rapidly absorbed by the lens barrel of a large telephoto. This is more likely the cause of issues when taking the lens from a warm environment to a cold one - the lens barrel will change temperature more rapidly than the internal elements, and the difference in thermal expansion coefficients can be enough to affect focus. The only solution to this is to give the lens enough time to equalize its internal temperature with the surrounding environment.
If you actually believe the problem is warm air trapped in the lens hood, just take the hood off so the warm air dissipates - which will only take a couple of seconds - and then put the hood back on.
As for the heat dissipating through the front element despite its low thermal capacity relative to the metal parts of the lens, remember that the elements are separated by sealed air gaps between the groups, so very little of the internal heat will be able to make its way to the front element in the first place.
Colin F wrote:
The material is irrelevant. Here, watch this:
That test is flawed because he apparently did not repeat the test by starting without the hood and then adding it afterwards, to determine if the hood was actually the cause of the problem, and not just a coincidence.
The real way to find out if the cause is heat from the front elements causing air currents would be to film the tests using a Schlieren camera.
molson wrote:
The two large permanent openings in the hood are to let light through to the front element so you can take a picture with the hood attached...
Lightweight metals like aluminum have a thermal coefficient a couple of orders of magnitude (i.e., more than 100x) greater than glass, so any heat trapped inside the lens will be rapidly absorbed by the lens barrel of a large telephoto. This is more likely the cause of issues when taking the lens from a warm environment to a cold one - the lens barrel will change temperature more rapidly than the internal elements, and the difference in thermal expansion coefficients can be enough to affect focus. The only solution to this is to give the lens enough time to equalize its internal temperature with the surrounding environment.
If you actually believe the problem is warm air trapped in the lens hood, just take the hood off so the warm air dissipates - which will only take a couple of seconds - and then put the hood back on.
As for the heat dissipating through the front element despite its low thermal capacity relative to the metal parts of the lens, remember that the elements are separated by sealed air gaps between the groups, so very little of the internal heat will be able to make its way to the front element in the first place....Show more →
Cool. thanks for the explanation of thermal coefficient.
what is your theory as to why the image is immediately sharper once the lens hood is removed in cold temps?
Paul_100A wrote:
an engineer would be capable of easily answering the last two/three questions put forth, no?
also why are there lens hoods with several, or more, permanent openings near the front element?
I thought those were so you could manipulate a filter (variable ND or Circular Polarizer)... nothing to do with heat etc
My combo of the OM-1 and the 150-400mm performs great. I’m not an expert on any of this, but I do hope OP has a chance to test the combo in an environment that rules out weather-related issues so he knows whether there’s something wrong with the body or lens.
In all cases where I had any long-lens system screw up, it was related to heat shimmers. That applies to Canon, Nikon and Olympus, as well as Sony. Exception was the Sony A7RIV and the 200-600mm, which just had issues.
johnvanr wrote:
My combo of the OM-1 and the 150-400mm performs great. I’m not an expert on any of this, but I do hope OP has a chance to test the combo in an environment that rules out weather-related issues so he knows whether there’s something wrong with the body or lens.
I'm now thinking that my muddy images were due to not just one, but two things; the whole heat/cold issue, and the IS-Auto setting which I have now set back to the default (1).
Did you try shooting again with IS 1 setting and without hood to see if it improves? I'm on the fence about buying this expensive lens and have heard many negative things about its performance given its extremely high price, so I'm a bit concerned.
HicHic wrote:
Did you try shooting again with IS 1 setting and without hood to see if it improves? I'm on the fence about buying this expensive lens and have heard many negative things about its performance given its extremely high price, so I'm a bit concerned.
I haven't had the chance yet, but I don't think you should have any concern about the lens itself, it's very good, and nothing else like it for m4/3. After all this helpful discussion, I think my issues were both the extreme temperatures, and the IS setting.
I wouldn't want to be limited to a fixed focal length like the 300mm, nor the 100-400, the 150-400 with built-in 1.25 TC is enormously versatile. I yearn for an update to the OM-1 however; I'm having a hard time adjusting from the 50 MP of the Sony A1.
Colin F wrote:
I haven't had the chance yet, but I don't think you should have any concern about the lens itself, it's very good, and nothing else like it for m4/3. After all this helpful discussion, I think my issues were both the extreme temperatures, and the IS setting.
I wouldn't want to be limited to a fixed focal length like the 300mm, nor the 100-400, the 150-400 with built-in 1.25 TC is enormously versatile. I yearn for an update to the OM-1 however; I'm having a hard time adjusting from the 50 MP of the Sony A1.
I'm very pleased with my 300/4 images, even with the 2x. I've seen very few images in the 150-400 thread that match what my 300/4 can do, but I see plenty of mediocre results. It's hard to say if the lens is poor, or if it's just due to the photographer. If the 150-400 can emulate what my 300/4 does, but with the added bonus of the flexibility to zoom out when the subject gets too close, then that would be perfect.
If you are shooting at 400mm with a 1.4x, then the results should be very close to the A1 when using a 600mm lens (given the same shooting distance), since you will need to crop significantly in post on the A1 in order to match the OM-1's framing.
HicHic wrote:
Did you try shooting again with IS 1 setting and without hood to see if it improves? I'm on the fence about buying this expensive lens and have heard many negative things about its performance given its extremely high price, so I'm a bit concerned.
Colin F wrote:
I haven't had the chance yet, but I don't think you should have any concern about the lens itself, it's very good, and nothing else like it for m4/3. After all this helpful discussion, I think my issues were both the extreme temperatures, and the IS setting.
I wouldn't want to be limited to a fixed focal length like the 300mm, nor the 100-400, the 150-400 with built-in 1.25 TC is enormously versatile. I yearn for an update to the OM-1 however; I'm having a hard time adjusting from the 50 MP of the Sony A1.
The 50MP with a similar length lens will win, but you won’t find a lens with a similar length and quality for FF unless you spend way more, use converters and are willing to schlepp that gear.
Colin F wrote:
It isn't the processing, because when I view the images from the day to do my culling, I'm using the "OM Workspace" software, and the files are simply and obviously terrible. I do get the odd one that is good, but again, all the stars have to be aligned just right for that to happen.
Oh, the OM workspace software is terrible. The only real use for it is generating TIFF files from hires raws.
Colin F wrote:
The material is irrelevant. Here, watch this:
I really doubt his explanation is accurate, although it's difficult to say what could be causing the results he mentioned without fully understanding how he conducted the test. The difference he showed really looks more like fogging of a lens element than heat distortion.
