noone

Thanks! I also use the 70-300 for wider shoot which is much easier because of AF working perfectly and less tight.
 
Yeah I mainly wait around the corners as on straightline they are really fast..
 
I haven't have the chance to use 600 yet but the lens it is so bloody light vs 150-600, the 150-600 is quite a beast for impression but the AF issue and VC constantly jumping is pain the bum! I was moving around the track through out the day and run back to pit when the cars are in (they give me 10 min notice so I have chance to run back in time), carry the 150-600 on c100/200 and big tripod and running around is quite tough. This R5 with 600mm will be much lighter! Though will still use the same big tripod for stability.
 

Not car racing but i think the same would apply as bike racing and years ago even a little with harness racing  and greyhound racing.
If possible, I would get on the exit side of a corner and facing them as they come out of it.
That way they are going slower and it also means you can use a shorter lens, then walk back a bit and do the same with a longer lens like your 600.     Closer to the corner will be almost head on.
Good luck with it!
What do you think of the 600?   

This is as good a read on this as any.
https://www.spiedigitallibrary.org/journals/optical-engineering/volume-57/issue-11/110801/Equivalence-theory-for-cross-format-photographic-image-quality-comparisons/10.1117/1.OE.57.11.110801.full?SSO=1
"Nevertheless, real world IQ differences (including total image noise) will inevitably occur in practice even when equivalent photos are taken. These will arise due to differences in the underlying camera and lens technology, such as:
• sensor quantum efficiency;
• read noise;
• sensor pixel count;
• lens aberrations;
• JPEG tone curve; and
• image processing.
In other words, since the total light received by each format is the same when equivalent photos are taken, it is factors such as those above that explain real-world cross-format IQ differences rather than format size. These factors will be discussed further in Sec. 4."

I Disagree!
Got ANY shred of evidence to support your case?
 

I think the biggest thing about digital zoom is if you start with a good lens, the results zoomed can still be better than lesser lenses.
These are in low light indoors so ISO 25600 even with flash used with a 300 2.8 at 2.8 and with 2x clearzoom.
 

This is as good a read on this as any.
https://www.spiedigitallibrary.org/journals/optical-engineering/volume-57/issue-11/110801/Equivalence-theory-for-cross-format-photographic-image-quality-comparisons/10.1117/1.OE.57.11.110801.full?SSO=1
"Nevertheless, real world IQ differences (including total image noise) will inevitably occur in practice even when equivalent photos are taken. These will arise due to differences in the underlying camera and lens technology, such as:
• sensor quantum efficiency;
• read noise;
• sensor pixel count;
• lens aberrations;
• JPEG tone curve; and
• image processing.
In other words, since the total light received by each format is the same when equivalent photos are taken, it is factors such as those above that explain real-world cross-format IQ differences rather than format size. These factors will be discussed further in Sec. 4."

1) Equivalence theory HAS been tested and is accepted by the majority of photographers and scientists.      Most accept it even though no one has done an EXACT match (IE the photos LOOK very similar but someone will always point out a tiny difference) to the satisfaction of SOME but the deniers have never shown evidence that it is wrong either.
The problem in getting an EXACT match is you would have to scale the equipment for an EXACT match and that would be near impossible.       To the point the EASIEST way might be to build from scratch very simple low element number formulas that test this (but may not be great images).
There ARE science and technology forums on photography on various sites, so much better to ask in those rather than old format warriors on a video forum.
2) Nah, it would work for me but there will still be tiny system differences (lens formula ETC) that way which again to me would easily explain tiny difference in the photos but not others.
Remember, focal reducers do not change cameras, they change lenses so everything else still applies (some lenses have been MADE by tacking a focal reducer group onto an otherwise different lens).
Third party lenses CAN apply corrections but it depends.
Sony for example opens its mount to other manufacturers and M43 is an open mount too (they have to sign confidentiality agreements.
Canon and Nikon do not and the likes of Sigma have to reverse design.
Even my Canon EF lenses on my A7s  report the EXIF but the lenses get recorded as different Sony lenses so it MIGHT be correcting things but doing it as if it is a different lens though it still might be doing it right.
Then again, most of my Canon lenses are older that need less correction (or none).
In camera correction is not necessarily a bad thing as it means they can make lenses better in other areas (or cheaper or both).
My old Canon EF 20-35 2.8 L is probably better corrected than its great great great grandson (the 16-35 2.8 L iii) but the newer lens is a MUCH better lens.     I would love to do a comparison to see how they both go adapted to my Sony but the cost to experiment is far to high.
Olympus M43 lenses are some of the MOST corrected in camera and yet they are still extremely nice (yet not so long ago the 43 DSLR lenses were made large enough to cover APSC (at least in some cases) and would hardly have needed any correction.
Sony E probably corrects for vignetting which probably explains why DXO  often shows FF E mount lenses with the F stop and T stop being the same.

For anyone wanting a bit more tactile control of the clear image zoom on Sony cameras, this Fotga RM-VS1 will give you a zoom rocker to operate it with as well as a shutter release, record button and power on/off.

If you are using a lens with servo zoom such as the PZ18-105mm f4 etc then it controls both the optical zoom and the clear image zoom as one (kind of continuous) lens. I say kind of because there is a slight pause when zooming in when it gets to the crossover point at the end of the optical range.
If you've got an RX100 then it also controls the optical and clear zoom extension in the same way.
There is no variable speed so don't expect to be doing variable speed zooms but its good for framing if nothing else.
Expect to pay around €16-18 on Ali or €20-25 on Amazon.
 

I've recently "discovered" some of the benefits of using the in-camera digital zoom.  These won't apply to everyone, but it's worth considering and I don't hear a anyone talking about it.
Let me illustrate by taking my GH5 as an example, but the principle applies much wider, especially as cameras go towards 8K and beyond.
The GH5 has a sensor that's 5184 pixels wide.  When you're shooting 4K, the camera downsamples the 5.2K to 4K, giving a higher quality image due to the benefits of oversampling.  The benefits of oversampling are well known, and many cameras have this.
The GH5 also has an ETC mode, which essentially does a 1:1 crop into the middle of the sensor.  This is a common feature across manufacturers.
If you use the ETC function in 4K, you get an additional 1.3x crop, and if you use the function in 1080p then you get a 2.7x crop.  
Both of these modes are shooting a 1:1, so you get a tighter FOV, but the image is no longer oversampled, so the quality goes down.
Enter the digital zoom.
In 1080p mode, the GH5 allows a 2x and 4x digital zoom.  The 2x digital zoom is less than the 2.7x 1:1 zoom from the ETC mode, so (assuming that the cameras image pipeline is designed well) the resulting 1080p image should be an image that is taken from the middle 2.6K pixels and downsampled to 1080p.
In other words, the 2x digital zoom is a way to punch-into the sensor but still keep the quality of an oversampled image.
This principle will occur any time that the digital crop is less than the crop of going to a 1:1 area on the sensor for whatever resolution you're shooting in.
The Sony ClearImage Zoom comes to mind here, where (I think?) you can zoom in by a lesser amount than the 4K 1:1 crop (which is something like 1.5x?).  Perhaps other manufacturers have similar functionality too.
Of course, the lower the resolution you're shooting then the more likely this will be available on your camera.  For those still shooting 1080p then this is worth looking at.
For those shooting 4K, this will increasingly be useful as sensors creep up towards 8K and beyond.
For me though, I've now abandoned the idea of having to buy an 85mm prime, because I can simply do a 2x digital zoom with my 42.5mm lens and get the same FOV and (basically) the same image quality, and if I happen to have my 7.5mm lens on and want to quickly grab a 15mm FOV shot then I know I won't be sacrificing quality to get one.
Had I known that this feature delivered such good results I may have actually bought different lenses, so it's not a trivial thing, and it's worth giving a quick go if your camera supports it.

Yes, it is a very good thing in the Fuji lenses. That's why I was asking about third party lenses, if they don't get corrections that puts them at a disadvantage.
And I wonder where a particular lens's correction information is stored, in the lens firmware or the camera firmware? Just curious.

Using the .13 crop factor would actually mean it IS very doable to "match"  (enough to satisfy me anyway) with a 600mm f9 (or even f8) 8x10 lens to M43.
Using .13 instead of .15 as the crop factor, you would need about a 39mm f1.2 lens for the f9 or an f1 lens for the f8. (again though, we do not know what it actually was).
A 40mm 1.2 would give a close enough photo. but you could even use an existing Kipon 40mm f0.85 (a lens for both M43 and APSC formats) and keep the change!
Just found that interesting and I would love to see someone do a direct comparison (between an 8x10 camera anyone got a digital back that size with a 600mm f8 lens who also has M43 with a Kipon  40 f0.85?   Great! I look forward to the tests).

Great lens. I've seen them go in the range of 50-100 euros. When in good condition with box and all, I would certainly bet on the higher end of that. The non-E pancake is more or less the same, is said to have better coating and fetches a somewhat higher price.

Decided to pick up a Nikon AIS 28mm f/2.8 for $160

lol, the only place I didn't look was in the thread title! 😂😂😂
There's a pretty well established principle that lenses sharpen up when you stop them down the first couple of stops.  As mentioned before this has exceptions, but those exceptions seem to be just that, exceptions.
DXOMark has a lot of interesting lenses and you can look at the graph of sharpness (perceptual megapixels) vs aperture to see how much it sharpens up when stopped down.  Typically they look like this:

Where wide open they aren't as good as when closed down a couple of stops.
So in that sense, the target aperture really matters, as the best way to get a sharp image at f2 might be to buy an f1.2 lens.  
The exception is normally much slower lenses that have the same kind of optical performance as the above, only don't open the aperture as much.

And that's exactly why I was asking for f2 or faster suggestions. So when I'm shooting in low-light conditions, I can still stop down a 1.4 lens to 2.8 and know I'll have a sharper image than using a 2.8 lens, wide open. 
 
And since this is for filmmaking, I'm mostly concerned about the center of the image anyway.
The Voigtlander is very sharp wide open at f/1.4. 

If you do NOT get things to match exactly there will ALWAYS be a small difference that will just leave SOME to say that because there is a difference the theory does not match the practice and THAT is what makes even trying a "fools errand"
All the tests to date look close enough for me, if they do not for you, that is your problem and you should be doing the tests to match YOUR theory.
You think the tests get close enough but then when you see a(often very small) difference you attribute that to a difference between formats instead of between the optics.
There is no reason you would get a difference in vignetting if you used identical formula lenses to match the crop (IE scaled).
 
As to your 600mm 8x10 above, 
That is a very different argument and actually plays into the original question and is again the reason WHY FF is necessary to ME.
I simply can NOT match my ancient 300 2.8 with M43 (other than the $35000 plus Arri 150 1.3) or my ancient 24 1.4 (because there are no 12mm m43 f0.7 lenses) or my ancient 85 1.2 (again, no 42.5mm f0.65 lenses which is approaching the limit in air).   No high quality tilt shift lenses either like my favourite 17 f4.
If I could do what i can with m43 (or Pentax Q) what i can with FF, I would only be using that.
A 8x10 camera with a 600mm lens will probably be something like a 600 f9 Nikon. 
A 600mm 8x10 f9 lens would be equivalent to about a 90mm 1.4 FF (so about a 45mm f0.7 M43).   If you COULD get a lens to match it  (it IS possible even if there are none) it would yield a very similar photo even without being the exact same lens design.
If the lens was 600mm f8, then that would be almost impossible to match with m43 as that would be about a 90mm f 1.2 FF so you would need an aprox 45 f0.65 to even give a similar if not exact photo.
You have yet to show that there is ANY difference BECAUSE of the differences in sensor size and so far all difference have been because of the optics and not getting an exact match.
After all if the Moon astronauts had been just 2% off course, where would they be now?

Thanks guys. I picked up a used G9. It popped up for 769$ and Icouldn't pass it up. Should be here Tuesday!

Absolutely.  I have f0.95 primes, so you're preaching to the choir here!
Actually, they didn't.  Or at least, when I just re-read this thread five times looking for it, I couldn't find it!
True.
The issue I took, and thus my slightly sarcastic reply, was that this is viewed far too simplistically by people.
Take two hypothetical lenses, one is f1.4 and the other is f2.8.  Let's say that the f1.4 one isn't so sharp wide open, but the f2.8 lens is.
The traditional, one-dimensional, thinking is that if you want sharp images then the 2.8 lens is the one to go for because "the f1.4 is soft wide-open but the f2.8 lens isn't", end of story, and mostly, end of how deep the persons knowledge is about the subject.
The problem with this thinking is that the f1.4 lens might be sharper at f2.8 than the f2.8 lens is, but the sharp-wide-open one-dimensional thinkers don't go that far.

I ended up picking up a voigtlander 40mm f/1.4.
not 50mm but close enough.

On the contrary, the last few pages of discussion gets right to the heart of the question raised. And I think many people would agree that the answer is:
The necessity or desirability of a format size depend on whether the lenses available for that format will give you the visual qualities that you value.

Of course he did.    But if you use the same optics in different formats you get the same result...it is not the format that makes the difference it is the lenses.
To get an exact match to satisfy everyone, 
You would need to firstly pick your cameras of different formats and get the EXACT crop factor.
Next you need a lens for one format.
You would need to know the actual focal length (not just the marked focal length),
You would need the  diameter and could then work out the exact f stop.
Using the crop factor to get an exact match, you would then need to do the same for the second format.
You will also probably need to have the exact same lens formula though to get the same T stop (and take away any possibility of being a difference for other reasons).
Yeah, it probably IS possible (maybe even easy for some).
I could not do it in a lifetime though and again, beyond being a academic exercise, what is the point?
It would HAVE to be done this way because otherwise some will point out (often tiny) differences but those differences .
So, unless you (or someone else) does THAT, I will always accept that the theory matches the practice and to date, all tests have satisfied me they do.    
Are there ANY tests that have been done matching equipment EXACTLY? 

Can you link to those posts?
I'm still no clearer on what the differences in DOF rendering due to large/small format lenses actually looks like in an image.

Well, I think that DOF as defined by circle of confusion etc can be matched because equivalence theory states that you can, if the lens for the smaller format is bright enough. However, I would expect to see a considerably softer image with lots of vignetting as you'd need a very fast lens to replicate the narrow DOF of this shot, and that's how lenses behave wide open. So although the DOF might be technically the same, the images will look different. But this is caused by the glass, not sensor size.
And yes, the selection of lenses available for different formats is different. So your choice of format will have an impact on the look of the image. But I think a lot of people are making the point that those differences are derived from the glass and are not inherent to the sensor size.
So theoretically, sensor size makes no difference to DOF. But in practice DOF is rendered qualitatively differently because the lenses are different / behave differently / must be set differently for different formats.
If true, it's an interesting dichotomy. But it does suggest that any equivalence test is really just a comparison of two different lenses. In the same way that one of my 50mm lenses looks different from the other 50mm lenses I have for the same format. So would you agree that once you match focal length and aperture for the same shot on different formats, you're comparing lenses?
 
 

PLEASE point me to that test then, because I feel like whatever magic properties that should be inherent to sensor size should manifest in sóme way under a controlled test. So far you are just shooting down any test provided as not being rigorous enough (why on Earth would foreground unsharpness matter in any way when according to your last example provided the special properties of large format are abundantly clear in a shot that has just as much elements in front of the focus point, that is a nose, as in the examples provided by Yedlin), but if the differences were significant so as to be meaningful there should be a way to test for this relatively easily right? I

When I use my two different FF 24mm lenses both made by Canon but one EF and the other FD (both quite old though), I can often  see almost as big a difference as between my FD 24 1.4 L and my RX100 iv at 24mm equivalent (actually the EF 20-35 2.8 lens is a closer match usually maybe because it fully passes exif to the camera while the FD adapter is dumb).     As with all of these, the small difference are down to many reasons mostly including the lens design but also the settings are usually not exact (IE one 24mm lens might be 24.5 while another might be 23.8mm).     The numbers to get an exact match between an 8,8mm lens on the RX100 and the 24mm on FF I use are aprox and the crop factors used are aprox.     This is why it would be almost impossible to get an exact match and I doubt even Lens Rentals and their optical bench could get one.    Since I very much doubt you will EVER see an exact match, some people will never accept the theory matches the practice and hence discussion like this are pointless (the why /why not use FF or any other format can be a very valid discussion but not the equivalence is real ones).
Read the other thread linked to earlier and what Dr Caldwell said (he designed the Metabones SpeedBooster as well as one of the highest performance lenses ever).    
Back to (trying to) be a spectator.