Disappearing Props.

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Mooshie1956
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Disappearing Props.

Post by Mooshie1956 »

So I was at Old Warden yesterday, and having a quick look through my photos I've noticed I really didn't catch the props. Can anyone help explain why this would happen. Using a Z50 and the native 50 250 DX lens. aperture f8 shutter speed 1/500 or 1/320 and iso 200. I was using a mix of auto tracking and centre point focus. I was using auto to select between electronic and mechanical shutter, as far as I'm aware it was using mechanical.
I don't think I've ever had this before while using a SLR so I'm confused if it's due to being a mirrorless camera or just a case of the weather. I've just done a quick edit to show the missing props, and from a quick scan it looks like it's on most if not all photos.

Harvard, the prop shows but not very well in my opinion
Image

Seafire, Again it's there in parts but just not right.
Image

Comet, totally missing the top prop blade.
Image
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cg_341
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Re: Disappearing Props.

Post by cg_341 »

That's prop blur, caused by a slow shutter speed blurring the motion of the blades. Most people aim to achieve some form of blur so it doesn't look like the aircraft is levitating with the engine off!

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Mooshie1956
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Re: Disappearing Props.

Post by Mooshie1956 »

cg_341 wrote:
Mon 02 May 2022, 9:24 am
That's prop blur, caused by a slow shutter speed blurring the motion of the blades. Most people aim to achieve some form of blur so it doesn't look like the aircraft is levitating with the engine off!
I know it's prop blurr but why don't I see any of the top engine prop in the comet example. Using the old DSLR I would always see some sort of blurr.
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Stagger2
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Re: Disappearing Props.

Post by Stagger2 »

I'm thinking that at your 'assumed' shutter speed of "1/500 or 1/320 and iso 200" would give more blade definition than I personally want. Therefore the only other issue with the flying shots could be over exposure/compensation to wrest some colour detail of the aircraft from a milky white sky?
A recent test of a Canon R5 convinced me that for aviation purposes I will retain my DSLR's for now as I can get them to do exactly what I want ! :wink:

Berf
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Re: Disappearing Props.

Post by Berf »

Interesting to think that you can't get the R5 to do what you want!

Brenden S
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Re: Disappearing Props.

Post by Brenden S »

I can see all the props. The issue is that due to your settings it blends in with the background as the props are overexposed. This is due to a low shutter causing prop plur. If you want to see the propellers make sure you shutter is around 1/1000

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Re: Disappearing Props.

Post by Pen Pusher »

Brenden S wrote:
Mon 02 May 2022, 11:55 pm
If you want to see the propellers make sure you shutter is around 1/1000
At that speed you end up with frozen prop blades. At Duxford I shoot at 1/350 to 1/400. If the images are Jpegs, then you are stuck with what you've got but in RAW and if I had a photo like that, I would move the exposure slider to the left, to darken the image and bring out any details in the sky if there are any, and move the Shadows slider to the right to recover details from the aircraft and tweak the other sliders from there.
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Berf
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Re: Disappearing Props.

Post by Berf »

Are you sure you had selected mechanical shutter?
If not it may be rolling shutter issues... see this video -

https://youtu.be/u1AjSGF_FCI

it has a prop example although I have not looked at it all.

Useful though for anyone who has not heard of rolling shutter and is new to mirrorless.

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Mooshie1956
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Re: Disappearing Props.

Post by Mooshie1956 »

Thanks for all the replies everyone, what I'm going to assume is that it's and mix of incorrect exposure and the bad weather. I don't think it's rolling shutter as I could always hear the mechanical shutter going off.
I've posted up 4 pics for now on the airshow photo section with a new flickr account I've just made, if anyone's interested I think you'll be able to read the exif files.
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Jakub.Zurek
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Re: Disappearing Props.

Post by Jakub.Zurek »

Seafire and Comet props definitely look unnatural to me - my initial thought would be the rolling shutter (though I don't use a mirrorless setup myself) - perhaps worth double checking all your settings again with the manual.

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Archer
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Re: Disappearing Props.

Post by Archer »

For reference purposes, a typical prop turns at something like 2400 RPM which is equal to 2400/60 = 40 Revs/second. Using a 1/500 shutter speed you'll get an arc which is (40/500)*360 or approximately 29 degrees of rotation. Let's call it 30 degrees. The Harvard photo is pretty close to that, so that checks out. The SeaFire/Hurricane photo (other thread) or the photos above appear to show a smaller arc, but they may be using a lower RPM setting of course. Still, it appears to be in the right ballpark. If the prop blade is mostly pointing towards your camera when you take the photo, you may end up with a photo very like that dH.88 Comet shot. It doesn't rule out a rolling shutter issue but could be just a case of bad luck as well.

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Re: Disappearing Props.

Post by FarnboroJohn »

Archer wrote:
Thu 02 Jun 2022, 12:55 pm
For reference purposes, a typical prop turns at something like 2400 RPM which is equal to 2400/60 = 40 Revs/second. Using a 1/500 shutter speed you'll get an arc which is (40/500)*360 or approximately 29 degrees of rotation. Let's call it 30 degrees. The Harvard photo is pretty close to that, so that checks out. The SeaFire/Hurricane photo (other thread) or the photos above appear to show a smaller arc, but they may be using a lower RPM setting of course. Still, it appears to be in the right ballpark. If the prop blade is mostly pointing towards your camera when you take the photo, you may end up with a photo very like that dH.88 Comet shot. It doesn't rule out a rolling shutter issue but could be just a case of bad luck as well.
I'm not altogether sure about this because big warbirds with in-line engines at least, have a reduction gear between the engine (which is where the 2400 rpm is measured) and the prop. I've seen suggestions that the ratio is about 2:1 giving prop rpm of about half the engine revs, so about 1200 rpm at the prop for 2400 rpm at the engine. The Harvard is a known exception with direct drive engine to prop. But I'm not an engineer and may have missed a point somewhere!

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Archer
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Re: Disappearing Props.

Post by Archer »

Good point, thanks. The Merlin uses a 0.477:1 reduction gearing (0.42:1 for some variants, typically the 'bomber' engines) and you'll get something like a 16:9 reduction on a R-2600, I'm not sure about other engines. That means that you'll see about half the arc I mentioned for a typical Merlin engined type, or about two-thirds of what I calculated for a large radial engine. I was mainly interested in seeing if I could match what the photos showed to what I would expect based on a simple calculation. Figuring in the reduction gearing actually means that the Seafire/Sea Hurricane photo is a 'believable' picture for the settings used.

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Re: Disappearing Props.

Post by Rockhopper »

The tips of the blades will be going much faster (in terms of MPH not RPM) than the root - I believe the tips on the Harvard go supersonic which is why it tends to make that strange noise.

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